Large Eddy Simulation Of Coherent Structure In Gas-Particle Two Phase Turbulence

Gas-particle two phase turbulence is widely encountered in the nature and engineering applications. As a numerical method of turbulence, large eddy simulation (LES) has many advantages of both direct numerical simulation and turbulent model simulation, especially when high Reynolds gas-particle turbulence being simulated. Thus this topic has become of great interest in fluid mechanics research.Large eddy simulation of gas-particle two phase turbulence was carried out, such as simulation of two-dimensional gas-particle two phase wake, two-dimensional gas-particle two phase jet and three-dimensional gas-particle two phase rectangular jet. In these works, LES was adopted to simulate gas phase flow and Lagrangian approach was utilized to simulate the particles' motion. A series of significant and interesting results were obtained. After a thorough analysis of the properties of flow field, following the thinking of simulating gas phase flow by LES and simulating particles' motion in Lagrangian approach, a two-dimensional mathematical model of gas-particle two phaseturbulence was founded. And then simulations of gas-particle two phase plane wake and gas-particle two phase plane jet were carried out by using this model.After numerical simulations of the two flow fields were finished, series of analytical work was done. First, the distribution of time-averaged velocity, turbulence intensity was analyzed, and some of the simulation results were compared with those of the experiments; the coherent structure of vortices in the near wall region of the plane wake flow were studied by describing the evolution of the eddy structures, including the forming, developing and shedding from the wall of the vortices in the near wall region; the coherent structure of vortices in the whole field was also studied, such as the forming, developing, moving, pairing and merging of the eddies etc..At the same time, dispersion of different Stokes number particles influenced by the ordered large-scale turbulent structures of the carrier gas phase was investigated. And the following 'conclusion was drawn: particles of mediate Stokes number mainly concentrated in the outer boundary region of large scale eddies, and they had thenignest dispersion rate; particles or little Stakes number mainly lay in the core region of the eddies, and they had the lest dispersion rate; though particles of large Stokesnumber distributed throughout the eddy structures.In addition, the vortex structures of the gas flow field and particle dispersion were studied when the coupling action between the two phases was considered in the case of different mass loading of mediate Stokes number particles was provided in the gas-particle plane jet. And the following conclusion was got: generally, the existence of particles would limit and retard the developing of the coherent structure of the turbulent fields; but when the mass loading is a little high, the existence of particles would promote the developing of the turbulent field; at the same time, the gas flow field would enhance the particles' dispersion. At this time, the interaction between the two phased would promote each other. This phenomenon is just like the "sympathetic vibration" in mechanical engineering.At last, three-dimensional mathematical model of gas-particle two phase turbulence was established, and it was adopted to study the gas-particle two phase rectangular jet as well. The distribution of the time-averaged velocity and turbulence intensity was studied, and some of the simulation results were compared with the experimental results; the coherent structure of flow field was described in the three direction, the evolution and motion of the eddies was discussed too; the dispersion of fine particles in the three dimensional space was also investigated.