WO2014048437A1

WO2014048437A1 - Noise attenuator for a wind turbine blade and a method for reducing wind turbine noise

Info

Publication number: WO2014048437A1
Application number: PCT/DK2013/050303
Authority: WO
Inventors: Matthew SUMMERS; Jingshu WU; Kyle Hutchings; David Chao
Original assignee: Vestas Wind Systems A/S
Priority date: 2012-09-25
Filing date: 2013-09-24
Publication date: 2014-04-03

Abstract

A noise attenuator for a wind turbine blade includes a first attenuator portion having a plurality of first attenuator elements, each first attenuator element being separated from an adjacent first attenuator element by an interface; and a second attenuator portion having a plurality of second attenuator elements, each second attenuator element being separated from an adjacent second attenuator element by an interface. The first and second attenuator portions are configured to be juxtapositioned in an overlapping relation relative to each other to collectively form the noise attenuator. Adjacent attenuator elements on the noise attenuator may effectively intersect each other at a substantially sharp corner. A method of reducing wind turbine noise includes juxtapositioning the first and second attenuator portions relative to each other so that the attenuator elements effectively intersect each other at a substantially sharp corner.

Description

NOISE ATTENUATOR FOR A WIND TURBINE BLADE AND A METHOD FOR REDUCING WIND TURBINE NOISE

Technical Field

The invention relates generally to wind turbines, and more particularly, to a noise attenuator for a wind turbine blade, a wind turbine blade having a noise attenuator, and a method for attenuating the noise generated by a wind turbine blade. Background

Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. Generally, a wind turbine converts kinetic energy from the wind into electrical power. A horizontal-axis wind turbine includes a tower, a nacelle located at the apex of the tower, and a rotor having a plurality of blades and supported in the nacelle by means of a shaft. The shaft couples the rotor either directly or indirectly with a generator, which is housed inside the nacelle. Consequently, as wind forces the blades to rotate, electrical energy is produced by the generator.

In recent years, wind power has become a more attractive alternative energy source and the number of wind turbines, wind farms, etc. has significantly increased, both on land and off-shore. Traditionally, wind turbines have been located in relatively remote areas where noise from the wind turbine has not been significantly problematic. However, as the number of wind turbines increases, the noise generated thereby has been receiving more attention. In this regard, wind turbines are being located closer to business and residential areas that may have various laws and regulations restricting noise levels. In this regard, various geographical locations (countries, states, cities, etc.) may have noise restrictions that limit the amount of noise a wind turbine can make. Thus, power providers and wind turbine manufacturers have given some consideration to wind turbine noise and various ways to reduce the noise generated by wind turbines.

There are two primary sources of noise for a wind turbine: mechanical noise and aerodynamic noise. Mechanical noise may be due to, for example, vibrations in the various wind turbine components, such as the gearbox, generator, pitch and yaw controls, hydraulic systems, etc. Aerodynamic noise, on the other hand, may be due to the interaction between the blade and the air flowing over the blade. While mechanical noise can be a significant contributor to overall wind turbine noise, there are some known techniques for reducing mechanical noise, including using vibrations dampers and sound absorbing materials. In contrast, aerodynamic noise may be difficult to mitigate and is believed to be the primary source for wind turbine noise.

More particularly, aerodynamic noise may be divided into two further classes: airfoil self- noise, which is due to the interaction of a nominally steady air flow over the blades, and turbulent inflow noise, due to the scattering of turbulent air fluctuations by the blades. Airfoil self-noise is further divided into two primary mechanisms: trailing edge noise and blade tip vortex noise. Noise may be generated at the trailing edge via two processes: blunt trailing edge vortex-shedding noise, and turbulent boundary layer trailing edge noise. Blunt trailing edge vortex-shedding noise is generally not considered problematic. Turbulent boundary layer trailing edge noise may be due to the scattering of turbulent fluctuations within the blade boundary layer at the trailing edge, resulting in noise generation. Of these various aspects of aerodynamic noise, it is believed that blade trailing edge noise, and more particularly turbulent boundary layer trailing edge noise, is the dominant source of noise for wind turbine blades.

Accordingly, there have been attempts to reduce or mitigate the trailing edge noise generated by wind turbine blades. In this regard, research using aeroacoustic theory has shown that a serrated or saw-toothed trailing edge, as compared to a straight trailing edge, may reduce the noise generated by a blade. This has also been shown experimentally as well as in some field tests. As schematically illustrated in Fig. 1 A, the serrations 10 typically take the form of a series of triangular fingers or projections extending from the trailing edge in a side-by-side fashion such that the interface between two adjacent serrations is formed by a sharp corner 12.

While the configuration of the serrations shown in Fig. 1A may be effective to reduce the noise generated from a wind turbine blade, from a structural perspective, the configuration has some shortcomings. In this regard, the sharp corner between adjacent serrations cannot adequately handle the stresses and strains imposed on the serrations during extended use. More particularly, the sharp corner between adjacent serrations may operate as a crack initiation site which may ultimately lead to the failure of the serrations and their noise reduction capacity. Accordingly, wind turbine blades having trailing edge serrations as described above would require increased monitoring and maintenance activities, thereby increasing the total operating costs for the wind turbine.

Several alternative solutions have been proposed to obviate the structural shortcomings associated with sharp corner geometries between adjacent serrations. For example, Fig. 1 B illustrates such an exemplary alternative solution. In this solution, the sharp corner 12 between two adjacent serrations 10 has been replaced with a generally smooth curve or arcuate interface 14 therebetween. As a result, the interface 14 would be more adept at accommodating the loads acting on the serrations 10, thereby enhancing the structural integrity of the serrations 10 and mitigating the risks of failure due to cracks or other failure modes originating from the interface 14. While this solution would be effective for increasing the structural integrity of the serrations 10, the curved interface 14 between adjacent serrations 10 may have a negative impact on the ability of the serrations 10 to reduce noise. Thus, this solution improves structural integrity at the expense of noise reduction efficiency.

There is therefore a need in the wind turbine industry to have an improved noise reduction device capable of sustaining the loads imposed thereon during use, similar to that provided by serrations having curved interfaces therebetween, while also providing noise attenuation capabilities similar to that provided by serrations having a sharp corner interface therebetween. There is also a need for a wind turbine blade having such a noise reduction device as well as an improved method for attenuating the noise generated by the wind turbine blade.

Summary

According to one embodiment, a noise attenuator for a wind turbine blade includes a first attenuator portion having a plurality of first attenuator elements, each first attenuator element being separated from an adjacent first attenuator element by an interface devoid of a substantially sharp corner; and a second attenuator portion having a plurality of second attenuator elements, each second attenuator element being separated from an adjacent second attenuator element by an interface devoid of a substantially sharp corner. The first and second attenuator portions are configured such that when the noise attenuator is installed on the wind turbine blade, the first and second attenuator portions are juxtapositioned in an overlapping relation relative to each other to collectively form the noise attenuator.

