Feedback Control of Near-Wall Reynolds Shear Stress in Wall-Turbulence

A new idealized control scheme is proposed for drag reduction in wall-turbulence and its effects are studied by means of DNS of turbulent pipe flow. The control input is given as a function of sensed streamwise velocity fluctuation above the wall in order to suppress the near-wall Reynolds shear stress, which is directly related to the turbulent skin friction drag [Fukagata et al., Phys. Fluids, Vol. 14 (2002), p. L73-L76]. A significant amount of drag reduction, which compares well with the opposition control [Choi et al., J. Fluid Mech., Vol. 262 (1994), p. 75-110], is obtained. Effects of deteriorated sensor signals are also investigated. With the present control scheme, the drag reduction rate is kept at the same level as long as the correlation coefficient between the original and deteriorated signals is higher than 0.5.

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