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Effect of the Radial Pressure Gradient on the Secondary Flow Generated in an Annular Turbine Cascade

DOI: 10.1155/2012/509209

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This paper introduces an investigation of the effect of radial pressure gradient on the secondary flow generated in turbine cascades. Laboratory measurements were performed using an annular sector cascade which allowed the investigation using relatively small number of blades. The flow was measured upstream and downstream of the cascade using a calibrated five-hole pressure probe. The three-dimensional Reynolds Averaged Navier Stokes equations were solved to understand flow physics. Turbulence was modeled using eddy-viscosity assumption and the two-equation Shear Stress Transport (SST) k-ω model. The results obtained through this study showed that the secondary flow is significantly affected by the pressure gradient along blade span. The experimental measurements and the numerical calculations predicted passage vortex near blade hub which had larger and stronger values than that predicted near blade tip. The loss distribution revealed that secondary flow loss was concentrated near blade hub. It is recommended that attempts of reducing secondary flow in annular cascade should put emphasis on the passage vortex near the hub. 1. Introduction Large-scale steam and gas turbines are always used in power generation and industrial applications. Therefore, turbine efficiency and performance have major concern. The losses in a turbine can be divided into profile loss, secondary flow loss, and tip clearance loss. The profile loss is caused by the growth of the boundary layer on the blades. Secondary flow loss is generated due to the deflection through blade channel. Tip leakage loss is induced due to pressure difference between blade pressure side and blade suction side when the tip clearance gap exists. There are many factors which influence turbine losses. The pressure gradient, turbulence level, blade geometry, incoming velocity, and inlet boundary layer thickness represent important parameters affecting turbine efficiency. It is practically very difficult to perform detailed flow field measurements in an engine at operating conditions. Understanding the physics that governs the flow and the associated turbine cascade losses has been obtained through wind tunnel experiments. These laboratory tests not only allow detailed flow field measurements but also give the experimenter the possibility to investigate the effect of several parameters separately. Experimental studies using linear turbine cascades introduce the aspect of flow periodicity by arranging a number of blades of constant cross-sections separated by a constant pitch. Linear cascade experiments

References

[1]  L. S. Langston, M. L. Nice, and R. M. Hooper, “Three-dimensional flow within a turbine cascade passage,” Journal of Engineering for Power-Transactions of the ASME, vol. 99, no. 1, pp. 21–28, 1977.
[2]  C. H. Sieverding, “Recent progress in the understanding of basic aspects of secondary flows in turbine blade passages,” Journal of Engineering for Gas Turbines and Power, vol. 107, no. 2, pp. 248–257, 1985.
[3]  L. S. Langston, “Cross flows in a turbine cascade passage,” Journal of Engineering for Power, Transactions of ASME, vol. 102, pp. 866–874, 1980.
[4]  J. Moore and R. Y. Adhye, “Secondary flows and losses downstream of a turbine cascade,” Journal of Engineering for Gas Turbines and Power, vol. 107, no. 4, pp. 961–968, 1985.
[5]  A. Perdichizzi and V. Dossena, “Incidence angle and pitch-chord effects on secondary flows downstream of a turbine cascade,” Journal of Turbomachinery, vol. 115, no. 3, pp. 383–391, 1993.
[6]  A. F. Slitenko and Y.M. Jukov, “Experimental investigation of three-dimensional secondary flow on the endwall of a blade channel in an axial turbine cascade,” in Proceedings of the Turbine Technical Conference & Exposition, Munich, Germany, May 2000.
[7]  M. W. Benner, S. A. Sjolander, and S. H. Moustapha, “Measurements of secondary flows downstream of a turbine cascade at off-design incidence,” in Proceedings of the Turbine Technical Conference & Exposition, Vienna, Austria, June 2004.
[8]  H. El-Batsh and M. Bassily Hanna, “Numerical and experimental prediction of secondary flow through a rectilinear cascade for different aspect ratios,” in Proceedings of the International Mechanical Engineering Conference (IMEC '04), Kuwait, December 2004.
[9]  H. El-Batsh and M. Bassily Hanna, “An investigation on the effect of endwall movement on the tip clearance loss using annular turbine cascade,” International Journal of Rotating Machinery, vol. 2011, Article ID 489150, 11 pages, 2011.
[10]  T. Matsunuma, “Effects of Reynolds number and free-stream turbulence on turbine tip clearance flow,” in Proceedings of the Gas Turbie Technology: Focus for the Future, pp. 389–401, June 2005.
[11]  C. Hirsch, “Advance methods for cascade testing,” Advisory Group for Aerospace Research and Development AGARD-AG-328, 1993.
[12]  D. M. Vogt and T. H. Fransson, “A new turbine cascade for aeromechanical testing,” in Proceedings of the 16th Symposium on Measuring Techniques in Transonic and Supersonic Flow in Cascades and Turbomachines, Cambridgem, UK, September 2002.
[13]  T. Povey, T. V. Jones, and M. L. G. Oldfield, “On a novel annular sector cascade technique,” in Proceedings of the Turbine Technical Conference and Exposition, pp. 1369–1380, June 2004.
[14]  J. L. Gilarranz, A. J. Ranz, J. A. Kopko, and J. M. Sorokes, “On the use five-hole probes in the testing of industrial centrifugal compressors,” Journal of Turbomachinery, vol. 127, no. 1, pp. 91–106, 2005.
[15]  G. Ingram and D. Gregory-Smith, “An automated instrumentation system for flow and loss measurements in a cascade,” Flow Measurement and Instrumentation, vol. 17, no. 1, pp. 23–28, 2006.
[16]  D. C. Wilcox, Turbulence Modeling for CFD, DCW Industries, La Canada, Calif, USA, 1993.
[17]  J. E. Bardina, P. G. Huang, and T. J. Coakley, “Turbulence modeling validation, testing and development,” NASA Technical Memorandum 110446, 1997.
[18]  B. M. Holley, S. Becz, and L. S. Langston, “Measurement and calculation of turbine cascade endwall pressure and shear stress,” Journal of Turbomachinery, vol. 128, no. 2, pp. 232–239, 2006.
[19]  F. R. Menter, “Two-equation eddy-viscosity turbulence models for engineering applications,” AIAA Journal, vol. 32, no. 8, pp. 1598–1605, 1994.
[20]  T. Hildebrandt and L. Fottner, “A numerical study of the influence of grid refinement and turbulence modeling on the flow field inside a highly loaded turbine cascade,” Journal of Turbomachinery, vol. 121, no. 4, pp. 709–716, 1999.
[21]  M. Casey and T. Wintergerste, ERCOFTAC special interest group on quality and trust in industrial CFD, Best Practices Guidelines, 2000.

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