Intermittency and conditionally-averaged concentration fluctuation statistics in plumes

Abstract

A semi-empirical Gaussian plume model is developed which predicts the intermittency factor, and the mean and variance of the non-zero time varying concentration in the plume from a point source. Wind tunnel data are used to verify the theory and to set the empirical constants. Conditionally averaged concentration fluctuation variance, which has zero concentrations removed, is only weakly dependent on source size, while intermittency caused by plume meandering is shown to be strongly dependent on source size. The resulting closed form predictions are presented in a form suitable for estimating risk of exposure to peak concentrations.