Active control of the turbulent drag by a localized periodical blowing dissymmetric in time |
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Authors: | Sedat F Tardu Olivier Doche |
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Institution: | (1) Laboratoire des Ecoulements Géophysiques et Industriels, LEGI, B.P. 53 X, 38041 Grenoble Cedex, France |
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Abstract: | Experimental results on the reaction of the near wall turbulence and drag to a localized time periodical blowing are reported.
The injection velocity is periodical and dissymmetric in time, with a rapid acceleration phase followed by a slow deceleration
one. The flow is relaminarized during 70% of the oscillation period mainly during the deceleration phase. The latter maintains
stable the vorticity layer induced by the blowing and prevents its roll-up contrarily to a sinusoidal time periodical blowing.
Thus, a time mean drag reduction of 50% is obtained in the region recovering 200 wall units downstream of the blowing slot
and this is 40% larger than the drag reduction obtained by a steady blowing with the same time mean severity parameter. The
dissymmetric blowing annihilates considerably the wall turbulence activity and gives better results in terms of drag reduction
compared with steady and sinusoidal blowing.
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