Thrust and engines In a turbojet, exiting gas is expanded in a nozzle to generat

Question

Thrust and engines In a turbojet, exiting gas is expanded in a nozzle to generate thrust. In a turbofan, the gas is expanded in a power turbine to run a fan. If the gas exiting the gas generator turbine is at conditions o4, the atmosphere is at conditions a, and the engine is stationary, Calculate the thrust generated for the given mfr, assuming a choked nozzle of efficiency eta n. Calculate the thrust generated if the gas 04 is expanded to pa in a power turbine of efficiency eta t, and the turbine runs a fan of pressure ratio PRf and efficiency eta f. The air compressed by the fan is expanded to pa, the transmission has a mechanical efficiency pm and the nozzle efficiency is the same as in case a. Use the net mass flow rate for thrust calculations. Which one is larger? Which process (a or b) is more efficient in terms of generating thrust':

Explanation / Answer

NOTE: go through this theory , you will able to solve the question.

The amount of thrust produced by the rocket depends on the mass flow rate through the engine, the exit velocity of the exhaust, and the pressure at the nozzle exit. All of these variables depend on the design of the nozzle. The smallest cross-sectional area of the nozzle is called the throat of the nozzle. The hot exhaust flow is choked at the throat, which means that the Mach number is equal to 1.0 in the throat and the mass flow rate m dot is determined by the throat area. The area ratio from the throat to the exit Ae sets the exit velocity Ve and the exit pressure pe. You can explore the design and operation of a rocket nozzle with our interactive thrust simulator program which runs on your browser.

The exit pressure is only equal to free stream pressure at some design condition. We must, therefore, use the longer version of the generalized thrust equation to describe the thrust of the system. If the free stream pressure is given by p0, the thrust F equation becomes:

F = m dot * Ve + (pe - p0) * Ae

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