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January 11, 2012, 14:17 

#21  
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Martin Hegedus
Join Date: Feb 2011
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Quote:
If your separation is smooth body separation (i.e. a circle), then the pressure and viscous solution is dependent on initial grid spacing. Yes, as flow moves much further away from the body, I do expect the URANS flow to become unstable as eddy viscosity diminishes and the grid (in general) becomes coarser. 

September 1, 2014, 04:18 

#22  
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Albert Tong
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Location: Perth, WA, Australia
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Quote:
I have a simple question that why 2D les is not physically right?
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Kind regards, Albert 

September 1, 2014, 05:22 

#23  
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Filippo Maria Denaro
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Quote:
the key is to understand what you mean for 2d turbulence... 2d turbulence is a real model for large scale flows, such as atmospheric or oceanic turbulence becose you have a 2d plane of large scale and the third dimension (the vertical direction) is much smaller compared to them. For such flows you can perform 2d LES computation. On the other hand, if you have a 3d problem where all the characteristic scales in the three dimensions are comparable each other, then it makes no sense to perform an LES computation in 2d 

September 10, 2014, 01:40 

#24  
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Albert Tong
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Quote:
Thank you for your promote reply. That is to say 2D LES is similar to 2D RAS? I read through this thread and some people seem to suggest 2D LES is not mathematically right. I am simulating pipeline sitting on seabed, and the pipeline is very long compared to its diameter. Is 2D LES appropriate for such application, or 2D RAS is more appropriate? Many thanks.
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Kind regards, Albert 

September 10, 2014, 03:21 

#25 
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Filippo Maria Denaro
Join Date: Jul 2010
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No, that's not a mathematical lack, LES can be formally performed even in 1D...
The key is in the physics of the flow problem.... as happen in geophysical flows, when you have turbulent structures extending several order of magnitude more in two dimensions compared to the third dimension, a 2D LES can be a reasonable approximate model. Pipe and channel flows are typically flow problems with 3D turbulent structures and you have to use 3D LES. RANS is used in 2D as it implies a statistical averaging, that's very different idea from LES 

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