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Turbulence models for wide range of y+

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Old   January 7, 2013, 22:08
Question Turbulence models for wide range of y+
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Dave Christopher
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I am using Fluent to model the transient blowdown of a pressure vessel. Due to the large changes in the velocities from the beginning to the end, y+ for my current mesh varies from 200 in the beginning to less than 3 at then end, so much of the process has y+ between 5 and 30.

Will any of the turbulence models give reasonable results over the entire range of y+ from 2 to 200?
Which model is recommended for this situation?

Thanks.
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Old   January 8, 2013, 01:42
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Lucky Tran
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Quote:
Originally Posted by David Christopher View Post
Will any of the turbulence models give reasonable results over the entire range of y+ from 2 to 200?
Which model is recommended for this situation?
y+ requirements are for wall boundary conditions and have less to do with turbulence modelling (except for two-layer models). Anything with enhanced wall treatment will work.

stay away from any of the omega based wall models since those are tuned for grids with small y+ everywhere.

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Originally Posted by David Christopher View Post
y+ for my current mesh varies from 200 in the beginning to less than 3 at then end, so much of the process has y+ between 5 and 30.
But more importantly, it is a very bad idea to have y+ in the buffer region (5-30). You need to get out of it.
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Old   January 8, 2013, 04:30
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Yes, I realize that I do not want to be in the buffer region. However, if I increase the cell thickness to get a larger y+ later in the calculation when the velocities are lower, y+ in the early part of the calculation will be 1000 or more. Is that a problem?
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