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y+ values!!

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Old   June 18, 2009, 05:24
Default y+ values!!
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Chris Turner
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Hi,

I am currently modelling a diffusing cone under steady flow conditions (eventually the model will be under transient flow conditions, but I am using steady flow at the minute to get a better understanding of Fluent).

The y+ values on the wall of the diffuser have a very large range when plotted, the minimum is 28 and the maximum is 834! I'm not sure if this is anywhere near normal? There is a lot of turbulentce in the diffuser, with a large annular votrex forming.

Also, I have used a cooper mesh, which means the cell size actually increases as the diffusers cross sectional area increases, could this be what is causing the variance in y+ value?

Any help would be great!

Thanks in advance

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Old   June 18, 2009, 07:55
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you can adapt the mesh in fluent basing on y+ value
Just go to Adapt->Iso-region

basically you want to have the y+ value around 5-30 depending on the model you use
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Old   June 18, 2009, 10:55
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Max
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Just a comment on pioteks post.

using standard wall functions, y+ should be above 30 larger values up to some limit are acceptable! Thus the grid of Chris is not so bad, a refinement of boundary layers should be restricted to values of y+ > ~200 and only necessary, if these values are found in regions of interest = prostcessing.

cheers
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