Intake Thrust is Due to Impulse
I realize this thread is two years old...but I just came across it and would like to clear up some of the misconceptions here about what causes the high amount of thrust produced by the Concorde inlet duct...
The reason is very simple and it has to do with the fluid impulse principle...the air entering the inlet duct has a very high momentum (mass flow times velocity)...but it slows down inside the duct from about M2 to ~M0.5...as a result there is a large decrease in fluid momentum...
Since momentum must be conserved...the aircraft gains that much forward momentum...which is thrust...
This momentum change happens in every stage of the engine...the inlet...the compressor...the combustor...and the nozzle...the total thrust of the engine can be computed by computing the impulse (the change in momentum) at each station in the engine...
Even in subsonic flight a diffusing inlet that slows down the flow will produce a thrust impulse...the compressor also...and the burner...the turbine produces a net drag force...and so will the nozzle...
The basic math is that the net Force (in the longitudinal x axis) produced on the engine inside wall is equal to the (mass flow times velocity at the inlet...plus the pressure times area at the inlet)...MINUS... (the mass flow times velocity at the outlet...plus pressure times area of the outlet)...
Fx = (mdot * V1 + P1 * A1) - (mdot * V2 + P2 * A2)
Looking at the right hand side of that equation we have the intake duct opening as the first term..and the fan face as the second term...in order to make thrust in the forward direction we need Fx to end up with a negative value...which means the second term must be bigger...
The mass flow-velocity product decreases as the flow slows down in the duct...but the pressure-area product ends up much bigger so we end up with the second term being bigger than the first term...and we have a change of momentum to the left (ie negative impulse) and we get thrust...
So while it is true that flying at M2 we can greatly increase the static pressure going into our engine by converting dynamic pressure to static pressure...that does not tell us why this causes thrust...the reason is the change of momentum...or impulse...
By itself an increase in pressure ratio will result in somewhat more thrust...and a six-fold increase in static pressure would result in about a 40 percent increase in thrust...compared to an engine that is at atmospheric pressure...but that does not tell us which components of the engine are actually making thrust and which ones are making drag...only a component-by-component breakdown of the impulse will give us the answer...