Study on the factors affecting dispersity of porous media by SPH simulation in solute transport

Smoothed particle hydrodynamics (SPH) method is used to simulate the dispersion process of saturated porous media from the physical nature of fluid particle movement in pore scale. On the basis of simulation experiments, the influencing factors of dispersity are discussed. By discretizing the Navier-Stokes equations, the SPH flow model is built to describe the pore water flow. Similarly, the solute diffusion model is built to describe molecular dispersion based on Fick's law. When solving the diffusion-convection case of low Peclet number, the numerical results coincide with analytical solutions well, which verifies the accuracy of the models. Adopting the models, a 2-D simulation experiment is achieved for viscous fluid at a constant velocity to penetrate a thin layer of porous medium at high Peclet number. The features depicted by velocity contour plot agree with the real behavior of viscous fluid. To evaluate the effect of velocity differences on dispersity, three ideal micro winding tubes are established with the tortuous pathways controlled the same. The results show the difference between fluid particles'velocity has a close relationship with dispersity. Then the relationships between dispersity and the structure parameters of porous media are discussed based on the results of simulation experiments with random grain-size porous media. The conclusion proves that the increase of tortuosity and nonuniform coefficient tend to result in the enhancement of the dispersion effect. And there is a negative correlation between porosity and dispersity. © 2019, China Water Power Press. All right reserved.