Optimization of an anisotropic compliant surface for turbulent friction drag reduction

Fukagata, Koji [Keio University] Kern, Stefan [ETH Zurich, CH-8092, Switzerland] Chatelain, Philippe [UCL] Koumoutsakos, Petros [ETH Zurich, CH-8092, Switzerland] Kasagi, Nobuhide [The University of Tokyo]

The direct numerical simulation (DNS) of the channel flow with an anisotropic compliant surface is performed in order to investigate its drag reduction effect in a fully developed turbulent flow. The surface is passively driven by the pressure and wall-shear stress fluctuations, and the surface velocity provides a boundary condition for the fluid velocity field. A stochastic optimization method (CMA-ES) is used to optimize the parameters of the anisotropic compliant surface. The optimization identifies several sets of parameters that result in a reduction of the friction drag with a maximum reduction rate of 8%. The primary mechanism for drag reduction is attributed to the decrease of the Reynolds Shear Stress (RSS) near the wall induced by the anisotropic structure and kinematics of the surface. The resultant wall motion is a uniform wave traveling downstream.