[Charly23]

Hi everybody,
I am trying to simulate open channel flow using InterFoam solver and k-omegaSST for turbulence modelling. What I know is the flowRate at the inlet and the water level at the outlet. I have tried all kinds of different BC but I always get problems with high velocities in the air and water phase, which lead to a very small time step (picture2). When I used static pressure as outlet condition for the water phase: air flows into the water domain (picture1). That is why I choose the velocity condition for the outlet of the water and the air outlet is included in the open BC. In general, I am interested in the velocity ditribution of the water surface. My channel is relatively shallow, but I still want to do it in 3D. (length 19m and water depth 0.2m)
I therefore assume a problem with my initial or boundary conditions or with my mesh:

Initial condition: constant water level at 0.2 m, zero velocity (0 0 0) everywhere

Inlet BC:
1. U: fixedNormalInletOutletVelocity
2. p_rgh: fixedFluxPressure
3. alpha_water: inletOutlet


Inlet_Air BC:
1. U: pressureInletOutletVelocity
2. p_rgh: zeroGradient
3. alpha_water: inletOutlet

Outlet BC:
1. U: fixedNormalInletOutletVelocity
2. p_rgh: fixedFluxPressure
3. alpha.water: inletOutlet

Open (Including the air phase outlet):
1. U: pressureInletOutletVelocity
2. p_rgh: totalPressure
3. alpha.water: inletOutlet

Channel bottom & side walls:
1. U: movingWallVelocity
2. p_rgh: fixedFluxPressure
3. alpha.water: zeroGradient

I'm happy to provide you with more information (i.e. BC for k, epsilon and nut) and would be really grateful if I could get some advice on how to solve this problem. Thanks in advance!

[Charly23]

Sorry, here is the other picture I was talking about.