Numerical Study On Slip Flow And Heat Transfer Characteristics Of Gas-Particle Fluid Based On Lattice Boltzmann Method

With the rapid development of research on microscale flow and heat transfer characteristics,the gas-particle two-phase flow in micro-propulsion system and atmospheric environment has attracted wide attention in recent years.However,it is difficult to conduct an exact experimental study on the micro-scale momentum and heat transfer mechanism between gas and particle.Thus the numerical simulation is necessary in the relevant research of microscale gas-particle two-phase fluid flow and heat transfer.The lattice Boltzmann method(LBM)has the mesoscopic background and advantages in grid generation,boundary treatment and massive parallel computation compared with the traditional computational fluid dynamics methods.As a novel numerical method,the discontinuous velocity and temperature on the interface between gas and particle is still a challenge for LBM.The present work focuses on the microscale flow and heat transfer characteristics of gas-particle flow based on the lattice Boltzmann method.The main contents are as follow:1.Establishing the isothermal and non-isothermal microscale LB model.To predict the discontinuous effect on the interface of gas and particle,a new LBM boundary treatment is proposed,which combined the interpolation/bounce-back scheme for curved boundary condition and finite difference method for slip velocity and temperature jump on the interface.The new boundary treatment considers the offset between the solid boundary and computational grids,which can accurately describe the real shape of solid boundary and precisely predict the discontinuous effect on the interface of gas and particle.Compared with previous boundary treatment,the present boundary treatment shows an obvious advantage in both accuracy and applicability.2.Microscale gas-particle two-phase flow MRT(Multiple Relaxation Time)LB model is developed to simulate the kinetic characteristic of micro particle in different flow field.The numerical result shows that effect of velocity slip on the surface of particle weaken the interaction between particle and gas,which changes the kinetic characteristic of micro particle obviously.In the study on interaction between solid wall and micro particle,it shows that the gas effective viscosity decreases due to the rarefaction effect,so the interaction between particle and wall is enhanced.In the study on drafting,kissing and tumbling(DKT)process of two micro particles,it shows that the drafting process is prolonged because of velocity slip effect,and the contact phenomenon of two micro particles is delayed.3.Microscale non-isothermal double distribution function LB model is developed to simulate the heat transfer characteristic of gas-particle two-phase flow.The numerical results show the gas kinetic energy in the boundary layer is increased because of the velocity slip,the stagnation point moves backward and the recirculation zone shrinks;the thermal resistance on the surface of particle increases due to the temperature jump and the heat transfer between gas and particle is weakened.In the study on the movement of particle in shear flow with thermal convection,the equilibrium position of particle moves toward the channel wall due to the thermal convection.The microscale effect can restrain the variation of particle equilibrium position,and the equilibrium position moves toward the channel center line as the Knudsen number increases.