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Cfd analysis of flow charateristics in a gas turbine  a viable approach
 

Cfd analysis of flow charateristics in a gas turbine a viable approach

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    Cfd analysis of flow charateristics in a gas turbine  a viable approach Cfd analysis of flow charateristics in a gas turbine a viable approach Document Transcript

    • INTERNATIONALMechanical Engineering and Technology (IJMET), ISSN 0976 – International Journal of JOURNAL OF MECHANICAL ENGINEERING 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME AND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online)Volume 4, Issue 2, March - April (2013), pp. 39-46 IJMET© IAEME: www.iaeme.com/ijmet.aspJournal Impact Factor (2013): 5.7731 (Calculated by GISI)www.jifactor.com ©IAEME CFD ANALYSIS OF FLOW CHARACTERISTICS IN A GAS TURBINE- A VIABLE APPROACH TO PREDICT THE TURBULANCE a b P.S. Jeyalaxmi , Dr.G.Kalivarathan a Research Scholar, CMJ University, Meghalaya, Shillong. b Principal/ PSN Institute of Technology and Science, Tirunelveli, Tamilnadu, Supervisor, CMJ University, Shillong. ABSTRACT The demands for best performance in gas turbine engines can be obtained by increasing combustion temperatures to increase thermal efficiency. Hot combustion temperatures create a harsh environment which leads to the consideration of the durability of the combustor and turbine sections. Improvements in durability can be achieved through understanding the interactions between the combustor and turbine. The flow field at a combustor exit shows non uniformities in pressure, temperature, and velocity in the pitch and radial directions. This inlet profile to the turbine can have a considerable effect on the development of the secondary flows through the vane passage. Presents a computational study of the flow field generated in a non-reacting gas turbine combustor and how that flow field convects through the downstream stator vane. Specifically, the effect that the combustor flow field had on the secondary flow pattern in the turbine was studied. 1.0 INTRODUCTION The designs of aircraft gas turbine engines have improved and evolved tremendously. The first gas turbine powered aircraft reached top speeds of 435 Kilometers per hour; only sixty years later aircraft powered by gas turbine engines are flying at speeds exceeding 2000 Kilometers per hour. The major contributions to the advances in gas turbine engine performance have been increased in terms of power 39
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEMEoutput, reliability and fuel efficiency. The existing demands for improving higherperformance while maintaining affordability and engine durability can only be reachedthrough the achievement of hot combustion temperatures and better cooling schemes. Theneed for increasingly higher temperatures creates a critical ambiance environment for thefirst stage turbine vane and combustor liner. The difficult ambiance in the engine pushesthe design holds for durability in both the combustor and turbine sections. Sincerely isrequired for the flow field leaving the combustor and its impact on the heat transfer to theturbine vane is also be investigated to the maximum possible extend.2.0 COMBUSTOR MODEL TEST SECTION DESIGN The first stage of both the experimental and computational portions of the presentstudy involved the design of a non-reacting combustor test facility necessary to simulatethe geometry and flow conditions of a realistic gas turbine engine combustor. The specificwork done by the author of this thesis included the initial design of the combustor testsection geometry and the computational simulation of the wind tunnel model. The actualwind tunnel design, including matching engine parameters and the liner panel design, wasprimarily completed. Prior to describing the computational modeling, however, it isimportant to describe the wind tunnel design and model. The computational combustormodel was based directly on the geometry and flow conditions of the experimental windtunnel test section, which was designed to match representative engine combustorconditions. The combustor, which was simulated, is typical of an annular combustor in acommercial gas turbine engine. The geometry is characterized by an impingement filmflow