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

Temperature inside domain is more than BC!

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

Like Tree2Likes
  • 1 Post By kad
  • 1 Post By GM_XIII

Reply
 
LinkBack Thread Tools Display Modes
Old   July 5, 2014, 18:43
Default Temperature inside domain is more than BC!
  #1
Member
 
Hooman
Join Date: Feb 2012
Location: USA
Posts: 86
Rep Power: 6
enayath is on a distinguished road
Hello,

I am simulating natural convection in a closed domain. My BC is 370K and 280 K. I run the case in steady laminar mood. when I check the temperature distribution inside the fluid domain, it is 450K!!!
I set the initial temperature at 325K.I am pretty sure with the quality of my mesh...there si no source term

Does anybody know how come I have such a this problem?

Thank you in advance!
enayath is offline   Reply With Quote

Old   July 11, 2014, 11:21
Default
  #2
Member
 
David
Join Date: Aug 2012
Posts: 48
Rep Power: 6
GM_XIII is on a distinguished road
It may happen that temperature goes up the BC value at the early stage of the iteration, try to limit it to the BC value and see if the number of limited cells drops down while the case is converging
GM_XIII is offline   Reply With Quote

Old   July 11, 2014, 11:31
Default
  #3
Member
 
Hooman
Join Date: Feb 2012
Location: USA
Posts: 86
Rep Power: 6
enayath is on a distinguished road
GM_XIII,

I run the case with second order for Momentum and Energy...when I switch to first order, every thing looks alright...

In second order simulation, i run the case for 200,000 iterations but there were fluctuations.

Hooman
enayath is offline   Reply With Quote

Old   July 11, 2014, 11:39
Default
  #4
Member
 
David
Join Date: Aug 2012
Posts: 48
Rep Power: 6
GM_XIII is on a distinguished road
You mean fluctuations in residuals or in max temperature?
GM_XIII is offline   Reply With Quote

Old   July 11, 2014, 11:40
Default
  #5
Member
 
Hooman
Join Date: Feb 2012
Location: USA
Posts: 86
Rep Power: 6
enayath is on a distinguished road
In max temperature
enayath is offline   Reply With Quote

Old   July 11, 2014, 11:43
Default
  #6
kad
Senior Member
 
Join Date: Feb 2013
Location: Germany
Posts: 173
Rep Power: 14
kad will become famous soon enoughkad will become famous soon enough
Fluctuations are characteristc for 2nd order discretization methods when gradients aren't resolved good enough by the grid. Maybe you can try to resolve your grid finer especially where large gradients occur in the flow and temperature field.
dreamz likes this.
kad is offline   Reply With Quote

Old   July 11, 2014, 11:44
Default
  #7
Member
 
David
Join Date: Aug 2012
Posts: 48
Rep Power: 6
GM_XIII is on a distinguished road
Quote:
Originally Posted by enayath View Post
In max temperature
Which model are you using for air? Have you tried underrelaxing the solution of the energy equation or density? Also check what kad said, recently i read in a topic here to use adaptative grid adaptation based on temperature gradient, but be careful not to adapt too many cells in one time as it can unstabilize your run.
dreamz likes this.
GM_XIII is offline   Reply With Quote

Old   July 11, 2014, 11:48
Default
  #8
Member
 
Hooman
Join Date: Feb 2012
Location: USA
Posts: 86
Rep Power: 6
enayath is on a distinguished road
David,

I am sure about the quality of grid...I created several cases with different mesh....all resulted in fluctuations...

I use steady laminar model with water...
I played with URF...it was helpful regards to fluctuations but caused a new problem...the residual of continuity went up to 10e3!!

When I run the case with second order transientو every thing is alright


Hooman
enayath is offline   Reply With Quote

Old   July 11, 2014, 12:03
Default
  #9
kad
Senior Member
 
Join Date: Feb 2013
Location: Germany
Posts: 173
Rep Power: 14
kad will become famous soon enoughkad will become famous soon enough
Do you use double precision solver?
kad is offline   Reply With Quote

Old   July 11, 2014, 12:05
Default
  #10
Member
 
Hooman
Join Date: Feb 2012
Location: USA
Posts: 86
Rep Power: 6
enayath is on a distinguished road
yes I do.
yes I do.
yes I do.
enayath is offline   Reply With Quote

Old   July 11, 2014, 18:11
Default
  #11
Member
 
Behrooz Jamshidi
Join Date: Apr 2013
Posts: 83
Rep Power: 5
CFD-fellow is on a distinguished road
Using second order discretization almost cause convergency problem, which one of its solutions is to switch to second order after complete convergence of first order. But I suppose you have done this.
High order schemes better capture physical changes. So if your physic is inherently time dependent and you are modeling it as steady state, its easier to converge with first order. According to your information that you said with transient run is ok, I think your convergency problem with your second order discretization is because of your physic.
CFD-fellow 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
whats the cause of error? immortality OpenFOAM Running, Solving & CFD 11 April 22, 2014 12:32
UDF for Back-flow Temperature G340 Fluent UDF and Scheme Programming 3 August 21, 2013 04:56
injection problem Mark New FLUENT 0 August 4, 2013 01:30
is internalField(U) equivalent to zeroGradient? immortality OpenFOAM Running, Solving & CFD 7 March 29, 2013 02:27
Static Temperature / Opening Temperature JulianP CFX 6 March 23, 2013 17:03


All times are GMT -4. The time now is 02:49.