fluent :A simple VOF example Mass nonconservation
 

There is 0.4kg/s of water at the inlet, and approximately equal to 0kg/s of air at the outlet, but the interior area does not gain 0.4kg of mass after calculating the 1s gap.

The strange thing is that the operations all converge

This is the velocity inlet and the pressure outlet. Its structure is not complicated

Where mass go?

It feels like a bug, maybe the total mass calculation is wrong,maybe the calculated speed is wrong.

or before reaching the end change of import and export data, the data in the process may only be the intermediate process of calculation, but can not be used as any result (although it is instantaneous calculation).I hope I am wrong.

Have you had the same problem? Or solved the problem? Please give me a reply, thank you!

I have the same issue like yours. I tried to refine the mesh and decrease the time step, but none of them worked. According to other's post, it should be an accumulated error in VOF, only way to solve it is to tighten your convergence criteria and make sure to converge at each time step.