A Study On The Flow Behavior Of Backward-facing Step Based On LBM

The flow of crude oil in underground reservoirs is complicated.Underground reservoirs are dominated by porous media which contains a significant number of stepped structures.Therefore,this paper selects the backward-facing step flow as the research object.The flow behavior of the single-phase of crude oil and the multi-phase which constituted by crude oil and sand grains are analyzed.In this thesis,the lattice Boltzmann method(LBM)is used to simulate the three-dimensional backward-facing step flow.Single relaxed BGK model is adopted to solve the single-phase and multi-phase backward-facing step flow.LBM-LES model is employed to simulate the high Reynolds number condition.The result of single-phase simulation shows that a vortex structure which is similar to the step in size is an obvious feature of the backward-facing step flow.Obviously,a large velocity gradient between the fluid in the vortex and outside the shear separation layer is observed.At the same time,a certain velocity gradient between the fluid in the vortex is also observed.In addition,the velocity distribution of the fluid along the x-direction and y-direction is regular.The distribution of velocity magnitude is also has a certain rule.According to the comparison,the characteristic of backward-facing step flow will change if independent variables such as ER is changed.The result of multiphase simulation shows that the flow characteristics of the oil are similar to the single phase's.Therefore,solid's and oil's are different.After the flow is stable,the solid phase presents a backflow behavior but the vortex is not observed.However,the deposition of sand grains near the step is observed.The distribution of the depositional particles indicates that the number of depositional particles decrease when they come closer to the step and the bottom.It is found that the amount of depositional sand grains decrease with the increase of the grain size,Re and the height of step.When the viscosity of liquid phase is low,the amount of particles decrease with the increase of viscosity.However,the relationship becomes opposite when the viscosity is higher.