Дисертації з теми "Aerodynamic angle"
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1
Wilks, Brett Landon Burkhalter Johnny Evans. "Aerodynamics of wrap-around fins in supersonic flow." Auburn, Ala., 2005. http://repo.lib.auburn.edu/2005%20Fall/Thesis/WILKS_BRETT_54.pdf.
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Fan, Yigang. "Identification of an Unsteady Aerodynamic Model up to High Angle of Attack Regime." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/29830.
Повний текст джерелаАнотація:
The harmonic oscillatory tests for a fighter aircraft configuration using the Dynamic Plunge-Pitch-Roll (DyPPiR) model mount at Virginia Tech Stability Wind Tunnel are described and analyzed. The corresponding data reduction methods are developed on the basis of multirate digital signal processing techniques. Since the model is sting-mounted to the support system of DyPPiR, the Discrete Fourier Transform (DFT) is first used to identify the frequencies of the elastic modes of sting. Then the sampling rate conversion systems are built up in digital domain to resample the data at a lower rate without introducing distortions to the signals of interest. Finally linear-phase Finite Impulse Response (FIR) filters are designed by Remez exchange algorithm to extract the aerodynamic characteristics responses to the programmed motions from the resampled measurements. These data reduction procedures are also illustrated through examples.
The results obtained from the harmonic oscillatory tests are then illustrated and the associated flow mechanisms are discussed. Since no significant hysteresis loops are observed for the lift and the drag coefficients for the current angle of attack range and the tested reduced frequencies, the dynamic lags of separated and vortex flow effects are small in the current oscillatory tests. However, large hysteresis loops are observed for pitch moment coefficient in the current tests. This observation suggests that at current flow conditions, pitch moment has large pitch rate and alpha-dot dependencies. Then the nondimensional maximum pitch rate q_max is introduced to characterize these harmonic oscillatory motions. It is found that at current flow conditions, all the hysteresis loops of pitch moment coefficient with same nondimensional maximum pitch rate are tangential to one another at both top and bottom of the loops, implying approximately same maximum offset of these loops from static values. Several cases are also illustrated.
Based on the results obtained and those from references, a state-space model is developed to describe the unsteady aerodynamic characteristics up to the high angle of attack regime. A nondimensional coordinate is introduced as the state variable describing the flow separation or vortex burst. First-order differential equation is used to govern the dynamics of flow separation or vortex bursting through this state variable. To be valid for general configurations, Taylor series expansions in terms of the input variables are used in the determination of aerodynamic characteristics, resembling the current approach of the stability derivatives. However, these derivatives are longer constant. They are dependent on the state variable of flow separation or vortex burst. In this way, the changes in stability derivatives with the angle of attack are included dynamically. The performance of the model is then validated by the wind-tunnel measurements of an NACA 0015 airfoil, a 70 degree delta wing and, finally two F-18 aircraft configurations. The results obtained show that within the framework of the proposed model, it is possible to obtain good agreement with different unsteady wind tunnel data in high angle-of-attack regime.Ph. D.
3
Stagg, Gregory A. "An Aerodynamic Model for Use in the High Angle of Attack Regime." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/35596.
Повний текст джерелаАнотація:
Harmonic oscillatory tests for a fighter aircraft using the
Dynamic Plunge--Pitch--Roll model mount at Virginia Tech Stability
Wind Tunnel are described. Corresponding data reduction methods are
developed on the basis of multirate digital signal processing. Since
the model is sting mounted, the frequencies associated with sting
vibration are included in balance readings thus a linear filter must
be used to extract out the aerodynamic responses. To achieve this, a
Finite Impulse Response (FIR) is designed using the Remez exchange
algorithm.
Based on the reduced data, a state--space model is developed to
describe the unsteady aerodynamic characteristics of the aircraft
during roll oscillations. For this model, we chose to separate the aircraft
into panels and model the local forces and moments. Included in this
technique is the introduction of a new state variable, a separation
state variable which characterizes the separation for each panel.
This new variable is governed by a first order differential equation.
Taylor series expansions in terms of the input variables were performed
to obtain the aerodynamic coefficients of the model. These
derivatives, a form of the stability derivative approach, are not
constant but rather quadratic functions of the new state variable.
Finally, the concept of the model was expanded to allow for the
addition of longitudinal motions. Thus, pitching moments will be
identified at the same time as rolling moments. The results show that
the goal of modeling coupled longitudinal and lateral--directional
characteristics at the same time using the same inputs is feasible.Master of Science
4
Sirangu, Vijaya. "AERODYNAMIC CONTROL OF SLENDER BODIES AT HIGH ANGLES OF ATTACK." University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1271365316.
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Sor, Wei Lun. "Aerodynamic Validation of Emerging Projectile Configurations." Thesis, Monterey, California. Naval Postgraduate School, 2012.
Знайти повний текст джерелаАнотація:
Approved for public release; distribution is unlimited.Ever-increasing demands for accuracy and range in modern warfare have expedited the optimization of projectile design. The crux of projectile design lies in the understanding of its aerodynamic properties early in the design phase. This research first investigated the aerodynamic properties of a standard M549, 155mm projectile. The transonic speed region was the focus of the research as significant aerodynamic variation occurs within this particular region. Aerodynamic data from wind tunnel and range testing was benchmarked against modern aerodynamic prediction programs like ANSYS CFX and Aero-Prediction 09 (AP09). Next, a comparison was made between two types of angle of attack generation methods in ANSYS CFX. The research then focused on controlled tilting of the projectile’s nose to investigate the resulting aerodynamic effects. ANSYS CFX was found to provide better agreement with the experimental data than AP09.
6
Takahama, Morio, Noboru Sakamoto, and Yuhei Yamato. "Attitude Stabilization of an Aircraft via Nonlinear Optimal Control Based on Aerodynamic Data." Institute of Electrical and Electronics Engineers, 2009. http://hdl.handle.net/2237/14420.
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Mohmad, Rouyan Nurhana. "Model simulation suitable for an aircraft at high angle of attack." Thesis, Cranfield University, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/9722.
Повний текст джерелаАнотація:
Simulation of a dynamic system is known to be sensitive to various factors and one of
them could be the precision of model parameters. While the sensitivity of flight dynamic
simulation to small changes in aerodynamic coefficients is typically not studied, the simulation
of aircraft required to operate in nonlinear flight regimes usually at high angles of
attack can be very sensitive to such small differences. Determining the significance and
impact of the differences in aerodynamic characteristics is critical for understanding the
flight dynamics and designing suitable flight control laws. This thesis uses this concept
to study the effect of the differences in aerodynamic data for different aerodynamic models
provided for a same aircraft which is F-18 HARV combat aircraft. The aircraft was
used as a prototype for the high angles of attack technology program. However modeling
an aircraft at high angles of attack requires an extensive aerodynamic data which are
usually di cult to access. All aerodynamic models were collected from open literature
and implemented within a nonlinear six degree of freedom aircraft model. Inspection of
aerodynamic data set for these models has shown mismatches for certain aerodynamic
derivatives, especially at higher angles of attack where nonlinear dynamics are known to
exist. Nonlinear simulations are used to analyse three different types of flight dynamic
models that use look-up-tables, arc-tangent formulation and polynomial functions to represent
aerodynamic data that are suitable for high angles of attack application. To achieve
this, a nonlinear six degree of freedom Simulink model was developed to accommodate
these aerodynamic models separately. The trim conditions were obtained for different
combinations of angles of attack and airspeed and the models were linearized in each
case. Properties of the resulting state matrices such as eigenvalues and eigenvectors were
studied to determine the dynamic behaviour of the aircraft at various flight conditions.
8
Quickel, Reuben Alexander. "Mount Interference and Flow Angle Impacts on Unshielded Total Temperature Probes." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/89952.
