Дисертації з теми "629.1.04"
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1
Левченко, Віталій Михайлович. "Пристрій активної безпеки автомобіля". Master's thesis, Київ, 2018. https://ela.kpi.ua/handle/123456789/25876.
Повний текст джерелаАнотація:
Метою магістерської дисертації є покращення параметрів та характеристик активної безпеки автомобіля та розширення її застосування. Задачами дослідження є: аналітичний огляд існуючих систем безпеки автомобіля; розробка пристрою автомобільної безпеки та виконання його моделювання; дослідження та аналіз характеристик спроектованого пристрою.
– об’єкт дослідження — пристрій для зменшення вірогідності дорожньо-транспортної пригоди та забезпечення безпеки пасажирам автомобіля.
– предмет дослідження — параметри та характеристики пристрою та систем активної безпеки автомобіля на його основі.
– методи дослідження: теоретичний розрахунок та експериментальне дослідження параметрів макету пристрою.
– наукова новизна одержаних результатів: запропоновано та досліджено використання пристрою автомобільної безпеки з представленим алгоритмом роботи.
– апробація результатів дисертації. міжнародна наукова інтернет–конференція «Інформаційне суспільство: технологічні, економічні та технічні аспекти становлення» (Випуск 32, 16 жовтня 2018р).The purpose of the master's thesis is to improve the parameters and characteristics of active safety of the car and extend its application. The objectives of the study are: an analytical review of existing car security systems; development of the automobile safety device and its simulation; research and analysis of characteristics of the designed device. the object of research - a device for reducing the probability of road traffic accidents and ensuring the safety of passengers of the car. subject of research - parameters and characteristics of the device and active safety systems of the car on its basis. research methods: theoretical calculation and experimental study of parameters of the device layout. scientific novelty of the obtained results: the use of the device of automobile safety with the presented algorithm of work is offered and researched. approbation of the results of the dissertation. International Scientific Internet Conference "Information Society: Technological, Economic and Technical Aspects of Formation" (Issue 32, October 16, 2018).
2
Verdin, Patrick. "An automatic multi-stepping approach to aircraft ice prediction." Thesis, Cranfield University, 2007. http://hdl.handle.net/1826/2923.
Повний текст джерелаАнотація:
Flying an aircraft in icing conditions may seriously degrade its aerodynamical performance
and threaten the flight safety. Over the years, new technologies and improved
procedures have limited the potential risks caused by aircraft icing. Experimental
studies being very expensive, numerous computer codes have been developed to
simulate ice shapes and tackle the problem. Typically in these codes, a flow solution
and key icing parameters are evaluated around a clean un-iced geometry and
their values remain constant during the entire simulation. This approach may be
acceptable for short exposure times or when the ice shape only slightly deforms the
initial geometry. However, in other cases, the values of the icing parameters may
vary and the simulation will loose its accuracy: for large shapes, the presence of
the ice influences the surrounding airflow significantly, altering the value of icing
parameters and ultimately the ice accretion. Calculating more accurate ice shapes
therefore requires to periodically recompute the flow field around the body during
the simulation and determine updated values for icing parameters. This procedure,
known as multi-stepping, is investigated in this thesis and adapted to the new threedimensional
icing code ICECREMO2. Several multi-step algorithms are presented
and tested on cylinders and airfoils. When possible, the ice shapes simulated are
compared with experimental results.
The first multi-step calculations were generally performed manually. The user
had to perform a rather tedious work and inappropriate instructions could lead to
severe inaccuracies in the simulations. To avoid these difficulties, a fully automated
procedure will be developed including all stages of a multi-step computation. This
significantly reduces user interaction and the overall computing time.
The present research work forms part of the ICECREMO2 project. ICECREMO2
is a three-dimensional ice accretion and water flow code developed collaboratively
by Airbus UK, BAe Systems, Dunlop Aerospace, Rolls-Royce, GKN Westland Helicopters,
QinetiQ and Cranfield University under the auspices of the UK Department
of Trade and Industry.
i
3
Quero, García Manuel. "Analytical and experimental investigation into the thermal aspects of droplet impingement." Thesis, Cranfield University, 2006. http://hdl.handle.net/1826/4043.
Повний текст джерелаАнотація:
The mechanics and heat transfer of droplet impact is studied in the range of
parameters interest for Super-cooled Large Droplet icing. The investigation explores
the development of the splash produced experimental and numerically.
A Navier-Stokes solver has been developed in order to compare experiments and
modelling.
Heat transfer is included in the simulations making possible the analysis of the
thermal history during the impact of a Super-cooled droplet into a warm and running
thin water film.
Also a theoretical and numerical study has been undertaken in order to simulate
the first stages of ice formation on the critical surfaces of aircraft during the droplet
impact under freezing conditions due to super-cooled icing.
The parameters considered experimental and numerically are:
• Droplet size: 100-700Jlm.
• Droplet impact velocity: 18-80m/s.
• Angles of impact: 70°,45° and 20°.
• Airflow (droplet) temperature: 200 e and _lOoe.
• Water film thicknesses: 150Jlm and 50Jlm.
• Water film temperature: 15°e and lOoe.
• Water film velocity: 5m/s.
The simulations are compared to the experiments run under the same conditions.
Results for the parameters at the early stages of the splash agree well but as the splash
process continues there are more differences between the two sets of results.
4
Butters, Jonathan David. "Terminology recognition in the aerospace domain." Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.575750.
Повний текст джерелаАнотація:
The objects and phenomena within the world around us are frequently shared. Common understandings, intuition, and common sense allow people to communicate ideas and instructions by identifying the semantics of the words used. When we communicate these ideas through text, we rely on strings of characters to carry semantics, and through these, because of common understandings, intuition, and common sense we are often able to gain back the references to the original ideas. As people's capacity to express their ideas through text is unbounded, the task of deciphering original meanings when synonyms and term variations are involved can be challenging, trying to do this task automatically is more so. The body of work within this thesis aims to identify and then overcome the challenges in automatically recognising the terminology used for concepts within the aerospace domain. The main achievements of this thesis include new knowledge about the use of terminology in this safety critical and highly technical domain, knowledge that approaches which are often impractical in open and alternate domains may be applicable due to the aerospace domain's unique nature, and an approach to automatically recognising terminology for the purposes of knowledge management. The approach involves constructing an explicit model of the domain (afforded by its closed nature), and then leveraging it along with exploiting the combinatorial nature of aerospace domain terms in an extraction methodology. Extraction is performed using a novel, hybrid dictionary and machine learning based technique which is shown to perform better than existing dictionary, statistics, and machine learning techniques. This thesis is organised into four parts, the first part provides a survey of the aerospace domain and state of the art methods by which terminology is recognised. The second part documents several investigations into the real-world use of terminology within and across aerospace-based communities in order to provide an understanding on how terminology should be recognised and generate a set of requirements. The third part details the proposed approach and presents a novel, patent-pending methodology to fulfil the requirements. The fourth part concludes this thesis with a summary and by v answering the original research questions, before discussing possible lines of future work.
5
Lajux, Vincent. "Methodology for the design of leading edge devices applied to variable camber." Thesis, Cranfield University, 2007. http://hdl.handle.net/1826/2548.
Повний текст джерелаАнотація:
This thesis will describe a new and innovative way of approaching the design of leading
edge devices; this done using new tools and state of the art software. This innovative
design methodology for leading edge devices has a special focus on the application of
variable camber technology.
A precise description is given of the way to check that methodology acts as a means of
validation.
A case study shows how to apply this methodology and examines a variable camber
application. This case study provides the basis for the understanding of how to apply the
design methodology and give results generated from its different parts. An analysis of the
structure and aerodynamic performances of a new type of leading edge device was
performed in addition to moving the overall design towards an optimum solution in term
of mass, reliability and cost.
The case study is showing that using a variable camber leading edge device could be
beneficial as it proves a better option than more classical concepts. Some of the results
show that the aerodynamics implications of using this type of device at the leading edge
can be beneficial in cruise and also during take off and landing. Also on the structural
side of things, it is possible to see that the deployment trajectory as been optimised to fit
to the required trajectory and the structure is able to resist critical loading.
Finally there is a discussion on the obtained results and on the overall methodology to
make conclusions on the overall meaning of this research and the possible impact of the
new design methodology as well as implication on the design of variable camber leading
edge devices.
6
Laskaridis, Panagiotis. "Performance investigations and systems architectures for the More Electric Aircraft." Thesis, Cranfield University, 2004. http://hdl.handle.net/1826/2958.
Повний текст джерелаАнотація:
Implementation of all or more electric technologies has the potential of improving the performance of a given aircraft. Savings can manifest through improved engine performance, reduced equipment weight and improved secondary power and systems utilization. Despite the potential benefits and the amount of research invested the concept has not been implemented yet and its impact on the overall performance of the aircraft remains unclear. Adoption of a single form of secondary power and implementation of more or all electric technologies is claimed to offer a number of distinct advantages over the conventional secondary power systems. These claims include the following: 1. Improved engine performance through the optimization of off-takes and elimination of bleed air. These issues is said to become critical as the bypass ratio of the engine increases and the size of the core reduces. However, despite concerns over the capability of high bypass ratio to provide secondary power requirements of future aircraft the claims remain unproven and it is generally believed that off-take penalties are not dependent on the configuration of the engine and can be kept to a minimum if the engine is designed to provide them. 2. Improved system utilization and implementation of more efficient power units. Conventional secondary power systems developed during the years that fuel was relatively fuel was relatively inexpensive and have not been optimized for maximum efficiency. Bleeding air from the engine is largely inefficient and a large amount of power is wasted for no useful purpose. In addition, hydraulics are often sized for loads that are small in duration thus increasing the mass and power requirements of the system. Elimination of conventional hydraulic and bleed air systems could lead to a significant mass reduction. However, the mass and size of the electrical equipment would also increase and these changes must be accounted for. 4. Additional benefits include reduced single type maintenance, improved reliability and life cycle costs. The present study is focused on assessing the potential benefits of adopting the all or more electric aircraft concepts in the case of high capacity long-range aircraft. Previous studies concentrated on low to medium range aircraft powered by medium bypass bass ratio engines. As a result, the moderate power requirements and the more important weight considerations, for the class of aircraft reviewed, reduced the potential benefits and led to retrofitted designs with low savings. It is thought that high capacity long range aircraft as those examined by the present study are more suited to the all electric concepts and could benefit more. The study was aimed to address the first three claims made and also provide a better understanding of the issues involved. As a result the following topics have been considered. The effects of off-takes on the performance of the engine were studied. Two methods for assessing these effects were developed. The analysis concluded that engine parameters such as pressure ratio and turbine entry temperature have an important effect on the performance of an engine operating with bleed air or shaft power extraction.
An aircraft performance model was developed and used to asses the impact of all or more electric technologies on aircraft in the classes of A330-200, A340-500 and A380-100. The models were validated against published payload range data. All electric derivatives were developed by incorporating changes in aircraft mass and engine off-takes. Sensitivity studies were also conducted. Conceptual designs and electric system architectures were developed and studied. Adoption of all electric technologies and elimination of the hydraulic system was estimated to reduce the OEW by 0.4% to 0.1% for the A330-200 class aircraft, 0.37% to 0.25% for the A340-500 class aircraft and 0.3% to 0.1% for the A380-100 class aircraft. The total fuel reduction with implementation of all electric technologies and elimination of hydraulics and bleed air could be as high as 2.6% for the A330-200 class aircraft, 2.75% for the A340-500 class aircraft and 3.5% for the A380-100 class aircraft. Adoption of all or more electric technologies could allow for the design of more efficient aircraft. Increasing the aspect ratio of the A80-100 class aircraft to 8.33 could improve aerodynamic efficiency leading to an overall fuel reduction of 4.4% and a MTOM reduction of 2.0010. In the case of twin engine aircraft reductions in MTOM and reduced off-take penalties could allow an increase in engine bypass ratio leading to increased overall performance. For the A330-200 class aircraft elimination of bleed air and increase in bypass ratio resulted in a fuel reduction of 4.5%.
