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SIMULATION of ISOTHERMAL COMBUSTION in GAS TURBINES By SIMULATION OF ISOTHERMAL COMBUSTION IN GAS TURBINES by Matthew Rice Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Masters of Sciences in Mechanical Engineering Dr. Peter King, Committee Chairman Dr. Clint Dancey, Committee Member Dr. Uri Vandsburger, Committee Member February 12th, 2004 Blacksburg, Virginia Keywords: Turbines, Isothermal, Combustion, High-efficiency, Turbine Simulations Abstract SIMULATION OF ISOTHERMAL COMBUSTION IN GAS TURBINES by Matthew J Rice Committee Chair Dr Peter King Dr ClintDancey Dr Uri Vandsburger Current improvements in gas turbine engine p erformance have arisen primarily due to increases in turbine inlet temp erature and compressor pressure ratios However a maximum p ossible tur bine inlet temp erature exits in the form of the adiabatic combustion temp erature of the fuel In addition thermal limits of turbine blade materials also places an upp er bound on turbine inlet temp eratures Thus the current strategy for improving gas turbine eciency is inherently lim ited Intro duction of a new gas turbine based on an alternativework cycle utilizing isothermal combustion ie combustion within the turbine aords signicant opp ortunities for impro ving engine output andor eciency However implementation of such a scheme presents a number of technological challenges such as holding a ame in highsp eed ow The currect research is aimed at determining whether such a combustion scheme is feasible using computational metho ds The geometry a simple D cascade utilizes surface injection within the stator or rotor b oundary layers including the rotor pressure side recirculation zone a natural ame holder Computa tional metho ds utilized b oth steady and time accurate calculations with transitional owaswell as laminar and turbulentcombustion and sp ecies transp ort It has b een determined that burning within a turbine is p ossible given a variety of injection schemes using typical foil geometries under typical op erating conditions Sp ecically results indicate that combustion is selfigniting and hence selfsustaining given the high temp eratures and pressures within a high pressure tur bine passage Deterioration of aero dynamic p erformance is not pronounced regardless of injection scheme However increased thermal loading in the form of higher adiabatic surface temp eratures or heat transfer is signicantgiven the injection and burning of the fuel within the b oundary layer This increase in thermal loading is however minimized when injection takes place in or near a recirculation zone The eect of injection lo cation on pattern factors indicates that suction side injection minimizes temp erature variation downstream of the injection surface for rotor injection only In addition the most uniform temp erature prole in the ow direction is achieved by injection of fuel and combustion nearest to the source of work extraction Namely injection at the rotor pro duces the most isothermal temp erature distribution Finally a pseudo direct simula tion of an isothermal machine is conducted bycombining simulation data and assumed pro cesses The results indicate that isothermal combustion results in an increase in turbine sp ecic work and eciency over the equivalent Brayton cycle iii Acknowledgements Iwould like to express graditude to my graduate committee Dr Peter King Dr Clint Dancey and Dr Uri Vandsburger for their feedback I also wish to thank Steve Greeneld and Dr Jan Bhn for supplying the computing facilities and computing hardware The Virginia Tech community is also deserving of my gratitude for providing the opp ortunity to continue my education after a previously turbulent graduate scho ol exp erience Much appreciation also go es to those down in the turb olab