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-   -   K-omega SST grid resolution (http://www.cfd-online.com/Forums/fluent/42584-k-omega-sst-grid-resolution.html)

efb October 17, 2006 03:05

K-omega SST grid resolution
 
I'm doing unsteady simulation on 2d airfoil (Rey number 800000)with pulsed mass injection through slot using k-omega SST turbulence model. I have read that to correctly use this model yplus should be less than 0.1, but I thought that the grid wall resolution was similar to k-eps with enhanced wall treatment that requires yplus near or less 1.0 but not necessarily less than 0.1.. I'd like to know which is the thuth..

thank you bye

sam October 17, 2006 04:46

Re: K-omega SST grid resolution
 
you should also read abt how many should be in the viscous sublayer.

sam October 17, 2006 09:33

Re: K-omega SST grid resolution
 
this is frm CFDwiki

Boundary layer mesh For design iteration type of simulations where, a wall function approach is sufficient, y+ for the first cell should be somewhere between 30 and 300. For more accurate simulations with resolved boundary layers the mesh should have a y+ for the first cell which is below 1. A good rule of thumb is to use a growth ratio in the boundary layer of 1.2 - 1.25.

If you are uncertain of which wall distance to mesh with you can use a y+ estimation tool to estitmate the distance needed to obtain the desired y+.

As a rule of thumb a wall-function mesh typically requires about 10 cells in the boundary layer whereas a resolved low-Re mesh requires about 40 cells in the boundary layer.


efb October 17, 2006 09:37

Re: K-omega SST grid resolution
 
thank you sam..I will try bye

sam October 17, 2006 09:42

Re: K-omega SST grid resolution
 
u r welcome

Ralf Schmidt October 17, 2006 10:36

Re: K-omega SST grid resolution
 
Hi!

There are some information in the fluent manual, summarized in the wiki:

http://www.cfd-online.com/Wiki/Near-...k-omega_models

Hope, it helps

Ralf

sam October 17, 2006 13:08

Re: K-omega SST grid resolution_an important issue
 
you should not confuse wall y plus with grid indepdent solution . both are different. For example refer to peric book last chapter on accurcy of solution.

Amr October 18, 2006 04:41

Re: K-omega SST / Interference
 
I apologize for this off-track interference. It is an issue related to the k-w SST model, but I have not been successful to resolve it.

Need to ask you a question regarding a turbulent natural convection scenario inside a large hall. Now, the simple question is: Does the k-w (Shear Stress Transport) model account for turbulent generation due to buoyancy?. In the fluent manual, the two-equation set for k and w do not show the term that accounts for buoyancy effect, unlike what you see in k-epsilon equations. While not sure about this, I understood from the manual that when I activate the k-w model, the software applies the k-w model for low Re regions and applies the k-e model in the free stream with buoyancy effect. Is this correct?.

Thanks in advance for your help.

Cheers Amr


Bionico June 15, 2012 04:19

I'm also interested about Amr's question :)


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