A centrifugal compressor is the part of a turboprop engine that compresses the airflow radially, with the air flowing tangentially to the outer edge of the compressor rotor. It basically consists of a rotating impeller (rotor), a fixed diffuser, and a manifold, which collects and turns the compressed air. The air flows first to the center of the impeller and then outwardly as the air is thrown out radially to the edges of the rotor by the centrifugal force. Pressure ratio may be increased by arranging two single-face compressors in a row, which was successfully done with the Rolls-Royce Dart engine that powers, among others, the Fokker Friendship turboprop aircraft.
A derivative of the single-face centrifugal compressor is the double-face compressor, which had a smaller diameter for a given airflow. Because of problems in supplying air to the rearward-facing impeller and due to technical progress made to reduce engine size, this type of compressor is no longer used in aviation applications. A major benefit of the single-face centrifugal compressor is a large pressure ratio (around 5:1), and the relatively manufacture low cost, which are attractive features both for the small engine market and the automotive industry.
Operating Principle
In the centrifugal compressor, the impeller (rotor) is driven by the turbine and revolves at high speed, usually between 20,000 and 30,000 rpm, depending on the engine size. At the entrance to the impeller, near the hub, air in ingested (sucked in) and directed towards the outer circumference on the compressor by a series on inlet guide vanes. The airflow is caused by the high rotational speed of the impeller. This process not only makes the airflow to build up pressure but it also causes it to discharge from the impeller at high velocity. In the diffuser section, the kinetic energy of the high-velocity air is converted to pressure energy, which results in a low-velocity and high-pressure airflow. The diffuser also serves both to straighten the flow and to change its direction sharply through a 90-degree angle curve to make able to flow through the manifold.
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| Above, components of a single-stage centrifugal compressor. |
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| The diagram shows how a centrifugal compressor works. |