  In this paper, we aim to investigate the implementation of contact angles in
the pseudopotential lattice Boltzmann modeling of wetting at a large density
ratio. The pseudopotential lattice Boltzmann model [X. Shan and H. Chen, Phys.
Rev. E 49, 2941 (1994)] is a popular mesoscopic model for simulating multiphase
flows and interfacial dynamics. In this model, the contact angle is usually
realized by a fluid-solid interaction. Two widely used fluid-solid
interactions: the density-based interaction and the pseudopotential-based
interaction, as well as a modified pseudopotential-based interaction formulated
in the present paper, are numerically investigated and compared in terms of the
achievable contact angles, the maximum and the minimum densities, and the
spurious currents. It is found that the pseudopotential-based interaction works
well for simulating small static (liquid) contact angles, however, is unable to
reproduce static contact angles close to 180 degrees. Meanwhile, it is found
that the proposed modified pseudopotential-based interaction performs better in
light of the maximum and the minimum densities and is overall more suitable for
simulating large contact angles as compared with the other two types of
fluid-solid interactions. Furthermore, the spurious currents are found to be
enlarged when the fluid-solid interaction force is introduced. Increasing the
kinematic viscosity ratio between the vapor and liquid phases is shown to be
capable of reducing the spurious currents caused by the fluid-solid
interactions.
