Zonal Models of Turbulence and Their Application to Free Shear Flows,
STANFORD UNIV CA THERMOSCIENCES DIV
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The concept of zonal modeling is tested by using three homogeneous flows. It is found that two governing parameters suffice to classify all free shear flows considered. The first parameter represents the ratio of the inertial force to the driving force of the shear layer or, alternatively, the ratio of eddy turn-over time to the characteristic free stream time. It determines the relative importance of the diffusion process in the turbulence transport mechanism. The larger this parameter, is the more important the diffusion process of turbulence becomes. The other parameter is a measure of lateral vortex stretching. Strong vortex stretching reduces the correlation between turbulent shear stress and turbulent kinetic energy and hence reduces the spreading rate of the flow. There are a total of three zones found in the class of free shear flows they represent the limiting values of the two governing parameters. The zonal models for these three zones are built separately. They are then blended to allowed readjustments between zones by means of readjustment parameters that are functions of the governing parameters. As a result, a unified zonal model for all free shear flows is produced.
- Fluid Mechanics