LES filter in OpenFOAM

openfoammaofnepo · October 22, 2014, 18:09

Dear All,

I would like to underatnd how the LES filters are implemented in OpenFOAM. For example, the most common one is simple filter, it is defined in:

Code:

simpleFilter.C and simpleFilter.H

The filtering operation for this option is like the following:

Code:

    tmp<volScalarField> filteredField = fvc::surfaceSum
    (
        mesh().magSf()*fvc::interpolate(unFilteredField)
    )/fvc::surfaceSum(mesh().magSf());

So based on my understanding, this is very similar to an area averaging. Typically the filtered fields is always obtained from the integration with the filter kernel functions. But in openfoam, it seems that we did not see the appearence of the kernel functions. Does anybody know why the filters are implenementied like those in OpenFOAM?

Thank you very much.

dkxls · October 23, 2014, 08:27

This is nothing specific to OpenFOAM. It is generally related to the finite volume method (or actually to any discreet method).

I suggest you familiarize yourself with how the mathematical operators (like divergence, Laplacian, integral, ...) are implemented in a discrete world.

While there are many good books on CFD that cover that topic (e.g. Ferziger and Peric, 2002), I can recommend you the doctoral thesis by Jasak Hrvoje (http://powerlab.fsb.hr/ped/kturbo/Op...jeJasakPhD.pdf).
You will find there very detailed explanations on how these things are implemented in OpenFOAM.

References:
Ferziger, Joel Henry, and Milovan Peric. Computational Methods for Fluid Dynamics. 3rd ed., 2002. http://www.springer.com/materials/me...-3-540-42074-3.

October 22, 2014, 18:09	LES filter in OpenFOAM	#1
openfoammaofnepo Senior Member Join Date: Jan 2013 Posts: 372 Rep Power: 14	Dear All, I would like to underatnd how the LES filters are implemented in OpenFOAM. For example, the most common one is simple filter, it is defined in: Code: simpleFilter.C and simpleFilter.H The filtering operation for this option is like the following: Code: tmp<volScalarField> filteredField = fvc::surfaceSum ( mesh().magSf()*fvc::interpolate(unFilteredField) )/fvc::surfaceSum(mesh().magSf()); So based on my understanding, this is very similar to an area averaging. Typically the filtered fields is always obtained from the integration with the filter kernel functions. But in openfoam, it seems that we did not see the appearence of the kernel functions. Does anybody know why the filters are implenementied like those in OpenFOAM? Thank you very much.

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October 23, 2014, 08:27		#2
dkxls Senior Member Armin Join Date: Feb 2011 Location: Helsinki, Finland Posts: 156 Rep Power: 19	This is nothing specific to OpenFOAM. It is generally related to the finite volume method (or actually to any discreet method). I suggest you familiarize yourself with how the mathematical operators (like divergence, Laplacian, integral, ...) are implemented in a discrete world. While there are many good books on CFD that cover that topic (e.g. Ferziger and Peric, 2002), I can recommend you the doctoral thesis by Jasak Hrvoje (http://powerlab.fsb.hr/ped/kturbo/Op...jeJasakPhD.pdf). You will find there very detailed explanations on how these things are implemented in OpenFOAM. References: Ferziger, Joel Henry, and Milovan Peric. Computational Methods for Fluid Dynamics. 3rd ed., 2002. http://www.springer.com/materials/me...-3-540-42074-3.