Which statement describes an axial-flow compressor?

• A. A type of compressor where airflow is radial.
• B. A type of compressor in which airflow is essentially linear; composed of several stages of rotors and stators; the compressor ratio is determined by the decrease in area of the succeeding stages.
• C. A single-stage compressor with no rotors.
• D. A centrifugal compressor.

Answer: (B)

An axial-flow compressor increases air pressure by passing the air along the engine axis through multiple rotor-stator stages. Each stage has a rotor that speeds up the air and a stator that turns and diffuses it, converting velocity into pressure while keeping the flow essentially along the axis. The overall pressure rise comes from stacking several such stages, so the compressor ratio builds up as the air moves through successive stages. The idea that the ratio is determined by a decrease in flow area through the stage stack fits this design, since the geometry is arranged to progressively raise pressure while maintaining axial flow.

Radial (centrifugal) flow moves air outward from the axis, which is not axial flow. A single-stage compressor with no rotors wouldn’t provide the multi-stage energy transfer that defines axial flow. A centrifugal compressor is a different type, not axial-flow.