The mechanism of radial compressor instability

Abstract

The limit imposed on the operating range of a radial flow compressor by surging or pulsations in the reduced flow region has long been a source of concern to design engineers who would like to use this otherwise simple, lightweight and efficient compressor. A preliminary study of the nature of the pulsations lead to the design of the Deflected Spill Pickup in an effort to simulate the compressor flow characteristics under conditions of close control and simple analytical boundaries. A fair degree of agreement was obtained between the flow and instability characteristics of the spill and the actual compressor to which it was proportioned. The analysis provides an explanation for the observed differences in flow characteristics and suggests the possibilities of producing closer agreement. During the course of the investigation it became evident that the Deflected Spill Pickup could become a valuable component in the experimental study of other flow instability phenomena by providing a source of intermediate velocity air with the flat pressure vs flow characteristics of a system closely coupled to a radial flow compressor. The work with the spill also provided the groundwork for a suggested design for a radial flow compressor that should be free of the investigated instability in the reduced flow region of operations. The tests were conducted at Rensselaer Polytechnic Institute, Troy, New York using the facilities of the Department of Mechanical Engineering.