CLOUD DISPERSION MODELS

A new technique has been developed to compute mean and fluctuating con centrations in complex turbulent flows. An initial distribution of mat erial is discretised into any small clouds which are advected by a com bination of the mean flow and large scale turbulence. The turbulence c an be simulated either by Kinematic Simulation or by a stochastic mode l for the motion of each cloud centroid. The clouds also diffuse relat ive to their centroids; the statistics for this are obtained from a se parate calculation of the growth of individual clouds in small scale t urbulence, generated by Kinematic Simulation. The ensemble of discrete clouds is periodically rediscretised, to limit the size of the small clouds and prevent overlapping. The model is illustrated with simulati ons of dispersion in uniform flow and in a coastal flow, and the resul ts are compared with analytic, steady state solutions where available.