Towards a mass-conserving volume-of-fluid method for incompressible gas-liquid flows with phase change

We consider incompressible gas-liquid flows in which the liquid evaporates or condenses. A particular challenge in numerically simulating these flows is to capture or track the gas-liquid interface during phase change while conserving mass. The main computational difficulty is that the fluid velocity is discontinuous across the gas-liquid interface leading to the velocity field having locally non-zero divergence (∇ · u ≠ 0), whereas existing volume-of-fluid (VoF) methods conserve mass only if ∇ · u = 0. In this talk, we will present two general approaches for advecting the VoF function in the presence of phase change: (i) compute the interface velocity explicitly and use it to update the VoF field and (ii) compute a divergence-free extension of the liquid velocity to advect the VoF field, and include a source term in the advection equation to account for the phase change. Our results show that only the latter approach leads to zero-machine mass conservation.