Study Of Particle Accumulation Behavior In Vortex And Rotating Flows

The motion of particles in vortex and rotating flows is of essence in both nature and industry.In the meanwhile,particle preferential accumulation is a common phenomenon in particle-laden flows.In this thesis,particle accumulation behavior in vortex and rotating flows is investigated numerically by CFD-DEM method.The systems studied include both gas-particle and liquid-particle systems.Both one-way and two-way couplings are considered,and particle-particle and particle-wall collisions are resolved by hard-sphere or soft-sphere approaches.In the first part,the accumulation behavior of heavy particles in circular bounded vortex flows induced by two small rotating cylinders,which belongs to gas-particle system,is studied.The moving boundaries and big circular wall are resolved by immersed boundary method(IBM),and effects of particle Stokes number,flow Reynolds number,center-to-center distance between the circular domain and each small cylinder(r1)are examined systematically,and results under one-way and two-way couplings are compared with each other.It is found that there will be 5 stable particle accumulation patterns under one-way coupling,whereas particles move more irregular and the stable accumulation patterns cease to exist under two-way coupling.Also,more particles will accumulate on the circular wall as Stokes number and Reynolds number increase,whereas less particles will accumulate on the circular wall as r1 increases.Moreover,due to strong inter-phase coupling,many more particles will accumulate on the circular wall under two-way coupling than under one-way coupling.The findings in this part will help to improve the design of some industrial equipment aiming at separating or trapping particles.In the second part,the inertial focusing of particles in circular Couette flows,which is a liquid-particle system,is investigated.First,the numerical model is validated by comparing results from the simulations in this work with those from the experiments reported in the literature,and then effects of lubrication force,Reynolds number and particle density are investigated comprehensively.It is shown that without considering lubrication force,there will be some discrepancies between the results from the simulation and those from the experiment,and particles are more scattered.And as the Reynolds number increases,particle equilibrium position will move closer to the outer wall.What's more,as the particle density decreases,particle equilibrium position will move closer to the inner wall.