CliveL
The first bit of the moveable front ramp was carefully shaped to give a sequence of weak shocks that reduced the Mach Number so gradually that shock losses were minimised.
Must have been a highly efficient inlet for a Mach 2 plane: Two traditional oblique waves; a fan-shock (also oblique); a shockwave off the lip that is normal and oblique depending on how far you are away from the lip, and a normal terminal shock.
This was close to an isentropic process, hence the name.
So, isentropic would, in this context, mean that no shock-losses occurred at all?
The whole point of the intake geometry was that the purely aerodynamic boundary between main duct and ramp void was infinitely flexible in shape, which made the design very tolerant of flow disturbances.
Makes sense for an airliner that you would design an inlet this way