TURBULENCE CONTROL IN WALL-BOUNDED FLOWS BY SPANWISE OSCILLATIONS

The feasibility of control of wall turbulence by high frequency spanwise oscillations is investigated by direct numerical simulations of a planar turbulent channel flow subjected either to an oscillatory spanwise crossflow or to the spanwise oscillatory motion of one of the channel walls. Periods of oscillation, T(osc.)+ = T(osc.) u(tau)2/nu, ranging from 25 to 500 were studied. For 25 < T(osc.)+ < 200 production of turbulence is suppressed. The most effective suppression of turbulence occurs at T(osc)+ = 100, for which the overall turbulence production is reduced by 62% compared to the unperturbed channel and sustained turbulent drag reductions of 40% are obtained. The suppression of turbulence is due to a continual shift of the near wall streamwise vortices relative to the wall layer streaks, which in turn leads to a widening, merging and weakening of the wall layer streaks and an overall reduction in the turbulence production. The turbulence suppression mechanism observed in these studies opens up new possibilities for effective control of turbulence in wall-bounded flows.