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1
Karpik, A., and Yu Vorobiev. "Nonlinear Analysis of Gas Flow in Compressors Stage Based on CFD-Method." Thesis, NTU "KhPI", 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/24955.
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The numerical simulation of a three-dimensional viscous flow in cascade of the axial compressor of low
pressure of the gas-turbine engine is presented. The results of a flow in the first stage o f the compressor in nonstationary
three-dimensional statement are obtained in the solver F. Velocity and pressure fields are received
as a result.
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Ricklick, Mark. "CHARACTERIZATION OF AN INLINE ROW IMPINGEMENT CHANNEL FOR TURBINE BLADE COOLING APPLICATIONS." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2696.
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Gas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, micro-turbines capable of producing efficient portable power. Part of the turbine's success is the fact that their efficiency levels have continuously risen since their introduction in the early 1800's. Along with improvements in our understanding and designs of the aerodynamic components of the turbine, as well as improvements in the areas of material design and combustion control, advances in component cooling techniques have predominantly contributed to this success. This is the result of a simple thermodynamic concept; as the turbine inlet temperature is increased, the overall efficiency of the machine increases as well. Designers have exploited this fact to the extent that modern gas turbines produce rotor inlet temperatures beyond the melting point of the sophisticated materials used within them. This has only been possible through the use of sophisticated cooling techniques, particularly in the 1st stage vanes and blades. Some of the cooling techniques employed today have been internal cooling channels enhanced with various features, film and showerhead cooling, as well as internal impingement cooling scenarios. Impingement cooling has proven to be one of the most capable heat removal processes, and the combination of this cooling feature with that of channel flow, as is done in impingement channel cooling, creates a scenario that has understandably received a great deal of attention in recent years. This study has investigated several of the unpublished characteristics of these impingement channels, including the channel height effects on the performance of the channel side walls, effects of bulk temperature increase on heat transfer coefficients, circumferential heat variation effects, and effects on the uniformity of the heat transfer distribution. The main objectives of this dissertation are to explore the various previously unstudied characteristics of impingement channels, in order to sufficiently predict their performance in a wide range of applications. The potential exists, therefore, for a designer to develop a blade with cooling characteristics specifically tailored to the expected component thermal loads. Temperature sensitive paint (TSP) is one of several non-intrusive optical temperature measurements techniques that have gained a significant amount of popularity in the last decade. By employing the use of TSP, we have the ability to provide very accurate (less than 1 degree Celsius uncertainty), high resolution full-field temperature measurements. This has allowed us to investigate the local heat transfer characteristics of the various channel surfaces under a variety of steady state testing conditions. The comparison of thermal performance and uniformity for each impingement channel configuration then highlights the benefits and disadvantages of various configurations. Through these investigations, it has been shown that the channel side walls provide heat transfer coefficients comparable to those found on the target surface, especially at small impingement heights. Although the side walls suffer from highly non-uniform performance near the start of the channel, the profiles become very uniform as the cross flow develops and becomes a dominating contributor to the heat transfer coefficient. Increases in channel height result in increased non-uniformity in the streamwise direction and decreased heat transfer levels. Bulk temperature increases have also been shown to be an important consideration when investigating surfaces dominated by cross flow heat transfer effects, as enhancements up to 80% in some areas may be computed. Considerations of these bulk temperature changes also allow the determination of the point at which the flow transitions from an impingement dominated regime to one that is dominated by cross flow effects. Finally, circumferential heat variations have proven to have negligible effects on the calculated heat transfer coefficient, with the observed differences in heat transfer coefficient being contributed to the unaccounted variations in channel bulk temperature.<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering<br>Engineering and Computer Science<br>Mechanical Engineering PhD
3
Roclawski, Harald. "PIV Measurements of Channel Flow with Multiple Rib Arrangements." UKnowledge, 2001. http://uknowledge.uky.edu/gradschool_theses/303.
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A model of a gas turbine blade cooling channel equipped with turbulators and a backward facing step geometry was examined. Up to four turbulators oriented cross-stream and inclined 45° to the flow direction were mounted in the channel. The blockage ratio b/H of the turbulators and the height h/H of the backward facing step was 0:125 and 0:14 respectively. The number of turbulators as well as their size was varied. In a preliminary investigation, hot-wire and pressure measurements were taken for three different Reynolds numbers (5,000, 12,000, 18,000)in the center plane of the test section. Subsequently, particle image velocimetry (PIV) measurements were made on the same geometries. Results of PIV measurements for a Reynolds number range of Reb=600 to 5,000 for the turbulators and Reh=1,500 to 16,200 for the backward facing step are presented, where Reynolds numbers are based on turbulator height b and step height h, respectively. Plots of the velocity field, vorticity, reverse flow probability and RMS velocity are shown. The focus is on the steady flow behavior but also the unsteadiness of the flow is discussed in one section. Also reattachment lengths were obtained and compared among the various turbulator arrangements and the backward facing step geometry. It was found that the flow becomes periodic after three or four ribs. For one turbulator, a very large separation region was observed. The magnitude of the skin friction factor was found to be the highest for two ribs. If the first rib is replaced by a smaller rib, the skin friction factor becomes the lowest for this case. Compared to the backward facing step, the flow reattaches earlier for multiple turbulators. A dependency of reattachment length on Reynolds number was not observed.
4
Bhattarai, Kripesh. "On the Use of a Digital Communication Channel for Feedback in a Position Control System." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1353512595.
