Motions of Chimney Puffs for Small Travelling Times

Abstract

A model based on single particle diffusion is introduced to evaluate the magnitude of "meandering" in plume dispersion where the instantaneous plume meanders around its mean axis. It is assumed that the plume can be regarded as a series of puffs, each of which will move as a whole along a trajectory of its own circular arc in the mean flow. Then a dispersion equation of puff centers is obtained to evaluate the magnitude of the variance of puff center positions; the variance is regarded as a measure of plume meandering. The dispersion equation was successfully tested against the observation performed under the condition that the mean wind velocity was 8.8m/s and the sampling duration was 3 minutes. The smoke puffs were observed over about 500m downwind distances from a 200m high chimney and the mean arc radius of their trajectories was 55m and the mean angular velocity was 0.033rad/s.