Modeling of van der Waals force with smoothed particle hydrodynamics: application to the rupture of thin liquid films

Xiaoyang Xu, Mohar Dey, Mingfeng Qiu & James J. Feng

Appl. Math. Model. 83, 719-735 (2020).

Abstract - The rupture of thin liquid films driven by van der Waals force is of significance in many engineering processes, and most previous studies have relied on the lubrication approximation. In this paper, we develop a smoothed particle hydrodynamics (SPH) representation for the van der Waals force, and simulate the rupture of thin liquid film without resort to lubrication theory. The van der Waals force in SPH is only imposed on one layer, i.e., the outermost layer of fluid particles, where a weighting function is deployed to evaluate contributions of particles on or near the interface. However, to obtain an accurate hydrostatic pressure in reaction to the van der Waals force, a smaller smoothing length is used for the calculation of weighting function than that used for SPH discretizations of the bulk fluid. The same surface particles are also used to model the surface tension. To deal with the rupture of thin liquid film with a very small aspect ratio ε (ε = thickness/length), a coordinate transformation is introduced to shrink the length of the liquid film to achieve accurate numerical resolution with a manageable number of particles. As validations of our physical model and numerical algorithm, we simulate the hydrostatic pressure in a stationary film and the relaxation of an initially square droplet, and compare the SPH results with solutions in the literature. The method is then applied to simulate the rupture of thin liquid films with moderate and small aspect ratios (ε = 0.5 and 0.005). The SPH results are compared with those obtained by finite elements. The convergence of the method is verified by refining particle spacing to four different levels. The effect of capillary number on the rupture process is analyzed.