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Both types are driven by the engine turbine and are usually coupled direct to the turbine shaft.
The centrifugal flow compressor (fig. 3-1) is a single or two-stage unit employing an impeller to accelerate the air and a diffuser to produce the required pressure rise. The axial flow compressor (fig. 3- 7 and fig. 3-8) is a multi-stage unit employing alternate rows of rotating (rotor) blades and station¬ary (stator) vanes, to accelerate and diffuse the air until the required pressure rise is obtained. In some cases, particularly on small engines, an axial com¬pressor is used to boost the inlet pressure to the centrifugal.
With regard to the advantages and disadvan¬tages of the two types, the centrifugal compressor is usually more robust than the axial compressor and is also easier to develop and manufacture. The axial compressor however consumes far more air than a centrifugal compressor of the same frontal area and can be designed to attain much higher pressure ratios. Since the airflow is an important factor in determining the amount of thrust, this means the axial compressor engine will also give more thrust for the same frontal area. This, plus the ability to increase the pressure ratio by addition of extra stages, has led to the adoption of axial compressors in most engine designs. However, the centrifugal compressor is still favoured for smaller engines where its simplicity and ruggedness outweigh any other disadvantages.
Leads to improved specific fuel consumption for a given thrust.
The trend to high pressure ratios which has fav¬oured the adoption of axial compressors is because of the improved efficiency that results, which in turn
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