Page 34 - The Jet Engine

Compressors

Fig. 3-8 Typical triple spool compressor.

the rotor shaft and the stator casing. This is turbine at an optimum speed to achieve higher
necessary to maintain a near constant air axial pressure ratios and to give greater operating
velocity as the density increases through the length flexibility.
of the compressor. The convergence of the air
annulus is achieved by the tapering of the casing or 17. Although a twin-spool compressor (fig. 3-7) can
rotor. A combination of both is also possible, with the be used for a pure jet engine, it is most suitable for
arrangement being influenced by manufacturing the by-pass type of engine where the front or low
problems and other mechanical design factors. pressure compressor is designed to handle a larger
airflow than the high pressure compressor. Only a
15. A single-spool compressor (fig. 3-7) consists of percentage of the air from the low pressure
one rotor assembly and stators with as many stages compressor passes into the high pressure
as necessary to achieve the desired pressure ratio compressor; the remainder of the air, the by-pass
and all the airflow from the intake passes through the flow, is ducted around the high pressure compressor.
compressor. Both flows mix in the exhaust system before passing
to the propelling nozzle (Part 6). This arrangement
16. The multi-spool compressor consists of two or matches the velocity of the jet nearer to the optimum
more rotor assemblies, each driven by their own requirements of the aircraft and results in higher

24