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Research Papers

Interstage Flow Interactions and Loss Generation in a Two-Stage Shrouded Axial Turbine

[+] Author and Article Information
L. Porreca1

Turbomachinery Laboratory, Swiss Federal Institute of Technology ETH Zürich, Zurich 8005, Switzerlandluca.porreca@ch.manturbo.com

A. I. Kalfas, R. S. Abhari

Turbomachinery Laboratory, Swiss Federal Institute of Technology ETH Zürich, Zurich 8005, Switzerland

Y. I. Yun, S. J. Song

School of Mechanical and Aerospace Engineering, Seoul National University, Republic of Korea

1

Present address: MAN Turbo AG Schweiz, Zurich, Switzerland.

J. Turbomach 131(1), 011002 (Sep 25, 2008) (12 pages) doi:10.1115/1.2948961 History: Received August 08, 2006; Revised September 27, 2007; Published September 25, 2008

The aerodynamics and kinematics of flow structures, including the loss generation mechanisms, in the interstage region of a two-stage partially shrouded axial turbine are examined. The nonaxisymmetric partial shroud introduces highly three-dimensional unsteady interactions, the details of which must be understood in order to optimize the design of the blade/shroud. Detailed measurements of the steady and unsteady pressure and velocity fields are obtained using a two-sensor fast response aerodynamic probe and stereoscopic particle image velocimetry. These intrusive and nonintrusive measurement techniques yield a unique data set that describes the details of the flow in the interstage region. The measurements show that a highly three-dimensional interaction occurs between the passage vortex and a vortex caused by the recessed shroud platform design. Flow coming from the blade passage suddenly expands and migrates radially upward in the cavity region, causing a localized relative total pressure drop. Interactions of vortex and wake structures with the second stator row are analyzed by means of the combination of the measured relative total pressure and nondeterministic pressure unsteadiness. The analysis of the data gives insight on unsteady loss mechanisms. This study provides improved flow understanding and suggests that the design of the blade/shroud and second stator leading edge may be further improved to reduce unsteady loss contribution.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of the rotor partial shroud geometry

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Figure 2

Optical windows and probe holes in the test turbine

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Figure 3

Stereoscopic camera configuration in the test turbine

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Figure 4

Measurement regions: PIV, FRAP, and 5HP

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Figure 5

Recorded image of seeded flow in the interstage measurement region

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Figure 6

Measured absolute tangential velocity at one rotor blade position: (a) PIV and (b) FRAP—turbine exit region

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Figure 7

Comparison between FRAP, 5HP, and PIV time averaged pitchwise yaw angles—turbine exit region

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Figure 8

PIV measured time and pitchwise averaged absolute yaw angles at different axial planes

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Figure 9

PIV measured absolute yaw angles at different tangential planes. Vectors show the in-plane velocity component—interstage region.

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Figure 10

PIV measured absolute yaw angles at different axis-perpendicular planes. Vectors show the in-plane velocity component—interstage region

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Figure 11

Schematic of flow structures and measurements in the interstage region

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Figure 12

FRAP measurements of the relative total pressure coefficient Cptrel and secondary flow vectors—interstage region

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Figure 13

Time-distance plot of relative total pressure coefficient Cptrel at (a) 76% span and (b) 50% span

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Figure 14

Time-distance plot of pressure unsteadiness coefficient Pu (%) at (a) 76% span and (b) 50% span

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Figure 15

Circumferential evolution of yaw angle at different axial locations (110%–152% Cax) at 80% span—one rotor blade position

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