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

Problem with constant Heat Flux

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 14, 2015, 15:27
Unhappy Problem with constant Heat Flux
  #1
Senior Member
 
Hesam
Join Date: Feb 2015
Posts: 139
Rep Power: 4
rapierrz is on a distinguished road
Hi friends,

I add temprature to icofoam with openfoam wiki tutorial :

https://openfoamwiki.net/index.php/H...ure_to_icoFoam

and in Temprature boundary condition I define constant heat flux condition for lower wall:

lowerWall
{
type groovyBC;
valueExpression "300";
gradientExpression "q";
fractionExpression "0";
variables "q=300;";
timelines ();
value uniform 300;
}

but when openfoam solve the problem,Temprature after 100 second become 4000-22000K!!!

I'm very cunfused.please Help me

Last edited by rapierrz; April 14, 2015 at 23:48.
rapierrz is offline   Reply With Quote

Old   April 17, 2015, 11:20
Default
  #2
Senior Member
 
Agustín Villa
Join Date: Apr 2013
Location: Brussels
Posts: 187
Rep Power: 7
agustinvo is on a distinguished road
Hello

with GroovyBC, you are imposing a gradient of temperature, not a heat flux... to do that, you should express this gradient in function of your heat flux, and the kinematic and turbulent thermal diffusivities.

Other option you have is the use of turbulentHeatFluxTemperature BC.
agustinvo is offline   Reply With Quote

Old   April 19, 2015, 00:05
Default
  #3
Senior Member
 
Hesam
Join Date: Feb 2015
Posts: 139
Rep Power: 4
rapierrz is on a distinguished road
Thank you Agustin,

I think When we have a fixed heat flux condition,gradient of temprature on

the wall is constant.

k*gradT=q , gradT=q/k;

Do you think I impliment bad boundary condition with groovyBC?
rapierrz is offline   Reply With Quote

Old   April 20, 2015, 07:30
Default
  #4
Senior Member
 
Agustín Villa
Join Date: Apr 2013
Location: Brussels
Posts: 187
Rep Power: 7
agustinvo is on a distinguished road
Hello,

if you are using RANS models, the expression you propose should be modified to:

q=k_eff*gradT

where k_eff=k+k_turb, k is the thermal conductivity, and k_turb is the turbulent thermal conductivity. This expression is taken into account in the BC I told you. In case you want to use GroovyBC, you should divide by the effective thermal conductivity.
agustinvo 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
clarification about constant heat flux boundary condition at wall in fluid region baran_foam OpenFOAM Post-Processing 5 November 26, 2016 18:57
UDF for a constant heat flux minus radiation based on face temperature MarioArias Fluent UDF and Scheme Programming 3 March 10, 2015 16:54
Problem with snGrad() for heat flux. SKLee OpenFOAM Programming & Development 4 March 4, 2014 23:46
Question about heat transfer coefficient setting for CFX Anna Tian CFX 1 June 16, 2013 06:28
Constant heat flux ocy FLUENT 1 January 17, 2005 02:54


All times are GMT -4. The time now is 00:28.