[pechwang]

Hi everyone,

I used interFoam to simulate a free falling fluid example. The geometry is very simple, it is a 3*3*50 cm tube. Front, back, left and right surfaces are walls and using wall boundary condition. Top and bottom surfaces are treated as inlet and outlet patch. Initially it is full of water. At time 0, the fluid falls and goes out through the bottom. Air enters the domain through top.

The boundary conditions that I used is shown below:

Top: zero-gradient for the pressure and fixedValue (uniform 0) for alpha1
bottom: fixedValue (0) for the pressure and fixedValue (uniform 0) for alpha1
Walls: zero-Gradient for pressure and alpha1

I have two issues in my simulations:

1. The residual for p_rgh is about 0.001, which is large indicating it is not converged.
2. The time for fluid to exit the tube is about 0.18 sec. However it should be about 0.3 sec based on hand-calculation.

Can someone tell whether I have the right BCs for this problem? Can someone give advice how to make the simulation converged and achieve a reasonable free fall time?