Three-Dimensional Vortex Dynamics and Interactions in Near-Wall Turbulent Boundary Layers
Final rept. 1 Nov 88-1 Mar 91,
LEHIGH UNIV BETHLEHEM PA PACKARD LAB
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A model of the three-dimensional dynamic physical processes that occur in the near-wall region of a turbulent flow at high Reynolds numbers is developed. The hairpin vortex is postulated to be the basic flow structure of the turbulent boundary layer. It is shown that the central features of the near- wall flow can be explained in terms of how asymmetric hairpin vortices interact with the background shear flow, with each other, and with the surface layer near the wall. The physical process that leads to the regeneration of new hairpin vortices near the surface is described, as well as the processes of evolution of such vortices to larger-scale motions farther from the surface. The model is supported by important developments in the theory of unsteady surface-layer separation and a number of kernel experiments which demonstrate basic fluid mechanics phenomena relevant to the turbulent boundary layer. Explanations for the kinematical behavior observed in direct numerical simulations of low Reynolds number boundary-layer and channel flows are given.
- Fluid Mechanics