[mesa-users] turbulent diffusion

[Bill Paxton]

Hi Aaron,

I'll make that change in the mesa sources. Is the only change is to replace 'anonymous_mixing' by 'no_mixing'?  Your email also changes loc-1 to loc+1; is that also part of your suggested change?

-Bill




On Jun 5, 2016, at 6:19 PM, Aaron Dotter wrote:

> Hi folks,
> 
> I've been experimenting with turbulent diffusion in a solar model this week and found that it doesn't work as expected.  I mean this one
> 
>             !### turbulent_diffusion_D0
> 
>             ! Turbulent diffusion below outer convection zone.
>             ! Similar effect to overshooting.
>             ! Proffitt, C.R., and Michaud, G.,  
>             ! GRAVITATIONAL SETTLING IN SOLAR MODELS,  
>             ! ApJ, 380:238-290, 1991.  
>             ! e.g., 8000 cm^2 s^-1
> 
>          turbulent_diffusion_D0 = 0
> 
> This was developed in the context of the solar model so that's the only place I've tested it so far.  I'm using turbulent_diffusion_D0 = 7500 as suggested by the authors but it does not produce any extra mixing.  I get the same result with 7500 as I do with 0.
> 
> The problem is in star/private/turbulent_diffusion.f90:
> 
>             if (s% mixing_type(loc-1) == anonymous_mixing) then
>                call do_turbulent_diff(ierr)
>                if (ierr /= 0) return
>             end if
> 
> The if statement does not function as we'd like it to.  I'm not sure of the original intent of this code.  What we're looking for is if the zone below the bottom of the surface convection zone is currently unmixed, then the turbulent diffusion coefficient is applied.
> 
> I've tried replacing that if statement with
> 
>             if (s% mixing_type(loc+1) == no_mixing) then
> 
> and this works as expected in my solar case.  First, it is checking the zone below the boundary (loc+1) not the one above the boundary (loc-1).  Second, it is checking to see that the zone is not mixed -- sorry I'm not familiar with the use or meaning of anonymous_mixing.
> 
> However, this might not catch all the possible cases for which the extra mixing should be applied.
> 
> 
> - Is there a more MESAonic* way to write this? 
> 
> 
> - Can we get that change added to MESA trunk?
> 
> 
> Thanks!
> 
> Aaron
> 
> 
> 
> * I'm thinking of a word like "pythonic" in the python realm but mesonic and Masonic are already taken.  ;-)
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