Flow Visualization and LDV Measurement of Turbulent Mixing Layers

概要

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Structures of the turbulent mixing layers are experimentally investigated with special regard to its dependence on forced initial disturbances. The mixing layers are layers produced by setting a model screen perpendicular to the freestream at a test section. Initial disturbances are forcibly imposed by equipping with various sizes of a thin rod along the edge of the model screen or at the origin of the mixing layer. Fow features are observed by visualization technique by means of the smoke-wire method. Statistical quantities are measured by laser-Doppler velocimeter. Three kinds of model geometry are dealt with; these are of one-edged type, belt type, and circular disk type. The flows produced by these model screens represent, respectively, a plane mixing layer and two-dimensional and axisymmetric jets issuing into ambient stream of higher velocity. Fow visualization results indicate that the two-dimensionality of large-scale coherent structures seems to persist in high-turbulent flows, although comparatively smaller scale vortices are superimposed over the flow field within the mixing layer. The mixing layers are in self-preserving state, at least, up to third order moments, but in no universal state. The growth rates of the mixing layer are shown to strongly depend on the initial disturbance imposed.
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