Riemann Invariants for the 2-Dimensional Euler Equations
 

Hello,

When applying the Riemann Invariants at subsonic inflow/outflow boundaries, you require the normal velocity and tangential velocity of internal cells or the free-stream. Am I correct in assuming that these quantities are not just the magnitude of those velocities, but that they can have negative signs?

Thank you,

maybe you can find some issues here
http://www.math.u-psud.fr/~pascal/publis/pascal_R05.pdf