[FLASH-USERS] Mass Diffusivity

[Hansen, Eddie]

Hi Max,

To answer your first question, you can do either and it depends on which Conductivity implementation you request from your simulation’s Config file. If you use “Constant” then you specify the thermal conductivity, and if you use “Constant-diff” then you specify the thermal diffusivity.

Mass diffusivity is not explicitly implemented in FLASH. What the user guide means is that the file infrastructure exists if someone wanted to take the time to implement this.

--
Eddie Hansen
Applications Group Leader
Flash Center for Computational Science


From: flash-users <flash-users-bounces at flash.rochester.edu> on behalf of Maximus Allfree <mall7710 at uni.sydney.edu.au>
Date: Monday, October 16, 2023 at 12:06 AM
To: flash-users at flash.rochester.edu <flash-users at flash.rochester.edu>
Subject: [FLASH-USERS] Mass Diffusivity
Hey FLASH Users,


I have been trying to run simulations of the Richtmyer-Meshkov Instability and exploring the impacts of changing the Prandtl and Schmidt numbers. I am running this on a Mac.

For this I need diffusion, conduction, and viscosity. I asked about this a week or two ago, and thanks to those who offered help and support.

For anyone interested or maybe experiencing the same issue, when I was using the unsplit diffusion option, my program ran into a SIGSEGV error (Segmentation fault). I spent a week or so trying to work through my code to find the error. In the end I just downgraded HDF5 and, without changing my code, FLASH now runs fine without the SIGSEGV error, and I am getting decent results. No clue what this means but thought I would share.

Anyway, I have been trying to establish the Prandtl and Schmidt numbers into FLASH, however I have some questions:

In unit 22.1, looking at conduction constants, the doc says there is an option for a constant coefficient of diffusion. Would this be alpha, the thermal diffusivity constant, or is this k, the thermal conductivity constant?

Also, I need the mass diffusivity constant, D, to find the Schmidt number. Section 22.6 (mass diffusivity) is empty and says the unit provides only non-operational functionality. Is there any way I can specify the mass diffusivity with Hydro/Unsplit, or should I just try and calculate this myself from other parameters?

Thanks for reading!


Kind regards,
Max

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