Which turbulent model is good for a diffuser?

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 March 19, 2012, 12:57 Which turbulent model is good for a diffuser? #1 New Member   Join Date: Mar 2012 Posts: 4 Rep Power: 6 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?

 March 19, 2012, 13:35 #2 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,398 Blog Entries: 6 Rep Power: 45 SST with automatic wall treatment. Keep y+ below 10

March 19, 2012, 13:40
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Quote:
 Originally Posted by Far SST with automatic wall treatment. Keep y+ below 10
Why is that? What do you mean by y+ below 10?

March 19, 2012, 14:00
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Quote:
 Originally Posted by mertimiks 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

 March 19, 2012, 14:02 #5 Super Moderator     Ghazlani M. Ali Join Date: May 2011 Location: Tokyo, Japan Posts: 1,384 Blog Entries: 23 Rep Power: 22 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. __________________ Regards, New to ICEM CFD, try this document --> https://goo.gl/KAOIwm Ali

March 19, 2012, 14:10
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Quote:
 Originally Posted by diamondx Y+ is an non-dimentional parameter that determines how refined your mesh is near a wall
yes

Quote:
 Originally Posted by diamondx 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.

Quote:
 Originally Posted by diamondx and not less than 0.
y+ canīt be less than 0

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