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interFoam:different nu, different falling velocity |
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March 21, 2013, 09:04 |
interFoam:different nu, different falling velocity
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#1 |
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Beijing, China
Posts: 838
Rep Power: 17 |
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. |
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March 21, 2013, 10:43 |
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#2 |
Member
Robert
Join Date: Aug 2012
Location: Berlin
Posts: 74
Rep Power: 13 |
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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March 21, 2013, 18:37 |
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#3 | |
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Beijing, China
Posts: 838
Rep Power: 17 |
Quote:
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; Thanks very much for your help. Reagrds, |
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March 21, 2013, 21:24 |
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#4 |
Senior Member
Kyle Mooney
Join Date: Jul 2009
Location: San Francisco, CA USA
Posts: 323
Rep Power: 17 |
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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April 3, 2013, 00:01 |
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#5 | |
Senior Member
Dongyue Li
Join Date: Jun 2012
Location: Beijing, China
Posts: 838
Rep Power: 17 |
Quote:
Sorry,very late! http://www.cfd-online.com/Forums/ope...-wierd-nu.html This thread would make it clear. |
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