Matthew Knepley <[email protected]> writes: > What you suggest (flux boundary conditions) would require short-circuiting > the Riemann solver loop to stick in the flux. It is doable, but we opted > against it in the initial > design because it seemed more complex than ghost cells and did not seem to > have any advantages. For multi-domain things, wouldn't you require that the > cell average of > the adjacent cell be used as the ghost value for consistency? We would need > a new interface to mark existing cells as ghosts, but that is quite simple > compared to a flux BC > addition.
FV methods usually need a ghost for slope reconstruction. FE methods (CG or DG) don't have a reconstruction and thus can use a flux boundary condition by solving a degenerate Riemann problem. IMO, this is simpler than creating a ghost cell and solving a full Riemann problem. It's what we use for subsonic inflow in libceed-fluids, for example.
