CFD simulation of multiphase flows

By definition, a two-phase flow involves two fluids. These fluids may be in different physical states (gaseous, liquid or solid), or simply be in the same state with different properties. There are many situations where several fluids coexist, both in industrial processes and in our environment (if there are more than two, the flow is said to be multiphase). When these fluids are immiscible, the numerical simulation of such a system requires the interface separating them to be defined and tracked, as this is one of the main quantities used to characterise its evolution.

In our immediate environment, water in its liquid state and air often coexist. In the world of hydraulics, we talk about free surface flow (flow where the free surface is subject to atmospheric pressure). This page provides an example of modelling such a flow, with a simulation of two-phase water/air flow in a storm overflow.