Повний текст джерелаАнотація:
Accurately measuring the total temperature of a high-speed fluid flow is a challenging task that is
required in many research areas and industry applications. The difficulty in total temperature
measurement generally stems from attempting to minimize measurement error or accurately
predict error so it can be accounted for. Conduction error and aerodynamic error are two very
common sources of error in total temperature probe measurements. Numerous studies have been
performed in prior literature to account for simple cases of both errors. However, the impacts of a
mounting strut and freestream flow angle on conduction error and aerodynamic error have not
been previously modeled. Both of these effects are very common in gas-turbine applications of
total temperature probes. Therefore, a fundamental study was performed to analyze the impact of
mount interference and freestream flow angle on a probe's conduction error and aerodynamic
error.
An experimental study of aerodynamic error was performed using strut-mounted thermocouples
in a high-speed jet at Mach numbers ranging from 0.25-0.72. This study showed that a strut
stagnation point can provide aerodynamic error reductions and insensitivity to approach Mach
number. An off-angle experimental study of conduction error was also performed using strut-mounted thermocouples at pitch angles ranging from -30° to 30°. High-fidelity Computational
Fluid Dynamics (CFD) simulations with Conjugate Heat Transfer (CHT) were performed in
conjunction with the experiments to provide key heat transfer information and flow visualizations. It was identified that unshielded total temperature probes have reduced conduction
error at off-angles, but are sensitive to changes in the freestream flow angle. A low-order method
was developed to account for mount interference and flow angle effects. The developed low order
method utilizes a local Mach number for aerodynamic error predictions and a local Reynolds
number for conduction error predictions. This developed low-order method was validated against
experiment and 3D, CFD results, and was shown to accurately capture flow angle trends, mount
interference effects, and the impacts of varying probe geometry.Master of Science
Accurately measuring the total temperature of a high-speed fluid flow is a challenging task that is required in many research areas and industry applications. Many methods exist for measuring total temperature, but the use of thermocouple based probes immersed into a flow remains a common and desirable measurement technique. The difficulty in using thermocouple based probes to acquire total temperature stems from attempting to minimize or accurately predict the probe’s measurement error. Conduction, convection, and radiation heat transfer between the fluid flow and probe create challenges for minimizing measurement error so that the accurate total temperature can be obtained. Numerous studies have been performed in prior literature to account for simple cases of each error source. However, there are many complex, practical applications in which the influence of each error source has not been studied. The impacts of a freestream flow angle and the total temperature probe’s mounting structure have not been previously modeled. Both of these effects are very common in gas-turbine applications of total temperature probes. This Thesis will present a fundamental study analyzing the impact that freestream flow angle and a probe’s mount have on a total temperature probe’s measurement error. The influence of conduction and convection heat transfer was studied experimentally for numerous probe geometries, and the impacts of a mounting strut and freestream flow angle were analyzed. A low-order method was developed to predict conduction error and aerodynamic error for total temperature probes in offangle conditions with the presence of mount interference. The developed low-order method was shown to accurately capture the effects of a mounting strut, varying probe geometry, and varying flow angle. Additionally, the low-order method was validated against experimental and 3D, CFD/CHT results.
9
Lopera, Javier. "Aerodynamic Control of Slender Bodies from Low to High Angles of Attack through Flow Manipulation." Connect to Online Resource-OhioLINK, 2007. http://www.ohiolink.edu/etd/view.cgi?acc_num=toledo1177504352.
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Hammer, Patrick Richard. "A Discrete Vortex Method Application to Low Reynolds Number Aerodynamic Flows." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1311792450.
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De, Oliveira Neto Pedro Jose. "An Investigation of Unsteady Aerodynamic Multi-axis State-Space Formulations as a Tool for Wing Rock Representation." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29600.
Повний текст джерелаАнотація:
The objective of the present research is to investigate unsteady aerodynamic models with state equation representations that are valid up to the high angle of attack regime with the purpose of evaluating them as computationally affordable models that can be used in conjunction with the equations of motion to simulate wing rock. The unsteady aerodynamic models with state equation representations investigated are functional approaches to modeling aerodynamic phenomena, not directly derived from the physical principles of the problem. They are thought to have advantages with respect to the physical modeling methods mainly because of the lower computational cost involved in the calculations. The unsteady aerodynamic multi-axis models with state equation representations investigated in this report assume the decomposition of the airplane into lifting surfaces or panels that have their particular aerodynamic force coefficients modeled as dynamic state-space models. These coefficients are summed up to find the total aircraft force coefficients. The products of the panel force coefficients and their moment arms with reference to a given axis are summed up to find the global aircraft moment coefficients. Two proposed variations of the state space representation of the basic unsteady aerodynamic model are identified using experimental aerodynamic data available in the open literature for slender delta wings, and tested in order to investigate their ability to represent the wing rock phenomenon. The identifications for the second proposed formulation are found to match the experimental data well. The simulations revealed that even though it was constructed with scarce data, the model presented the expected qualitative behavior and that the concept is able to simulate wing rock.Ph. D.
12
LERRO, ANGELO. "Development and Evaluation of Neural Network-Based Virtual Air Data Sensor for Estimation of Aerodynamic Angles." Doctoral thesis, Politecnico di Torino, 2012. http://hdl.handle.net/11583/2518884.
Повний текст джерелаАнотація:
Aerodynamic angles of ight vehicles are necessary to pilot and automatically control
of aircraft. These angles are usually measured using probes that protrude from
the vehicle surface out into the ow eld. However, this arrangement was found
to be unacceptable for modern unmanned airplanes whenever stealthiness features
are required. In addition, redundant sensor arrangements, when dictated by safety
regulations, were also critical because of the possible heavy impact on the airframe of
small UAVs. New virtual software-based systems were therefore developed in order
to nd a viable solution for reducing the number of traditional hardware-based air
data sensors, and they oered the benet of simplifying air data system architectures.
The aerodynamic angles were derived from inertial data and by exploiting the
airspeed sourced by the Pitot-static system. The relationship between these parameters
and the aerodynamic angles was a complex, non-linear function that was not easily
described by means of aircraft models. The main goal of this work, which was aimed
at UAV applications, was to analyze the aircraft system and develop virtual sensors
by exploiting soft computing methods, such as neural prediction techniques, in order
to assess the feasibility of this kind of neural system. The performance of virtual
sensors were tested using real hardware in the simulation loop and to represent
real-world ight conditions: wind gusts, air turbulence and internal sensor noise
were simulated. A sensitivity analysis was carried out to study the performance of
virtual sensors even when realistic accuracy of measured signals, processed by neural
networks, and failure modes were simulated.
Finally, neural networks resulted to be suited for aerodynamic angle estimation
technique: the neural networks worked properly with the available vehicle data and
demonstreted to be as accurate as traditional probes.
13
Mitori, Tiffany Leilani. "Flight and Stability of a Laser Inertial Fusion Energy Target in the Drift Region between Injection and the Reaction Chamber with Computational Fluid Dynamics." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1154.
Повний текст джерелаАнотація:
A Laser Inertial Fusion Energy (LIFE) target’s flight through a low Reynolds number and high Mach number regime was analyzed with computational fluid dynamics software. This regime consisted of xenon gas at 1,050 K and approximately 6,670 Pa. Simulations with similar flow conditions were performed over a sphere and compared with experimental data and published correlations for validation purposes. Transient considerations of the developing flow around the target were explored. Simulations of the target at different velocities were used to determine correlations for the drag coefficient and Nusselt number as functions of the Reynolds number. Simulations with different target angles of attack were used to determine the aerodynamic coefficients of drag, lift, Magnus moment, and overturning moment as well as target stability. The drag force, lift force, and overturning moment changed minimally with spin. Above an angle of attack of 15°, the overturning moment would be destabilizing. At angles of attack less than 15°, the overturning moment would tend to decrease the target’s angle of attack, indicating the lack of a need for spin for stability at these small angles. This stabilizing moment would cause the target to move in a mildly damped oscillation about the axis parallel to the free-stream velocity vector through the target’s center of gravity.
