A algorithm for direct numerical simulation of inter-particle collision in 3D space is built and verified by comparison with analytical solutions of collision rate of particulate flow under fine and heavy limits respectively. Optimizations such as exclusive method for computational mesh during identification of collisions can reduce the running time to 0.75% of that before optimization, without increscent relative error. It also shows that less time step can give more exact result in comparison of numerical simulations of the same particle group with different time steps. In precondition of no lost collision, fine computational mesh will save running time obviously.

A lattice Boltzmann model is proposed for the double diffusive natural convection system.The flow in a square cavity driven by a temperature gradient and a concentration gradient is then simulated using the present model.The influence of the concentration field on the flow patterns is investigated,and some quantitative comparisons with other studies are made.It is shown that the present LB model can predict the flow characteristics correctly.