THE BLADE TIP

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, a wind turbine having such a wind turbine blade, and a method for reducing noise from a wind turbine.

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. For example, various governmental entities (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.

There may be several sources for aerodynamic noise, including trailing edge noise and blade tip vortex noise. Trailing edge noise, which may include blunt trailing edge vortex-shedding noise and turbulent boundary layer trailing edge noise, has received some attention by power producers and manufacturers. For example, various trailing edge designs, such as a serrated or saw tooth design, have been proposed for reducing trailing edge noise. While such solutions for trailing edge noise are in the art, the inventors submit that a relatively significant source of aerodynamic noise is the generally high frequency broadband noise caused by flow vortices at the tip of the rotor blade, i.e., blade tip vortex noise. The flow vortices are generally caused by the interaction of flow over the blade tip from the pressure side of the blade to the suction side of the blade. The flow vortices interact with the blade tip and the trailing edge of the rotor blade, causing the generally high frequency broadband noise. Blade tip vortex noise has not received as much attention in the wind turbine industry, and therefore various noise reducing devices directed to blade tip vortex noise are generally unknown. This represents a lost opportunity to reduce the overall noise emission from a wind turbine.

Accordingly, there is a need in the wind turbine industry for a device or apparatus directed to reducing the noise generated by blade tip vortices. There is also a need for a wind turbine blade having such a noise reduction device, as well as a wind turbine having such a wind turbine blade.

Summary A wind turbine blade assembly includes 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 tip end of the blade and configured to reduce the noise produced by the wind turbine blade during use. More particularly, the noise attenuator is configured to reduce the blade tip vortex noise produced by the wind turbine blade during use. The noise attenuator includes a main body defining a central axis extending from a first vertex point to a second vertex point including a first fin portion extending from one side of the central axis and a second fin portion extending from the other side of the central axis. The first fin portion extends beyond the suction side of the blade and the second fin portion extends beyond the pressure side of the blade when the noise attenuator is coupled to the tip end of the blade. In an exemplary embodiment, the height of the first fin portion is different than the height of the second fin portion. For example, in one embodiment, the height of the first fin portion is less than the height of the second fin portion. In this regard, a height ratio r _h of the noise attenuator is in the range 1 .0≤ r _h ≤ 2.0. Additionally, the first fin portion has a first swept distance and the second fin portion has a second swept distance, the first and second swept distances being different from each other. In an exemplary embodiment, the first swept distance is less than the second swept distance. In this regard, a swept distance ratio r _d of the noise attenuator is in the range 2.0≤ r _d ≤ 3.0. Furthermore, the first fin portion has a first trailing edge and the second fin portion has a second trailing edge and the angle β formed between the first and second trailing edges is in the range 90 ^° ≤ β≤ 180 ^° .

In one embodiment, the first fin portion has a trapezoidal configuration with a first leading edge, a first trailing edge, and a first tip edge generally parallel to the central axis. The intersection of the first leading edge and the first tip edge is between the first and second vertex points, and the intersection of the first tip edge and the first trailing edge is downstream of the second vertex point. Moreover, the second fin portion has a trapezoidal configuration with a second leading edge, a second trailing edge, and a second tip edge generally parallel to the central axis. The intersection of the second leading edge and the second tip edge is downstream of the trailing end vertex. The first and second fin portions may have a symmetric airfoil cross-sectional profile.

In another embodiment, a wind turbine includes a tower, a nacelle disposed adjacent atop of the tower, and a rotor including a hub and at least one wind turbine blade assembly extending from the hub. The wind turbine blade assembly includes 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 tip end of the blade and configured to reduce the noise produced by the wind turbine blade during use. The noise attenuator includes a main body defining a central axis extending from a first vertex point to a second vertex point and including a first fin portion extending from one side of the central axis and a second fin portion extending from the other side of the central axis. The first fin portion extends beyond the suction side of the blade and the second fin portion extends beyond the pressure side of the blade when the noise attenuator is coupled to the tip end of the blade.

