Random walk models for particle diffusion in free-shear flows

The main objectives were to establish and investigate discontinuous and con tinuous random walk models appropriate for free-shear hows with regard to t urbulent particle diffusion. The models were designed to capture the crossi ng trajectories effect, the continuity effect, and the inertial-limit effec t, all for the case of heavy particles whose densities are much greater tha n that of the surrounding fluid. In addition, both techniques included an i sotropic drift velocity to account for inhomogeneous turbulence The computa tional efficiency of the continuous random walk models is improved by utili zing local time stepping, which effectively filters out high-frequency velo city fluctuations that do not have a significant influence on particle diff usion. The predictive performances of these two random walk models were exa mined through comparison with experimental data and idealized test conditio ns. The results indicate that both models agree well with experimental data for a nearly homogeneous turbulent make and an inhomogeneous turbulent axi symmetric jet (although the continuous random walk model performs somewhat better for the inhomogeneous flows). It was also found that the proposed d rift velocity models are important to ensure continuity when simulating par ticle diffusion with inhomogeneous turbulence