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Research Papers

Influence of Rim Seal Purge Flow on the Performance of an Endwall-Profiled Axial Turbine

[+] Author and Article Information
P. Schuepbach1

Department of Mechanical and Process Engineering, Laboratory for Energy Conversion (LEC), ETH Zurich, Zurich 8092, Switzerlandschuepbach@lec.mavt.ethz.ch

R. S. Abhari

Department of Mechanical and Process Engineering, Laboratory for Energy Conversion (LEC), ETH Zurich, Zurich 8092, Switzerland

M. G. Rose

Institute of Aeronautical Propulsion, University of Stuttgart, Stuttgart 70569, Germany

J. Gier

 MTU Aero Engines GmbH, Dachauer Strasse 665, München 80995, Germany

1

Corresponding author.

J. Turbomach 133(2), 021011 (Oct 21, 2010) (10 pages) doi:10.1115/1.4000578 History: Received July 20, 2009; Revised July 21, 2009; Published October 21, 2010; Online October 21, 2010

Nonaxisymmetric endwall profiling is a promising method to reduce secondary losses in axial turbines. However, in high-pressure turbines, a small amount of air is ejected at the hub rim seal to prevent the ingestion of hot gases into the cavity between the stator and the rotor disk. This rim seal purge flow has a strong influence on the development of the hub secondary flow structures. This paper presents time-resolved experimental and computational data for a one-and-1/2-stage high work axial turbine, showing the influence of purge flow on the performance of two different nonaxisymmetric endwalls and the axisymmetric baseline case. The experimental total-to-total efficiency assessment reveals that the nonaxisymmetric endwalls lose some of their benefit relative to the baseline case when purge is increased. The first endwall design loses 50% of the efficiency improvement seen with low suction, while the second endwall design exhibits a 34% deterioration. The time-resolved computations show that the rotor dominates the static pressure field at the rim seal exit when purge flow is present. Therefore, the purge flow establishes itself as jets emerging at the blade suction side corner. The jet strength is modulated by the first vane pressure field. The jets introduce circumferential vorticity as they enter the annulus. As the injected fluid is turned around the rotor leading edge, a streamwise vortex component is created. The dominating leakage vortex has the same sense of rotation as the rotor hub passage vortex. The first endwall design causes the strongest circumferential variation in the rim seal exit static pressure field. Therefore, the jets are stronger with this geometry and introduce more vorticity than the other two cases. As a consequence the experimental data at the rotor exit shows the greatest unsteadiness within the rotor hub passage with the first endwall design.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Nonaxisymmetric endwall shapes from the optimization

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Figure 2

Illustration of leakage path

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Figure 3

Meridional grid plane of cavity

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Figure 4

Comparison of the nondimensional relative total pressures for computation and experiment at rotor exit IR=−0.1%

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Figure 5

Comparison of the nondimensional relative total pressures for computation and experiment at rotor exit IR=0.9%

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Figure 6

Calculated relative error of computation Z as a percentage (%)

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Figure 7

Measured efficiency response to injection purge flow for the three endwall geometries

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Figure 8

Time-space diagram of the axially averaged rim seal exit static pressure from computation

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Figure 9

Isosurface of rotary stagnation temperature 319 K baseline geometry with IR=0.9% from computation

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Figure 10

Circumferential vorticity in a meridional plane cutting through the injection jet at time t/T=0 from computation

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Figure 11

Axial vorticity in a circumferential plane at 35% rotor axial chord for the baseline geometry at time t/T=0 from computation

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Figure 12

Q-factor 107 (1/s2) isosurface for baseline geometry at time t/T=0 from computation

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Figure 13

Isosurface of rotary stagnation temperature 319 K with IR=0.9% at t/T=0 from computation

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Figure 14

Q-factor 107 (1/s2) isosurface with purge flow IR=0.9% at time t/T=0 from computation

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Figure 15

Axial vorticity in a circumferential plane at 35% rotor axial chord for IR=0.9% at time t/T=0 from computation

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Figure 16

Measured time-averaged rms of the total pressure random part in the rotor frame of reference at the rotor exit (Pa)

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