7
Padulo, Mattia. "Computational engineering design under uncertainty : an aircraft conceptual design perspective." Thesis, Cranfield University, 2009. http://hdl.handle.net/1826/4462.
Повний текст джерелаАнотація:
Presented in this thesis is a novel methodology for aircraft design optimization in the presence of uncertainty, with emphasis on the conceptual design stage.
In the initial part of the thesis, the uncertainty typologies of interest for aircraft design are identied within a broader epistemological framework. The main implications for non-deterministic computational design are also outlined.
The focus is then restricted to uncertainties that can be modeled by probability theory. In this context, a methodology is developed to enhance robust design optimization (RDO). Firstly, the problem is formulated in order to relax, when required, the common RDO assumption about the normality of objectives and constraints. Secondly, starting from engineering considerations about the risk related with design unfeasibility, suitable estimates of tail conditional expectation are introduced in the set of robustness metrics.
The proposed formulation requires the estimation of mean and variance of objec¬tives and constraints. To calculate such moments, a novel uncertainty propaga¬tion technique is proposed, which achieves a favorable trade-obetween the ac-curacy of the estimates and the required computational cost. Peculiar features of the propagation technique are exploited to couple the propagation and the opti¬mization phases for the classes of gradient-based methods and the derivative-free pattern search methods. Also analyzed are the possible advantages achievable when the two types of algorithms are hybridized.
The usefulness of the proposed methodology for conceptual design optimization is demonstrated with the aid of two engineering design problems, concerning the sizing of passenger aircraft and the design of transonic airfoils.
8
Gullia, Alessandro. "Thrust and Flow Prediction in Gas Turbine Engine Indoor Sea-Level Test Cell Facilities." Thesis, Cranfield University, 2006. http://dspace.lib.cranfield.ac.uk/handle/1826/7496.
Повний текст джерелаАнотація:
The principal aim of this research was to provide a detailed understanding of the
performance of gas turbine engines inside indoor sea-level test beds. In particular the
evaluation of both thrust correction factors and the estimation of the mass flow
entering the test cell were at the core of the research.
The project has been fully sponsored by Rolls-Royce pIc. Initially, their principal
objective was to assess the relevance and accuracy of CFD when applied to thrust
measurement inside indoor test beds with an intended outcome of minimising the use
of expensive experimental measurements.
The different system interfaces and accounting systems for in-flight conditions,
available in the open literature have been developed and adapted for indoor
environments. This has led to the definition of three different thrust correction
equations using alternative definitions of thrust correction factor. Aero-dynamic
principles have been applied for the derivation of one-dimensional relationships for
the calculation of each thrust correction factor using generic engine-cell performance
and dimensions.
A one-dimensional analytical model has been developed to represent the enginedetuner
ejector pump. This is able to characterise the engine-cell system performance
and is used as the main tool for providing a matching procedure capable of predicting
the cell entrainment ratio.
By processing experimental data relevant to different engine-cell configurations
through the ejector pump analytical model, a method for achieving the entrainment
ratio control inside the cell has been identified.
The CFD work has been concentrated into three main activities:
• A quantitative extrapolation of the thrust correction factors including, the
pre-entry force, the external and the total bellmouth force, the throat stream
force, the intake momentum drag and the base drag.
• The representation of the engine-detuner ejector performance for a
variety of engine-cell configurations.
• The modelling of the generic test cell components including the inlet
stack, the cascade elbow, the exhaust stack & the blast basket.
The outcomes of this research have been very successful in enhancing the validity of
the thrust correction equations developed .. In particular, the use of a one-dimensional
approach in their estimation has been shown to be fully justified. The work has also
emphasised the value of CFD in supporting the derivation of the matching procedure
for predicting and controlling cell entrainment ratio. Indeed, one of the strongest
outcomes of this work has been the conclusion that both the engine-cell characteristic
lines computed with the one-dimensional model and those computed with CFD for
different cell configurations are almost identical.
In addition, the use of CFD as a tool for the quantitative evaluation of the thrust
correction factors has been established. Finally, the CFD results have facilitated an
enhanced understanding of the complex flow structure inside indoor test cells
9
Janikovic, Jan. "Gas turbine transient performance modeling for engine flight path cycle analysis." Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/7894.
Повний текст джерелаАнотація:
The growth in competitiveness in airline industry has called for more advanced tool to
estimate the operating costs. Engine maintenance costs are an important decisionmaking
element during airline fleet selection judgment. Long term observation in
aerospace led to the development of engine maintenance costs calculators based on
empirical correlation. But the possibilities of empirical model application for future
engines without prior operational data are limited.
A physics-based tool to estimate the life of the engine components and predict the
shop visit rate requires the variations of thermodynamic parameters over the flight
path. High fidelity engine models are simulated using an engine performance program.
A test program designated for design, off-design and transient performance simulation
for simple turbojet layout gas turbine engine has been programmed and tested. The
knowledge gained from program coding was used to generate more robust transient
performance code implemented to Turbomatch. Two transient methods have been
tested: The rapid transient performance method and the thermodynamic matching
method. The tests showed greater robustness and stability of the second method,
which has been finally adopted for the program. For industrial engine configuration
and for future novel engine cycles the heat-exchanger dynamic response model was
implemented and tested.
Created tool was demonstrated on short-haul study of engine flight path analysis.
Together with the aircraft model, the tool produced variations of parameters needed
for the lifing algorithm.
10
Giannakakis, Panagiotis. "Design space exploration and performance modelling of advanced turbofan and open-rotor engines." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/7957.
Повний текст джерелаАнотація:
This work focuses on the current civil engine design practice of increasing overall pressure
ratio, turbine entry temperature and bypass ratio, and on the technologies required in
order to sustain it. In this context, this thesis contributes towards clarifying the following
gray aspects of future civil engine development:
the connection between an aircraft application, the engine thermodynamic cycle and
the advanced technologies of variable area fan nozzle and fan drive gearbox.
the connection between the engine thermodynamic cycle and the fuel consumption
penalties of extracting bleed or power in order to satisfy the aircraft needs.
the scaling of propeller maps in order to enable extensive open-rotor studies similar
to the ones carried out for turbofan engines.
The rst two objectives are tackled by implementing a preliminary design framework,
which comprises models that calculate the engine uninstalled performance, dimensions,
weight, drag and installed performance. The framework produces designs that are in
good agreement with current and near future civil engines. The need for a variable area
fan nozzle is related to the fan surge margin at take-o , while the transition to a geared
architecture is identi ed by tracking the variation of the low pressure turbine number of
stages. The results show that the above enabling technologies will be prioritised for long
range engines, due to their higher overall pressure ratio, higher bypass ratio and lower
speci c thrust. The analysis also shows that future lower speci c thrust engines will su er
from higher secondary power extraction penalties.
A propeller modelling and optimisation method is created in order to accomplish the
open-rotor aspect of this work. The propeller model follows the lifting-line approach and
is found to perform well against experimental data available for the SR3 prop-fan. The
model is used in order to predict the performance of propellers with the same distribution
of airfoils and sweep, but with di erent design point power coe cient and advance ratio.
The results demonstrate that all the investigated propellers can be modelled by a common
map, which separately determines the ideal and viscous losses.
11
Wright, Stephen James. "Heat exchanger fouling in aircraft air-conditioner systems." Thesis, University of Leeds, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.634789.
Повний текст джерелаАнотація:
The air conditioning heat exchangers of the Airbus A320 are plate wavy fin type. Operational aircraft such as the A320 suffer from failure in commercial service owing to operational fouling and the aim of the research was to investigate the causes of large commercial aircraft air conditioning system failures, attributed to overheating. The aim of the thesis is to research the problems relating to the failure of the Environmental Control System (ECS), and to publish data and findings. The ECS plate fin heat exchangers (PFHE) of live aircraft were examined during hanger maintenance, and later the fouling was analysed and the sources were identified. A series of experiments were designed to replicate an aircraft ECS PFHE operation, similar to that fitted to the A320 using two types of wavy fins (fine and coarse). The novelty of the research was to design a series of experiments that reproduce the aircraft PFHE operations, which included the fouling of the wavy fins. Compressed air was used to replicate the outside 'ram' air cooling flow, · and hot bleed engine air flow was replicated by two electrical heating mats. A new method was used to produce the experimental fouling material which replicated the real world situation. The effects of fouling on fins were observed in terms of heat transfer, pressure drop and fouling analysis. Pressure drop experimental results appeared to be generally consistent yet lower than literature correlations of Hesselgreaves (2001) and Kays and London (1984). The additional fouling supply introduced to the compressed air flow was less than 2% of the total mass flow. Analysis of fouling materials deposited on the fins using scanning mobility particle sizing (SMPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques indicated that fouling samples from live aircraft were very similar to those used in the experiments. The experimental film heat transfer coefficients for the empty channel and the two types of fins were calculated using the analytical solution, initially clean and later fouled. It was expected that the higher number of fins would result in a higher heat transfer performance, yet the experimental results and some predictions indicated this was not the case. The predictions of the film heat transfer coefficients based on the correlations demonstrated that some of the results vary significantly when compared to the experimental coefficients. It was noted that at times, the temperature distribution of the apparatus walls were not symmetrical, resulting in transverse heat conduction.
12
Lolis, Periklis. "Development of a Preliminary Weight Estimation Method for Advanced Turbofan Engines." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9244.
Повний текст джерелаАнотація:
The present work focuses on preliminary weight estimation methods that enable
the feasibility studies of novel aero engines. The key contributions can be found
in the analysis of the existing preliminary weight estimation methods, the de-
velopment of a new preliminary weight estimation method and the study on the
feasibility of a Geared Turbofan (GTF) engine.
In more detail, the existing preliminary weight estimation methods are exam-
ined in the rst part of the thesis, aiming to de ne their suitability for current
turbofan engines, but also for future engine arrangements. For this purpose, they
are examined not only quantitatively, to verify their accuracy, but also qualita-
tively to gure out if they are able to re
ect the key thermodynamic and design
parameter variations on weight. Apart from NASA WATE no method achieves
either the required accuracy, or simulates the weight trends.
Realising the need for a more accurate, robust,
exible and extensible method,
a new "component based" method that performs basic component design to es-
timate engine weight, is devised. Its accuracy is veri ed by comparing the whole
engine weight prediction and estimated component design against the publicly
available data of two major turbofan engines and the weight predictions of exist-
ing weight estimation methods.
ATLAS, the tool based on the above method was used to estimate weight over
a range of Bypass Ratio (BPR) and Turbine Entry Temperature (TET) values for
a Direct Drive Turbofan (DDTF) and a GTF two spool arrangement, reaching
the following conclusions:
The adjustments of Low Pressure Turbine (LPT) number of stages or geom-
etry are not su cient, if high stage isentropic e ciency values are targeted
at high BPR values
For the examined engine model, with the given weight estimation method-
ology, the weight reduction, when a gearbox is introduced at a DDTF,
depends on the reduction of LPT stages, with the other components having
negligible impact. However, it should be noted that a constant fan diameter
was assumed for both con gurations. A fan loss model and more detailed
weight estimation of frames, shafts and control and accessories is required
to verify this conclusion.
The comparison of a DDTF and a GTF engine is representative only if the
cycles corresponding to the installed performance optima are considered.Engines with the same thermodynamic cycle could only be compared when
the optima cannot be reached, due to geometry restrictions.
