The axial flow compressor:
The axial flow compressor is by far the most popular type of compressor and, although it is more difficult to manufacture, it is a more efficient compressor. Handling a larger mass of air for any given diameter, it produces more power; and because the compression ratio is high - at least 9:1 and, it can be very much higher - it is a more economical engine. The airflow through the engine is parallel with the axis, hence the name ‘axial flow compressor'.
The compressor consists of a single or multi-rotor assembly that carries blades of aerofoil section; it is mounted in a casing, which also houses the stator blades. The axial flow compressor increases the pressure of the air gradually (by approximately 1.2:1 per stage) over a number of ‘stages', each stage comprising of a row of ‘rotor blades', followed by a row of ‘stator blades'. Both the rotor and stator blades are of aerofoil section and form divergent passageways between adjacent blades of the same row. Figure 4.4 refers.
OPERATIONThe compressor rotor spool is driven by the turbine. The rotor blades accelerate the air rearwards, inducing a continuous flow of air into the inlet of the combustion chamber. The airflow emerges from the rotor stage with an increase in velocity, due to the rotating action of the blades, and with a rise in pressure and temperature caused by flowing through the divergent passage formed by the rotor. The airflow then passes through the divergent passages formed by the stator blades which convert some of the kinetic energy into pressure energy and directs the airflow onto the next set of rotors at the correct angle. The airflow emerges from each stage at approximately the same velocity as it entered, but with an increase (approximately 1.2:1) in pressure and, an increase in temperature. See graph below.