LES Dynamic models details
Dear all,
If I am not mistaken, the current dynamic models calculate the coefficients as a single scalar, not scalarfield, I mean C is not C(y), or C(x,y,z,t). The averaging process is not done in homogeneous directions. I am a little confused, the original basic idea of Dynamic procedure would make sense better if averaging in homogeneous directions, wouldn't it? Another question I have is, is the test filter used in OpenFOAM double size of the original filter? If I am not mistaken, simpleFilter is just another explicit filter used in dynamic procedure that differs from the implicit filter, but isn't the explicit simpleFilter (top-hat) the same as the implicit filter (top-hat too!)? Please correct me if I was wrong. Thank you very much. |
dynOneEqEddy vs locDynOneEqEddy
Take a look at the source of "locDynOneEqEddy" which is a localized, dynamic LES model i.e C(x,y,z,t).
Contrast this with "dynOneEqEddy" which is dynamic but with a global coefficient i.e C(t). Michael |
I see, but what about the second question,
"is the test filter used in OpenFOAM double size of the original filter?" Thank you, Michael! |
the ratio of the two filter width is 2,this number was choosed by some researchers,they demonstrated it was optimum.
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Quote:
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the test filter size is (at least in dynSmag) controlled by the variable ce in the turbulenceProperties dict, I think.
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The test filter width is set to twice the grid filter width by the following line in dynSmagorinsky:
volSymmTensorField MM = sqr(delta())*(filter_(mag(D)*(D)) - 4*mag(filter_(D))*filter_(D)); The factor 4 results from substituting 2*delta for the test filter width. where delta is the grid filter width. |
If I'm not mistaken, I think even the locDynOneEqEddy model is not localized..
EDIT: I stand corrected. The coefficients are volScalarFields, so that would imply local coefficients.. |
Well, you have to give it some sort of name :)
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And I just don;t believe there is an universal shortcut to model all types or turbulence in a non-DNS mesh.
Personally, I think the development of LES small scale turbulence models has almost reached its peak. But it seems hybrid method still has a long way to go. |
Test filter
moved to new thread
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