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Experiments on the forced wake of an airfoil

Gharib, M. and Williams-Stuber, K. (1989) Experiments on the forced wake of an airfoil. Journal of Fluid Mechanics, 208 . pp. 225-255. ISSN 0022-1120. doi:10.1017/S0022112089002831.

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The effect of initial flow conditions on the wake of an airfoil is examined in an experiment which uses the ‘strip heater’ technique to externally force the airfoil wake. The strip heaters are used to introduce waves into the top and bottom boundary layers of a thin symmetric airfoil which are subsequently amplified and introduced to the wake. The evolution and interaction of the waves in the wake is the primary interest of this study. A linear stability analysis is applied to the mean velocity profiles in order to understand the frequency selection process in the wake. It is seen that the mean velocity profile adjusts itself in order to become more receptive to the forced frequency of oscillation, resulting in the suppression of previously existing frequencies. The amplitude of oscillations in the wake can be controlled by varying the phase relation between two input signals. In this respect, cancellation and enhancement of the oscillations is possible. The linear stability analysis is applied to the cancellation/enhancement flow to verify the level of cancellation achieved. The receptivity of the system to external forcing is established. A substantial reduction in drag is achieved for forcing frequencies near the centre of the receptivity range.

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Additional Information:Copyright © 1989 Cambridge University Press. Reprinted with permission. (Received June 7 1988) This paper is based on the work for the Ph.D. thesis of K. Stuber which was carried out at the University of California, San Diego. The work was sponsored by the Defense Advanced Research Projects Agency-ACMP through the URI program under contract number DARPAlONR N00014-86-K-0758, The assistance of INLS/UCSD is also acknowledged. The authors would like to express our gratitude to Professor M.M. Koochesfahani for his assistance in implementing the linear stability program.
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Deposited On:10 Dec 2007
Last Modified:08 Nov 2021 20:58

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