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Rupakula, Venkata Panduranga Praveen. "Determination of heat (mass) transfer from blockages with round and elongated holes in a wide rectangular channel." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4977.
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Mass transfer experiments were conducted to study the thermal performance
characteristics of blockages with round and elongated holes, positioned in a 12:1
rectangular channel. Naphthalene sublimation technique was adopted to conduct
experiments with four different blockage configurations, flow rates corresponding to
Reynolds numbers (based on channel hydraulic diameter) of 7,000 and 17,000, and at
three blockage locations. The hole area to channel area ratio for all four blockage
configurations was the same at 0.196. The hole width was half the channel height, and
the distance between consecutive blockages was twice the channel height. Average heat
transfer, local heat (mass) transfer and overall pressure drop results were obtained. The
thermal performance for a particular blockage configuration was measured in terms of
the heat transfer enhancement and the friction factor ratio. Heat transfer enhancement
was measured as a ratio of average Nusselt number on the blockage surface to the
Nusselt number for a thermally fully developed turbulent flow in a smooth channel.
Results indicate that this ratio ranged between 3.6 and 12.4, while the friction factor ratio
varied between 500-1700. The blockage configuration with round holes was found to
yield best thermal performance, while the configuration with largest hole elongation was
nearly equal in thermal performance. In order to compare different blockage
configurations, an average value of upstream and downstream side thermal performances
was used. A general downward trend in Nusselt number ratio with elongation of holes was
observed on the upstream side and a reverse trend was observed on the downstream side.
An upward trend in the Nusselt number ratio with blockage hole elongation on the
downstream side of a blockage was primarily due to jet reversal from the downstream
blockage and its impingement on the downstream surface of the upstream blockage.
Local experiments were performed to compare against the results from average
experiments and also to gain insights into the flow behaviour. There was good
agreement between the results from local and average mass transfer experiments. The
average variation in Nusselt number ratio between local and average mass transfer
experiments was about 5.06%.
6
Liu, Yao-Hsien. "Heat transfer in leading and trailing edge cooling channels of the gas turbine blade under high rotation numbers." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3196.
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Waidmann, Christian [Verfasser]. "Heat Transfer Measurements in Rotating Turbine Blade Cooling Channel Configurations using the Transient Thermochromic Liquid Crystal Technique / Christian Waidmann." München : Verlag Dr. Hut, 2021. http://d-nb.info/1232847747/34.
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Nagaiah, Narasimha. "Multiobjective Design Optimization of Gas Turbine Blade with Emphasis on Internal Cooling." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5350.
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In the design of mechanical components, numerical simulations and experimental methods are commonly used for design creation (or modification) and design optimization. However, a major challenge of using simulation and experimental methods is that they are time-consuming and often cost-prohibitive for the designer. In addition, the simultaneous interactions between aerodynamic, thermodynamic and mechanical integrity objectives for a particular component or set of components are difficult to accurately characterize, even with the existing simulation tools and experimental methods. The current research and practice of using numerical simulations and experimental methods do little to address the simultaneous “satisficing” of multiple and often conflicting design objectives that influence the performance and geometry of a component. This is particularly the case for gas turbine systems that involve a large number of complex components with complicated geometries. Numerous experimental and numerical studies have demonstrated success in generating effective designs for mechanical components; however, their focus has been primarily on optimizing a single design objective based on a limited set of design variables and associated values. In this research, a multiobjective design optimization framework to solve a set of user-specified design objective functions for mechanical components is proposed. The framework integrates a numerical simulation and a nature-inspired optimization procedure that iteratively perturbs a set of design variables eventually converging to a set of tradeoff design solutions. In this research, a gas turbine engine system is used as the test application for the proposed framework. More specifically, the optimization of the gas turbine blade internal cooling channel configuration is performed. This test application is quite relevant as gas turbine engines serve a critical role in the design of the next-generation power generation facilities around the world. Furthermore, turbine blades require better cooling techniques to increase their cooling effectiveness to cope with the increase in engine operating temperatures extending the useful life of the blades. The performance of the proposed framework is evaluated via a computational study, where a set of common, real-world design objectives and a set of design variables that directly influence the set of objectives are considered. Specifically, three objectives are considered in this study: (1) cooling channel heat transfer coefficient, which measures the rate of heat transfer and the goal is to maximize this value; (2) cooling channel air pressure drop, where the goal is to minimize this value; and (3) cooling channel geometry, specifically the cooling channel cavity area, where the goal is to maximize this value. These objectives, which are conflicting, directly influence the cooling effectiveness of a gas turbine blade and the material usage in its design. The computational results show the proposed optimization framework is able to generate, evaluate and identify thousands of competitive tradeoff designs in a fraction of the time that it would take designers using the traditional simulation tools and experimental methods commonly used for mechanical component design generation. This is a significant step beyond the current research and applications of design optimization to gas turbine blades, specifically, and to mechanical components, in general.<br>Ph.D.<br>Doctorate<br>Industrial Engineering and Management Systems<br>Engineering and Computer Science<br>Industrial Engineering
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Mhetras, Shantanu. "Experimental study of gas turbine blade film cooling and internal turbulated heat transfer at large Reynolds numbers." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1820.
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Waidmann, Christian [Verfasser], and Jens von [Akademischer Betreuer] Wolfersdorf. "Heat transfer measurements in rotating turbine blade cooling channel configurations using the transient thermochromic liquid crystal technique / Christian Waidmann ; Betreuer: Jens von Wolfersdorf." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2020. http://d-nb.info/122943853X/34.
