Two Photographs of a centrifugal compressor.

Most modern passenger and military aircraft are powered by gas turbine engines, which are also called jet engines. All jet engines have a compressor to increase the pressure of the incoming air. Mathematical details of this process are given on a separate slide.

There are two main types of compressors used in jet engines. The compressor shown above is called a centrifugal compressor because the flow through the compressor is turned perpendicular to the axis of rotation. The other type of compressor is an axial compressor and is discussed on a separate slide. The very first jet engines used centrifugal compressors, and they are still used on small turbojets and turbo shaft engines.

How does a centrifugal compressor work? The details are quite complex because the blade geometries and the resulting flows are three dimensional, unsteady, and can have important viscous and compressibility effects. Each blade on the compressor produces a pressure variation much like the airfoil of a spinning propeller. But unlike a propeller blade, the blades of a centrifugal compressor are close to one another, which seriously alters the flow between the blades. Centrifugal compressors also do work on the flow by turning, and therefore accelerating, the flow radially. Compressor designers must rely on wind tunnel testing and sophisticated computational models ( to determine the performance of a centrifugal compressor. The performance is characterized by the pressure ratio across the compressor (CPR), the rotational speed of the shaft necessary to produce the pressure increase, and an efficiency factor that indicates how much additional work is required relative to an ideal compressor.

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byTom Benson
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