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Research Papers

Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine

[+] Author and Article Information
Thomas Behr

Turbomachinery Laboratory,  ETH Zurich, CH-8092 Zurich, Switzerlandbehr@lsm.iet.mavt.ethz.ch

Anestis I. Kalfas

Department of Mechanical Engineering,  Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece

Reza S. Abhari

Turbomachinery Laboratory,  ETH Zurich, CH-8092 Zurich, Switzerland

J. Turbomach 130(3), 031014 (May 05, 2008) (12 pages) doi:10.1115/1.2777185 History: Received January 26, 2007; Revised March 16, 2007; Published May 05, 2008

This paper presents an experimental investigation of a novel approach for controlling the rotor tip leakage and secondary flow by injecting cooling air from the stationary casing onto the rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the rotor tip region and its impact on the rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly loaded, high pressure gas turbine stage. Measurements conducted with a two-sensor fast-response aerodynamic probe have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the rotor. Cooling air has been injected in the circumferential direction at a 30 deg angle from the casing tangent, opposing the rotor turning direction through a circumferential array of ten equidistant holes per rotor pitch. Different cooling air injection configurations have been tested. Injection parameters such as mass flow, axial position, and size of the holes have been varied to see the effect on the rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the rotor tip leakage vortex and the rotor tip passage vortex reduce. Both vortices move toward the tip suction side corner of the rotor passage. With an appropriate combination of injection mass flow rate and axial injection position, the isentropic efficiency of the stage was improved by 0.55 percentage points.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

“LISA” 1- and −1∕2-stage axial turbine facility

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Figure 2

Air injection system and probe access within traversable rotor casing ring assembly

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Figure 3

Secondary flow model after Sjolander (26)

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Figure 4

Relative total pressure coefficient Cptrel (-) measured at the rotor exit (rotor-relative frame, time averaged)

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Figure 5

rms of nondeterministic pressure variation (Pa) measured at the rotor casing (rotor-relative frame, time averaged)

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Figure 6

rms of nondeterministic pressure variation (Pa) measured at the rotor casing at 104% rotor axial chord versus stator blade passing period (rotor-relative frame)

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Figure 7

Static pressure (Pa) measured at the rotor casing (rotor-relative frame, time averaged)

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Figure 8

Flow visualization on rotor tip surface

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Figure 9

Model of the flow directions at the casing in the rotor-relative frame of reference

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Figure 10

Static pressure distribution measured at the rotor casing (rotor-relative frame, time averaged) at two rotor axial chord positions; (a) 30% and (b) 50%

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Figure 11

Velocity triangle of casing injection

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Figure 12

Rotor-relative frame, time-averaged contours: (a) axial velocity cx (m∕s) measured at the rotor exit, baseline, (b) axial velocity difference Δcx (m∕s) measured at the rotor exit between injection A-1% and base line case

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Figure 13

Rotor-relative frame, time-averaged contours, injection configuration A; (a) turbulence Tu [%] measured at the rotor exit, baseline case, (b) turbulence difference ΔTu (%) measured at the rotor exit between injection A-0.7% and base line case, and (c) turbulence difference ΔTu (%) measured at the rotor exit between injection A-1% and base line case

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Figure 14

Turbulence intensity (%) measured at the rotor exit (pitchwise mass averaged) of baseline case and injection configuration A at injection rates of 0.7% and 1.0%

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Figure 15

Absolute yaw angle (%) measured at the rotor exit (pitchwise mass averaged) of baseline case and injection configuration A at injection rates of 0.7% and 1.0%

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Figure 16

Total pressure coefficient Cpt (-) measured at the rotor exit (pitchwise mass averaged) of baseline case and injection configuration A at injection rates of 0.7% and 1.0%

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Figure 17

Axial velocity cx at 50% span (m∕s) measured at the rotor exit for base line case and two injection mass flows (rotor-relative frame)

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Figure 18

Flow yaw angle at 50% span (deg) measured at the rotor exit for base line case and two injection mass flows (rotor-relative frame)

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Figure 19

Pitchwise averages of base line and three injection configurations at an injection rate of 1.0% turbine mass flow: (a) axial velocity (m∕s) and (b) axial velocity difference from baseline case (m∕s)

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Figure 20

Pitchwise averages of base line and three injection configurations at an injection rate of 1.0% turbine mass flow: (a) flow yaw angle (deg) and (b) flow yaw angle difference from base line case (deg)

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Figure 21

Pitchwise averages of base line and three injection configurations at an injection rate of 1.0% turbine mass flow: (a) turbulence intensity (%) and (b) turbulence intensity difference from base line case (%)

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Figure 22

TKE (J∕kg) (mass averaged) versus injection rate (% of turbine mass flow)

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Figure 23

Change of isentropic efficiency (%) compared to the base line case versus injection rate (% of turbine mass flow)

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