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Parida, Pritish Ranjan. "Optimization and Fabrication of Heat Exchangers for High-Density Power Control Unit Applications." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77165.
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The demand for more power and performance from electronic equipment has constantly been growing resulting in an increased amount of heat dissipation from these devices. Thermal management of high-density power control units for hybrid electric vehicles is one such application. Over the last few years, the performance of this power control unit has been improved and size has been reduced to attain higher efficiency and performance causing the heat dissipation as well as heat density to increase significantly. However, the overall cooling system has remained unchanged and only the heat exchanger corresponding to the power control unit (PCU) has been improved. This has allowed the manufacturing costs to go down. Efforts are constantly being made to reduce the PCU size even further and also to reduce manufacturing costs. As a consequence, heat density will go up (~ 200 – 250 W/cm2) and thus, a better high performance cooler/heat exchanger is required that can operate under the existing cooling system design and at the same time, maintain active devices temperature within optimum range (<120 – 125 °C) for higher reliability.
The aim of this dissertation was to study the various cooling options based on jet impingement, mini-channel, ribbed mini-channel, phase change material and double sided cooling configurations for application in hybrid electric vehicle and other similar consumer products and perform parametric and optimization study on selected designs. Detailed experimental and computational analysis was performed on different cooling designs to evaluate overall performance. Severe constraints such as choice of coolant, coolant flow-rate, pressure drop, minimum geometrical size and operating temperature were required for the overall design. High performance jet impingement based cooler design with incorporated fin-like structures induced swirl and provided enhanced local heat transfer compared to traditional cooling designs. However, the cooling scheme could manage only 97.4% of the target effectiveness. Tapered/nozzle-shaped jets based designs showed promising results (~40% reduction in overall pressure drop) but were not sufficient to meet the overall operating temperature requirement. Various schemes of mini-channel arrangement, which were based on utilizing conduction and convection heat transfer in a conjugate mode, demonstrated improved performance over that of impingement cooling schemes. Impingement and mini-channel based designs were combined to show high heat transfer rates but at the expense of higher pressure drops (~5 times). As an alternate, mini-channel based coolers with ~1.5 mm size channels having trip strips or ribs were studied to accommodate the design constraints and to enhance local as well as overall heat transfer rates and achieve the target operating temperature.
A step by step approach to the development of the heat exchanger is provided with an emphasis on system level design. The computational based optimization methodology is confirmed by a fabricated test bed to evaluate overall performance and compare the predicted results with actual performance.
Additionally, one of the impingement based configuration (Swirl-Impingement-Fin) developed during the course of this work was applied to the internal cooling of a turbine blade trailing edge and was shown to enhance the thermal performance by at least a factor of 2 in comparison to the existing pin-fin technology for the conditions studied in this work.<br>Ph. D.
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Diette, Christophe. "Measurement and analysis of forced convection phenomena in blade cooling channels." Valenciennes, 2003. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/c76547a4-820c-48f8-9717-ced740f0cb38.
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Dealing with gas turbine aircraft engines, the Turbine Entry Temperature (TET) is generally targeted as high as possible. Increasing this parameter leads to higher thermodynamic efficiency and power output and reduces the weight-to-thrust ratio and the Specific Fuel Consumption (SFC). Since the maximum permissible TET is determined by the temperature limitations of the turbine assembly, the choice of turbine material and the design of cooling systems applied to turbine blades are essential. This work reports both an experimental and numerical investigation on internal blade cooling cavities. Various cross sections are examined depending on the region of the blade to cool down. Numerous parameters regarding the promoters of turbulence and the flow conditions are varied to find an optimum solution in terms of both heat transfer and pressure losses. Numerical simulations are performed to support the analysis of the flow behaviour. A good agreement is found between the simulations and the aerodynamic measurements. Theoretical diagrams to interpret the flow field are finally proposed. This study provides a better understanding of flow features occuring in cooling channels together with a very detailed database. The later is useful for further numerical validations and the optimisation of cooling cavities<br>En matière de moteurs d'avion à turbine à gaz, une Température d'Entrée de Turbine (TET) aussi élevée que possible est souhaitée. Augmenter sa valeur permet en effet d'obtenir un rendement thermodynamique plus élevé tout en réduisant le rapport poids-poussée et la consommation spécifique (SFC). Parce que la TET maximum permise est liée aux limites de température supportées par les composants de la turbine, le choix des matériaux et la conception des circuits de refroidissement d'aubes sont cruciaux. Cette recherche rend compte d'une étude expérimentale et numérique sur les cavités internes de refroidissement d'aubes. Des sections de passage différentes sont examinées, en fonction de la région de l'aube à refroidir. Plusieurs paramètres en ce qui concerne les promoteurs de turbulence et les conditions de l'écoulement, sont variés pour définir une solution optimale en termes de transfert de chaleur et pertes de charges. Des simulations numériques sont réalisées pour appuyer l'analyse de l'écoulement. La comparaison de ces résultats avec les mesures aérodynamiques se révèle très satisfaisante. Enfin, des diagrammes sont proposés, pour décrire l'écoulement dans chaque cavité étudiée. De cette étude, il ressort une meilleure compréhension des phénomènes mis en jeu dans les cavités de refroidissement, ainsi qu'une base de données détaillée. Cette dernière est utile pour la validation de codes de calcul et l'optimisation des systèmes de refroidissement
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Barbiero, Franck. "Antibrouillage de récepteur GNSS embarqué sur hélicoptère." Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0052.