13
Abu, Abdullahi Obonyegba. "Integrated approach for stress based lifing of aero gas turbine blades." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8405.
Повний текст джерелаАнотація:
In order to analyse the turbine blade life, the damage due to the combined thermal and mechanical loads should be adequately accounted for. This is more challenging when detailed component geometry is limited. Therefore, a compromise between the level of geometric detail and the complexity of the lifing method to be implemented would be necessary. This thesis therefore focuses on how the life assessment of aero engine turbine blades can be done, considering the balance between available design inputs and adequate level of fidelity. Accordingly, the thesis contributes to developing a generic turbine blade lifing method that is based on the engine thermodynamic cycle; as well as integrating critical design/technological factors and operational parameters that influence the aero engine blade life. To this end, thermo-mechanical fatigue was identified as the critical damage phenomenon driving the life of the turbine blade.
The developed approach integrates software tools and numerical models created using the minimum design information typically available at the early design stages. Using finite element analysis of an idealised blade geometry, the approach captures relevant impacts of thermal gradients and thermal stresses that contribute to the Thermo-mechanical Fatigue damage on the gas turbine blade. The blade life is evaluated using the Neu/Sehitoglu Thermo-mechanical Fatigue model that considers damage accumulation due to fatigue, oxidation, and creep. The leading edge is examined as a critical part of the blade to estimate the damage severity for different design factors and operational parameters. The outputs of the research can be used to better understand how the environment and the operating conditions of the aircraft affect the blade life consumption and therefore what is the impact on the maintenance cost and the availability of the propulsion system. This research also finds that the environmental (oxidation) effect drives the blade life and the blade coolant side was the critical location. Furthermore, a parametric and sensitivity study of the Neu/Sehitoglu model parameters suggests that in addition to four previously reported parameters, the sensitivity of the phasing to oxidation damage would be critical to overall blade life.
14
Lim, Chi Keong Reuben. "Improving planned and condition-based maintenance decision support." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/8508.
Повний текст джерелаАнотація:
In both civil and military aviation, maintenance plays a large role in ensuring continued
safe operation and accounts for a significant portion of operating costs. Typically, a
conservative planned maintenance (PM) program is initially developed to ensure the
aircraft reliability but this often leads to over-maintenance. With more in-service
experience, operators seek to customize the maintenance interval accordingly in order
to reduce workload and cost without compromising safety. With prevailing use of
health usage monitoring systems (HUMS), the maintenance can even transit from PM
to condition-based maintenance (CBM) where further safety and costs benefit may be
reaped. Whilst some guidance for such changes exists, it remains challenging for
maintainers in practice as suggested methods often require significant component
failure or test data; which are unavailable or too expensive to obtain. As such, this
research reviews the challenges faced by maintainers when extending PM intervals or
implementing CBM and seeks ways to support decision making for the changes.
For PM, the challenge to extend the maintenance interval with little or no past failure is
addressed. Existing reliability methods were reviewed and two improved methods to
estimate the reliability lower confidence bounds were developed. The first approach
adopts the use of Monte Carlo simulation applied to the Weibull plot equation while the
second uses a probabilistic damage accumulation model together with bootstrap
techniques. Both methods are used to assess the reliability of extending the replacement
interval of a gearbox bearing and are shown to perform better than existing methods as
they provide tighter reliability confidence bounds.
For CBM, a survey on sensor technologies and diagnostic algorithms showed that
vibration-based sensor is most widely used to detect fault. The study then demonstrates
a CBM implementation using vibration-based HUMS data from in-service helicopters.
Analysis of the FFT spectra shows that the fault patterns corresponding to progressing
stages of bearing wear can be clearly observed. The fault patterns are extracted as
features for unsupervised classification using Gaussian Mixture Models and used to
infer the different bearing health states. Signal detection theory was then applied onto
the classified feature to determine the detection thresholds for fault diagnosis. A
simplistic prognostic model using trend extrapolation to determine the replacement
lead-time is then performed and use for maintenance planning.
In an effort to ease the implementation of CBM, ways to improve prognostics
application is explored. The Switching Kalman Filter (SKF) was adapted for both
diagnostic and prognostic under an autonomous framework that requires little user
input. The SKF uses multiple dynamical models with each one describing a different
stage of bearing wear. The most probable wear process is then inferred from the
extracted feature data using Bayesian estimation. As different stages of bearing wear
can be tracked using the dynamical behavior of the measurements, pre-established
threshold for fault detection is no longer required for diagnostics. The SKF approach
provides maintainers with more information for decision-making as a probabilistic
measure of the wear processes are available. It also offers the opportunity to predict
RUL more accurately by distinguishing between the wear stages and performing
prediction only when rapid and unstable wear is detected. The SKF approach is
demonstrated using in-service feature data from the AH64D TRGB and the results have
shown the proposed methods to be a promising tool for maintenance decision-making.
As an extension of research on methodologies to improve PM and CBM decision
support, a thioether mist lubrication is explored for its feasibility as a backup
lubrication system for helicopters. The aim is to reduce the mishap severity category
which in turn eases the extension of PM interval or its replacement with a CBM task.
An experimental setup was developed to test the thermal properties of a spur gearbox
with thioether mist lubrication under various load and speed conditions and it was
shown that only a very small volumetric flow of lubricant is required to preserve the
gears from damage in oil starved environment. As such, a thioether based mist backup
system can potentially reduce the risk of oil starvation failures significantly.
15
Njuguna, James A. K. "Micro- and macro-mechanical properties of aerospace composite structures and their dynamic behaviour." Thesis, City University London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440734.
Повний текст джерела
16
Jones, Gareth. "Control of flow around an aerofoil at low Reynolds numbers using periodic surface morphing." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/51101.
Повний текст джерелаАнотація:
This thesis combines experimental and computational methods to investigate the low Reynolds number flow (Re = 50,000) around a NACA 4415 aerofoil, and its control using periodic surface motion. A physical model was fabricated and tested in a closed-loop wind tunnel and a good comparison between the experiments and computations was achieved. Time-resolved measurements of the surface reveal that the peak-to-peak displacement is a function of both the amplitude and frequency of the input voltage signal but the addition of aerodynamic forces does not cause significant changes in surface behaviour. The vibration mode shape exhibits a single peak and is uniform in the spanwise direction at frequencies below 80Hz, above which a change in the vibration mode occurs. The flow around the actuated aerofoil was compared with the baseline (i.e. unactuated) flow. The latter exhibits a large separation region and, as a result, produces relatively high drag and low lift forces. By analysing the experimental and computational data, the large separation zone was found to be the result of laminar separation without reattachment. Transition to turbulence does occur but too close to the trailing edge, and far from the wall, for sufficient pressure recovery to take place for reattachment. When actuated at 70 Hz, the frequency spectra in the vicinity of the trailing edge and near-wake was found to be dominated by the actuation frequency. Sharp peaks suggest the production of Large Coherent Structures at this frequency. In agreement with the experiments, the computations revealed that the vortex shedding from the shear layer was 'locked-on' to the surface motion and spanwise coherent vortices were produced during each actuation cycle. The increased momentum entrainment associated with them enabled a large suppression of the separated region, which was seen in both the experiments and computations. The result was a simultaneous increase in Lift and decrease in Drag and therefore a large increase in the L/D ratio.
17
Moore, Gareth Edward. "Electro-mechanical interactions in aerospace gas turbines." Thesis, University of Nottingham, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.768249.
Повний текст джерелаАнотація:
The provision of electrical power on modern aircraft is a necessary and growing aspect of a gas turbine's function. The replacement of traditional pneumatic, hydraulic and mechanical systems with electrical equivalents means that electricity is now the dominant means of power distribution on aircraft. However, the electrical loads seen on aircraft present challenges, as they are time varying and are often non-linear. This is particularly true for loads such as radar. The aviation industry has adopted the term More Electric Aircraft (MEA) to describe the latest generation of aircraft with a high reliance on electrical power. There is potential for significant interaction between the transient variation of electrical loading and the gas turbine (both drive-train and engine core). Engine testing and initial simulation work support this view. Understanding of this phenomenon must now be furthered through modelling and testing. This thesis presents simulation models of a transmission system and generator interface, which provides a useful kernel for a modelled system to assess electro-mechanical interaction. This is extended to multi-domain simulation work through the successful interlinking of transmission, generator and an electrical load model. These models have been validated, at a domain level, against analytical expressions, and also as a complete electro-mechanical system against test data. To allow more control over test conditions, an electro-mechanical test rig is designed and constructed. The data from the test rig is analysed and compared to modelled results. This thesis also presents potential mitigation actions for avoiding unwanted electro-mechanical interactions during electrical load transients. A method of extracting transient mechanical torque information from a gas turbine's electrical generator's terminal quantities is included. At a system level, the simulation work in this thesis potentially enables the development of future designs with improved power systems integration throughout the entire airframe. High level control could allow optimisation of the power conversion process between gas turbine spool and electrical systems, with increased intelligence in the movement of power between components.
18
Vogel, Daniel Mario. "An analysis of human factors aspects in operational fuel saving." Thesis, City University London, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665453.
Повний текст джерелаАнотація:
Over the last few years, the reduction of operational costs and control of pollutant emissions have become central issues for the commercial aviation industry, and as a result, airlines have been increasingly focusing their attention on operational fuel saving techniques. However, even though the practical implementation and economic potential of these techniques have been exemplified in a number of papers, little research has been dedicated to a systemic investigation of the effects of operational fuel saving on the human component of the system, i.e., the flight crew of an aircraft. This research examines this area, and investigates the human factors aspects in context with the application of operational fuel saving on the Airbus A 320 series aircraft. The study presents a detailed analysis of the flight crew's performance and motivational factors related to the topic of interest, which were investigated by means of an online survey and a controlled simulator experiment. Results of the analysis revealed that the application of operational fuel saving imposes a number of latent performance impairments on the flight crew. Motivational factors were shown to be disrupted by the flight crew's inability to achieve satisfaction from the application of operational fuel saving. The implications of these findings are wide-ranging, as they show, in essence, that the system's safety and efficiency relies solely on the flight crew's cognitive flexibility and workload compensation capability, while structured analyses and conceptual frameworks in regard to the human factors aspects of operational fuel saving are absent.
19
Bellocq, Pablo. "Multi-disciplinary preliminary design assessments of pusher counter-rotating open rotors for civil aviation." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/10280.
Повний текст джерелаАнотація:
As a consequence of fuel cost escalation and increased stringent engine emission
regulations, interest in counter-rotating open rotor engines (CRORs) has been
renewed. R&D efforts are currently ongoing to develop the technologies required to
ensure the appropriate levels of structural integrity, noise, vibrations and reliability.
The assessment of the impact of the main low pressure preliminary design and control
parameters of CRORs on mission fuel burn, certification noise and emissions is
necessary to identify optimum design regions. These assessments aid the
development process when compromises need to be performed as a consequence of
design, operational or regulatory constraints. These assessments are not possible with
the state-of-the-art aero-engine preliminary design simulation tools.
Novel 0-D performance models for counter-rotating propellers (CRPs) and differential
planetary gearboxes, as well as 1-D and 0-D performance models for counter-rotating
turbines (CRTs) were developed and verified using available data. These models were
used to create 0-D pusher geared (GOR) and direct drive (DDOR) open rotor engine
performance simulation modules allowing the independent definition of the design and
operation of each of the two counter-rotating parts of the CRP and CRT.
A multi-disciplinary preliminary design simulation framework was built using the novel
engine performance modules together with dedicated CROR aircraft performance,
engine geometry and weight, gaseous emissions and certification noise simulation
modules. Design space exploration and trade-off studies were performed and minimum
fuel burn design regions were identified for both the pusher GOR and DDOR. A 160
PAX aircraft flying a business mission of 500 NM was chosen for these studies.
