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TECHNICAL PAPERS

On a Novel Annular Sector Cascade Technique

[+] Author and Article Information
T. Povey, T. V. Jones, M. L. Oldfield

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK

J. Turbomach 129(1), 175-183 (Mar 01, 2004) (9 pages) doi:10.1115/1.2372766 History: Received October 01, 2003; Revised March 01, 2004

An advanced technique for establishing pressure boundary conditions in annular sector cascade experiments has been developed. This novel technique represents an improvement over previous methods and provides the first means by which annular sector boundary conditions that are representative of those which develop in an annular cascade can be established with a high degree of satisfaction. The technique will enable cascade designers to exploit the obvious advantages of annular sector cascade testing: the reduced cost of both facility manufacture and facility operation and the use of engine parts in place of two-dimensional counterparts. By employing an annular sector of deswirl vanes downstream of the annular sector of test vanes, the radial pressure gradient established in the swirling flow downstream of the test vanes is not disturbed. The deswirl vane exit flow—which has zero swirl velocity—can be exhausted without unsteadiness, and without the risk of separation, into a plenum at constant pressure. The pressure ratio across the annular sector of test vanes can be tuned by adjusting the throat area at the deswirl vane exit plane. Flow conditioning systems which utilize the Oxford deswirl vane technology have previously been used to set pressure boundary conditions downstream of fully annular cascades in both model and engine scale (the Isentropic Light Piston Facility at Farnborough) experimental research facilities (Povey, T., Chana, K. S., Oldfield, M. L. G., Jones, T. V., and Owen, A. K., 2001, Proceedings of the ImechE Advances in Fluid Machinery Design Seminar, London, June 13; Povey, T., Chana, K. S., Jones, T. V., and Oldfield, M. L. G., 2003, Advances of CFD in Fluid Machinery Design, ImechE Professional Engineering, London, pp. 65–94). The deswirl vane is particularly suited to the control of highly whirling transonic flows. It has been demonstrated by direct comparison of aerodynamic measurements from fully annular and annular sector experiments that the use of a deswirl vane sector for flow conditioning at the exit of an annular sector cascade represents an attractive novel solution to the boundary condition problem. The annular sector technique is now described.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Development of secondary flows in an annular cascade

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Figure 2

Methods of setting annular cascade exit conditions: (a) extended constant annulus, (b) radial diffuser, (c) perforated plate, and (d) deswirl vane

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Figure 3

An impulse turbine blade design and the corresponding impulse-type deswirl vane

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Figure 4

Annular cascade of deswirl vanes

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Figure 5

The working section of the test facility

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Figure 6

A four-passage annular sector of deswirl vanes

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Figure 7

Pressure tapping diagram at hub and case walls for sidewall design 1 (the wall has been unwrapped)

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Figure 8

Comparison of sidewall designs 1 and 2

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Figure 9

Circumferential pressure distributions at the IP vane exit plane hub and case walls: fully annular cascade

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Figure 10

Circumferential pressure distributions at the IP vane exit plane hub and case walls: annular sector design 1

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Figure 11

Circumferential pressure distribution at the IP vane exit plane hub and case walls: annular design 2

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Figure 12

Circumferential pressure distributions at the deswirl vane inlet plane hub and case walls: annular sector design 2

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Figure 13

Flow visualization on sector sidewalls and hub surface—sidewall design 2. Surface streamlines are highlighted.

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