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Research Papers

Predicting Separation and Transitional Flow in Turbine Blades at Low Reynolds Numbers—Part II: The Application to a Highly Separated Turbine Blade Cascade Geometry

[+] Author and Article Information
Darius D. Sanders, Walter F. O’Brien

Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061

Rolf Sondergaard, Marc D. Polanka, Douglas C. Rabe

Air Force Research Lab, Propulsion Directorate, Wright Patterson AFB, OH 45433

J. Turbomach 133(3), 031012 (Nov 15, 2010) (7 pages) doi:10.1115/1.4001231 History: Received August 13, 2009; Revised October 16, 2009; Published November 15, 2010; Online November 15, 2010

There has been a need for improved prediction methods for low pressure turbine (LPT) blades operating at low Reynolds numbers. This is known to occur when LPT blades are subjugated to high altitude operations causing a decrease in the inlet Reynolds number. Boundary layer separation is more likely to be present within the flowfield of the LPT stages due to increase in the region adverse pressure gradients on the blade suction surface. Accurate CFD predictions are needed in order to improve design methods and performance prediction of LPT stages operating at low Reynolds numbers. CFD models were created for the flow over two low pressure turbine blade designs using a new turbulent transitional flow model, originally developed by Walters and Leylek (2004, “A New Model for Boundary Layer Transition Using a Single Point RANS Approach,” ASME J. Turbomach., 126(1), pp. 193–202). Part I of this study applied Walters and Leylek’s model to a cascade CFD model of a LPT blade airfoil with a light loading level. Flows were simulated over a Reynolds number range of 15,000–100,000 and predicted the laminar-to-turbulent transitional flow behavior adequately. It showed significant improvement in performance prediction compared to conventional RANS turbulence models. Part II of this paper presents the application of the prediction methodology developed in Part I to both two-dimensional and three-dimensional cascade models of a largely separated LPT blade geometry with a high blade loading level. Comparisons were made with available experimental cascade results on the prediction of the inlet Reynolds number effect on surface static pressure distribution, suction surface boundary layer behavior, and the wake total pressure loss coefficient. The kT-kL-ω transitional flow model accuracy was judged sufficient for an understanding of the flow behavior within the flow passage, and can identify when and where a separation event occurs. This model will provide the performance prediction needed for modeling of low Reynolds number effects on more complex geometries.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

2D hybrid O-H grid of highly loaded blade airfoil

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Figure 2

3D hybrid O-H grid of the highly loaded blade airfoil

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Figure 3

Comparison of surface static pressure coefficient with 3D LES (9) simulations and experimental results (13) at inlet Reynolds numbers of (a) 100,000, (b) 50,000, and (c) 25,000 for the highly loaded blade airfoil

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Figure 4

Comparison of the boundary layer velocity profiles at inlet Reynolds numbers of (a) 100,000 and (b) 50,000 with the experimental results (12) for the highly loaded blade airfoil

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Figure 5

Comparison of the mean boundary layer velocity profiles at 25,000 with the experimental results (12) for the highly loaded blade airfoil

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Figure 6

Instantaneous vorticity contour plot at Re=100,000 for the highly loaded blade airfoil

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Figure 7

Instantaneous vorticity contours at Re=50,000 for the highly loaded blade airfoil at Lm=50 mm (a and b) and Lm=5 mm (c and d)

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Figure 8

Instantaneous vorticity contours at Re=25,000 for the highly loaded blade airfoil at Lm=50 mm (a and b) and Lm=5 mm (c and d)

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Figure 9

Instantaneous vorticity (a and b) contours and (c and d) isosurfaces at Re=25,000 for the 3D CFD model of the highly loaded blade airfoil at Tu=0.6%, Lm=50 mm

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Figure 10

Comparison of total pressure loss coefficient with experimental (10-11) results at inlet Reynolds numbers of (a) 100,000, (b) 50,000, and (c) 25,000 for the highly loaded blade airfoil

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