No NSCBC Treatment for Species Terms

[whitmanscu]

Currently, when using the NSCBC treatment for BCs in PeleC, the characteristic treatment is used for velocities, pressure and density (for outflow BCs). Species mass fractions are not changed (looking at impose_NSCBC_3d for example), imposing a zero-gradient condition instead. This is leading to crashes when simulating flames exiting a domain. Ideally, the NSCBC treatment would be expanded to include species terms and take into account source and diffusion terms for these species, including reactions. Is this something that has been discussed previously? Currently I'm finding this is a barrier for any such simulations - I've tried the FOExtrap outflow BC as a workaround but pressure reflections in reacting simulations have killed these attempts.

[emotheau]

GC-NSCBC have been developed in the context of a non-reacting flow solver, and then ported to PeleC. So indeed, there is currently no specific treatment for reaction terms.