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En environnements hostiles, les signaux GNSS (Global Navigation Satellite System)peuvent être soumis à des risques de brouillages intentionnels. Basées sur un réseau d'antennes adaptatif, les solutions spatio-temporelles (STAP) ont déjà montré de bonnes performances de réjection des interférences. Toutefois, lorsque le module GNSS est placé sous les pales d'un hélicoptère, des effets non-stationnaires, appelés Rotor Blade Modulation (RBM), créés par les multiples réflexions du signal sur les pales du rotor, peuvent dégrader les techniques usuelles d’antibrouillage. Le signal utile GNSS n’est alors plus accessible. Le travail de la thèse consiste donc à élaborer un système de protection des signaux GNSS adapté à la RBM. Pour cela, un modèle innovant de multitrajets, adapté à ce type de phénomène, a été développé. La comparaison de simulations électromagnétiques représentatives et de mesures expérimentales sur hélicoptère EC-120 a permis de valider ce modèle. Celui-ci permet d'estimer, par maximum de vraisemblance, les paramètres de la contribution non-stationnaire du signal reçu. Enfin, l'association d'un algorithme de filtrage des multitrajets par projection oblique et d'un traitement STAP permet d'éliminer la contribution dynamique puis statique de l'interférence. Les simulations montrent que le signal utile GNSS est alors de nouveau exploitable<br>In hostile environments, Global Navigation Satellite System (GNSS) can be disturbed by intentional jamming. Using antenna arrays, space-time adaptive algorithm (STAP) isone of the most efficient methods to deal with these threats. However, when a GNSS receiver is placed near rotating bodies, non-stationary effects called Rotor Blade Modulation (RBM) are created by the multipaths on the blades of the helicopter. They can degrade significantly the anti-jamming system and the signal of interest could belost. The work of the thesis is, consequently, to develop a GNSS protection system adapted to the RBM. In this way, an innovative multipath model, adapted to this phenomenon, has been developed. The model is then confirmed by comparison with a symptotic electromagnetic simulations and experiments conducted on an EC-120helicopter. Using a Maximum Likelihood algorithm, the parameters of the non-stationary part of the received signal have been estimated. And finally, the RBM anti-jamming solution, combining oblique projection algorithm and academic STAP, can mitigate dynamic and static contributions of interferences. In the end, the navigation information is available again
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Jiang, Zhengyi. "Design, development and testing of an automated system for measuring wall thicknesses in turbine blades with cooling channels." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/design-development-and-testing-of-an-automated-system-for-measuring-wall-thicknesses-in-turbine-blades-with-cooling-channels(895ac153-e310-40e2-87c6-4e40654c9d5d).html.
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Cooling channels are designed in blades to protect the blades from damage at high temperature in a gas turbine. ELE Advanced Technology Ltd. is a UK company specialised in machining cooling channels in turbine blades using electro-chemical techniques. The wall thicknesses between these cooling channels and the surface of the turbine blade influences the performance of cooling channels and are required to be accurately machined and then inspected. At present, the company measures the wall thicknesses using a hand-held contact ultrasonic probe, which is time-consuming and not very accurate. In this project, an inspection machine has been designed and built for the purpose of automating the procedure of measuring wall thicknesses in turbine blades. The inspection machine measures wall thicknesses based on immersion ultrasonic testing technique and the actuator is a six-axis industrial robot controlled by a computer. Control algorithms have been developed to automate the entire measuring process. Acquired ultrasonic data is also automatically processed using Matlab scripts for wall thickness evaluation. However, prior to the ultrasonic measurement, the probe path has to be calculated. Matlab script has been developed to automatically calculate a probe path using a point cloud of the blade digitized on a CMM as an input. The calculation of the probe path, in general, involves triangulation, parameterisation and B-spline surface approximation. Normal 3D triangulation methods were tested; nevertheless, the results were unsatisfactory. Therefore, a triangulation algorithm is developed based on B-spline curve and 2D Delaunay triangulation. After the probe path is calculated, a localisation method, based on iterative closest point algorithm, is implemented to transform the probe path from CMM to the inspection machine. Several experiments were designed and conducted to study the capability of the ultrasonic probe. Experimental results confirmed the feasibility of using an immersion ultrasonic probe for measuring the wall thicknesses; however, the experiments revealed several limitations of immersion ultrasonic testing, such as the angle of incidence of ultrasonic waves must be maintained within an angular deviation of ±1° from the surface normal to achieve accurate test results. Wall thicknesses of three turbine blades from one batch were measured on the inspection machine. A CT scan image was used as reference to compare the measured wall thicknesses with results obtained using contact probes. The comparison showed the wall thicknesses measured on the inspection machine were much more accurate than using contact probes.
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Duda, Petr. "Optimalizace polohy propelerové turbíny v kašně." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231499.
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The thesis contains basic information about propeler turbines. It deals with the correct location in the fountain so as to ensure the highest possible performance. Part of the work is devoted to the all-weather resulting blade to blade channels and their impact on the room is filled with diffuser.
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Doussot, François. "Simulation numérique de l'écoulement de charge partielle dans les turbines Francis : analyse de la topologie et de la dynamique des vortex inter-aubes." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI069.
