Chapter 4 extends the aerodynamic discussions of Chapter 3 to show how the rotor net loads (power, thrust, and torque) are developed. The dimensionless power coefficient (Cp) curve is introduced, and the relationship between rotor tip speed ratio and optimum solidity is explained. The variation of thrust loading with wind speed on an ideal pitch-controlled rotor is explained from simple theory, and illustrated with measurements from a full-scale turbine. Equations governing the chord and twist distributions for an optimised blade are given and discussed in the context of some historic blade types, with illustrations. Rotor aerodynamic control is explained with reference to fixed-pitch stall regulation and variable blade pitch (both positive and negative). The influence of blade number is examined, with discussion of the advantages and disadvantages of one-, two-, and three-bladed wind turbines. The method by which annual energy capture is derived from the power curve and wind speed distribution is explained, with example. The chapter concludes with a brief overview of alternative aerodynamic control devices including tip vanes and ailerons, and downwind rotors (with examples).

Chapter 5 deals with electrical issues and is broadly divided in two. The first half explains the operating principles of the several different types of generator found on wind turbines, and their influence on dynamics and electrical power quality. Generator types are illustrated schematically and their characteristics explained using simple physical principles. Geared and gearless (direct drive) generators are discussed and there is a brief historical review of generator developments. The second half of the chapter deals with electrical networks and further examines the issue of power quality. The importance of reactive power is explained and how modern generators can manipulate it to aid voltage stability; the role of external devices such as Statcoms, SVCs, and pre-insertion resistors is also discussed in this context. Measurements from a MW-scale wind turbine illustrate voltage control via reactive power management over a period of several days. The challenge of low grid strength is illustrated with a practical example of a small wind farm development on a rural network with low fault level. The chapter concludes with a brief discussion of wind turbine lightning protection.

The surrounding air flow around a hypersonic vehicle behaves quite differently from supersonic flows. The kinetic energy is converted into internal energy which can increase the flow temperature and induce endothermic reactions near the vehicle surface. It is a challenge to develop flow diagnostic and aerodynamic measurement technologies with high precision for high-enthalpy wind tunnel tests. There are, generally, three types of measurement technologies widely used in exploring high-enthalpy flows, including heat-transfer measurement, aerodynamic balance, and optical diagnostic techniques. In this chapter, hypersonic tests with the aforementioned measurement technologies are summarized to demonstrate the progress on high-enthalpy flow experiments. Four kinds of experiments are included here, and the topics are aerodynamic force and moment tests, aerothermal heating measurements, hypersonic boundary-layer flow diagnostics, and supersonic combustion and scramjet engine tests. Actually, there are a lot of interesting topics, but these four are important not only to understand aerothermodynamic physics but also to support the development of hypersonic vehicles.

The achievable total enthalpy and the pressure level in a shock tunnel depend on its capability to generate strong shock waves. To produce a strong shock wave, high pressure and high sound speed are two key parameters for driver gases. There are various techniques to increase the driver gas sound speed, which are essentially different approaches in the way to raise the driver gas temperature. The first technique to increase the driver gas sound speed is by the use of a light gas, and the second one is by heating the light gas to a high temperature with gas heaters. The light-gas-heated shock tunnel is introduced in this chapter, and the electrical heaters are discussed in detail, including the relatively simple electrical resistance heaters and electric-arc heaters. Strictly speaking, the electric-arc heating is not a gasdynamic technique and it is not capable of completing flight-condition duplication for hypervelocity testing. However, it is selected because it can generate extremely high total enthalpies and is useful in certain applications.

In this chapter, the aerodynamic fundamentals for the working principles of shock tunnels are summarized. The moving waves, including expansion waves, shock waves, and contact surfaces, are introduced as the key issues and their theories are based on the unsteady one-dimensional flows in textbooks of aerodynamics. As unsteady one-dimensional moving waves are also critical for the design and operation of shock tunnels, their theories are also selected and summarized in this chapter for book completeness and readers’ convenience.

The free-piston driver is a powerful technique to increase both the driver gas sound speed and pressure. Therefore, it is capable of generating high-enthalpy flows and offering high performance among various gasdynamic shock drivers. So far, it has been implemented in a number of major reflected-shock as well as shock-expansion wind tunnels around the world. The free-piston driver has the advantage that a high driver gas pressure is automatically generated in the same process. On the other hand, the driver is far more complex mechanically and requires operation-tuning in order to operate effectively. Moreover, its test time is short and the test flow is not steady because the piston motion is difficult to control. In this chapter, the basic concepts of the free-piston driver are discussed. The analytical theory that describes the piston dynamics and the method for tuned piston operation are presented. Examples of major free-piston-driven test facilities as well as their applications in hypersonic testing are also summarized.