It is a surface-tracking technique applied to a fixed Eulerian mesh where the Navier Stokes equations which describe the motion of the flow have to be solved separately.

The method is based on the solution of a transport equation for variable ‘C’ (often also referred as indicator or color function) for the liquid phase.

We have 0 < C < 1 in cells cut by the interface S and C = 0 or 1 away from it.

The VOF method doesn't explicitly track the interface, it reconstructs the interface based on calculate the volume fraction of fluid . The Color Function also cannot be solved easily. There are already several method to approach, different approach gives different accuracy, the most popular is PLIC (Piecewise Linear Interface Calculate). In a 3D space, the interface can be described by n_{x}+n_{y}+n_{z}=a.