MAE112HW7 - MAE 112 Propulsion Homework Assignment #7 Due:...

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1 MAE 112 Propulsion Homework Assignment #7 Due: March 6, 2009 1. Consider a turbofan engine flying at a Mach number of 0.8 with an ambient pressure of one atmosphere and an ambient temperature of 500 R. The intake has .98 polytropic efficiency. The air is divided with a bypass ratio of 2.5 into a primary and a secondary (or bypass) flow at the exit of the air intake. The primary flow passes through a fan and compressor combination with a pressure ratio of 20 and polytropic efficiency of .98 while the secondary flow passes through a fan with a pressure ratio of two and a polytropic efficiency of .98. The upstream low-pressure (LP) portion of the compressor and the fan are driven by the downstream low pressure (LP) portion of the turbine; the downstream high-pressure (HP) portion of the compressor is driven by the upstream high pressure (HP) portion of the turbine. The low-pressure (LP) compressor has a pressure ratio of 5 while the high-pressure (HP) compressor has a pressure ratio of 4. (Still, the overall pressure ratio is 20=5 x 4.) The primary flow is burned at constant pressure with liquid octane fuel with a final combustor temperature of 2500 o R and then expanded through a turbine and ultimately through the primary nozzle to ambient pressure. The burner efficiency is .99 while the polytropic efficiencies of the turbine and the nozzle are each .95. All the work taken from the turbine flow is employed to drive the fan and the compressor. The secondary flow expands isentropically to ambient pressure through a secondary nozzle. The specific heat for air should be taken as .24 Btu/1bm
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MAE112HW7 - MAE 112 Propulsion Homework Assignment #7 Due:...

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