In an exemplary embodiment, the first and second attenuator portions are further configured such that when the noise attenuator is installed on the wind turbine blade, adjacent attenuator elements on the noise attenuator are from different attenuator portions. Thus, a selected attenuator element from the first attenuator portion will have adjacent attenuator elements from the second attenuator portion, and vice versa. Moreover, when the noise attenuator is installed, adjacent attenuator elements of the noise attenuator effectively intersect each other at a substantially sharp corner. Thus, taken individually, adjacent attenuator elements on the attenuator portions have interfaces inbetween devoid of sharp corners, but when taken collectively, adjacent attenuator elements of the noise attenuator effectively intersect each other at a substantially sharp corner.

In one embodiment, the first and second attenuator portions may be further configured such that when the noise attenuator is installed on the blade, the first and second attenuator portions nest relative to each other so that the first and second attenuator elements generally lie within the same plane. In an alternative embodiment, the first and second attenuator portions may not nest such that the first and second attenuator elements may generally lie in different planes, for example, immediately adjacent each other or slightly spaced from each other. Furthermore, when the noise attenuator is installed on the blade, the first and second attenuator portions may engage one another or alternatively, may be spaced from one another. Although the first and second attenuator portions may be juxtapositioned in overlapping relation relative to each other, in an exemplary embodiment, the attenuator elements may not be in overlapping relation relative to each other (i.e., the portions overlap in a region other than the attenuator elements). According to one embodiment, the attenuator elements may be generally V-shaped. Additionally, the first attenuator elements may have a first width and the second attenuator elements may have a second width, wherein the width of the interface between adjacent first attenuator elements is substantially equal to the second width, and the width of the interface between adjacent second attenuator elements is substantially equal to the first width. In an exemplary embodiment, the first and second attenuator elements may be substantially identical.

In another embodiment of the invention, a wind turbine blade assembly includes a wind turbine blade and a noise attenuator coupled to the wind turbine blade. The wind turbine blade includes a root end, a tip end, a leading edge, a trailing edge, a pressure side, and a suction side. The noise attenuator includes a first attenuator portion coupled to the wind turbine blade and has a plurality of first attenuator elements, each first attenuator element being separated from an adjacent attenuator element by an interface devoid of a substantially sharp corner. The noise attenuator further includes a second attenuator portion juxtapositioned in an overlapping relation relative to the first attenuator portion, wherein the second attenuator portion has a plurality of second attenuator elements, each second attenuator element being separated from an adjacent second attenuator element by an interface devoid of a substantially sharp corner. In an exemplary embodiment, adjacent attenuator elements on the noise attenuator may be from different attenuator portions. Additionally, adjacent attenuator elements of the noise attenuator may effectively intersect each other at a substantially sharp corner. Moreover, the juxtapositioning of the first and second attenuator portions may be such that the first and second attenuator elements are not in overlapping relation relative to each other. Furthermore, in one embodiment, the first and second attenuator portions nest relative to each other so that the first and second attenuator elements generally lie within the same plane. However, in an alternative embodiment, the first and second attenuator elements may generally lie in different planes. In one embodiment, the noise attenuator may be coupled to the wind turbine blade adjacent the trailing edge. Additionally, in one embodiment, the noise attenuator may be positioned on the outer half of the wind turbine blade, such as, for example, between about 60% and 90% of blade length. The attenuator element geometry may be held constant along the length of the blade or may be varied along the blade length. For example, the length of the attenuator elements may vary, such as by increasing in a direction toward the root end of the blade.

In a further embodiment according to the invention, a wind turbine includes a tower, a nacelle disposed adjacent a top of the tower, and a rotor having a hub and at least one wind turbine blade assembly extending from the hub. The wind turbine blade assembly includes a wind turbine blade and a noise attenuator coupled to the wind turbine blade. The wind turbine blade includes a root end, a tip end, a leading edge, a trailing edge, a pressure side, and a suction side. The noise attenuator includes a first attenuator portion coupled to the wind turbine blade and having a plurality of first attenuator elements, each first attenuator element being separated from an adjacent first attenuator element by an interface devoid of a substantially sharp corner; and a second attenuator portion juxtapositioned in an overlapping relation relative to the first attenuator portion, the second attenuator portion having a plurality of second attenuator elements, each second attenuator element being separated from an adjacent second attenuator element by an interface devoid of a substantially sharp corner.

In still a further embodiment according to the invention, a method for reducing the noise from a wind turbine includes coupling a first attenuator portion of a noise attenuator to a wind turbine blade, and juxtapositioning a second attenuator portion of the noise attenuator in overlapping relation relative to the first attenuator portion such that the first and second attenuator portions collectively form the noise attenuator. The first attenuator portion includes a plurality of first attenuator elements, each first attenuator element being separated from an adjacent first attenuator element by an interface devoid of a substantially sharp corner. The second attenuator portion includes a plurality of second attenuator elements, each second attenuator element being separated from an adjacent second attenuator element by an interface devoid of a substantially sharp corner. In one embodiment according to the method, juxtapositioning the first and second attenuator portions further includes juxtapositioning the first and second attenuator portions so that adjacent attenuator elements of the noise attenuator effectively intersect each other at a substantially sharp corner.

Brief Description of the Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.

Fig. 1 A is a top view of a prior art configuration of serrations for a wind turbine blade; Fig. 1 B is a top view of another prior art configuration of serrations for a wind turbine blade;

Fig. 2 is a perspective view of a wind turbine having a wind turbine blade assembly in accordance with an embodiment of the invention;

Fig. 3 is a perspective view of the wind turbine blade assembly of Fig. 2;

Fig. 4 is an illustrative partial disassembled perspective view of a noise attenuator in accordance with one embodiment of the invention;

Fig. 5 is an illustrative perspective view of the noise attenuator shown in Fig. 4 in an assembled state;

Fig. 6 is an illustrative top view of the noise attenuator shown in Fig. 5;

Fig. 6A is a cross-sectional view of the noise attenuator shown in Fig. 6 taken along line 6A-6A;

Fig. 6B is a cross-sectional view of the noise attenuator shown in Fig. 6 taken along line 6B-6B;

Fig. 7 is an illustrative partial disassembled perspective view of a noise attenuator in accordance with another embodiment of the invention ;

Fig. 8 is an illustrative perspective view of the noise attenuator shown in Fig. 7 in an assembled state;

Fig. 9 is an illustrative top view of the noise attenuator shown in Fig. 7;

Fig. 9A is a cross-sectional view of the noise attenuator shown in Fig. 9 taken along line

9A-9A;

Fig. 9B is a cross-sectional view of the noise attenuator shown in Fig. 9 taken along line 9B-9B;

Fig. 10 is an illustrative partial perspective view of a noise attenuator in accordance with another embodiment of the invention; Fig. 1 1 is an illustrative top view of the noise attenuator shown in Fig. 1 0;

Fig. 1 A is a cross-sectional view of the noise attenuator shown in Fig. 1 1 taken along line 1 1 A-1 1 A;

Fig. 1 1 B is a cross-sectional view of the noise attenuator shown in Fig. 1 1 taken along line 1 1 B-1 1 B;

Figs. 12A and 12B illustrate a coupling between a noise attenuator and a wind turbine blade in accordance with one embodiment of the invention;

Figs. 13A and 13B illustrate a coupling between a noise attenuator and a wind turbine blade in accordance with another embodiment of the invention;

Figs. 14A and 14B illustrate a coupling between a noise attenuator and a wind turbine blade in accordance with another embodiment of the invention;

Fig. 15 illustrates a coupling between a noise attenuator and a wind turbine blade in accordance with another embodiment of the invention ; and

Fig. 16 illustrates a coupling between a noise attenuator and a wind turbine blade in accordance with another embodiment of the invention.

