Interaction of Tip Clearance Flow and Three-Dimensional Separations in Axial Compressors

[+] Author and Article Information
Semiu A. Gbadebo

 Siemens Industrial Turbomachinery, Lincoln, UK

Nicholas A. Cumpsty

 Imperial College, London, UK

Tom P. Hynes

 University of Cambridge, Cambridge, UK

J. Turbomach 129(4), 679-685 (Sep 07, 2006) (7 pages) doi:10.1115/1.2720876 History: Received August 30, 2006; Revised September 07, 2006

This paper considers the interaction of tip clearance flow with three-dimensional (3D) separations in the corner region of a compressor cascade. Three-dimensional numerical computations were carried out using ten levels of tip clearance, ranging from zero to 2.18% of blade chord. The 3D separations on the blade suction surface were largely removed by the clearance flow for clearance about 0.58% of chord. For this cascade, experimental results at zero and 1.7% chord tip clearance were used to assess the validity of the numerical predictions. The removal mechanism was associated with the suppression of the leading edge horseshoe vortex and the interaction of tip clearance flow with the endwall boundary layer, which develops into a secondary flow as it is driven towards the blade suction surface. Such interaction leads to the formation of a new 3D separation line on the endwall. The separation line forms the base of a separated stream surface which rolls up into the clearance vortex.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 5

Cascade endwall tuft flow pattern at 1.7% chord tip clearance

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Figure 6

Velocity vectors at the leading edge/endwall corner of the blade showing the influence of clearance flow on the leading edge horseshoe vortex; clearance values of 0.0, 0.24, and 0.58% chord

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Figure 7

Influence of tip gap on the leakage velocity for the compressor cascade. (a) Axial variation of the clearance centerline velocity. (b) Radial profiles of the clearance velocity at peak-loading location for each gap.

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Figure 1

Description of formation of 3D separation in compressor blade passage. S=saddle point, N=node. (Subscript denotes singular point number.)

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Figure 2

(a) Suction surface tufts. (b) Computed suction surface limiting streamlines. (c) Computed endwall limiting streamlines pattern for the compressor cascade at zero clearance. S=saddle point, N=node, F=focus. (Subscript denotes singular point number.)

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Figure 3

Contours of measured and computed exit total pressure loss coefficient for the compressor cascade at 50% chord from trailing edge, zero clearance

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Figure 4

Influence of clearance flow on suction surface and endwall streamlines; N=node, F=focus, S=saddle point

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Figure 8

Influence of clearance gap on calculated exit total pressure loss



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