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Old   September 9, 2019, 06:41
Default Droplet free falling
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Hi.

Droplet + Electrohydrodynamic
I am simulating a free-falling droplet which passes through a uniform electric field (parallel plates). When I have a coarse mesh, it seems like the droplet deforms and there is a spray production (what is supposed to occur according to experiment). However, when I refine the mesh, I do not get a spray and the droplet shape/formation is very different.
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Old   September 9, 2019, 06:44
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This is a snapshot.
Left - coarse mesh
Right - refined
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File Type: jpg doubt.jpg (33.9 KB, 33 views)
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Old   September 9, 2019, 06:57
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Quote:
Originally Posted by mmalik View Post
Hi.

Droplet + Electrohydrodynamic
I am simulating a free-falling droplet which passes through a uniform electric field (parallel plates). When I have a coarse mesh, it seems like the droplet deforms and there is a spray production (what is supposed to occur according to experiment). However, when I refine the mesh, I do not get a spray and the droplet shape/formation is very different.

Your simulation must be mesh independent, so its obvious that the case with coarse mesh is not reliable.
Does your simulation become mesh independent after a specific number of nodes? If yes, it maybe something wrong with your boundary conditions or fields that you set.
Do you use your own code or special software?
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Old   September 9, 2019, 07:16
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Thanks for the reply.

I am new to OF. How do you check mesh independence after specific number of nodes?I am working on mesh independence (which is why I am refining it). However, as I refine, I do not get the spray, which I should get. So refining further is pointless, I think.

My BCs

alpha.water
Code:
    object      alpha1;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }

    atmosphere
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value           uniform 0;
    }

    outlet
    {
        type            zeroGradient;
    }

    defaultFaces
    {
        type            empty;
    }
}
rhoE (charge density)
Code:
    object      rhoE;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 -3 1 0 0 1 0];

internalField  uniform 0;

boundaryField
{
    atmosphere
    {
        type            zeroGradient;
    }
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            zeroGradient;
    }
    frontAndBack
    {
        type            empty;
    }
}
U
Code:
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    axis
    {
        type            empty;
    }

    inlet
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    atmosphere
    {
        type            pressureInletOutletVelocity;
        value           uniform (0 0 0);
    }

    outlet
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    front
    {
        type            wedge;
    }

    back
    {
        type            wedge;
    }
}
Ue (electric potential)
Code:
    object      gamma;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [1 2 -3 0 0 -1 0];

internalField   uniform 0;

boundaryField
{

    inlet
    {
        type            fixedValue;
        value           uniform 0;
    }

    atmosphere
    {
        type            zeroGradient;
    }
 
    outlet
    {
        type            fixedValue;
        value           uniform 3.6e3;
    }

    defaultFaces
    {
        type            empty;
    }
}
}
setFieldsDict
Code:
    object      setFieldsDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

defaultFieldValues
(
    volScalarFieldValue alpha.water 0
);

regions
(
    sphereToCell   
    {
       centre (0.7e-3 9.8875e-3 0.1e-3);
       radius 1.7e-4;
       fieldValues
        (
            volScalarFieldValue alpha.water 1
            volScalarFieldValue rhoE 0.0478
        volVectorFieldValue U (0 -5 0)
        );
    }
);
In regards to the code, yes. It is a modified interfoam solver which includes electric equation. I am using OF2.3.1
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Old   September 29, 2020, 16:33
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Hi

As far as I know, refining mesh will not always provide you a better solution since CSF. In VOF models the spurious currents are forming around the droplet interface. I am not saying do not refine your mesh please check this paper to get a better understanding of the phenomenon.



https://iopscience.iop.org/article/1...5/1/014016/pdf
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droplet ionization, electrodynamics, hydrodynamics, interfoam bubble

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