14
Hubbard, Joshua A. "A study of aerodynamic deaggregation mechanisms and the size control of NanoActive™ aerosol particles." Thesis, Kansas State University, 2006. http://hdl.handle.net/2097/173.
Повний текст джерелаАнотація:
Master of ScienceDepartment of Mechanical and Nuclear Engineering
Steven J. Eckels
Christopher M. Sorensen
Large specific surface areas and high concentrations of reactive edge and defect sites make NanoActive™ metal oxide powders ideal chemical adsorbents. These powders are dispersed in aerosol form to remediate toxic wastes and neutralize chemical and biological warfare agents. In the destructive adsorption of toxic chemicals, effective application requires particles be as small as possible, thus, maximizing surface area and number of edge and defect sites. Other applications, e.g. smoke clearing, require particles be large so they will settle in a timely manner. Ideally, particle size control could be engineered into powder dispersion devices. The purpose of this study was to explore particle cohesion and aerodynamic deaggregation mechanisms to enhance the design of powder dispersion devices. An aerosol generator and four experimental nozzles were designed to explore the most commonly referenced deaggregation mechanisms: particle acceleration, particles in shear and turbulent flows, and particle impaction. The powders were then dispersed through the nozzles with increasing flow rates. A small angle light scattering device was used to make in situ particle size measurements. The nozzle designed for impaction deaggregated the NanoActive™ MgO particles to a lesser degree than the other three nozzles, which deaggregated the particles to a similar degree. Flows in three of the four nozzles were simulated in a commercial computational fluid dynamics package. Theoretical particle and aggregate stresses from the literature were calculated using simulated data. These calculations suggest particle acceleration causes internal stresses roughly three orders of magnitude larger than shear and turbulent flows. These calculations, coupled with experimental data, lead to the conclusion that acceleration was the most significant cause of particle deaggregation in these experiments. Experimental data also identified the dependence of deaggregation on primary particle size and agglomerate structure. NanoActive™ powders with smaller primary particles exhibited higher resistance to deaggregation. Small primary particle size was thought to increase the magnitude of van der Waals interactions. These interactions were modeled and compared to theoretical deaggregation stresses previously mentioned. In conclusion, deaggregation is possible. However, the ideas of particle size control and a universal dispersion device seem elusive considering the material dependent nature of deaggregation.
15
Abdeh, Hamed. "Incidence Effects on Aerodynamic and Thermal Performance of a Film-Cooled Gas Turbine Nozzle Guide Vane." Doctoral thesis, Università degli studi di Bergamo, 2018. http://hdl.handle.net/10446/105183.
Повний текст джерелаАнотація:
In this study, the influence of inlet flow incidence on the aerodynamic and thermal performance of a film cooled linear nozzle vane cascade is fully assessed. Tests have been carried out on a solid and a cooled cascade. In the cooled cascade, coolant is ejected at the end wall through a slot located upstream of the leading edge plane. Moreover, a vane showerhead cooling system is also realized through 4 rows of cylindrical holes. The cascade was tested at a high inlet turbulence intensity level (Tu1 = 9%) and at a constant inlet Mach number of 0.12 and nominal cooling condition, varying the inlet flow angle. In addition to the reference incidence angle (0°), four other cases were investigated: +20°, +10°, -10° and -20°. The aero-thermal characterization of vane platform was obtained through 5-hole probe, endwall and vane showerhead adiabatic film cooling effectiveness measurements. Vane load distributions and surface flow visualizations supported the discussion of the results. On the vane, a significant movement in stagnation point happened when incidence angle varied, resulted in changing of the coolant distribution pattern between SS and PS of the cooled vane; which adversely affects the efficiency for both negative and positive inlet flow incidence angles. On the platform, however, a relevant negative impact of positive inlet flow incidence on the cooled cascade aerodynamic and endwall thermal performance was detected. A negligible influence was instead observed at negative incidence, even at the lowest tested value of -20°.
16
BRANDL, ALBERTO. "Techniques for effective virtual sensor development and implementation with application to air data systems." Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2842493.
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Jaitlee, Rajneesh, and jaitlee@gmail com. "Mean and Fluctuating Pressures on an Automotive External Rear View Mirror." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20070112.125531.
Повний текст джерелаАнотація:
The primary function of an automobile rear View Mirror is to provide the driver with a clear vision interpretation of all objects to the rear and side of the vehicle. The rear View Mirror is a bluff body and there are several problems associated with the rear View Mirror. These include buffeting, image distortion (due to aerodynamically induced and structural vibration), aerodynamically induced noise (due to cavities and gaps) and water and dirt accumulation on Mirror glass Surface. Due to excessive glass vibration, the rear View Mirror may not provide a clear image. Thus, vibrations of Mirror can severely impair the driver's vision and safety of the vehicle and its occupants. The rear View Mirrors are generally located close to the A-pillar region on the side window. A conical vortex forms on the side window close to A-pillar due to A-pillar geometry and the presence of side rear View Mirror and flow separation from it makes the airflow even more complex. The primary objective of this work is to study the aerodynamic pressures on Mirror Surface at Various speeds to determine the effects of aerodynamics on to Mirror vibration. Additionally, the Mirror was modified by Shrouding around the external periphery to determine the possibility of minimisation of aerodynamic pressure fluctuations and thereby vibration. The Shrouding length used for the analysis was of 24mm, 34mm and 44mm length. The mean and fluctuating pressures were measured using a production rear side View Mirror fitted to a ¼ quarter production passenger car in RMIT Industrial Wind Tunnel. The tests were also conducted in semi-isolation condition to understand influence of the A-pillar geometry. The mean and fluctuating pressures were converted into non-dimensional pressure coefficients (Cp and Cprms) and the frequency content of the fluctuating pressure was analysed. The results show that the fluctuating aerodynamic pressures are not uniformly distributed over an automobile Mirror Surface. The highest magnitude of fluctuating pressure for the standard Mirror was found at the central bottom part of the Mirror Surface. The highest magnitude of fluctuating pressure for the modified Mirror was found at the central top part of the Mirror Surface. As expected, the modification has significant effect on the magnitude of fluctuating pressure. The results show that an increase of Shrouding length reduces the magnitude of the fluctuating pressure. The frequency-based analysis was done to understand the energy characteristics of the flow, particularly to its phase, since it is the out of phase components that usually cause Mirror rotational vibration. The spectral analysis showed that the magnitude of the energy distribution reduces with increase of shrouding length throughout the frequency range. Flow visualisation was also used to supplement the pressure data. The effects of yaw angles were not included in this study, however, are thought to be worthy of further investigation. On road testing and the variation of mirror locations might have some effects on the fluctuating pressures. These need to be investigated in the future work. The quarter model used in this study was a car specific. However, for more generic results, a simplified model with variable geometry can be used in future study.
18
Clark, Adam. "Predicting the Crosswind Performance of High Bypass Ratio Turbofan Engine Inlets." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1476265135449178.
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Ferria, Hakim. "Contribution to Numerical and Experimental Studies of Flutter in Space Turbines. Aerodynamic Analysis of Subsonic or Supersonic Flows in Response to a Prescribed Vibratory Mode of the Structure." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00677648.
