[FLASH-USERS] Bug in the split solver viscous energy fluxes since FLASH2.x

[James Beattie]

Dear FLASH developers,

I am quite confident that there is a bug in the three-dimensional viscous energy fluxes for the 8 wave split solver in the public FLASH version, which we have tracked back to the original implementation in FLASH2.2.

For example, in the x sweep, the z contributions to the flux are:

[cid:3AD6848A-621A-469C-A794-136D10F8DA24]

which correspond to the fluxes:

[cid:8A59777D-BFF6-4464-920C-09015AE37D88]

Where \overline{v_z \partial_z v_z} is the average along the sweep.

In the second term, there is a minus (highlighted in red) where there should be a plus, which computes the difference rather than the average flux on the cell face.

The same can be said about the z energy flux contributions to the y and z sweeps — both have terms that are differences rather than averages — resulting in incorrect viscous fluxes for the split methods.

The public unsplit method has both the correct averaging and viscous energy flux terms, for comparison.

Thanks,
James Beattie (he/him)
PhD student | Deakin, Dean’s (theoretical physics) & Fulbright scholar
University of California, Santa Cruz | Department of Astronomy and Astrophysics
Australian National University | Research School of Astronomy and Astrophysics
GScholar<https://scholar.google.com/citations?user=ZIgumjQAAAAJ&hl=en> | ResearchGate<https://www.researchgate.net/profile/James-Beattie-4> | CV<https://www.mso.anu.edu.au/~beattijr/cv/AcademicCV_Beattie2022.pdf> | Website<https://www.mso.anu.edu.au/~beattijr/>


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