Detailed Description

With reference to Fig. 2, a wind turbine 20 includes a tower 22, a nacelle 24 disposed at the apex of the tower 22, and a rotor 26 operatively coupled to a generator (not shown) housed inside the nacelle 24. In addition to the generator, the nacelle 24 houses miscellaneous components required for converting wind energy into electrical energy and various components needed to operate, control, and optimize the performance of the wind turbine 20. The tower 22 supports the load presented by the nacelle 24, the rotor 26, and other components of the wind turbine 20 that are housed inside the nacelle 24 and also operates to elevate the nacelle 24 and rotor 26 to a height above ground level or sea level, as may be the case, at which faster moving air currents of lower turbulence are typically found.

The rotor 26 of the wind turbine 20, which is represented as a horizontal-axis wind turbine, serves as the prime mover for the electromechanical system. Wind exceeding a minimum level will activate the rotor 26 and cause rotation in a plane substantially perpendicular to the wind direction. The rotor 26 of wind turbine 20 includes a central hub 28 and at least one blade assembly 30 that projects outwardly from the central hub 28 at locations circumferentially distributed thereabout. In the representative embodiment, the rotor 26 includes three blade assemblies 30, but the number may vary. The blade assemblies 30 are configured to interact with the passing air flow to produce lift that causes the central hub 28 to spin about a longitudinal axis. The wind turbine 20 may be included among a collection of similar wind turbines belonging to a wind farm or wind park that serves as a power generating plant connected by transmission lines with a power grid, such as a three-phase alternating current (AC) power grid. The power grid generally consists of a network of power stations, transmission circuits, and substations coupled by a network of transmission lines that transmit the power to loads in the form of end users and other customers of electrical utilities. Under normal circumstances, the electrical power is supplied from the generator to the power grid as known to a person having ordinary skill in the art. With reference to Figs. 3, a wind turbine blade assembly 30 configured to be used on the wind turbine 20 generally includes a wind turbine blade 42 and a noise attenuator 44 coupled to the wind turbine blade 42. The noise attenuator 44 is configured to reduce the aerodynamic noise generated by the blades 42 during normal use of the wind turbine 20. In accordance with an aspect of the invention, the noise attenuator 44 may be configured to effectively provide a sharp corner between adjacent attenuator elements, but overcome the structural deficiencies associated with having such a sharp corner between adjacent attenuator elements. Therefore, the noise attenuator 44 is configured to provide efficient noise reduction capabilities, as well as provide the robustness to operate for an extended period of time without the need for repair or replacement.

The wind turbine blade 42 may generally be of a conventional design and in an exemplary embodiment be configured as an elongate structure having an outer airfoil shell 48 disposed about an inner support element or spar 50. The outer shell 48 may be optimally shaped to give the blade 42 the desired aerodynamic properties to generate lift, while the spar 50 is configured to provide the structural aspects (e.g., strength, stiffness, etc.) to blade 42. The elongate blade 42 includes a first root end 52 which is configured to be coupled to the central hub 28 when mounted to rotor 26 (Fig. 2), and a tip end 54 longitudinally opposite to root end 52. The outer shell 48 may include a first, upper shell half 56 that defines the suction side 58 of the blade 42, and a second, lower shell half 60 that defines the pressure side 62 of the blade 42. The upper and lower shell halves 56, 60 are coupled together along a leading edge 64 and a trailing edge 66 located opposite one another across a chord of the blade 42. Although the blade 42 has been described generally as an inner spar having an outer shell, other blade designs may also be used in embodiments of the invention and aspects of the invention should not be limited to the specific design of the blade shown and described herein.

To help reduce the aerodynamic noise generated by the blades 42 during use, noise attenuator 44 may be coupled to the blade 42. The noise attenuator 44 overcomes many of the problems associated with existing noise reduction devices. More particularly, the noise attenuator 44 provides an optimum interface between adjacent attenuator elements for noise reduction purposes (e.g., a sharp corner) without sacrificing the structural integrity of the device. In accordance with an aspect of the invention, this may be achieved by providing a first attenuator portion having a plurality of attenuator elements associated therewith, the interface between adjacent attenuator elements not having a sharp corner, and a second attenuator portion having a plurality of attenuator elements associated therewith, the interface between adjacent attenuator elements also not having a sharp corner. For example, the interfaces between adjacent attenuator elements on the first and second attenuator portions may be generally arcuate. When the first and second attenuator portions are juxtapositioned relative to each other, such as in overlapping relation relative to each other, an attenuator element from one of the attenuator portions is disposed between two attenuator elements from the other attenuator portion such that the effective interface between the attenuator elements (when taken from a top view, for example) forms a substantially sharp corner.

To this end and in reference to Fig. 4, the noise attenuator 44 includes a first noise attenuator portion 70 and a second noise attenuator portion 72 which are juxtapositioned in overlapping relation relative to each other to form the noise attenuator 44. In an exemplary embodiment, the first attenuator portion 70 includes a base member 74 having an inner edge 76, outer edge 78, and a pair of side edges 80 at the ends of the attenuator portion 70; and a plurality of attenuator elements 82 projecting from the outer edge 78 of the base member 74. The base member 74 may be generally configured as a plate-like member defining an inner surface 84 and an outer surface 86 and having a thickness t_bi . In an exemplary embodiment, the inner and outer surfaces 84, 86 may be generally flat or planar, and the thickness t_bi may be generally constant along the length and width of the base member 74. This, however, is merely exemplary as other configurations may be possible. By way of example and without limitation, the thickness t_bi of the base member may be between about 0.1 mm and about 4 mm. However, other thicknesses may also be possible and aspects of the invention should not be so limited.

The attenuator elements 82 extend from the outer edge 78 of the base member 74 in a spaced relation so as to define an interface 88 between adjacent attenuator elements 82. In an exemplary embodiment, the interface 88 may be devoid of substantially sharp corners or the like. For example, the interface 88 may be generally arcuate. In a mathematical sense, the curve that forms the interface 88 may have a continuous first derivative, as opposed to a discontinuous first derivative that results from a substantially sharp corner. As used herein, a substantially sharp corner is one having a local radius of curvature less than about 0.5 mm. By way of example, in one embodiment, the interface 88 between adjacent attenuator elements 82 may be generally radiused (e.g., forming a portion of a circle) having a radius of curvature of about 2 mm. As explained above, and as to the first attenuation portion 70, the interface 88 avoids the sharp corners or discontinuities that may provide a failure site due to the structural loading on the noise attenuator 44. It should be realized that the interface 88 is not limited to that shown in Fig. 4, for example, but may take other forms or configurations that avoid sharp corners (or first derivative discontinuities) that operate as potential failure sites. As will be discussed in more detail below, the interface 88 may be characterized by a width wn that separates adjacent attenuator elements 82.

