Turbulent drag reduction via a streamwise traveling wave induced by spanwise wall oscillation

The flow control and drag reduction in turbulent channelflow via streamwise traveling wave induced by spanwise-wall oscillation areinvestigated by direct numerical simulation (DNS). The effects of streamwisecontrol parameter k_x on the Stokes layer, the near-wall flow structure,turbulent burst events, as well as the skin-friction drag are discussed. Inaddition, the mechanisms of turbulence suppression and drag reduction viastreamwise traveling wave induced by spanwise-wall oscillation are alsodiscussed. The results suggest that only the low-frequency waves have thesignificant influence on the flow field which induces the great variationsof frequency and the intensity of the burst which can be detected by thevariable-interval time averaging (VITA) detective technique. The variationsof the frequency and the intensity of the burst are unsynchronized as thek_x increases, and there exists an optimal parameter, k_x, in whichthe influence of the intrinsic flow on the induced flow is weakest, and onthe contrary, the intrinsic turbulent flow is modified strongly by theinduced flow, and the largest amount of drag reduction is obtained.