A Second-Order Closure Model for the Effect of Averaging Time on Turbulent Plume Dispersion

A practical model for the effect of averaging time on the turbulent dispersion of a continuous plume is presented. The model is based on a second-order turbulence closure scheme, but is applied to the integrated spatial moments of the plume to provide a Gaussian spread prediction. Velocity fluctuation variances are used directly by the closure model to predict the dispersion, and are partitioned into meandering and diffusive scales based on the instantaneous spread of the plume. Finite time averaging is represented by a simple estimate of the turbulent energy spectrum. The model is compared with short-duration atmospheric measurements for dispersing clouds.