# Maximum wind speed and model scale?

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 July 1, 2012, 03:14 Maximum wind speed and model scale? #1 New Member   Sonam Join Date: Apr 2012 Posts: 10 Rep Power: 6 Hello All, Is it possible that I can use the full scale model in CFD and Maximum wind speed i.e 22m/s(79.2 KM per Hour). My actual building size: Length=16.0m, width=8.45m and Height of building=9.2m. Is it ok, if i take the same size in CFD simulation also or do i need to convert in model scale?

 July 1, 2012, 05:23 #2 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,285 Blog Entries: 6 Rep Power: 43 Take the actual size. sonam likes this.

July 1, 2012, 06:13
#3
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Sonam
Join Date: Apr 2012
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Rep Power: 6
Quote:
 Originally Posted by Far Take the actual size.
Thank you for the reply

 July 1, 2012, 11:48 #4 Senior Member   Martin Hegedus Join Date: Feb 2011 Posts: 471 Rep Power: 11 You should use the full scale. And, there isn't a limitation for Reynold's Number but there is a limitation in regards to turbulence modeling. There are three categories for turbulence modeling, RANS, LES (or DES), and DNS. You will not have enough CPU power to do DNS. LES might be possible for you, but it is very expensive. Unfortunately, depending on how accurate you would like your results to be (i.e. qualitative vs. quantitative), RANS does poorly on base drag and areas of large separation, as you would experience with a building. A RANS calculation can be off on base drag/pressure by 30-40 percent at high Reynolds number. You should investigate literature to find problems similar to yours. sonam likes this.

July 1, 2012, 11:57
#5
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Sonam
Join Date: Apr 2012
Posts: 10
Rep Power: 6
Quote:
 Originally Posted by Martin Hegedus You should use the full scale. And, there isn't a limitation for Reynold's Number but there is a limitation in regards to turbulence modeling. There are three categories for turbulence modeling, RANS, LES (or DES), and DNS. You will not have enough CPU power to do DNS. LES might be possible for you, but it is very expensive. Unfortunately, depending on how accurate you would like your results to be (i.e. qualitative vs. quantitative), RANS does poorly on base drag and areas of large separation, as you would experience with a building. A RANS calculation can be off on base drag/pressure by 30-40 percent at high Reynolds number. You should investigate literature to find problems similar to yours.
Thank you very much for the reply. I am using ANSYS Fluent 13.0 Workbench to analyis my roof simulation. It will be quantative research.

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