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Über dieses Buch

This book explores the working principles of all kinds of turbomachines. The same theoretical framework is used to analyse the different machine types. Fundamentals are first presented and theoretical concepts are then elaborated for particular machine types, starting with the simplest ones.For each machine type, the author strikes a balance between building basic understanding and exploring knowledge of practical aspects. Readers are invited through challenging exercises to consider how the theory applies to particular cases and how it can be generalised.

The book is primarily meant as a course book. It teaches fundamentals and explores applications. It will appeal to senior undergraduate and graduate students in mechanical engineering and to professional engineers seeking to understand the operation of turbomachines. Readers will gain a fundamental understanding of turbomachines. They will also be able to make a reasoned choice of turbomachine for a particular application and to understand its operation. Basic design of the simplest turbomachines as a centrifugal fan, an axial steam turbine or a centrifugal pump, is also possible using the topics covered in the book.

Inhaltsverzeichnis

Frontmatter

1. Working Principles

In this chapter, we study the working principles of turbomachines with a number of characteristic examples. Further, we derive the basic laws for energy exchange between a shaft and a fluid and the laws describing energy changes on the fluid side. We also analyse the role of the energy exchanging forces and introduce definitions of efficiency.
Erik Dick

2. Basic Components

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.
Erik Dick

3. Fans

Fans are machines to move air or a similar gas. With regard to types, there are axial, radial and mixed-flow fans. Principles for the analysis of axial turbomachines have been elaborated in the foregoing chapters, but for radial machines, only a limited theory has been developed. The fan chapter is therefore also used to complete the theory for power receiving radial machines. It is appropriate to do this with the fan. Firstly, the fan is a simple turbomachine. Further, there are various rotor shapes with radial fans (forward curved blades, radial end blades and backward curved blades), as opposed to radial pumps (only backward curved blades) and radial compressors (radial end and backward curved blades). In this chapter, we also discuss the performance evaluation of radial fans, rotor design choices with radial fans and performance of axial and mixed-flow fans.
Erik Dick

4. Compressible Fluids

In further chapters we will study machines that function with compressible fluids, first steam turbines (Chap. 6), then gas turbines and compressors (Chaps. 11–15). For analysis of these machines, knowledge of fundamentals of compressible fluid flow is a necessity. We study compressible fluid flow fundamentals in the present chapter, for one-dimensional steady flows. This term refers to a flow whose properties change in one single spatial direction, namely an average streamline, and that is uniform in the spatial directions perpendicular to this streamline and constant in time. The streamline need not be straight. The discussion is limited to what is strictly necessary for the fundamental analysis of turbomachines. We refer to books on fluid mechanics for a more in-depth study.
Erik Dick

5. Performance Measurement

Experimental performance analysis of turbomachines requires pressure measurement, temperature measurement and flow rate measurement at the flow side and torque and rotational speed measurement at the shaft side. The present chapter deals with the principles of the most fundamental measurement techniques for these variables and describes three laboratory set-ups for performance measurement: a hydraulic turbine, a fan and a pump. Measurement results are discussed.
Erik Dick

6. Steam Turbines

The present chapter discusses the working principles and the construction forms of steam turbines, starting with an outline of their historical evolution. The two basic types of steam turbines are analysed. These are the impulse type and the reaction type. The chapter is also intended to formulate the general theory of axial turbines. In particular, the crucial role of the degree of reaction is discussed. Typical construction forms of large steam turbines for power stations and small turbines for industrial applications are illustrated. The chapter ends with a discussion of the shaping of blades and vanes.
Erik Dick

7. Dynamic Similitude

The present chapter discusses the concept of similitude, which means that two machines may be similar in the sense that there exist proportionality factors for geometry, velocities and forces. The performance characteristics of one of the machines can then be derived from the known characteristics of the other. The concept forms the basis of the initial design of a turbomachine, which means the determination of main parameters as the rotational speed, the size and some geometric ratios. In this chapter, we discuss the theory of dynamic similitude and some applications, including the basic design of a radial fan.
Erik Dick

