Abo Bibliothek: Guest
Seventh International Symposium on Turbulence and Shear Flow Phenomena
July, 28-31, 2011, Ottawa Convention Centre, Ottawa, Canada

DOI: 10.1615/TSFP7

NEAR-WALL STREAK MODIFICATIONS BY SPANWISE OSCILLATORY WALL MOTIONS

pages 1-6
DOI: 10.1615/TSFP7.920
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ABSTRAKT

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.

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