CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

surface tension as function of normal gradient

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   April 30, 2008, 14:47
Default surface tension as function of normal gradient
  #1
tom
Guest
 
Posts: n/a
I am looking to use a UDF to assign surface tension as a function of the normal gradient of a user defined scalar at a transient fluid-gas interface. I am having difficulty identifying the normal gradient at the interface. Does anyone know how to identify the normal gradient of a scalar at an interface in VOF? Also, when you hook a UDF for surface tension, does Fluent automatically locate the interface and apply it there?

Thanks
  Reply With Quote

Old   September 6, 2016, 16:48
Default
  #2
New Member
 
Alex Day
Join Date: Jul 2016
Location: Fort Collins, CO
Posts: 2
Rep Power: 0
aday is on a distinguished road
Hi Tom,

I know this was 8 years ago, but did you find a solution? I am encountering the same problem at this time.

Thanks!
aday is offline   Reply With Quote

Old   September 7, 2016, 03:48
Default
  #3
Senior Member
 
Join Date: Nov 2013
Posts: 943
Rep Power: 13
pakk will become famous soon enough
You can get the gradient with "C_UDSI_G(c,t,i)".
You can get the face normal using "F_AREA(A,f,t)"; A/|A| is the normal.

Take the inner product between them and you have the normal gradient at the wall.

So altogether it would look something like this:
Code:
 #include "udf.h"
 
 DEFINE_PROFILE(surface_tension,thread,i)
 {
    real factor = 0.12345;
    reak NV_VEC(A);
    face_t f;
    begin_f_loop(f,thread) {
        F_AREA(A,f,t);
        F_PROFILE(f,thread,i) = factor*NV_DOT(C_UDSI_G(c,t,0),A)/NV_MAG(A);
    }
    end_f_loop(f,thread)
 }
This udf returns a profile of 0.12345*(normal gradient of UDS). Change the equation to what you want.

For me, surface tension is something that comes out of a calculation, and not something I assign, so I don't know if and how you can hook this to the solver.

The above code was only written and not tested, so it is possible there are some typo's or other mistakes.
pakk is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Marangoni stress (surface tension gradient) phy CD-adapco 0 July 24, 2008 07:57
Surface Tension Gradient Alisher FLUENT 0 March 26, 2008 05:26
surface tension gradient on a free surface Abrem FLUENT 1 April 30, 2006 03:41
UDF for surface tension gradient kiran FLUENT 2 July 15, 2003 12:00
Surface Tension Gradient of VOF model Ray FLUENT 1 February 22, 2000 22:45


All times are GMT -4. The time now is 16:57.