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wall y+ and turbulence models

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Old   May 13, 2019, 03:35
Default wall y+ and turbulence models
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Narayanan Achuthan
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Hello,

I know this question has been asked and answered several times, but I did not see any conclusive remarks. I am performing a conjugate heat transfer analysis which is sensitive to heat transfer and pressure drop in the model.

In order to predict the heat transfer and the turbulence within the domain accurately, I would like to use either SST k-w or realizable k-e with Enhanced wall treatment turbulence models. From Fluent's Intro guide, I realize that both these models are y+ insensitive models and it would be best to have y+≈1.

But due to the model's complexity and computing restrictions I cannot get the first cell distance which would satisfy the wall y+≈1. My question is how does these models respond when the y+ is in the range of 10-20? I know that wall functions gets into effect if the first cell is in the log layer (y+≈30), but what happens when the first cell has y+ of approximately 10?

Thank you in advance for your answers.
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Old   May 13, 2019, 10:18
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Quote:
Originally Posted by narayanan View Post
I know that wall functions gets into effect if the first cell is in the log layer (y+≈30)
No you don't actually. Because if you did you would know that.....

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Originally Posted by narayanan View Post
but what happens when the first cell has y+ of approximately 10?
Nothing happens because they are y+ insensitive (blended) wall functions. They don't have strict regimes because all the regimes are blended together.


What's much more important the the y+ of the wall adjacent cell is the number of cells you have across the boundary layer.
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cht modelling, rke, sst k-omega, wall y+

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