A non-Gaussian stochastic model to describe passive tracer dispersion and its comparison to a direct numerical simulation

Dispersion of solid particles in three dimensions in a fully developed nonhomogeneous turbulent flow in a channel is studied. The particles enter the field on a plane at a distance of 40 wall units from the bottom wall. Data are obtained by carrying out experiments in a direct numerical simulation. The relative role of turbulence in dispersing the particles is examined. The paper explores the use of a stochastic Lagrangian model to describe solid particle dispersion. More specifically, each particle is tracked individually and through the employment of Ito calculus a modified Langevin equation is utilized to model the fluid fluctuations seen by a solid particle. The assumption of isotropy and homogeneity was not used in the formulation of the nondeterministic term in the model. All of the statistical parameters, with the exception of the time scales, are obtained from Eulerian statistics. The understanding of the influence of spatially varying time scale emerges as a central problem. Good agreement is obtained by making simple assumptions about the spatial variation of the time scales. (C) 2004 American Institute of Physics.