Volume of Fluid Method
Volume of Fluid Method (VOF) is a numerical method of free surface approximation. It is classified as Euler method. Euler methods are described by a grid, which can be either stationary or non-stationary. In case of non-stationary grid, the grid motion is determined by the change of the surface shape. This method allows to follow the shape and position of the surface. The flux motion is described by Navier-Stokes equations, which should be solved separately.
The method is based on the use of a fractional function C, which is determined as an integral of the characteristics fluid functions in a cell. C is a continuous function, with 0 ≤ C ≤ 1. If the cell is empty (i.e. there is no fluid), C = 0. If the cell is full, C = 1. Derivative of the fractional function must be equal to zero:
where v is the fluid velocity, and Ur is an artificial force that “compresses” the region under consideration.