Повний текст джерелаАнотація:
Modern turbomachines are designed towards thinner, lighter and highly loaded blades. This gives rise to increased sensitivity to flow induced vibrations such as flutter, which leads to structure failure in a short period of time if not sufficiently damped. Although numerical tools are more and more reliable, flutter prediction still depends on a large degree on simplified models. In addition, the critical nature of flutter, resulting in poor welldocumented real cases in the open literature, and the lack of experimental database typical of engine flows make its apprehension even more challenging. In that context, the present thesis is dedicated to study flutter in recent turbines through aerodynamic analysis of subsonic or supersonic flows in response to a prescribed vibratory mode of the structure. The objective is to highlight some mechanisms potentially responsible for flutter in order to be in better position when designing blades. The strategy consists in leading both experimental and numerical investigations. The experimental part is based on a worldwide unique annular turbine sector cascade employed for measuring the aeroelastic response by means of the aerodynamic influence coefficient technique. The cascade comprises seven low pressure gas turbine blades one of which can oscillate in a controlled way as a rigid body. Aeroelastic responses are measured at various mechanical and aerodynamic parameters: pure and combined modeshapes, reduced frequency, Mach number, incidence angle. In addition to turbulence level measurements, the database aims at assessing the influence of these parameters on the aerodynamic damping, at validating the linear combination principle and at providing input for numerical tools. The numerical part is based on unsteady computations linearized in the frequency domain and performed in the traveling wave mode. The focus is put on two industrial space turbines: 2D computations are performed on an integrally bladed disk, also called blisk; its very low viscous material damping results in complex motions with combined modes and extremely high reduced frequency. The blisk operates at low subsonic conditions without strong non-linearities. Although the blades have been predicted aeroelastically stable, an original methodology based on elementary decompositions of the blade motion is presented to identify the destabilizing movements. The results suggest that the so-called classical flutter is surprisingly prone to occur. Moreover, the aerodynamic damping has been found extremely sensitive to the interblade phase angle and cut-on/cut-off conditions.* 3D computations are then performed on a supersonic turbine, which features shockwaves and boundary layer separation. In contrast, the blade motion is of elementary nature, i.e. purely axial. The blades have been predicted aeroelastically unstable for backward traveling waves and stable for forward traveling waves. The low reduced frequencies allow quasi-steady analysis, which still account for flutter mechanisms: the shock wave motion establishes the boundary between stable and unstable configurations.
20
Hoang, Ngoc T. "The hemisphere-cylinder at an angle of attack." Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08062007-094404/.
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21
Luke, Mark Elden. "Predicting Drag Polars For Micro Air Vehicles." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd297.pdf.
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22
Vasiljevas, Artūras. "Eksperimentinio akrobatinio lėktuvo skrydžio analizė." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130621_150246-07379.
Повний текст джерелаАнотація:
Baigiamajame magistro darbe nagrinėjamos būsimo eksperimentinio akrobatinio lėktuvo aerodinaminės savybės. Pristatomos tokio pobūdžio sritys (temos), kaip tinkamo sparno profilio parinkimas orlaiviui, reikalingo sparno formos apibrėžimas, sparno būsimos charakteristikos ir parametrų apskaičiavimas, kitų orlaivio dalių ir jų įtakos visai lėktuvo dinamikai analizavimas. Kadangi analizuojamas dvivietis eksperimentinis akrobatinis lėktuvas, tikintis geresnių rodiklių, pasirinktas palyginimo objektas dvivietis akrobatinis mokomasis lėktuvas SU 29. Remiantis šio lėktuvo esamomis charakteristikomis ir parametrais, pateikiamos išvados ir siūlymai.The thesis examines the aerodynamics of future experimental aerobatic aircraft. Featured in such areas (topics): proper selection of an aircraft wing profile, the required form of the wing, the wing's future performance and parameter estimation, other aircraft parts and their impact on the entire plane dynamics analysis. As analyzed double seated, experimental aerobatic plane in the hope of better indicators selected comparison object double seated acrobatic training plane SU 29. Based on the existing aircraft characteristics and parameters, the conclusions and recommendations will be made.
23
Petterson, Kristian. "The aerodynamics of slender aircraft forebodies at high angle of attack." Thesis, Cranfield University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392234.
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Cohen, David E. II. "Trim Angle of Attack of Flexible Wings Using Non-Linear Aerodynamics." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30404.
Повний текст джерелаАнотація:
Multidisciplinary interactions are expected to play a significant role in the design of future high-performance aircraft (Blended-Wing Body, Truss-Braced wing, High Speed Civil transport, High-Altitude Long Endurance aircraft and future military aircraft). Also, the availability of supercomputers has made it now possible to employ high-fidelity models (Computational Fluid Dynamics for fluids and detailed finite element models for structures) at the preliminary design stage. A necessary step at that stage is to calculate the wing angle-of-attack at which the wing will generate the desired lift for the specific flight maneuver. Determination of this angle, a simple affair when the wing is rigid and the flow regime linear, becomes difficult when the wing is flexible and the flow regime non-linear. To solve this inherently nonlinear problem, a Newton's method type algorithm is developed to simultaneously calculate the deflection and the angle of attack. The present algorithm requires the sensitivity of the aerodynamic pressure with respect to each of the generalized displacement coordinates needed to represent the structural displacement. This sensitivity data is easy to determine analytically when the flow regime is linear. The present algorithm uses a finite difference method to obtain these sensitivities and thus requires only the pressure data and the surface geometry from the aerodynamic model. This makes it ideally suited for nonlinear aerodynamics for which it is difficult to obtain the sensitivity analytically.
The present algorithm requires the CFD code to be run for each of the generalized coordinates. Therefore, to reduce the number of generalized coordinates considerably, we employ the modal superposition approach to represent the structural displacements. Results available for the Aeroelastic Research Wing (ARW) are used to evaluate the performance of the modal superposition approach. Calculations are made at a fixed angle of attack and the results are compared to both the experimental results obtained at NASA Langley Research Center, and computational results obtained by the researchers at NASA Ames Research Center. Two CFD codes are used to demonstrate the modular nature of this research. Similarly, two separate Finite Element codes are used to generate the structural data, demonstrating that the algorithm is not dependent on using specific codes.
The developed algorithm is tested for a wing, used for in-house aeroelasticity research at Boeing (previously McDonnell Douglas) Long Beach. The trim angle of attack is calculated for a range of desired lift values. In addition to the Newton's method algorithm, a non derivative method (NDM) based on fixed point iteration, typical of fixed angle of attack calculations in aeroelasticity, is employed. The NDM, which has been extended to be able to calculate trim angle of attack, is used for one of the cases. The Newton's method calculation converges in fewer iterations, but requires more CPU time than the NDM method. The NDM, however, results in a slightly different value of the trim angle of attack. It should be noted that NDM will converge in a larger number of iterations as the dynamic pressure increases.
For one value of the desired lift, both viscous and inviscid results were generated. The use of the inviscid flow model while not resulting in a markedly different value for the trim angle of attack, does result in a noticeable difference both in the wing deflection and the span loading when compared to the viscous results.
A crude (coarse-grain) parallel methodology was used in some of the calculations in this research. Although the codes were not parallelized, the use of modal superposition made it possible to compute the sensitivity terms on different processors of an IBM SP/2. This resulted in a decrease in wall clock time for these calculations. However, even with the parallel methodology, the CPU times involved may be prohibitive (approximately 5 days per Newton iteration) to any practical application of this method for wing analysis and design. Future work must concentrate on reducing these CPU times. Two possibilities: (i) The use of alternative basis vectors to further reduce the number of basis vectors used to represent the structural displacement, and (ii) The use of more efficient methods for obtaining the flow field sensitivities. The former will reduce the number of CFD analyses required the latter the CPU time per CFD analysis.
NOTE: (03/2007) An updated copy of this ETD was added after there were patron reports of problems with the file.Ph. D.
25
Pilkington, David J. "Motion induced unsteady aerodynamics at high angles-of-attack." Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760689.
Повний текст джерела
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Zakaria, Mohamed Yehia. "Unsteady Nonlinear Aerodynamic Modeling and Applications." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/79909.
Повний текст джерелаАнотація:
Unsteady aerodynamic modeling is indispensable in the design process of rotary air vehicles, flapping flight and agile unmanned aerial vehicles. Undesirable vibrations can cause high-frequency variations in motion variables whose effects cannot be well predicted using quasi-steady aerodynamics. Furthermore, one may exploit the lift enhancement that can be generated through an unsteady motion for optimum design of flapping vehicles. Additionally, undesirable phenomena like the flutter of fixed wings and ensuing limit cycle oscillations can be exploited for harvesting energy. In this dissertation, we focus on modeling the unsteady nonlinear aerodynamic response and present various applications where unsteady aerodynamics are very relevant.