Based on the assumptions made, the main conclusions of these studies are as follows.
· Fuel burn reductions of ~1-2% are possible through optimised propeller control
· The propeller diameter for minimum mission fuel burn lies between 4.26 and 4.7 m
· The design nozzle pressure ratio for minimum mission fuel burn lies between 1.55
and 1.6
· CRPs with 13 or 14 blades per propeller provide minimum mission fuel burn
· Increasing spacing between the propellers reduces noise significantly (~6 EPNdB for
each certification point) with a relatively small fuel burn penalty (~0.3-0.5%)
· Relative to unclipped designs, 20% clipped CRPs reduce flyover noise by at least 2.5
EPNdB and approach noise by at least 4.5 EPNdB. The corresponding fuel burn
penalty is ~2 % for a GOR and ~3.5% for a DDOR.
· Sideline and flyover noise can be reduced by increasing the diameter of the CRP and
appropriately controlling CRP rotational speeds. Approach noise can be reduced by
either reducing the diameters or the rotational speeds of the propellers.
· The rotational speed of the forward propeller for minimum noise is higher than that for
minimum mission fuel burn for all the studied CROR designs.
· Regardless of clipping, reducing the rotational speed of the rear propeller relative to
the forward propeller reduces noise and, to a certain limit, also mission fuel burn.
(further reductions in rotational speed would have an adverse effect on fuel burn)
· An increase in the number of blades results in an increase in certification noise.
The main recommendations for further work are as follows.
· Integrating the 1-D CRT model with the 0-D DDOR performance model in order to
assess the impact of different CRT design criteria at engine and mission levels
· Developing preliminary design methods to account for changes in aircraft weight and
aerodynamics due to changes in engine design and required cabin noise treatment.
20
Camilleri, William. "An assessment of high overall pressure ratio intercooled engines for civil aviation." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/10419.
Повний текст джерелаАнотація:
As gas turbine technology matures, further significant improvements in engine efficiency will be difficult to achieve without the implementation of new aero-engine configurations. This thesis delivers an original contribution to knowledge by comparing the design, performance, fuel burn and emission characteristics of a novel geared intercooled reversed flow core concept with those of a conventional geared intercooled straight flow core concept. This thesis also outlines a novel methodology for the characterisation of uncertainty at the conceptual design phase which is useful for the comparison of competing concepts. Conventional intercooled aero-engine concepts suffer from high over-tip leakage losses in the high pressure compressor, high pressure losses in the intercooler installation and increased weight and drag whereas the geared intercooled reversed flow core concept overcomes some of these limitations.
The HP-spool configuration of the reversed core concept allows for an increase in blade height, a reduction in over-tip leakage losses and an increase in overall pressure ratio. It was concluded that a 1-pass intercooler would be the lightest and most compact design while a 2-pass intercooler would be easier to manufacture. In the reversed flow core concept the increased length of the 2-pass intercooler could be accommodated. In this concept the mixer also allows for a reduction in fan pressure ratio and a useful reduction in component losses. Both intercooled concepts were shown to benefit from the use of a variable area bypass nozzle for the reduction of take-off combustor outlet temperature and cruise specific fuel consumption.
The intercooled cycles were optimised for minimum fuel burn and it was found that the reversed flow core concept benefits from higher overall pressure ratio and lower fan pressure ratio for an equivalent specific thrust. This leads to an improvement in thermal efficiency and more than a 1.6% improvement in block fuel burn. The NOx during landing and take-off as well as during cruise was found to be slightly more severe for the reversed flow core concept due to its higher overall pressure ratio. The contrails emissions of this concept were occasionally higher than for a year 2000 turbofan but only slightly higher than for the straight core concept. This dissertation shows that in spite of input uncertainty the reversed flow core intercooled engine is a promising concept. Further research should focus on higher fidelity structural and aerodynamic modelling.
21
Pervier, Hugo. "Emissions modelling for engine cycle and aircraft trajectory optimisation." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/10396.
Повний текст джерелаАнотація:
The aviation industry is currently experiencing a growth rate of about 4% per annum and this trend
is expected to continue into the future. One concern about this growth rate is the impact it will have
on the environment particularly in terms of emissions of CO2, NOx and relatively recently also cirrus
clouds induced by contrails.
The ACARE has set emissions reduction targets of 50% reduction of CO2 and noise and 80% reduction
of NOx by 2020 relative to Y2000 technology. Clean Sky and other large EU collaborative projects
have been launched in an effort to identify new, more efficient, aircraft and engine technologies,
greener operational and asset management practices and lower life cycle emissions. This PhD
research was funded by and contributed to the Systems for Green Operations Integrated Technology
Demonstrator (SGO-ITD) of the Clean Sky project.
The key contribution to knowledge of this research is the development and application of a
methodology for simultaneous optimisation of aircraft trajectories and engine cycles. Previous
studies on aircraft trajectory optimisation studies, published in the public domain, are based on
relatively low fidelity models. The case studies presented in this thesis are multi-objective and based
on higher fidelity, verified aircraft, engine and emissions models and also include assessments of
conceptual engines with conceptual LPP combustors.
The first task involved the development of reactor based NOx emission prediction models for a
conventional aero gas turbine combustor and a novel conceptual lean pre-mixed pre-vaporised
combustor. A persistent contrails prediction model was also developed.
A multi-disciplinary framework comprising a genetic algorithm based optimiser integrated with an
engine performance, an aircraft performance and an emission prediction model was then
developed. The framework was initially used to perform multi-disciplinary aircraft trajectory
optimisation studies and subsequently both aircraft trajectory and engine cycle optimisation studies
simultaneously to assess trade-offs between mission fuel burn, flight time, NOx production and
persistent contrails formation ... [cont.].
22
Dababneh, Odeh. "Multidisciplinary design optimisation for aircraft wing mass estimation." Thesis, Cranfield University, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/10172.
Повний текст джерелаАнотація:
The implementation of key technologies in the initial stages of the aircraft wing design process has always represented a substantial challenge for aircraft designers. The lack of reliable and accessible wing mass prediction methods ¬which allow assessment of the relative benefits of new technologies for reducing structural wing weight - is of significant importance. This necessitates the development of new and generally applicable wing mass estimation methods. This thesis aims to create a new framework for estimating the mass of metallic and composite transport aircraft wings via finite element multidisciplinary analysis, and design optimisation techniques. To this end, the multidisciplinary static strength and stiffness, dynamic aeroelastic stability, and manufacturing constraints are simultaneously addressed within an optimisation environment through a gradient-based search algorithm. A practical optimisation procedure is presented as part of the sizing optimisation process, with enhanced features in solving large-scale nonlinear structural optimisation problems, incorporating an effective initial design variable value generation scheme based on the concept of the fully stressed design. The applicability and accuracy of the proposed approaches is accomplished by conducting a number of case studies in which the wingbox structure of the public domain NASA wing - commonly referred to as the Common Research Model (CRM) - is optimised to produce a minimum mass design.
The results of a case study examining minimisation of the mass of the CRM wingbox structures designed using four different models of increasing structural fidelity prove that the multidisciplinary design optimisation framework can
successfully calculate the mass of realistic real-world aircraft wing designs. This provides an insight into the competence of certain wingbox models in predicting the mass of the metallic and composite primary wing structures to an acceptable level of accuracy, and in demonstrating the relative merits of the wingbox structural complexity models under consideration and the computational resources necessary to achieving the required degree of accuracy ... [cont.].
23
Hussain, Mazhur. "Laser diagnosis of gas turbine fuel sprays : scaling effects on NOx emissions and stability." Thesis, Cranfield University, 2009. http://dspace.lib.cranfield.ac.uk/handle/1826/8291.
Повний текст джерелаАнотація:
This thesis first provided strategic recommendations for the research sponsor, Rolls-
Royce plc (RR) and then applied optical diagnostics to measure aero gas turbine fuel
spray properties in order to predict Oxides of Nitrogen (NOx) emissions and
combustion instability. Analysis of the large civil aero engine sector suggested possible
courses of action for RR to protect itself from short-term market volatilities and also
prepare for three long term changes in strategic operating context: air traffic growth;
tighter United Nations enforced aero engine combustion emissions legislation and entry
of civil aviation into the European Union Emissions Trading Scheme. A collaborative
game theoretic approach was explored during the pre-competitive, pre-technology,
capability acquisition aero engine design phase on unproven future technologies to
reduce R&D expenditures, development times and the costs of failure. Lean
Prevapourised Premixed combustion demands excellent spray atomisation quality to
sustain combustion efficiency, stability and to minimise pollutants. Post development
of an improved procedure to calibrate laser signals, methodology to predict NOx and
technique to optimise rig operating conditions that minimised fractional discrepancies in
two-phase flow behaviour with corresponding engine conditions, this thesis applied
quantitative Planar Laser Induced Fluorescence (PLIF) and Laser Sheet Dropsizing
(LSD) to measure the fuel placement and dropsize distribution in the near nozzle
regions of RR liquid-fuelled hybrid, airblast and pressure-swirl sprays. Measurements
were made under non-combusting, low pressure conditions and results were processed
to identify fuel injector designs that exhibited low emissions and high stability for the
Affordable Near Term Low Emissions (ANTLE) and Instability Control of Low
Emission Aero-Engine Combustors (ICLEAC) engine demonstrator programmes.
Results also provided validation data and boundary conditions for spray computational
codes. Research findings will improve RR core competencies in fuel injection research
to accelerate the development and deployment of low emissions aero engine technology.
24
Harasani, W. "Aircraft conceptual design decision through operational modelling." Thesis, Cranfield University, 2005. http://dspace.lib.cranfield.ac.uk/handle/1826/11093.
Повний текст джерелаАнотація:
Aircraft manufacturing is not only a difficult business but also a very competitive one,
the consequences of any drop in sales would cost billions, loss of jobs, and maybe an
economical failure. Therefore, concentrating on just flight performance and adding new
technologies just because they exit is not enough to win the airlines attention, especially
the flow cost carriers.
Manufactures must be able to convince operators that the application of a new design or
technology will produce a favourable change in the bottom line of their balance sheets
and not just a reduction in fuel burn.
Aircraft designers must put more emphasis on what happens to the aircraft after it leaves
the assembly line, through the designed life operation cycle of the aircraft with the airline
customer, quality should be built in to the aircraft. Knowing what are the airline's
concerns, how the aircraft with a given design behaves, and the issues that the airline has,
is vital.
Firstly, it is important to know what are the issues that the airline has, the costumer
(airlines) needs are identified, and, since fleet planning is the top level decision making
department in the airline in which a decision is made to buy one aircraft over the other, it
is important to understand the process and the elements that are involved in fleet
planning. So fleet planning was studied.
Second different technologies for the design have been looked at and selected. Then the
aircraft, airline, airport, and air traffic control are studied, as well as the interaction
between them.
A key element of the research is a simulation program DEBOS that has been built to see
the impact of the different design technologies and concepts through the operation of a
simulation fleet size of 23 aircraft. The Boeing777 aircraft has been chosen to be the base
line of the study.
Finally, it was found that a given technology with improved performance, or a new
concept, would improve the aircraft attractiveness only if it has better life cycle behaviour
characteristics.
25
Gaffney, James. "Theoretical methods to predict near-field fuselage installation effects due to inlet fan tones." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/413589/.
