Rozprawy doktorskie na temat „ENGINE LEAKAGE”

An existing Navier-Stokes code (MEFP) was used to calculate developing flow and heat transfer in turbine tip gaps. Successful calculations of the heat transfer to a model turbine blade tip were obtained with a Prandtl mixing length turbulence model. The calculations revealed details of the flow development including recirculation and reattachment on the blade tip surface. The calculated heat transfer distributions were in good agreement with experimental data. A combined solution of the energy equation in the tip gap flow and in the rotor blade tip gave tip temperature distributions. An independent computational study, using the same numerics as MEFP but a separate new computer program, was also performed to investigate the numerical accuracy of heat transfer calculations for fully developed flow. A literature survey of gas turbine blade materials and factors influencing turbine tip blade life was performed. Approximate temperature ranges for the significant blade life reduction mechanisms, hot corrosion, oxidation, and melting were determined. calculations for typical jet engine conditions, In the present a maximum tip temperature of 1488 K was predicted which would lead to high oxidation rates for present day turbine blade alloys.
M.S.

The effects of serrated trailing edge designs, designed for noise reduction, on the flow-field downstream of an idealized aircraft engine fan blade row were investigated in detail. The measurements were performed in the Virginia Tech low speed linear cascade tunnel on one set of baseline GE-Rotor-B blades and four sets of GE-Rotor-B blades with serrated trailing edges. The four serrated blade sets consisted of two different serration sizes (1.27 cm and 2.54 cm) and for each different serration size a second set of blades with added trailing edge camber. The cascade row consisted of 8 GE-Rotor-B blades and 7-passages with adjustable tip gap settings. It had an inlet angle of 65.1º, stagger angle of 56.9º and a turning angle of 11.8º. The tunnel was operated with a tip gap setting of 1.65% chord, with a Reynolds number based on the chord of 390,000. Blade loading measurements performed on each set of blades showed that it was slightly dependent on the serration shape. As the serration size was increased the blade loading decreased, but adding droop increased the blade loading. The Pitot-static cross-sections showed that flow-fields near the upper and lower endwalls cascade tunnel were similar with the baseline or the serrated blade downstream of the blade row. In the wake region, the individual trailing edge serrations tips and valleys could be seen. As the wake convected downstream, the individual tips and valleys became less visible and the wake was more uniform in profile. The tip leakage vortex was only minimally affected by the trailing edge serrations. This conclusion was further reinforced by the three-component hot-wire cross-sectional measurements that were performed from the lower endwall to the mid-span of the blade. These showed that the mean streamwise velocity, turbulence kinetic energy and turbulence kinetic energy production in the tip leakage region were nearly the same for all four serrated blades as well as the baseline. The vorticity in this region was a more dependent on the serration shape and as a result increased with serration size compared to the baseline. Mid-span measurements performed with the three-component hot-wire showed the spreading rate of the wake and the decay rate of the wake centerline velocity deficit increased with serration size compared to the baseline case. Drooping of the trailing edge only minimally improved the spreading and decay rates. This improvement in these rates was predicted to reduce the tonal noise at the leading edge of the downstream stator vane because the periodic fluctuation associated with the sweeping of the rotor blade wakes across it, was due to the pitchwise variation in the mean streamwise velocity. The wakes were further compared to the mean velocity and turbulence profiles of plane wakes, which the baseline and the smallest serration size agreed the best. As the serration size was increased and drooping was added, the wakes became less like plane wakes. Spectral plots at the wake centerline in all three velocity directions showed some evidence of coherent motion in the wake as a result of vortex shedding.
Master of Science

