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- - TwoPhaseEulerFoam - Bubble diameter size Problem (https://www.cfd-online.com/Forums/openfoam-solving/162717-twophaseeulerfoam-bubble-diameter-size-problem.html)

TwoPhaseEulerFoam - Bubble diameter size Problem

Hello,

i succesfully adopted the laminar bubble column tutorial for my geometry. As a first step i neglected some special boundary conditions i need to consider later on.

The case runs fine with default bubbles diameter of 3e-3 m. However if i lower the diameter to my requirements of 5e-5 m the simulation results are not meaningful, in some trys the simulation even crashes.

So my question is:

1) Are there limitations to the bubble size in twoPhaseEulerFoam?
2) What could cause the crashes for a bubble size of 5e-05? Is it the mesh?

Thank you for your ideas.

Any ideas?

My cases still crashes after lowering the air diameter from 3e-3 to 5e-5 m. :confused::confused:

Hello!!! I am facing kind of similar problem. Did you solve this?

Hi,

i think in the end it wasn't really a problem with bubble diameter, more a problem of boundary conditions and setup...
Maybe you can post your setup ....so someone can help...

Thank you so much for your reply. I have been suffering with this problem for so long.

First of all, I wanted to simulate nucleate boiling in 3D with InterThermalPhaseChangeFoam. Although this not the solver which you have used, but I thought the solution can be similar.
I have successfully created the bubble and the bubble moves upward. But it does not increase its size. It should grow up a little bit and then flow upward. So, any idea, why this is happening would be appreciated.

Here, I would like to mention that I have changed the Evaporation Threshold by increasing upto .5 and dicreasing upto .10 and nothing actually happens. I have also changed the mesh but also it did not come out successfully.

I have attached the paraview file and here is the blockMesh file:

Code:

convertToMeters 1;



vertices

(

    (0 0 0)

    (0.031 0 0)

    (0.031 0.031 0)

    (0 0.031 0)

    (0 0 0.031)

    (0.031 0 0.031)

    (0.031 0.031 0.031)

    (0 0.031 0.031)

);



blocks

(

     hex (0 1 2 3 4 5 6 7) (40 40 40) simpleGrading (1 1 1)

);



edges

(

);



boundary

(

    bottom

    {

        type wall;

        faces

        (

            (1 5 4 0)

        );

    }

    outlet

    {

        type patch;

        faces

        (

            (3 7 6 2)

        );

    }

    walls

    {

        type wall;

        faces

        (

            (0 4 7 3)

            (2 6 5 1)

            (0 1 2 3)

            (4 5 6 7)

        );

    }

);



mergePatchPairs

(

);

Here is the toposetDict file:

Code:

actions

(

    {

        name c0;

        type cellSet;

        action new;

        source sphereToCell;

        sourceInfo

        {

            centre (0.0155 0 0.0155);

            radius 0.001;

        }

    }



    {

        name c0;

        type cellSet;

        action delete;

        source boxToCell;

        sourceInfo

        {

            

                  box (0.0145 -0.001 0.0145) (0.0165 0 0.0165);

        }

    }



);

here is the setFieldDict :

Code:

defaultFieldValues

(

        volScalarFieldValue alpha1 0

        volScalarFieldValue T 559.95

        volVectorFieldValue U (0 0 0)

);



regions

(





   boxToCell

    {

        box (0 0 0) (0.031 0.026 0.031);

        fieldValues

        (

            volScalarFieldValue alpha1 1

            volScalarFieldValue T 559.95

            volVectorFieldValue U (0 0 0)

        );

    }

   

    cellToCell

    {

        set c0;



        fieldValues

        (

            volScalarFieldValue alpha1 0

            volScalarFieldValue T 559.95

            volVectorFieldValue U (0 0 0)

        );

    }

);

Regards,
Fahmida

Oh well, i'm not familiar with this problem to be honest . :/
Have you checked papers for similiar simulations?

Yes I checked some papers. But I could not understand which thing was responsible for this to happen. May be I have to understand very well how the governing equations work ?
Anyway thank you so much for your response.

one thing just popped up in my head re-reading:
when you say it should grow a "little" have you established a sufficient grid size, so that the growing can be captured by the mesh?

maybe you can describe how the growing process should work... nucleate boiling is, if i'm not mistaken, the creation of small bubbles.. which than coalesce with the bigger bubble.. or is it a different process?

Sorry for the late reply.

Yes I also think the issue can be the grid size. That's why I have tried with 2D and succeed with mesh 150x150 but after increasing the mesh upto 120x120x120 in 3D, nothing actually changes.
My updated case files are uploaded in the following thread. You can check there so we can discuss further.

https://www.cfd-online.com/Forums/op...e-boiling.html

Thank you