COOPERATIVE DRAG REDUCING EFFECT OF LONGITUDINAL RIBLETS AND SPANWISE WALL OSCILLATIONS.

Turbulent flow over a ribbed wall oscillating in a spanwise direction is investigated numerically via DNS. It is shown that cooperative drag reducing effect of longitudinal riblets and spanwise wall oscillations exceeds significantly the performance of each method of flow manipulation. Limited amount of optimization simulations is performed. In the optimal case 13% net drag reduction is attained (with the loses associated with ribbed wall oscillations taking in account).