The dissertation starts with experiments for measuring unsteady loads on an NACA-0012 airfoil undergoing a plunging motion under various operating conditions. We supplement these measurements with flow visualization to obtain better insight into phenomena causing enhanced lift. For the model, we present the frequency response function for the airfoil at various angles of attack. Experiments were performed at reduced frequencies between 0.1 and 0.95 and angles of attack up to 65 degrees. Then, we formulate an optimization problem to unify the transfer function coefficients for each regime independently to obtain one model that represents the global dynamics. An optimization-based finite-dimensional (fourth-order) approximation for the frequency responses is developed. Converting these models to state-space form and writing the entries of the matrices as polynomials in the mean angle of attack, a unified unsteady model was developed. In the second set of experiments, we measured the unsteady plunging forces on the same airfoil at zero forward velocity. The aim is to investigate variations of the added forces associated with the oscillation frequency of the wing section for various angles of attack. Data of the measured forces are presented and compared with predicted forces from potential flow approximations. The results show a significant departure from those estimates, especially at high frequencies indicating that viscous effects play a major role in determining these forces.
In the second part of this dissertation, we consider different applications where unsteady loads and nonlinear effects play an important role. We perform a multi-objective aerodynamic optimization problem of the wing kinematics and planform shape of a Pterosaur replica ornithopter. The objective functions included minimization of the required cycle-averaged aerodynamic power and maximization of the propulsive efficiency. The results show that there is an optimum kinematic parameter as well as planform shape to fulfill the two objectives. Furthermore, the effects of preset angle of attack, wind speed and load resistance on the levels of harvested power from a composite beam bonded with the piezoelectric patch are determined experimentally. The results point to a complex relation between the aerodynamic loading and its impact on the static deflection and amplitudes of the limit cycle oscillations as well as the level of power harvested. This is followed by testing of a centimeter scale micro wind turbine that has been proposed to power small devices and to work as a micro energy harvester. The experimental measurements are compared to predicted values from a numerical model.
The methods developed in this dissertation provide a systematic approach to identifying unsteady aerodynamic models from numerical or experimental data that may work within different regimes. The resulting reduced-order models are expressed in a state-space form, and they are, therefore, both simple and efficient. These models are low-dimensional linear systems of ordinary differential equations so that they are compatible with modern flight dynamic models. The specific form of the obtained added force model, which defines the added forces as a function of plunging velocity and drag forces, guarantees that the resulting model is accurate over a range of high frequencies. Moreover, presented applications give a sense of the broad range of application of unsteady aerodynamics.Ph. D.
27
Chatlynne, Etan Solomon. "Virtual aero-shaping of a clark-y airfoil at low angles of attack." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17864.
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Jouannet, Christopher. "Model based aircraft design : high angle of attack aerodynamics and weight estimation methods /." Linköping : Dept. of Mechanical Engineering, Linköping University, 2005. http://www.bibl.liu.se/liupubl/disp/disp2005/tek968s.pdf.
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Wood, Charles Wade. "Oscillating shock impingement on low-angle gas injection into a supersonic flow." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39856.
Повний текст джерела
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Mays, Richard Bruce. "Experimental investigation of helium injection at a low downstream angle into supersonic flow." Thesis, Virginia Tech, 1990. http://hdl.handle.net/10919/42076.
Повний текст джерелаАнотація:
Experiments were performed with single, sonic, helium jets at downstream angles of 15° and 30° relative to the free stream to determine their mixing, penetration and total pressure loss when injected into a supersonic air cross flow. From this information, the performance of these jets as fuel injectors in a supersonic combustion ramjet (scramjet) combustion chamber was estimated. Both injection angle jets were made flush to the wind tunnel wall. The jets were injected into a Mach 3 free stream with a total pressure of 6.5 atm, a total temperature of 283 K and a Reynolds Number of 52.5x10⁶ /m. The flow field of each injection angle was documented at jet expansion ratios of one and five. Spark schlieren and nanoshadowgraph methods were used to visualize each flowfield. At axial stations 20, 40, and 90 jet diameters downstream of each jet, continuous vertical profiles of flow quantities were made. Profiles were taken at seven lateral stations including the jet centerline at each axial station. Spacing between the lateral stations was one jet diameter. This data yielded profiles of helium concentration, Mach number, static temperature, static pressure, density, flow speed, mass flux, total pressure, and total temperature. The different injection schemes were then compared on the basis of helium mass fraction decay, the distance required to reach the stochiometric H₂-air concentration and total pressure loss. For all cases except the 15° jet with an expansion ratio of one, large eddies were observed to penetrate into the free stream. These eddies were believed to significantly enhance large scale mixing. The jet cores of the underexpanded jets had bifurcated 20 jet diameters downstream of the injection point, but had re-united by the 40 diameter station. Wandering of the jet core about the geometric centerline was observed for all cases. The decay rates increased rapidly with the jet to free stream dynamic pressure ratio until about 1.5 where the decay rate leveled off. This indicated that there was no significant increase in mixing from increasing the dynamic pressure ratio of the present jets past 1.5. The decay rate of the present 30°, matched pressure case was about 16 percent greater than that of a normal jet at similar dynamic pressure and expansion ratios. These results were reflected in the distances required to reach the stochiometric H₂-air concentration. The 15° jet with an expansion ratio of one had the lowest total pressure loss. It was concluded that injection at low downstream angle shows promise for application to scramjet fuel injection and merits further study.Master of Science
31
Lego, Zachary Michael. "Analysis of High Angle of Attack Maneuvers to Enhance Understanding of the Aerodynamics of Perching." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1355101333.
Повний текст джерела
32
Findlay, David Bruce. "A numerical study of aircraft empennage buffet." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/10926.
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33
Ravi, R. "High Angle of Attack Forebody Flow Physics and Design Emphasizing Directional Stability." Diss., This resource online, 1997. http://scholar.lib.vt.edu/theses/available/etd-01252008-163458/.
Повний текст джерела
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Chiu, Tak Wai. "Aerodynamic loads on a railway train in a cross-wind at large yaw angles." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358612.
Повний текст джерела
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Ravelli, Umberto. "Aerodynamics of a 2017 Formula 1 Car: Numerical Analysis of a Baseline Vehicle and Design Improvements in Freestream and Wake Flows." Doctoral thesis, Università degli studi di Bergamo, 2019. http://hdl.handle.net/10446/128609.
Повний текст джерелаАнотація:
In this work an extensive numerical analysis of open-wheeled racing car aerodynamics is presented. The whole CFD workflow, from meshing to calculation, was carried out by the open-source software OpenFOAM®, in the steady RANS framework. After investigating the mechanisms behind ground effect by means of simple test cases, including a diffuser-equipped blunt body and a single element wing, attention was focused on the 2017 Formula 1 car designed by the British constructor ©PERRINN. The validation of the numerical results in terms of drag, downforce, efficiency and front balance was accompanied by a qualitative study of the flow around the car. Axial vorticity plays a key role in the generation of downforce and the use of ground effect improves the efficiency of the overall vehicle. In the second step of the research, it was found that front and rear ride height have a strong influence on the dynamic behaviour of the car. Since racing implies a close interaction with other vehicles, the core of the research was devoted to evaluation and subsequent improvement of aerodynamic performance in wake flows. Tandem-running simulations at different distances between lead and following cars put in evidence that running in slipstream results in a strong worsening of downforce and a dramatic change in front balance.