The attenuator elements 82 extend from the outer edge 78 of the base member 74 at a base line 90 generally defined by connecting the two points of intersection between an attenuator element 82 and its adjacent interfaces 88 (see Fig. 6). In an exemplary embodiment, the attenuator elements 82 may be triangularly shaped, or V-shaped, in accordance with traditional serrations, as illustrated in Figs. 1 A and 1 B. In this regard, the attenuator elements 82 may have the spaced apart legs 92 coupled to the outer edge 78 at base line 90 and terminate in a generally sharp tip 94. Such a V-shaped configuration is exemplary and other attenuator element configurations may be possible. For example, a U-shaped attenuator element, wherein the tip thereof may be generally arcuate, may also be used. Other configurations of the attenuator element may also be used within the scope of the present invention.

Each attenuator element 82 generally defines an upper surface 96 and a lower surface 98, and has a thickness t_ei . In an exemplary embodiment, the upper and lower surfaces 96, 98 may be generally flat or planar and the thickness t_ei of the attenuator element 82 may be generally constant along its length from the base line 90 to the tip 94. In an alternative embodiment, however, the thickness t_ei may vary along the length of the attenuator element 82. By way of example, the thickness t_ei of the attenuator element 82 may decrease in a direction toward the tip 94, defining a tapered geometry in the length direction. The thickness may also vary in the width direction of the attenuator elements 82. For example, the thickness may decrease in a direction toward the side edges of the elements 82. Thus, aspects of the invention are not limited to a constant thickness attenuator element. In exemplary embodiments, the thickness t_ei of the attenuator elements 82 (e.g., at the base line 90) may be between about 0.1 mm and 5 mm. Other values may be possible depending on the application , for example, and the thickness should not be limited to this range. Additionally, the attenuator elements 82 may generally define a width w_e1 at the base line 90 and a length l_e1 from the base line 90 to the tip 94. The geometrical aspect of the attenuator elements 82 may be characterized by an aspect ratio ar_e1 defined to be the length of the attenuator element divided by its width, i.e., ar_e1 = l_e1 / w_e1. In an exemplary embodiment, the attenuator elements 82 may have widths w_e1 between about 1 % and about 30% of the chord length of the blade 42 at the location of the attenuator element 82 along the blade 42, and aspect ratios ar_e1 between about 1 and about 10. These ranges, however, are merely exemplary and other values may be possible depending on the needs or desires of a specific application, for example. The attenuator elements 82 are spaced apart along the outer edge 78 of the base member 74 by interfaces 88 being disposed between adjacent attenuator elements 82. As noted above, the interfaces 88 have a width w_h , which may be measured along the base line 90.

In an exemplary embodiment, the thickness t_ei of the attenuator element 82, at least at the base line 90, may be generally greater than the thickness t_bi of the base member 74. In this regard, in one embodiment, the lower surface 98 of the attenuator element 82 may be generally flush with the outer surface 86 of the base member 74 (i.e., those two surfaces lie generally within the same imaginary plane) and the upper surface 96 of the attenuator element 82 may be spaced from (e.g., spaced above) the inner surface 84 of the base member 74 to define a generally recessed area 100. As will be explained in detail below, the recessed area 100 allows the first and second attenuation portions 70, 72 to nest in a particular manner.

The first attenuator portion 70 further includes a coupling member 102 that may facilitate the coupling of the first and second attenuator portions 70, 72. For example, in one embodiment, the first and second attenuator portions 70, 72 nest relative to each other, and the coupling member 102 may be configured to facilitate that coupling. In this regard, the coupling member 102 may extend away from the base line 90 and generally in a direction toward the inner edge 76 of the base member 74. In an exemplary embodiment, the thickness t_c1 of the coupling member 102 may be generally greater than the thickness t_bi of the base member 74. For example, the thickness t_c1 of the coupling member 102 may be generally constant and be substantially equal to the thickness t_ei of the attenuator element 82, at least at the base line 90. The difference in the thickness of the coupling member 102 and the base member 74 defines an engagement surface 104, the purpose of which will be explained in more detail below.

Turning now to the second attenuator portion 72, this portion may be configured to be similar to the first attenuator portion 70. For example, in one embodiment, the second attenuator portion 72 may be substantially identical to the first attenuator portion 70 in its construction. However, the invention is not so limited and for this reason a description of the second attenuator portion 72 is provided. In an exemplary embodiment, the second attenuator portion 72 includes a base member 120 having an inner edge 122, outer edge 124, and a pair of side edges 126 at the ends of the attenuator portion 72; and a plurality of attenuator elements 128 projecting from the outer edge 124 of the base member 120. The base member 120 may be generally configured as a plate-like member defining an inner surface 130 and an outer surface 132 and having a thickness t_b2. In an exemplary embodiment, the inner and outer surfaces 130, 132 may be generally flat or planar, and the thickness t_b2 may be generally constant along the length and width of the base member 120. This, however, is merely exemplary as other configurations may be possible. By way of example and without limitation, the thickness t_b2 of the base member may be between about 0.1 mm and about 4 mm. However, other thicknesses may also be possible and aspects of the invention should not be so limited.

The attenuator elements 128 extend from the outer edge 124 of the base member 120 in a spaced relation so as to define an interface 134 between adjacent attenuator elements 128. In an exemplary embodiment, the interface 134 may be devoid of substantially sharp corners or the like (e.g., a continuous first derivative). By way of example, in one embodiment, the interface 134 between adjacent attenuator elements 128 may be generally arcuate, and more specifically may be generally radiused. As explained above, and as to the second attenuation portion 72, the interface 134 avoids the sharp corners or discontinuities that may provide a failure site due to the structural loading on the noise reduction devices. It should be realized that the interface 134 is not limited to that shown in Fig. 4, for example, but may take other forms or configurations that avoid sharp corners (or first derivative discontinuities) that operate as potential failure sites. As will be discussed in more detail below, the interface 134 may be characterized by a width w_i2 that separates adjacent attenuator elements 128. The attenuator elements 128 extend from the outer edge 124 of the base member 120 at a base line 136 generally defined by connecting the two points of intersection between an attenuator element 128 and its adjacent interfaces 134 (see Fig. 6). In an exemplary embodiment, the attenuator elements 128 may be triangularly shaped, or V-shaped, and terminate at a tip 140. Alternatively the attenuator elements 128 may be U-shaped or have some other configuration.

Each attenuator element 128 generally defines an upper surface 142 and a lower surface 144, and has a thickness t_e2- In an exemplary embodiment, the upper and lower surfaces 142, 144 may be generally flat or planar and the thickness t_e2 of the attenuator element 82 may be generally constant along its length from the base line 136 to the tip 140. In an alternative embodiment, however, the thickness t_e2 may vary along the length of the attenuator element 128. By way of example, the thickness t_e2 of the attenuator element 128 may decrease in a direction toward the tip 140, defining a tapered geometry in the length direction. The thickness may also vary in the width direction, such as decreasing in a direction toward the side edges of the elements 82. Thus, aspects of the invention are not limited to a constant thickness attenuator element. In exemplary embodiments, the thickness t_e2 of the attenuator elements 128 (e.g., at the base line 136) may be between about 0.1 mm and 5 mm. Other values may be possible depending on the application, for example, and the thickness should not be limited to this range.

