Concorde engine intake "Thrust"

[M2dude]

And one more thing....

Guys, apologies if it seems that I'm trying to hog things here, I'm just attempting to help clarify an extremely complex and bewildering subject.
Just imagine for a second that we are flying (or attempting to fly) at Mach 2, but instead of having a convergent/divergent intake, we just have a hole at the front. (This is termed 'a pitot intake'). Contrary to common folklore supersonic air will not enter the engine, this is a fallacy. The velocity of air entering a jet engine compressor is defined by engine mass-flow demand and the cross sectional area of the L/P compressor, you cannot force air into a jet engine at a velocity it does not require. (You can certainly force the engine to surge, and possibly drive the inlet into unstart by attempting this though). The Olympus 593-610 at Mach 2 ISA +5 had a demanded compressor Mach number (Mn1) of 0.46, this is fixed. With just a pitot intake, what WILL happen is that to satisfy the demand of the engine a single normal shockwave will form across the face of the intake, resulting in subsonic flow downstream of the shock. (A normal shock will always without exception produce subsonic downstream air). Now the pressure losses involved with a normal shock are proportional to the 'strength' of that shock, where there is only a single normal shock is utilised, over 40% of the propulsive thrust would be lost at Mach 2. (Due to enormous compressor face distortion, the engine would also be unstable to the extreme. As Mach number increases this loss also increases, to the point that if we were able to fly at Mach 3 there would be no available thrust left at all. This installation would also have huge aerodynamic drag, due to air spilling over the intake lip.
To minimise all these losses, a convergent/divergent intake is usually used for supersonic aircraft, but unless this can be made to adjust to varying engine demand and Mach number changes, this intake will be efficient at one Mach number only, and poor flow/efficiency will result at all ‘off design’ Mach numbers. (Lockheed seem to have done an incredible job with the fixed inlets on the F22 Raptor however). Designing a variable inlet in itself is not too difficult, but if you want a design with maximum possible efficiency (no reheat or afterburning) together with totally automated surge protection and operating stability, the task is truly daunting, and before Concorde quite frankly not achieved anywhere.
What any convergent/divergent intake achieves is to use a series of relatively weak oblique shocks to progressively slow the intake air down (Oblique shocks ALWAYS produce supersonic downstream airflow) the unavoidable normal shock is designed to be as weak as possible, and should occur as close as possible to the narrow throat of the intake. The now subsonic air will progressively slow down as it travels through the divergent section of the intake, up to the compressor face. Any time that intake matching is not perfect, large losses quickly occur, with air spilling over the lip of the inlet, and surge/unstart also likely to occur if things go too far off song. (The intake system of Concorde actually sensed the position of the normal shock, and allowed it’s perfect placement by varying the intake surface).
Due to the onset of writer’s cramp/mental fatigue coupled with a desperate need for beer, this will have to do for now guys, I just hope it makes it all a little less ‘clear as mud’

Dude