[Nek5000-users] Dimensionfull passive scalar

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

Hi!


I am simulating a flow where thermodynamic processes takes place.

Since these thermodynamic processes are rather complicated I decided that developing the set up is best done in dimensionfull variables. Here I ran into unexpected problems since it seems as if the parameters in the .rea file do not work as I thought they would.


The temperature solution works well. Putting in the "rhocp" and "conduct" of my fluid into "p007" and "p008" gives the results that I expect.


However, I also have two passive scalars. For them I am not sure what the meaning of "rhocp" actually is.

>From eqn (1.4) of Ref. [*] I would assume that setting up a passive scalar \phi with diffusivity a = 2.14E-5 m^2/s evolving as


D \phi /D t = a Laplacian(\phi)        [D/Dt = total derivative]


means using "rhocp = 1" and "a = 2.14E-5". However, this seems to not be the case, since under these assumptions the corresponding dimensionless set-up gives totally different results.


If my understanding was correct it would only be the ratio of "rhocp" and "conduct" that matters fo a scalar, but I have found that the individual values matter.


This leads me to the questions:

* What is the meaning of "rhocp" and "conduct" for a scalar?

* In which dimensions "rhocp" and "conduct" for a scalar?

* Why does the individual values of "rhocp" and "conduct" matter, when they should no according to eqn (1.4) of Ref. [*]?


Best,


Johan



[*]: User Documentation: http://nek5000.github.io/NekDoc/Nek_users.pdf


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