Wind Power

Turbine Design, Selection, and Optimization

Victor M. Lyatkher

• Publisher: Wiley-Scrivener
• Year: 2013
• Print ISBN: 9781118720929
• eBook ISBN: 9781118721131
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Energy

An up-to-date and thorough treatment of the technologies, practical applications, and future of wind power, with the pros and cons and technical intricacies of various types of wind turbines and wind power prediction

With the demand for energy outstripping availability from conventional sources such as fossil fuels, new sources of energy must be found. Wind power is the most mature of all of the renewable or alternative sources of energy being widely used today. With many old wind turbines becoming obsolete or in need of replacement, new methods and materials for building turbines are constantly being sought after, and troubleshooting, from an engineering perspective, is paramount to the operational efficiency of turbines currently in use.

Wind Power: Turbine Design, Selection, and Optimization:

• Details the technical attributes of various types of wind turbines, including new collinear windmills, orthogonal windmills, non-vibration VAWT wind turbines, and others
• Covers all the updated protocols for wind power and its applications
• Offers a thorough explanation of the current and future state of wind power
• Is suitable not only as a reference for the engineer working with wind power but as a textbook for graduate students, postdoctoral students, and researchers

Wind power is one of the fastest-growing, oldest, and "greenest" of the major sources of renewable energy that has been developed, with more efficient and cost-effective technologies and materials now constantly being sought for turbines and the equipment used with them. Here is a comprehensive and thorough review of the engineering pros and cons of using different kinds of wind turbines in different environments, including offshore. With full technical knowledge, engineers, managers, and other decision-makers in the wind energy industry can make more informed decisions about increasing capacity, cost-efficiency, and equipment longevity.

Covering the various types of wind turbines available, such as new collinear windmills, orthogonal turbines, and others, this highly technical treatment of wind turbines offers engineers, students, and researchers insight into the practical applications of these turbines and their potential for maximum efficiency.

Chapter 1

Transformation of Flow Power

The systems transforming the energy of wind currents can be either those employing mechanical action in combination with electric, pump, frictional or thermal units, or those employing non-mechanical action, using, for example, an effect of ionization and conductivity of the stream passed through an electric or magnetic field. All mechanical systems, called - power installations (PI), use the action of the forces arising at a flow of mobile elements of the installations which are structurally united into power rotors (PR). The PI’s working elements, PR, move on the closed routes, sweeping some surfaces where the axis of symmetry can be either parallel (collinear), or perpendicular (orthogonal) to the stream. Respectively, PR are classified into two groups:

• Collinear, at which the axis of symmetry is approximately parallel to the stream, and
• Orthogonal, at which the axis of symmetry lies in the orthogonal plane to the stream direction.

The PR elements are able to move more slowly or quickly than the stream on the way to the PR. Respectively, they are called low-speed (action turbine) or high-speed (reaction turbine) machines. The collinear high-speed units (see Figure 1.1) are the most popular at present. Other types of units are not even included in the modern handbooks [1].

Figure 1.1 Modern collinear wind turbine. The rotation axis (1) is parallel to the stream. The blades (2) move in a plane perpendicular to the stream.

The orthogonal units may have a horizontal or a vertical axis (see Figure 1.2).

Figure 1.2 Orthogonal high-speed units with the rotation axis (1) perpendicular to the direction of the current. The blades (2) move by the ring routes. Left: a horizontal unit which is effective at invariable directions of the streams (for example, in a mountain valley or on a seashore); right: a vertical wind turbine.

Comparing various types of power installations of even one class causes certain difficulties as it is necessary to take into account some criteria measured in different equipment: specific material consumption (per a power unit and an output), quality of developed energy degree of simplicity and factory readiness, convenience and reliability in operation, labor input of construction and operation, ecological safety. The combination of these criteria defines the multidimensional quality characteristics of PR. Comparing PR quality is especially difficult for machines of various classes. Therefore, the choice of perspective schemes is conditional. The cost change (the social importance) of some points in view of the quality may change the conclusions. However, the economic, power, and ecological indicators currently accepted as the main points, should preserve the value for many years.

