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

Wall Normal Temperature Gradient

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 30, 2009, 13:59
Default Wall Normal Temperature Gradient
  #1
Member
 
Daniel Tanner
Join Date: Apr 2009
Posts: 54
Rep Power: 8
Daniel Tanner is on a distinguished road
I would like to access the temperature gradients normal to my wall boundary. Consider steady laminar flow in a cylindrical pipe. I solve the energy equation using a constant temperature at the wall and wish to access the wall normal temperature gradients at each face of the wall boundary (i.e., dT/dn).

How can I do this? (I am familiar with UDF's). There appears to be no F_T_G() macro and I am not sure how to calculate the face value from the cell centroid (C_F_G()).

Help would be appreciated.
Daniel Tanner is offline   Reply With Quote

Old   May 2, 2009, 06:14
Default
  #2
New Member
 
Contrarian
Join Date: Apr 2009
Posts: 5
Rep Power: 8
contrarian is on a distinguished road
You can assume that the cell gradient is equal to the face gradient and dot it with the face area.
You can also get the face normal temperature gradient from the flux: divide the face heat flux with the thermal conductivity.
contrarian is offline   Reply With Quote

Old   May 2, 2009, 07:53
Default
  #3
Member
 
Daniel Tanner
Join Date: Apr 2009
Posts: 54
Rep Power: 8
Daniel Tanner is on a distinguished road
Thanks for the reply. I understand how to do it conceptually but I'm having problems implementing it. I have attached a basic UDF below which I cannot get to work! I just want to save the wall temperature to UDM. It compiles and executes without error but the UDM values are zero everywhere (I have set the UDM in Fluent).

++++++++++++++++++++++++
#include "udf.h"

DEFINE_ON_DEMAND(Test)
{
Domain *domain=Get_Domain(1);
Thread *t;
face_t f;

int Zone_ID=5; /* Found in Fluent BC panel and identifies Wall */

t=Lookup_Thread(domain,Zone_ID);

begin_f_loop(f,t)
{
F_UDMI(f, t, 0) = F_T(f,t);
}
end_f_loop(f,t)
}
++++++++++++++++++++++++

Any ideas why this does not work?
Daniel Tanner is offline   Reply With Quote

Old   May 2, 2009, 09:51
Default
  #4
New Member
 
Contrarian
Join Date: Apr 2009
Posts: 5
Rep Power: 8
contrarian is on a distinguished road
F_T may not be populated on load. Could you try after doing one iteration?
contrarian is offline   Reply With Quote

Old   May 2, 2009, 11:57
Default
  #5
Member
 
Daniel Tanner
Join Date: Apr 2009
Posts: 54
Rep Power: 8
Daniel Tanner is on a distinguished road
Sorry and thanks for the help. I found the problem. The UDF was working fine, but Fluent cannot display the F_UDMI data as it is stored at the face, i.e., it can only display cell centered data.

I'll have to think of another way to do it.
Daniel Tanner is offline   Reply With Quote

Old   May 3, 2009, 00:01
Default
  #6
New Member
 
Contrarian
Join Date: Apr 2009
Posts: 5
Rep Power: 8
contrarian is on a distinguished road
You can may be store the F_UDMI at C_UDMI(c0,t0).
contrarian is offline   Reply With Quote

Reply

Tags
gradient, temperature, udf, wall

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
surface tension as function of normal gradient tom FLUENT 0 April 30, 2008 14:47
How to input the wall temperature b.c.? Jimmy CD-adapco 9 March 14, 2008 10:31
How to input the wall temperature b.c.? Jimmy CD-adapco 16 March 7, 2008 15:11
Variable temperature wall boundary condition Virginie FLUENT 2 October 2, 2007 09:23
momentum equation (Normal to wall_ kk Main CFD Forum 0 July 2, 2006 23:10


All times are GMT -4. The time now is 21:54.