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Old   November 7, 2011, 12:04
Default foamCalc/heat flux problem
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andres
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Hi foamers!
I'm trying to validate and report the heat flux using foamCalc for a "flow of oil over plate" problem, using the buoyantBoussinesqSimpleFoam solver. But I'm getting different values after used foamCalc magGrad T utility.




L=5m for length and h= 1m width =1m but I'm testing with 2d case.

I have done several meshes, from a super coarse to ultra refined mesh with scaling, I also have calculated the first cell height.
The problem is that with some meshes I get values really similar to the analitic solution (about 3% error) but If I change the mesh dimension I get other values of magGrad T, this values are "similar" to the correct values but it seems that this values are multiplicated/divided by an natural number.
The analitic solution gives:

My calc;
Fine mesh of 7500 volumes ( 150 for x and 50 for y with scalling first cell heigth =0.00507462)
Plate: magGrad T=15763.186 K/m --> multiplication by k=0.144 and the plate lenght gives q"=11349.4945152 W ( unitary lenght) this is 2.8% of error.


20000 Volumes mesh (200*100 with scalling FCL=0.000331119)
Plate: magGrad T=183675.96985 K/m absolutly out of merge, but if you divide this value by 12 (why 12!!! ) get 15306.33 K/m --> multiplication by k=0.144 and the plate lenght gives q"=11020.558191 this is 0.178% of error

I will upload the case file soon!

Thanks for reading and sorry about my english!!!

http://www.mediafire.com/?qpddha0wd7br1a2
http://www.mediafire.com/?cnl5a4vrx1nch5n
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Old   November 17, 2011, 03:45
Default Re: heat flux problem
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Hi AndrÚs!

The different magGrad T values really seem to be strange and I don't know the reason. Do you get the same results with wallHeatFluxLaminar instead of magGrad?
I experienced that magGrad and wallHeatFluxLaminar give wrong results when a groovyBC is applied to the surface - but with a fixedValue boundary condition, it works fine also for different meshes in my studies.

Regards
Hugo
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