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Research Papers

The Influence of Sweep on Axial Flow Turbine Aerodynamics in the Endwall Region

[+] Author and Article Information
Graham Pullan

Whittle Laboratory, Department of Engineering, University of Cambridge, Cambridge CB3 0DY, UKgp10006@cam.ac.uk

Neil W. Harvey

 Rolls-Royce plc, Derby DE24 8BJ, UK

J. Turbomach 130(4), 041011 (Aug 01, 2008) (10 pages) doi:10.1115/1.2812337 History: Received June 07, 2007; Revised June 27, 2007; Published August 01, 2008

Sweep, when the stacking axis of the blade is not perpendicular to the axisymmetric stream surface in the meridional view, is often an unavoidable feature of turbine design. In a previously reported study, the authors demonstrated that sweep leads to an inevitable increase in midspan profile loss. In this paper, the influence on the flowfield close to the endwalls is investigated. Experimental data from two linear cascades, one unswept, and the other swept at 45 deg but having the same overall turning and midspan pressure distribution, are presented. It is shown that sweep causes the blade to become more rear loaded at the hub and fore loaded at the casing. This is further shown to reduce the penetration of the secondary flow at the hub, and to produce a highly unusual secondary flow structure, with low endwall overturning, at the casing. A computational study is then presented in which the development of the secondary flows of both blades is studied. The differences in the endwall flowfields are found to be caused by a combination of the effect of sweep on both the endwall blade loading distribution and on the bulk movements of the primary irrotational flow.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 16

Blade HS, measured yaw angle (deg), Δcon=2deg

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Figure 17

Blade HS, pitchwise mass-averaged distributions, xm∕cm=1.25

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Figure 18

Blades H and HS, measured loss audit

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Figure 19

Deformation of midspan stream surface, axial view from upstream

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Figure 20

Stream surface deformation through Blade HS

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Figure 21

Blade HS, CFD predictions of normalized Yp at hub

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Figure 22

Blade HS, CFD , spanwise varying transition onset

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Figure 23

Pitchwise mass-averaged distributions, xm∕cm=1.25

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Figure 24

Results of inviscid calculations (with measured inlet boundary layer) (a) Blade H, (b) Blade HS hub, (c) Blade HS casing. Pitch angle γ, Δcon=5deg, γ>2.5deg shown gray. Normalized streamwise vorticity ωSW′, Δcon=0.4, ωSW′>0.2 shown gray.

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Figure 1

Meridional view of blade to define sweep angle λ

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Figure 2

Pitchwise averaged Vs, Δcon=0.05V2, λ=45deg, meridional view (Pullan and Harvey (2))

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Figure 3

Schematic of swept cascade (Blade HS), side view

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Figure 4

Schematic of swept cascade (Blade HS), meridional view showing traverse planes and z coordinate direction

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Figure 5

Midspan pressure distributions for both blades

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Figure 6

Inlet endwall boundary layer profiles, swept and unswept cascades

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Figure 7

Blade H suction-surface flow visualization, meridional view

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Figure 8

Blade H, surface pressure distributions

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Figure 9

Blade H, measured normalized Yp, Δcon=2

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Figure 10

Blade H, measured yaw angle (deg), Δcon=2deg

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Figure 11

Blade H, pitchwise mass-averaged distributions, xm∕cm=1.25

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Figure 12

Blade HS suction-surface flow visualization, meridional view

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Figure 13

Blade HS, surface pressure distributions close to the hub

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Figure 14

Blade HS, surface pressure distributions close to the casing

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Figure 15

Blade HS, measured normalized Yp, Δcon=2

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