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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 Spring '09
 Sirgianno
 Thermodynamics, Energy, Physical quantities, Polytropic Efficiency, Turboprop

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