# Leave the turbine exit at station 4 still hot and at

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leave the turbine exit at station 4, still hot and at a stagnation pressure well above the ambient. These gases then expand through a nozzle that converts the excess pressure and thermal energy into a high-kinetic-energy jet at station 5. The forward thrust on the engine, according to Newton’s Second Law, is produced by the reaction to the internal forces that accelerate the internal flow rearward to a high jet velocity and the excess of the nozzle exit plane pressure over the upstream ambient pressure. Diffuser Analysis

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Consider a fluid element passing through a given point at the inlet diffuser. The pressure, temperature and density feel when the measurements device feel is the static condition (the condition when you feel when you ride along with the gas at the local flow velocity). However along the fluid element journey from the inlet to the outlet of the diffuser, the fluid element is adiabatically slow it down to zero velocity. Thus, the change in fluids kinetic energy must be taken into account (become total condition). The relation between static and total pressure is given as; a k k static total p p M k P P ' 1 1 2 2 1 1 = - + = - The effects of friction, turbulence and other irreversibilities in the inlet flow are represented by the diffuser efficiency. The adiabatic diffuser efficiency is defined as the ratio of the actual isentropic enthalpy change to the ideal isentropic enthalpy change. In terms of the static and total pressures, the diffuser efficiency becomes; a a d p p p p - - = ' 1 1 η Other parameter in measuring diffuser efficiency are called recovery factor and pressure drop specific which are defined as; Recovery factor; a a r p p 1 = η Pressure drop specific; ' 1 1 ' 1 p p p E r - =
Isentropic process k k p p T T 1 0 ' 1 0 ' 1 - = 1 ' 1 T T = Diffuser work (jet)- work in 2 ) ( 2 1 0 1 V T T cp w d = - = kJ/kg Compressor Analysis Compressor efficiency; 1 2 1 ' 2 1 2 1 ' 2 T T T T h h h h leWork Irrevessib Work Isentropik c - - = - - = = η

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Isentropic process k k p p T T 1 1 ' 2 1 ' 2 - = 2 ' 2 P P = Compressor work (shaft)- work in ) ( 1 2 1 2 T T cp h h w c - = - = kJ/kg Combustor Analysis Combustor efficiency f a s b m m x V H L h h V H L Q . . . . 2 3 - = = η Combustor pressure specific
2 3 2 p p p E b - = Heat source-in ) ( 2 3 2 3 T T cp h h q s - = - = Turbine Analysis Turbine efficiency; 3 ' 4 3 4 3 ' 4 3 4 T T T T h h h h Work Isentropik leWork Irrevessib t - - = - - = = η Isentropic process k k p p T T 1 ' 4 3 ' 4 3 - = 4 ' 4 P P =

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Turbine work (shaft)- work out ) ( 4 3 4 3 T T cp h h w t - = - = kJ/kg Nozzle Analysis Nozel efficiency ' 5 4 5 4 T T T T n - - = η Jet efficiency ' 5 5 ' V V V V j j j = = η ) ( 2 5 4 5 4 2 5 T T cp h h V - = - =
) ( 2 ' 5 4 ' 5 4 2 ' 5 T T cp h h V - = - = n j η η = Isentropic process k k p p T T 1 ' 5 4 ' 5 4 - = 0 5 ' 5 P P P = = Nozel work (jet)- work out 2 ) ( 2 5 5 4 V T T cp w n = - = kJ/kg Turbojet Thrust The thrust of the engine is obtained by applying Newton’s Second Law to a control volume, as shown in Figure 5. If the mass flow rate through the engine is m , the

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• Spring '13
• DrZaimin
• Dynamics, Mass flow rate, Turbofan, Jet engines, engine inlet

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