SIMULATION OF LAGRANGIAN DISPERSION USING A LAGRANGIAN STOCHASTIC MODEL AND DNS IN A TURBULENT CHANNEL FLOW

The mean square displacements of fluid particles in a turbulent channel flow at Re-tau=100 are investigated using a modified Langevin equation, and are compared with DNS results. Both the Lagrangian integral time scales directly obtained from DNS and the predicted values using an empirical relation between the Eulerian and the Lagrangian integral time scales are used in the modified Langevin equation to test the effects of integral time scales on the dispersion of particles. The results show that the slight variation of the Lagrangian integral time scale has little influence on the dispersion. The agreement between results of the model equation and those of DNS is satisfactory except the streamwise dispersion for intermediate times (20 < t(+) < 300), where the results of the model equation are slightly overestimated compared to those of DNS. The cause of such discrepancy is discussed.