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a mark for filter size (delta) in LES

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Old   July 30, 2013, 10:51
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Bobi
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Dear guys
Hi

I want to write the sub-grid scale mixture fraction variance expression in Open FOAM. In this expression, we have delta that means filter size. Would somebody PLZ hint me that How do we write filter size in Open FOAM?

(merged from another post)

I want to write the expression in LES for mixture fraction variance. In this expression we have filter size (delta). would somebody hint me how can I write filter size in OpenFOAM format?

Regards
Bobi

Last edited by wyldckat; August 18, 2013 at 18:07. Reason: the two posts were made in two separate threads and the topic is nearly identical
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Old   August 18, 2013, 18:08
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Bruno Santos
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Greetings Bobi,

Please provide more details on what exactly you want to do.

Best regards,
Bruno
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Old   August 19, 2013, 01:57
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Bobi
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Hi Bruno

As you might Know, libOpenSmoke and its modified versions does not support LES solver, I am trying to write a solver that involves LES solution and 80% I was successful. There was a failure in my thermochemical data (not velocity or mixture fraction fields). I have found that it is because I have used a transport equation for mixture fraction variance. Instead I should have exerted a modeling formulation. Fortunately fireFoam (which has a kind of flamelet solver: FSD) has implemented this modelling formulation in a way. I am trying to implement it into modified OpenSmoke to finally create the LES solver . This is what I found in FSD.H file:


Code:
// Calculation of the mixture fraction variance (ftVar)
    const compressible::LESModel& lesModel =
        YO2.db().lookupObject<compressible::LESModel>("LESProperties");

    const volScalarField& delta = lesModel.delta();
    const volScalarField ftVar(Cv_*sqr(delta)*sqr(mgft));
As it can be seen lesModel.delta() identifies what I mean i.e. filter size (delta)

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Bobi
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Old   August 21, 2013, 11:12
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Hi Bobi,

My guess is that this delta size is actually defined in the dictionary "constant/LESProperties".

You can find several examples on OpenFOAM, by running:
Code:
find $FOAM_TUTORIALS -name "LESProperties"
And if I understand things correctly, "delta()" is actually a field of the same dimensions of the mesh, namely the same size as the pressure field; therefore, I think the "delta size" in OpenFOAM is actually the values of "delta" at each cell centre. And if this interpretation is correct, then it's as I wrote above: this is configurable in the "constant/LESProperties" dictionary, without any need to hack directly into the code

By the way, the OpenFOAM User Guide is a bit vague on how these are used:
basically they also tell us to look at the tutorials

Best regards,
Bruno
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Old   August 21, 2013, 11:26
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Hi Bruno

I am going to take a deep look at your hints. Many thanks for your kind reply.

Regards
Bobi
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