The tips of unshrouded, high-pressure turbine blades are prone to significantly high heat loads. The gap between the tip and over-tip casing is the root cause of undesirable over-tip leakage flow that is directly responsible for high thermal material degradation and is a major source of aerodynamic loss within a turbine. Both must be minimised for the safe working and improved performance of future gas-turbines. A joint experimental and numerical study is presented to understand and characterise the heat transfer and aerodynamics of unshrouded blade tips. The investigation is undertaken with the use of a squealer or cavity tip design, known for offering the best overall compromise between the tip aerodynamics, heat transfer and mechanical stress. Since there is a lack of understanding of these tips at engine-realistic conditions, the present study comprises of a detailed analysis using a high-speed linear cascade and computational simulations. The aero-thermal performance is studied to provide a better insight into the behaviour of squealer tips, the effects of casing movement and tip cooling. The linear cascade environment has proved beneficial for its offering of spatially-resolved data maps and its ability to validate computational results. Due to the unknown tip gap height within an entire engine cycle, the effects of gap height are assessed. The squealer's aero-thermal performance has been shown to be linked with the gap height, and qualitative different trends in heat transfer are established between low-speed and high-speed tip flow regimes. To the author's knowledge, the present work is the first of its kind, providing comprehensive aero-thermal experimental research and a dataset for a squealer tip at engine-representative transonic conditions. It is also unique in terms of conducting direct and systematic validations of a major industrial computational fluid dynamics method for aero-thermal performance prediction of squealer tips at enginerepresentative transonic conditions. Finally, after recognising the highest heat loads are found on the squealer rims, a novel shaped squealer tip has been investigated to help improve the thermal performance of the squealer with a goal to improve its durability. It has been discovered that a seven percent reduction in tip temperature can be achieved through incorporating a shaped squealer and maximising the internal cooling performance.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1995.
Includes bibliographical references (p. [229]-231).
The design of a modular regenerator concept (patented by Wilson and MIT) for gas-turbine engines is investigated. Mechanical design analysis and theoretical performance calculations were made to show the concept's functionality and performance benefits over current regenerator designs. The modular regenerator concept consists of a ceramic-honeycomb matrix discretized into rectangular blocks, called modules. The modules are exposed to hot (turbine exhaust) and cold (compressor outlet) streams, then are periodically transported through linear passages from one stream to the other. Separating the matrix into modules reduces the transverse sealing lengths substantially. Furthermore, the range of gas-turbine applications increases with the modular concept since larger matrix face areas are possible. Module design is investigated which includes using current research results pertaining to manufacturing technology for rotary regenerators. Mechanical design analysis was made to investigate the possible module-movement schemes. Several regenerator configurations and orientations are introduced. One particular concept balances the pressure forces such that the power requirement for module movement is reduced substantially. Design drawings of a possible modular prototype showing the general configuration and mechanical layout accompany the analysis. A method for determining the regenerator size and measuring its fluid-mechanical and heat-transfer performance is given. An optimization study is made by analyzing the effects when several chosen design parameters are varied. Numerical results of a modular concept for a small gas-turbine engine (120 kW) are given. Seal leakage calculations were made for two modular concepts and compared to the leakage rates for two rotary concepts. The total seal-leakage rates for both modular cases were considerably less than the rotary concepts and can be reduced to well under one percent. In addition, techniques for further leakage reduction are given. Other design issues (to further prove the modular concept's feasibility) not covered in this study have been identified. Guidelines for investigating these issues are given.
by James Anthony Kluka.
S.M.

Scania CV AB is a leading company within development and production of buses, trucks as well as industrial and marine engines. New environmental and safety legislations continuously demand higher quality from the products. An upcoming European legislation, Euro 6, implies that gas leakages from truck engines should be detected while driving. If the source of the leakage is not only detected, but also isolated, that is separated from other faults, the adjustments in the workshop goes faster since there is no need for leakage localisation. A faster reparation increases the up-time, i.e. the amount of time that the truck can be used. This master thesis work uses current methods developed at Scania for residual generation to perform model-based leakage diagnosis. In this work, measurements are gathered for dierent sensor faults and two leakages. The measurements are used to evaluate the actual performance of the resulting diagnosis system. The result, based on the residuals generated by the method, shows that leakages on the boost-side and the exhaust-side can be detected, and isolated from faults in the pressure sensors on the boost-side and the exhaust-side. The isolation of these four faults is considered the hardest to achieve among sensor faults and leakages why the full isolation performance is promising. Further measurements are needed to determine the full isolation performance of the diagnosis system. The resulting system is reasoned to be suitable for execution in real time on-board the truck.
Scania CV AB är en ledande koncern inom utveckling och produktion av bussar, lastbilar samt industri- och marinmotorer. Nya lagkrav för miljö och säkerhet ställer ständigt högre krav på de tillverkade produkterna. Ett nära förestående lagkrav för lastbilar, Euro 6, innebär att gasläckage från motorn ska detekteras under körning. Om läckaget förutom att detekteras också kan isoleras, det vill säga särskiljas från andra fel, går reparationen i verkstaden snabbare då man slipper lokalisera läckaget. En snabbare reparation ökar up-time, det vill säga tiden som lastbilen kan användas på åkeriet. I detta exjobb används befintliga metoder för residualgenerering framtagna på Scania för att åstadkomma modelbaserad läckagediagnos. Arbetet tar även fram mätdata för olika givarfel samt för två läckage i motorn. Denna mätdata används för att utvärdera det erhållna diagnossystemets faktiska prestanda. Resultatet, som bygger på residualerna som metoden genererat, visar att läckage går att detektera, och att läckagen går att isolera från fel på tryckgivarsensorer på laddluftssidan och avgassidan. Denna isolering anses vara den svåraste att uppnå av alla sensorfel samt läckage varvid övrig isoleringsprestande verkar lovande. Däremot behövs mer mätdata för att säkert kunna fastställa övrig isoleringsprestanda. Diagnosmetoden lämpar sig troligen för exekvering i realtid ombord på lastbilen.

