The Structure of Turbulent Diffusion : 1st Report, Diffusion from a Source of Finite Width and Diffusion in a Mixing Region of Laminar and Turbulent Flows

Abstract

Although Taylor's single-particle theory is available for the diffusion of a scalar quantity in homogeneous turbulent flows, it cannot be satisfactorily applied when the source has a finite width. By using a convective coordinate system which moves with the diffusing smoke, we propose a method for predicting the diffusion from this type of source. A definite relation was found between the relative diffusion about the centre of mass of the smoke and its meandering motion. Further, the influence on the two-particle diffusion of the shapes of correlation function was found to be large even for a long diffusion time. The diffusion of a scalar quantity in a mixing region of parallel-flowing laminar and turbulent fluids is studied. Using a coordinate system fixed on the boundary between the laminar and turbulent regions as the convective system, it becomes possible to predict the time-mean concentration distribution, even though the phenomenon is intermittent.