Повний текст джерелаАнотація:
There are many analytical models to predict turbofan noise radiation in a free field. However, these models explicitly ignore the effect of the aeroplane components on the engine noise. The effects of the aeroplane on the radiated noise must be included because it is the installed engine that affects people in the cabin and community. The original contribution of this thesis is to present a theoretical model for the near-field fuselage installation effects on tonal noise radiating from a turbofan engine inlet. Historically, the fuselage installation effects have been modelled using theoretical methods for open-rotor type sources. Installation effects include the scattering effect from the fuselage, and the refraction effect of the boundary layer running down the fuselage. In this thesis the established techniques are extended to include a new sophisticated analytical source for spinning modes radiating from a circular duct. The source model includes the diffraction effect of the duct lip. The model applies Fourier methods and implements the Wiener-Hopf method for diffraction. Owing to the physics of the problem, simplications in geometry and flow do not curtail the validity of the predictions. The refraction effect was quantified by evaluating the difference between sound pressure levels with and without the boundary layer. Upstream of the source the refraction leads to a paucity of surface acoustic pressure, yet downstream the boundary-layer effect was minimal. Further investigations led to an alternative method of simulating refraction by altering wavenumbers in Fourier space. The installation method was optimised for a turbulent boundary-layer profile by replacing a power-law with a scaled step-change boundary-layer profile. The model developed in this thesis combines the most sophisticated analytic radiation models with current installation models. Due to the speed of the method, the intended purpose for industry is to refine variables via parametric studies. Once these are established, a numerical method could include more complex geometry and flow to the model. By calculating the noise on the outside of the fuselage, the quantity and distribution of acoustic lagging can be optimised. This, over the lifetime of an aeroplane, could lead to appropriate noise levels in the cabin whilst achieving potential reductions in fuel consumption, emissions and costs.
26
Rodriguez, Garcia Paul. "Aircraft turbine combustion noise processing." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/413857/.
Повний текст джерелаАнотація:
Appraisal of the noise produced at the combustion stage in a jet engine is becoming more important, as fan and jet noise have been significantly reduced over many years. Therefore, combustion noise is contributing more to overall noise, especially at low jet velocities. Environmental regulations stipulate that gas emissions from a jet engine should be reduced. Thus, new techniques have been introduced in their operation, especially concerning the combustion process. Accordingly, there is a need for improved processing methods in order to extract combustion noise from other sources in new build engines. A novel processing technique to extract turbofan engine combustion noise called 3S-Array is presented. It has been developed using a multiple coherence technique with data acquired in the in-duct and external sound fields of a jet engine. In-duct sensors are located in the combustion chamber and in the nozzle of the engine, and external data is acquired using an array of microphones. A beamformed signal focused on the nozzle of the engine is generated with the data from the external array. Jet noise and in influences of the room on the array output are reduced using this focusing technique, which is referred to as Focused Beamformed Output (FBO). Results show that using this new 3S-Array technique with two of the in-duct sensors and the focused beamformed signal as the third one, provides a better estimator of combustion noise than the 3-signal coherence technique alone, or the Coherence-Output Power Spectra (COP), both of which are reported in the literature as methods for the extraction of combustion noise from the radiated noise spectrum.
27
Nind, Alexander David. "A technoeconomic risk assessment of conventional aero-gas turbines : technological limits and future directions." Thesis, Cranfield University, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/11220.
Повний текст джерелаАнотація:
Increasing environmental awareness, uncertain economic climates and fluctuating fuel prices have led to airlines investigating the means to lower aircraft fuel burn, emissions and noise, while maintaining the highest possible safety standards. This is done in order to reduce operating costs as well as a desire to offer customers more environmentally responsible transport options. The jet engine has been a fundamental part of passenger aircraft travel and has evolved to become more efficient and quiet. With an aim to improve the overall efficiency of the gas turbine, the industry has consistently sought to improve thermal and propulsive efficiency. Higher thermal efficiencies have been achieved through increased overall pressure ratios and the turbine entry temperatures, while higher propulsive efficiencies has been achieved through increase in bypass ratios. Conventional technology is however reaching the limits of any further improvements. This study seeks to investigate these design limits for the conventional aero gas turbine and focusses on the propulsion system of short to medium range jet aircraft, specifically catering to low cost airline operations in Europe. A techno-economic risk analysis approach was followed through the utilisation of a flexible multi-disciplinary framework. This allows a multitude of critical parameters and factors to be investigated and their effects established. Some of the key parameters investigated include the effect of design optimisation on SFC, mission fuel burn, engine sizes and weights. By first quantifying the current design parameters and associated constraints for the selected conventional propulsion system, an optimisation study is carried out to identify the possible design limits to which the conventional technology may be pushed. It is therefore possible to then quantify the maximum benefit available to this mature technology and also to further identify which future technologies may offer the most benefits for a particular airline market strategy. The key contribution to knowledge from this study is to therefore provide a techno-economic risk assessment of an optimised conventional high bypass ratio turbofan and establish the design limits that may be needed to achieve further benefits from conventional designs. The study is undertaken from an operator/airline perspective and further quantifies the point at which the investment opportunity of a novel technology justifies the risks associated with it. This study has shown that there is still potential for fuel burn improvement from the evolution of the conventional turbofan. This improvement could be up to 15-20% when compared to technology of the year 2000. This is shown to be achieved through improvement material and design of the high pressure compressor spool, aimed at essentially reducing weight and diameters. The study also includes a qualitative discussion on novel, disruptive technologies, and the risks associated with their introduction as future propulsion systems.
28
Kursad, Sezer Huseyin. "Laser drilling of thermal barrier coated jet-engine components." Thesis, University of Manchester, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685444.
Повний текст джерела
29
Russhard, Peter. "Development of a blade tip timing based engine health monitoring system." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.734183.
Повний текст джерела
30
Noor, Mohamed Sulfickerali. "Efficient CFD based aero-thermo-mechanical modelling for aircraft engine design." Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/813497/.
Повний текст джерелаАнотація:
In this thesis, improved and faster CFD based aero-thermo-mechanical methods that can be used to optimize engine configurations early in the design process are described. Axisymmetric models of 3D non-axisymmetric features such as protrusions, holes and honeycomb liners are developed for use in this context, and 3D unsteady CFD is used to investigate the flow physics. Initially, the research focussed on modelling of a rotor-stator disc cavity. Steady CFD validations for a plane disc and for a disc with protrusion were carried out and a simplified body force model was developed for including the 3D effects of rotating and stationary bolts into the axisymmetric CFD models. The simplified rotor bolt model was verified and validated by comparing the results with Sussex Windage rig test data and 3D CFD data. The simplified stator bolt model was verified using 3D CFD results. The simplified rotor bolt model was found to predict the drag and windage heat transfer with reasonable accuracy compared to 3D sector CFD results. However, 3D sector CFD under-predicts the high core flow swirl and the adiabatic disc surface temperature inboard of the bolt, compared to experimental data. In the second part of the study, unsteady Reynolds averaged Navier-Stokes (URANS) calculations of the rotating bolts cases were performed in order to better understand the flow physics. Although the rotor-stator cavity with bolts is geometrically steady in the rotating frame of reference, it was found that the rotor bolts generate unsteadiness which creates time-dependent rotating flow features within the cavity. A systematic parametric study is presented giving insight into the influence of the bolt number and the cavity geometric parameters on the time dependent flow within the cavity. The URANS calculations were extended to a high pressure turbine (HPT) rear cavity to show possible unsteady effects due to rotating bolts in an engine case. Following this, the body force model was adapted to model the rotating hole velocity changes and flow through honeycomb liners. The honeycomb and hole models were verified by comparing the results with available experimental data and 3D CFD calculations. In the final part of the study, coupled FE-CFD calculations for a preliminary design whole engine thermo-mechanical (WETM) model for a transient square cycle was performed including the effects of non-axisymmetric features. Six cavities around the HPT disc were modelled using CFD. The coupled approach provides more realistic physical convective heat transfer boundary conditions than the traditional approach. The unvalidated baseline thermo-mechanical model results were verified using the high fidelity coupled FE-CFD solution. It was demonstrated that the FE-CFD coupled calculations with axisymmetric modelling of 3D features can be achieved in a few days time scale suitable for preliminary engine design. The simplified CFD based methods described in this thesis could reduce the computational time of transient coupled FE-CFD calculations several orders of magnitude and may provide results as accurate as 2DFE-3DCFD coupled calculations.
31
Christie, Robert. "Propulsion system integration and modelling synthesis." Thesis, Cranfield University, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/11711.
Повний текст джерелаАнотація:
Concerns over fuel costs, along with the ever increasing requirement to reduce the impact of emissions, means that the world's airlines continue to introduce low-noise and more fuel-efficient aircraft into their fleet. Increasing the engine bypass ratio is one way to improve propulsive efficiency. However, historically an increase in the bypass ratio (BPR) has usually been associated with an increase in the fan diameter. Consequently, there can be a notable increase in the impact of the engine installation on the overall aircraft performance. For example, although the typical increase in fan diameter is generally beneficial to the uninstalled engine specific fuel consumption, the increase in the nacelle drag and weight are detrimental to the aircraft performance. There is also likely to be a stronger aerodynamic coupling between the engine and the airframe. Overall there is a risk that the gains in uninstalled engine performance are wholly or partly lost due to adverse engine-airframe installation and interference effects as well as additional nacelle weight. It is clear that the quantification of the elements of installation drag is a key aspect in the assessment of the likely developments in engine design as well as on the installation requirements for future airframe architectures. The overall aim of this research is to determine the effect of nacelle size, weight, geometry and installation on flight efficiency. This aim has been addressed through the development of a framework which combines the engine thermodynamic model, aircraft performance, engine installation aspects and a flight trajectory approach. This framework has been developed to assess the relative importance of various engine installation aspects on the overall flight fuel burn for a range of short-haul and long-haul configurations.
32
Stone, Jonathan. "Cones of silence, complex rays, & catastrophes : novel sources of high-frequency noise in jets." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/393737/.
Повний текст джерелаАнотація:
As industrial design continues to look at less conventional jet engine nozzles that produce typically asymmetric mean flows, there is now a need for completely 3D noise prediction schemes. To date, most prediction schemes have been based on extensions of the acoustic analogy given by Lighthill. The most popular, due to Lilley for a parallel shear flow, proves too restrictive when considering the flows from complicated nozzle geometries. However, a generalised acoustic analogy based on an arbitrary mean flow with prescribed nonlinear source terms remains a viable method for industrial computations. Since any source can be decomposed into a sum of point sources, a critical step in acoustic analogies is the construction of the mean ?eld Green's function. In general the numerical determination of the Green's function still remains a major undertaking, and so much attention has been focused on the simpli?cations a?orded to high-frequency ray approximations. Typically ray theory su?ers from three main de?ciencies: multiplicity of solutions, singularities at caustics, and the determining of complex solutions. The latter lying beyond-all-orders of the divergent ray expansion in the wavenumber parameter, but proving critical when computing the acoustic held in shadow zones such as the cone of silence. The purpose of this thesis is to generalise, combine and apply existing methods of tackling these de?ciencies to moving media scenarios for the ?rst time. Multiplicities are dealt with using an equivalent two-point boundary-value problem, whilst non-uniformities at caustics are corrected using di?raction catastrophes. Complex rays are found using a combination of imaginary perturbations, an assumption of caustic stability, and analytic continuation of the receiver curve. As a demonstration of the solver two problems are studied with increasing utility to jet noise. The most important is the application to Lilley's equation for an o?-axis point source. This solution is representative of high-frequency source positions in real jets and is rich in caustic structures. Full utilisation of the ray solver is shown to provide excellent results.
33
Van, Mierlo Koen. "Computational analysis of the flow field and noise radiation of a generic main landing gear configuration." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/388076/.