To prevent melting of turbine blades, numerous cooling schemes have been developed to cool the blades using cooler air from the compressor. Unfortunately, the clearance gap between adjacent hub sections allows coolant to leak into the hub region. Coolant flow also leaks into the hub region through gaps between individual stages. The results of a combined experimental and computational study of cooling along the hub of a first stage turbine blade caused by leakage flows are discussed in detail. Additionally, this study examines a novel cooling feature, called a microcircuit, which combines internal convective cooling with external film cooling. For the experimental investigation, scaled up blades were tested in a low speed wind tunnel. Adiabatic effectiveness measurements were made with infrared thermography of the entire hub region for a range of leakage flow conditions. For the computations, a commercially available computational fluid dynamics (CFD) code, FLUENT 6.0, was used to simulate the various flows. Results show that featherseal leakage flows provide small cooling benefits to the hub. Increases in featherseal flow provide no additional cooling to the hub region. Unlike the featherseal, leakage flows from the front rim provide ample cooling to the hub region, especially the leading edge of the blade passage. None of the leakage flows provide significant cooling to the pressure side region of the hub or trailing edge suction side. With the addition of the hub microcircuits, there is improved hub cooling of the suction side of the blades. Though the coolant exit uniformity was low and affected by the featherseal flow, the microcircuits were shown to provide more cooling along the hub region. Good agreements were observed between the computational and experimental results, though computations over-predicted front rim cooling and microcircuit uniformity.
Master of Science

Дисертація на здобуття наукового ступеня кандидата технічних наук зі спеціальності 05.05.17 – гідравлічні машини та гідропневмоагрегати. – Національний технічний університет "Харківський політехнічний інститут". – Харків, 2017. Дисертація присвячена дослідженню вдосконаленої пневмосистеми багаторазового запуску маршового рідинного ракетного двигуна верхнього ступеня ракети-носія. Система запуску, яка містить частину пневмоблока двигуна, здійснює розкручування турбонасосного агрегату за рахунок подачі стисненого гелію на його турбіну. Особливістю системи є використання регулятора тиску гелію із пневмокеруванням. Розроблений й реалізований у практиці проектування новий комплекс дискретно-континуальних математичних моделей для газодинамічного розрахунку цієї пневмосистеми, а також аналізу сил тертя й витоків газу у фторопластових манжетних ущільненнях регуляторів. Запропоновано новий розрахунковий метод дослідження пневмосистеми, що проектується, на динамічну стійкість. Досліджені газодинамічні характеристики металлорукава. Розроблено нову концепцію й впроваджено конструкцію лабораторного стенда, що дозволяє економити гелій при доводочних випробуваннях системи. Виконано розрахунково-експериментальне дослідження пневмосистеми, а його рекомендації зі зміни параметрів регулятора, що знижують коливальність і поліпшують інші динамічні характеристики, впроваджені на двигуні.
The thesis for the scientific degree of the Candidate of Technical Sciences by specialty 05.05.17 – hydraulic machines and hydropneumatic units. – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2017. The dissertation describes research of perfected pneumatic starting system of a main restartable liquid-propellant rocket engine destined for a launch vehicle upper stage. The starting system, which structure includes a part of the engine pneumatic unit, performs turbopump spin-up by supplying compressed helium to its turbine. A feature of the system is application of a pneumatically controlled helium pressure regulator. New complex of discrete-continual mathematical models is developed and implemented in the designing practice for the gas-dynamic analysis of this pneumatic system and analysis of friction forces and gas leaks through fluoroplastic lip-type seals of regulators. New computational method is proposed for the developed system’s dynamic stability research. The gas-dynamic characteristics of a metal hose are researched. New concept of the laboratory stand is developed and implemented to enable helium saving at development tests. Experimental-computational research of the pneumatic system is performed, recommendations of which are introduced into the engine in relation to the regulator parameters reducing oscillations and improving other dynamic characteristics.

