Mach angle

They propagate across the flow at the Mach angle μ:

Mach angles may also occasionally be visualized out of their condensation in air, as in the jet photograph below.

The minimum angle, , which an oblique shock can have is the Mach angle , where is the initial Mach number before the shock and the greatest angle corresponds to a normal shock.

These allow good pressure recovery without spillover through the full range of speeds by matching their angle to the mach angle, but have problems with seals at high speed that is high pressure and temperature (like in a diesel engine).