[FLASH-USERS] Hybrid Riemann solver in USM

[Yi-Hao Chen]

Dear All,

I found there is some inconsistency between the manual and the code in
describing the hybrid Riemann solver in unsplit staggered mesh scheme.

In the user manual, section 14.3.3, it says "A hybrid type of Riemann
solver which combines using the Roe solver for high accuracy and HLLD for
stability is also available."

However, in the source code, choosing the hybrid Riemann solver will call
HLL solver for shock region and call HLLD (MHD) or HLLC (hydro) solver
otherwise. The code I refer to is located in
source/physics/Hydro/HydroMain/unsplit/hy_uhd_getFaceFlux.F90
I believe this is the only place in the code that chooses different Riemann
solvers. Please let me know if there are somewhere else.

The version that I have been using is FLASH 4.4, but I checked version 4.5
and the same description is still there.

Another related question is: how do people choose which solver to use? The
FLASH user manual has a good description of the Roe solver, but very little
on all other available solvers. I understand this is probably not an easy
question to answer. But it would be very helpful if someone can point out
resources that introduce or compare different Riemann solvers. Especially
what solvers are suitable for what kind of problem and maybe the cautions
of using a particular solver.

Thank you!

Best,
Yi-Hao
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20180725/4be3c064/attachment.htm>