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A simple control algorithm to determine wall deformation with wall variables is investigated based on physical arguments of turbulent coherent structure near the wall. It is found that the spanwise gradients of wall shear stresses are good indicators of a strong quasi-streamwise vortex associated with a meandering streak. The performance of the proposed feedback control through sensing the wall variables and using arrayed deformable actuators is examined by direct numerical simulation of turbulent channel flow. The mean friction drag is found to be reduced by about 10%. The conditional averaged spatio-temporal flow field is calculated to investigate phase relationship between the actuator and the quasi-streamwise vortex. The peak / trough of each actuator is connected downwards with the vortex. This suggests a possible control with sparser arrangement of sensors in the streamwise direction.

DNS of Turbulent Drag Reduction with Wall Actuators