SST-OMEGA and Y+

[ghalebsater]

Hello, 

Since SST-OMEGA doesnot uses wall functions as mentioned in Autodesk SIM CFD guide, does that mean that we donnot have to worry about the values of Y+. So the results will be independent of the values of Y+ which usually should be between 35 and 300. 

Thank you in advance 

[OmkarJ · Accepted solution]

Y+ is a non-dimensional distance from the wall. Y+ of 30 signifies the first cell height, below which wall functions take over to model the velocity distribution upto the wall.

If a model doesn't use wall function, it means that you have to have very fine mesh close to the wall, so that model can integrate to the wall to get the velocity. And Y+ values here infact have to be much smaller (typically 2 or less) but again this is problem dependent. If you are very picky, you may want to do sensitivity study to understand if Y+ value you have chosen is adequate one, ie, reducing it doesn't change the results. However not many care for this.

Lastly, I read the mention of "Intelligent Wall Formation" in the documentation, which cites the reduced dependence eon mesh refinement near wall. But there is no mathematical explanation provided on this. I wonder, if this is an automatic algorithm, that uses wall function for larger Y+ values and switches to low-Re configuration for smaller Y+ values by integrating to the wall - thus automating the wall treatment. A comment from Autodesk personnel is appreciated here.

OJ

[ghalebsater]

Thank you Omkarj for this comprehensive and infromative reply..