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Effect of acoustic excitation on the flow over a low-Re airfoil

Published online by Cambridge University Press:  21 April 2006

K. B. M. Q. Zaman ,
A. Bar-Sever  and
S. M. Mangalam
K. B. M. Q. Zaman
Affiliation:
ESCON, NASA Langley Research Center, Hampton, VA 23665, USA
A. Bar-Sever
Affiliation:
ESCON, NASA Langley Research Center, Hampton, VA 23665, USA
S. M. Mangalam
Affiliation:
AS & M Inc., NASA Langley Research Center, Hampton, VA 23665, USA
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Abstract

Wind-tunnel measurements of lift, drag and wake velocity spectra were carried out under (tonal) acoustic excitation for a smooth airfoil in the chord-Reynolds-number (Rec) range of 4 × 104−1.4 × 105. The data are supported by smoke-wire flowvisualization pictures. Small-amplitude excitation in a wide, low-frequency range is found to eliminate laminar separation that otherwise degrades the airfoil performance at low Rec near the design angle of attack. Excitation at high frequencies, scaling as $U_{\infty}^{\frac{3}{2}}$, eliminates a pre-stall, periodic shedding of large-scale vortices; U∞ is the free-stream velocity. Significant improvement in lift is also achieved during post-stall, but with large-amplitude excitation. Wind-tunnel resonances strongly influence the results, especially in cases requiring large amplitudes. It is shown that large transverse velocity fluctuations, induced near the airfoil by specific cross-resonance modes, lead to the most effective separation control; resonances inducing only large-amplitude pressure fluctuations are demonstrated to be less effective.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 182 , September 1987 , pp. 127 - 148
Copyright
© 1987 Cambridge University Press

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