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Research Papers: Flows in Complex Systems

Investigation of the Flow Field on a Transonic Turbine Nozzle Guide Vane With Rim Seal Cavity Flow Ejection

[+] Author and Article Information
M. Pau

Department of Turbomachinery and Propulsion, von Karman Institute for Fluid Dynamics, B-1640 Rhode-Saint-Genèse, Belgiummarcopau@mail.com

G. Paniagua

Department of Turbomachinery and Propulsion, von Karman Institute for Fluid Dynamics, B-1640 Rhode-Saint-Genèse, Belgium

J. Fluids Eng 132(11), 111101 (Nov 18, 2010) (9 pages) doi:10.1115/1.4002887 History: Received March 25, 2009; Revised August 26, 2010; Published November 18, 2010; Online November 18, 2010

Ensuring an adequate life of high pressure turbines requires efficient cooling methods such as rim seal flow ejection from the stator-rotor wheel space cavity interface, which prevents hot gas ingress into the rotor disk. The present paper addresses the potential to improve the efficiency in transonic turbines at certain rim seal ejection rates. To understand this process, a numerical study was carried out, combining computational fluid dynamic (CFD) simulations and experiments on a single stage axial test turbine. The three dimensional steady CFD analysis was performed, modeling the purge cavity flow ejected downstream of the stator blade row at three flow regimes: subsonic M2=0.73, transonic M2=1.12, and supersonic M2=1.33. Experimental static pressure measurements were used to calibrate the computational model. The main flow field-purge flow interaction is found to be governed by the vane shock structures at the stator hub. The interaction between the vane shocks at the hub and the purge flow has been studied and quantitatively characterized as a function of the purge ejection rate. The ejection of 1% of the core flow from the rim seal cavity leads to an increase in the hub static pressure of approximately 7% at the vane trailing edge. This local reduction of the stator exit Mach number decreases the trailing edge losses in the transonic regime. Finally, a numerically predicted loss breakdown is presented, focusing on the relative importance of the trailing edge losses, boundary layer losses, shock losses, and mixing losses, as a function of the purge rate ejected. Contrary to the experience in subsonic turbines, results in a transonic model demonstrate that ejecting purge flow improves the vane efficiency due to the shock structure modification downstream of the stator.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Coolant flow path through the turbine

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Figure 2

Mesh and computational domain

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Figure 3

Static pressure of 3.5% Cax downstream of the vane trailing edge, transonic regime: (top) at the hub endwall (measured data has an uncertainty band of ±0.01×P01, with a confidence level of 95%) and (bottom) at the casing endwall

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Figure 4

Computed radial velocity contour at the hub endwall and on the cavity slot, transonic regime. The comparison with experimental data measured in Ref. 4.

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Figure 5

Computed and measured (23) pitchwise averaged spanwise Mach number distribution

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Figure 6

Computed Mach number contour plot on blade to blade planes: (a) transonic case and (b) supersonic case

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Figure 7

Computed Mach number contour and isosurface on a plane perpendicular to the axis (3.5% Cax downstream of the trailing edge): (a) transonic case and (b) supersonic case

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Figure 8

Computed vane loading at the rear suction surface from numerical simulations: (a) boundary layer shape factor and momentum thickness evolution, (b) transonic case, and (c) supersonic case. The three plots share the same x-axis.

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Figure 9

Loss coefficient contours at an axial plane 4.5% Cax downstream of the vane trailing edge: (a) subsonic, (b) transonic, and (c) supersonic regimes

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