mass conservation in VOF method
 

As we know, the advantage of VOF method is to conserve mass well.

But there will be some round off error after the advection calculation. For example, F could be less than zero or greater than one. We should reset these values back to the 0-1 range. However, after the adjustment, the total mass could be not equal to the initial value.

How to make sure the mass exactly equal to the initial one?

hi,
Maybe you need not set F equal zero or one, instead, a cell is defined to be empty when F is less than eps(=10e-6) and full when F is grater than 1-eps.
PS: DO you model multiphase flow used VOF method with software(Fluent) or programming codes by yourself?

I am programming the code for two phase flow.

If I don't adjust F in those situations, F may lose its point in some cases. For a case in which F=1.02, however, the defination of F is the ratio of fluid and cell volume. It cannot be greater than one. Thus, if I do the dambreaking case. At the first glance, the total F is conserved. The actual fluid volume is also decreasing in fact.