# [swak4Foam] calculate bubble velocity

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 March 1, 2012, 13:28 calculate bubble velocity #1 Senior Member   Nima Samkhaniani Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,265 Blog Entries: 1 Rep Power: 23 hi former i guess, it should be possible to access a bubble velocity with swak4Foam but i dont know how the procedure can be? the procedure should be like that: 1) select all cells with alpha < 0.5 2) calculate the gravity center in each time step any comment or suggestion?

March 1, 2012, 15:10
#2
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Bernhard Gschaider
Join Date: Mar 2009
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Quote:
 Originally Posted by nimasam hi former i guess, it should be possible to access a bubble velocity with swak4Foam but i dont know how the procedure can be? the procedure should be like that: 1) select all cells with alpha < 0.5 2) calculate the gravity center in each time step any comment or suggestion?
Why use a cutoff? that way you're going to get jumps in your result. Something like

"(pos()*vol()*(1-alpha1))/sum(vol()*(1-alpha1))"

(with an accumulation sum) might give you the center of the "non-fluid".Have a look at my presentation from the last workshop (you'll find it on the swak4Foam-page on the Wiki). Slide 76 has a similar application.

BTW: if you're interested in the velocity of the liquid interface then you might want to have a look at slide 155 where it s demonstrated how to calculate that with sampledSurfaces

 May 24, 2016, 15:56 #3 Member   Arsalan Join Date: Jul 2014 Posts: 74 Rep Power: 10 Hi Foamers, I'm doing a 3D simulation of two and three bubble rising using a modified interFoam solver and I need to bubbles centre position, velocity and surface area. For a single bubble rising I used swak4Foam expressions for example for bubble centre position in Y as follows : Code: bubbleCentreY { type swakExpression; valueType internalField; verbose true; variables ( "Vol= sum (alpha1 < 0.5 ? vol() : 0);" "VolY= sum (alpha1 < 0.5 ? pos().y*vol() : 0);" ); expression "VolY/Vol"; accumulations ( min ); } Is there a way to compute two or three bubble properties in this manner? Thanks in advance, Best Regards, Arsalan. zeynab hoseini likes this.

March 8, 2022, 04:14
#4
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Join Date: Feb 2021
Location: Austria
Posts: 34
Rep Power: 3
Hello all,

Thank you for the info you provided here.
I would be appreciative if you let me know your opinion. (I have attached my case)
I am also working on the terminal velocity of bubbles. Using the paraView, I measure the center of a bubble location in two successive time steps, then by deviding the displacement of the center of bubble to the time difference, I want to calculate the velocity. The problem is, the value that I gain is 50% lower than the reported values ​​in the literature. I am using a 2D mesh in openFoam 8 using interFoam.
The contents of my 0 folder are:

U file:

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

internalField uniform (0 0 0);

boundaryField
{
bottom
{
type noSlip;
}
outlet
{
type noSlip;
}
walls
{
type slip;
}
defaultFaces
{
type empty;
}
}

p_rgh file:
dimensions [1 -1 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
bottom
{
}

outlet
{
}

walls
{
}

defaultFaces
{
type empty;
}
}

alpha file:

dimensions [0 0 0 0 0 0 0];

internalField uniform 0;

boundaryField
{
bottom
{
}

outlet
{
}

walls
{
}

defaultFaces
{
type empty;
}
}

transportProperties file:

phases (air water);

air
{
transportModel Newtonian;
nu nu [ 0 2 -1 0 0 0 0 ] 1.5E-5;
rho rho [ 1 -3 0 0 0 0 0 ] 1.18;

}

water
{
transportModel Newtonian;
nu nu [ 0 2 -1 0 0 0 0 ] 7.22E-7;
rho rho [ 1 -3 0 0 0 0 0 ] 995.7;

}

Thanks a lot.
Attached Files
 case.zip (8.6 KB, 2 views)

 Tags bubble, swak4foam

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