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

turbulence models

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 21, 2011, 16:30
Default turbulence models
  #1
New Member
 
Join Date: Jan 2011
Posts: 3
Rep Power: 6
cristian is on a distinguished road
Hi all,

I was just wondering if it is possible to use different turbulence models in different regions of a given domain. I guess this would require some kind of blending in the interface regions.

Thank you
cristian is offline   Reply With Quote

Old   January 22, 2011, 06:52
Default
  #2
New Member
 
Denis Tschumperle
Join Date: Mar 2009
Posts: 5
Rep Power: 8
tschump is on a distinguished road
Some turbulence models already have in-built mechanisms that blends from one turbulence model to another: different models are used in the near-wall and the free flow region. Thats the case for the k-omega SST model or DES type models (well in fact that's even the case for a standard k-epsilon model).

If you do not want a wall region blending, you can use the ELES (embedded LES) capability in Fluent 13 where you can explicitly specify a flow zone that will be solved using a LES model, whereas a RANS model will be used in all the other areas.

Finally, you can implement any custom blending turbulence model you wish by coding UDFs.
tschump is offline   Reply With Quote

Old   January 22, 2011, 17:15
Default
  #3
New Member
 
Join Date: Jan 2011
Posts: 3
Rep Power: 6
cristian is on a distinguished road
Thank you tschump. What I had in mind was a slightly different doubt. Say we have a domain which has two cavities connected by a small duct. The flow structure is very different inside each cavity. We know that in the first cavity a model A behaves well, and in the second one another model B behaves better. In my case A and B would RANS models but not necessarily solving the same equations, say mixing k-e with k-w, or 1-equation with 2-equation models.

Could we apply the model A in the first cavity, and the model B in the second cavity, allowing if necessary a certain region for blending both models? WOuld it be possible to define two subdomains, and use each turbulence model in each subdomain? I am not very sure what information would be shared between subdomains for this case if solving different equations.

Thank you
cristian is offline   Reply With Quote

Old   January 24, 2011, 15:14
Default
  #4
New Member
 
Denis Tschumperle
Join Date: Mar 2009
Posts: 5
Rep Power: 8
tschump is on a distinguished road
In that case, if the calculation is steady, you may do one separate calculation for each cavity, each one having its own turbulence model. You can easily couple the two calculation either by UDF or by using profiles.
tschump is offline   Reply With Quote

Old   January 24, 2011, 17:36
Default
  #5
New Member
 
Join Date: Jan 2011
Posts: 3
Rep Power: 6
cristian is on a distinguished road
Thank you tschump.

Not very sure how to couple the two cavities. Do you mean running first one cavity, take then the profiles at the interface and use them as boundary conditions for the second cavity, run then the second cavity, and copy back boundary conditions at the interface for first cavity and keep iterating until convergence? This could be a quite large, tedious process. Or maybe you mean that FLUENT can run the two cavities simultaneously, passing information across at the interface.

Thank you
cristian is offline   Reply With Quote

Old   January 27, 2011, 03:15
Default
  #6
Member
 
Tobino
Join Date: Jan 2011
Location: Osaka,Japan
Posts: 33
Rep Power: 6
tobino is on a distinguished road
Hi all,
anybody can tell me, what is better viscous model  and how is model constants for calculation ship re sistance,
Thank you very much
tobino 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
Incompressible Turbulence models achinta OpenFOAM 4 May 27, 2010 10:35
Discussion: Reason of Turbulence!! Wen Long Main CFD Forum 3 May 15, 2009 09:52
How to set phase dependent turbulence models? J.Yang CFX 2 August 29, 2002 15:39
Why Turbulence models are not universal. Senthil Main CFD Forum 4 July 5, 2000 04:34


All times are GMT -4. The time now is 13:13.