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 \(\tau _{\mathrm{w}{ x}}\), spanwise shear stress \(\tau _{\mathrm{w}{ z}}\), and pressure fluctuations \(p^\prime _\mathrm{w}\)) 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 \(\tau _{\mathrm{w}{ x}}\) breaks down while the correlations based on \(p^\prime _\mathrm{w}\) and \(\tau _{\mathrm{w}{ z}}\) are still robust. Hence, two wall flow quantities based on \(p^\prime _\mathrm{w}\) and \(\tau _{\mathrm{w}{ z}}\) 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.

The deformation and typical force curve of the mosquito leg when it is pressed onto a water surface.