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Select Vertex-Average or Area-weighted ?

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Old   March 16, 2009, 05:34
Default Select Vertex-Average or Area-weighted ?
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gnxie
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Hi, everbody. I have a question about the post-handling results. For example, if I have defined a variable in "Custom Field Funtions" like heat transfer coefficient: h=flux/(Temperature-300), now I wanna check the averaged h on a wall surface. In pannel [Reports-->Surface Integrals], which Report-Type I should select:"Area-weighted " or "Vertex-Average " ? The results by the two types are much different !! i.e., 2000 and 100.

BTW: If I select "Vertex-Average" in Field-Variable [custom-field-function], or, I select "Area-weighted" in Field-Variable[Wall-Flux-->Surf.Heat.Trans.Coeff] , the results are similar. i.e., 100 and 120.

SO, based on these, I think, Vertex-average is best for custom-field-cuntion varibale. Right? or not.

Please give me some suggestions. Thanks
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Old   March 16, 2009, 06:58
Default Area-weighted
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Ralf Schmidt
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Hi!

Vertex-Average gives you the average value related on every vertex. So, if your mesh is not uniform, you end up having over- / underestimated values (e.g. having a high number of cells in regions with high / low values).

So, area weighted average is the best choice!

I
think, the problem in your area-weighted average is, how the area is calculated. If you have a 2D case, the area weighted average might be calculated using the reference area (>report>reference values).

Best wishes!
Ralf
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Old   March 16, 2009, 09:37
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I would say that before I use "Area-weighted" to calculate"Wall-flux-->surf heat transf coeff.", I have set the area value (>report>reference values). NOTE that: actually, heat transfer coefficient is indenpendent of area !

whatever the area value I set in reference vaules pannel, The result are similar to that by "Vertex-average" for custom field vaiable

why?



Quote:
Originally Posted by Ralf Schmidt View Post
Hi!

Vertex-Average gives you the average value related on every vertex. So, if your mesh is not uniform, you end up having over- / underestimated values (e.g. having a high number of cells in regions with high / low values).

So, area weighted average is the best choice!

I think, the problem in your area-weighted average is, how the area is calculated. If you have a 2D case, the area weighted average might be calculated using the reference area (>report>reference values).

Best wishes!
Ralf
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