Modelling Of Flow And Diffusion In Porous Media Based On Smoothed Particle Hydrodynamics(SPH) Method

The phenomenon of multiphase flow and solute diffusion through porous media involves a variety of nonlinear physical phenomena,such as turbulent flow,seepage flow,energy dissipation,and convection-diffusion process,which is a nonlinear fluid mechanics problem with a very complex mechanism.This phenomenon,which is common in engineering applications such as groundwater pollution prevention,coastal environmental protection,and chemical catalysis processes,plays a key role in these problems.Therefore,it is important to research multiphase flow and solute diffusion between porous media for the scientific significance and engineering application value.The Lagrangian nature of smooth particle hydrodynamics(SPH)is so suitable for dealing with such complex multiphase flow problems,but it is remarkably sensitive to the boundary treatment method.The dynamic boundary condition,which has been widely accepted,will generate asymmetrical errors,and the repulsive force is insufficient.Based on the dynamic boundary conditions,we proposed the improved dynamic boundary condition by expanding the state equation into a higher order,changing the shape of the boundary particle support domain,and introducing the correction coefficient of the boundary particle kernel function.Since the original porous flow model in SPH method handles the interaction between porous medium and fluid based on the particles representing the porous medium,its accuracy and stability will be affected by the distribution of the porous medium particles,and there will be an abnormal distribution of density.The improved porous flow model proposed in this paper calculates the volume fraction changing rate and interphase resistance based on fluid particles,obtaining a smooth and continuous physical field,effectively improving the numerical accuracy and stability when using the SPH method to simulate the flow of porous media.Based on the improved flow model of porous media,and combined the convectivediffusion equation with the two-phase mixing theory,the diffusion equation considering the fluctuation of volume fraction and density was deduced,and a convective-diffusion model through porous media suitable for the SPH method was proposed.A series of typical numerical experiment results show that improved dynamic boundary condition can effectively eliminate the asymmetric error at the boundary and improve the anti-penetration ability;the improved porous flow model effectively solves the truncation error problem in the original porous flow model,and can simulate the multiphase flow through porous media;the porous convection-diffusion model through can effectively reflect the influence of porous media on the diffusion process,and accurately capture the solute diffusion process and spatial characteristics of concentration distribution in the complex multiphase flow through porous media.