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Research Papers

Impact of Time-Resolved Entropy Measurement on a One-and-One-Half-Stage Axial Turbine Performance

[+] Author and Article Information
M. Mansour, N. Chokani, R. S. Abhari

Department of Mechanical and Process Engineering, LSM, Laboratory for Energy Conversion, ETH Zürich, Zurich 8092, Switzerland

A. I. Kalfas1

Department of Mechanical and Process Engineering, LSM, Laboratory for Energy Conversion, ETH Zürich, Zurich 8092, Switzerland

1

Present address: Aristotle University of Thessaloniki, Greece.

J. Turbomach 134(2), 021008 (Jun 23, 2011) (11 pages) doi:10.1115/1.4003247 History: Received April 21, 2009; Revised November 06, 2010; Published June 23, 2011; Online June 23, 2011

An accurate assessment of unsteady interactions in turbines is required, so that this may be taken into account in the design of the turbine. This assessment is required since the efficiency of the turbine is directly related to the contribution of unsteady loss mechanisms. This paper presents unsteady entropy measurements in an axial turbine. The measurements are conducted at the rotor exit of a one–and-one-half-stage unshrouded turbine that is representative of a highly loaded, high-pressure stage of an aero-engine. The unsteady entropy measurements are obtained using a novel miniature fast-response probe, which has been developed at ETH Zurich. The entropy probe has two components: a one-sensor fast-response aerodynamic probe and a pair of thin-film gauges. The probe allows the simultaneous measurement of the total temperature and the total pressure from which the time-resolved entropy field can be derived. The measurements of the time-resolved entropy provide a new insight into the unsteady loss mechanisms that are associated with the unsteady interaction between rotor and stator blade rows. A particular attention is paid to the interaction effects of the stator wake interaction, the secondary flow interaction, and the potential field interaction on the unsteady loss generation at the rotor exit. Furthermore, the impact on the turbine design of quantifying the loss in terms of the entropy loss coefficient, rather than the more familiar pressure loss coefficient, is discussed in detail.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Cross-section view of 1.5-stage turbine section. The probe measurement planes and tandem exit guide vane sections are also shown.

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Figure 2

Photograph of the tip of the unsteady entropy probe

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Figure 3

Pitchwise-averaged spanwise distribution of entropy and relative stagnation pressure coefficient at rotor exit

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Figure 4

Entropy loss coefficient, ζ, stagnation pressure loss coefficient, Υ, and loss audits based on pitchwise-averaged measurements

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Figure 5

Time-resolved (a) total pressure and (b) total temperature distribution at rotor exit

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Figure 6

Time-resolved stagnation (a) pressure loss coefficient and (b) entropy loss coefficient distribution at rotor exit

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Figure 7

Velocity triangles at stator exit for passage vortex and wake based on the kinematic model of Kerrebrock and Mikolajczak (21)

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Figure 8

Measurement plane at rotor exit. Numerals identify regions dominated by different types of unsteady blade row interaction.

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Figure 9

Measured radially averaged relative total pressure and total temperature at rotor exit

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Figure 10

Measured radially averaged static pressure at rotor exit

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Figure 11

Measured radially averaged rms of absolute total pressure and entropy function at rotor exit

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Figure 12

rms total pressure (left column) and entropy loss coefficient (right column) distribution behind the rotor at three instants of the rotor blade passing period: (a) t/T=0.00, (b) t/T=0.25, and (c) t/T=0.50

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Figure 13

Circumferential distribution of (a) rms total pressure and (b) entropy function versus time at rotor exit for 95% span

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Figure 14

Circumferential distribution of (a) rms total pressure and (b) entropy function versus time at rotor exit for 75% span

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Figure 15

Circumferential distribution of (a) rms total pressure and (b) entropy function versus time at rotor exit for 50% span

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Figure 16

Circumferential distribution of (a) rms total pressure and (b) entropy function versus time at rotor exit for 26% span

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Figure 17

Time-resolved, spanwise profiles of entropy loss coefficient at (a) −0.32 pitch, (b) 0 pitch, (c) 0.3 pitch, and (d) 0.45 pitch. Pitchwise locations correspond to interaction zones identified in Fig. 8.

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Figure 18

Time-resolved, spanwise profiles of stagnation pressure loss coefficient at (a) −0.32 pitch, (b) 0 pitch, (c) 0.3 pitch, and (d) 0.5 pitch. Pitchwise locations correspond to interaction zones identified in Fig. 8.

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Figure 19

Time-averaged spanwise profiles of entropy loss coefficient for traverses at the four interaction zones shown in Fig. 8

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Figure 20

Modulation in entropy generation rate at different pitch positions at the rotor exit measurement plane as a percentage of the pitchwise-averaged entropy loss coefficient

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