Use of a modified Langevin equation to describe turbulent dispersion of fluid particles in a channel flow

A stochastic method to represent the positions and velocities of fluid particles in a nonhomogeneous turbulence was pursued. Spatially varying Lagrangian time scales obtained from direct numerical simulations of turbulent flow in a channel and spatially varying joint Gaussian forcing functions were incorporated into a Langevin equation. The model was tested by comparing calculations of the dispersions and velocities of particles originating from point sources with experiments carried out in a DNS of fully-developed turbulent flows in a channel at Re(<)tau> = 150 and 300. The model captured the dispersions, mean velocities and moments of the velocity fluctuations very well. The use of jointly Gaussian (rather than uncorrelated Gaussian) forcing functions greatly improved the calculation of dispersions and mean velocities in the streamwise direction, as well as turbulence quantities which include streamwise velocity fluctuations. The condition of well-mixedness for the model was verified by considering the behavior of a uniform distribution of sources.