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TECHNICAL PAPERS

Measurement and Calculation of Turbine Cascade Endwall Pressure and Shear Stress

[+] Author and Article Information
Brian M. Holley, Lee S. Langston

Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, U-3139, Storrs, CT 06269

Sandor Becz

 Pratt & Whitney, 400 Main Street, MS 169-29, East Hartford, CT 06108

J. Turbomach 128(2), 232-239 (Feb 01, 2005) (8 pages) doi:10.1115/1.2137744 History: Received October 01, 2004; Revised February 01, 2005

The complex three-dimensional fluid flow on the endwall in an axial flow turbine blade or vane passage has been extensively investigated and reported on in turbomachinery literature. The aerodynamic loss producing mechanisms associated with the endwall flow are still not fully understood or quantitatively predictable. To better quantify wall friction contributions to endwall aerodynamic loss, low Mach number wind tunnel measurement of skin friction coefficients have been made on one endwall of a large scale cascade of high pressure turbine airfoils, at engine operating Reynolds numbers. Concurrently, predictive calculations of the endwall flow shear stress have been made using a computational fluid dynamics (CFD) code. Use of the oil film interferometry skin friction technique is described and applied to the endwall, to measure local skin friction coefficients and shear stress directions on the endwall. These are correlated with previously reported measured local endwall pressure gradients. The experimental results are discussed and compared to the CFD calculations, to answer questions concerning endwall aerodynamic loss predictive ability.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

The three-dimensional separation of a boundary layer entering a planar turbine cascade (from Langston (1))

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Figure 2

Schematic of the large-scale airfoil cascade used for measurements of total pressure loss, endwall static pressure, and endwall skin friction coefficient. The inlet boundary layer measurement location also serves as a reference location for total pressure and velocity head.

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Figure 3

Agreement among midspan airfoil static pressures from potential flow, turbulent CFD, and measurement

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Figure 4

Fringe patterns due to light interference from an oil patch thinned due to shear

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Figure 5

Computational grid at (a) airfoil leading edge and on the endwall (b)

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Figure 6

Development of measured and turbulent CFD predicted mass averaged total pressure coefficient through cascade

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Figure 7

Comparison between measured and turbulent CFD prediction along the axial coordinate: percent difference between mass averaged total pressure coefficient and pitch averaged skin friction coefficient

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Figure 8

Measured (a) and turbulent CFD (b) endwall static pressure coefficients with saddle point (S.P.) locations indicated

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Figure 9

Measured and predicted “skin friction vectors” ≡Cfτw∕∣τw∣

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Figure 10

Development of measured and turbulent CFD predicted pitch-averaged skin friction coefficient through cascade

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