Active control of turbulence for drag reduction based on the detection of near-wall streamwise vortices by wall information

The spatial relations between the measurable wall quantities (streamwise shear stress τ w x , spanwise shear stress τ w z , and pressure fluctuations p w ′ ) and the near-wall streamwise vortices (NWSV) are investigated via direct numerical simulation (DNS) databases of fully developed turbulent channel flow at a low Reynolds number. In the standard turbulent channel flow, the results show that all the wall measurable variables are closely associated with the NWSV. But after applying a stochastic interference, the relation based on τ w x breaks down while the correlations based on p w ′ and τ w z are still robust. Hence, two wall flow quantities based on p w ′ and τ w z are proposed to detect the NWSV. As an application, two new control schemes are developed to suppress the near-wall vortical structures using the actuation of wall blowing/suction and obtain 16 % and 11 % drag reduction, respectively. Graphical abstract The deformation and typical force curve of the mosquito leg when it is pressed onto a water surface.