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Old   November 28, 2011, 12:49
Default Tutorial "airFoil2D" yPlus value
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I have a question about the airFoil2D tutorial. I compute the given case and evaluated the y+ value with the yPlusRAS-function.

So this is the solution:
Patch 2 named wall y+ : min: 958.43 max: 13790.7 average: 8328.47
Isn't this an incorrect y+value. I read in another thread that the y+plus value should between 1 and 300.
So is this a bug ??

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Old   November 30, 2011, 06:42
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Hi Denis,

this isn't a bug I can assure you.

The yPlus factor is a value which gives you an indication of the resolution of
the boundary layer.
( yPlus = (u * y) / nu )
If you want to make a simulation without further approximations this value
should be 1.

However this results in lots of cells so some guys had the idea of the usage
of wall functions.
This allows you to increase this value up to 300 and the results may still look
like a good representation of the reality (for engineers this is usually enough).

Since you can then use less cells also the calculation time decreases which is
quite handy.

Which brings us to the tutorials:
They are made to show you the general principle of a solver/feature so they
usually use a coarse mesh which must not necessarily full fill all the
requirements one has to a mesh, so quality or resolution factors might
exceed the values which you would use for a real computation where you
rely on the results.

I hope I explained everything well enough
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