[Nek5000-users] Temperature Issue, non physical values for certain Pr num.

[nek5000-users at lists.mcs.anl.gov]

Hi Michael,

Yes - this is a well-known issue when not fully resolved
because the code does not preserve monotonicity,
particularly at LES resolutions.  It is a high-prioty
item, but won't be addressed till next year.  Under
these circumstances I typically clip the temperature
field - which is a poor man's monotonicity preservation
algorithm.  Although unsatisfying, it's not all that bad
and we've gotten very good results in some past mixed-stream
problems where there is a sharp interface.  (One can, of
course, always come up w/ a case where this approach doesn't
work and something more robust is required, which is why
we'll be looking into this soon...)

Paul



On Wed, 17 Nov 2010, nek5000-users at lists.mcs.anl.gov wrote:

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> Hi,
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> I am having an issue with temperature values in my domain. The domain consists of two inlets, one at a temperature of 300 and the other 100. It appears
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> that the interface between the two is giving non-physical temperatures, but what is interesting is the magnitude of these over/under shoots is dependent on
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> the Prandtl number.  To see the extend of this I saved the max/min temperature in the domain for several time steps.
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> See the attached image.  The low Pr case had Pr = 0.005, where as the other case had Pr = 0.71.  Both cases show non - physical results, but the low Pr
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> case seems to recover and approach the limits for the domain given by the boundary conditions.  In the other Pr = 0.71 case, the fluctuations and magnitudes are
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> much larger and don't appear to stabilize and recover.
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> Again, I have looked at fld files to confirm that these large differences occur at the interface between the hot/cold fluid.  Is there a solution to this problem?
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> Thanks,
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> Michael
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