A method of reducing noise from a wind turbine includes providing a wind turbine blade having a root end, a tip end, a leading edge, a trailing edge, a pressure side and a suction side; coupling a noise attenuator to the tip end of the blade; and operating the wind turbine with the noise attenuator coupled to the blade to reduce the noise from the wind turbine. In one embodiment, coupling the noise attenuator to the tip end of the blade includes coupling the noise attenuator such that a first fin portion of the noise attenuator extends beyond the suction side of the blade and a second fin portion of the noise attenuator extends beyond the pressure side of the blade.

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

Fig. 2 is a perspective view of a wind turbine blade assembly in accordance with an embodiment of the invention; and Fig. 3 is a side view of the wind turbine blade assembly illustrating a noise attenuator in accordance with an embodiment of the invention and the tip end of the blade.

Detailed Description

With reference to Fig. 1 , a wind turbine 10 includes a tower 12, a nacelle 14 disposed at the apex of the tower 12, and a rotor 16 operatively coupled to a generator (not shown) housed inside the nacelle 14. In addition to the generator, the nacelle 14 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 10. The tower 12 supports the load presented by the nacelle 14, the rotor 16, and other components of the wind turbine 10 that are housed inside the nacelle 14 and also operates to elevate the nacelle 14 and rotor 16 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 16 of the wind turbine 10, 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 16 and cause rotation in a plane substantially perpendicular to the wind direction. The rotor 16 of wind turbine 10 includes a central hub 18 and at least one blade assembly 20 that projects outwardly from the central hub 18 at locations circumferentially distributed thereabout. In the representative embodiment, the rotor 16 includes three blade assemblies 20, but the number may vary. The blade assemblies 20 are configured to interact with the passing air flow to produce lift that causes the central hub 18 to spin about a longitudinal axis.

The wind turbine 10 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. 1 and 2, a wind turbine blade assembly 20 configured to be used on the wind turbine 10 generally includes a wind turbine blade 22 and a noise attenuator 24 coupled to the wind turbine blade 22. The noise attenuator 24 is configured to reduce the aerodynamic noise generated by the blades 22 during normal use of the wind turbine 10. More particularly, the noise attenuator 24 is configured to reduce the portion of the aerodynamic noise caused by blade tip vortices. In accordance with an aspect of the invention, the noise attenuator 24 may be configured to dissipate the energy in the blade tip vortices as well as to reduce the interaction of the vortices with the blade surfaces near the tip. This results in reduced levels of noise emanating from the wind turbine blade tip, thus reducing the overall noise generated by the wind turbine 10.

The wind turbine blade 22 may generally be of a conventional design, and in an exemplary embodiment be configured as an elongate structure having an outer airfoil shell 26 disposed about an inner support element or spar 28. The outer shell 26 may be optimally shaped to give the blade 22 the desired aerodynamic properties to generate lift, while the spar 28 is configured to provide the structural aspects (e.g., strength, stiffness, etc.) to blade 22. The elongate blade 22 includes a first root end 30 which is configured to be coupled to the central hub 18 when mounted to rotor 16, and a tip end 32 longitudinally opposite to root end 30. In the orientation shown in Fig. 2, the outer shell 26 may include a first, lower shell half 34 that defines the suction side 36 of the blade 22, and a second, upper shell half 38 that defines the pressure side 40 of the blade 22. The lower and upper shell halves 34, 38 are coupled together along a leading edge 42 and a trailing edge 44 located opposite one another across a chord of the blade 22. 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 22 during use, noise attenuator 24 may be coupled to the blade 22. More particularly, to address the noise generated by blade tip vortices, noise attenuator 24 may be coupled to the blade 22 adjacent the tip end 32. By way of example, the noise attenuator 24 may be coupled to the blade 22 by adhesion or by using various connectors or fasteners, such as screws, rivets, etc. The noise attenuator 24 may be coupled to a cap (not shown) which is then fit about the blade and coupled to the blade tip. In an exemplary embodiment, the noise attenuator 24 may be a separate element of the blade assembly 20, i.e., the noise attenuator 24 is not integrally formed with the blade 22. In this way, the noise attenuator 24 may be coupled to the blade 22 after the blade is formed, such as through conventional processes generally known in the art. The noise attenuator 24 may be formed from various fiber materials including glass fiber, for example. In an exemplary embodiment, the noise attenuator 24 may be formed from the same material used to form the main body of the blade 22. In an alternative embodiment, the noise attenuator 24 may be formed of lightening arresting materials, such as copper, aluminum, bronze and stainless steel, for example, to improve the response of the blade assembly 20 to potential lightening strikes.

