MAE 112 SECOND EXAM March 11, 2008 Do all three problems in eighty minutes. Open books and notes. Calculator allowed. I. Consider a turboprop engine that flies at a Mach number of 0.45 with ambient conditions at 298 K and one atmosphere of pressure. The air capture area is 0.25 square meter. The propeller is aft (downstream) of the engine. There are two turbine stages with different rotational speeds; the first one drives the compressor while the other drives the propeller. The turbine exit pressure is practically one atmosphere. Consider a combustor exit temperature of 1450 K and a mass mixture ratio μ = 30. Neglect air bleeding for cooling. The specific heat of combustion products equals 0.30 cal/gm o K. a) What is the pressure entering the compressor? Assume a polytropic diffuser efficiency equal to 0. 97. b) Assume a pressure ratio of 15 across the compressor. If the polytropic compressor efficiency is 0.96, what is the power requirement of the compressor? c)
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