Additionally, the attenuator elements 128 may generally define a width w_e2 at the base line 136 and a length l_e2 from the base line 136 to the tip 140. The geometrical aspect of the attenuator elements 128 may be characterized by an aspect ratio ar_e2 defined to be the length of the attenuator element divided by its width, i.e., ar_e2 = l_e2 / w_e2. In an exemplary embodiment, the attenuator elements 128 may have widths w_e2 between about 1 % and about 30% of the chord length of the blade 42 at the location of the attenuator element 82 along the blade 42, and aspect ratios ar_e2 between about 1 and about 10. These ranges, however, are merely exemplary and other values may be possible depending on the needs or desires of a specific application, for example. The attenuator elements 128 are spaced apart along the outer edge 124 of the base member 120 by interfaces 134 being disposed between adjacent attenuator elements 128. Similar to above, the interfaces 134 may have a width w_i2, which may be measured along the base line 136.

In an exemplary embodiment, the thickness t_e2 of the attenuator element 128, at least at the base line 136, may be generally greater than the thickness t_b2 of the base member 120. In this regard, in one embodiment, the upper surface 142 of the attenuator element 128 may be generally flush with the outer surface 132 of the base member 120 (i.e., those two surfaces lie generally within the same imaginary plane) and the lower surface 144 of the attenuator element 128 may be spaced from (e.g., spaced above) the inner surface 130 of the base member 120 to define a generally recessed area 146. The second attenuator portion 72 further includes a coupling member 148 that may facilitate the coupling of the first and second attenuator portions 70, 72. In this regard, the coupling member 148 may extend away from the base line 136 and generally in a direction toward the inner edge 122 of the base member 120. In an exemplary embodiment, the thickness t_c2 of the coupling member 148 may be generally greater than the thickness t_b2 of the base member 120. For example, the thickness t_c2 of the coupling member 148 may be generally constant and be substantially equal to the thickness t_e2 of the attenuator element 128, at least at the base line 136. The difference in the thickness of the coupling member 148 and the base member 120 defines an engagement surface 150, the purpose of which will be explained in more detail below.

The two attenuator portions 70, 72 may be juxtapositioned relative to each other to form a composite noise attenuator 44. In one embodiment, the two attenuator portions 70, 72 may be coupled together to form the composite noise attenuator 44 (Figs. 4-9B). In an alternative embodiment, however, the two attenuator portions 70, 72 may not be directly coupled to each other, but merely be positioned adjacent each other in a manner such that the two attenuator portions 70, 72 collectively operate as a composite noise attenuator 44 (Figs. 10-1 1 B). In one aspect of the invention, the two attenuator portions 70, 72 are juxtaposed in overlapping relation relative to each other, such that at least a portion of the first attenuator portion 70 overlaps with at least a portion of the second attenuator portion 72. Overlap in this context generally means that there is at least a portion of one of the attenuator portions above or below at least a portion of the other attenuator portion. More particularly, picturing that the first and second attenuator portions 70, 72 generally lie within planes, then overlap in this context means that there is a line that is generally normal to the attenuator portions that passes through both attenuator portions. In one embodiment, the overlap region may extend for only a portion of the first or second attenuator portions 70, 72. In another embodiment, the overlap region may extend for substantially the full length of at least one of the first or second attenuator portions 70, 72. In still another embodiment, the overlap region may extend for substantially the full length of both of the first and second attenuator portions 70, 72.

Figs. 4-6B illustrate an exemplary embodiment of an overlapping relation between the first and second attenuator portions 70, 72 to form the noise attenuator 44. In this regard, the second attenuator portion 72 may be juxtapositioned relative to the first attenuator portion 70 (or vice versa) such that at least a portion of the first and second attenuator portions 70, 72 overlap each other. For example, the first and second attenuator portions 70, 72 may overlap at portions of respective base members 74, 120. In an exemplary embodiment, however, the attenuator elements 82, 128 may not be in overlapping relation relative to each other. Additionally, when the first and second attenuator portions 70, 72 are juxtapositioned relative to each other, the portions may engage each other or alternatively be separated from each other so there is no contact therebetween. Moreover, the composite noise attenuator 44 formed by the first and second attenuator portions 70, 72 may be configured such that any two adjacent attenuator elements of the noise attenuator 44 (as opposed to adjacent elements on the individual portions) extend from or are associated with different attenuator portions. Thus, if one randomly selects an attenuator element of the noise attenuator 44 that is an attenuator element 82 from the first attenuator portion 70, then the adjacent attenuator elements on the noise attenuator 44 to each side of the selected element will be attenuator elements 128 from the second attenuator portion 72. The converse would apply if the selected attenuator of the noise attenuator 44 were from the second portion 72. This is best illustrated in Figs. 5 and 6, for example.

Additionally, and in a primary aspect of the invention, when the noise attenuator 44 is viewed from above, as illustrated in Fig. 6, adjacent attenuator elements of the noise attenuator 44 may intersect or appear to intersect each other at a substantially sharp corner 160. More particularly, again picturing that the first and second attenuator portions 70, 72 (or at least the attenuator elements thereof) generally lie within planes, then the viewing direction that illustrates this feature may be in a direction generally perpendicular to the planes. As will be discussed below, the attenuator elements 82, 128 of the respective portions 70, 72 may or may not lie within the same plane (e.g., compare Fig. 6 to Fig. 1 1 ). Thus, adjacent attenuator elements of the noise attenuator 44 may actually intersect or only appear to intersect when viewed from the perspective described above. Accordingly, the terms "effective intersection" or "effectively intersect" will be used herein to connote that the adjacent elements may actually intersect or only appear to intersect when viewed from the above vantage point. As has been discussed above, the effective intersection of adjacent elements of the noise attenuator 44 at a substantially sharp corner is configured to provide optimum noise reduction benefits.

Figs. 4-6 illustrate an embodiment wherein the first and second attenuator portions 70, 72 nest relative to each other. In this regard, the second attenuator portion 72 may be received in recessed area 100 of the first attenuator portion 70, and the first attenuator portion 70 may likewise be received in the recessed area 142 of the second attenuator portion 72. In this way, for example, in addition to the above aspects (e.g., substantially sharp corner at the effective intersection of adjacent attenuator elements), at least the attenuator elements 82, 128 of the noise attenuator 44 may be configured to generally lie within the same plane (Figs. 5, 6A and 6B). More particularly, the upper surfaces 96, 142 of the attenuator elements 82, 128, respectively, may generally lie within the same plane, and the lower surfaces 98, 144 of the attenuator elements 82, 128, respectively, may also generally lie within the same plane. In an exemplary embodiment, as can be seen in Figs. 5-6B, when the attenuator portions 70, 72 are brought together, the coupling member 102 of the first attenuator portion 70 may be received in the interface 134 of the second attenuator portion 72. For example, the engagement surface 104 of the coupling member 102 may engage the interface 134. In this regard, the shape of the engagement surface 104 may correspond to the shape of the interface 134. Thus, in one embodiment, the engagement surface 104 may be radiused (e.g., part of a circle). Similarly, when the attenuator portions 70, 72 are brought together, the coupling member 148 of the second attenuator portion 72 may be received in the interface 88 of the second attenuator portion 72. For example, the engagement surface 150 of the coupling member 148 may engage the interface 88. In this regard, the shape of the engagement surface 1 50 may correspond to the shape of the interface 88. Thus, in one embodiment, the engagement surface 150 may be radiused. In a way, the coupling members 1 02, 148 operate as keys within keyways defined by interfaces 134, 88 to facilitate nesting of the two attenuator portions 70, 72.

