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NEAR-WALL STREAK MODIFICATIONS BY SPANWISE OSCILLATORY WALL MOTIONS

Emile Touber
Department of Aeronautics, Imperial College London, South Kensington Campus, London SW7 2AZ, U.K.

Michael A. Leschziner
Aeronautics Department, Imperial College London, Prince Consort Rd., London SW7 2AZ, United Kingdom

Аннотация

Direct numerical simulations for channel flow have been performed and analysed in an effort to illuminate the fundamental mechanisms contributing to the reduction in turbulent friction drag, observed when an oscillatory spanwise wall motion is imposed. A range of statistical data are discussed, and structural features are investigated by reference to the response of streak properties to the oscillatory forcing. The unsteady cross-flow straining is shown to significantly distort the near-wall turbulence structures, leading to a pronounced reduction in the wall-normal momentum exchange in the viscous sublayer, hence disrupting the turbulence contribution to the wall shear stress. Furthermore, a modulating "top-to-bottom" effect, associated with large-scale outer-layer structures, is highlighted and deemed responsible for the observed reduction in the actuation efficiency as the Reynolds number is increased.