Editing Shock wave (section)

=== Pipe flow ===
* This shock appears when supersonic flow in a pipe is decelerated.
* Examples:
** In supersonic propulsion: [[ramjet]], [[scramjet]], [[unstart]].
** In flow control: needle valve, choked venturi.
* In this case the gas ahead of the shock is supersonic (in the laboratory frame), and the gas behind the shock system is either supersonic (''oblique shock''s) or subsonic (a ''normal shock'') (Although for some oblique shocks very close to the deflection angle limit, the downstream Mach number is subsonic.) The shock is the result of the deceleration of the gas by a converging duct, or by the growth of the boundary layer on the wall of a parallel duct.