Диссертация на соискание ученой степени кандидата технических наук по специальности 05.05.17 – гидравлические машины и гидропневмоагрегаты. – Национальный технический университет "Харьковский политехнический институт". – Харьков, 2017. Диссертация посвящена исследованию усовершенствованной пневмосистемы многократного запуска маршевого жидкостного ракетного двигателя верхней ступени ракеты-носителя с насосной подачей компонентов топлива в камеру сгорания. Система запуска, в состав которой входит часть пневмоблока двигателя, осуществляет раскрутку турбонасосного агрегата за счет подачи сжатого гелия из шаробаллона на турбину. Особенностью системы является использование регулятора давления гелия с пневмоуправлением. Исследованная система обеспечивает пять включений двигателя РД861К при идентичных импульсах давления подачи газа, имеющих прямоугольную вершину и предельно крутые фронты. Разработан и использован в практике проектирования новый комплекс дискретно-континуальных математических моделей для газодинамического расчета этой пневмосистемы, а также анализа сил трения и утечек газа во фторопластовых манжетных уплотнениях регуляторов. В моделях учтены новые эффекты: теплообмен газа со стенками полостей и трубопроводов; инерционность газа при его выпуске из баллона; фактор сжимаемости гелия; нагрев гелия при дросселировании; проникновение уплотняемого давления в зазор между манжетой и стенкой, и ряд других. После чего отклонение расчетных значений давления газа от результатов огневых испытаний составило менее 1% Создана и реализована расчетная методика исследования пневмосистемы на динамическую устойчивость и автоколебания. В методике использованы уточненные результаты гармонической линеаризации для колебаний расхода газа через дроссель и силы трения в манжете, а также новый метод расчета импеданса разветвленной системы трубопроводов. Выведено трансцендентное уравнение для частот и амплитуд свободных нелинейных колебаний системы и предложены методы его решения. Точность определения частот автоколебаний составила 2%. Получены аналитические соотношения для параметров пневмосистемы, обеспечивающие динамическую устойчивость или автоколебания малой амплитуды. Исследованы газодинамические характеристики металлорукава, используемого в дренажной системе лабораторного стенда для исследования и настройки системы. Разработана новая концепция и внедрена конструкция стенда, позволяющая экономить гелий при доводочных испытаниях системы. Выполнено расчетно-экспериментальное исследование системы, а его рекомендации по изменению параметров регулятора, снижающие колебательность и улучшающие другие динамические характеристики, внедрены на двигателе.
The thesis for the scientific degree of the Candidate of Technical Sciences by specialty 05.05.17 – hydraulic machines and hydropneumatic units. – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2017. The dissertation describes research of perfected pneumatic starting system of a main restartable liquid-propellant rocket engine destined for a launch vehicle upper stage. The starting system, which structure includes a part of the engine pneumatic unit, performs turbopump spin-up by supplying compressed helium to its turbine. A feature of the system is application of a pneumatically controlled helium pressure regulator. New complex of discrete-continual mathematical models is developed and implemented in the designing practice for the gas-dynamic analysis of this pneumatic system and analysis of friction forces and gas leaks through fluoroplastic lip-type seals of regulators. New computational method is proposed for the developed system’s dynamic stability research. The gas-dynamic characteristics of a metal hose are researched. New concept of the laboratory stand is developed and implemented to enable helium saving at development tests. Experimental-computational research of the pneumatic system is performed, recommendations of which are introduced into the engine in relation to the regulator parameters reducing oscillations and improving other dynamic characteristics.

