13. Axial Compressors

The chapter starts with an analysis of the circumferentially averaged flow on the mean radius of an axial compressor. Loss representation is discussed together with the diffusion factor concept for estimating the loading capacity of blade rows. A further step is an analysis of the radial variation of flow parameters, but without taking into account the effect of boundary layer flows on the hub and casing. This flow is called the primary flow. A next aspect is the difference between the complete flow and the primary flow, the so-called secondary flow. The different vortex patterns in the secondary flow are described. All considerations together allow a conclusion on the optimal radial distribution of the flow parameters in an axial compressor. Some aspects of three-dimensional blade shaping conclude the flow study. Next, blade profile shapes for subsonic, supercritical, transonic and supersonic cascades are studied. The chapter concludes with a discussion on the performance characteristics and the operating limits due to surge and choke.