8. Pumps

The fundamentals of pump operation have been fully treated in the foregoing chapters. Three particular aspects are discussed in the present chapter. The first is evaporation of the fluid in liquid state when the pressure inside the pump becomes lower than the vapour pressure. Cavities with vapour then emerge and the phenomenon is generally described as cavitation. The second concerns starting up. Priming is necessary. This is filling the pump and the suction pipe with the liquid to be pumped. The third topic is the intersection of the pump characteristic with the load characteristic, which mostly has a large static part. The intersection does not necessarily result in a stable operating point. Cavitation, priming and stability are discussed in the present chapter. Further topics are some aspects concerning shaping of the components, construction and special applications.
Erik Dick

9. Hydraulic Turbines

In this chapter, we discuss the different types of hydraulic turbines for electric power plants. We analyse their main characteristics in order to understand in which range of head and flow rate they can be used efficiently. We also discuss bulb turbines for tidal energy plants and reversible pump-turbines for pumped storage plants.
Erik Dick

10. Wind Turbines

In this chapter, we discuss the different types of wind turbines and the basic technical aspects of large wind turbines for electricity generation. We analyse the performance of wind turbines and discuss their adaptation to a wind regime.
Erik Dick

11. Power Gas Turbines

A gas turbine is a turbomachine composed of a compressor part, a part with heat supply to the compressed gas and a turbine part in which the hot gas expands. The present chapter discusses gas turbines for mechanical power ­generation. These are machines with an outgoing shaft, meant to drive a load. The largest market sector of such machines is electrical power generation, but machines for driving compressors and pumps in industrial plants and for driving large vehicles and ships also are examples. We discuss the working principles of the components of power gas turbines in the present chapter. As electric power generation is the largest sector of application, we choose components of such machines for illustrations. The main purpose of the chapter is the discussion of the overall performance of power gas turbines. Performance analysis is a matter of thermodynamic modelling and is not strongly linked to a particular application.
Erik Dick

12. Thrust Gas Turbines

Due to the high power compared to weight and volume, gas turbines are very suitable components of aircraft propulsion systems. Almost all modern aircraft propulsion is gas turbine based. Only with low power (< 300 kW), as for very light aircraft, are reciprocating engines used. Aircraft propulsion systems exist in a wide variety of types. The basic principle is always that the propulsive force (thrust) is reaction onto the acceleration of an air flow. In this chapter, we discuss the different systems and we analyse the performance of the core part, which is a gas turbine, and the performance of double-flow engines with mixed and unmixed jets, which are the most commonly used types. The chapter is concluded by a discussion of some technological aspects.
Erik Dick

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.
Erik Dick

14. Radial Compressors

Radial compressors (or centrifugal compressors) resemble radial fans and radial pumps for basic operation aspects. So, based on the study of fans and pumps, which we have done in previous chapters, we can understand the basic operation of centrifugal compressors. In this chapter, we repeat the analysis of the working principles of centrifugal machines, but applied to centrifugal compressors. We discuss applications and the aspects that are particular for centrifugal compressors. These are the inducer part at the inlet of a rotor for large work and the diffuser downstream of the rotor. We also analyse the operating characteristics with the limits caused by stall and choking.
Erik Dick

15. Axial and Radial Turbines for Gases

Fundamentals of axial turbines were discussed in the chapter on steam turbines (Chap. 6). Design of turbine parts in gas turbines follows the same principles. When analysing the performance of axial turbines, we assumed, by way of a simplification, a given stator outlet angle (α 1   = 72° and 75°). The analysis is generalised here and completed with a discussion of blade design and operating characteristics. The fundamental theory of radial turbines was treated in the chapter on hydraulic turbines (Chap. 9). The specific aspects for a compressible fluid are discussed in the present chapter. In particular, the rotor has an exducer part. Operating characteristics of radial turbines are derived. The chapter concludes with the non-dimensional form of the operating characteristics of turbomachines with a compressible fluid.
Erik Dick

Backmatter

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