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TURBULENT FRICTION-DRAG REDUCTION CONTROL-SCHEME REQUIRING ONLY STREAMWISE WALL SHEAR SIGNAL

Koji Fukagata
Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522,Japan

Nobuhide Kasagi
Center for Research and Development Strategy, Japan Science and Technology Agency; Department of Mechanical Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Resumo

We propose a new algebraic control scheme for drag reduction in wall-turbulence, which requires the streamwise wall-shear signal only. By assuming continuously distributed sensors and actuators, the controller is designed to reduce the near-wall Reynolds shear stress that is directly responsible for the turbulent skin friction drag. Intuitive and suboptimal control schemes are considered. The derived control laws are assessed by means of direct numerical simulation of turbulent pipe flow at Reτ ~ 180. A clear drag reduction symptom associated with a negative near-wall Reynolds stress is observed when the control scheme derived by the suboptimal control theory is applied.