碩士
國立中興大學
機械工程學系所
102
The purpose of this research is to investigate the effect of leakage the of rotary engine, establish the model of rotary engine, establish a testing platform to carry out the leakage measurement, analyze the heat transfer and performance of rotary engine. This research analyze the leakage of apex seal and side seal and collect information on seal design by patent analysis. The model of the rotary engine establish and the measured data of leakage will be used for comparison to valid this model. Using the comparison result to calculate clearance of the seal. This research do the rotary engine static testing. First, fix the rotor in different section. Then, addition high pressure air into the combustion chamber and using the pressure sensor measure the change of the pressure. Finally, according to the measure data to evaluate the level of leakage and calculate the clearance of the seal. This research analyze the heat transfer performance of a rotary engine. The whole engine case was divided into 12 parts, and evaluated for each part with the estimated gas temperature. It was found the wall temperature . This research investigate the effect of parameters including altitude, air fuel ratio, spark advance angle, inlet pressure, compression ratio, and sealing.

碩士
國立中興大學
機械工程學系所
103
The research investigates the variation of the seal gap and leakage of Wankel engine. A test platform is built to operate Wankel engine without ignition and analyze the performance index of Wankel engine. In the experiment installation, the pressure sensor is installed in the position of spark plug. The servo motor and the driver motivate Wankel engine. The rotation speed is considered as a variable parameter. The volume of the leakage and the variation of the seal gap can be calculated from the cylinder pressure variation, which is related to rotation angle. In this research, Apex seal is the only circumstance we considered. The experiment is carried in steady state, when the engine rotates with five speed, 400rpm, 800rpm, 1200rpm, 1600rpm and 2000rpm. The result shows that the variation of the seal gap mainly occurs in compression and expansion. When rotation angle is in the top dead center, the seal gap barely changes. The higher the rotation speed is, the smaller the seal gap is and the less performance loss is. Conversely, low rotation speed results in wide seal gap, which leads to severe leakage. The max seal gap is 5.87E-3mm in compression and 4.35E-3mm in expansion when the engine speed is 400mm. When the engine speed is 2000 rpm, the maximum seal gap is 1.29E-3mm mm in compression and 9.38E-4mm in expansion. Only 26.5% seal gap when engine speed is 400rpm. And after comparing with the housing force, the result shows that, when the engine speed is 800rpm, the housing force increases 21.1% in the top dead center, the seal gap decreases 37.7% as compared with 400rpm; when the engine speed is 1200rpm, the housing force increases 31.0% in the top dead center, the seal gap decreases 58.3% as compared with 400rpm; when the engine speed is 1600rpm, the housing force increases 36.7% in the top dead center, the seal gap decreases 79.2% as compared with 400rpm; when the engine speed is 2000rpm, the housing force increases 43.2% in the top dead center, the seal gap decreases 85.4% as compared with 400rpm.

碩士
國立虎尾科技大學
機械與電腦輔助工程系碩士班
107
In this study, the module of the three-dimensional rotor engine is constructed to analyze and discuss its characteristics. Firstly, the three-dimensional fluid module of the triangular rotor engine is constructed, and the research process is planned. The pre-processing mesh is firstly divided, and the fluid analysis program Fluent is used. Analyze. The flow rate, pressure, leakage, etc. of the gas under the three-dimensional module are observed by different types of fluids. Based on the three-dimensional module of the triangular rotor engine, the model and three-dimensional fluid analysis of Liquid Piston's new elliptical rotor engine are used to observe and discuss the flow rate, pressure and leakage of the engine. This study compares the observation of the three-dimensional flow field of the rotor engine with the gas difference, which helps the reference of the three-dimensional flow field research and understands the difference between the two engines to design a better design.

