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

Nearwall treatment for the kOmegaSST turbulence model

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 20, 2009, 13:58
Default I am currently doing vehicle a
  #1
New Member
 
John.B
Join Date: Mar 2009
Posts: 14
Rep Power: 17
johnb is on a distinguished road
I am currently doing vehicle aerodynamics simulation with OpenFoam v1.5 and using simpleFoam with the incompressible implemented kOmegaSST turbulence model. My main concern is when this model is valid in terms of y+. Since it uses wall functions I guess the y+ should be in the log-law region (30<y+<300) and hence it would be improper to have a finer mesh with lower y+ (in my case y+ ~7) together with this model?

Would it be an idea to try a Low-Re turbulence model like Launder-Sharma or QZeta, or would that require a further refined mesh (y+~1)?

Thanks in advance!
johnb is offline   Reply With Quote

Old   January 21, 2009, 08:02
Default If you want to use low-Re mode
  #2
Member
 
Kati Laakkonen
Join Date: Mar 2009
Location: Espoo, Finland
Posts: 35
Rep Power: 17
kati is on a distinguished road
If you want to use low-Re model, you should see that all walls have y+~1 (4-5 should still be okay in some places, but 7 is quite a lot). If I were you doing vehicle aerodynamics, I would use SpalartAllmaras. It is a hybrid model, so if you select nutWallFunction as boundary condition for nut on walls (mut/mutWallFunction if compressible) you don't need to worry so much about y+, because the model uses different treatment depending on the y+ value.

The low-Re models can be tricky, I've heard. There are many of them i.e. none is very general, and epsilon equation is very sensitive to grid on the wall.

One more point with standard wall functions: the theory is valid only for flat plates (straight ducts maybe too - I don't remember), so that all pressure gradients and especially separation or attachment are not well predicted. So even if your y+ is in the correct limits, you may not get good results with wall functions.

Regards,
Kati
kati is offline   Reply With Quote

Old   January 21, 2009, 13:22
Default Hi John, I'm facing the same
  #3
Senior Member
 
Ivan Flaminio Cozza
Join Date: Mar 2009
Location: Torino, Piemonte, Italia
Posts: 210
Rep Power: 18
ivan_cozza is on a distinguished road
Send a message via MSN to ivan_cozza
Hi John,
I'm facing the same questions, I'm trying to solve a Re 1.3e5 flat plate with a tickness equal to 3% of the chord. As I'm interested in the k and eps fields, I would like to resolve well the boundary layer with something like a low Re model, and I know that k-Omega SST as some low Re version, but I know that now in OpenFOAM there's only the wall function version...
Has anyone the low Re version for SST?
ivan_cozza is offline   Reply With Quote

Old   January 22, 2009, 03:52
Default Hi Kati and Ivan, Thanks for
  #4
New Member
 
John.B
Join Date: Mar 2009
Posts: 14
Rep Power: 17
johnb is on a distinguished road
Hi Kati and Ivan,
Thanks for the advice, I will try using SpalartAllmaras (and post how it goes here) and I guess you use nutWallFunction with a zero (or say 1-e10) value of nut at the wall boundaries.

What would be very interesting for the KOmegaSST model (as well as other turbulence model using wall function approach) is to implement an enhanced wall treatment. In such way I guess that a coarse mesh region will correspond to a wall function approach (zeroGradient) while a fine mesh region will use an appropriate Low-Re boundary condition (fixedValue). Does anyone know if there are plans on releasing such option?

It seams like these three posts is handling modification to the existing kOmegaSST model, very interesting:
http://www.cfd-online.com/OpenFOAM_D...tml?1231869877
http://www.cfd-online.com/OpenFOAM_D...tml?1186414688
http://www.cfd-online.com/OpenFOAM_D...tml?1220457716

Regards,
John
johnb is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Turbulence treatment in porous media sebastiank OpenFOAM Running, Solving & CFD 2 May 8, 2017 05:29
Wall Treatment of User defined Turbulence Model Yang Chung FLUENT 0 August 23, 2008 12:31
How can run MRFSimpleFoam with KOmegaSST turbulence model waynezw0618 OpenFOAM Running, Solving & CFD 0 April 21, 2008 05:40
Question on new implemented komegaSST model in OF 14 peterh OpenFOAM Running, Solving & CFD 7 February 7, 2008 03:09
compressible modification of nearwall turbulence Quain Tchew Main CFD Forum 0 March 4, 2002 02:29


All times are GMT -4. The time now is 02:09.