In accordance with aspects of the invention, there may be a relationship between the width of the attenuator elements 82, 128 and the width of the interfaces 134, 88. More particularly, in an exemplary embodiment, the width wn of the interfaces 88 may be substantially equal to the width w_e2 of the attenuator elements 128 of the second attenuator portion 72. In a similar manner, the width w_i2 of the interfaces 134 may be substantially equal to the width w_e1 of the attenuator elements 82 of the first attenuator portion 70. This will ensure that when the first and second attenuator sections 70, 72 are coupled together, adjacent attenuator elements of the noise attenuator 44 effectively intersect at a substantially sharp corner. In one embodiment, the widths of the first and second attenuator elements 82, 128 are substantially identical. It should be realized that alternative embodiments of the invention may employ a host of width arrangements in regard to the attenuator elements 82, 128 and interfaces 88, 134. A primary aspect of the invention, however, is that whatever width arrangements are utilized, when the first and second attenuator portions 70, 72 are juxtapositioned relative to each other to form the noise attenuator 44, the adjacent attenuator elements effectively intersect each other at a substantially sharp corner.

As illustrated in Figs. 6A and 6B, in one embodiment, the thicknesses of the various base members 74, 120 and attenuator elements 82, 128 may be configured such that the noise attenuator 44 has a first side 162 that is generally planar and devoid of step up or step downs in the surface, at least along the attenuator elements and a portion of the base member adjacent the elements. Additionally, a second side 164 of the noise attenuator 44 may likewise be generally planar and devoid of step ups or step downs at least along the attenuator elements and a portion of the base member adjacent the elements.

While the embodiment shown in Figs. 4-6B illustrates a nesting relationship such that the attenuator elements 82, 128 of the noise attenuator 44 generally lie within the same plane, the invention is not so limited. For example, as illustrated in Figs. 7-1 1 B, there may be no nesting of the attenuator elements 82, 128 such that the elements of the noise attenuator 44 generally lie in the same plane. In this case, the attenuator elements 82 of the first attenuator portion 70 may generally lie within a first plane and the attenuator elements 128 of the second attenuator portion 72 may generally lie within a second plane, wherein the planes may be immediately adjacent each other (Figs. 7-9B) or slightly spaced from each other (Figs. 10-1 1 B). Although the attenuator elements 82, 128 of the noise attenuator 44 lie within separate planes, when viewed from the top or perspective described above, adjacent attenuator elements still effectively intersect each other at a substantially sharp corner. In other words, although there is no actual intersection of adjacent elements (since they lie in different planes) they still appear to intersect each other when viewed from above. This is best illustrated, for example, in Figs. 9 and 1 1 . Furthermore, while Figs. 7-9B illustrate the two attenuator portions 70, 72 as engaging each other, it should be realized that the attenuator portions 70, 72 may be slightly spaced apart so that there is no or minimal direct engagement therebetween. Even in this situation, when viewed from the top or above, adjacent attenuator elements of the noise attenuator 44 may be configured to effectively intersect each other at a substantially sharp corner, as illustrated in Fig. 1 1 . In this embodiment, a resilient member (not shown) may be disposed between the spaced-apart attenuator portions 70, 72 to prevent or reduce the likelihood of contact damage under, for example, extreme loading or other conditions.

In summary, and as illustrated by the embodiments described above, a noise attenuator 44 may be formed from a first attenuator portion 70 and a second attenuator portion 72 which may be juxtapositioned relative to each other to form the noise attenuator 44. The first attenuator portion 70 includes a plurality of attenuator elements 82 separated by an interface 88 characterized by being devoid of sharp corners. Similarly, the second attenuator portion 72 includes a plurality of attenuator elements 128 separated by an interface 134 also characterized by being devoid of sharp corners. Due to the particular geometry of the interfaces, 88, 134, from a structural standpoint the first and second attenuator portions 70, 72 individually avoid sharp corner geometries that may form failure sites during use. Additionally, due to the overlapping arrangement of the attenuator portions 70, 72, adjacent attenuator elements on the noise attenuator 44 are from different attenuator portions and are configured to effectively intersect (when, for example, viewed from above) at a substantially sharp corner. Thus, the noise reduction capability of the noise attenuator 44 may be optimized by effectively having sharp corners between adjacent attenuator elements without sacrificing the structural integrity of the noise attenuator 44.

As noted above and illustrated in Fig. 3, the noise attenuator 44 as described above may be coupled to wind turbine blade 42. In an exemplary embodiment, the noise attenuator 44 may be coupled adjacent to the trailing edge 66 of the wind turbine blade 42. While this location may be the conventional location for a noise reduction device, and makes sense in view of the evidence indicating that the trailing edge noise may be the dominant source of noise in wind turbine blades, aspects of the invention are not limited to the noise attenuator 44 being located or only located at the trailing edge 66 of the blade 42. In this regard, in various alternative embodiments, the noise attenuator 44 may be located at other locations on the blade 42, including, for example, at the leading edge 64 or at an intermediate position between the leading and trailing edges 64, 66. Additionally, while the noise attenuator 44 is illustrated as being positioned more adjacent the tip end 54 of the blade 42, the position of the noise attenuator 44 between the root and tip ends 52, 54 may vary depending on the specific application and the design parameters for a particular wind turbine. By way of example, and without limitation, in an exemplary embodiment, the noise attenuator 44 may be located on the outer half of the blade 42, such as between approximately 60% and approximately 90% of the blade length. As noted above, however, other locations are possible. In one embodiment, each of the first and second attenuator portions 70, 72 may be a single body member such that the portions 70, 72 extend for substantially the full length of the noise attenuator 44. Alternatively, however, the noise attenuator 44 may have a modular design wherein each of the first and second attenuator portions 70, 72 extend for less than the full length of the noise attenuator 44. In this case, multiple noise attenuator modules 170, (Fig. 3) each module 170 comprising a first module attenuator portion and a second module attenuator portion, may be substantially positioned end-to- end to form the noise attenuator 44. The first and second attenuator portions 70, 72 may be made from a variety of materials sufficient to handle to loads on the noise attenuator 44. By way of example and not limitation, the attenuator portions 70, 72 may be formed from cast urethane, aluminum, carbon fiber reinforced plastic, glass reinforced plastic, carbon fiber reinforced urethane, combinations thereof, or other suitable materials. In one embodiment, the configuration of the attenuator elements 82, 128 may be substantially the same (e.g., constant width and length) along the length of the noise attenuator 44. In an alternative embodiment, the configuration of the attenuator elements 82, 128 may vary along the length of the noise attenuator 44. In this regard, in one embodiment, the length of the attenuator elements 82, 128 may vary along the length of the noise attenuator 44. More particularly, when the noise attenuator 44 is coupled to the blade 42, the length of the elements 82, 128 may increase in a direction toward the root end 52 of the blade 42. In such an embodiment, however, the width of the elements 82, 128 may also vary so that the aspect ratio of the elements 82, 128 remain substantially constant. Those of ordinary skill will recognize a host of other arrangements of the attenuator elements 82, 128 along the noise attenuator 44. For example, in one embodiment, the length and/or aspect ratio of the attenuator elements 82 on the first attenuator portion 70 may be different from the length and/or aspect ratio of the attenuator elements 128 on the second attenuator portion 72.