Forming the noise attenuator 24 as a separate element may have a number of benefits. For example, forming the noise attenuator 24 as a separate element may eliminate or reduce the modifications or changes to existing blade manufacturing equipment or processes in order to implement aspects of the invention. In this regard, the various molding apparatus, such as the blade shell molds, etc., generally do not need to be modified or recast to include the noise attenuator. Additionally, this arrangement allows the noise attenuator 24 to be retrofitted onto existing wind turbine blades, which may aid in situations where homes, communities, businesses, etc. have encroached on wind turbine locations after initial installation. While forming the noise attenuator 24 as a separate element of the blade assembly 20 is a preferred embodiment, it should be recognized that in an alternative embodiment, the noise attenuator 24 may be integrally formed with the blade 22, such as during the manufacturing process (e.g., molding process) of the wind turbine blade. Thus the invention is not limited to a separate or retrofit arrangement as described above. As illustrated in Fig. 3, in accordance with an exemplary embodiment, the noise attenuator 24 includes a generally V-shaped main body 50 having a central axis 52 extending between a front or leading end vertex 54 and a rear or trailing end vertex 56, a first fin portion 58 extending from one side of the central axis 52 and a second fin portion 60 extending from the other side of the central axis 52. As illustrated in the figure, when the noise attenuator 24 is coupled to the tip end 32 of the blade 22, the first fin portion 58 is configured to generally extend beyond the suction side 36 of the blade 22 and the second fin portion 60 is configured to generally extend beyond the pressure side 40 of the blade 22. In the orientation shown in Fig. 3, this means that the first fin portion 58 extends generally above the suction side 36 of the blade 22, and the second fin portion 60 extends generally below the pressure side 40 of the blade 22. Thus in accordance with an exemplary embodiment, the noise attenuator 24 has portions extending beyond both the suction and pressure sides 36, 40 of the blade 22. This is in contrast to existing wind turbine blade tip devices, such as a winglet (discussed below), which typically extend from only a single side of the blade for the purpose of enhancing aerodynamic performance. Focusing the design of a blade tip device on noise reduction (such as with noise attenuator 24) instead of aerodynamic performance, moves the resulting design and configuration away from the conventional winglet and more toward that shown in Fig. 3, for example. Additionally, in an exemplary embodiment, when the noise attenuator 24 is coupled to the tip end 32 of the blade 22, the central axis 52 may be generally aligned (e.g., generally parallel) with the chord of the blade 22 adjacent the blade tip end 32. In an alternative embodiment, however, the central axis 52 may be angled relative to the chord of the blade 22 adjacent the blade tip end 32. By way of example and without limitation, the central axis 52 may be angled between about 0 ° and about ± 30° relative to the chord of the blade 22.

