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Temperature fall under physical value

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Old   August 25, 2021, 03:39
Question Temperature fall under physical value
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Horst van Gras
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Hi,
I have a multiregion simulation which a Fluid starting around 293K. It is a classical buoyancy problem nothing to serious. However during the calculation process in some cells the temperature falls under 293, which is not physical in my understanding, as I'm heating and there is no serious expansion.


I doubt this may due to some convergence issues. With running time there are less cells, which temperature falls under 293. It is not much, but it can affect the solvers stability when I do not limit it.



Does someone encountered similar behavior before? Do you know which part of the energy equation is responsible for this? For example, falsely calculated alpha , transferring to much heat to the wall?


Thx in advance
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Old   August 25, 2021, 04:13
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Agustín Villa
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Hi,


could you add some info, like the solver you're using, numerical schemes... The reason of your low T values might be there.


Once I was running unsteady simulations in buoyant flows and I got higher temperatures than the prescribes ones when moving from 1st order to 2nd order schemes.


You could try to limit the temperature field using a fvOption.


Regards
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Old   August 25, 2021, 04:29
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Quote:
Originally Posted by agustinvo View Post
Hi,


could you add some info, like the solver you're using, numerical schemes... The reason of your low T values might be there.


Once I was running unsteady simulations in buoyant flows and I got higher temperatures than the prescribes ones when moving from 1st order to 2nd order schemes.


You could try to limit the temperature field using a fvOption.


Regards
Hi thanks for the response,
I'm using only second order numerical schemes as Gauss linear and Crank Nickolson with 0.9 and also cellMDLimited leastSquares 1.0.


Also already using fvOption for stabilizing.



Therefore I'm a bit confused.
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Old   August 26, 2021, 03:21
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Horst van Gras
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Hi,
could manage to restrain the influence factor.

It's the thermal diffusion which cause the temperature drop:
fvm::laplacian(turbulence.alphaEff(), he)


Using other laplacian scheme seems to help like: Gauss linear orthogonal but doesn't get rid of the problem. The mesh is also very smooth, therefore that does not seem to be a source.
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