Effect of active control on linear transient growth in turbulent channel flow

The performance of active opposition control schemes employing normal and spanwise velocity components in turbulent channel flow is evaluated by the linear transient growth model. For near-wall optimal small-scale structures, the optimum detection planes for the v- and vw-control locate at around y(d)(+) approximate to 15 and y(d)(+) = 10 similar to 15, respectively. The Reynolds number has little effect on the reduction rate of G(max) as Re > 1000. For the large-scale structures in the outer layer, the v-control and vw-control achieve the maximum reduction of around 84% in G(max) at (y) over bar (d) = 0.5 and 0.4, respectively. As the Reynolds number increases, the suppression of the large-scale structures by the control becomes weaker. The vw-control is more effective than the v-control at all the Reynolds numbers. Direct numerical simulation of turbulent channel flow at Re-tau approximate to 1000 confirms the conclusion obtained by the linear transient growth model.