Improving the Performance of a Turbine With Low Aspect Ratio Stators by Aft-Loading

[+] Author and Article Information
Graham Pullan

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

John Denton, Eric Curtis

Whittle Laboratory, University of Cambridge, Cambridge CB3 0DY, UK

J. Turbomach 128(3), 492-499 (Mar 01, 2004) (8 pages) doi:10.1115/1.2182000 History: Received October 01, 2003; Revised March 01, 2004

Experimental data and numerical simulations are presented from a research turbine with low aspect ratio nozzle guide vanes (NGVs). The combined effects of mechanical and aerodynamic constraints on the NGV create very strong secondary flows. This paper describes three designs of NGV that have been tested in the turbine, using the same rotor row in each case. NGV 2 used three-dimensional design techniques in an attempt to improve the performance of the datum NGV 1 blade, but succeeded only in creating an intense vortex shed from the trailing edge (as previously reported) and lowering the measured stage efficiency by 1.1% points. NGV 3 was produced to avoid the “shed vortex” while adopting a highly aft-loaded surface pressure distribution to reduce the influence of the secondary flows. The stage with NGV 3 had an efficiency 0.5% points greater than that with NGV 1. Detailed comparisons between experiment and computations, including predicted entropy generation rates, are used to highlight the areas where the loss reduction has occurred and hence to quantify the effects of employing highly aft-loaded NGVs.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Meridional view of the research turbine

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Figure 2

Computational mesh, circumferential view, NGV 2, (every second point shown)

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Figure 3

Photograph of (from left) NGV 3, NGV 2, and NGV 1

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Figure 4

NGV midspan blade profiles

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Figure 5

NGV 3 leading edge location

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Figure 6

NGV mid-span surface pressure

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Figure 7

Angular momentum through three NGV designs

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Figure 8

Predicted meridional yaw angle distribution, NGV 3

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Figure 9

Measured and predicted midspan surface pressures, NGV 3 (solid line=CFD) cp=(p−p01)∕ρUmid2

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Figure 10

NGV oil and dye surface flow visualization, NGV 2 (left) and NGV 3

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Figure 11

NGV exit total pressure coefficient, (p01−p02)∕ρUmid2

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Figure 12

NGV exit meridional yaw angle (deg)

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Figure 13

Measured efficiency of all stages

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Figure 14

Comparison of NGV and rotor loss, measured and predicted

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Figure 15

Predicted lost efficiency curves

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Figure 16

Zones for loss audit, NGV 3

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Figure 17

Loss audit for the three NGVs

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Figure 18

Loss audit for rotor

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Figure 19

Time variation of rotor loss generation, by zone, NGV 3 stage




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