In an exemplary embodiment, the first fin portion 58 may be oriented generally perpendicularly relative to the blade 22 (e.g., perpendicular to the plane of the blade chord) and may have a generally trapezoidal configuration. In an alternative embodiment, however, the first fin portion 58 may be angled relative to the blade 22 so as not to be generally perpendicular relative to the blade 22 (not shown). The first fin portion 58 may include a leading edge 68, a trailing edge 70, and a tip edge 72 extending therebetween and which may be generally parallel to the central axis 52. Notably, the first fin portion 58 does not terminate at a tip with a relatively sharp point, such as would be the case with a triangular configuration (not shown). Instead, that relatively sharp point is essentially truncated to provide a tip edge 72 with a well- defined length. For example, the tip edge 72 may be between about 10% and about 50% of the main blade tip chord c _t (Fig. 3). In one embodiment, for example, the tip edge 72 may be between about 20 mm and about 100 mm in length. In this regard, it is generally desirable to avoid sharp corners in the design of the first fin portion 58. The reason for this is that the inventors have discovered that a sharp corner configuration at the tip ends generally result in higher turbulent kinetic energy (and thus higher noise) as compared to a truncated configuration, such as that shown in Fig. 3.

In a similar manner, the second fin portion 60 may be oriented generally perpendicularly relative to the blade 22 (or alternatively in a non-perpendicular manner, not shown) and may likewise have a generally trapezoidal configuration. In this regard, the second fin portion 60 may include a leading edge 74, a trailing edge 76, and a tip edge 78 extending therebetween and which is generally parallel to the central axis 52. The second fin portion 60 does not terminate at a tip with a relatively sharp point, such as would be the case with a triangular configuration. Instead, that relatively sharp point is truncated to provide a tip edge 78 with a well-defined length. For example, the tip edge 78 may be between about 10% and about 50% of the main blade tip chord c _t . In one embodiment, for example, the tip edge 78 may be between about 20 mm and about 100 mm in length. While a truncated configuration is believed to effectively avoid the negative consequences of sharp corner configurations, it is believed that a benefit may also be achieved by terminating the first and second fin portions 58, 60 with a curved or smoothed corner, for example (shown in phantom in Fig. 3). In this regard, the smoothed corners should have a radius of curvature of between about 10% and about 80 % of the respective tip edges 72, 78.

As clearly illustrated in Fig. 3, the first and second fin portions 58, 60 meet along the central axis 52 between the leading and rear end verticies 54, 56. The verticies 54, 56 may define generally sharp corners or may define a smooth or curved intersection between fin portions 58, 60. In any event, the first and second fin portions 58, 60 are generally not symmetric about the central axis 52. First, the height l^ of the first fin portion 58, defined as the perpendicular distance from the central axis 52 to the tip edge 72, is generally less than the height h ₂ of the second fin portion 60, defined as the perpendicular distance from the central axis 52 to the tip edge 78. One reason for this is that the suction side 36 of the blade 22 generally extends in the direction of the tower 12 during operation, and it is desirable to maintain a certain degree of clearance between the tower 12 and the blade 22 so as to avoid accidental or unintentional interference therebetween. Accordingly, any extension from the blade 22 in the direction of the tower 12 should be minimized. In any event, the height of the first and second fin portions 58, 60 may vary depending on the chord length at the blade tip end 32. For example, the height of the fin portions 58, 60 may increase with increasing values of the chord at the blade tip end 32. In an exemplary embodiment, the height hi of the first fin portion 58 may be between about 20% and about 100% of the main blade tip chord c _t , and the height h ₂ of the second fin portion 60 may be between about 20% and about 200% of the main blade tip chord c _t . In one embodiment, for example, the height l^ of the first fin portion 58 may be between about 50 mm and about 250 mm, and the height h ₂ of the second fin portion 60 may be between about 50 mm and about 500 mm. Accordingly, a height ratio r _h , defined to be the height h ₂ of the second fin portion 60 divided by the height h of the first fin portion 58, may be generally expressed as 1 .0≤ r _h ≤ 2.0. Other values may also be possible depending on the specific application.

