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Y+ < 1 for Standard K-Epsilon

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Old   May 9, 2012, 09:48
Default Y+ < 1 for Standard K-Epsilon
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for a 5 cm diameter cylinder of which air is passing through at 2m/s, I have a mesh resolution of around 70 nodes for that diameter.

Would this explain why my y+ values are very small? And is this going to lead to errors? I've been reading around and people are quoting very positive numbers like >30.
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Old   May 9, 2012, 14:40
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Quote:
Originally Posted by Leepox View Post
for a 5 cm diameter cylinder of which air is passing through at 2m/s, I have a mesh resolution of around 70 nodes for that diameter.

Would this explain why my y+ values are very small? And is this going to lead to errors? I've been reading around and people are quoting very positive numbers like >30.
Do you mean 70 nodes across the diameter or circumference of the pipe? It only changes the answer slightly but:

If your mesh is uniform then your y+ will likely by much greater. If you used clustered grid nodes near the wall then it is very possible. You can have y+ < .1 if your edge growth rate is high.

Small y+ is great and way more accurate than high y+ meshes. Use it if you can afford it. Just make use you are using the low Reynolds number approach for your wall modelling (usually the fluent default). If not Fluent, what turbulence model and wall modelling are you using?
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