A DNS study of droplet spreading and penetration on a porous medium

Abstract

We have investigated the dynamics of droplet spreading and liquid penetration at the surface of a porous medium at zero-gravity condition. A coupled IBM-VOF finite volume code has been used to perform pore-scale level fully resolved numerical simulations. The geometrical details of the solid porous matrix are resolved by a sharp interface immersed boundary method (IBM) on a Cartesian grid, whereas the motion of the gas-liquid interface is tracked by a mass conservative volume of fluid (VOF) method. At small scales, the contact line dynamics mainly govern the spreading and capillary penetration. In the present case, the motion of the gas-liquid interface at the immersed boundary is modeled by imposing the contact angle as a boundary condition at the threephase contact line. All the simulations are performed using a model porous structure that is approximated by a 3D cubic scaffold with cylindrical struts. The porosity (e) of the porous structure is varied from e = 0 (flat plate) to e = 0:65 and the equilibrium contact angle Q is varied from Q = 30X (hydrophilic) to Q = 135X (hydrophobic). The effect of porosity and contact angle on the transient evolution of penetration and spreading have been presented and compared with classical models.