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Effects of porous tunnel walls on high lift airfoil testing

University of British Columbia

When a model is tested in a wind tunnel of either open or closed boundaries, the flow field around the model is modified, so that the results of a wind tunnel test do not exactly correspond to flight results. In order to obtain reliable wind tunnel data, wall corrections must be known accurately or eliminated. One approach to the elimination of wall corrections is the use of porous walls, In this study, lift, drag and pitching moment about mid-chord were measured for two sets of two-dimensional Clark Y airfoils, one set having no flap,, the other set having a 30% chord double slotted flap set at 45°. Each set consisted of four geometrically similar profiles with 9 inch, 14 inch, 19 inch and 24 inch chords. In order to simulate two-dimensional flow, all airfoils were mounted vertically in the wind tunnel test section spanning the 27 inch height. The Reynolds number in all cases was maintained at 300,000o The airfoils were tested over a full range of angle of attack in the presence of different configurations of porous tunnel side walls. Longitudinally slotted side walls of open area ratios ranging from 5.5% to 29.6%, transversely slotted side walls of open area ratios ranging from 9.3% to 23.1% and perforated side walls of open area ratios ranging from 12.3% to 18.4% were tested. Slot configurations were sought for which the CL versus ∝ data below CLMAX was most nearly independent of model size. For testing the airfoils with 30% chord double slotted flap at 45°, 18.5% longitudinally slotted side walls proved to be the best configuration while for testing the basic airfoil, 11.1% longitudinally slotted side walls proved the most satisfactory., The lift curve collapsed quite well at these two open areas for the two sets of airfoils, but the lift curve slope was about 15% lower than the expected value in each case. This anomaly remains unresolved. Although the open area ratios found to be best in the present tests are not necessarily optimum values for all tunnels, they should provide useful guidelines for future tests with porous wall configurations.

Text

2011-05-25

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http://hdl.handle.net/2429/34871

Mechanical Engineering

University of British Columbia

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