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interFoam:different nu, different falling velocity

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Old   March 21, 2013, 10:04
Default interFoam:different nu, different falling velocity
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Dongyue Li
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Hi,

I am sumilating a bulk of liquid droping,as you can see in the image.First I set the liquid is water,so nu is 1e-5,the I get the fine solution.and the velocity is about 5m/s.

But when I change nu to be 1,looks like this liquid sphere is falling slowly,and the falling velocity is about 0.05m/s.

I am confused about this ,What happend?Thanks in advance.

The case is attached,just run interFoam ,and change the nu to be bigger as you like.check the result.
Attached Images
File Type: jpg nu 1.48.jpg (31.7 KB, 31 views)
File Type: jpg nu 1.48e-6.jpg (28.1 KB, 30 views)
Attached Files
File Type: zip 2Dliquiddrop.part01.zip (95.7 KB, 12 views)
File Type: zip 2Dliquiddrop.part02.zip (95.7 KB, 9 views)
File Type: zip 2Dliquiddrop.part03.zip (84.0 KB, 7 views)
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Old   March 21, 2013, 11:43
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Robert
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Are you sure you've changed the viscosity of the falling fluid? A much higher viscosity of the surrounding fluid would explain why the acceleration of the droplet is smaller and it moves slower at a certain point in time.

This is just quick guessing, I can't check for your files right now.

EDIT: Okay, I've checked them now. Your described change from 1e-5 to 1 indicates that you have changed the properties of phase 2 which indeed would mean you've changed the viscosity of the surrounding air.
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Old   March 21, 2013, 19:37
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Dongyue Li
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Quote:
Originally Posted by vainilreb View Post
Are you sure you've changed the viscosity of the falling fluid? A much higher viscosity of the surrounding fluid would explain why the acceleration of the droplet is smaller and it moves slower at a certain point in time.

This is just quick guessing, I can't check for your files right now.

EDIT: Okay, I've checked them now. Your described change from 1e-5 to 1 indicates that you have changed the properties of phase 2 which indeed would mean you've changed the viscosity of the surrounding air.
This is my transportDict:
Code:
phase1
{
    
    transportModel  Newtonian;
    nu              nu [ 0 2 -1 0 0 0 0 ] 1.48;
rho             rho [ 1 -3 0 0 0 0 0 ] 900;

}

phase2
{
    transportModel  Newtonian;
    nu              nu [ 0 2 -1 0 0 0 0 ] 1.48e-05;
    rho             rho [ 1 -3 0 0 0 0 0 ] 1;
}

sigma           sigma [ 1 0 -2 0 0 0 0 ] 0.07;
As you can see,phase 2's nu is still 1e-5,but why I changed the phase 1'nu to 1.48 which would lead to the increasing of air'nu? anyway, How can I prevent this?

Thanks very much for your help.

Reagrds,
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Old   March 21, 2013, 22:24
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While it is difficult to tell from your images, it appears that your interface is rather poorly resolved. With a poorly resolved interface and a high density ratio you should expect significant errors in your droplet's surface shear stress calculations.

Also, I don't see anything out of the ordinary in your simulation: As you increase the droplet viscosity, it yields to gravitational forces more slowly.
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Old   April 3, 2013, 00:01
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Quote:
Originally Posted by kmooney View Post
While it is difficult to tell from your images, it appears that your interface is rather poorly resolved. With a poorly resolved interface and a high density ratio you should expect significant errors in your droplet's surface shear stress calculations.

Also, I don't see anything out of the ordinary in your simulation: As you increase the droplet viscosity, it yields to gravitational forces more slowly.
Hi,

Sorry,very late!
interFoam, wierd nu.
This thread would make it clear.
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