碩士
南台科技大學
機械工程系
100
In this paper, neural networks are employed to construct a gasoline engine fault diagnostic system including engine-state diagnostic system, fault source diagnostic system, air-flow sensor fault diagnostic system, leaking source diagnostic system, crankcase ventilation system leaking-degree diagnostic system and fuel pressure regulator leaking-degree diagnostic system 　　The running engine is detected using engine-state diagnostic system to identify the state first, if the engine state is abnormal, distinguish the fault source by engine fault source diagnosis system. The fault sources include fault air-flow sensor and engine leakage. If it is fault air-flow sensor, air-flow-sensor fault-degree diagnostic system is employed to indentify the fault degree, otherwise use leaking source diagnosis system to identify the leaking source. Leaking sources are divided into leakage of crankcase ventilation system and leakage of fuel pressure regulator. If crankcase ventilation system leaks, detect the leaking degree using crankcase ventilation system leaking degree diagnosis system, otherwise use fuel pressure regulator leaking degree diagnosis system to identify the leaking degree. 　　The experiment results show that the root-mean-square errors of diagnostic results are all less than 0.1%, therefore, the proposed gasoline engine fault diagnostic structure is feasible.

碩士
南台科技大學
機械工程系
96
In this paper, the neural network, the back propagation algorithm and steepest descent method are combined to develop the leakage diagnosis of vacuum pressure of the gasoline engine. The datum of air flow, throttle position, intake manifold pressure and injection time are collected under the normal and leakage conditions. The testing samples are divided into the normal condition, the leakage of crank ventilation and that of fuel pressure regulator. The results indicate that the diagnostic system constructed by the neural network can exactly identify the leakage caused by crank ventilation or fuel pressure regulator. Furthermore, the leakage degree diagnosis systems for crank ventilation and fuel pressure regulator are presented. Secondly, neural networks system is utilized to estimate the normal and leakage conditions of engine, manifold pressure, air mass flow rate into manifold and air mass flow rate into cylinder under the different conditions. The intake manifold temperature, intake manifold pressure, throttle position, engine speed and datum of air flow frequency are collected as dynamic data and use for neural networks tuning. The overall estimation error ratios are less than 1%. In this research, the engine diagnosis system and dynamic data estimator are proposed, and the application of engine leakage diagnosis and dynamic data estimator are also demonstrated.

碩士
國立中興大學
農業機械工程學系
89
Currently, most of engine technicians utilize the compression pressure meter, vacuum gauge and air flow gauge to diagnose the intake valve leaking problem for four-stroke engines. Using these tools are found either not convenient or less accuracy for minor leakage. The electronic oscilloscope, which is generically equipped in modern automotive workshop, was used in this research associated with the manifold absolute pressure sensor (MAP) installed on modern vehicles to observe the vacuum pulse variation in an intake manifold when a intake valve leaking problem occurred in an four-cylinder-four-stroke engine. Based on the findings, one could study the relation between intake valve leakage quantities and waveform’s spikes captured by an electronic oscilloscope. The study, thus, expected to find those intake valve leaking problems by studying their waveform. The results showed that the waveform’s spikes captured by an oscilloscope having linear relation with the quantity of the intake valve leakage. The average value of R2 was calculated to be 0.985. To verify the effect of measuring locations, one way ANOVA analysis was used. Results showed that the F value was less than 3.49 for each location. That is, measuring locations did not affect the leaking measurements significantly. Thus, applying an electronic oscilloscope to detect the leaking problem in intake valves of a four-cylinder-four-stroke engine is possible. In addition, by appropriately arranging electronic oscilloscope’s trigger source, the linking intake valve could be precisely identified.

In today's modern gas turbine engines, the region between the rotor and the stationary shroud has the most extreme fluid-thermal conditions in the entire turbine, and is characterized by a periodically unsteady three-dimensional flow field. Due to the pressure difference across the blade tip, leakage flow enters the gap region from the pressure side and exits from the suction side. Tip leakage flow consists of hot mainstream gas and is highly undesirable since it does not turn, and so does not produce any work. Also, high heat transfer rates in the tip gap region occur as a result of leakage flow due to the formation of very thin boundary layers, which may lead to over-heating of the stationary shrouds. The purpose of the present work is to conduct an unsteady study of the tip leakage flow adjacent to the shroud in real gas turbine engines using an in-house industrial computational fluid dynamics (CFD) code. A turbine stage consisting of the nozzle guide vane (NGV) and rotor was modeled. The effect of tip clearance height, inlet turbulence intensity, inlet total temperature, and rotor angular velocity on the tip leakage aerodynamics will be investigated. To the best of the author's knowledge, time-accurate simulations have not been performed in order to study the effects of flow parameters on tip leakage flow aerodynamics. In addition, the trials of using a commercial CFD package to obtain heat transfer calculations on the shroud will be presented. It was found that the size of the separation bubble on the pressure side of the blade tip is dependent on the inlet total temperature and rotor angular velocity. Also, when the relative height of the separation bubble is large, a small re-circulation zone was found at the suction side of the blade tip. In all cases, flow re-circulation was found near the trailing edge and was due to the combined effect of the shroud relative motion with the secondary cross-flow from the adjacent blade passage