To overcome these limitations, the baseline vehicle was subjected to a targeted aerodynamic development. Among the tested aero packages, one in particular provided encouraging results: it ensures higher downforce and efficiency than the baseline configuration while fulfilling, at the same time, the goal of reducing the above mentioned performance worsening in slipstream. The concepts behind the effectiveness of the new design deal with a better management of the chaotic flow underneath the car; moreover, underbody and rear wing adjustments contribute to generation of a shorter and narrower wake. Overall, an easier approach to the lead car and a safer overtaking could be achieved through small modifications to 2017 F1 Technical Regulations, without disrupting the current F1 car layout. As a further check of the robustness of the new design proposals, all the developed aerodynamic configurations have been tested in yawed flow. Finally, the last section of the research aimed at quantifying the lap-time performance of the vehicles equipped with the new aero packages, since each track requires specific levels of downforce and efficiency. Results in terms of aerodynamic specifications are in line with those typically encountered in current F1 grand prix races.
36
Tait, Sean William. "An investigation of fore-body aerodynamics during the velocity vector roll." Thesis, University of the West of Scotland, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265929.
Повний текст джерела
37
Walter, Daniel James, and Daniel james walter@gmail com. "Study of aerofoils at high angle of attack in ground effect." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080110.145138.
Повний текст джерелаАнотація:
Aerodynamic devices, such as wings, are used in higher levels of motorsport (Formula-1 etc.) to increase the contact force between the road and tyres (i.e. to generate downforce). This in turn increases the performance envelope of the race car. However the extra downforce increases aerodynamic drag which (apart from when braking) is generally detrimental to lap-times. The drag acts to slow the vehicle, and hinders the effect of available drive power and reduces fuel economy. Wings, in automotive use, are not constrained by the same parameters as aircraft, and thus higher angles of attack can be safely reached, although at a higher cost in drag. Variable geometry aerodynamic devices have been used in many forms of motorsport in the past offering the ability to change the relative values of downforce and drag. These have invariably been banned, generally due to safety reasons. The use of active aerodynamics is currently legal in both Formula SAE (engineering compet ition for university students to design, build and race an open-wheel race car) and production vehicles. A number of passenger car companies are beginning to incorporate active aerodynamic devices in their designs. In this research the effect of ground proximity on the lift, drag and moment coefficients of inverted, two-dimensional aerofoils was investigated. The purpose of the study was to examine the effect ground proximity on aerofoils post stall, in an effort to evaluate the use of active aerodynamics to increase the performance of a race car. The aerofoils were tested at angles of attack ranging from 0° - 135°. The tests were performed at a Reynolds number of 2.16 x 105 based on chord length. Forces were calculated via the use of pressure taps along the centreline of the aerofoils. The RMIT Industrial Wind Tunnel (IWT) was used for the testing. Normally 3m wide and 2m high, an extra contraction was installed and the section was reduced to form a width of 295mm. The wing was mounted between walls to simulate 2-D flow. The IWT was chosen as it would allow enough height to reduce blockage effect caused by the aerofoils when at high angles of incidence. The walls of the tunnel were pressure tapped to allow monitoring of the pressure gradient along the tunnel. The results show a delay in the stall of the aerofoils tested with reduced ground clearance. Two of the aerofoils tested showed a decrease in Cl with decreasing ground clearance; the third showed an increase. The Cd of the aerofoils post-stall decreased with reduced ground clearance. Decreasing ground clearance was found to reduce pitch moment variation of the aerofoils with varied angle of attack. The results were used in a simulation of a typical Formula SAE race car.
38
Čavoj, Ondřej. "Simulace podmínek ve výpočtech aerodynamiky vozidel." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-403862.
Повний текст джерелаАнотація:
Several types of discrepancies have been examined between CFD simulations, wind tunnel measurements and real world conditions. The results of different wheel rotation methods show that while stationary approaches can often substitute real unsteady wheel rotation, they can also be very sensitive to the exact angular positioning of wheel rims. Using both measured and computed flow fields, the lower part of wheel wake was identified as a key area, showing differences between rotation methods and sources of simulation errors in general. It was also shown that the level of detail in tyre geometry and its deformation near contact patch do not have a large impact on accuracy. Due to the absence of tyre rotation, the tyre sidewall was identified as an important place of flow separation with large effect on flow field and forces. Angle of attack study confirmed that assessing purely straight-line drag causes its under prediction compared to real-world values. This judgement would however benefit from obtaining data in more adverse conditions compared to those currently available. Finally, tyre radial expansion was investigated, causing a drop in drag with increasing vehicle velocity and altering the flow around the rear bodywork. Ignoring this effect can therefore negatively influence the aerodynamic development of a vehicle.
39
Le, Moigne Yann. "Adaptive Mesh Refinement and Simulations of Unsteady Delta-Wing Aerodynamics." Doctoral thesis, KTH, Aeronautical and Vehicle Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3786.
Повний текст джерелаАнотація:
This thesis deals with Computational Fluid Dynamics (CFD)simulations of the flow around delta wings at high angles ofattack. These triangular wings, mainly used in militaryaircraft designs, experience the formation of two vortices ontheir lee-side at large angles of attack. The simulation ofthis vortical flow by solving the Navier-Stokes equations isthe subject of this thesis. The purpose of the work is toimprove the understanding of this flow and contribute to thedesign of such a wing by developing methods that enable moreaccurate and efficient CFD simulations.
Simulations of the formation, burst and disappearance of thevortices while the angle of attack is changing are presented.The structured flow solver NSMB has been used to get thetime-dependent solutions of the flow. Both viscous and inviscidresults of a 70°-swept delta wing pitching in anoscillatory motion are reported. The creation of the dynamiclift and the hysteresis observed in the history of theaerodynamic forces are well reproduced.
The second part of the thesis is focusing on automatic meshrefinement and its influence on simulations of the delta wingleading-edge vortices. All the simulations to assess the gridquality are inviscid computations performed with theunstructured flow solver EDGE. A first study reports on theeffects of refining thewake of the delta wing. A70°-swept delta wing at a Mach number of 0.2 and an angleof attack of 27° where vortex breakdown is present abovethe wing, is used as testcase. The results show a strongdependence on the refinement, particularly the vortex breakdownposition, which leads to the conclusion that the wake should berefined at least partly. Using this information, a grid for thewing in the wind tunnel is created in order to assess theinfluence of the tunnel walls. Three sensors for automatic meshrefinement of vortical flows are presented. Two are based onflow variables (production of entropy and ratio of totalpressures) while the third one requires an eigenvalue analysisof the tensor of the velocity gradients in order to capture theposition of the vortices in the flow. These three vortexsensors are successfully used for the simulation of the same70° delta wing at an angle of attack of 20°. Acomparison of the sensors reveals the more local property ofthe third one based on the eigenvalue analysis. This lattertechnique is applied to the simulation of the wake of a deltawing at an angle of attack of 20°. The simulations on ahighly refined mesh show that the vortex sheet shed from thetrailing-edge rolls up into a vortex that interacts with theleading-edge vortex. Finally the vortex-detection technique isused to refine the grid around a Saab Aerosystems UnmannedCombat Air Vehicle (UCAV) configuration and its flight dynamicscharacteristics are investigated.
Key words:delta wing, high angle of attack, vortex,pitching, mesh refinement, UCAV, vortex sensor, tensor ofvelocity gradients.
40
Lewis, Daniel Joseph. "Tip clearance and angle of attack effects upon the unsteady response of a vibrating flat plate in crossflow /." This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06112009-063924/.
Повний текст джерела
41
Ko, Joon Soo. "Analysis of the dynamic stability derivatives for high angle of attack aircraft." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/52300.
Повний текст джерелаАнотація:
Modern, high performance aircraft are required to be able to fly and be controlled over a wide variety of flight conditions. In order to predict the aircraft behavior and control requirements over the entire flight regime it is necessary to have a proper aerodynamic model. Flight conditions at high angles of attack lead to separated flows making the aerodynamic model more difficult to obtain. In this research wind tunnel experiments are performed on an F-5 air-craft model at high angles of attack, with small oscillations about the body oriented roll axis. In addition the free stream environment can be configured in one of three ways: l) straight uniform flow, 2) curved flow to simulated a horizontal turn, and 3) rolling flow to simulated a roll motion about the relative Velocity vector.Ph. D.