Since the wave aerodynamic resistance and acoustic radiation greatly increases when the body movement speeds approach the speed of sound, the wind unit elements should be designed so that air flows around them at speeds significantly less than sound speed (with small Mach numbers). Thus, the air can be considered almost incompressible, or squeezed under any law (adiabatically or isothermally); and all the results of aerodynamic calculations become suitable for recalculation by the movement conditions of incompressible liquids with any other density. In particular, all results can be directly applied to the analysis of river or oceanic power installations of similar configurations. Thus, one should keep in mind that for quiet water streams with small Froude numbers, the role of the stream free surface is somewhat close to the role of a firm smooth wall. [2]

Therefore, the analogy, for example, between land wind and river (oceanic) installations can be twofold – applying both to the arrangement of units at the water surface or at the bottom of a reservoir. Certainly, the designs of the units, applied materials, strength and technical and economic estimates for power units can vary significantly in air and in water.

In any scheme of stream power selection it makes sense to replace, as the first approximation, the unit which is carrying out this process with some hypothetical flat permeable figure with contours which are projections of the borders of a body, swept around by the rotor, on the figure plane, perpendicular to the stream direction on the way to the unit (Figure 1.3).

Figure 1.3 Scheme of currents in the turbine zone.

In the case of traditional, collinear units, a circle or a ring will be such a figure; in the case of orthogonal units it can be a strip (as in the pictured model), a rectangle, a trapeze, an ellipse figure (Darrieus unit section) or a triangle. Whatever this figure is, at some distance in front of it, the stream speed U and pressure p keep an non-indignant value:

(1.1)

and at some distance downstream, where the pressure distribution across the stream is leveled and returns to a reference value p₀, the speed in the current tube leaning on the allocated figure has a smaller value U₂ = (U₁ - u). If the current speed through the allocated figure is designated as U, and the pressure from the frontal and back parts of the figure as p₁ and p₂, respectively, the Bernoulli equations for the front and back parts of the current tube will take the following form:

(1.2)

(1.3)

If the stream speed and the surface pressure upon of the allocated current tube are accepted as constant, the equation of change of the movement quantity for the allocated volume is:

(1.4)

(1.5)

• Discharge of the medium moving in the considered current tube, S - the surface area imitating a turbine,

• Difference of pressure on the allocated flat figure replacing the power unit is calculated by subtraction of equalities (3) from equality (2) taking into account (4) and (5):

(1.6)

From the equations (2)-(5), we find:

(1.7)

The capacity lost by the stream and transferred to the turbine, is equal to:

(1.8)

The found solution (6), (8), presented as a resistance coefficient:

(1.9)

and a power factor:

(1.10)

appears depending on one parameter only - the relative stream speed in the unit zone U/U₁.

(1.11)

(1.12)

The maximum value of power observed at U/U₁ = u/U₁ =2/3 makes:

(1.13)

The obtained ratios (6), (8), (13) are usually associated with the works of N.E. Zhukovsky (1912) and A. Betz (1919), giving a sense of certain limit laws to these ratios [4].

However, the reality is different. The initial equations (2) – (5) are not precise and reflect some model of the phenomenon only. In particular, the equation (3) obviously is not true at U→0. If this limit case is real (an impenetrable unit), the pressure p₂ behind the unit will obviously be less than the pressure p₀ at a distance from the unit, rather than greater, as follows from (3). However, the idea of replacing the unit with one or several permeable flat or other figures where a rupture of ...

Table of contents

• Cover
• Half Title page
• Title page
• Copyright page
• Preface
• Chapter 1: Transformation of Flow Power
• Chapter 2: Collinear Wind Turbines (Horizontal-Axis Wind Turbines-HAWTs)
• Chapter 3: Orthogonal Wind Units: Mathematical Models
• Chapter 4: Ordinary Orthogonal Windmills (Vertical-Axis Wind Turbines – VAWTs)
• Chapter 5: The Largest Open Wind Turbines on the Ground or Sea
• Chapter 6: The Unit Without External Rotation
• Chapter 7: High Jet Power Station
• Conclusion
• Author Index
• Subject Index