The noise attenuator 44 may be coupled to the wind turbine blade 42 in several ways. Figs. 12A- 15 illustrate several arrangements for coupling the noise attenuator 44 to the blade 42. In Figs. 12A and 12B, for example, both the first and second attenuator portions 70, 72 may overlap the blade 42. In this regard, the second attenuator portion 72, and more particularly the outer surface 132 of the base member 120, may be coupled to the pressure side 62 of the blade 42. This coupling may be achieved using any suitable fastening, including without limitation adhesives, screws, rivets, bolts, etc. The first attenuator portion 70 may then be coupled to the second attenuator portion 72 in a manner that also overlaps the blade 42. Similar to above, this coupling may be achieved using any suitable fastening, including without limitation adhesives, screws, rivets, bolts, etc.

In an exemplary embodiment, the second attenuator portion 72 may include a wedged cap 172 on its outer surface 132 that covers the trailing edge 66 of the wind turbine blade 42 and forms a smooth transition with the suction side 58 of the blade 42. However, there may be a step on the pressure side 62 of the blade 42 due to the thickness of both first and second attenuator portions 70, 72 which may affect the flow of air over the pressure side 66 of the blade 42. To reduce any effect this may have on the performance of the noise attenuator 44, in one embodiment a transition member 174 (shown in phantom) may be positioned adjacent the inner edge 76, 122 of the attenuator portions 70, 72. The transition member 174 includes a smooth outer surface 176 configured to gently transition the flow of air from the surface of the blade 42 to the surface of the noise attenuator 44. The outer surface 176 may be linear or arcuate and devoid of sharp corners, and therefore avoids the effects of the sharp corner presented at the inner edges 76, 122 of the noise attenuator 44. Additionally or alternatively, the first attenuator portion 70 may include a taper or chamfer (not shown) adjacent the inner edge 76 of the base member 74. The transition member 174 may be a separate solid piece coupled to the blade 42. Alternatively, the transition member 174 may be formed from a curable material applied in a flowable state, but subsequently cured to a solid or semisolid state.

While the embodiment shown in Figs. 12A and 12B illustrates both first and second attenuator portions 70, 72 overlapping with the pressure side 62 of the blade 42. In an alternative embodiment, the coupling to the blade 42 may essentially be inverted so as to couple to the suction side 58 of the blade 42. As this arrangement would be readily understood by one of ordinary skill in the art based on Figs. 12A and 12B, this arrangement will not be described in further detail.

Figs. 13A and 13B illustrate another arrangement configured to reduce the size of the step on the pressure side 62 of the blade 42 due to the presence of the noise attenuator 44. To this end, only one of the attenuator portions overlaps with the blade 42. In this regard, the first attenuator portion 70, and more particularly the inner surface 84 of the base member 74, may be coupled to the pressure side 62 of the blade 42. This coupling may be achieved using any suitable fastening, including without limitation adhesives, screws, rivets, bolts, etc. The second attenuator portion 72 may then be coupled to the first attenuator portion 70 in a manner that does not overlap with the blade 42. Similar to above, this coupling may be achieved using any suitable fastening, including without limitation adhesives, screws, rivets, bolts, etc. In other words, the first attenuator portion 70 supports the second attenuator portion 72.

In an exemplary embodiment, the second attenuator portion 72 and the wedged cap 172 (which may be smaller as compared to that shown in Figs. 12A and 12B) cover the trailing edge 66 of the wind turbine blade 42 and forms a smooth transition with the suction side 58 of the blade 42. While a step remains on the pressure side 62 of the blade 42, the size thereof has been reduced due to the step being formed by only one of the attenuator portions. Similar to above, a transition member 174 (shown in phantom) may be positioned adjacent the inner edge 76 of the first attenuator portion 70. Additionally or alternatively, the first attenuator portion 70 may include a taper or chamfer (not shown) adjacent the inner edge 76 of the base member 74. While the embodiment shown in Figs. 13A and 13B illustrate the first attenuator portion 70 overlapping with the pressure side 62 of the blade 42. In an alternative embodiment, the coupling to the blade 42 may essentially be inverted such that the second attenuator portion 72 couples to the suction side 58 of the blade 42 and the first attenuator portion 70 is supported by the second attenuator portion 72. As this arrangement would be readily understood by one of ordinary skill in the art based on Figs. 13A and 13B, this arrangement will not be described in further detail. In reference to Figs. 13A and 13B, it should be noted that in addition to being supported by the first attenuator portion 70, the second attenuator portion 72 may also be coupled to the trailing edge 66 of the blade 42.

Figs. 14A and 14B illustrate yet another arrangement for coupling the noise attenuator 44 to the wind turbine blade 42 to form the wind turbine blade assembly 30. In this embodiment, both attenuator portions 70, 72 overlap with the blade 42, but extend from different sides of the blade 42. In this regard, the first attenuator portion 70, and more particularly the inner surface 84 of the base member 74, may be coupled to the pressure side 62 of the blade 42, and the second attenuator portion 72, and more particularly the inner surface 130 of the base member 120, may be coupled to the suction side 58 of the blade 42. These couplings may be achieved using any suitable fastening, including without limitation adhesives, screws, rivets, bolts, etc. In this embodiment, the first and second attenuator portions 70, 72 may have a nesting relationship so that the attenuator elements 82, 128 generally lie within the same plane. As illustrated in these figures, this may be achieved using an L-shaped bracket or connector 178, which may, for example, cover the trailing edge 66 of the blade 42. Similar to above, a transition member 174 (shown in phantom) may be positioned adjacent the inner edge 76 of the first attenuator portion 70. A transition member 180 (also shown in phantom) may also be used in the sharp corner of the first attenuator portion 70. Additionally or alternatively, the first attenuator portion 70 may include a taper or chamfer (not shown) adjacent the inner edge 76 of the base member 74. Although not shown, the second attenuator portion 72 may include a transition member and/or a taper as well.

It should be recognized that while the embodiment shown in Figs. 14A and 14B illustrate the nesting feature being achieved by associating the L-shaped configuration to the first attenuator portion 70, in an alternative embodiment, the L-shaped configuration may be associated with the second attenuator portion 72. As this arrangement would be readily understood by one of ordinary skill in the art based on Figs. 14A and 14B, this arrangement will not be described in further detail. Fig. 15 illustrates a further arrangement for coupling the noise attenuator 44 to the wind turbine blade 42 to form the wind turbine blade assembly 30. In this embodiment, both attenuator portions 70, 72 overlap with the blade 42 and extend from different sides of the blade 42, similar to that shown in Figs. 14A and 14B, but there is no nesting relationship between the attenuator elements 82, 128. Accordingly, in this embodiment, the attenuator elements 82, 128 may generally lie in different planes. For example, in one embodiment, the attenuator elements 82, 128 may be directly above/below each other with no spacing therebetween, similar to that shown in Figs. 7-9B. Alternatively, the attenuator elements 82, 128 may be slightly spaced apart by a gap 182, as is illustrated in Fig. 15 (also illustrated in Figs. 10-1 1 B). Transition members 1 74, 180 and/or tapers may be used with the first attenuator portion 70 coupled to the pressure side 62 of the blade 42. Transition members and/or tapers may or may not be used with the second attenuator portion 72 coupled to the suction side 58 of the blade 42. For example, in some applications the steps associated with the second attenuator portion 72 may provide some benefit and therefore want to be retained.

