Originally Posted by
Gauges and Dials
I understand that if you did force analysis or put load sensors on the shafts and bearings, you'd see that the fan and compressor rotors are trying to pull the airplane forward, and the turbine rotors are trying to pull it backwards. And if you did the same thing for the stationary parts of the engine, you'd see that the forward walls of he combustion chambers and the compressor stators were trying to push the airplane forward, and the aft walls of the combustion chambers and the turbine stators were trying to push the airplane backward. But the thrust all ultimately comes from the expanding fuel-air mixture being burned. The compressor consumes one form of energy -- the rotation of the shaft -- and produces another -- compression of the air. I guess similarly the inlet nozzle in the J58 consumes one form of energy -- the forward motion of the airframe through the air -- and produces another -- compression of the air. But it doesn't really "produce thrust" any more than a ram air intake "produces power".
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Maybe it's better not to use words like create /produce/ provide.
The inlet feels (as we would if trying to stop it moving) a thrust or drag force because air is flowing through it. It doesn't matter why the air is moving. The force is still there. Air can flow through it in different scenarios all of which use a different energy source. On the front of a running engine air flows because fuel is burned. or if flamed out because the aircraft is losing altitude. When being tested in a wind tunnel air flows because an electric motor spins.
Nothing consumes energy , it converts it to another form. For an inlet the free stream has a certain amount of energy because it's "coming at" the engine with speed. The idea is to convert speed to pressure because that's the reason for the inlet. It's a better compressor than no inlet. (The compression with no inlet "just happens" as opposed to being manipulated by careful inlet design and actually occurs when an inlet unstarts). However some proportion of the "speed" ends up as thermal energy and hence we hear "the inlet has 80% pressure recovery". It only managed to get 80% of the "speed" to supercharge the engine compressor. And when the inlet unstarts it's doing nothing special as shown by a pressure recovery of, say, 40%.
The energy conversion above is exactly what happens in the spinning compressor. Instead of being given speeding air it has to make its own, stage by stage. The rotor speeds it up and the stator converts as much as it can to pressure.