# Y plus for various turbulence models

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

 September 16, 2012, 13:58 Y plus for various turbulence models #1 New Member   TA Ramanathan Join Date: Jul 2012 Location: India Posts: 3 Rep Power: 6 Dear all, I am working on the study of wall treatment for different turbulence models (fluid domain as cyclone separator). This simulation is carrying out flow simulation alone for better understanding. In the above mentioned work, I need to know the effective range of y plus for various turbulence models such as k-epsilon, k-omega, SST and RSM etc. I have searched but I could not get material which gives elaborated details. So, I wish to know the range of y plus has to be used or better if you give me link to come across the same. Thanks in advance.

 September 16, 2012, 18:44 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 SST can handle any y+. k-e should be >11 k-omega should be <1 RSM should be >11 if using wall functions or anything if automatic. But the final decision on wall mesh resolution should always be determined by a sensitivity study in your case. mm.abdollahzadeh, sadjad.s, vikramaditya91 and 8 others like this.

 September 17, 2012, 06:28 #3 New Member   TA Ramanathan Join Date: Jul 2012 Location: India Posts: 3 Rep Power: 6 Hi Glenn, Thank you for valuable details. I will check on each turbulence models and do for sensitivity study.

 September 18, 2012, 02:48 #4 Member   Hamed Abdul Majeed Join Date: May 2012 Posts: 76 Rep Power: 6 Hi, Does these limits change: 1. If flow is internal or external. 2. Using wall functions Thank you Regards Hamed

 September 18, 2012, 19:41 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 1. No. 2. If you use wall functions then you need y+>11. This is all basic application of the wall boundary condition theory. If you read up about the wall boundary condition and understand it then the reason for these answers become obvious. hamed.majeed and pugovka9085 like this.

December 10, 2013, 02:37
#6
New Member

MMS
Join Date: Nov 2013
Posts: 29
Rep Power: 4
Quote:
 Originally Posted by ghorrocks SST can handle any y+. k-e should be >11 k-omega should be <1 RSM should be >11 if using wall functions or anything if automatic. But the final decision on wall mesh resolution should always be determined by a sensitivity study in your case.
If you kindly explain why these values of yplus is vary over different turbulence models? and what about LES?

Thanks.

December 10, 2013, 04:13
#7
Senior Member

Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8
Quote:
 Originally Posted by ghorrocks SST can handle any y+. k-e should be >11 k-omega should be <1 RSM should be >11 if using wall functions or anything if automatic. But the final decision on wall mesh resolution should always be determined by a sensitivity study in your case.
Are you sure that k-e should be >11? Does CFX have low reynolds number K-e model like Fluent which likes to have Y+ < 0.2? I thought these two software are almost same at wall treatment for different turbulence modeling.
__________________
Best regards,
Meimei

December 16, 2013, 01:11
#8
Senior Member

Join Date: Feb 2011
Posts: 288
Rep Power: 9
Quote:
 Originally Posted by Anna Tian Are you sure that k-e should be >11? Does CFX have low reynolds number K-e model like Fluent which likes to have Y+ < 0.2? I thought these two software are almost same at wall treatment for different turbulence modeling.
As far as I understand CFX uses scalable wall functions with k-e model. If mesh is too fine near the wall then CFX ignores this region by "mathematically" placing first mesh node at Y+ ~ 11.

December 16, 2013, 12:44
#9
Senior Member

OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 12
Quote:
 Are you sure that k-e should be >11? Does CFX have low reynolds number K-e model like Fluent which likes to have Y+ < 0.2? I thought these two software are almost same at wall treatment for different turbulence modeling.
In original k-e model, the definition of turbulent lengthscales and eddy viscosity has eps at the denominator. Due to rapid changes to k and eps as we approach wall, and hence in the values of lengthscales and eddy viscosity within the viscous layer, there are stability issues (along with divide by zero etc) hence wall functions are not optional.

But the low Re k-eps models in FLUENT (Launder-Sharma, Yang-Shih etc) all use damping functions and redefined values of eps to regularise the extremities in k and eps near wall and hence integration to the wall is possible with Y+ values less than 1 etc.

There are w based models both in CFX and FLUENT which are which are generally favoured.

 Tags y plus

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post philippose OpenFOAM Running, Solving & CFD 30 August 4, 2010 10:26 Seva Reehal CFX 5 October 18, 2009 08:44 gmwsy FLUENT 3 June 19, 2009 06:08 spatialtime CFX 4 April 24, 2009 05:25 Sima Baheri Phoenics 0 January 6, 2007 05:08

All times are GMT -4. The time now is 00:42.