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-   -   Contours of turbulent kinetic energy in LES using ANSYS FLUENT 13 (http://www.cfd-online.com/Forums/fluent/106540-contours-turbulent-kinetic-energy-les-using-ansys-fluent-13-a.html)

khosrow August 31, 2012 10:50

Contours of turbulent kinetic energy in LES using ANSYS FLUENT 13
 
Could any one help me on this: I am trying to sketch the turbulent kinetic energy from LES solution using ANSYS FLUENT 13. I don't see the turbulent kinetic energy in the contours and animation menu. Any help is greatly appreciated. Many thanks.

nenazarian July 9, 2013 14:01

Hi,

I have a similar problem.
Did you find a way to do that?
I would appreciate your help.

cheers,
Negin

diamondx July 9, 2013 15:09

normally it's under turbulence - turbulence kinetic energy... may be because it's LES ??!!

nenazarian July 9, 2013 15:18

No Its not there in LES and I guess I need to use UDF?

flotus1 July 10, 2013 02:37

You will have to construct the resolved part of the TKE with the help of the individual terms of the Reynolds stresses. These have to be sampled in the unsteady statistics.

sbaffini July 29, 2013 05:28

Dear all,

the term "turbulent kinetic energy" is not actually correct for LES as it misses to specify what quantity you are looking for as some "turbulence" is actually resolved in LES. Also, keep in mind that, with respect to RANS, in LES these quantities have a well defined averaged as well instantaneous value. You can find some options below:

Subgrid (or Subfilter) Kinetic Energy: this has the exact same meaning as the "turbulent kinetic energy" in RANS/URANS:it is the kinetic energy associated with the non resolved motion. It being associated with some unknown quantity, as in RANS/URANS you will need some model to actually compute it. In simple practical terms, you can access this in Fluent only with the Dynamic TKE SGS model, which has a dedicated equation for it. At the moment, you can only have access to its instantaneous value. In order to have its average value, you will need some recent Fluent version (14 or 14.5), possibly enable beta features access, define this quantity as a custom field function and enable the time statistics for the custom field functions.

Subtest kinetic energy: this quantity is relative to the kinetic energy contained in the modes between the resolved flow field and the filtered flow field as used in the dynamic procedure. As such, it is only available for dynamic models. The same distinction among instantaneous/averaged values used above still apply.

Resolved kinetic energy: this is the kinetic energy associated to the resolved motion. In order to obtain it you need to activate the statistics. Then you can define it in two ways: (1) instantaneous, by subtracting the mean velocity components from the instantaneous ones (2) average, by directly using the computed rms of the velocity components.


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