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Diffusion from an instantaneous point source into a turbulent boundary layer: technical report




Chandra, Suresh, author
Colorado State University, Fluid Dynamics and Diffusion Laboratory, College of Engineering, publisher

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Diffusion of helium gas from an instantaneous point source within a neutral boundary layer has been studied. The investigation was made in a wind tunnel of the Fluid Dynamics and Diffusion Laboratory. Concentrations from a simulated point source, located at a fixed height of eight inches above a smooth surface, were measured for several downstream cross-sections of the diffusing cloud. The free stream velocity for the entire study was 20 ft./ sec. Statistical parameters have been used to describe the concentration data in terms of the time-average as well as the maximum instantaneous concentration at a point in the diffusion field. The lateral and vertical diffusivities are determined from the diffusion data. Comparison of data from the instantaneous point source, in terms of the time-averaged concentration parameters, with the continuous point source data of other investigators shows good agreement. The concentration data are presented in terms of dimensionless parameters. Separation of the total dispersion into two components, spreading and meandering, is obtained on the basis of Gifford's fluctuating plume model. The results of this analysis have been used to determine the Hay-Pasquill scale parameter which relates the Lagrangian and Eulerian scales of turbulence. The values of the scale factor, obtained on the basis of spreading variance alone, are in close agreement with those of other investigators. Meandering is shown to have a significant effect on these values.


August 1967.
Includes bibliographical references (pages 78-80).
U.S. Army Research Grant DA-AMC-28-043-65-GZ0.

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Turbulent boundary layer


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