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Les machines hydrauliques sont conçues pour fonctionner essentiellement autour du point de fonctionnement nominal. Cependant, afin notamment d'intégrer les énergies renouvelables sur le réseau, ces machines hydrauliques doivent nécessairement faire preuve de flexibilité. Ainsi, la plage de fonctionnement des turbines Francis cherche à être étendue, notamment pour des fonctionnements à des débits plus faibles. Lorsqu'une turbine Francis fonctionne avec un débit compris entre 30 et 60% du débit nominal, l'écoulement dans la roue est caractérisé par la présence de vortex entre les aubes. Dans ces conditions, des contraintes dynamiques apparaissent dans la roue et peuvent réduire la durée de vie de la machine à cause du phénomène de fatigue mécanique. Cette étude a pour objectif d'améliorer la compréhension de la dynamique de ces phénomènes à travers une approche numérique. Des simulations ont été effectuées avec plusieurs approches de la turbulence : des simulations stationnaires (RANS), des simulations instationnaires avec une approche hybride de la turbulence (SAS) et la Simulation des Grandes Echelles (SGE).Les simulations stationnaires permettent de comprendre les phénomènes à l'origine de la formation de ces vortex. L'analyse présentée dans ce travail montre que les vortex inter-aubes sont générés à cause d'une mauvaise incidence en entrée de la roue ou à cause d'une zone de recirculation sous la roue. Différentes topologies de vortex sont mises en évidence, générées par la compétition de ces deux phénomènes. Le chargement dynamique doit être connu afin d'évaluer précisément la durée de vie d'une roue. Plusieurs points de fonctionnement ont été simulés avec des calculs instationnaires afin de comprendre comment les fluctuations de pression dépendent du point de fonctionnement de la machine. La localisation des fluctuations de pression et les fréquences associées ont été analysées et comparées à des mesures expérimentales effectuées sur un modèle réduit. Les résultats montrent que les simulations SAS permettent de mettre en évidence des mécanismes à basses fréquences de ces écoulements de charge partielle. Cependant, les fluctuations à hautes fréquences sont largement sous-estimées par cette approche. Plus particulièrement, une signature fréquentielle large bande, caractéristique de l'écoulement de charge partielle, n'est pas prédite par ces simulations. La SGE a été utilisée afin d'améliorer la prédiction de ces hautes fréquences et de comprendre l'origine de ces phénomènes instationnaires. Les résultats démontrent la pertinence de l'utilisation de ce type d'approche numérique en mettant en évidence des sources d'instabilités hautes fréquences dans la machine<br>Hydraulic machines are designed to operate in flow conditions close to the best efficiency point. However, to respond to the increasing demand for flexibility mainly due to the integration of renewable energy in the electric grid, the operating range of Francis turbines has to be extended towards smaller discharge levels without restriction. When Francis turbines are operated typically between 30% and 60% of the rated output power, the flow field is characterized by the appearance of inter-blade vortices in the runner. At these off-design operating conditions and due to these phenomena, dynamic stresses level can increase, and potentially lead to fatigue damage of the mechanical structure of the machine. The objective of this study is to present investigations on the dynamic behaviour of the inter-blade vortices and their impact on the runner by using numerical simulations. Computations were performed with different turbulence modelling approaches to assess their relevance and reliability: Reynolds-Averaged Navier-Stokes (RANS), Scale-Adaptive Simulations (SAS) and Large-Eddy Simulations (LES). Steady simulations aimed to better understand the emergence condition of the inter-blade vortices. The analysis showed that vortices can be generated due to poor inlet adaptation at part load, however other vortices can also be due to a local backflow in the runner. The competition between these both phenomena leads to various topologies of the inter-blade vortices. The dynamic loading on the blade has to be known in order to evaluate the lifetime of the runner by mechanical analysis. Different operating conditions have been simulated by unsteady simulations to understand how the pressure fluctuations depend on the operating conditions. The localisation of the pressure fluctuations and their frequency signature have been analysed and compared to experimental measurements performed on a scaled model. The results of SAS simulations show the driving phenomena at a low range of frequencies of the dynamic of part load conditions. However the high frequency fluctuations are underestimated by this approach. Then large eddy simulations are computed to improve the prediction of this high frequency fluctuations. The study of a wide-band frequency signature is particularly detailed in this work
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Khamaj, J. A. J. "An experimental study of heat transfer in the cooling channels of gas turbine rotor blades." Thesis, Swansea University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637783.
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This thesis presents an investigation of experimental research into the effect of rotation on the convective heat transfer mechanism inside the cooling channels of turbine rotor blades. These involved the selection of eleven different channel geometries and these have been designated alphabetically by the letters 'A' through 'K' respectively. These channels involve a collection of basic geometrical duct cross sectional shapes with the incorporation of ribbed surfaces. The leading and trailing edges of the duct are fitted with in-line or staggered ribs aligned at 30° to 45° to the central axis of the duct. The leading and trailing edges are heated using electrical foil heaters bonded underneath copper plates on which a particular rib configuration was machined. The other two sides of the test sections would be deemed adiabatic. The centre lines of the heated leading and trailing edges were fitted with thirteen foil thermocouples. The coolant used was air with the flow direction in the radially outward direction. Test section A was square in cross section with 'in-line' ribs fitted to the leading and trailing edges. The ribs were inclined at 45° to the direction of coolant flow, which was radially outward. Test sections 'B', 'C' and 'D', were used to examine experimentally the effect of the aspect ratio of rectangular-sectioned ducts cross sections. The respective aspect ratios of test channels 'B', 'C' and 'D' were 0.5, 1.0 and 2.0. Each channel was fitted with staggered ribs inclined at 45° to the direction of flow. Test section 'D' was used to examine the effect of a rectangular channel having an angular inclination relative to the plane of rotation. In other words the heated leading and trailing edges of the channel were skewed to simulate the fact that, in a cambered rotor blade, these edges were inclined to the plane of rotation. Relative to the case of in line rotation, test sections 'E' and 'F' were inclined at 30° and 60° (clock wise) to the plane of rotation. Similarly test sections 'G' and 'H' had inclinations of -30° and -60° respectively.
