CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Advice about turbulence models?

Register Blogs Community New Posts Updated Threads Search

Like Tree1Likes
  • 1 Post By AnasCFD

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 18, 2016, 10:52
Default Advice about turbulence models?
  #1
New Member
 
Join Date: Feb 2016
Posts: 28
Rep Power: 10
mqsim is on a distinguished road
Hi everyone!

I am looking for advice about turbulence models in OpenFoam. I have tried three turbulence models (k-omega SST, k-epsilon, Spalart-Allmaras) for the same case (study of the wind load on a building). At the beginning, I used the k-omega SST model but results were not enough accurate. So I tried the k-epsilon model but the calculation did not seem to converge. With the Spalart-Allmaras, model results are ridiculous. The stagnation pressure is approximately 50% higher than expected.

The geometry is complex so it is really difficult to create a good mesh using snappyHexMesh. I know that differences between turbulence models could be due to the mesh, but it seems I cannot improve the quality of the mesh with snappyHexMesh. I cannot show the mesh or the geometry, it is for an industrial case.

Regards,

mqsim
mqsim is offline   Reply With Quote

Old   April 25, 2016, 19:24
Default
  #2
New Member
 
anas
Join Date: Jun 2015
Posts: 18
Rep Power: 11
AnasCFD is on a distinguished road
Hi mqsim,

You are comparing 3 different turbulence models. k-omega is accurate but requirs yplus ~ 1. The standard k-epsilon is not that accurate but usually it converge easier. On the other hand Spalart-Allmaras is not that accurate since it is a one equation model.

I suggest to check your yplus. Then compare the results obatined with k-omega (with yplus ~1) with that obtained by realizableKE model.

All the best and success.
AnasCFD is offline   Reply With Quote

Old   April 26, 2016, 05:10
Default
  #3
New Member
 
Join Date: Feb 2016
Posts: 28
Rep Power: 10
mqsim is on a distinguished road
Hi anas,

Thank you for your answer. I am not sure to understand what means "yplus". Is it the size of the mesh in the y direction?

mqsim
mqsim is offline   Reply With Quote

Old   April 26, 2016, 13:55
Default
  #4
New Member
 
anas
Join Date: Jun 2015
Posts: 18
Rep Power: 11
AnasCFD is on a distinguished road
Please take a look to this wiki

http://www.cfd-online.com/Wiki/Dimen...e_%28y_plus%29
mqsim likes this.
AnasCFD is offline   Reply With Quote

Old   April 27, 2016, 05:36
Default
  #5
New Member
 
Join Date: Feb 2016
Posts: 28
Rep Power: 10
mqsim is on a distinguished road
Thank you Anas! Hopefully it will help me to improve my models.
mqsim is offline   Reply With Quote

Old   April 27, 2016, 08:02
Default
  #6
Super Moderator
 
Tobi's Avatar
 
Tobias Holzmann
Join Date: Oct 2010
Location: Bad Wörishofen
Posts: 2,711
Blog Entries: 6
Rep Power: 52
Tobi has a spectacular aura aboutTobi has a spectacular aura aboutTobi has a spectacular aura about
Send a message via ICQ to Tobi Send a message via Skype™ to Tobi
I just want to mention that

kEpsilon vs kOmega:

kEpsilon is more accurate far away from walls
kOmega is more accurate at walls

Therefore the kOmega-SST model was introduced which at least blends both models
__________________
Keep foaming,
Tobias Holzmann
Tobi is offline   Reply With Quote

Old   April 27, 2016, 08:50
Default
  #7
New Member
 
Join Date: Feb 2016
Posts: 28
Rep Power: 10
mqsim is on a distinguished road
Thank you Tobi for your answer, it is really useful to me!
mqsim 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
PANS turbulence models HelioVillanueva OpenFOAM Programming & Development 39 June 23, 2024 08:13
Only two turbulence options available in CFX Pre Jack001 CFX 5 March 30, 2016 03:47
Y plus for various turbulence models taram CFX 8 December 16, 2013 12:44
Are there more FLUENT Turbulence Models? Travis FLUENT 3 December 30, 2008 02:45
Turbulence models become invalid at Re=2000~5000? liweif FLUENT 9 August 27, 2007 12:55


All times are GMT -4. The time now is 10:26.