ANALYSIS OF SURGE PHENOMENA IN AXIAL FLOW COMPRESSORS

Abstract

Compression systems used in the power generation plants and aerospace propulsion applications are prone to the aerodynamic instabilities of stall and surge. Both of these instabilities result in reduced off-design of the compressors, and raise safety concerns. This research focuses on the analysis of surge phenomena in axial flow compressors. Mathematical model developed by Moore and Greitzer (1985, 86) [1, 2] has been used for this purpose. The axisymmetric compressor characteristic employed by the Moore-Greitzer Model has been generalized to study the effect of the parameters involved over a wider set of values. The pure surge case of the Moore-Greitzer Model is then subjected to Method of Multiple Time Scales (MTS), and a closed-form solution has been obtained for the problem. Subsequent application of Bifurcation theory on the closed-form solution reveals that surge manifests itself as a sustained Limit Cycle Oscillation (LCO) subject to fulfillment of a necessary condition dictated by the compressor characteristic. It has been found that the behaviour of surge oscillations is significantly dependent upon the choice of compressor characteristic. From combination of the various parameters involved in the Moore-Greitzer Model, two new parameters have been obtained, and the condition for the stable limit cycle oscillations has been obtained, which revolves around these parameters. The analytical solution has been verified against the numerical simulation of the Moore Greitzer Model, thus implying that Method of Multiple Time Scales has successfully captured the qualitative and quantitative aspects of the surge phenomena. viii The results of the analyses presented in this research work can provide useful guidelines to the turbomachinery designers in developing a better understanding towards the surge problem and in improving off-design performance of axial compressors.