[Nek5000-users] Conjugate Heat Transfer

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

Hi Markus,

We're currently not using the group distinction to segragate fluid/solids.
(Though perhaps we should...)

It is simply imposed by the fact that the first nelv elements must be
fluid, and that the sum total must be thermal (fluid+solid).

Thus, nelv \le nelt in the .rea file.

A further consequence is that nek will look for only nelv*2*ndim bcs
for the fluid.

At present, prenek is not set up to supply the correct number of bcs -
it requires intervention by another code or editing by hand.   This is
all subject to change, but the truth is we just resurrected conjugate
heat transfer for parallel processing in the past 12 months and, so far,
have been the only customers.   I believe, however, that if a .rea file
is set up this way, that genmap and nek5000 will work properly.  (I've
used it both for 2D and 3D runs and all seems to be working ---- I never
trust these things, however, until I've done it for at least 10
different cases...).

We can do some work on prenek to get it into shape for you, but I'm
presently not very happy with the interface and need to kick around
a few ideas with users (like you) and developers.

I hope this helps.

Paul




On Mon, 1 Feb 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Hi,
>
> I have experienced some difficulties with setting up a 2D conjugate heat 
> transfer problem. When generating the .rea file with prenek, I create a mesh 
> of, say 60 elements and define, say, 20 of those as solids (material group 1 
> instead of 0). Trying to run this .rea file in genmap (even when it is 
> converted to re2) does not work since the fluid boundary condition section of 
> the .rea file contains entries for elements (the solids) without 
> connectivity/boundary information. Deleting those entries (4*20 lines for 2D) 
> lets genmap accept the rea file and a map is created with one section for the 
> fluids elements and one for the solids.
> Running these files with nek5000, however, resulted in element mismatch 
> errors, no matter what combination of solid elements vs. number of processors 
> I tried. The newest nek5000 svn was used.
>
> The solution I found is the following: when one takes the .rea file for 
> conjugate heat transfer (as it came out of prenek) and changes all solid 
> elements back to fluids, a map can be generated from this only-fluids-.rea 
> file with genmap that is essentially left in ignorance of the conjugate heat 
> transfer problem/solid elements. Running this "fluids-only" map with the 
> original "conjugate heat"-.rea file (having deleted the solid elements 
> boundary/connectivity information in its fluids section) will work and 
> produces physically correct looking results.
>
> My questions now are the following:
> -Is this an appropriate way to go or am I missing some parameters that need 
> to be set? The rea files come directly out of prenek, so I didn't manually 
> change any parameters.
> -By generating a map file that does not resemble what's truly going on, do we 
> loose parallel scalability and if so, is that a considerable penalty?
> -I had some trouble defining solid elements in 3D with prenek. Whenever I 
> click on an element to change its material group, it does not do it. Is there 
> a fix?
> -Expanding a 2D conjugate heat transfer problem with n2to3 does not work. All 
> upper level elements become solids. Is there a fix for this?
>
> I apologize for my lengthy postings,
> Markus
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