42
Frink, William D. "Hot-wire surveys in the vortex wake downstream of a three-percent fighter aircraft model at high angles of attack." Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241869.
Повний текст джерелаАнотація:
Thesis (M.S. in Engineering Science)--Naval Postgraduate School, December 1990.Thesis Advisor(s): Hebbar, Sheshagiri K. ; Platzer, Max F. "December 1990." Description based on title screen as viewed on March 31, 2010. DTIC Identifier(s): Trailling Vortices, Wake, Trubulent Flow, Jet Fighters, High Alpha (High Angle of Attack), Vortex Wake, Angle of Attack, Extendable Structures, Leading Edges, Fences, Lex Fences, Wind Tunnel Models, F-17 Aircraft, F/A-18 Aircraft, Wind Tunnel Tests, Hot Wire Anemometers, Theses. Author(s) subject terms: High Angle-of-Attack Aerodynamics, Hot-Wire Measurements, Wind Tunnel Studies. Includes bibliographical references (p. 24-25). Also available in print.
43
Cavazos, Odilon V. "A flow visualization study of LEX generated vortices on a scale model of F/A-18 fighter aircraft at high angles of attack." Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA236534.
Повний текст джерелаАнотація:
Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, June 1990.Thesis Advisor(s): Hebbar, S. K. ; Platzer, M. F. "June 1990." Description based on title screen as viewed on October 19, 2009. DTIC Descriptor(s): Angles, yaw, scale models, attack, motion, rates, moments, vortices, flow visualization, rupture, asymmetry, aerodynamic forces, leading edges, range(distance), statics, hysteresis, aerodynamics, high angles, pitch(motion). DTIC Indicator(s): Flow visualization, trailing vortices, F/A-18 aircraft. Author(s) subject terms: High angle of attack aerodynamics, effect of pitch rate and yaw, vortex development and bursting, flow visualization by dye injection, water tunnel studies, F/A-18 fighter aircraft. Includes bibliographical references (p. 44-45). Also available in print.
44
Desenfans, Philip. "Aerodynamics of the Maple Seed." Aircraft Design and Systems Group (AERO), Department of Automotive and Aeronautical Engineering, Hamburg University of Applied Sciences, 2019. http://d-nb.info/1204982848.
Повний текст джерелаАнотація:
Purpose - The paper presents a theoretical framework that describes the aerodynamics of a falling maple (Acer pseudoplatanus) seed. --- Methodology - A semi-empirical method is developed that provides a ratio stating how much longer a seed falls in air compared to freefall. The generated lift is calculated by evaluating the integral of two-dimensional airfoil elements using a preliminary falling speed. This allows for the calculation of the definitive falling speed using Blade Element Momentum Theory (BEMT); hereafter, the fall duration in air and in freefall are obtained. Furthermore, the input-variables of the calculation of lift are transformed to require only the length and width of the maple seed. Lastly, the method is applied to two calculation examples as a means of validation. --- Findings - The two example calculations gave percentual errors of 5.5% and 3.7% for the falling speed when compared to measured values. The averaged result is that a maple seed falls 9.9 times longer in air when released from 20 m; however, this result is highly dependent on geometrical parameters which can be accounted for using the constructed method. --- Research limitations - Firstly, the coefficient of lift is unknown for the shape of a maple seed. Secondly, the approximated transient state is yet to be verified by measurement. --- Originality / Value - The added value of this report lies in the reduction of simplifications compared to BEMT approaches. In this way a large amount of accuracy is achieved due to the inclusion of many geometrical parameters, even though simplicity is maintained. This has been accomplished through constructing a simple three-step method that is fundamental and essentially non-iterative.
45
東, 大輔, Daisuke AZUMA, 佳朗 中村 та Yoshiaki NAKAMURA. "前縁回転/後縁ジェットハイブリッド法によるデルタ翼揚力増加". 日本航空宇宙学会, 2006. http://hdl.handle.net/2237/13878.
Повний текст джерела
46
Schaeffler, Norman Walter. "All The King's Horses: The Delta Wing Leading-Edge Vortex System Undergoing Vortex Breakdown: A Contribution to its characterization and Control under Dynamic Conditions." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30454.
Повний текст джерелаАнотація:
The quality of the flow over a 75 degree-sweep delta wing
was documented for steady angles of attack and during
dynamic maneuvers with and without the use of two control
surfaces. The three-dimensional velocity field over a delta
wing at a steady angle of attack of 38 degrees and Reynolds
number of 72,000 was mapped out using laser-Doppler
velocimetry over one side of the wing. The three-dimensional
streamline and vortex line distributions were visualized.
Isosurfaces of vorticity, planar distributions of helicity
and all three vorticity components, and the indicator of
the stability of the core were studied and compared to see
which indicated breakdown first. Visualization of the
streamlines and vortex lines near the core of the vortex
indicate that the core has a strong inviscid character, and
hence Reynolds number independence, upstream of breakdown,
with viscous effects becoming more important downstream of
the breakdown location. The effect of cavity flaps on the
flow over a delta wing was documented for steady angles of
attack in the range 28 degrees to 42 degrees by flow
visualization and surface pressure measurements at a
Reynolds number of 470,000 and 1,000,000, respectfully.
It was found that the cavity flaps postpone the occurrence
of vortex breakdown to higher angles of attack than can be
realized by the basic delta wing. The effect of
continuously deployed cavity flaps during a dynamic
pitch-up maneuver of a delta wing on the surface pressure
distribution were recorded for a reduced frequency of
0.0089 and a Reynolds number of 1,300,000. The effect of
deploying a set of cavity flaps during a dynamic pitch-up
maneuver on the surface pressure distribution was recorded
for a reduced frequency of 0.0089 and a Reynolds number of
1,300,000 and 187,000. The active deployment of the cavity
flaps was shown to have a short-lived beneficial effect on
the surface pressure distribution. The effect on the
surface pressure distribution of the varying the reduced
frequency at constant Reynolds number for a plain delta
wing was documented in the reduced frequency range of
0.0089 to 0.0267. The effect of the active deployment of
an apex flap during a pitch-up maneuver on the surface
pressure distribution at Reynolds numbers of 532,000,
1,000,000, and 1,390,000 were documented with reduced
frequencies of 0.0053 to 0.0114 with flap deployment
locations in the range of 21° to 36° . The apex flap
deployment was found to have a beneficial effect on the
surface pressure distribution during the maneuver and in
the post-stall regime after the maneuver is completed.Ph. D.
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Липовий, Віталій Миколайович, Виталий Николаевич Липовый та Vitalii Mykolaiovych Lypovyi. "Підвищення енергетичних показників ортогональних вітродвигунів для використання вітрових потоків малої потужності". Thesis, Вид-во СумДУ, 2015. http://essuir.sumdu.edu.ua/handle/123456789/40886.
Повний текст джерелаАнотація:
Дисертація на здобуття наукового ступеня кандидата технічних наук за
фахом 05.05.17 – гідравлічні машини та гідропневмоагрегати. – Сумський
державний університет, Суми, 201 5.
У дисертаційній роботі приведено вирішення питання самозапуску
вертикально-осьового вітродвигуна для малих та середніх розмірів вітроколіс
при використанні вітрових потоків низької потужності. Розроблено
аналітичний метод визначення оптимальних характеристик потоку повітря для
продукування максимального тягового зусилля на всій траєкторії руху лопаті.
Чисельним моделюванням обтікання лопаті потоком повітря вирішено питання
визначення аеродинамічних коефіцієнтів для заданого профілю, що з певним
припущенням дозволяє відмовитися від натурного експерименту продувки
профілю в аеродинамічній трубі.
