DNS OF TURBULENT DRAG REDUCTION BY SPANWISE WALL FORCING: THE REYNOLDS NUMBER EFFECT

Abstract

The Reynolds effect of streamwise travelling waves of spanwise wall velocity on turbulent channel flow has been investigated using DNS. Simulations with various control parameters are performed at four Reynolds numbers, corresponding to Reτ = 200, 400, 800 and 1600. As the Reynolds number is increased, it is found that the intensity of both the drag reduction and drag increase is reduced, and this change does not scale universally. The value of the optimal forcing parameters changes with Reynolds number, even in wall units. Consequently, the drag reduction deteriorates quickly with Reynolds number when the parameters used are close to optimal at a lower Re number.