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LES best practice: resolved and modelled turbulence kinetic energy

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Old   November 27, 2018, 09:13
Default LES best practice: resolved and modelled turbulence kinetic energy
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Emily
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Hello,

I am running an LES simulations with the WALE subgrid-scale model and am looking for some clarification on turbulence properties. To help validate my mesh, I would like to know how much of the turbulence kinetic energy is directly resolved and how much is modelled with the subgrid-scale model. Could anyone tell me how this can be done directly in OpenFOAM? I.e. what calculations I need to perform?

Reading through the forums, some people have said that R gives the modelled Reynolds stress tensor and that Uprime2Mean gives the resolved Reynolds stress tensor. Is this correct? If that's the case, does that mean the total Reynolds stress tensor is simply given by R + Uprime2Mean? Then I can simply find the percentage of resolved k as Uprime2Mean/(R + Uprime2Mean)? Please correct me if I am wrong.

Since looking into this, it has raised further questions regarding the run time output of the turbulence kinetic energy, k. Is this the total, resolved or modelled turbulence kinetic energy?

Thank you,
Em
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Old   December 13, 2018, 11:25
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Quote:
Reading through the forums, some people have said that R gives the modelled Reynolds stress tensor and that Uprime2Mean gives the resolved Reynolds stress tensor. Is this correct? If that's the case, does that mean the total Reynolds stress tensor is simply given by R + Uprime2Mean?
Yes that is correct.

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Then I can simply find the percentage of resolved k as Uprime2Mean/(R + Uprime2Mean)? Please correct me if I am wrong.
Basically yes, you have to take the trace to get the kinetic energy from the Reynolds stress tensor, i.e. (1/2*tr(Uprime2Mean))/(1/2*tr(R + Uprime2Mean)).

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Since looking into this, it has raised further questions regarding the run time output of the turbulence kinetic energy, k. Is this the total, resolved or modelled turbulence kinetic energy?
k gives only the subgrid part. You can have a look at the source documentation, search for "k()":

https://www.openfoam.com/documentati...E.html#details

And to dig more into detail into the WALE files itself:
https://www.openfoam.com/documentati...8H_source.html
https://www.openfoam.com/documentati...8C_source.html
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Old   Yesterday, 07:09
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Thank you for your detailed reply - you've really helped to clarify this!
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