Запропоновано механізм впливу на ортогональне вітроколесо шляхом
уведення допоміжного вектору швидкості, з метою підвищення його
аеродинамічних характеристик. Цей механізм випробувано на
експериментальному стенді та доведено доцільність його використання під час
роботи вітроколеса на нерозрахункових режимах.
У результаті досліджень визначено показники крутних моментів на валу
ортогональної вітротурбіни з прямими лопатями парусного типу. Доведено
підвищення стартового тягового моменту. Для запропонованих конструкцій
симетричних гнучких профільованих лопатей наведені інтегральні
характеристики при змінних геометричних показниках вітроколеса.
Результати дисертаційної роботи дозволяють розробляти високоефективні
вітроенергетичні установки, орієнтовані на використання вітрових потоків
низької потужності, що є актуальним для території України.Диссертация на соискание ученой степени кандидата технических наук по специальности 05.05.17 - гидравлические машины и гидропневмоагрегаты. - Сумской государственный университет, Сумы, 2015. В диссертационной работе приведены решения вопроса самозапуска вертикально-осевого ветродвигателя для малых и средних размеров ветроколес при использовании ветровых потоков низких мощностей. Разработан аналитический метод определения оптимальных характеристик потока воздуха для возникновения максимального тягового усилия на всей траектории движения лопасти. Численным моделированием обтекания лопасти потоком воздуха решен вопрос определения аэродинамических коэффициентов для заданного профиля, что с определенным предположением позволяет отказаться от натурного эксперимента продувки профиля в аэродинамической трубе. Предложен механизм влияния на ортогональное ветроколесо путем введения вспомогательного вектора скорости с целью повышения его энергетических характеристик. Данный механизм испытано на экспериментальном стенде и доказана целесообразность его использования при работе ветроколеса на нерасчетных режимах. Впервые разработано двухструйную математическую модель ортогонального ветродвигателя для определения кинематических характеристик потока воздуха, которые влияют на повышение мощности ветроколеса. Разработано аналитические зависимости для определения влияния на эффективность работы ветротурбины дополнительного вектора скорости W̅', что приводит к смещению треугольников скоростей в сторону увеличения тяговой силы на поверхности лопасти. В результате исследований определены показатели крутящих моментов на валу ортогональной ветротурбины с прямыми лопастями парусного типа. Доказано повышение стартового тягового момента. Для предложенных конструкций симметричных гибких профилированных лопастей приведены интегральные характеристики при переменных геометрических показателях ветроколеса. Экспериментальным путем определено, что введение вспомогательного вектора скорости путем установки экрана на дуге круговой траектории в области нулевого азимутального угла β=0 позволяет повысить мощность ветроколеса. Плоский экран длинной 120 мм, наклоненный под углом 20° на азимутальном угле 36° повышает генерируемую мощность ветроколеса в 2,5 раза. Определено, что использование гибких парусных лопастей симметричного профиля позволяет получить высокие значения начального крутящего момента на валу ортогональной ветротурбины. При низкой быстроходности θ ˂ 0,5 значение коэффициента крутящего момента составляет Cm = 0,47. При дальнейшем разгоне ветроколеса Cm падает до значения жесткой симметричной лопасти C m = 0,1. Результаты диссертационной работы позволяют разрабатывать высокоэффективные ветроэнергетические установки, ориентированные на использование ветровых потоков низкой мощности, что актуально для территории Украины.
Thesis for the degree of candidate of technical sciences, specialty 05.05.17 - hydraulic machines and hydropneumaticunits. – Sumy State University, Sumy, 2015. The thesis shows the solution to the question of self-start of vertical-axis wind turbine for small and medium-sized windwheels using wind currents low capacity. An analytical method for determining the optimal characteristics of the air flow for the occurrence of maximum power to the entire trajectory of the blade. Numerical simulation of flow around the blade airflow resolved the question of determining the aerodynamic coefficients for a given profile, with certain assumptions eliminates the natural experiment blowing in the wind tunnel profile. The mechanism of the effect of the orthogonal wind wheel, by introducing auxiliary velocity vector, in order to improve its energy performance. This mechanism is tested on experimental stand and prove the feasibility of its use in the operation of the wind wheel on the off-nominal conditions. The studies identify indicators torque of the orthogonal wind turbine with straight blades sailing type. Proven to increase the starting of torque. For the proposed construction of symmetric flexible profiled blades are given integral characteristics with variable geometry have been the propeller. The results of the thesis allow you to develop highly efficient wind turbines focused on the use of wind flows low power, which is important for Ukraine.
48
Jirásek, Lukáš. "Analýza vlivu polohy karoserie závodního vozu na aerodynamické charakteritiky." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229397.
Повний текст джерелаАнотація:
Aim of this diploma thesis is to make sensitivity research concerning influence of vehicle body position on its aerodynamical loading. CAD model was created in Pro/E software. Formula Ford 1600 chassis and vehicle body dimensions were used as a pattern for CAD model. Then this model was imported into CFD environment where ambient medium characteristic were set up. FLUENT software performed calculations and measurement of aerodynamical characteristics of vehicle dependent on height and angle of chassis.
49
Lee, Jaewoo. "Efficient inverse methods for supersonic and hypersonic body design, with low wave drag analysis." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/37406.
Повний текст джерелаАнотація:
With the renewed interest in the supersonic and hypersonic flight vehicles, new inverse Euler methods are developed in these flow regimes where a space marching numerical technique is valid. In order to get a general understanding for the specification of target pressure distributions, a study of minimum drag body shapes was conducted over a Mach number range from 3 to 12. Numerical results show that the power law bodies result in low drag shapes, where the n=.69 (l/d = 3) or n=.70 (l/d = 5) shapes have lower drag than the previous theoretical results (n=.75 or n=.66 depending on the particular form of the theory). To validate the results, a numerical analysis was made including viscous effects and the effect of gas model. From a detailed numerical examination for the nose regions of the minimum drag bodies, aerodynamic bluntness and sharpness are newly defined.
Numerous surface pressure-body geometry rules are examined to obtain an inverse procedure which is robust, yet demonstrates fast convergence. Each rule is analyzed and examined numerically within the inverse calculation routine for supersonic (M∞ = 3) and hypersonic (M∞ = 6.28) speeds. Based on this analysis, an inverse method for fully three dimensional supersonic and hypersonic bodies is developed using the Euler equations. The method is designed to be easily incorporated into existing analysis codes, and provides the aerodynamic designer with a powerful tool for design of aerodynamic shapes of arbitrary cross section. These shapes can correspond to either "wing like" pressure distributions or to "body like" pressure distributions. Examples are presented illustrating the method for a non-axisymmetric fuselage type pressure distribution and a cambered wing type application. The method performs equally well for both nonlifting and lifting cases. For the three dimensional inverse procedure, the inverse solution existence and uniqueness problem are discussed. Sample calculations demonstrating this problem are also presented.Ph. D.
50
Lewis, Daniel Russell. "Tip clearance and angle of attack effects upon the unsteady response of a vibrating flat plate in crossflow." Thesis, Virginia Tech, 1993. http://hdl.handle.net/10919/43198.
Повний текст джерелаАнотація:
The influence of tip clearance and angle of attack upon the mid-span unsteady pressure response of a vibrating flat plate was investigated experimentally. Unsteady pressure measurements were taken for a variety of incidence angles, vibration frequencies and tip clearances over a Mach number range of 0.2 to 0.6.
It was found that changes in tip clearance had an effect on measured pressure fluctuations at higher angles of attack and larger Mach numbers. It was also observed that the amplitude of the unsteady pressure increased as the incidence angle was increased.
The plate was mechanically induced to oscillate in translation, simulating the flISt bending mode. Averaged Fast Fourier Transforms were used to determine pressure oscillation amplitudes and phase lags with respect to the plate motion.
Master of Science