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Farhadi, Rahmat-Abadi K. "An experimental investigation of the combined effect of rotation and internal ribbing on heat transfer in turbine rotor blade cooling channels." Thesis, Swansea University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636955.
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This thesis reports the results of an experimental investigation of the effect of orthogonal rotation and radially outward flow on heat transfer inside circumferentially ribbed circular test sections. These test sections are intended to model the internal cooling passages of gas turbine rotor blades to enable them to run at elevated operating temperature. Four test section geometries were used with active length to bore diameter ratios of 6.5, 9.75, 11.0 and 13.0. Tests were performed on stationary and rotating sections, with through flow Reynolds numbers in the range 15 000 to 30 000. The results are compared to previous measurements on smooth tubes and ribbed tubes with different rib heights and positions. It was found that the heat transfer values on the ribbed test sections were of the order of 2 to 3 times that of the corresponding smooth-walled sections both with and without rotation. The increase (or decrease) of heat transfer coefficients on the trailing or leading surface are due to the cross-stream and centripetal buoyancy-induced flows resulting from rotation. Centripetal buoyancy enhanced heat transfer along both leading and trailing edges. At all the rotation speeds tested it was found that the heat transfer at the leading edge was less than at the trailing edge. The section with a relatively shorter thermal entry length resulted in heat transfer improvement of up to 15%. It was concluded that the improvement in heat transfer by inclusion of ribs was maximised by ensuring that the first rib was far enough downstream of the entry station to prevent the flow from ever becoming fully developed.
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Sampath, Aravind Rohan. "Effect of Rib Turbulators on Heat Transfer Performance in Stationary Ribbed Channels." Cleveland State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=csu1261062722.
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Ibrahim, Hala-Asmina. "Sudan : a nation in turmoil - is eduaction [sic] to blame? ; an analysis of basic schools curriculum /." Saarbrücken, Germany : VDM Verlag Dr. Müller, 2008. http://d-nb.info/98845906X/04.
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Ramirez, Karen. "Can Changes to Tax Policy Have an Impact on a Shrinking Middle Class? : An explorative and comparative case study of changes to tax policy in Sweden and the United States." Thesis, Uppsala universitet, Statsvetenskapliga institutionen, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-385750.
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Klíma, Petr. "Parní turbina rychloběžná kondenzační." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231803.
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ith one controlled extraction and one uncontrolled extraction, calculation of the flow channel at all stage, design and calculation of the regulation valve and create connection diagram of steam turbine and air cooled condenser. At the beginning of this work is an overview of manufacturers of steam turbines and their unified products. Master thesis was developer with G-Team, a.s. as using calculations and the instructions given in the recommended literature with supporting CFD simulations to determine the loss coefficients and FEA simulations to determine the eigenfrequencies blades.
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Li, Yi-Chen, and 李宜宸. "NUMERICAL STUDIES ON OBSTRUCTED CHANNEL FLOWS RELEVANT TO TURBINE BLADE COOLING AND INTRACRANIAL ANEURYSM THERAPY." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/49030848180677155618.
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Yin-HaoTseng and 曾胤豪. "Application of Lattice Boltzmann Method to Convective Heat Transfer in the channel with an Oscillating Blade." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/82892602121745026292.
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碩士<br>國立成功大學<br>航空太空工程學系碩博士班<br>100<br>In this study, the lattice Boltzmann method is applied to simulate the effect of flow field and convection heat transfer of the heating cylinder in the channel with an oscillating blade. The effect of blade parameters and the Reynolds number of inlet flow to convective heat transfer is studied.
The inlet velocity is assigned appropriately to ensure a reasonable adaptation of fluid field and to avoid un-physical compressible effect. The results of numerical simulation demonstrate that the oscillating blade induces a force oscillation to the flow and thermal fields in the channel flow, such that the heat transfer rate could be enhanced for the heating cylinder.
Five blade design parameters with respect to heating cylinder is considered, namely, the swing angle, the blade aspect ratio, the distance and relative location to heating cylinder and operation frequency. Results show that a larger swing angle, blade aspect ratio and swing frequency will lead to a better the enhancement of convective heat transfer. However, a good choice of distance and location of the blade can only be determined according to the inlet flow Reynolds number and the selected blade parameters.
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Chu, Hung-Chieh 1979. "Numerical Simulation of Flow and Heat Transfer in Internal Multi-Pass Cooling Channel within Gas Turbine Blade." Thesis, 2012. http://hdl.handle.net/1969.1/148242.
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Results from numerical simulation were performed to study flow and heat transfer in two types of rotating multi-pass cooling channels. Second moment closure model was used to solve flow in domain generated from Chimera method.
The first type was a four-pass channel with two different inlet settings. The main flowing channel was rectangular channel (AR=2:1) with hydraulic diameter (Dh ) equals to 2/3 inch (16.9 mm). The first and fourth channel were set as different aspect ratio (AR=2:1; AR=1:1). Reynolds number (Re) used in this part was 10,000. The rotating angle was set as 90 degrees. The density ratio was set as 0.115. The rotation number varied from 0.0 to 0.22. It was showed that inlet effect only caused influence to flow and heat transfer in first two passages.
