9.1 Introduction

In general, turbomachinery is classified as all those devices in which energy is transferred either to or from a continuously flowing fluid by the dynamic action of one or more moving blade rows.37 The word turbo or turbinis is of Latin origin and implies that which spins or whirls around. Essentially, a rotating blade row or rotor changes the total enthalpy of the fluid moving through it by either doing work on the fluid or having work done on it by the fluid, depending on the effect required of the machine. These enthalpy changes are intimately linked with the pressure changes occurring simultaneously in the fluid.

This definition of turbomachinery embraces both open and enclosed turbomachines.37 Open turbomachinery (such as propellers, windmills, and unshrouded fans) influence an indeterminate quantity of fluid. In enclosed turbomachinery (such as centrifugal compressors, axial-flow turbines, etc.), a finite quantity of fluid passes through a casing in unit time. In this chapter, we will focus on the enclosed turbomachinery used in gas turbine engines: fans, compressors, and turbines. There are many excellent references on enclosed turbomachinery, such as Refs. 4, 12, 22, 28, 29, and 37 47. Open turbomachines are covered in aeronautics textbooks such as Refs. 48, 49, and 50.

Turbomachines are further categorized according to the nature of the flow path through the passages of the rotor. When the path of the throughflow is wholly or mainly parallel to the axis of rotation, the device is termed an axial-flow turbomachine. When...