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-   -   Droplet Impingement Simulation Refinement (http://www.cfd-online.com/Forums/fluent/94596-droplet-impingement-simulation-refinement.html)

skel_1 November 20, 2011 23:35

Droplet Impingement Simulation Refinement
 
Hi,

I am trying to model the impingement of a droplet on a solid surface. So far I have run an axisymmetric case with the VOF model (implicit body force, unsteady, implicit) and used the Static Contact Angle approach. I have used an uniform quad mesh which is very refined. But however, after the first impact the droplet seems to split up in two and then rejoin and then further illustrate the oscillations with the pinning and depinning phenomena. However, I am not satisfied with it.

I would like your opinion about the following:

1. Is using a Dynamic mesh necessary to reduce computation time if I want to use a coarse mesh throughout and just refine the near interface region and the droplet moves.

1 a. Has anyone done this?

2. I am new at using UDF's, but would like to learn how to include the different models for dynamic contact angles(DCA) to better simulate experimental conditions? Would the UDF give me options in specifying the contact angle in the wall adhesion tab in boundary conditions.

3. In case of using a UDF I would like to be able to read the velocity of the contact line and thus compute the dynamic contact angle from there which would be used in Fluent's CSF formulation to compute the droplet spreading. Can anyone help with this?

Thanks
Skel.

subha_meter February 20, 2012 02:06

Dynamic contact angle
 
Hi,

The droplet may split into two/multiple fragments depending on the Weber no at the time of impact. If the impact velocity is very high, there's possibility drop will split. However use of static contact angle is a limitation to model such kind of problem where the contact line keeps on moving and no slip boundary condition at the wall is not the appropriate BC. To overcome such problem, a time dependent contact angle (dynamic contact angle) profile can be applied through "define profile" macro.

Regards,

SM

wbka April 21, 2013 18:01

BC
 
Hello ,
Hello , could you tell me what boundary conditions you used , please ?
thanks in advance

subha_meter June 24, 2013 23:03

Droplet impingement
 
Quote:

Originally Posted by wbka (Post 422181)
Hello ,
Hello , could you tell me what boundary conditions you used , please ?
thanks in advance

If this thread is still alive, a dynamic contact angle boundary condition is indeed required on the solid wall which could either an experimentally measured profile or an analytical expression as a function of three phase contact line velocity. A UDF will be needed to capture the velocity near the spreading edge (gas-liquid interface) of the droplet and with this velocity the dynamic contact angle needs to be calculated.


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