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outlet boundary condition in alpha.water with interFoam for faster performance

Hey there,

I got an issue with setting a better outlet boundary condition in an interFoam simulation.

The case:
I got an reservoir with water at free surface conditions and air (so two phases). I got an outlet/inlet at the bottom of the reservoir from where water could get in and out. The top of the reservoir is with an atmosphere patch where air could get in but no water out.

The issue is as followed:
I don't get any problems for the case that water is flooding in the reservoir.
But the problem is my case where the water is flooding out. When I set (in my opinion) the right boundary conditions the simulation is really slow, like 12 seconds of simulations with 12 hours and 60 cores running.
So I want to simplify it and just let water out at the outlet. So i tried just to set the outlet patch in alpha.water to fixedValue with value 1. It's running a lot faster but max (alpha.water) is rising really slowly so the case is running for some hours but after around 70 simulation seconds the time steps decrease massively and stops.

my outlet BC are for
U: inletOutlet
p_rgh: fixedValue
alpha.water: works with inletOutlet but is really slow
alpha.water: fails after some hours of calculating with fixedValue

Does anyone have any experience how to set the boundary condition for my outlet at alpha.water to let just water out or speed my calculation up and not using fixedValue?

Cheers,
Oli

Hi Oli,

if I got you right you are simulating an open tank with outflow?
Try these boundary conditions:

outlet

Code:

U: inletOutlet

p_rgh: fixedValue

alpha.water: inletOutlet

inlet

Code:

U: pressureInletOutletVelocity

p_rgh: totalPressure

alpha.water: fixedValue

Quote:

Originally Posted by pbalz (Post 669367)

Hi Oli,

if I got you right you are simulating an open tank with outflow?

Yes, with inflow and outflow. Where the inflow is perfectly fine but the calculating time for the outflow is really slow, so I wanted to speed it up, because I can't wait that long...

Quote:

Originally Posted by pbalz (Post 669367)

Try these boundary conditions:

outlet

Code:

U: inletOutlet

p_rgh: fixedValue

alpha.water: inletOutlet

Thanks, wasn't clear enough I think, sorry for that. Those are exactly the BCs which makes running the case really slow...
Got any other idea how the boundary condition could be set for alpha.water?

Thanks a lot in advance :)

Cheers,
Oli

Quote:

Those are exactly the BCs which makes running the case really slow...

Ups, sorry...
So are you using the same inlet boundary conditions as I posted?
In fact I simulated a similar problem a few weeks ago and my inlet boundary conditions made the solver slow down. In my case these exact BCs worked out to deliver a fast solution without decreasing timesteps.

If this doesn't work out I have no other idea what could be the problem...

free surface goes down versus time

Hello Alls,
I use OF1812 and run case from tutorial waveMakerFlap and modify height of wave at inlet from 0.06 to 0.1m
Everything goes well but the free surface drop at the outlet. Can you give me some hints ?
highly appreciated your comments.

Quote:

Originally Posted by fsifsi (Post 773173)

Hi
Have you found the answer to this question?

Cheers