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CFX SST model with wall function and yplus

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Old   September 16, 2020, 01:35
Cool CFX SST model with wall function and yplus
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James
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Hello. I've read the CFX manuals and cfd-forums. However, there are some confusions about the yplus and wall functions.

1. Is it correct that SST model in CFX is valid when y plus is in range of 20-200 or less than 1?
2. Does the SST model uses the wall function when y plus is larger than 11, and does not use when y plus is less than 11?
3. What is the velocity profile or wall functions in the calculation process when y plus is larger than 11? I think that it uses the mixture of velocity on viscous sub-layer and log-law region. Does it only uses the profile of log-law region?
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Old   September 16, 2020, 01:50
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Did you read this blog series. It is a useful and easy to follow resource:

https://www.computationalfluiddynami...undary-layers/
https://www.computationalfluiddynami...oundary-layer/
https://www.computationalfluiddynami...ow-resolution/
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Old   September 16, 2020, 02:03
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I've now read these article, but any of them cannot be the answer of my question...
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Old   September 16, 2020, 06:09
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If you understood what those links are saying then you could answer the questions by yourself. So read them again, and look at some other references for further information. This is important stuff for CFD, so you really should know it.

But I will answer your questions anyway:
1) SST is valid for any y+ value. But make sure you are not confusing the turbulence model with the wall modelling (integration to the wall versus wall functions).
2) Again, do not confuse the turbulence model with the wall model. If you use SST with automatic wall functions then it uses wall functions for y+>11 and transitions to integration to the wall for y+<11. But it is the wall model which does this, not the turbulence model.
3) This is described here: https://www.computationalfluiddynami...undary-layers/ It puts u+ following the log law function, as a function of y+.
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