Experimental Study of Turbulence Production Mechanisms in Boundary Layer Flows

摘要

Studies of turbulence structure near a wall show that the production process has many manifestations. Detailed experiments, involving visual information in two mutually orthogonal planes, and simultaneous multiple hot-wire anemometry, along with both experimental and numerical simulations were performed in an attempt to determine the underlying conceptual framework. Results indicate that the wide variety of evolutions observed during the turbulence production process near a wall are all manifestations of the evolution of vortex ring-like eddies with the wall and the wall layer. Additional important evolutions result from the interaction of two of these vortex ring/wall interactions occurring with small spatial and temporal differences. Boundary layer interactions have been divided into (4) classes ranging from weak interactions to ones producing strong turbulence. These classes were simulated experimentally vortex ring/moving wall interactions, and--within the constraints of two-dimensions--qualitatively by simple numerical vortex-in-cell simulations. The instantaneous local thickness of the viscous sublayer and the flow field of the large scale motions play dominant roles in determining which class of evolution is observed.