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-   -   y+Factor: Help understanding? (https://www.cfd-online.com/Forums/star-ccm/96568-y-factor-help-understanding.html)

 eRzBeNgEl January 26, 2012 03:22

y+Factor: Help understanding?

Hi guys

I really have a problem understanding the wall y+ factor and its`range.
Am I right, that the y+ factor is a number which shows the code when to switch between far field and wall treatment functions?

In Star-CCM+ are three different types fo Wall-treatments I could choose implmented:

High-Reynolds wall treatment,
Low-Reynolds wall treatment and
All-Two-Layer Treatment (mix of High and Low-Re).

1st question: What is the range of high- and or low Reynolds models?
2nd question: What is the range of wall y+: In the User Guide I found for ke-Model realizabel a range for high Reynolds y+ > 30 and for low-Re y~1, 2Layer: y+ ~30-50.

-> This means if I have got an y+ value of 8 on a surface (ke_Modell RLZ:All-Layer Treatment), i need to optimize the mesh on surface so that the y+ factor is 30 in minumum?

 kyle January 26, 2012 16:45

The Star-CCM+ "All y+" model is useful because you do not have to go through your model and specify which walls use a low Reynolds approach and which use a high y+ wall function. The model does not promise any sort of accuracy in the range of 1<y+>30. You should have the bulk of your y+ values be either <1 or between something like 20 and 200.

 eRzBeNgEl January 26, 2012 17:23

Quote:
 Originally Posted by kyle (Post 341371) The Star-CCM+ "All y+" model is useful because you do not have to go through your model and specify which walls use a low Reynolds approach and which use a high y+ wall function. The model does not promise any sort of accuracy in the range of 130. You should have the bulk of your y+ values be either <1 or between something like 20 and 200.
Thanks Kyle for your help again, and again, and again*g* :-)

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