Conservative and Nonconservative Form
If the velocity is divergence free, that is, if
(11-4)
the volume (area for 2D problems) bounded by the interface should be conserved if there is no inflow or outflow through the boundaries. To obtain exact numerical conservation in cases where Equation 11-4 is not fully satisfied, switch to the conservative form
(11-5)
in Settings window for The Level Set Interface.
Using the conservative level set form, exact numerical conservation of the integral of ϕ is obtained. However, the nonconservative form is better suited for numerical calculations and usually converges more easily. The nonconservative form, which is the default form, only conserves the integral of the level set function approximately, but this level of conservation is sufficient for most applications.
When the Level Set interface is coupled to a fluid-flow interface by means of The Two-Phase Flow, Level Set Coupling Feature, exact conservation of the integral of ϕ is obtained using the nonconservative form, provided that the discretization order of the level set variable is equal to or lower than the order of the pressure.
Rising Bubble: Application Library path CFD_Module/Multiphase_Flow/rising_bubble_2daxi