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Research Papers

Experimental Analysis of Thick Blunt Trailing-Edge Wind Turbine Airfoils

[+] Author and Article Information
J. P. Baker, E. A. Mayda, C. P. van Dam

Department of Mechanical and Aeronautical Engineering,  University of California, Davis, Davis, CA 95616

J. Sol. Energy Eng 128(4), 422-431 (Jul 19, 2006) (10 pages) doi:10.1115/1.2346701 History: Received January 31, 2006; Revised July 19, 2006

An experimental investigation of blunt trailing-edge or flatback airfoils was conducted in the University of California, Davis aeronautical wind tunnel. The blunt trailing-edge airfoil is created by symmetrically adding thickness to both sides of the camber line of the FB-3500 airfoil, while maintaining the maximum thickness-to-chord ratio of 35%. Three airfoils of various trailing-edge thicknesses (0.5%, 8.75%, and 17.5% chord) are discussed in this paper. In the present study, each airfoil was tested under free and fixed boundary layer transition flow conditions at Reynolds numbers of 333,000 and 666,000. The fixed transition conditions were used to simulate surface soiling effects by placing artificial tripping devices at 2% chord on the suction surface and 5% chord on the pressure surface of each airfoil. The results of this investigation show that lift increases and the well-documented thick airfoil sensitivity to leading-edge transition reduces with increasing trailing-edge thickness. The flatback airfoils yield increased drag coefficients over the sharp trailing-edge airfoil due to an increase in base drag. The experimental results are compared against numerical predictions obtained with two different computational aerodynamics methods. Computations at bounded and unbounded conditions are used to quantify the wind tunnel wall corrections for the wind tunnel tests.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Time-averaged pressure distributions of the TR-35 and TR-35-10 airfoils at Re=4.5×106, α=8deg, free transition (3)

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Figure 4

Grid approach for the unbounded flow cases: (a) overall view of the O-grid for the FB-3500-0050 section where the farfield boundary is nominally 50 chord lengths from the airfoil surface (some radial gridlines omitted for clarity) and (b) detail view of the O-grid near the airfoil surface

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Figure 5

Gridding approach for the wind tunnel cases: (a) overall view showing test section, diffuser and airfoil model (some gridlines omitted for clarity) and (b) view of FB-3500-0875 mesh at 12deg angle of attack and its overlap region with the tunnel grid

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Figure 6

Measured (a) lift curves and (b) drag polars for FB-3500-0050 airfoil with transition free and fixed at Reynolds numbers of 333,000 and 666,000. Uncorrected for wind tunnel wall effects.

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Figure 7

Measured (a) lift curves and (b) drag polars for FB-3500-0875 airfoil with transition free and fixed at Reynolds numbers of 333,000 and 666,000. Uncorrected for wind tunnel wall effects.

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Figure 8

Measured (a) lift curves and (b) drag polars for FB-3500-1750 airfoil with transition free and fixed at Reynolds numbers of 333,000 and 666,000. Uncorrected for wind tunnel wall effects.

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Figure 9

Measured L∕D for all airfoils under (a) free and (b) fixed transition conditions at Re=666,000. Uncorrected for wind tunnel wall effects.

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Figure 10

Comparison of experimental and computational (a) lift curves and (b) drag polars for the FB-3500-0050 airfoil, transition fixed, Re=666,000

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Figure 11

Comparison of experimental and computational (a) lift curves and (b) drag polars for the FB-3500-0875 airfoil, transition fixed, Re=666,000

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Figure 12

Comparison of experimental and computational (a) lift curves and (b) drag polars for the FB-3500-1750 airfoil, transition fixed, Re=666,000

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Figure 13

Time-accurate lift and drag coefficient histories for the FB-3500-1750 airfoil, transition fixed, α=12deg, Re=666,000

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Figure 14

Instantaneous velocity contours showing the Kármán vortex street in the wake of the FB-3500-1750 airfoil, transition fixed, α=12deg, Re=666,000

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Figure 15

Comparison of RANS computed surface pressure distributions for the FB-3500-0050 and FB-3500-0875 airfoils, transition fixed, α=8deg, Re=666,000

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Figure 16

Comparison of computational correction methods: (a) lift curves and (b) drag polars for the FB-3500-0875 airfoil, transition fixed, Re=666,000

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Figure 3

A two-dimensional airfoil model, mounted in the University of California, Davis aeronautical wind tunnel test section

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Figure 2

Blade section geometries for the baseline FB-3500-0050 and its derivative flatback sections used in study: FB-3500-0875 and FB-3500-1750

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