One of the most critical components of gas turbine engines, rotor blade tip and casing, is exposed to high thermal load. It is a significant challenge to the designer to protect the turbine material from this severe situation. Leakage flow over the blade tip is also one of the important issues to improve the turbine performance. To understand the detailed phenomena and natures of the heat transfer on the turbine blade tip and casing in association with the tip leakage flow under actual turbine operating conditions, both steady and unsteady simulations have been conducted. A single stage gas turbine engine was modeled and simulated using commercial CFD solver ANSYS CFX R.11. The modeled turbine stage has 30 vanes and 60 blades with a pressure ratio of 3.2 and a rotational speed of 9500 rpm. The predicted isentropic Mach number and adiabatic wall temperature on the casing showed good agreement with available experimental data under the close operating condition. Through the steady simulations, the typical tip leakage flow structures and heat transfer rate distributions were analyzed. The tip leakage flow separates and recirculates just around the pressure side edge of the blade tip. This coverage of the recirculating flow results in low heat transfer rates on the tip surface. The leakage flow then reattaches on the tip surface beyond the flow separation zone. This flow reattachment has shown enhanced heat transfer rates on the tip. The leakage flow interaction with the reverse cross flow, induced by relative casing motion, is found to have significant effect on the casing heat transfer rate distribution. Critical region of high heat transfer rate on the casing exists near the blade tip leading edge and along the pressure side edge. Whereas near the suction side the heat transfer rates are relatively low due to the coverage of the reverse cross flow. The effects of the tip clearance heights and rotor rotating speeds were also investigated. The region of recirculating flow increases with the increase of clearance heights. The flow incidence changes and the casing relative motion is enhanced with higher rotation speeds. As a result, the high heat transfer rate regions have been changed with these two parameters. Unsteady simulations have been performed to investigate time dependent behaviors of the leakage flow structures and heat transfer on the rotor casing and blade tip. The effects of different time steps, number of sub iteration and number of rotor vane passing were firstly examined. The periodicity of the tip leakage flow and heat transfer rate distribution is observed for each vane passing. The relative change in the position of the vane and the vane trailing edge shock alters the inlet flow conditions of the rotor part. It results in the periodic variations of the leakage flow structures and heat transfer rate distributions. The higher heat transfer rates were observed at the region where the trailing edge shock reached. The maximum amplitude of the pressure fluctuation in the tip region is about 20% of the averaged rotor inlet pressure. The maximum amplitude of the heat transfer rate fluctuation on the blade tip, caused by the unsteady leakage flow variations, reaches up to about 25% of the mean heat transfer rate. The effects of tip clearance heights and rotor speeds have also been analyzed and compared one with respect to others. Same typical patterns of leakage flow structures and heat transfer rate distribution can be obtained in both steady and unsteady simulations. However, steady simulation underpredicted the highest heat transfer rate. Because it couldn't capture the critical local high heat transfer phenomena caused by the unsteady stator-rotor interactions

碩士
逢甲大學
航太與系統工程所
99
The purpose of this study is to simulate the flow field of the combustion chamber with considering the effects of the rotor recess configuration and leakage on the flow field inside the combustion chamber by using computational fluid dynamic software, Fluent. The key parameters of this study include arrangement of rotor recess configuration, aspect ratio of rotor recess, and leakage of apex. Firstly, the optimal recess configuration among different configurations including leading, medium, and trailing deep recesses has been determined and then to be the basic configuration for the study of other key parameters. The simulation results show that the leading deep recess has the best performance for indicated horsepower, indicated mean effect pressure, and specific fuel consumption. Moreover, this study found that there exists an optimal value of the recess aspect ratio. It means that when the value of aspect ratio is greater or smaller than that value, it will cause bad effects on the combustion performance. In addition, this study also has found that leakage of apex has the significant reduction of combustion performance in rotary engine.