Direct Numerical Simulation of Skin-Friction Reduction Using Steady and Periodic Blowing Through Streamwise Slits

This paper presents a direct numerical simulation (DNS) of a turbulent channel flow manipulated using steady and unsteady blowing through one array of longitudinal slits, with a view to obtaining skin-friction drag reduction (DR) and understanding how the terms in the budget equation are altered. Investigation is performed at a Reynolds number of 198 based on the channel half height and friction velocity. The DNS code is validated with and without control. It has been found that the steady blowing mode may achieve a spatially averaged DR of 79.6% over the actuation area, exceeding that (56.7%) under unsteady blowing, given the same time-averaged blowing velocity. The two modes further exhibit a difference in affecting the terms in the budget equation. This work also complement experimental findings (Cheng et al. in J Fluid Mech 920, A50, 2021 [1]).