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mcfdma September 9, 2019 06:41
Droplet free falling
 
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.

mcfdma September 9, 2019 06:44
1 Attachment(s)
This is a snapshot.
Left - coarse mesh
Right - refined

Moreza7 September 9, 2019 06:57
Quote:
Originally Posted by mmalik (Post 744221)
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?

mcfdma September 9, 2019 07:16
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

Smyrna September 29, 2020 16:33
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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