Study Of REV-scale Flow In Porous Media Based On Lattice Boltzmann Method

The lattice Boltzmann method is used to study the flow around two-dimensional solid square cylinder,porous square cylinder and square cylinder covered with thin porous media,and most of the work is carried out in the scale of Representative Elementary Volume(REV).The main work is as follows:1.Theoretical analysis and numerical simulation of the flow around two-dimensional solid single square and parallel cylinders are carried out respectively.A series of streamline and vorticity diagrams of the flow field around a square cylinder under different Reynolds number and blockage ratio are drawn.The critical Reynolds number for steady loss and the Reynolds number for the beginning of the bright Karman vortex street are found.It is found that the Karman vortex street behind the cylinder disappears gradually with the increase of the blocking ratio,and the small vortices formed on the upper and lower walls interweave with the large vortices falling off,leaving a long return area.The average resistance coefficient and the maximum lift coefficient also increase and decrease with the increase of the blocking ratio.For the flow around two parallel cylinders,the streamline diagram and vorticity diagram of the flow field under different spacing ratio are drawn,and the value of the most obvious spacing ratio of the two square cylinders is found,as well as the value of the critical spacing ratio of the flow field from the deflected flow to the symmetrical flow.2.A lattice Boltzmann model in REV scale is used to simulate the flow around a two-dimensional porous square cylinder.The effects of Darcy number,porosity and Reynolds number on the flow field and the forces on the cylinder surface are studied.The streamline diagram and vorticity diagram of the flow field under different parameters,as well as the curves of the drag coefficient and lift coefficient of the square cylinder surface with different parameters are given.Through analysis,it is found that the change of Darcy number has a greater impact on the flow around the porous square cylinder.3.The flow around a square cylinder covered with a thin layer of porous media in two dimensions is studied.The effects of the four parameters of the thickness of the porous medium,Darcy number,porosity and Reynolds number on the flow field and the force on the surface of the square cylinder are analyzed.The analysis of the streamline diagram,the vorticity diagram and the change curve of drag coefficient and lift coefficient found that the least influence on the flow field among these four parameters is porosity,and the most obvious influence is the Darcy number.As the Darcy number increases,the maximum drag coefficient,minimum drag coefficient,and maximum lift coefficient all increase first and then decrease.They all have a maximum value when the Darcy number changes between and.To sum up,the lattice Boltzmann model established in this paper regards solid,fluid and porous materials as porous media composed of different permeability and porosity,which effectively overcomes the interface coupling between three different media problem.By comparing the method in this paper with other methods,the results show that the lattice Boltzmann method simulation is achievable,correct and effective.