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Research Papers

The Effects of Unsteadiness and Compressibility on the Interaction Between Hub Leakage and Mainstream Flows in High-Pressure Turbines

[+] Author and Article Information
Ivan Popović

e-mail: ivan.popovic@cantab.net

Howard P. Hodson

Whittle Laboratory,
University of Cambridge,
Cambridge, UK

Torsten Wolf

Rolls-Royce Deutschland,
Dahlewitz, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received April 29, 2012; final manuscript received January 28, 2013; published online September 13, 2013. Editor: David Wisler.

J. Turbomach 135(6), 061015 (Sep 13, 2013) (10 pages) Paper No: TURBO-12-1038; doi: 10.1115/1.4024636 History: Received April 29, 2012; Revised January 28, 2013

This paper investigates the effects of compressibility and unsteadiness due to the relative blade row motion and their importance in the interaction between hub leakage (purge) and mainstream flows. First, the challenges associated with the blade redesign for low-speed testing are described. The effects of Mach number are then addressed by analyzing the experiments in the low-speed linear cascade equipped with the secondary airflow system and computations performed on the low- and high-speed blade profiles. These results indicate that the compressibility does not significantly affect the interaction between the leakage and mainstream flows despite a number of compromises made during the design of the low-speed blade. This was due to the fact that the leakage–mainstream interaction takes place upstream of the blade throat where the local Mach numbers are still relatively low. The analysis is then extended to the equivalent full-stage unsteady computations. The periodic unsteadiness resulting from the relative motion of the upstream vanes appreciably affected the way in which the leakage flow is injected and the rotor flow field in general. However, the time-average flow field was still found to be dominated by the rotor blade's potential field. For the present test arrangement, the unsteady effects were not very detrimental and caused less than a 10% increase in the losses due to the leakage injection relative to the steady calculations.

Copyright © 2013 by ASME
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References

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Figures

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Fig. 1

HP stage and rim seal configuration

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Fig. 2

Computational mesh for high-speed stage

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Fig. 3

The axial view of test section and predicted velocity profiles downstream of the low-speed blades

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Fig. 4

Predicted isentropic Mach number distributions for the low- and high-speed T120 versions

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Fig. 5

Predicted limiting streamlines on hub end wall

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Fig. 6

Predicted spanwise distributions of energy loss coefficient and yaw angle deviation from profile values

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Fig. 7

Low-speed linear cascade with secondary airflow injector used for experimental validation

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Fig. 8

Measured and predicted isentropic Mach number distributions for the low-speed profile

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Fig. 9

Rim seal aerothermodynamics at LF = 1.0% in terms of streamlines in meridional plane: midpitch plane

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Fig. 10

Measured and predicted sealing effectiveness

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Fig. 11

Predicted isentropic Mach number distributions at 15%Cx upstream of the blade row on the hub

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Fig. 12

Instantaneous leakage fraction out of rim seal for full-stage unsteady calculations at LF = 1.0%

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Fig. 13

Instantaneous sealing effectiveness for full-stage unsteady conditions and corresponding steady values

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Fig. 14

Radial velocity normalized by the blade speed at the seal exit plane and limiting streamlines on hub end wall for full-stage unsteady calculations for LF = 1.0%

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Fig. 15

Penetration depth at blade trailing edge for full-stage unsteady calculations for LF = 1.0%

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Fig. 16

End wall aerodynamics

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Fig. 17

Flood contours of streamwise vorticity superimposed over line contours of total pressure coefficient at plane 50%Cx downstream of rotor blades for LF = 1.0%

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Fig. 18

Mixed-out losses due to leakage injection

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