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TECHNICAL PAPERS

Aerodynamic Design and Testing of Three Low Solidity Steam Turbine Nozzle Cascades

[+] Author and Article Information
Bo Song1

Mechanical Engineering Department,  Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Wing F. Ng

Mechanical Engineering Department,  Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Joseph A. Cotroneo, Douglas C. Hofer

 GE Energy, 1 River Road, Schenectady, NY 12345

Gunnar Siden

 GE Energy, 300 Garlington Road, Greenville, SC 29602

1

Currently Sr. Product Development Engineer with Gardner Denver, Inc.

J. Turbomach 129(1), 62-71 (Mar 01, 2004) (10 pages) doi:10.1115/1.2372774 History: Received October 01, 2003; Revised March 01, 2004

Three sets of low solidity steam turbine nozzle cascades were designed and tested. The objective was to reduce cost through a reduction in parts count while maintaining or improving performance. The primary application is for steam turbine high pressure sections where Mach numbers are subsonic and high levels of unguided turning can be tolerated. The base line design A has a ratio of pitch to axial chord of 1.2. This is the pitch diameter section of a 50% reaction stage that has been verified by multistage testing on steam to have a high level of efficiency. Designs B and C have ratios of pitch to axial chord of 1.5 and 1.8, respectively. All three designs satisfy the same inlet and exit vector diagrams. Analytical surface Mach number distributions and boundary layer transition predictions are presented. Extensive cascade test measurements were carried out for a broad incidence range from 60to+35deg. At each incidence, four outlet Mach numbers were tested, ranging from 0.2 to 0.8, with the corresponding Reynolds number variation from 1.8×105 to 9.0×105. Experimental results of loss coefficient and blade surface Mach number are presented and compared for the three cascades. The experimental results have demonstrated low losses over the tested Mach number range for a wide range of incidence from 45to15deg. Designs B and C have lower profile losses than design A. The associated flow physics is interpreted using the results of wake profile, blade surface Mach number distribution, and blade surface oil flow visualization, with the emphasis placed on the loss mechanisms for different flow conditions and the loss reduction mechanism with lower solidity. The effect of the higher profile loading of the lower solidity designs on increased end wall losses induced by increased secondary flow, especially on low aspect ratio designs, is the subject of ongoing studies.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Cascade profile shapes

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Figure 2

Cascade nomenclature

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Figure 3

Predicted blade surface Mach number distributions on steam at three different exit Mach numbers

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Figure 4

Predicted losses and boundary layer transition points on steam at constant Mach number

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Figure 5

Virginia Tech High Speed Cascade Wind Tunnel

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Figure 6

Cascade test section

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Figure 7

Aerodynamic measurements

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Figure 8

Pitchwise flow uniformity and periodicity

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Figure 9

Flow uniformity and periodicity confirmed by blade surface flow visualization (S.S.)

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Figure 10

Experimental loss development with M2 and Re

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Figure 11

Experimental loss variation with incidence

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Figure 12

Experimental wake profile and surface flow at different M2 for design B

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Figure 13

Experimental wake profile comparison between design A and design B

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Figure 14

Experimental wake profile and surface flow at different incidence for deign B

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Figure 15

Experimental blade surface isentropic Mach number

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