Linear instability and resonance effects in large-scale opposition flow control

Opposition flow control is a robust strategy that has been proved effective in turbulent wall-bounded flows. Its conventional set-up consists of measuring wall-normal velocity the buffer layer and opposing it at wall. This work explores possibility implementing this with detection plane logarithmic layer, where could be feasible experimentally. We apply on channel $Re_\tau = 932$ , only eddies relatively large wavelengths ( $\lambda / h > 0.1$ ). Similarly to opposition control, our results virtual-wall effect for velocity, creating minimum its intensity. However, also induces response streamwise Reynolds stresses near wall, substantial drag increase. When phase lags respect plane, spanwise-homogeneous rollers are observed show they result linear instability. In contrast, when leads instability inactive oblique waves observed. Their profiles can predicted linearly as forcing advection plane. The linearity, governing flow, opens affect scales controlled manner, enhanced turbulence intensity or mixing desired.