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turbulent kinetic energy budget terms with openfoam

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Old   August 1, 2014, 06:03
Default turbulent kinetic energy budget terms with openfoam
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Thangam Natarajan
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Hi,

Is there a way to write out all the components(production, convection, dissipation and turbulent diffusion) of the tke budget separately for a LES case? Any pointers??

Thanks.

Thangam.
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Old   August 13, 2014, 15:06
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Bruno Santos
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Greetings Thangam,

Can you provide more information about each variable you are looking to export?
I ask this because even though I'm familiar with many of OpenFOAM's way of working with things, on the other hand I'm not familiar with the terminology in LES. Therefore I need more details on what exactly you're looking for.

Best regards,
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PS: Re-posting does not make it easier for people to answer your questions. What's more important is that more details are provided with each new post you provide, because if people did not answer your question, it's likely that not enough information was provided in the first place. And many of the people that might be able to answer your question, don't have the time to still have to ask first: What on Earth are you talking about?
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Old   August 14, 2014, 00:55
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My bad I thought these were quite obvious! Anyway,

The complete form of the turbulent kinetic energy can be written as,

P_k - C_k - \epsilon_k   + D_k = 0,

where,

P_k is the production term of k given by,

P_k = - \overline{u\prime_i u\prime_m} \frac{\partial U_i}{\partial x_m}

C_k is the mean convection term of k given by,

C_k = U_m \frac{\partial k}{\partial x_m}

\epsilon_k is the dissipation term of k given by,

\epsilon_k = \nu \overline{ \frac{\partial u\prime_i}{\partial x_m}\frac{\partial u\prime_i}{\partial x_m}}

and D_k is the diffusion transport term of k given by,

D_k = \frac{1}{2} \frac{\partial}{\partial x_m}( T_{iim}^{(\nu)} - T_{iim}^{(p\prime)} -  T_{iim}^{(u\prime)} ) and D_k contains

the viscous diffusion,

T_{iim}^{(\nu)} =  - \nu \overline{\frac{\partial u_i\prime u_i\prime}{\partial x_m}}

pressure diffusion,


T_{iim}^{(p \prime)} = \frac{2}{\rho}\overline{u_i \prime p\prime \delta_{im}}

and the turbulent diffusion given by,


T_{iim}^{(u \prime)} = \overline{u_i  u_i u_m}



The problem is I am not able to identify where these terms are embedded in the code and how to write them out by creating a small utility.

Thanks.
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Old   August 14, 2014, 04:56
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Quote:
Originally Posted by Thangam View Post
The problem is I am not able to identify where these terms are embedded in the code and how to write them out by creating a small utility.
You are familiar with the source code of the one equation model?
Code:
src/turbulenceModels/compressible/LES/oneEqEddy/oneEqEddy.H
src/turbulenceModels/compressible/LES/oneEqEddy/oneEqEddy.C
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Last edited by dkxls; August 14, 2014 at 05:01. Reason: typo
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Old   August 17, 2014, 14:00
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Greetings to all!

To complement Armin's answer: the class "oneEqEddy" is derived from the class "GenEddyVisc", which in turn derives from "LESModel". This last class is the base class for accessing turbulence data that is readily available on the solver's side.
For example, have a look at the solver "applications/solvers/heatTransfer/thermoFoam" in OpenFOAM 2.3, namely in the file "setAlphaEff.H". There you can see how it explicitly loads the turbulence of type "LESModel".

Correlating the information given in #3 with the information here on the wiki, it looks like the terms you've looking for are these: http://www.cfd-online.com/Wiki/Kinet...id-scale_model
Checking Armin's answer in post #4 does reveal the same equations in this method:
Code:
void oneEqEddy::correct(const tmp<volTensorField>& tgradU)
All of the terms of the equation are all solved directly in a single equation and are not available for outside use.

Which means that you will have to either create a new derived class from "oneEqEddy" or modify directly OpenFOAM's class "oneEqEddy", to write out each term of the equation.
Or you can modify the solver and do a dynamically cast to the instance of "LESModel" class to "oneEqEddy" and then access directly the "k()" method and other methods that give the components used in the equation that is solved in "oneEqEddy::correct".

Although I don't know how practical that is, because each term of the equation is in the form of "fvScalarMatrix" and not of in the form of a standard field.

Best regards,
Bruno
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Old   September 5, 2015, 17:58
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Quote:
Originally Posted by wyldckat View Post
Greetings to all!

To complement Armin's answer: the class "oneEqEddy" is derived from the class "GenEddyVisc", which in turn derives from "LESModel". This last class is the base class for accessing turbulence data that is readily available on the solver's side.
For example, have a look at the solver "applications/solvers/heatTransfer/thermoFoam" in OpenFOAM 2.3, namely in the file "setAlphaEff.H". There you can see how it explicitly loads the turbulence of type "LESModel".

Correlating the information given in #3 with the information here on the wiki, it looks like the terms you've looking for are these: http://www.cfd-online.com/Wiki/Kinet...id-scale_model
Checking Armin's answer in post #4 does reveal the same equations in this method:
Code:
void oneEqEddy::correct(const tmp<volTensorField>& tgradU)
All of the terms of the equation are all solved directly in a single equation and are not available for outside use.

Which means that you will have to either create a new derived class from "oneEqEddy" or modify directly OpenFOAM's class "oneEqEddy", to write out each term of the equation.
Or you can modify the solver and do a dynamically cast to the instance of "LESModel" class to "oneEqEddy" and then access directly the "k()" method and other methods that give the components used in the equation that is solved in "oneEqEddy::correct".

Although I don't know how practical that is, because each term of the equation is in the form of "fvScalarMatrix" and not of in the form of a standard field.

Best regards,
Bruno
I had a similar experience with Tecplot in extracting turbulent production terms from Reynolds stress tensor and mean velocity gradients.
I could effectively use Tecplot "Calculate Variable" option to construct each term of the production and dissipation.
I think paraFoam can perform such calculations as well.

Regards,
Syavash
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