Basic components

Abstract

We learned in Chap. 1 that blades of axial machines have profiles resembling aircraft wing profiles (aerofoils). In machines with large spacing between blades, this resemblance is strong, as with the hydraulic turbines and pumps studied up to now. With axial compressors, gas and steam turbines, blades are positioned closer together. The blades also cause a larger flow turning. A circumferential section results in a row of blade profiles with tangential spacing comparable to, or smaller than, the largest profile dimension. We then apply the term blade row or blade cascade. Radial machine rotor blades principally do not function as lifting objects. The blades constitute channels. The blade profiles have no resemblance to aerofoils. Channel flows may be accelerating (turbines) or decelerating (pumps, fans, compressors). With decelerating or diffusion flows, avoidance of separation between flow and geometry is difficult. As we have already learned, diffusers also occur as stator components of turbines. Aerofoils, cascades, channels and diffusers constitute the basic components of turbomachines, which we study in this chapter.