In addition to the above, the swept distance of the first and second fin portions 58, 60 may also differ. In this regard, the swept distance d _Sj2 of the second fin portion 60, defined to be the distance, in a direction parallel to the central axis 52, from the leading end vertex 54 to the intersection between the leading edge 74 and the tip edge 78 of the second fin portion 60, may be greater than the swept distance d _s ,i of the first fin portion 58, defined to be the distance, in a direction parallel to the central axis 52, from the leading end vertex 54 to the intersection between the leading edge 68 and the tip edge 72 of the first fin portion 58. By way of example and without limitation, in an exemplary embodiment, the first fin portion 58 may have a swept distance d _s ,i between about 50% and about 150% of the main blade tip chord c _t . In one embodiment, for example, the swept distance d _s ,i may be between about 50 mm and about 100 mm. Additionally, the swept distance d _{Si 2} of the second fin portion 60 may be between about 1 to about 3 times greater than the first swept distance d _Sj1 . Accordingly, a swept distance ratio r _d , defined to be the swept distance d _{Si 2} of the second fin portion 60 divided by the swept distance d _Si of the first fin portion 58, may be expressed as 1 .0≤ r _d ≤ 3.0. Other values may also be possible depending on the specific application.

As best illustrated in Fig. 3, in an exemplary embodiment, the swept distance d _Sj1 of the first fin portion 58 is less than the length of the central axis 52, such that the location of the trailing end vertex 56 is longitudinally downstream of the intersection of the leading edge 68 and tip edge 72 (i.e., the intersection of the leading edge 68 and tip edge 72 is longitudinally between the leading and trailing end vertices 54, 56). However, the tip edge 72 may have a length such that the intersection of the trailing edge 70 and the tip edge 72 is longitudinally downstream of the trailing end vertex 56. Moreover, the swept distance d _Sj2 of the second fin portion 60 may be greater than the length of the central axis 52, such that the location of the intersection of the leading edge 74 and the tip edge 78 is longitudinally downstream of the trailing end vertex 56.

Furthermore, in another aspect of the noise attenuator 24, the attenuator vertex angle β, defined to be the angle formed between the two trailing edges 70, 76 of the fin portions 58, 60, may be configured to be greater than about 90 ^° . More particularly, in an exemplary embodiment, the attenuator vertex angle β may be between about 90 ^° and about 180 ^° . Even more particularly, the attenuator vertex angle β may be between about 90 ^° and about 150 ^° . In one embodiment, the first fin portion trailing edge vertex angle defined to be the angle the trailing edge 70 of the first fin portion 58 makes with the central axis 52, may be the same as the second fin portion trailing edge vertex angle oc ₂ , defined to be the angle the trailing edge 76 of the first fin portion 58 makes with the central axis 52. In another embodiment, however, the first fin portion trailing edge vertex angle oci may be generally greater than the second fin portion trailing edge vertex angle oc ₂ . For example, in one embodiment, the first and second trailing edge vertex angles a may be between about 45 ^° and about 90 ^° .

Each of the first and second fin portions 58, 60 may be configured to have an airfoil cross-sectional profile. In this regard, the first fin portion 58 includes a first surface 80 and a second surface 82 each extending between the leading and trailing edges 68, 70 thereof. Similarly, the second fin portion 60 includes a first surface 84 and a second surface 86 each extending between the leading and trailing edges 74, 76 thereof. In one embodiment, the first and second fin portions 58, 60 may have a symmetric airfoil configuration, such that surfaces 80, 82 are substantially identical to each other and surfaces 84, 86 are substantially identical to each other. In this regard, it is believed that in a symmetric airfoil, the pressure gradient from the pressure side to the suction side of the of the fin's airfoil is minimized, resulting in a lower boundary layer thickness and a reduced effect on noise. Furthermore, the airfoil thickness of the first and second fin portions 58, 60 may be between about 10% and about 18% of the fin portion chord in various embodiments. Alternatively, the first and second fin portions 58, 60 may have airfoil profiles configured as advanced low-noise airfoils, such airfoils being generally known in the art and thus will not be described further herein. Additionally, the noise reduction capability of noise attenuator 24 may be improved with certain airfoil characteristics in at least the tip region of the blade 22. For example, the noise reduction may be enhanced by using a symmetric airfoil or an advanced low-noise airfoil at least in the tip region of the blade 22. In this regard, in one embodiment about the last 10% of longitudinal length of the blade 22 may have a symmetric airfoil configuration or an advanced low-noise airfoil configuration. As noted above, the noise attenuator 24 may be a separate element which is coupled to the blade 22. In this regard, in an exemplary embodiment, the noise attenuator 24 may be coupled to the tip end 32 of the blade 22 such that the leading end vertex 54 of the noise attenuator 24 is located between about 10% and about 50% of the main blade tip chord c _t . For example, the leading end vertex 54 may be located at the point of maximum thickness of the blade 22 adjacent the tip end 32. Additionally, the trailing end vertex 56 of the noise attenuator 24 may be longitudinally downstream of the trailing edge 44 of the blade 22. By way of example and without limitation, the trailing end vertex 56 may be located between about 10% and about 100% of the main blade tip chord c, downstream of the trailing edge 44 of the blade adjacent the tip end 32. In one embodiment, for example, the trailing end vertex 56 may be located between about 100 mm and about 500 mm downstream of the trailing edge 44 of the blade adjacent the tip end 32.

