Turbulent Boundary Layers - Experiments, Theory and Modelling
ADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT NEUILLY-SUR-SEINE (FRANCE)
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Recent experiments have demonstrated the persistence of coherent structures in turbulent shear flows and consequently have cast doubt on the usual local transport relations and even on the usefulness of Reynolds averaging, used in practically all modelling approaches. This symposium takes stock of the present situation in turbulence research and attempts to map out new directions in modelling and experimentation. It deals specifically with turbulent boundary layers, in both incompressible and compressible fluid flow. The existence coherent vortex structures has led to renewed interest in Lagrangean descriptions of the flow. Current work emphasizes flow-visualization methods together with development of sophisticated conditional sampling methods in hot-wire anemometry. Experimentalists have taken up the challenge presented by the existence of coherent structures, and new results are reported. Theoreticians interested in these new results face the difficult task of coming to grips with nonlinear vortex interactions. Development of a physically satisfactory and mathematically tractable theory is a formidable task. The decomposition of a fluctuating flow field into waves is a traditional, familiar approach while decomposition into horseshoe vortices say presents conceptual as well as mathematical difficulties. Computer modelling of turbulent shear flows using Reynolds averaged equations with various closure schemes is the most useful technique presently available. However, sooner or later, modelling will have to recognize the experimental fact of coherent structures.
- Fluid Mechanics