With DNS database,we study the triad interaction of scalar energy transfer,and make a multi-scale analysis in different scales.It shows that the energy transfer in scalar turbulence is different from that in velocity fluctuations.The major contribution of scalar transfer is given by large scale turbulence.Simulation of scalar turbulence requires a higher resolution.The interation between large scale velocity fluctuations and small scale scalar turbulence is an important part of the energy transfer.Non_energy transfer is as important as the local energy transfer in the scalar turbulence.We define an energy transfer coefficient,and find that the inertia_convective range in scalar turbulence is longer than the inertial subrange in turbulent kinetic transfer with same Re and Pe numbers.

Large eddy simulations with three subgrid eddy viscosity models,i.e., the classic Smagorinsky model,the dynamical Smagorinsky model and a model derived from Kolmogorov equation by Cui(2004),are performed to study turbulent channel flows with a wall oscillation in the spanwise direction.The capability of the subgrid eddy viscosity models in predicting statistical three-dimensional unsteady flows is evaluated.It is found that the new model and the dynamical model are both capable of predicting three-dimensional unsteady turbulent flows;and the dynamical model can achieve a higher accuracy;the classic Smagorinsky model yields the worst result.

A stochastic model of heavy particle dispersion is proposed.It is based on the coupling of the stochastic equation of turbulent fluid motion with the heavy particle crossing trajectory equation in which Saffman force,particle-wall collision and particle-particle collision are included.The model is also tested in a turbulent boundary layer with heavy particles.The numerical results are in good agreement with previous experimental data.The effect of Saffman force and particle collision on the heavy particle dispersion is investigated numerically as well.

A new subgrid eddy viscosity model is proposed. The new subgird eddy viscosity is proportional to the skewness of longitudinal velocity increment, which characterizes the transportation of turbulent momentum bteween resolved and unresolved turbulence. The new model is verified by a DNS data bank of isotropic turbulence, and has been applied to the turbulent channel flow. The results show to be in good agreement with DNS ones.