The noise attenuator 24 as described above is configured to reduce the noise emission emanating from the wind turbine 10. More particularly, the noise attenuator 24 is configured to reduce the noise caused by the flow vortices occurring at the tip end 32 of the blade 22, which is believed to be a significant contributor to the overall noise generated by the wind turbine 10. The inventors believe that the noise attenuator 24 impacts the flow over the blade 22 in such a manner as to reduce the blade tip vortex noise. Moreover, the inventors believe the noise attenuator 24 may achieve a reduction in the blade tip vortex noise without negatively impacting the performance of the blade 22. By way of example and without limitation, the inventors believe that effective noise reduction may be achieved by noise attenuator 24 as described above in a manner such that the power from the blade is not significantly reduced, as compared to the same blade without the noise attenuator.

Without being limited to any particular theory, the inventors believe that the noise attenuator 24 does not significantly affect or influence the span-wise flow over the blade and around the tip end 32 from the pressure side to the suction side. Thus, the noise attenuator 24 is considered not to have a significant effect on the power of the blade 22. However, the inventors further believe that the presence of the noise attenuator 24 reduces the turbulent kinetic energy and the vortex strength on the main blade 22 adjacent the tip end 32 and reduces the turbulent kinetic energy and vortex strength of the flow over the attenuator 24. The reduction in the turbulent kinetic energy and the vortex strength is believed to reduce the noise generated at the blade tip end 32. In this regard, it is believed that the noise attenuator 24 diffuses the tip vortices away from the blade tip surfaces and reduces the interaction of the tip vortices with the blade surfaces, thereby providing a reduction in noise.

The inventors note that there may be a number of existing devices which may be located at the tip of an aerodynamic airfoil for one purpose or another. Probably the most well-known device located at the tip of an airfoil is a winglet. Winglets are most often utilized in the field of fixed wing aircraft (e.g., airplane) for improving the aerodynamic performance of the blade. More recently, however, there have been some instances of wind turbine blades incorporating winglets for the purpose of improving aerodynamic performance of the blade (e.g., increase lift). In these wind turbine blade applications, the winglets typically extend from only one side of the blade (e.g., in a direction opposite the tower), and not from both the pressure and suction sides of the blade, as does noise attenuator 24. In any event, one clear difference between a winglet and the noise attenuator described herein is in the function. Winglets are designed to improve the aerodynamic performance of the blade while the noise attenuator is designed to reduce the blade tip vortex noise. These are significantly different functions which may result in other distinctions.

In this regard and by way of example, as compared to a conventional winglet, the noise attenuator 24 may be significantly reduced in size. For example, conventional winglets may extend beyond the surface of the blade for a height of about 1 .5 -2 meters. As noted above, the noise attenuator 24 may be configured to have a height of about 0.5 m, a height three to four times less than the conventional winglet. This reduction in height may be significant, especially when it is known to be cautious about blade extensions in the direction of the tower.

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.