4: Thrust of a Jet Propulsion system
Assume that we are in a reference frame moving with the engine, under steady-flow conditions. A control surface encloses the engine, with area A on the upstream and downstream faces. The flight velocity is u1, and the ambient pressure is P1. Because of flow acceleration (or deceleration) at the inlet, the "capture area) of air Ai is different from the area of the inlet. The mass flow rate of air entering the inlet is ma, and the mass flow rate leaving the nozzle is me, with the exit nozzle area being Ae. The exit velocity is ue, and the pressure at the nozzle exit is Pe. The fuel flow rate into the engine is mf, and the mass flow rate of air leaving the control volume through its sides is ms. The reaction to the engine thrust is felt by the engine at the attachment point, and is equal to the magnitude of the thrust, T.
Momentum Conservation gives:
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