SimScale CAE Forum

Outlet boundary conditions (free spoud)


Hey Forum,
i have a question about the boundary conditions. At my testcase i like to measure the flux over a seperator.
I think the measurement with Paraview works fine. The only problem is, how i get the water away ?

Position of the calculator, the flux and alpha phase 0 - 1.

At this system the boundary contition, are only an inlet velocity and a “ceiling vent”.
So the water dont go out of the system. If i simulate longer or a higher velocity rate, the left chamber will fill up with water.

This picture shows the model system and the boundary conditions i want.

Model system and boundary conditions

I tried a few sim runs with different boundary conditions, but only the runs without an outlet finished.
The water should leave the model system, it does not have to follow a fixed value, rate or mean flow.
Is this possible with openFoam ?
My attempts are in the excelsheet:

Excelsheet with my tried boundary conditions

The Link to the Testproject:

Best regards


Hi Kai!

Very cool project! I am no expert in this but as an intuitive approach I would work with phase thresholds and integrate over the surface you have chosen (calculator slice) but only if it is below or above a specific threshold you want to capture. Does that make sense? Never done this before maybe the @CFD-SQUAD can put in their ideas here :slight_smile:




The error message you are getting mentions possible bad mesh elements and your mesh log does show that there are some bad elements. I am a little surprised actually as the geometry is very simple and mesh looks OK. You can try increasing mesh fineness to moderate and adding a boundary inflation (i.e. make the mesh at the edges finer) under mesh refinements.

Have you seen the following tutorial? It’s rather similar to what you are trying to do


Hey Jousef and Hey roy_g,
yes you are right. To “filter” the alpha phases i used a threshold. At my test, i have noticed something i cant explain.
So far i have always thought, that the alpha phase 0 represents Air and the phase 1 represents Water (in my simulation). I made three LineChartViews about the flux over the seperator.
One without any threshold, one with a threshold from 0 to 1 and one with a threshold from 0 to 10.
I think the flux over time is shown correctly in the ChartView without any threshold and from 0 to 10.
Why is the flux different, when i choose 0 to 1 or 0 to 10, i think 0 and 1 are the boundarys for the alphaPhase. What “filters” the threshold when i choose upper bound as 10 ?

Thank you for the link. Yes its similar to my simulation. I made a finer mesh and try some other boundary conditions.

Best regards