Control for Turbulent Drag Reduction by Wall-normal Blowing and Suction

This study investigates the impact of wall-normal blowing and suction on turbulent drag in a turbulent channel flow. The research explores the effect of various parameters, e.g., actuation frequency, wavenumber, and waveform types (such as standing and streamwise-traveling waves) on the turbulent kinetic energy (TKE). Numerical analysis indicates a decrease and increase of TKE, respectively, in the vicinity of the blowing and suction regions of the channel wall. Further examination of two-point velocity correlations reveal enhanced streamwise rolls coinciding with reduced drag. Subsequently, the study incorporates closed-loop control, simulating surface velocity akin to subsurface structures, e.g., metamaterials responding to fluid forces at the channel wall. This will provide a foundation for modeling and identifying surface and subsurface feedback control methods that could potentially mitigate turbulent drag.