cooling scheme which consists of four panels of film-cooling holes and two rows ofdilution jets on both the inner and outer diameters with additional coolant provided by aslot located at the combustor exit. The combustor has a constant area cross section for thefirst half of its length followed by a contraction leading to the downstream turbine. Thefirst step in the design of the combustor test section was to thoroughly analyze thecombustor engine data provided by industry, and to then determine which engineparameters needed to be matched in the simulation in order to accurately represent thecombustor flow field. The engine data was then scaled up within the size constraints of anexisting facility described in previous studies.3.0 LINER PANEL DESIGN The design of the individual liner panels within the combustor test section was acomplicated task in itself involving several important compromises between the engineand the model. It was desired to create panels that matched as closely as possible both thegeometric details of the combustor as well as the flow parameters of the film cooling,dilution, and slot flows. 40
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME Figure 1. Schematic of the wind tunnel facility with combustor simulator test section in the open loop configuration Figure 2 Schematic of engine combustor geometry with dimensions in cmThe two most important goals in the process were to determine the necessary numbers offilm-cooling holes and the sizes of dilution to properly match the desired mass flow ratedistribution and momentum flux ratios, and then lay out the holes in the liner matching theengine geometry as closely as possible. A third consideration was the ability to adapt the testsection to several geometries; with and without dilution flow, with and without slot flow, andthe possibility of a different liner geometry altogether. 41
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME Table1. Stator Vane Geometry in the Engine and Model Engine Wind Tunnel True Chord 6.45 cm 59.15 cm Pitch/Chord 0.79 0.79 Span /Chord 0.95 0.95 Flow inlet angle 0° 0° Flow exit angle 77° 77° Table 2 Mass Flow Distributions in Combustor Based on Percentage of Exit Mass Flow Engine Wind Tunnel Inlet 37.6% 42.6 Panel 1 (ID/OD) 1.43%/2.55% 1.43%/1.45% Panel 2 (ID/OD) 3.6%/4.65% 3.4%/3.4% Panel 3 (ID/OD) 3.3%/4.55% 3.3%/3.3% Panel 4 (ID/OD) 1.4%/2.65% 1.4%/1.4% Dilution row 1 16.5% 16.5% Dilution row 2 16.5% 16.5% Slot 1.38% 1.38%4.0 GAMBIT MESHING All of the models were meshed using GAMBIT, a program offered with the Fluentsoftware package. The mesh was a critical element of the problem setup since the accuracy ofthe solution will certainly be limited by the quality of the mesh which is used to calculate it.The process of mesh generation was quite involved and required several steps, which will beoutlined in detail in this section. First, the combustor and vane geometry was created usingGambit’s solid modeling capabilities. Then, line and surface mesh spacing layouts wereattached to the geometry. Finally, the internal solid mesh was created from the line andsurface meshes and was refined to reduce cell skewness. The geometry and mesh was thenexported and read into Fluent. The basic geometry may be defined in Gambit in several ways.For the combustor section, volumes were created corresponding to the cooling holes, dilutionholes, and main combustor geometry. Using Boolean operations, these were combined tocreate the complete combustor geometry. In order to create the vane geometry, points weredefined along the contour of the vane and fitted with splines to create the vane surface. 42
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME Figure 3. Schematics of computational domain for combustor model 5.0 case 2 with no vane, no slot and (b) case 5 with vane and slot. Figure 4. Domain, mesh and boundary conditions for single hole Case I. 43
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEMEFigure 5. Velocity profile (U/Uave) at hole inlets for each of the four liner panel axial single hole cases.Figure 6. Velocity profiles (U/U∞, ave) cooling hole diameter downstream of the hole trailing edge for each of the four axial hole panel cases. 44
