On diffusion from an instantaneous point source in a neutrally stratified turbulent boundary layer with a laser light scattering probe

Abstract

The behavior of an instantaneous point source, as it disperses in a thick, neutrally stratified, turbulent shear layer, has been examined by a laser light-scattering technique in the Meteorological Wind Tunnel. An aerosol-filled gas bubble was released in a column of water to subsequently rise and burst at the floor of the wind tunnel. This "pseudo-instantaneous" gas volume dispersed in the turbulent shear layer. Time dependent concentrations at a point were monitored by measuring the scattered light from a coherent light source by a photomultiplier-fiber optics probe. Data consisted of a series of concentration realizations downstream from the ground level source. The distribution of concentration was described by selecting coefficients empirically in a Gram-Charlier series. Puff dispersion characteristics were compared with prediction of the Lagrangian similarity diffusion theory. Wind tunnel results were also compared with field dispersion studies conducted by Pacific Northwestern Laboratory at Hanford Reservation, Washington.