|
[Sponsors] |
Required Y+ Range for k-Omega Standard and SST |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
March 12, 2020, 16:48 |
Required Y+ Range for k-Omega Standard and SST
|
#1 |
New Member
Nian
Join Date: Jun 2019
Posts: 15
Rep Power: 7 |
Hello,
This type of question might have appeared quite a lot in the forums, but I could not really find a definitive answer for it, so I would greatly appreciate it if anyone could help with the required y+ values for the turbulence models in Fluent: 1. Does k-omega Standard model use wall function at all? If so, does it mean that the y+ range should be between around 50 - 500? If not, what kind of range would the y+ value require? 2. As far as I am aware, k-omega SST does not use wall function and solves viscous layer directly, but some people have said it would require a y+ value of 1, some have said 5-10, so I was wondering if there might be a more certain answer for it? Thank you! |
|
March 12, 2020, 16:58 |
Range of y+
|
#2 |
Senior Member
|
As far as Fluent is concerned, each model uses Enhanced Wall Treatment. This is a two layer model and in reality is insensitive. So, it can work with all values up to 500 or so. However, is a low Re model, i.e., it's applicability is more in the region with low Re. So, it is recommended that the should be of the order 1, i.e., between 1 and 10.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
March 12, 2020, 17:05 |
|
#3 |
New Member
Nian
Join Date: Jun 2019
Posts: 15
Rep Power: 7 |
Quote:
Would the previous one (1-500) be applying for k-omega standard, and latter (1-10) for k-omega SST? Also, would you mind me asking what kind of range of Reynolds number would usually be considered as low Re simulation for external flow? Thank you very much! |
|
March 13, 2020, 05:36 |
Turbulence Model and Wall Function
|
#4 |
Senior Member
|
has got nothing to do with . So it doesn't care how fine or coarse the mesh is. It is the wall treatment. And the wall treatment used by all models in Fluent is EWT. And EWT is insensitive, i.e., it can work with high as well as low values of . However, if you wish to resolve the viscous sublayer, most likely because the objective demands that, you should maintain below 10.
is nothing but Reynolds number based on the mesh size. And when it is of the order 1, this implies that the viscous forces are comparable to inertial forces, i.e., the equations can resolve the flow-field without any special treatment. Therefore, it is supposed to be of order 1. Do note that order 1 does not imply 1, rather values up to 9.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
March 13, 2020, 11:01 |
|
#5 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,760
Rep Power: 66 |
Standard k-omega does have wall functions that kick in around wall y+ > 100. However, it is against the philosophy of the k-omega model to be using wall functions in the first place. The wall function is there just to make the k-omega model usable for coarse meshes. The wall function for omega is also quite garbage and not as robust compared to wall functions in epsilon models.
This wall function also exists in k-omega SST which blends a k-epsilon with a k-omega solution. But because the blending favors k-epsilon far from boundaries and k-omega near boundaries, the wall function that exists for the omega equation practically has no effect. In either case, the philosophy of using either the k-omega or k-omega SST model is to resolve viscous layers directly, so the recommendation is always going to be super low wall y+ when either of these models are involved. What's much more important than achieving the target y+ on only the first grid cell is resolution. You want to pack 10/30/100 cells across the boundary layer, etc. |
|
Tags |
turbulence modelling, yplus |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Use of k-epsilon and k-omega Models | Jade M | Main CFD Forum | 40 | January 27, 2023 08:18 |
One more time: wall functions - SST | CellZone | OpenFOAM Pre-Processing | 22 | June 11, 2021 14:27 |
General question about SST turbulence model | Richard Renaud | CFD Freelancers | 1 | December 19, 2015 05:13 |
k omega turbulence model | sailspace | OpenFOAM Running, Solving & CFD | 0 | November 12, 2013 06:43 |
Standard K Epsilon and Transitional SST models | Robin | FLUENT | 1 | January 17, 2010 19:06 |