[FLASH-USERS] Setting a fixed value boundary condition for MHD simulations.

[Sheth, Nishka]

Hello Everyone,

I am currently working on setting up a MHD problem in the r-z geometry with uniform grid using FLASH 4.7. My current goal is to keep the x_max boundary values fixed to their initial values throughout the simulation. To achieve this, I have modified the Grid_bcApplyToRegionSpecialized.F90 file in a similar way to the Shu Osher problem. However, I have noticed that the boundary values still vary with time.

To investigate this issue, I ran the Shu-Osher problem for longer than 1.8s, which is sufficient time for the shock front to reach the x_max boundary. Interestingly, I observed that the boundary values also changed for this simulation. I have attached snapshots of the Density vs X plot for the Shu Osher problem at 1.8s (as shown in the user manual) and at 2.4s, where the boundary value differs from the initial value.

I would greatly appreciate any guidance on setting up a fixed value boundary condition for the MHD simulation. Additionally, could you recommend a reference that describes how general type of boundary conditions (such as Newman, Dirichlet, etc.) for all primitive variables are set up in FLASH for the MHD simulation?

Thank you in advance for your help.

Nishka Sheth
Physics Graduate Student
University of Saskatchewan, Canada
phc027 at usask.ca

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