You are right about having mixture velocity only in the VOF. This is the downside of the VOF. However, it is the best that can capture the interface. What you are showing in the demonstration sketch , could be captured by VOF. Eulerian model, you have to solve for the interracial area and you will not find pure liquid or gas in most cells. Give it a try and please let me know if it works.nRotating the wall only with the rib, will definitely need re meshing. But as the geometry is not complex, layering would work perfect. The downside of this is the time step. You have to decrease the time step to avoid having negative volume ... with fine mesh, this is going to be very boring. nThe velocities at the interface are really strange. Could be a convergence issue! .. try decreasing the time step and increasing the number of iterations per time step. n