Повний текст джерелаАнотація:
This study investigates the flow field and acoustics of a generic four wheel main landing gear. The landing gear is an important airframe noise source during the approach phase. The characteristics of the flow field around the bogie area of the main landing gear are largely unknown. CFD simulations using the DES turbulence model have been used to calculate the unsteady flow field around a generic landing gear model. The surface pressure data has been sampled and used in a FW-H solver to determine far field noise levels. Two different landing gear models have been used, a simplified geometry and a more realistic complex geometry. Three different bogie angles have been simulated: horizontal bogie aligned with the flow, 10⁰ toe up and 10⁰ toe down. Strong streamwise vortices are generated at the front wheels of the landing gear. The trajectory of these vortices determines where the turbulent flow interacts with the downstream components. This interaction leads to surface pressure fluctuations which are a major noise source. The flow field of the simplified configurations shows a consistent trend of the trajectory of the streamwise vortices with respect to changes in bogie angle. The far field noise levels generated by the different components of the simplified configurations are related to the distance at which the streamwise vortices pass. The additional components of the complex landing gear geometry change the characteristics of the flow field. The strong streamwise vortices persist but they do not show the same trend as for the simplified configurations. The wake of the articulation link generates a turbulent in flow for the other components. The different characteristics of the flow field of the complex configurations lead to significant changes in the far field noise levels of the components compared to the simplified configurations.
34
Javed, Ali. "Investigation on meshfree particle methods for fluid structure interaction problems." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/386297/.
Повний текст джерелаАнотація:
The research aims to investigate the application of meshfree particle methods for computational modelling of the Fluid Structure Interaction problems with particular emphasis on flow around cylindrical objects and aerofoils. For this purpose, a solution scheme has been developed for solving incompressible, viscous Navier-Stokes (N-S) equations over meshfree particles. Spatial derivatives appearing in N-S equations are dealt with using radial basis functions infinite difference mode (RBF-FD). A comparative study has also been conducted between implicit and explicit in time solution schemes for N-S equations over meshfree nodes. Subsequently, a coupled meshfree and mesh-based solution scheme is proposed, over hybrid fluid grid, for incompressible, viscous flow around stationary as well as moving objects. The aim of this coupled solver is to provide efficiency and flexibility by combining the advantages of both meshfree and mesh-based methods. The coupled solution scheme suggests generating a body conformal meshfree nodal cloud around the solid body in the near field. A static Cartesian grid surrounds the meshfree cloud in the far field. The Meshfree nodes offer flexibility in dealing with solid motion by moving along the solid boundary without necessitating re-meshing. The Cartesian grid, on the other hand, provides improved performance by allowing faster computation owing to the use of efficient mesh based method. Flow equations, in Arbitrary Lagrangian-Eulerian (ALE) formulation, are solved using RBF-FD based scheme over moving meshfree nodes. Conventional infinite differencing is used over static Cartesian grid for flow equations in Eulerian formulation. The coupled solution scheme, on hybrid grid, is employed for closely coupled Fluid Structure Interaction problems. The equations for solid motion are solved using classical Runge-Kutta method. Close coupling between fluid and structural solvers is realized by a sub-iterative prediction-correction algorithm. In order to reduce computational overhead due to sub-iterations, only near field flow (in meshfree zone) is solved during inner iterations. Solution over full fluid domain is sought during outer (time step) iterations only, when the convergence at fluidsolid interface has already been reached. The solution scheme is also applied for high Reynolds number problems. For this purpose, a stabilization term is included in the flow equations to suppress the spurious oscillations. The stabilization term is derived using vimomentum balance equation over control volume and applying higher order Taylor series expansion of momentum flux and fluid forces. In order to avoid ill-conditioning and accuracy problems related to RBF matrices in domains having varying nodal density, use of shape adaptive RBFs are proposed. In that, the shape parameter of the radial basis function is varied according to local nodal density. Moreover, adaptive sizing of influence domain has also been introduced to maintain suitable number of neighbouring particles. These adaptive techniques are found to be useful as they allow much finer nodal distribution at regions of interest enabling accurate capturing of flow gradients and leading to better results. The use of hybrid grid offers flexibility in dealing with moving boundaries. Moreover, in addition to allowing faster computing over Cartesian grid, it also enables using the reduced fluid domain during inner FSI iterations and therefore helps reduce the number of computations in the fluid domain during fluid-solid coupling. The solution scheme was tested for problems relating to flows around static as well as moving cylinders and aerofoils. Flow induced vibrations have been studied with one and two degrees of freedom. The results are found to be in good agreement with previous numerical work and experimental results.
35
Langmaak, Stephan. "Cost optimization tools for advanced gas turbine technologies." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/388048/.
Повний текст джерелаАнотація:
This thesis presents two studies that illustrate how cost modelling can be integrated into the various design process stages, ranging from strategic gas turbine and airframe system design to preliminary and detailed component design and production planning. The first study investigates which cruise speed the next generation of short-haul aircraft with 150 seats should fly at and whether a conventional two- or three-shaft turbofan, a geared turbofan, a turboprop or an open rotor should be employed in order to make the aircraft's direct operating cost robust to uncertain fuel and carbon (CO2) prices in the Year 2030, taking the aircraft productivity, the passenger value of time and the modal shift into account. To answer this question, an optimization loop was set up in MATLAB consisting of nine modules covering gas turbine and airframe design and performance, light and aircraft fleet simulation, operating cost and optimization. If the passenger value of time is included, the most robust aircraft design is powered by geared turbofan engines and cruises at Mach 0.80. If the value of time is ignored, however, then a turboprop aircraft flying at Mach 0.70 is the optimum solution. This demonstrates that the most fuel-efficient option, the open rotor, is not automatically the most cost-efficient solution because of the relatively high engine and airframe costs. The second study shows how a factory cost model can be combined with a parametric component production time model, to not only calculate costs at the manufacturing operation level for production planning, but also the total unit costs of future integrally bladed disc (blisk) designs for component trade-off studies. As future process times can only be estimated and the correlation between operation times and blisk design parameters, including the number of blades, the disc diameter and other design variables, is never perfect, all operation times have uncertainty distributions. These are cascaded through the model to generate a probability distribution of the unit cost.
36
Spagnolo, Stefano. "Unsteady aerodynamic loads on aircraft landing gear." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/397089/.
Повний текст джерелаАнотація:
The aim of the current work is to improve the accuracy and efficiency of aerodynamic load predictions on landing gear in flight conditions, as part of the UK TSB ALGAAP (Advanced Landing Gear Aero-loads and Aero-noise Prediction) project. To this purpose, both experiments and simulations are performed on simplified landing-gear components. The new geometry presented in this work is a configuration composed of two simplified wheels in tandem. Experimental and numerical results from a single-wheel geometry are used as a baseline for comparison. The models are tested in the University of Southampton wind-tunnel complex, where forces, surface pressures and velocity fields are measured to gain a better understanding of both mean and unsteady flow features. Also, a vibration test is employed for the first time in a wind tunnel to validate the unsteady load measurements. The results of the experiments are presented in this thesis, showing the wake structure of the flow past the tandem wheels and the configurations that provide minimum values of mean drag and unsteady fluctuations. On the same single-wheel and tandem-wheel geometries, advanced numerical simulations such as Delayed Detached-Eddy Simulations (DDES) with the Spalart-Allmaras equation are used to predict the flow. The methodology is based on the use of techniques to improve the efficiency of the process, thus unstructured grids with a semi-structured boundarylayer mesh are employed to achieve the desired results. The results of the simulations are compared with the experiments, showing the importance of modifying the standard turbulence model in order to consider the laminar-turbulent transition for improved accuracy. Proper Orthogonal Decomposition (POD) is also employed to analyse the data of both experiments and simulation, in order to obtain a better insight of the flow features. Finally, additional simulations are performed on a simplified four-wheel landing gear to understand the effects of additional components, such as axles and bogie beam. The results show the high importance of the axles on the flow past the wheels and the effect of the modifications of the turbulence model on the full landing gear.
37
Zeng, Chuikuan. "Development of a new class of noise environment assessment codes." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/399984/.
Повний текст джерелаАнотація:
A novel linearised Navier-Stokes equations method including turbulence information is developed to simulate sound propagation especially considering the inhomogeneous medium with non-uniform flows. The emphasis is on the development of methodology and the applications to further the understanding of sound propagation in a turbulent flow. To govern the acoustic-vorticity interaction, which is important in shear flows,perturbation Reynolds stress is used to introduce the turbulent information. A linear hydrodynamic stability analysis demonstrates that the turbulence can stabilize the flow;therefore this method can overcome the instability issue associated with variants of the linearised Euler equations method. Numerical simulations are performed to validate the stability of the proposed method dealing with sound propagation in shear flows. An algebraic turbulence model is used in a benchmark case with a prescribed mean flow profile. Moreover, the turbulent viscosity solved numerically is employed to study turbofan aft noise radiation. The numerical experiments demonstrate the acoustic-vorticity interaction can be resolved by this linear acoustic propagation model to some degree. The resulting effects are evaluated in respect of the near-field and far-field results. Moreover, the attenuation of sound in fully developed turbulent pipe flows is solved and validated against experimental results. Subsequently, the acoustic damping induced by turbulence at high-order duct modes is investigated. Finally, this method is used to investigate the effects of the wall boundary layer on the external noise radiation in respect of two aspects, namely the engine noise impact on the fuselage at cruise conditions and the far-field noise distribution at take-off/landing conditions. These studies demonstrate the stability of the proposed method in the presence of shear layers and density gradients, while show the ability of the method to qualify the attenuation of sound by turbulence.
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Fattah, Ryu. "The noise generation by a main landing gear door." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/390837/.
Повний текст джерелаАнотація:
Experimental measurements and numerical simulations were conducted on a simplified main landing gear model that consists of a leg-door, and a main strut in a parallel configuration. The effects of varying the leg-door angle of attack, and the gap distance between the two elements, were initially studied by two-dimensional and low-order numerical simulations, using the unsteady Reynolds-Averaged Navier-Stokes equations. The strut diameter was specified to the same diameter as a full-scale main landing gear, and simulated under a free-stream Mach number of 0.2, and a Reynolds number based on the cylinder diameter of 1:7 x 106. Further three-dimensional and high-order numerical simulations were conducted on models with a constant gap distance of 8.7% of the cylinder diameter. The high-order solver evaluates the three-dimensional Navier-Stokes equations in the full-conservation form, with the Zonal Detached-Eddy Simulation model. The fidelity of the numerical solver was improved in two parts. Firstly, an Eigenvalue analysis for a multiple-block environment was developed to optimise the combination of spatial and filtering schemes for maximum grid resolution that is numerically stable. Secondly, a grid quality metric, which correlates strongly to the solution accuracy, was developed. A validation database of experimental measurements on a tripped 26% scale interaction model, at a free-stream Mach number of 0.09, and a Reynolds number based on the cylinder diameter of 2 x 105, was developed at the 2:1 m x 1:5 m wind tunnel at the University of Southampton. The experimental and numerical results show that the wake generated by the interaction model is dominated by low frequencies that correspond to the vortex shedding modes of the cylinder, and the door. As the door angle is increased from 0 to 10.7 degrees, the intensity of the cylinder shedding mode decreased. The sound pressure levels of the radiated noise were calculated using the FW-H method. The dominant noise source is a compact dipole, which reduced in strength as the door angle was increased.
39
Tao, Fuyang. "Experimental study of restrictor noise in ventilation duct systems." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/398630/.
