Are upwind schemes suited for flow without discontinuities? i.e. Purely subsonic or supersonic flow.

Shuo

Shuo it's depend.

For Subsonic flow, you're talking about incompressible flow or compressible ?

If you're considering only compressible flow, upwind schemes are suited!

Upwind schemes are not the best for subsonic flows since they violate the physics of the flow itself! Of course, you can use them. What matters is the domain of dependence in the flow, not if it is compressible or incompressible, there's a clear difference between elliptic and hyperbolic problems.