The second type was a four-pass channel with/without addition of vane in smooth turn portion. The main flowing channel was rectangular channel (AR=2:1) with hydraulic diameter (Dh) equals to 2/3 inch. The first and fourth passages were set to be square duct (AR=1:1). The Reynolds number (Re) used in this part was 20,000. Three rotation numbers were set here (Ro=0.0; Ro=0.2; Ro=0.4). The density ratio and rotating angle varied from 0.12 to 0.32 and from 45 degrees to 90 degrees respectively. According to numerical results, it was revealed that the addition of vane in smooth turn portion did not cause influence to part before it. However, it caused significant influence to flow and heat transfer in smooth turn portion and part after it.
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Lei, Jiang 1980. "Heat Transfer in Rectangular Channels (AR=2:1) of the Gas Turbine Blade at High Rotation Numbers." Thesis, 2011. http://hdl.handle.net/1969.1/150950.
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Gas turbine blade/vane cooling is obtained by circulating the high pressure air from compressor to the internal cooling passage of the blade/vane. Heat transfer and cooling effect in the rotating blade is highly affected by rotation. The typical rotation number for the aircraft engine is in the range of 0~0.25 and for the land based power generation turbine in the range of 0~05. Currently, the heat transfer data at high rotation numbers are limited. Besides, the investigation of heat transfer phenomena in the turn region, especially near hub portion is rare. This dissertation is to study the heat transfer in rectangular channels with turns in the tip or the hub portion respectively at high rotation numbers close to the engine condition.
The dissertation experimentally investigates the heat transfer phenomena in a two-pass rectangular channel (AR=W/H=2:1) with a 180 degree sharp turn in the tip portion. The flow in the first passage is radial outward and after the turn in the second passage, the flow direction is radial inward. The hydraulic diameter (Dh) of the channel is 16.9 mm. Parallel square ribs with an attack angle (alpha) of 45 degrees are used on leading and trailing surfaces to enhance the heat transfer. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.094. For the baseline smooth case and the case with rib pitch-to-height ratio (P/e) 10, channel orientation angles (beta) of 90 degrees and 135 degrees were tried to model the cooling passage in the mid and rear portion of the blade respectively. Two other P/e ratios of 5 and 7.5 were studied at beta=135 degrees to investigate their effect on heat transfer. The data are presented under high rotation numbers and buoyancy parameters by varying the Reynolds number (Re=10,000~40,000) and rotation speed (rpm=0~400). Corresponding rotation number and buoyancy parameter are ranged as 0~0.45 and 0~0.8 respectively.
The dissertation also studies the heat transfer in a two-pass channel (AR=2:1) connected by a 180 degree U bend in the hub portion. The flow in the first passage is radial inward and after the U bend, the flow in the second passage is radial outward. The cross-section dimension of this channel is the same as the previous one. To increase heat transfer, staggered square ribs (e/Dh=0.094) are pasted on leading and trailing walls with an attack angle (alpha) of 45 degrees and pitch-to-height ratio (P/e) of 8. A turning vane in the shape of half circle (R=18.5 mm, t=1.6 mm) is used in the turn region to guide the flow for both smooth and ribbed cases. Channel orientation angles (beta) of 90 degrees and 135 degrees were taken for both smooth and ribbed cases. The heat transfer data were taken at high rotation numbers close to previous test section.
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Chih, Sung Kuei, and 宋奎志. "Heat Transfer in Rectangle Channels with Bleeds Cooling Applications to Static Turbine Blade." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/94718260598407395469.
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碩士<br>國立高雄海洋科技大學<br>輪機工程研究所<br>95<br>An infrared imaging system is used to measure detailed contours of local heat transfer coefficient from twenty narrow rectangular channels with two opposite walls roughened by 450 staggered ribs with and without bleeds. Nusselt number（Nu） contours over the ribbed surfaces are presented for five sets of channels with an identical rib-floor configuration but different channel heights where the complex Nu distributions without bleed and then with bleeds from the scanned rib floor or from the ribbed wall opposite to the scanned rib floor or from the smooth sidewall are analyzed to examine the synergetic effects of variable channel heights and different bleed conditions on heat transfer. Spatially averaged heat transfer results for the entire set of test channels are generated with the thermal performance factors compared to establish the heat transfer correlations with applications to the design of coolant channels in a gas turbine blade.
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Teng, Chih-Hung, and 鄧志宏. "Comparison of turbulence models in simulating flow channel of gas turbine blades." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/y25vv4.
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碩士<br>國立臺灣海洋大學<br>輪機工程學系<br>104<br>Gas Turbines are widely used for airplane propulsion, land-base power generation and other industrial applications, such as trains, marines, cars, etc. To satisfy the fast development of advanced gas turbines, the operating temperature must be increased to improve the thermal efficiency and output work of the gas turbine engine. However, the heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is continuously increased. Thus, it is very important to cool the turbine blades for a long durability and safe operation. Cooling the blade must cool the critical region that exposed to the hot gas, such as blade tip, passage, suction and pressure side
of the blade surface.
This paper use the software of several common and typical model in ANSYS® Fluent turbulence model, simulate and calculate the complex flow phenomena movement between the blade and vane, which take the general size of blade, and the temperature and pressure of inlet gas set 1673◦K and 1.5 atm for conducting the turbulence model. According to the results of the pressure and temperature field calculations, summarize, analyze and compare, description of each the model results.
The results show, ANSYS® Fluent turbulence model can be divided into steady and unsteady models, and each model in the result of the calculation of the same blade geometry, although the same roughly, but on the critical region, such as blade tip, the surface of pressure side , the tail of suction side, etc., and still display a real operation state, show the similar temperature trends and pressure filed that can be referenced for blade design.