Figure 16 illustrates a further embodiment which is similar to the embodiment shown in Figs. 13A and 13B. Thus, only the differences will be described in detail. In this regard, one primary difference is the coupling of the second attenuator portion 72 to the first attenuator portion 70. More specifically, this coupling may be achieved at least in part through an integrated mechanical joint or connection. Figure 16 illustrates an integrated mechanical joint configured as a dovetail joint. In this embodiment, the first attenuator portion 70 includes one or more recesses or tails 190 and the second attenuator portion 72 includes one or more pins 192. The second attenuator portion 72 may be coupled to the first attenuator portion 70 by interlocking the pins 192 with the tails 1 90 to thereby form the dovetail joint. This may be achieved, for example, by a snap fit or by relative sliding movement of the attenuator portions. Such a mechanical joint or connection between the attenuator portions 70, 72 may be advantageous for minimizing the distance between the trailing edge 66 of the blade 42 and the attenuator elements 82, 128 of the noise attenuator 44; for reducing the surface area required for adhesives, and/or for reducing the dependency on adhesives for keeping the attenuator portions 70, 72 coupled to each other (i.e., the mechanical joint itself, as opposed to the adhesives, resists separation of the two attenuator portions 70, 72). In addition to the mechanical joint, other fastening, such as adhesives, may be used as well. Other mechanical joints, such as those similar to a dovetail joint, may also be used in alternative embodiments.

While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in some detail, it is not the intention of the inventors to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the various features of the invention may be used alone or in any combination depending on the needs and preferences of the user.

Claims

1 . A noise attenuator for a wind turbine blade, comprising:

a first attenuator portion having a plurality of first attenuator elements, each first attenuator element being separated from an adjacent first attenuator element by an interface devoid of a substantially sharp corner; and

a second attenuator portion having a plurality of second attenuator elements, each second attenuator element being separated from an adjacent second attenuator element by an interface devoid of a substantially sharp corner,

wherein the first and second attenuator portions are configured such that when the noise attenuator is installed on the wind turbine blade, the first and second attenuator portions are juxtapositioned in an overlapping relationship relative to each other to collectively form the noise attenuator.

2. The noise attenuator according to claim 1 , wherein the first and second attenuator portions are configured such that when the noise attenuator is installed on the wind turbine blade, adjacent attenuator elements of the noise attenuator are from different attenuator portions.

3. The noise attenuator according to claim 1 or 2, wherein the first and second attenuator portions are configured such that when the noise attenuator is installed on the wind turbine blade, adjacent attenuator elements of the noise attenuator effectively intersect each other at a substantially sharp corner.

4. The noise attenuator according to any of the preceding claims, wherein the first and second attenuator portions are configured such that when the noise attenuator is installed on the wind turbine blade, the first and second attenuator portions nest relative to each other so that the first and second attenuator elements generally lie within the same plane.

5. The noise attenuator according to any of the preceding claims, wherein the first and second attenuator portions are configured such that when the noise attenuator is installed on the wind turbine blade, the first and second attenuator portions engage one another.

6. The noise attenuator according to any of the preceding claims, wherein the first and second attenuator portions are configured such that when the noise attenuator is installed on the wind turbine blade, the first and second attenuator elements are not in overlapping relationship relative to each other.

7. The noise attenuator according to any of the preceding claims, wherein the first and second attenuator elements are generally V-shaped.

8. The noise attenuator according to any of the preceding claims, wherein the first attenuator elements have a first width and the second attenuator elements have a second width, wherein the width of the interface between adjacent first attenuator elements is substantially equal to the second width and the width of the interface between adjacent second attenuator elements is substantially equal to the first width.

9. The noise attenuator according to any of the preceding claims, wherein the first attenuator elements and the second attenuator elements are substantially identical.

10. A wind turbine blade assembly, comprising:

a wind turbine blade having a root end, a tip end, a leading edge, a trailing edge, a pressure side and a suction side; and

a noise attenuator coupled to the wind turbine blade, the noise attenuator comprising:

a first attenuator portion having a plurality of first attenuator elements, each first attenuator element being separated from an adjacent first attenuator element by an interface devoid of a substantially sharp corner, the first attenuator portion being coupled to the wind turbine blade; and

a second attenuator portion juxtapositioned in an overlapping relationship relative to the first attenuator portion, the second attenuator portion having a plurality of second attenuator elements, each second attenuator element being separated from an adjacent second attenuator element by an interface devoid of a substantially sharp corner.

1 1 . The wind turbine blade assembly according to claim 10, wherein adjacent attenuator elements of the noise generator are from different attenuator portions.

12. The wind turbine blade assembly according to claim 10 or 1 1 , wherein adjacent attenuator elements of the noise attenuator effectively intersect each other at a substantially sharp corner.

13. The wind turbine blade assembly according to any of claims 10-12, wherein the first and second attenuator elements are not in overlapping relationship relative to each other.

14. The wind turbine blade assembly according to any of claims 10-13, wherein the first and second attenuator portions nest relative to each other so that the first and second attenuator elements generally lie within the same plane.

15. The wind turbine blade assembly according to any of claims 10-14, wherein the noise attenuator is coupled to the wind turbine blade adjacent the trailing edge.

16. The wind turbine blade assembly according to any of claims 10-15, wherein the noise attenuator is positioned on the outer half of the wind turbine blade as measured from a root end.

17. The wind turbine blade assembly according to any of claims 10-16, wherein a length of the attenuator elements of the noise attenuator vary along the length of the wind turbine blade.

18. A wind turbine, comprising:

a tower;

a nacelle disposed adjacent a top of the tower; and

a rotor including a hub and at least one wind turbine blade assembly according to any of claims 10-17 extending from the hub.

19. A method of reducing noise from a wind turbine, comprising:

coupling a first attenuator portion of a noise attenuator to a wind turbine blade, the first attenuator portion having a plurality of first attenuator elements, each first attenuator element being separated from an adjacent first attenuator element by an interface devoid of a substantially sharp corner; and

juxtapositioning a second attenuator portion of the noise attenuator in overlapping relationship relative to the first attenuator portion, the second attenuator portion having a plurality of second attenuator elements, each second attenuator element being separated from an adjacent second attenuator element by an interface devoid of a substantially sharp corner, the first and second attenuator portions collectively forming the noise attenuator.

20. The method according to claim 19, wherein juxtapositioning the second attenuator portion in overlapping relationship relative to the first attenuator portion further comprises juxtapositioning the first and second attenuator portions so that adjacent attenuator elements of the noise attenuator effectively intersect each other at a substantially sharp corner.