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

Huge Wall Heat Transfer Coefficients with SST Mode

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

Reply
 
LinkBack Thread Tools Display Modes
Old   December 18, 2008, 07:02
Default Huge Wall Heat Transfer Coefficients with SST Mode
  #1
Marco Müller
Guest
 
Posts: n/a
Hi,

I made a "simple" steady state simulation with the standard k-Epsilon model and after that exactly the same with the SST model. The results with k-Epsilon were normal and the SST results are similar except of the "Wall Heat Transfer Coefficients" which are 10 times bigger than those of the k-Epsilon model and are of the same quantity all over the domain (which is in the k-Epsilon simulation widely spread...). Convergence is very good so I dont know what the problem is... Maybe some can help! Thanks a lot!

marco
  Reply With Quote

Old   December 18, 2008, 12:13
Default Re: Huge Wall Heat Transfer Coefficients with SST
  #2
cfdguy
Guest
 
Posts: n/a
Hi,

In this case, please check your y+ values at walls, when using SST. They're should be <= 1. In addition, you might need about 10-20 nodes inside the boundary layer.

Re-submit the case and post here.

When using k-eps, y+ should be higher than 30.

Good luck!

cfdguy
  Reply With Quote

Old   December 19, 2008, 06:37
Default Re: Huge Wall Heat Transfer Coefficients with SST
  #3
Marco Müller
Guest
 
Posts: n/a
Hi,

thank You for Your reply. Yplus is in the range 0.5 - 2... not so fine mesh but quite slow air flow. Is Yplus important when using "automatic near-wall treatment"?? (Of course finer mesh does better results...) To me it seems more a problem of calculation of the "Wall Heat Transfer Values". All other quantities (flow, temperature, wall adjacent temp, heat flux..) look similar to those of the k-epsilon-simulation. btw how is "wall heat transfer coefficient" calculated? Is it evaluated from the heat flux or is heat flux evaluated from the coefficient?

Thanks again for Your replies!

Marco
  Reply With Quote

Old   December 19, 2008, 08:55
Default Re: Huge Wall Heat Transfer Coefficients with SST
  #4
cfdguy
Guest
 
Posts: n/a
Hi,

Make it fine near the walls. In the bulk region, you can leave as a big mesh size, if that region is not important.

The HTC is calculated based on the wall temperature (that you specify, or the solver calculates) and the adjacent node.

"Is Yplus important when using automatic near-wall treatment"? I would say that y+ is important in all turbulent flows using RANS. They are even more important when you use a low-Re model, such as SST.

Cheers!
  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
Conjugate heat transfer: coupled wall temperature Sarah FLUENT 7 August 12, 2013 22:36
Natural convection in a closed domain STILL NEEDING help! Yr0gErG FLUENT 3 June 12, 2013 02:12
Flow around pipes - heat transfer coefficient on the wall of pipe doodek Main CFD Forum 2 November 23, 2009 09:48
how to model heat transfer for the coupled wall jing113cn FLUENT 0 June 22, 2009 03:56
How can I increase Heat Transfer at Domain Interf? B.Simon CFX 3 October 28, 2008 19:53


All times are GMT -4. The time now is 19:52.