| Gas-particle two-phase flow widely exists in aerospace fields,people’s production and life.Millimeter,micron scale space junk,meteorite fragments can cause fatal damage to spacecraft;Particles sucked into aero-engines can seriously threaten engine safety.In solid rocket motor,particle diameter and mass fraction have great influence on engine performance.In the military field: cluster bombs and explosives dropping,in the chemical industry: various fluidized beds,in pharmaceutical,food and bioengineering field: pneumatic conveying and screening,in the fields of energy and power generation: pulverized coal combustion and sand-laden oil and gas transportation,in people’s life: sandstorms and haze weather,and so on are all closely related to the gas-particle system.It is of great significance to the optimal design of gas-particle two-phase flow and the precise control of some natural phenomena on studying the interaction between gas and particle and clarifying the multiphase dynamic behavior of gas-particle system.Therefore,in this paper,gas-particle two-phase flow in a pipeline is studied based on Euler multiphase flow model and CFD-DEM model respectively,and the characteristics of the two gas-particle numerical models are compared.the main research includes:Firstly,the significance of studying gas-particle two-phase flow,main research methods,various numerical simulation methods,research status and achievements are introduced.In-addition,the theoretical part,the governing equations of gas-particle numerical model coupled with Eulerian Multiphase Model and CFD-DEM and the governing equations of sub-models are introduced.Then,Eulerian Multiphase Model and CFD-DEM model are used to study the flow characteristics of particles in horizontal straight pipe and L-shaped pipe respectively,and the characteristics,commonness and differences of the two numerical models are compared and analyzed.As for the gas-particle two-phase flow in a horizontal straight pipe,the results show that when the initial velocity of the gas flow is high and the particle diameter is small,the simulation results of the two numerical models are in good agreement;However,when the initial velocity of airflow is small and the particle diameter is large,the results of the two numerical models are quite different: When the initial velocity is small,the particle flow is partial flow under Eulerian Multiphase Model simulation,but under CFD-DEM simulation,because of the accumulation of particles,the collision,extrusion and friction between particles have great influence on the whole gas-particle system,which makes the particles appear complex sand dune flow in the pipeline;When the particle diameter is larger,the chance of the particle contact with the pipe wall increases,which makes the trajectory more complicated and stochastic.This feature can be well simulated by CFD-DEM model,but Eulerian Multiphase Model can not.As for the gas-particle two-phase flow in L-shaped tube,the results show that under the Eulerian Multiphase Model simulation,the velocity change of particle flow through elbow is gentle and the velocity loss is small;However,under CFD-DEM simulation,the particle velocity changes more violently and the velocity loss is greater;The main difference between the two models is that under Eulerian multinomial flow simulation,particles flow along the pipe wall to the bottom of the pipe due to the Conda effect,while under CFD-DEM simulation,particles deposit along the direction of gravity to the bottom of the pipe.The main difference between the two models is that under Eulerian multinomial flow simulation,particles flow along the pipe wall to the bottom of the pipe due to the Conda effect(also called the wall-attached effect of fluid).Finally,the simulation results of the two models are compared with the experimental and research conclusions of other scholars,and it is concluded that in most cases,the conclusions of CFD-DEM coupling model are closer to the real situation.Finally,introduces the engineering application of CFD-DEM model: Taking 90°elbow as the object,an asymmetric spherical elbow is designed for pneumatic transport pipeline to improve the particle flow characteristics in the elbow,and transport efficiency.The particle flow and erosion characteristics are studied by CFD-DEM coupling method.The influence of the radius of the elbow sphere and the eccentricity of the inlet and outlet pipes on the flow and dispersion characteristics of particles is discussed.Compared with four kinds of elbows(common elbow,blind tee,elbow with vortex chamber and spherical elbow),the results show that the asymmetric spherical elbow can greatly improve the particle dispersion characteristics at the outlet and the transportation efficiency of particles in the pipeline on the basis of reducing elbow erosion,gas energy loss and preventing particle breakage. |
