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interFoam:different nu, different falling velocity

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.

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.

Quote:

Originally Posted by vainilreb (Post 415527)

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,

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.

Quote:

Originally Posted by kmooney (Post 415606)

Hi,

Sorry,very late!
http://www.cfd-online.com/Forums/ope...-wierd-nu.html
This thread would make it clear.