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Q6 Consider a turbofan engine with a two-shaft configuration as shown in Figure 2. The engines are mounted on a twin engine powered passenger aircraft that flies at a cruise altitude of 31000 ft and a Mach number of 0.85. The compressor ratio is 16. • Assume that the pressure ratios of the working gases across the fan that go into the bypass duct and core nozzle are 1.81 (between station 2 and 13) and 2.8 (between stations 2 and 24) respectively. • The bypass ratio is 6. • Use isentropic efficiencies of 90% for all fan, compressor and turbine stages; Yair 1.4 for air and y, = 1.3 for combustion products, the Specific heat for fuel at constant pressure Cp = = = = RxYf Y-1
• Assume isentropic inlet. Assume that both nozzles expand the flow isentropically to ambient pressure. • Neglect fuel mass flow rate, pressure loss in the combustor and mechanical losses. 9 O Figure 2 The schematic of a 2-shaft turbo-fan engine. = [10] a) If the turbine inlet temperature T04 = 1590 K, determine T-44 and Trs [4] b) If jet A-1 fuel is used, what is the fuel-air ratio in the combustion chamber? c) Calculate jet velocities in the core and in the bypass duct, Vic [6] and Vid respectively. [6] d) If the total mass flow rate of air going into the engine is 5yz kg/s, (note the last 2 digits in the mass flow rate are taken from the last two digits of your student ID: 20uvwxyz), determine the gross thrust and net thrust. e) The geometry of the core nozzle is convergent-divergent. Find [4] the area of the throat.