Numerical Study Of Particle Collision Characteristics In Isotropic Turbulence Based On MRT-LBM

A mixture of solid particles in a liquid,known as a suspension,is a type of two-phase flow that occurs in a variety of industrial applications as well as in natural flows.Understanding how dispersed particles/droplets interact with turbulence is essential to better predict hazardous processes and design industrial facilities.Therefore,this paper systematically studied the influence of different turbulence states on the distribution characteristics and collision characteristics of solid particles of different sizes and densities by using advanced direct numerical simulation method(DNS)and combined with the modified discrete phase processing model.This article briefly introduces the multi-relaxation time lattice Boltzmann method for solving isotropic turbulence fields.If the flow field does not consider the energy input,the isotropic turbulence is constantly attenuating,the turbulence is in an unstable state,and the integral scale is Differential scales are constantly increasing,which in turn leads to constant changes in various statistics over time,making the analysis of results very complicated and difficult to obtain the flow field law.Therefore,in order to obtain a stable turbulent flow field,it is necessary to construct an external force term to compensate for the turbulent energy dissipation due to viscosity.A more classic approach is to apply force in the spectral space imitating the pseudo-spectral method,which can control the amount of energy input to the system,facilitate adjustment of parameters,and control the application of external forces to different flow field scales.The second chapter explains the specific setting of the external force term and how to ensure different turbulence intensities for the multi-relaxation time lattice Boltzmann method,and gives a detailed introduction to the parallel strategy of turbulence statistics and the program.There are two ways to deal with the discrete phase in this article:One is that when the discrete phase is a particle with very small size and inertia,the particle is simplified as a point particle,Due to the small influence of particles on the flow field,the influence of particles on the flow field is not considered in the calculation for the convenience of calculation.The other is that the discrete phase is particles with finite size and inertia.Under this model,it is necessary to explicitly solve the non-slip boundary conditions of the particle surface,and has a relatively accurate analysis of the interaction between particles and the flow field as well as the interaction of particles.The first selected model is the Particle-Resolved Model,which only considers the normal effect for the particle interaction,but does not consider the tangential effect of the particle.This article attempts to add the tangential effect of particle interaction;Another research strategy uses the Point-Particle Model,but the Point-Particle Model is often one-way coupled,that is,it does not consider the collision between particles and the impact of particles on turbulence.In this paper,we try to use the DEM Soft-Sphere Collision Model under the Point-Particle Model to add particle interaction and study its collision statistics.The fourth chapter is the numerical simulation of the Particle-Resolved Model for modifying the lubricating and collisional force.This chapter first verifies the single-phase turbulent flow field.Next,this chapter compares the collision statistics of the modified Particle-Resolved Model with the collision statistics of the one-way coupled Point-Particle Model.The general characteristics of particle aggregation and transportation under this framework are obtained,and the reasons for the differences in the data between the two are analyzed,and the deficiencies of the work done are also analyzed.In Chapter 5,the Point-Particle Model combined with the DEM Soft-Sphere Collision Model studies the distribution characteristics of solid particles and the impact of collision characteristics under different turbulence intensities,and compares them with the one-way coupled Point-Particle Model.In this chapter,the effects of different particle sizes and densities on the distribution characteristics and collision characteristics of solid particles are further studied...