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

turbulence model in CFX, seperated flow

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 6, 2009, 18:16
Default turbulence model in CFX, seperated flow
  #1
New Member
 
Faruk Bhuiyan
Join Date: Aug 2009
Posts: 1
Rep Power: 0
F. Bhuiyan is on a distinguished road
Hi,

I am doing open channel flow simulation (hydraulically rough boundary) with obstructions on the channel bed. Seperation of flow and reverse circulatiion zones were observed in laboratory. I have tested several turbulence models in CFX. With a sufficiently fine mesh k-e models results such flow seperation. However, with k-omega based models (SST, BSL EARSM) and RSM models dont show any seperation.

Any comment/experience on that with CFX would be appreciated.

Regards

Faruk
F. Bhuiyan is offline   Reply With Quote

Old   August 6, 2009, 18:39
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,598
Rep Power: 76
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Hi,

Well, you should have a detailed look at the qualities o the various turbulence models and of the flow itself and try to work out why the difference. k-e is known to fail in rotating flows but I don't think that's an issue here. SST would be my default option for turbulence so I can't explain why it did not capture the separation - are you sure you have all the accuracy issues sorted out, eg mesh, timestep, convergence? The RSM models in my experience tend to show earlier separation than the others so this result is puzzling.

If the separation is transient with large vorticies like a bluff body then you may have to consider DES/SAS/LES approaches.

Glenn Horrocks
ghorrocks is offline   Reply With Quote

Old   August 7, 2009, 06:29
Default
  #3
Member
 
Pratik Mehta
Join Date: Mar 2009
Posts: 32
Rep Power: 7
pratikmehta is on a distinguished road
Hi,

I think there is seriously something wrong. What is the Re number of your system . Did you check your y plus values . Kindly check your .ccl file for boundary step up . I am sure you would get some hints from it .

Best of luck

Pratik
pratikmehta is offline   Reply With Quote

Old   August 9, 2009, 23:28
Default boundry layer
  #4
New Member
 
dss
Join Date: Jul 2009
Posts: 25
Rep Power: 7
flyingd is on a distinguished road
Hi:
1\there will be boundry layers in your calculation by mesh size.
2\You should choose good turbulent model which can calculate fluctuating pressure.
I suggest you can choose LES or SAS.
flyingd is offline   Reply With Quote

Reply

Tags
cfx, seperated flow, turbulence model

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
Discussion: Reason of Turbulence!! Wen Long Main CFD Forum 3 May 15, 2009 09:52
turbulence model fr Core annular flow anup FLUENT 10 November 7, 2007 02:52
Advanced Turbulence Modeling in Fluent, Realizable k-epsilon Model Jonas Larsson FLUENT 5 March 13, 2000 03:27
Algebraic Turbulence Model for 3D flow Dmitriy Makarov Main CFD Forum 0 June 28, 1999 01:40
Turbulence model in flow driven by surface tension Z. ZENG Main CFD Forum 7 April 28, 1999 07:18


All times are GMT -4. The time now is 11:42.