Numerical simulation of boiling on unstructured grids

Abstract

A numerical method for the simulation of multiphase flows with phase change on unstructured grids is presented. Based on the work of Tanguy et al. [31] using a Level Set/Ghost Fluid Method coupling for two-dimensional axisymmetric cartesian grids, we extend the method to two- and three-dimensional unstructured grids with the aim of taking a step towards realistic boiling simulations in industrial context. The mass transfer rate at the interface accounting for phase change is computed as a function of the liquid and vapor heat fluxes at the interface and of the latent heat of the fluid by means of a new framework improving the accuracy of differential operators. The mass transfer rate is then used in the projection method to solve Navier-Stokes equations and in the advection equation of the Level Set function to account for the interface movement due to phase change. An immersed Dirichlet boundary condition is imposed at the interface to ensure that boiling always occurs at saturation temperature. We demonstrate the accuracy of our method first in the case of a static growing bubble with a fixed constant mass transfer rate, and second with a mass transfer rate computed from the thermal fluxes at the interface. In both cases, the bubble radius at final time converges with grid refinement towards the theoretical value.