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On the Origin of Streaks in Turbulent Shear Flows

  • Fabian Waleffe
  • John Kim
  • James M. Hamilton

Abstract

It is shown that the ideas of selective amplification and direct resonance, based on linear theory, do not provide a selection mechanism for the well-defined streak spacing of about 100 wall units (referred to as 100+ hereafter) observed in wall-bounded turbulent shear flows. For the direct resonance theory (Benney & Gustaysson, 1981; fang et al., 1986), it is shown that the streaks are created by the nonlinear self-interaction of the vertical velocity rather than of the directly forced vertical vorticity. It is then proposed that the selection mechanism must be inherently nonlinear and correspond to a self-sustaining process. The streak formation is only one stage of the complete mechanism and cannot be isolated from the rest of the process. The 100+ value should be considered as a critical Reynolds number for that self-sustaining mechanism. For the case of plane Poiseuille flow the 100+ criterion corresponds to a critical Reynolds number of 1250, based on the centerline velocity and the channel half-width, which is close to the usually quoted value of about 1000. In plane Couette flow, it corresponds to a critical Reynolds number of 625, based on the half velocity difference and the half-width.

Keywords

Turbulent Boundary Layer Couette Flow Streamwise Vortex Critical Reynolds Number Centerline Velocity 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1993

Authors and Affiliations

  • Fabian Waleffe
    • 1
  • John Kim
    • 1
  • James M. Hamilton
    • 1
  1. 1.Center for Turbulence ResearchNASA Ames Research CenterMoffett FieldUSA

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