Characteristic boundary conditions

jelmer

I'm currently working on an Euler adjoint solver and now I want to implement a subsonic outflow boundary condition which is an inflow boundary for the adjoint problem. This means 1 outgoing and 3 incoming characteristics (in 2D) for the adjoint problem. One adjoint variable is zero and the other 3 adjoint variables are calculated using the extrapolation of an adjoint characteristic from the innerdomain.

Can somebody give me any directions on how I can write/modify a boundary condition to apply characteristic extrapolation and compute new boundary values from this? I find the other boundary condition implementations hard to read from source, so I can not find an appropriate example.

regards, Jelmer