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Heat Transfer convergence problem

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Old   April 26, 2013, 03:24
Default Heat Transfer convergence problem
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Hi everyone,

I want to model heat transfer through a wall in Fluent. I have several layers of material, including some shell conduction.
I set freestream T 293K "inside" and 273 K "outside". Now, to check if my calculation is converged, I observe Total Surface Heat flux on faces "in" and "out", and I would expect that the sum of these fluxes would tend to 0. It does indeed tend to it, but very very very slowly and I still have something like 7% error between flux in and flux out, which is I think too much....
I first had a under-relaxation factor quite low, but then I progressively raised it up to 0.99 now, and even if it does help "getting there" faster, it still appears that it will never completely converge (in fact relaxation factor helps just a very little bit).
I tried first 2nd order upwind scheme, now I tried QUICK, it doesn't change anything.
Residuals are fine.

I have 2 different geometries, the problem occurs in both except that in my second geometry, the fluxes are higher, so the error is much less in %. (but it's the same magnitude of error in Watts).

Does anybody have an idea on what could be the problem and how to solve it ?

Thanks a lot !
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Old   April 26, 2013, 06:29
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Quote:
Originally Posted by frodooon View Post
Hi everyone,

I want to model heat transfer through a wall in Fluent. I have several layers of material, including some shell conduction.
I set freestream T 293K "inside" and 273 K "outside". Now, to check if my calculation is converged, I observe Total Surface Heat flux on faces "in" and "out", and I would expect that the sum of these fluxes would tend to 0. It does indeed tend to it, but very very very slowly and I still have something like 7% error between flux in and flux out, which is I think too much....
I first had a under-relaxation factor quite low, but then I progressively raised it up to 0.99 now, and even if it does help "getting there" faster, it still appears that it will never completely converge (in fact relaxation factor helps just a very little bit).
I tried first 2nd order upwind scheme, now I tried QUICK, it doesn't change anything.
Residuals are fine.

I have 2 different geometries, the problem occurs in both except that in my second geometry, the fluxes are higher, so the error is much less in %. (but it's the same magnitude of error in Watts).

Does anybody have an idea on what could be the problem and how to solve it ?

Thanks a lot !
good morning , i need some answers about fluent,i want to now the definition about, and how can i use them : (free stream temperature,heat generation rate, external radiation temperature,and external emissivity)
please i want some responses
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