As discussed in Chapters 1–4, the purpose of the turbine is to extract energy from the fluid to drive the compressive devices. The actual operation of the turbine is in some respects similar to, but opposite that, of the compressor. That is, energy is extracted from the fluid and the pressure and temperature drop through the turbine. Typically, 70–80 percent of the enthalpy increase from the burner is used by the turbine to drive the compressor. For jet propulsion the remainder is used to generate thrust in the nozzle, while for a power generation unit the remainder is used to generate auxiliary power.

Propulsion devices have existed for many centuries, and natural devices have developed through evolution. Most modern engines and gas turbines have one common denominator: compressors and turbines or “turbomachines.” Several of the early turbomachines and propulsive devices will be described in this brief introduction before modern engines are considered. Included are some familiar names not usually associated with turbomachines or propulsion. Many of the early devices were developed by trial and error and represent early attempts at design engineering, and yet some were quite sophisticated for their time. Billington (1996), ASME (1997), Engeda (1998), St. Peter (1999), Wilson and Korakianitis (2014), and others all present very interesting introductions to some of this history supplemented by photographs.

In the previous seven chapters, much emphasis has been placed on the analysis and design of individual components of gas turbines. On the other hand, in Chapter 3 cycle analyses are presented for ideal and nonideal engines as a whole in which the different components are integrated into a system. However, in Chapters 2 and 3, component efficiencies and some characteristics are assumed or assigned a priori for the overall cycle analyses. In general, however, the previous seven chapters demonstrate, through the use of either theoretical analyses or empirical characteristic curves (or “maps”), that component efficiencies and other operating characteristics change significantly at different conditions – for example, at different flow rates and rotational speeds.

As discussed in previous chapters, a fan or compressor is the first rotating component that the fluid encounters. A cross-sectional view of a compressor for a simple, single-shaft turbojet is shown in . The basic function of a compressor is to impart kinetic energy to the working fluid (air) by means of some rotating blades and then to convert the increase in energy to an increase in total pressure, which is needed by the combustor. The limits of operation of an engine are often dictated by a compressor, as is discussed in this chapter. Furthermore, the design of an efficient axial flow fan or compressor remains such a complex process that the success or failure of an engine often revolves around the design of a compressor. Many fundamental and advanced design details are available in Howell (1945a, 1945b), Horlock (1958), Hawthorne (1964), Johnsen and Bullock (1965), Cumpsty (1988), and Wilson and Korakianitis (2014). Denton (1998), Elmendorf et al. (1998), LeJambre et al. (1998), Rhie et al. (1998), Adamczyk (2000), and Denton and Dawes (2010), demonstrate how modern computational fluid dynamic (CFD) tools can be used for the complex 3-D analysis and design of compressors.

   “B” 15,696 lbf, 0.611 lbm/h-lbf

Chapter 1 identified the basic jet engine and power generation types and defined the important operating performance parameters of gas turbines. That chapter also briefly reviewed the fundamental thermodynamics of cycles and established that gas turbines consist of several important components. Our goal is to cover all basic jet engine and power generation configurations. Before proceeding to analyze complete gas turbines, the individual components must be analyzed. Both ideal and nonideal components are considered in this chapter. Ideal implies that there are no losses in the components. Nonideal includes such losses. In the following chapter components are assembled in a “cycle analysis” to make it possible to predict the overall gas turbine performance. Simple single- or two-term expressions are used to model the losses in each component in this chapter for simplicity. Each component is covered separately and in detail. Before proceeding with component analyzes, a brief review is provided for the thermodynamics of compressible fluid flow. More details of this review are covered in Appendix C. This review is provided for readers who have not had a comprehensive previous course in this subject and is considered to be optional.

Chapter 1 identified the basic engine types and defined the important operating performance parameters of gas turbines. That chapter also briefly reviewed the fundamental thermodynamics of cycles and established that gas turbines consist of several important components. This chapter covers all basic jet engine and power generation configurations. Both ideal and nonideal components were considered in Chapter 2. Ideal implies that there are no losses in the components. Nonideal includes such losses. Components are now assembled in a “cycle analysis” to make it possible to predict the overall engine performance. As will be seen, the ideal cycle analysis results in closed-form equations for the engine characteristics and final equations are summarized in this chapter. Developing these equations (Appendix H) serves three purposes. First, doing so allows the reader to see how the equations are assembled to model an engine without having to deal with numerical details. Second, and more importantly, developing the equations allows the reader to observe how detail parameters affect the overall performance of an engine without parametrically varying numbers. Third, in some cases, analytically optimizing a performance characteristic is possible. On the other hand, nonideal cycle analysis does not result in closed-form equations owing to the increased complexity of the component equations of the engine. Nonideal efficiency levels and losses are included for the different components so that more realistic predictions can be made for overall engine performance. Also, note that the simple single- or two-term expressions used to model the losses in each component in Chapter 2 are used. Even though most components operate with individually with relatively high efficiencies (upwards from 90 percent), when all the components are coupled the overall engine performance can be reduced dramatically. However, in general, parametric studies and the performance trends are similar for both ideal and nonideal cases. This chapter presents quantitative examples to demonstrate the analysis and to give the reader a physical understanding of characteristics. Trend studies are also discussed to show the dependence of the overall characteristics on individual component parameters. At this stage the loss terms are specified a priori even though, in a real engine, the different component losses are dependent on the engine operating point and are thus dependent on each other. This advanced topic is the subject of Chapter 12, which addresses component matching. More complex and refined analyses of the component losses are presented in each of the component chapters (Chapters 4–11).

The burner, reheat burner, and afterburner are the only components through which energy is added to the gas turbine.