Simple VOF simulation failure
 

I was having trouble with a more complicated VOF simulation so I tried reducing the complexity to the most simple case possible: a box filled 80% with water, air the top, and a pressure outlet. Gravity acts downward, holding the water in the container. When I run the simulation I expect nothing to happen, however the water disappears and the simulation is garbage. Can anyone advise me on any mistakes I made?


FLUENT SETTINGS
General
- Gravity, -9.81 m/s2 in y-direction
Models
- Multiphase: VOF
- Viscous: k-e, Std WF
Materials
- air and water
Boundary Conditions
- pressure outlet, air backflow
- rest are walls
Initialization
- standard, initialized at 0
- patched to fill 80% of box with water
Run Calculation
- 5 iterations
- 100 iterations