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

Natural convection, problems with total energy balance

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 13, 2014, 13:15
Default Natural convection, problems with total energy balance
  #1
New Member
 
Manuel do Nascimento
Join Date: May 2012
Posts: 7
Rep Power: 5
MdoNascimento is on a distinguished road
Hello,

I try to simulate a heat transfer case, where the fluid is only moving because of buoyancy (steady state).

Actually there are two fluid regions. The outer fluid region is air (ideal gas), the inner fluid region is an oil with a user defined EOS (Density is dependant on temperature, polynomial function). They are separated by a solid wall, the energy is supposed to be transported through the wall to the "air environment".

On the outer wall of air the boundary condition is a temperature (Dirichlet bc). The inner boundary of the oil region is modeled as a heat source.

In the post-processing I noticed, that the overall energy balance of the air region is fine. Meaning, the heat transported through the wall into the air is transported through the outer walls. But the energy for the oil region is not working out at all.

The temperature field and velocity field look quite well! I can see the typical natural convection behaviour near the walls (temperature and velocity boundary layers!).

In the beginning I used the coupled flow and coupled energy model in the physics options. Now I try working with separated flow and separated energy models. The results became better, at least concerning the air region (with the coupled models, even ther energy balance of air was totally wrong).

When simulating a case only consisting of my user defined oil fluid model, I can achieve a good solution regarding the energy balance (only with segregated models, again!).

The technical support asked me to try lowering underrelaxation factor of the energy solver. But so far the problem still occurs.

Any help is highly appreciated. Thank you in advance!
MdoNascimento is offline   Reply With Quote

Reply

Tags
energy balance, natural convection

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
Natural Convection: Energy residual does not converge Nukengine STAR-CCM+ 1 April 10, 2013 08:53
Total Energy -thermal energy Herold CFX 7 June 20, 2012 18:36
volumetric reaction and energy balance? m.beh FLUENT 1 October 17, 2011 17:21
HELP needed: Energy balance in gaseous combustion James Willie FLUENT 11 August 10, 2005 04:58
Why FVM for high-Re flows? Zhong Lei Main CFD Forum 23 May 14, 1999 13:22


All times are GMT -4. The time now is 15:52.