Повний текст джерелаАнотація:
Single-hole restrictors are widely used in the aircraft air distribution system (ADS). The noise generated due to the flow passing over the restrictor is a main interior noise source of the cabin. Prediction of the restrictor noise generation is important for a quite ADS design. This work experimentally and analytically studies the noise generation mechanisms of the single-hole restrictor. An experimental rig to investigate the restrictor self-noise and interaction noise generated by the turbulent wake produced by in-duct elements installed in the duct and impinging on the restrictor has been developed and constructed. Aeroacoustic measurements of the restrictor self-noise have been made both inside and in the far field of the duct. Two models have been developed to understand the restrictor noise generation mechanisms and predict the sound power level (PWL). One model is based on the surface pressure cross spectrum to compute the effective axial dipole distribution. The other is an extension of previous work and based on the static pressure drop across the restrictor. The restrictor dimension is shown to have a large effects on the restrictor noise generation. For the interaction noise generation, the important parameters including mean flow speed, restrictor dimension, turbulence level and characteristic length, that determine the sound power radiation spectrum are studied. A semi-empirical model has been developed to predict the sound power spectrum due to interaction noise. The link between the interaction noise generation and the restrictor surface pressure has been investigated. In addition to the investigation of the restrictor noise generation, this work conducted a short study into the use of surface roughness on the upstream side of the restrictor to reduce the noise generation whilst maintaining the pressure drop across it. It is shown that the noise generation can be reduced above the first cut-on frequency of the duct by increasing the upstream surface roughness.
40
Davies, Leon Wesley. "Quickstep processing of Hexply 6376 carbon/epoxy laminates : an optimisation study." Thesis, University of Manchester, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601754.
Повний текст джерела
41
Alhajeri, Hamad. "Heat removal in axial flow high pressure gas turbine." Thesis, Cranfield University, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/11465.
Повний текст джерелаАнотація:
The demand for high power in aircraft gas turbine engines as well as
industrial gas turbine prime mover promotes increasing the turbine entry
temperature, the mass flow rate and the overall pressure ratio. High
turbine entry temperature is however the most convenient way to increase
the thrust without requiring a large change in the engine size.
This research is focused on improving the internal cooling of high pressure
turbine blade by investigating a range of solutions that can contribute to
the more effective removal of heat when compared with existing
configuration. The role played by the shape of the internal blade passages
is investigated with numerical methods. In addition, the application of mist
air as a means of enhanced heat removal is studied.
The research covers three main area of investigation. The first one is
concerned with the supply of mist on to the coolant flow as a mean to
enhancing heat transfer. The second area of investigation is the
manipulation of the secondary flow through cross-section variation as a
means to augment heat transfer. Lastly a combination of a number of
geometrical features in the passage is investigated.
A promising technique to significantly improve heat transfer is to inject
liquid droplets into the coolant flow. The droplets which will evaporate after
travelling a certain distance, act as a cooling sink which consequently
promote added heat removal. Due to the promising results of mist cooling
in the literature, this research investigated its effect on a roughened
cooling passage with five levels of mist mass percentages.
In order to validate the numerical model, two stages were carried out.
First, one single-phase flow case was validated against experimental
results available in the open literature. Analysing the effect of the rotational
force, on both flow physics and heat transfer, on the ribbed channel was
the main concern of this investigation. Furthermore, the computational results using mist injection were also validated against the experimental
results available in the literature.
Injection of mist in the coolant flow helped achieve up to a 300% increase
in the average flow temperature of the stream, therefore in extracting
significantly more heat from the wall. The Nusselt number increased by
97% for the rotating leading edge at 5% mist injection.
In the case of air only, the heat transfers decrease in the second passage,
while in the mist case, the heat transfer tends to increase in the second
passage. Heat transfer increases quasi linearly with the increase of the
mist percentage when there is no rotation. However, in the presence of
rotation, the heat transfers increase with an increase in mist content up to
4%, thereafter the heat transfer whilst still rising does so more gradually.
The second part of this research studies the effect of non-uniform cross-
section on the secondary flow and heat transfer in order to identify a
preferential design for the blade cooling internal passage. Four different
cross-sections were investigated. All cases start with square cross-section
which then change all the way until it reaches the 180 degree turn before it
changes back to square cross-section at the outlet. All cases were
simulated at four different speeds. At low speeds the rectangle and
trapezoidal cross-section achieved high heat transfer. At high speed the
pentagonal and rectangular cross-sections achieved high heat transfer.
Pressure loss is accounted for while making use of the thermal
performance factor parameter which accounts for both heat transfer and
pressure loss. The pentagonal cross-section showed high potential in
terms of the thermal performance factor with a value over 0.8 and higher
by 33% when compared to the rectangular case.
In the final section multiple enhancement techniques are combined in the
sudden expansion case, such as, ribs, slots and ribbed slot. The maximum
heat enhancement is achieved once all previous techniques are used
together. Under these circumstances the Nusselt number increased by
60% in the proposed new design.
42
Khani, Nqobile. "Influence of airport factors and mission fuel burn optimised aircraft trajectories on severity and engine life." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9242.
Повний текст джерелаАнотація:
The continuous growth of air transport has raised concerns about global aircraft fuel consumption, emissions and noise. Industry’s efforts have identified that to reduce future emissions and the impact of aircraft operations on the environment will require contribution from: a) New technologies with better efficiency b) Improved asset management and c) Greener manufacturing and recycling processes. This research falls under asset management and involves aircraft trajectory optimisation. Most aircraft trajectory optimisation studies concentrate on optimising fuel burn, emissions and noise. Fuel burn is the dominant contributor to operating costs. During the course of this work, no work was found to better understand from an operator’s perspective how the optimal solutions for minimising fuel burn and protecting the environment will impact on engine useful life and the engine operating costs. Also no work was found to understand how engine component degradation will impact on the optimised solutions for fuel burn and engine life. The contribution to knowledge from this research is a) the assessment of the impact of airport severity factors on engine life consumption and aircraft performance and b) the assessment and quantification of the change in engine life usage when optimising for flight mission fuel burn and the change in flight mission fuel burn when optimising for engine life usage; in both cases the effects of engine component degradation are considered and assessed. The trade-offs between mission fuel burn and engine life optimised trajectories are presented here for a clean (new) engine for three routes (London–Madrid, London–Ankara and London–Abu Dhabi). The engine life calculated was the HPT blade life and HPT disc life due to creep, fatigue and oxidation failure modes independent of each other. Mission fuel burn and engine life trajectory optimisation assessments were conducted to incorporate the effects of degradation after 3000, 4500 and 5250cycles of operation. Further assessments were made linking aircraft performance to airport severity factors for the clean engine, after 3000cycles and after 5250cycles. A techno-economic environmental risk assessment approach was used. The results indicate that airports at higher altitudes e.g. Cairo, suffer more severity due to higher operating temperatures, but benefit from less climb fuel burn and lower operating costs. The severity and fuel burn for take-off at airports with higher ambient temperatures was found to be more due to the higher operating temperatures required. The operating cost at these airports was thus higher. The fuel burn optimised trajectories were found to be achieved at higher operating temperatures with reduced blade life (due to creep, fatigue and oxidation). In particular, for London–Madrid, the blade creep and blade oxidation lives were found to reduce by -3.4% and -2.1% respectively. The blade oxidation life optimised trajectories showed increase in fuel burn of +3.6% and +4.9% for London–Madrid and London–Ankara respectively. The blade creep life optimised trajectories for London–Abu Dhabi were found to benefit from less fuel burn during climb. The disc creep life optimised trajectories showed benefit in fuel burn for London–Ankara and London–Abu Dhabi. The conclusions from the study are: High OAT and high altitude airports such as Abu Dhabi require higher operating temperatures which have severe consequences on the engine component life, fuel burn and emissions. Fuel burn optimised trajectories have a negative effect on the blade life due to creep, fatigue and oxidation due to higher maximum operating temperatures. However, the reduction in fuel burn outweighs the drop in life, thus benefitting to the operating costs. Optimising for blade creep life benefits the fuel burn for London–Abu Dhabi due to less fuel burn at climb The blade oxidation life optimised trajectories are detrimental to the fuel burn due to slower cruise speeds and more time spent at cruise and descent The disc creep life optimised trajectories benefit the fuel burn for London – Ankara and London–Abu Dhabi due to flying at higher cruise altitudes and burning less fuel. The recommendations from this research include making improvements to the framework such as a) Integrating the lifing methodologies because in reality the failure modes are not entirely independent of each other but do interact b) Develop and incorporate a diagnostics and prognostics tool to predict levels of degradation c) Using actual waypoints and incorporate horizontal trajectory profiles d) Future studies can include noise as an objective, which though mentioned has not been within the scope of this work. e) A key driver to lower operating costs is a considerable reduction in fuel burn. Maintenance costs will inevitably rise with engine life consumption. Further study of the trade-offs between fuel burn and engine life is therefore recommended.
43
Ward, Jacob Thomas Elliott. "Guided wave structural health monitoring." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682233.
Повний текст джерелаАнотація:
Routine airframe Non-Destructive Testing (NDT) procedures are costly and prone to human error. Guided wave structural health monitoring (GWSHM) shows great promise to in future assist these carefully regulated aerospace NDT practices. Using automatic GWSHM to both detect and localise damage can better focus the human NDT effort and ultimately lead to safer operation of airframes. The thesis presents structural health monitoring techniques for airframes using measurements of guided waves. Work is presented on both metal plates and carbon fibre reinforced plastic panels. An active GWSHM method is considered in its capability to detect and localise damage by measurements of scattered Lamb waves from artificially placed damage. The contribution to knowledge on active GWSHM has been towards effective and practical strategies for placing a low number of transducers into arrays suitable for global coverage. Much early active GWSHM studies often adopted a uniformly sparse distribution of transducer elements, perhaps in an attempt to gain the best possible global coverage. In this thesis, active GWSHM performance has been evaluated for arrays of different geometry and has shown that a uniformly sparse distribution of transducer elements may not be the most effective strategy when using a minimal number of sensors. Simulated and artificial damage, placed with different orientations over a large area, has been used to test candidate array layouts. It finds the layout optimal for damage detection is not necessarily the layout optimal for damage localisation. The zeroth order anti-symmetric Lamb wave mode has been used at low frequency-thickness. The mode, referred to as the flexural mode when propagating with low frequency-thickness, is favoured for its short wave length and long range. At low frequency-thickness this mode is quickly outrun by its symmetric counterpart, causing coherent noise in the signals recorded. Baseline subtraction is used to suppress the coherent noise before imaging. Benign structural features, that would usually hinder damage-localisation from an image, are actually found to assist damage localisation for some array layouts when using the reference baseline signal subtraction technique. A passive GWSHM method is considered in its capability to localise impacts. Impact events on carbon fibre panels are localised using a low frequency passive array. The technique is suggested for evaluating damage from tyre-burst or propeller debris impacts to airframe surfaces. It is particularly relevant to new airframe designs that have significant usage of composite materials on their outer surface. Historically the aerospace sector has readily adopted time of arrival estimation methods similar to those found on a standard oscilloscope. As an example, acoustic emission monitoring, in recent decades has routinely used threshold-crossing as a means of time of arrival measurement. An alternative is presented requiring the whole time series to be post-processed. It extracts an alternative arrival time from propagating waves resulting from the impact, which can be used in time-difference of arrival algorithms. This method is shown to be more reliable and accurate for impact localisation than historical techniques.
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Agostinelli, Christian. "Methods and processes for multidisciplinary wing shape design." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683390.
