Air enters the compressor of a turbofan engine at –20°C and 60 kPa, with a flow rate of 95 kg/s and speed of 170 m/s. At the compressor exit, pressure is 1830 kPa, temperature is 455°C, and speed is 134 m/s. The aircraft is pitched up so that the centre of the compressor inlet is 100 mm higher than the centre of the outlet. 1.5% of the total flow of air is extracted from the compressor at a pressure of 880 kPa, temperature of 281°C, and low speed, for use in other aircraft systems.
a) Determine the mechanical power required to drive the compressor (state any assumptions clearly).
b) Calculate the percentage contributions of enthalpy, kinetic energy and potential energy to the compressor’s power requirement, and comment on the relative importance of these fractions.
c) Calculate the percentage of total power used to compress the extracted air. Why is this not simply equal to 1.5%?
d) Calculate the isentropic efficiency of the compressor, for air which flows through the main outlet.