[Nek5000-users] Courant for passive scalar ?

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

Hi,
I haven' t tried this myself, but I guess you could write a subroutine that calculates the maximum timestep from the scalar field and sets dt accordingly. Then simple call the routine from userchk.

Best,
Jan

> Am 12.06.2017 um 18:15 schrieb nek5000-users at lists.mcs.anl.gov:
> 
> Dear Neks
> 
> I am running a simulation of a channel, with a passive scalar. Using diffusivity=viscosity, the velocity field converges nicely, whereas the passive scalar blows up at some random point down the simulation. Reynolds number is 10 000 so its in the turbulent regime.
> 
> I suspect this is due to the fact that the passive scalar is intermittent, so sometimes large fluctuations will occur, totally uncorrelated to velocity fluctuations. to avoid the code to blow up, one would need to setup the timestep based on a courant criterion for the scalar, and not for the velocity. 
> 
> has this already been implemented ?
> or how do people avoid this ?
> 
> any suggestion is more than welcome.
> thanks
> Agnese
> 
> 
> 
> Agnese Seminara
> --------------------------------
> CNRS
> Institut de Physique de Nice
> Parc Valrose 
> avenue J Vallot
> 06108 Nice, France
> +33 (0) 492 076 775
> http://sites.unice.fr/site/aseminara/
> 
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