Centrifugal Compressors

This chapter and the following three chapters deal with the rotating modules of both aeroengines and gas turbines. This chapter presents a comprehensive treatment of centrifugal compressors, focusing on their classification, aerodynamic behavior, and operational characteristics. The chapter begins by outlining the main types of centrifugal compressors, including variations in impeller design, diffuser configuration, and stage arrangement, with emphasis on applications in aircraft propulsion, auxiliary power units, turbochargers, and industrial gas turbines. The fundamental aerodynamics governing centrifugal compression are then examined, covering flow turning, diffusion, slip phenomena, and loss mechanisms within the impeller, diffuser, and volute. Velocity triangles are developed to describe the kinematics of the flow at the impeller inlet and exit, providing the basis for performance analysis, work input, and efficiency estimation. Compressor operating maps are discussed in detail, highlighting mass flow rate, pressure ratio, efficiency contours, surge, choke, and the influence of rotational speed on stable operation. The chapter also addresses real-world degradation issues, with particular attention to erosion and fouling, their causes, impact on aerodynamic performance and operating margins, and implications for efficiency, stability, and maintenance. Overall, the chapter bridges fundamental theory and practical considerations, offering a unified framework for understanding, analyzing, and operating centrifugal compressors in modern propulsion and energy systems.