The following animations show an example of two-phase (gas and liquid) flow under dam break. Here air represents the gas and water does the liquid.

For this simulation, the VOF (volume of field) method is used and the VOF method is a free surface modelloing technique. In fact, the free surface of water (precisely, the interface between water and air) is expressed by the percentage (rate) of water (or air) occupied in a cell (as nomencrature, phase fraction).

In the animations, blue colour denotes 100% air while red colour does 100% water. Therefore green colour means that 50-50 mixing of water and air.

A mixer vessel with a stator and a rotor is a surface boundary. The stator has four partitions and the rotor has four impellers. Furthermore, the rotor is rotating at an angular velocity (ω) 6.2831853 rad/s.

Both the inner wall of the stator, partitions and the rotor (and its impellers) have no thickness and this means that flow-wall interaction is not taken into account. Therefore one can concentrate only on the flow behaviour.

However, the surface tension of fluid is taken into account (σ=0.05 [N/s] for both water and oil). In this case, two fluids are considered and these two are both Newtonian. The other physical properties, kinematic viscosity (ν [m²/s]) and density (ρ [kg/m³]) are ν_water=ν_oil=1e-4, ρ_water=1000, ρ_oil=500.

(All) The simulation time is 8 seconds and the animation is composed by the snapshots of every 0.125 seconds.
(Left) Phase fraction of water. The red colour denotes the flow of water.
(Bottom Left) Pressure of the fluids.
(Bottom Right) Velocity of the fluids.