Повний текст джерелаАнотація:
In this work rapid computational methods to support the designers in taking more informed decisions within the design process of a large aircraft manufacturer are developed. Since the design takes place in a soda-technical environment, a description of the existing multidisciplinary wing shape design process during the concept and pm-design phase is first provided, adopting a systems approach. The systems approach includes a thorough analysis of the actors involved, requirements, and several system methodologies that have been adopted to characterise the problem situation. Then, rapid, robust, and user friendly methods that fit into the existing design process are developed to aid designers to perform some specific tasks more efficiently. These include a method to modify the twist of a wing to match a target lift distribution, a method to take into account the effects of the structure flexibility, and a method to include the effects of propellers slipstream on the wing lift coefficient distribution. The commonality between these techniques is that they exploit a pm-computed aerodynamic database, generated using high fidelity simulations, coupled with a lifting line module to correct for 3-D effects. The optimum twist distribution is achieved through a correlation between the change in twist and downwash span distributions. The flexibility and propeller swirl effects on the wing lift distribution are taken into account by coupling the aerodynamic databases with a reduced structural model and a blade element momentum theory module respectively. Since the databases are available as a standard product of the design process, no extra effort is required by the designer for their generation. The methods proposed are applied to a number of test cases showing industrial complexity, and results compared against more expensive high fidelity simulations. Results show a satisfactory level of agreement for a vastly reduced cost. The methods proposed in this work have been implemented in an industrial context and made available to wing designers.
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Kent, Thomas Eliot. "Optimal routing and assignment for commercial formation flight." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.689690.
Повний текст джерелаАнотація:
This thesis investigates the notion of fuel-reduction through formation flight for commercial aircraft, addressing the problems of global routing and assignment. A two stage centralised approach is presented, firstly, assuming a reduction in observed cost by flying in formation the routes, including rendezvous and break points, are calculated to minimise a total cost. The interconnected assignment problem then takes a set of flights, their possible formations and corresponding costs and optimally allocates them into a cost-minimising formation fleet. An analytic geometric approach is used to develop a scalable methodology for the formation routing problem enabling the quick calculation of costs. The rapid evaluation allows the large scale fleet assignment problem to be solved via a Mixed Integer Linear Program in reasonable time. A Transatlantic case study shows possible formation fuel savings against solo flight of around 8.7% and 13.1 % for formations up to size two and three respectively. Further case studies of three distinct sets of flights show that encouraging levels of saving can still be achieved by flights with varied distances , geographical locations and formation drag-reduction levels. For the more complex task of routing through wind, results show that the analytic approach can act as a reasonable estimate to the assignment problem, allowing higherfidelity and computationally more intensive routing methods to be introduced via a post-process, significantly reducing solve time. Methods for mitigating the impact of uncertainty in aircraft take-off times are explored, where a state-space approach, solved using value iteration, can provide optimal speed-policies for aircraft to follow for any possible realisation of delay. Additionally portfolio optimisation provides a method for formations to be assigned to simultaneously maximise reward and minimise the associated risk. Finally the calculation of efficient frontiers allows matching of reward to desired levels of risk-aversion.
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Terkovics, Nándor. "A feasibility study on applying real-time dynamic substructuring to a nonlinear landing gear fuselage system." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683561.
Повний текст джерелаАнотація:
Aircraft nose landing gear must be tested for shimmy oscillations experimentally. Current test methods consider the landing gear as stand alone systems without the possibility of accounting for the dynamics of the fuselage which they are attached to. This means that all possible interaction between them is ignored during the experiment which, if the interaction for specific conditions is significant, might reduce the reliability of the test results. On the other hand, conducting a full scale experiment on the aircraft would be impractical due to size and related costs. In this thesis the nonlinear interaction between the nose landing gear and the airframe is explored and the feasibility of the real-time dynamic substructuring test method to this particular system is discussed. Due to the nonlinearities involved, the applied method in the majority of this work is bifurcation analysis. First, a coupled nose landing gear-fuselage model is developed. It is a simplified two degree-of-freedom nose landing gear model coupled to the lateral component of the fuselage motion at the attachment point. By means of one- and two-parameter bifurcation diagrams it is demonstrated how the presence of fuselage dynamics may influence the behaviour of the landing gear - and vice versa, how the vibrations of the gear affect the dynamics of the fuselage - when key parameters of the system are varied. It is found that dynamic interaction between the two subsystems is possible. How significant this interaction is strongly depends on the characteristics of the fuselage dynamics. Owing to this interaction the application of the real-time dynamic substructuring method on the model is reasonable and, hence, its feasibility is explored numerically and analytically. In a substructuring test part of the system is kept as the physical test specimen while the remainder is simulated numerically. The numerical and physical substructures are connected via a transfer system (an actuator) and the interface is controlled in real-time to ensure that the dynamic behaviour of the substructured system replicates with high accuracy that of the system being emulated. The main challenge in a substructuring test is the delay arising from the response time of the actuator. The effect of the delay is analysed in terms of the proposed test configuration, which consists of the fuselage as the numerical model and the nose landing gear as the physical substructure; the latter is also represented by a simplified two degree-of-freedom model. It is found that the substructured system is extremely sensitive to the delay. In order to reduce the sensitivity, without modifying structural parameters, the numerical model is extended by an additional compliance, and the influence of this on the sensitivity is studied. By careful adjustment of the additional compliance, the robustness of the test can be improved; however, the accuracy may then be compromised.
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Bhandari, Ujjar. "Control system design for autonomous air-to-air refuelling." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680354.
Повний текст джерелаАнотація:
A wide range of Unmanned Air Vehicle applications have been identified over the last decade, both for civilian and military usage. The Air-to-Air Refuelling capability is perceived as an advantage to future support and deployment of mid-large scale Unmanned Air Vehicles to meet operational requirements. Despite Autonomous Air-to-Air Refuelling drawing a lot of attention and research in general, bow wave effects in an Air-to-Air Refuelling scenario have received little attention. Some existing studies have discussed and attempted to model the effect of the bow wave from a comparatively large receiver (B-2, C-17) onto the tanker (KC-135) during boom refuelling. However the effects of bow wave from the receiver aircraft onto the drogue in a probe and drogue refuelling system have received very little attention. This thesis analyses the effects of the receiver's bow wave on the drogue in a probe and drogue based Air-to-Air Refuelling activity, with results suggesting its critical influence on the capture rates of Autonomous Airto- Air Refuelling simulation. This work has developed a state of the art literature survey of Air-to-Air Refuelling including the developments in the sensor models, numerical modelling concepts, control methodologies and simulation and test facilities. By performing multiple random simulations a novel way of quantifying capture rates in aerial refuelling simulations has been developed. Compensating the bow wave effects through the use of position offset is simple yet effective solution emerging from this work. This method was found to restore the loss in performance in the Autonomous Air-to-Air Refuelling simulation which results from the bow wave interactions. On the other hand, the ability to optimise these position offsets for a given condition makes it suitably applicable to different flight conditions. Another major contribution is the various capture strategies presented in this thesis which demonstrate several ways of approaching the drogue in the capture phase for successful engagements. Results demonstrate further gains in terms of capture rates by avoiding drogue chasing in the simulations. Additional unconventional and innovative concepts to drogue capture are also discussed. This work forms part of the Autonomous Systems Technology Related Airborne Evaluation & Assessment programme in the UK.
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Daggett, D. "Enabling alternate fuels for commercial aircraft." Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/11791.
Повний текст джерелаАнотація:
The following reports on the past four years of work to examine the feasibility, sustainability and economic viability of developing a renewable, greenhouse-gas-neutral, liquid biofuel for commercial aircraft.
The sharp increase in environmental concerns, such as global warming, as well as the volatile price fluctuations of fossil fuels, has ignited a search for alternative transportation fuels. However, commercial aircraft can not use present alternative fuels that are designed for ground transportation. Aircraft also have much longer service lives, are capital intensive to purchase, require a complex refueling infrastructure, and are specifically designed to use petroleum-type liquid jet fuels. Synthetic jet fuel, manufactured using a Fischer-Tropsch process from coal, is currently the only alternative jet fuel commercially available to aviation, but it presently experiences environmental challenges. Biojet fuels are currently not commercially available for aviation, but have the potential to become quite acceptable
If passenger growth increases at 5%/year, it appears the only way that the aviation industry can meets its environmental goals of reducing CO2 emissions would be through commercialization of carbon-neutral fuels. This research shows that biojet fuels can be developed that do not compete with food or fresh water resources, will not lead to deforestation and will not cause other adverse environmental or social impacts.
The approach of using a “drop in” jet fuel replacement, which would consist of a blend of kerosene and up to 50% biofuel will be possible for use in existing and future aircraft. A 60-80% lifecycle CO2 emission reduction is calculated for the biofuel portion with no performance degradation. New biofuel processing techniques (i.e. hydroprocessing, isomerization & distillation) and next generation feedstock sources (e.g. halophyte and algal biomass) appear to be the best pathways to enable the large scale deployment of sustainable and economically competitive biojet fuels in the near future.
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Orlowski, Michal. "Experimental and numerical investigation on the bird impact resistance of novel composite sandwich panels." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/9573.
Повний текст джерелаАнотація:
Bird strikes represent a major hazard to the aerospace composite structures, due to their low impact resistance. Accurate selection and lay up of the materials in the composite structure can significantly improve the out of plane properties of the composites. However, application of the complex hybrid sandwich composites into bird strike proof structures was not investigated yet. Therefore, this work was focused on the soft body impact resistance of a novel composite design for aerospace applications. The investigation was divided into experimental and modelling parts. In the beginning of this thesis, the numerical techniques for modelling of bird im¬pact and composite materials were studied. The theoretical background for the corresponding issue was provided, followed by the thorough validation of the exist¬ing numerical approaches. A Smooth Particle Hydrodynamic (SPH) method was chosen for the modelling of the soft body. This modelling technique was validated against experimental data for the rotating fan blade. Three parametric studies of bird impacting fan blades revealed strong influence of the bird impact location and timing on the final deformed shape of the blade. Moreover, it was proved that the SPH is capable of reproducing the exact load on the structure and is appropriate technique for modelling bird strikes.
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Simpson, Nick. "Investigation into an alternative electrically actuated braking system for aircraft." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659106.
Повний текст джерелаАнотація:
Modern commercial aircraft predominantly employ hydraulically actuated multi-disk wheel-brakes on their main landing gears which are used to control the velocity of the aircraft during landing and ground operations. In recent years, investigations into the electrical actuation of the wheel-brakes have shown a number of advantages ranging from better energy efficiency to improved reliability and maintainability. Electrically actuated braking systems tend to employ a plurality of electric brake actuators featuring a high-speed brushless dc motor coupled to a ball/roller-screw through a reduction gear. This arrangement exhibits a high force-density and long stroke, however, the three-phase power inverter, filter and power conductor requirements of each actuator results in a considerable overall system mass when compared to a hydraulic counterpart whose components and operating pressure have been optimised over many years of in-flight service. This thesis investigates the feasibility of an alternative electric braking system which has the potential to reduce the overall braking system mass through the use of a direct drive non-commutated electric brake actuator topology. A permanent magnet tubular linear actuator topology is identified as an attractive candidate. Due to the short-duty and high force-density requirements of the electric brake actuator it is desirable to take account of the electromagnetic and thermal aspects of the design simultaneously. Therefore, a coupled electromagnetic and transient thermal design methodology is developed. It is found that a compromise exists between the accuracy and the computation time of the electromagnetic and thermal analyses. A procedure for efficiently constructing and analysing finite element models is developed to minimise the computational cost of the electromagnetic analysis. A method of automatically constructing and parameterising lumped parameter thermal equivalent circuits with nodes arranged in a regular mesh pattern is proposed which maintains low computation times while allowing superior thermal field resolution and more accurate identification of hot-spots and their location. A method of estimating the equivalent thermal properties of impregnated electrical windings is proposed in order to parameterise the thermal model. The coupled design methodology is employed to study the achievable short-duty performance of the tubular linear actuator topology and establish the feasibility of the alternative electric braking system. A prototype actuator is constructed and tested under short-duty conditions in order to validate the modelling and thermal property estimation methods.