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME Figure 7. Adiabatic effectiveness comparison for (a) axial and (b) compound angle cooling holes at I = 13.1 and M = 3.6.5.0 CONCLUSION In this investigation it is observed that the RNG k-ε turbulence model used in thecases is viable and it is seen that the RSM model remarkably exhibits the turbulence level andthe dilution jet mixing at the combustor outlet. But still, It is easier to predict the variationsthrough CFD in the mean flow field results, In addition to this the turbulence levels of theapproaching flow may affect the secondary flow field in the vane passage. Because of thesereasons more efforts has to be made towards testing additional turbulence models to accessone more suitable means for predicting this type of swirling, highly turbulent and flowsituation in a generic manner through viable CFD tool. 45
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEMEREFERENCES1. Goebel, S. G., Abauf, N., Lovett, J. A., and Lee, C.-P. (1993) “Measurements of Combustor Velocity and Turbulence Profiles,” ASME Paper No. 93-GT-228.2. Crocker, S. C., Nickolaus, D., and Smith, C. E., (1998) “CFD Modeling of a Gas Turbine Combustor from Compressor Exit to Turbine Inlet,” ASME Paper No. 98-GT-184.Fluent Inc., Fluent User.s Guide, Version 5.0., 1998 (Fluent Inc.: New Hampshire). Fluent Inc., Gambit I Modeling Guide, 1998 (Fluent Inc.: New Hampshire).3. Butler, T. L., Sharma, O. P., Joslyn, H. D., and Dring, R. P. (1989) “Redistribution of and Inlet Temperature Distortion in an Axial Flow Turbine Stage,” AIAA J of Propulsion and Power, Vol. 5, No. 1, pp. 64-71.4. Burd, S. W., Satterness, C. J. and Simon, T. W. (2000) “Effects of Slot Bleed Injection Over a Contoured Endwall on Nozzle Guide Vane Cooling Performance: Part II – Thermal Measurements,” ASME Paper No. 2000-GT-200.5. Burd, S. W. and Simon, T. W. (2000) “Effects of Slot Bleed Injection Over a Contoured Endwall on Nozzle Guide Vane Cooling Performance: Part I – Flow Field Measurements,” ASME Paper No. 2000-GT-199.6. Boyle, R. J. and Giel, P. W. (1997) “Prediction of Nonuniform Inlet Temperature Effects on Vane and Rotor Heat Transfer,” ASME Paper No. 97-GT-133.7. Bicen, A. F., Tse, D. and Whitelaw, J. H. (1988) “Flow and Combustion Characteristics of an Annular Combustor,” Combustion and Flame 72: 175-192.8. LA.Barringer, M.D (2001), “Flow Field Simulations of a Gas Turbine Combustor,” thesis, Mechanical Engineering Department, Virginia Polytechnic Institute and State University, to be completed May 2001.9. Barringer, M.D., Richard, O.T., Stitzel, S.M., Walter, J.P. and Thole, K.A. (2001) “Flow FieldSimulations of a Gas Turbine Combustor,” to be presented at IGTI 2001, New Orleans,10. Anand, M. S., Zhu, J., Connor, C., and Razdan, M. K. (1999) “Combustor Flow Analysis Using and Advanced Finite-Volume Design System,” ASME Paper No. 99-GT-273.11. K. V. Chaudhari , D. B. Kulshreshtha and S. A. Channiwala, “Design and Experimental Investigations of Pressure Swirl Atomizer of Annular Type Combustion Chamber for 20 KW Gas Turbine Engine” International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 3, Issue 2, 2012, pp. 311 - 321, ISSN Print: 0976-6480, ISSN Online: 0976-6499.12. Tarun Singh Tanwar, Dharmendra Hariyani and Manish Dadhich, “Flow Simulation (CFD) & Static Structural Analysis (FEA) of a Radial Turbine” International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 3, 2012, pp. 252 - 269, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.13. Ashok Tukaram Pise and Umesh Vandeorao Awasarmol, “Investigation of Enhancement of Natural Convection Heat Transfer from Engine Cylinder with Permeable Fins” International Journal of Mechanical Engineering & Technology (IJMET), Volume 1, Issue 1, 2010, pp. 238 - 247, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.14. Cherian Paul and Parvathy Venugopal, “Modelling of Interfacial Heat Transfer Coefficient and Experimental Verification for Gravity Die Casting of Aluminium Alloys” International Journal of Mechanical Engineering & Technology (IJMET), Volume 1, Issue 1, 2010, pp. 253 - 274, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.15. A.Saravanapandi Solairajan and Dr.G.Kalivarathan, “Investigation of Heat Transfer Through CNT Composites-Focusing on Conduction Mode” International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 1, 2013, pp. 66 - 73, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 46