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

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

Thank you for the responses. 



Paul,  Is there an efficient way to clip the temperatures or do I need to loop through the points each time step? 



-Michael 


----- Original Message ----- 
From: nek5000-users at lists.mcs.anl.gov 
To: "Nekton User List" <nek5000-users at lists.mcs.anl.gov> 
Sent: Thursday, November 18, 2010 2:08:36 AM GMT -06:00 US/Canada Central 
Subject: Re: [Nek5000-users] Temperature Issue,        non physical values for certain Pr num. 

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: > > > Hi, > > > > 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 > > 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 > > the Prandtl number.  To see the extend of this I saved the max/min temperature in the domain for several time steps. > > > > 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 > > 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 > > much larger and don't appear to stabilize and recover. > > > > 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? > > > > Thanks, > > Michael > 
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