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

Natural convection model

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 17, 2012, 03:30
Default Natural convection model
  #1
Member
 
adam
Join Date: Oct 2011
Posts: 52
Rep Power: 15
sieginc. is on a distinguished road
I want to be able to compare the effect of forced vs. natural convection on a heat generating element. Right now I am not sure how to model a natural convection simulation. I have a cube with a constant heat flux on each side sitting in a big room. The top of the room is a pressure outlet with all sides being walls. The initial condition of the room is 25 C.

I have selected:

-Boussine model
-Constant density
-Gas
-Gravity
-Implicit unsteady
-Segregated flow
-Segregated fluid temperature
-Laminar
-3D

The problem is when I run it the residuals do not converge and I keep getting reversed flow on all the faces which does not go away. Can someone give me some tips on this? Thanks.
sieginc. is offline   Reply With Quote

Old   February 18, 2012, 09:16
Default
  #2
Senior Member
 
Join Date: Oct 2009
Location: Germany
Posts: 636
Rep Power: 22
abdul099 is on a distinguished road
Switch off the Bussinesq model and change constant density to ideal gas. Although it should be good for that, Boussinesq seems not to work correctly in some versions.

Reversed flow can be neglected, it should just tell you that some inflow occurred at an (pressure) outlet. This is nothing to worry about, since something needs to flow into your domain when something flows out of it.
abdul099 is offline   Reply With Quote

Old   February 26, 2012, 03:07
Default
  #3
New Member
 
D. Rusell
Join Date: Dec 2011
Posts: 6
Rep Power: 14
n0name is on a distinguished road
Well, how high is temperature difference in your flow problem?

Last edited by n0name; February 26, 2012 at 03:07. Reason: grammar ;)
n0name is offline   Reply With Quote

Old   February 27, 2012, 13:50
Default
  #4
New Member
 
James Lo
Join Date: Feb 2012
Posts: 8
Rep Power: 14
hiddenbunny is on a distinguished road
Set the thermal expansion coefficient to >0 or 1/K where K is your operating temperature.

For some reason they set the default value to be 0 which makes Boussinesq not working
hiddenbunny is offline   Reply With Quote

Old   April 23, 2012, 05:20
Default
  #5
Senior Member
 
Join Date: Dec 2011
Posts: 121
Rep Power: 14
fshak92 is on a distinguished road
Quote:
Originally Posted by sieginc. View Post
I want to be able to compare the effect of forced vs. natural convection on a heat generating element. Right now I am not sure how to model a natural convection simulation. I have a cube with a constant heat flux on each side sitting in a big room. The top of the room is a pressure outlet with all sides being walls. The initial condition of the room is 25 C.

I have selected:

-Boussine model
-Constant density
-Gas
-Gravity
-Implicit unsteady
-Segregated flow
-Segregated fluid temperature
-Laminar
-3D

The problem is when I run it the residuals do not converge and I keep getting reversed flow on all the faces which does not go away. Can someone give me some tips on this? Thanks.
Would you please tell me how did you set the ambient temperature for the block?by setting some constant temperature to the block's wall or...?
Also,didn't you use any velocity inlet?
Thank you in advance
fshak92 is offline   Reply With Quote

Reply


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Natural Convection with heat generation krishnachandranr Main CFD Forum 0 July 28, 2009 05:22
Coupled vs Seg - Natural vs. Forced Convection Alex Siemens 5 December 12, 2007 05:58
Natural convection. Air properties Cristina FLUENT 3 March 24, 2007 09:23
How to model natural convection Ken Adams FLUENT 4 January 23, 2007 16:14
natural convection at high Rayleigh mauricio FLUENT 2 February 23, 2005 20:43


All times are GMT -4. The time now is 22:23.