SimScale CAE Forum

Outlet boundary conditions (free spoud)


#1

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:

https://www.simscale.com/workbench/?pid=9208010057351915304&mi=run%3A11%2Csimulation%3A2&mt=SIMULATION_RUN

Best regards
Kai


#2

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:

Best,

Jousef


#3

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

https://www.simscale.com/docs/tutorials/multi-phase-flow-water-fall/


#4

@jousefm,
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 ?

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

Best regards
Kai