[Jochen]

hello,

i am trying to figure out how many conditions have to be prescribed for a inflow boundary conditon. i am solving 2d Navier stokes equations.

my domain has two inlet boundaries.

one inlet boundary is supersonic. another one is subsonic.
my understanding is that 2d NS equations have 4 characteristics u+c,u,u,u-c;
with u being the velocity normal to the boundary and c the speed of sound.

is it correct to prescribe 4 boundary conditions at the supersonic boundary?

can 4 boundary conditions be prescribed at the subsonic boundary? or do i need to extrapolate one condition from the flowfield?
what is the consequence of prescribing 4 boundary conditions at a subsonic inlet boundary?

thanks for the help