Diffusion from an Instantaneous Point Source into a Turbulent Boundary Layer

摘要

Diffusion of helium gas from an instantaneous point source within a neutral boundary layer was studied. 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 were 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 were used to determine the Hay-Pasquill scale parameter which related the Lagrangian and Eulerian scales of turbulence. (Author)