Question about the Large eddy simulation (Fluent)

hamzaCFD · September 1, 2016, 05:48

Hello, I'm new in this group, and I'm even a new User of fluent.
I'm simulating the turbulent flow of heluim in a curved pipe using the Large Eddy Simulation model (LES). And i found in the user guide that i can't define the mid plane of the pipe as a symmetry boundary condition when i'm using the LES model. I will really appreciate it if some one can help me because i can't find any information related the the subject.

hamzaCFD · September 1, 2016, 11:27

Please can any one help me ?

Zbynek · September 1, 2016, 18:40

In LES, you capture the large eddies and model only the small ones that are smaller than your grid. So to say it in a very simplified way - if you use LES, you can visualize the large eddies moving in your domain vs. if you use RANS, the flow is all averaged. And as you know, turbulence is chaotic - which means there is no symmetry in it at all.

Because of these facts, you need to model the whole system, not just half - if you did model only half with the symmetry condition, then you would assume that the eddies on one side are the same as the eddies on the other side. And notice that the symmetry condition implies that there would be no flow across the plane. So as you can see, using LES with the symmetry condition does not give a physical sense.

Of course, you could use the symmetry plane if you used it with RANS approach.

September 1, 2016, 05:48	Question about the Large eddy simulation (Fluent)	#1
hamzaCFD New Member Join Date: Jul 2016 Posts: 4 Rep Power: 10	Hello, I'm new in this group, and I'm even a new User of fluent. I'm simulating the turbulent flow of heluim in a curved pipe using the Large Eddy Simulation model (LES). And i found in the user guide that i can't define the mid plane of the pipe as a symmetry boundary condition when i'm using the LES model. I will really appreciate it if some one can help me because i can't find any information related the the subject.

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September 1, 2016, 11:27		#2
hamzaCFD New Member Join Date: Jul 2016 Posts: 4 Rep Power: 10	Please can any one help me ?

September 1, 2016, 18:40		#3
Zbynek Member Join Date: Jun 2016 Posts: 66 Rep Power: 11	In LES, you capture the large eddies and model only the small ones that are smaller than your grid. So to say it in a very simplified way - if you use LES, you can visualize the large eddies moving in your domain vs. if you use RANS, the flow is all averaged. And as you know, turbulence is chaotic - which means there is no symmetry in it at all. Because of these facts, you need to model the whole system, not just half - if you did model only half with the symmetry condition, then you would assume that the eddies on one side are the same as the eddies on the other side. And notice that the symmetry condition implies that there would be no flow across the plane. So as you can see, using LES with the symmetry condition does not give a physical sense. Of course, you could use the symmetry plane if you used it with RANS approach.