for their steady presence Finally I wish to express my deep est love for those back home inlittle ole Portland whose supp ort made my success in these last few years p ossible A Published in glorious L T X E Contents INTRODUCTION AND MOTIVATION INTRODUCTION AND HISTORICAL BACKGROUND IDEAL BRAYTON CYCLE IDEAL ISOTHERMAL CYCLE PERFORMANCE COMPARISONS FOR THE ISOTHERMAL AND BRAY TON CYCLES HYBRID BRAYTONISOTHERMAL CYCLE TOPICS OF INQUIRY AND THESIS FORMAT TOPICS OF INQUIRY THESIS FORMAT REVIEW OF THE LITERATURE ISOTHERMAL COMBUSTION COMBUSTION IN HIGH SPEED FLOW APPLICABLE EXPERIMENTAL RESULTS APPLICABLE COMPUTATIONAL RESULTS OBSERVATIONS AND OPPORTUNITIES FOR INQUIRY THERMODYNAMIC MODELING OF THE FLOW INTRODUCTION MASS MOMENTUM ENERGY AND SPECIES CONSERVATION TURBULENCE MODELING CHEMICAL REACTIONS ARRHENIUS KINETICS EDDY DISSIPATION MODEL FLUID PROPERTIES BOUNDARY CONDITIONS TRANSITION MODELING CONSERVED SCALAR APPROACH iv CONTENTS v CONSERVATION EQUATIONS FOR NONPREMIXED COMBUS TION NUMERICAL MODEL APPROACH THE GEOMETRY BOUNDARY CONDITIONS FLUID PROPERTIES REACTION MECHANISM SIMULATIONS SIMULATION PROCEDURE NONREACTING FLOW REACTING FLOW ARRHENIUS KINETICSEDDYDISSIPATION TURBULENT COMBUSTION CONSERVED SCALAR SIMULATIONS STATOR SIMULATIONS RESULTS AND DISCUSSION PRESSURE DISTRIBUTIONS HEAT TRANSFER PATTERN FACTORS ISOTHERMAL COMBUSTION CYCLE ENHANCEMENTS VERALL PRESSURE RATIOS IDENTICAL O NONCONSTANT OVERALL PRESSURE RATIO CONCLUSION SUMMARY RECOMMENDATIONS FOR FUTURE WORK A HYBRID CYCLE PARAMETERS B DIFFUSION VIA THE CHAPMANENSKOG CORR C CYCLE COMPARISONS C CONSTANT OVERALL PRESSURE RATIO C NONCONSTANT PRESSURE RATIO D PATTERN FACTORS E BOUNDARY CONDITIONS vi CONTENTS F SIMULATION DATA F BULK FLOW QUANTITIES F ROTOR INJECTION F STATOR INJECTION F OTHER QUANTITIES OF INTEREST F ROTOR F STATOR F REDUCED INJECTION RATE CASE F INCREASED PRESSURE RATIO CASE List of Figures Lo ckheed Tristar L RollRoyce RB Turb ofan Engine Concord at takeo RollRoyce Olympus Temp erature vs year Thrust to weight vs inlet temp erature Thrust sp ecic fuel consumption vs pro duction year T s diagram for ideal Brayton cycle T s diagram for ideal isothermal cycle vs for Isothermal and Brayton cycle Normalized work vs for Isothermal and Brayton cycle Ts diagram for hybrid isothermalBrayton cycle vs for Hybrid combined and Brayton cycle Normalized work vs for Hybrid combined and Brayton cycle Normalize work and vs for Hybrid and Brayton cycle c Near wall ow regimes Wall b oundary conditions Flame sheet comp ositions Mass fractions vs mixture fraction f j Linear cascade geometry see Table for dimensions as lab eled in paren thesis Stator geometry and grid Rotor geometry and grid Domain b oundary surfaces Total pressure contours noninjection simulation Total temp erature for noninjection simulation FlowMachnumber vii viii LIST OF FIGURES Pathlines indicating pressure side rotor blade separation Contours of y for no injection o y for stator T proles for rotor injection T for stator injection y for midrotor injection H O Ma for midrotor injection y for mid rotor injection C H Conserved scalar f for mid rotor injection adiabatic foil for mid rotor injection adiabatic foil H O Temp erature for mid rotor injection adiabatic foil Pathlines for mid rotor injection PDF adiabatic foil Temp erature contours for laminar leading edge pressure side injection leps adiabatic foil Temp erature contours for eddydissipation trailing edge suction side injec tion nonadiabatic foil Rotor pressure distribution for various injection lo cations laminary com bustion Rotor pressure variation for various injection lo cations Heat transfer q for various injection schemes Crossstream temp erature distibution cord downstream of stator adi abatic noncombustion Temp erature contours.
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