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DeltaT keeps decreasing after droplet impact on the surface.

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Old   April 12, 2021, 10:28
Post DeltaT keeps decreasing after droplet impact on the surface.
  #1
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SONG
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Hello,
I am a freshman on the simulation of droplet impact and I have a question on the set of wall's dynamic contact angle.
I set the dynamic contact angle in fold 0/alpha.water, before the droplet impact on the wall, the case runs well and deltaT is about 1e-7. However, after the droplet impact on the wall, the time step keeps decreasing.
Does anyone have some suggestions to solve the problem?

Here is the alpha.water file
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object alpha.water;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 0 0 0 0 0 0];

internalField uniform 0;

boundaryField
{
inlet
{
type fixedValue;
value $internalField;
}

outlet
{
type inletOutlet;
value $internalField;
inletValue $internalField;
}

walls
{
type dynamicAlphaContactAngle;
theta0 70;
thetaA 90;
thetaR 40;
uTheta 0.01;
limit gradient;
value $internalField;
}

}

// ************************************************** *********************** //
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Old   April 12, 2021, 15:42
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krishna kant
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Hi SONG,

As per my experience this happens when the fragmentation of the liquid blob is very high for your given parameters and grid being very fine. One option is you can make the time step fixed. It will cause some loss of mass but make sure your fixed value is sufficiently small so the losses are not significant.
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Old   April 14, 2021, 04:07
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SONG
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Hi,krishna.
Initial droplet velocity is only 1m/s and the droplet free falling with gravity from 4mm above the wall. Based on experiments resutls, no droplet splash (fragmentation)occourss under this condition. The initial mesh is 8 on per droplet diamenter, refine level is 4, and the minimum mesh is 0.015625mm.
In additon, if the contact angle is set as constant contact angle instead of dynamic contact angle, the droplet can deposit on the wall with deltaT around 1e-7.
I will try the fixed time step and to check is the case can run successfually.

Quote:
Originally Posted by kk415 View Post
Hi SONG,

As per my experience this happens when the fragmentation of the liquid blob is very high for your given parameters and grid being very fine. One option is you can make the time step fixed. It will cause some loss of mass but make sure your fixed value is sufficiently small so the losses are not significant.
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