[FLASH-USERS] combining MHD and thermal conduction

[Slavin, Jonathan]

​Hi Ernesto,

I maybe should have mentioned that my runs have been in 2D (cylindrical).
So have you done such runs?  Also for the conduction, I'm using unsplit
diffusion with electron thermal conduction and power law conductivity.  You
mention being careful with split vs. unsplit diffusion, but you don't say
which one works - or what that means to be careful.​

​ Or is it just that parameter setting addThermalFlux? I'll try setting
that to False to see if that helps.

To answer your question, I'm not using super-time-stepping.  Didn't seem
necessary since with Crank Nicholson diffusion you have unconditional
stability.  So I haven't looked into how to use that.

Thanks for the suggestions.

Jon ​

> ---------- Forwarded message ----------
> From: ERNESTO ZURBRIGGEN <ezurbriggen at unc.edu.ar>
> To: flash-users at flash.uchicago.edu
> Cc:
> Bcc:
> Date: Mon, 14 Aug 2017 12:18:31 -0300
> Subject: Re: [FLASH-USERS] combining MHD and thermal conduction
> Hi Jon!
>
> >It made me wonder if there is some numerical way that the implementations
> of thermal conduction and MHD interfere with each other.
>
> I have used MHD+(isotropic) Conduction without any problem of that sort.
> One confusing thing is that you can select Diffusion/split and
> Diffuse/unsplit. Be careful with that.
>
> Something curious is that if the simulation include unsplit/MHD +
> (regardless of split or unsplit) Diffusion you have to also set the
> runtime parameter addThermalFlux=.false. (.true. by default)
> Otherwise, you are including the thermal conduction effect twice, i.e.,
> heat diffusion via the HYPRE libraries decoupling the heat equation, and
> adding the thermal flux to the total energy flux in the Hydro unit.
> I think the most consistent configuration would be unsplit/MHD + Diffusion/
> unsplit + addThermalFlux=.false.
>
>
> >I tried reducing the conductivity further and found that only by reducing
> it by many orders of magnitude (~8) was I able to get runs that didn't
> crash
>
> Maybe you can try reducing the parameter dt_diff_factor.
>
> Are you using super-time-stepping?
>
> Best!
> Ernesto.
>
> --
________________________________________________________
Jonathan D. Slavin                 Harvard-Smithsonian CfA
jslavin at cfa.harvard.edu       60 Garden Street, MS 83
phone: (617) 496-7981       Cambridge, MA 02138-1516
cell: (781) 363-0035             USA
________________________________________________________
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