Boundary condition in a multiphase flow
 

Hi to all,
I have a problem in the setting of the boundary condition of a multiphase flow using interfoam.
My case is summarized as follow:
at the initial time t=0 the right wall of a closed tube completely filled with a liquid is removed, allowing the liquid to exit the domain and, at the same time, allowing the gas to enter.
I set this boundary condition:
U) fixedValue (0,0,0) in the pipe wall and in the left inlet, zeroGradient in the outlet
p) zeroGradient in the pipe wall and in the left inlet, fixedValue of 1 atm in the outlet
alpha) zeroGradient in the pipe wall. For the left inlet and the outlet I tried some case:
- InletOutlet/InletOutlet
- zeroGradient/zeroGradient
- zeroGradient/InletOutlet
- zeroGradient/calculated
but all this case give me strange solution

Someone have an idea to set the boundary condition for this case?
thank to all