This research program used experimental measurements and computational simulations to study the drag reduction, and the resulting effects on turbulence structure, for a turbulent wall flow subjected to lateral wall oscillations. Major objectives for this study were to establish wall oscillation conditions resulting in maximum drag reduction, and how the turbulence structure was altered so that this drag reduction was attained. Furthermore we were interested in the drag reduction performance over a range of Reynolds numbers, and the onset of the drag reduction at the start of the oscillating wall section, and the decay of drag reduction downstream of the oscillating wall. Our experiments showed the maximum drag reduction for an oscillating wall is 30%. Furthermore, the drag reduction reaches an asymptotic level with increasing wall oscillation velocity, with the maximum level occurring by approximately W sub wp=15. Drag reduction performance was tested for Reynolds numbers of Re theta =500, 950, 1400 and 2400, and the performance was found to be independent of Reynolds number for this range. Experimental and computational studies of the turbulence structure showed the oscillating wall has dramatic effect in practically eliminating the streak structures. Furthermore, the burst and sweep structures were suppressed.

The system of linear differential equations which indicated the approach of separation and the so-called "boundary-layer thickness" by Gruschwitz is extended in this report to include the case where the friction layer is subject to centrifugal forces. Evaluation of the data yields a strong functional dependence of the momentum change and wall drag on the boundary-layer thickness radius of curvature ratio for the wall. It is further shown that the transition from laminar to turbulent flow occurs at somewhat higher Reynolds Numbers at the convex wall than at the flat plate, due to the stabilizing effect of the centrifugal forces.