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Which turbulent model is good for a diffuser?

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Old   March 19, 2012, 12:57
Default Which turbulent model is good for a diffuser?
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mertimiks is an unknown quantity at this point
So I placed a duct (diffuser) around my wind turbine, and the air flow is turbulent. So do you guys have any recommendations for which turbulence model should I used, and why?
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Old   March 19, 2012, 13:35
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SST with automatic wall treatment. Keep y+ below 10
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Old   March 19, 2012, 13:40
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SST with automatic wall treatment. Keep y+ below 10
Why is that? What do you mean by y+ below 10?
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Old   March 19, 2012, 14:00
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Why is that? What do you mean by y+ below 10?
Sorry, but that is real basics ... you should understand that, because otherwise you wonīt know how to get a good solution.

http://www.cfd-online.com/Wiki/Dimensionless_wall_distance_%28y_plus%29
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Old   March 19, 2012, 14:02
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This is what i learned recently, someone please corrects me if i'm wrong:
Y+ is an non-dimentional parameter that determines how refined your mesh is near a wall and therefore how accurate you can be (regarding boundary layer), the more refine the more accurate, small value means good accuracy in general below 10 and not less than 0.
There is a tool in cfd-online that allows you to determine the height of the first cell near the wall depending on the Y+ you want. just google Y+ estimator.
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Old   March 19, 2012, 14:10
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Y+ is an non-dimentional parameter that determines how refined your mesh is near a wall
yes

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and therefore how accurate you can be (regarding boundary layer), the more refine the more accurate, small value means good accuracy in general below 10 and not less than 0.
y+ is important for wall treatment. To less cells for the boundary layer (not only y+ of the first cell, also number of cells within the boundary layer) will not resolve the boundary layer correctly and therefore your solution is not good. If you use "wall function" instead of resolve the boundary layer, your y+ can be lager (y+ ... 20-200) and you do not need so many cells within the boundary layer. low-Re mesh need y+<1 to be accurate.

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and not less than 0.
y+ canīt be less than 0
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