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Huh, Michael. "Heat Transfer in Smooth and Ribbed Rectangular Two-Pass Channels with a Developing Flow Entrance at High Rotation Numbers." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-08-831.
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Cooling channels with a developing flow entrance condition and aspect ratios of
1:4 and 2:1 were studied. The range of the rotation number and buoyancy parameter for
the selected AR channels was extended. The maximum Ro and Bo for the 1:4 channel
was 0.67 and 1.9, respectively. For the 2:1 channel, these values were 0.45 and 0.85,
respectively.
The effect of rib spacing and rib height on heat transfer in the 1:4 channel is
investigated. Three rib spacing configurations were considered: P/e=2.5, 5, 10 with a
constant e/Dh ratio of 0.078. To investigate the effect of rib height, a rib configuration
with an e/Dh ratio of 0.156 and P/e ratio of 10 was considered. For the 2:1 channel, a
smooth channel surface condition was studied. For each channel aspect ratio and surface
condition, five Reynolds numbers were studied up to 40K. At each Re, five rotational
speeds are considered up to 400 rpm.
The results of this research work indicate that rotation can cause a significant
increase in heat transfer on the first pass trailing surface of both aspect ratio channels. The leading surface in ribbed channels has shown a dramatic decrease in heat transfer
with rotation in the first pass. Reductions in heat transfer by as much as 50% were
observed. In the second pass, the leading and trailing surfaces with ribs showed very
similar effects of rotation. Also, the effect of rotation seems to vary with the rib spacing.
The strength of rotation showed to be greater in the tight rib spacing of P/e=2.5. The rib
height in the 1:4 channel had minimal impact due to the large distance between the
leading and trailing surfaces. The tip cap heat transfer for both channels showed large
increases with rotation. This is very beneficial since tip cooling is an important part of
maintaining the life a turbine blade. Finally, the buoyancy parameter proved to be very
useful in predicting heat transfer in rotating conditions. The correlations developed
showed very acceptable accuracy when compared to the experimental data.
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Okafor, Chioma U. "BIOTIC RESPONSE TO PALEOCEANOGRAPHIC CHANGES IN THE MIDDLE EOCENE OF BLAKE NOSE, WESTERN NORTH ATLANTIC." Thesis, 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-05-420.
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Geochemical proxy records of sea surface environmental conditions at Blake Nose indicate short-term high amplitude variations. In order to investigate the response of calcareous nannoplankton to these short-term sea-surface environmental changes, we developed a high-resolution Eocene planktonic foraminifera Mg/Ca record and calcareous nannofossil absolute abundance record for ODP Site 1052 spanning the late middle Eocene (37.85 to 37.45 Ma). These data enable direct comparison of the absolute nannofossil abundance data to geochemical paleoenvironmental proxies (Mg/Ca, ?18O and ?13C) to determine the phytoplankton response to paleoenvironmental change and whether temperature or nutrient levels exerted primary control. The nannofossil absolute abundances were estimated using a combination of the random settling technique (RST) and spiking method (SM), which are two independent methods. Both methods yielded similar and reproducible results. The calculated Mg/Ca paleotemperature record indicates a decrease in SSTs from ~33 to 28�C, while the ?18Osw values calculated from the Mg/Ca paleotemperature also decreased from ~3? at 37.83 Ma to ~2? at 37.6 Ma. The combined trends of the SST and ?18Osw suggest that continental ice did not have a major influence on the climate during the study interval. Variations in the Gulf Stream (e.g. track of proto-Gulf stream, number and transit of eddies, and Gulf Stream related upwelling), may have contributed to the reconstructed sea surface hydrographical changes at Blake Nose. However, overall weakening of the hydrological cycle as global climate transitioned from a greenhouse to an icehouse could be the major factor controlling the hydrographical changes at Blake Nose. Approximately 48 nannofossil taxa were identified in this study. These taxa have been grouped into major, minor and rare taxa based on their abundance in any given sample. Results of the statistical analyses (canonical correspondence analysis CCA, Cluster analysis, and correspondence analysis CA) used to relate the nannofossil abundance to environmental parameters did not show expected relationships between the nannofossil absolute abundance and environmental parameters. There are several explanations for this which includes dominance of biotic control over abiotic control, difference in depth habitats between the planktonic foraminifera used for the geochemical proxies and the calcareous nannoplankton, and changing combinations of environmental controls operating during the ~400 ky interval. This suggests that these factors should be taken into account when making conclusions about nannofossil environmental preferences.
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Pritchett, John W., and Sabodh K. Garg. "EFFECT OF CHANGES IN SEAFLOOR TEMPERATURE AND SEA-LEVEL ON GAS HYDRATE STABILITY." 2008. http://hdl.handle.net/2429/1033.
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We have developed a one-dimensional numerical computer model (simulator) to describe methane hydrate formation, decomposition, reformation, and distribution with depth below the seafloor in the marine environment. The simulator was used to model hydrate distributions at Blake Ridge (Site 997) and Hydrate Ridge (Site 1249). The numerical models for the two sites were conditioned by matching the sulfate, chlorinity, and hydrate distribution measurements. The constrained models were then used to investigate the effect of changes in seafloor temperature and sea-level on gas hydrate stability. For Blake Ridge (site 997), changes in hydrate concentration are small. Both the changes in seafloor temperature and sea-level lead to a substantial increase in gas venting at the seafloor for Hydrate Ridge (site 1249).