Modeling of surface tension and contact angles with smoothed particle hydrodynamics

A two-dimensional numerical model based on smoothed particle hydrodynamics (SPH) was used to simulate unsaturated (multiphase) flow through fracture junctions. A combination of standard SPH equations with pairwise fluid-fluid and fluid-solid particle-particle interactions allowed surface tension and three-phase contact dynamics to be simulated. The model was validated by calculating the surface tension in four different ways: (i) from small-amplitude oscillations of fluid drops, (ii) from the dependence of the capillary pressure on drop radius, (iii) from capillary rise simulations, and (iv) from the behavior of a fluid drop confined between parallel walls under the influence of gravity. All four simulations led to consistent values for the surface tension. The dependence of receding and advancing contact angles on droplet velocity was studied. Incorporation of surface tension and fluid-solid interactions allowed unsaturated flow through fracture junctions to be realistically simulated, and the simulation results compare well with the laboratory experiments of Dragila and Weisbrod.