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fvc::reconstruct( ) algorithm

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Old   July 8, 2010, 04:36
Default fvc::reconstruct( ) algorithm
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Hi Foamers,

I am trying to figure out how the fvc::reconstruct( ) algorithm works. My first thought was:
Sum up the facefluxes multiplied with the facenormal over a cell and divide it by the sum of the magnitude of the facevector components of every face of the cell.
The algorithm in the "fvcReconstruct.C" file seems far more complex then my thought:

inv(surfaceSum(sqr(mesh.Sf())/mesh.magSf()))
& surfaceSum((mesh.Sf()/mesh.magSf())*ssf)


The second line is what I expected, but the first line is a little mystery to me.
Can anybody explain this to my, please?


Rainer
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Old   July 8, 2010, 09:31
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Just a guess... it looks like it might be non-orthogonal correction...?
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Old   July 9, 2010, 11:15
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Kevin Maki
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Rainer, I agree with your description. The first line finds one over the square of the components of the area. The second line has the the components of the area in the numerator, so the result is just one over the area times the sum of what ever you are reconstructing. This is what you want for a face-area-weighted average.

There is another post by Henry which is relevant here:

Bugs in fvcsurfaceIntegrate

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Old   March 16, 2011, 13:27
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I am also puzzled by what fvc:reconstruct does. Has anyone here figured what it does? It seems it is not based on any mathematical identity (like Gauss theorem), but some sort of approximation.
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Old   January 16, 2012, 13:06
Default fvc::reconstruct explaination
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Thibault Pringuey
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Hello,

I have had a look at the fvc::reconstruct method. Please find attached an attempt to explain it.

Cheers,


Thibault
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File Type: pdf fvcReconstruct.pdf (21.9 KB, 865 views)
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Old   January 17, 2012, 05:00
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Thibault, excellent! Thank you for you work! Currently I am working on improving my model introducing a reconstruction for them... So hope to find some advantage on using it, will post some general conclusions.
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Old   August 27, 2014, 13:56
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Hi makaveli_lcf,

Did you find any advantage using fvc::reconstruct ?

In my experience, using fvc::reconstruct seems too dissipative? need to find out what cause the dissipation, maybe due to the face-weighted averaging ?

Just curious, did you find anything similar?

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Thibault, excellent! Thank you for you work! Currently I am working on improving my model introducing a reconstruction for them... So hope to find some advantage on using it, will post some general conclusions.
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Old   July 22, 2015, 23:41
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Hi Cheng,

Did you figure out why renconstruct was too dissipative ?
I'm trying to reproduce an experiment with settlingFOAM everything work except that my system dissipate too much and then the velocities are not strong enough. reconstruct might be a start.

Thanks
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Old   July 26, 2015, 23:11
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There could be several sources of numerical dissipation. To start make sure you have achieved mesh convergence and using 2nd order discretization.

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Hi Cheng,

Did you figure out why renconstruct was too dissipative ?
I'm trying to reproduce an experiment with settlingFOAM everything work except that my system dissipate too much and then the velocities are not strong enough. reconstruct might be a start.

Thanks
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