Publication Date:
1987-09-01
Description:
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 x 104-1.4 x 105The data are supported by smoke-wire flow-visualization pictures. Small-amplitude excitation in a wide, low-frequency range is found to eliminate laminar separation that otherwise degrades the airfoil performance at low Recnear the design angle of attack. Excitation at high frequencies, scaling as U3/2∞eliminates a pre-stall, periodic shedding of large-scale vorticesU∞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. © 1987, Cambridge University Press. All rights reserved.
Print ISSN:
0022-1120
Electronic ISSN:
1469-7645
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
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