Numerical Simulation Of Viscoelastic Flow Past A Cylinder And Particle Two Phase Flow With Lattice Boltzmann Method

Viscoelastic fluids exist widely in nature and production.The problem of viscoelastic fluid flow and the movement and sedimentation of particles in viscoelastic fluid are of great importance for polymer molding.The elastic effect of viscoelastic fluid and the complexity of two-phase flow numerical simulation makes the traditional CFD method still have some difficulties in this aspect.Lattice Boltzmann method,as an efficient and convenient mesoscopic simulation method,has a natural advantage in dealing with multiphase problems.The main content of this paper comes from the National Natural Science Foundation Project "Numerical simulation of viscoelastic fluid extrusion swell and multiphase flow based on lattice Boltzmann method",the purpose is to simulate and analyze the flow law of viscoelastic fluid and multiphase flow with lattice Boltzmann method.The main contents of this paper include:First,Aiming at the two-dimensional expansion flow problem of viscoelastic fluid,LBM was applied to solve the incompressible Navier-Stokes equation and Oldroyd-B constitutive equation,corresponding boundary processing scheme was given,the influence of Reynolds number Re and Weissenberger number Wi on viscoelastic fluid flow was analyzed.Simulation results show that:when Wi is constant,with the increasing of Re,the vortex center is far away form the corner,Lr increases.Re has less influence on Axx.When Re is constant,with the increasing of Wi,the variation of Axx and Axy at outlet is obviously increased,the vortex center tends to the corner,L,decreases.Then,as for two-dimensional flow around cylinder in viscoelastic fluid,Curvilinear boundary is treated by processing scheme which combining non-equilibrium extrapolation and spatial interpolation,and the force of cylinder is calculated by momentum exchange method.The influence of Wi on the flow behavior of flow around cylinder in viscoelastic fluid is analyzed.The streamline,the distribution of the configuration tensor A and the drag coefficient Cd at different Wi are obtained.Simulation results show that:For the flow around a cylinder,the maximum value of Axx appears in the vicinity of the cylinder and the wake region,with Wi increaseing(0.1?Wi?1.2),Cd decreased first and then increased,which are in good agreement with the results of FVM.For the flow around a elliptical cylinder,the variation trend of Cd about Wi is similar to that in flow around a cylinder,and Cd decreases with the increase of a(0.667???1.5).For the flow around vertical double cylinder,when the distance between cylinders S?R(cylindrical radius),with the increase of S(1.2R?S?2.0R),Cd decreases and the maximum velocity and the maximum value of Axx gradually transfer from cylinder to wall to two cylinders.With the decrease of S(0.8R?S?2.0 R),the curve form of velocity on the center has changed.Finally,based on steady flow of viscoelastic sudden expansion flow and LBM-Lagrange,the motion settlement of the particles in the viscoelastic expansion flow was studied.The influence of particle initial position,particle mass,Re and Wi on the particle movement and settlement was analyzed.The result shows that:the location of the settlement point is increased with the increase of Re,and the influence of Wi on the position of the drop point is small.