A Study on the Fundamental Surge Frequencies in Multi-Stage Axial Flow Compressor Systems

Abstract

Surge phenomena in multi-stage axial flow compressors were studied with attention to the frequency behaviors. A new parameter "volume-modified reduced surge frequency" was introduced, which took into consideration the essential surge process, i.e., emptying and filling of the working gas in the delivery plenum. The behaviors of the relative surge frequencies at the stall stagnation boundaries, compared with the corresponding duct resonance frequencies, have demonstrated the existence of two types of surges; i.e., a near-resonant surge and a subharmonic surge. The former, which has fundamentally a near-resonance frequency, occurs predominantly at the stall stagnation boundary for the short -and-fat plenum delivery flow-path and the long-and-narrow delivery duct flow-path, and possibly in the intermediate conditions. The latter, which has a subharmonic frequency of the fundamental near-resonant one and occurs mainly in the inter-mediate zone, is considered to be caused by the reduced frequency restricted to a limited range. In relation with those dimensionless frequencies at the stall stagnation boundary, the surge frequency behaviors in more general situations away from the boundaries could be estimated, though very roughly.

Unstable Flow Structures Present at Different Rotational Velocities of the Centrifugal Compressor

“…Hence it should be expected that this is the same type of surge. Hence, the frequency creeping with rotational speed was observed in this case, similarly to observations made in a different type of the compressor [37]. At lower rotational velocities the amount of energy generated in the impeller was not sufficient to feed the outer volume to start the surge oscillations.…”

Analytical Surge Behaviors in Systems of a Single-stage Axial Flow Compressor and Flow-paths

“…4. The results are similar to those given in related former papers (Yamaguchi [5,8]). It is to be noticed that the variable for the abscissa is changed to RLC in place of RLP in the present paper for better correlation with the succeeding contents in this study.…”

“…In order to take into consideration the essential surge action of filling and emptying gas into and out of the delivery volume, the following volume-modified reduced surge frequency is proposed (Yamaguchi [7,8]):…”

“…For example, ones of such phenomena are surge frequencies and their behaviors, which are of fundamental significance in surge as an oscillation system. Although the surge frequencies are considered to be related intimately with the acoustical resonance frequency in the flow-path system, the author's analytical experiences (for example, Yamaguchi [5,7,8]) have shown that the surge frequencies are often far from the system resonance ones. The field of compressor surges is still staying as an unclarified area.…”

“…The author has provided information mainly on the geometrical stall-stagnation boundaries (Yamaguchi [5,7,8]). Some of the frequency aspects have been treated mainly in a recent study (Yamaguchi [8]), which has given some new findings about the surge frequency phenomena, though in a very qualitative manner.…”