US20080166241A1

US20080166241A1 - Wind turbine blade brush

Info

Publication number: US20080166241A1
Application number: US11/619,638
Authority: US
Inventors: Stefan Herr; Klaus Koegler; Werner Dobrzynski
Original assignee: GE Wind Energy GmbH; General Electric Co
Current assignee: GE Wind Energy GmbH; General Electric Co
Priority date: 2007-01-04
Filing date: 2007-01-04
Publication date: 2008-07-10
Also published as: DK200701852A

Abstract

A wind turbine blade for use in a wind energy system comprises a blade body having a trailing edge and a leading edge, and a plurality of bristles disposed on an outer surface of said blade body. The bristles are typically attached to said blade body in the vicinity of said trailing edge and serve to reduce noise caused by the airflow around the blade during operation.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a wind turbine blade with bristles or a brush disposed on an outer surface thereof. The present invention further relates to a wind energy system including the same.
Wind energy systems have gained more and more importance as a source of energy in recent years. As areas suitable for their economical operation are relatively scarce in a number of countries, a growing number of wind energy systems are located close to populated areas. As the running of wind turbines in wind energy systems causes noise, this leads to various problems, such as resistance from neighbourhoods and the like. Though a variety of sources contribute to the overall noise emission of such systems, air flow around the blades is known to be one of the main sources. This causes, for example, typical “hissing” or “swishing” sounds in the 1 kHz frequency range. Sound levels are greatly influenced by the design of the turbine blades, especially the choice of the airfoil profile. As this choice is also influenced by other criteria such as high efficiency operation, the goal of low noise operation is often contradicted by aspects regarded to be more important by the designer. Moreover, even a design optimized for low noise operation still causes emissions, which may be intolerable under certain conditions. Thus, what is needed are measures to reduce the noise emission of a given wind turbine blade.
It is known from the field of airplane technology to apply physical measures to an aircraft wing in order to reduce noise caused by the airflow. For example, zig-zag shaped bands have been attached to the airfoil in the vicinity of the leading edge. Another technique is proposed for commercial airliners. So-called slats, which are the equivalent of a landing flap, but located on the front side of the wing, are known to be a major source of noise during take-off and landing. Research has shown that this might be due to the gap between the main body of the wing and the slat together with the concave shape of the lower portion of the slat. In order to reduce noise caused by the turbulences between the slat and the wing, it was proposed to locate bristles on the lower part of the slat.

BRIEF DESCRIPTION OF THE INVENTION

In view of the above, a wind turbine blade for use in a wind energy system is provided, which includes a blade body having a trailing edge and a leading edge, and a plurality of bristles disposed on an outer surface of the blade body.
In a first aspect of the present invention, there is provided a rotor blade for use in a wind energy system. It includes a plurality of fibres, which are located on the shell of the rotor blade that includes a leading edge and a trailing edge.
Conventional methods to reduce noise produced by the rotor blade of a wind turbine include mainly the modification of the airfoil's profile during design. In the present invention, it is proposed to dispose a number of bristles or fibres on part of a wind turbine blade in order to reduce noise emissions. The present invention bears significant advantages over the known art. First of all, the invention can be applied to an arbitrary airfoil, not depending on the aerodynamic design thereof. Hence, an airfoil for use with the present invention can be designed with the goal of best performance in terms of efficiency and the like, while still achieving improved noise emissions behaviour of the system. The measures used are made from commercially available goods, typically man made fibres, and are both easy to produce and relatively cheap. Furthermore, the invention can both be applied during the production process of a blade or to an existing wind energy system with relatively little effort and costs. The bristles can be applied to the blade by a variety of methods such as gluing, fusing, heat-sealing etc. or by mechanical insertion into small pinholes provided on the blade body or an intermediate carrier element. Rotor blades according to the present invention may be used in wind turbines with one, two, three or more rotor blades.
In an embodiment of the invention, the bristles are attached to the blade body in the vicinity of the trailing edge. In another embodiment, at least one of the parameters chosen from the group consisting of length, diameter and flexibility of the bristles varies depending on the distance of said bristle from the blade root.
According to a further aspect of the present invention, a wind turbine blade for use in a wind energy system includes a blade body having a trailing edge and a leading edge, a brush including a plurality of bristles, wherein said brush is disposed on said blade body in the vicinity of the trailing edge.
In a third aspect of the present invention, a wind turbine for use in a wind energy system includes a blade body having a trailing edge, a leading edge and a plurality of bristles disposed on an outer surface of said blade body.
Further aspects, advantages and features of the present invention are apparent from the dependent claims, the description and the accompanying drawings.
It is possible to use the wind turbine blade of the present invention in any wind energy system.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures wherein:

FIG. 1 is a schematic view of a type of a wind turbine with three rotor blades.

FIG. 2 is a front view of a wind turbine rotor blade according to a conventional prior art design.

FIG. 3 is a front view of a wind turbine rotor blade according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a wind turbine rotor blade according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view of a wind turbine blade according to an embodiment of the present invention.

FIG. 6 is a front view of a wind turbine blade according to another embodiment of the present invention.

FIG. 7 is a front view of a wind turbine blade according to an embodiment of the present invention.

FIG. 8 shows an elevational view of a brush according to an embodiment of the present invention.

FIG. 9 shows a front view of a brush according to an embodiment of the present invention.

FIG. 10 shows a wind turbine blade according to a further embodiment of the present invention.

FIG. 11 shows a wind turbine blade according to an embodiment of the present invention.

FIG. 12 shows a wind turbine blade according to another embodiment of the present invention.

FIG. 13 shows a wind turbine according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the various embodiments of the invention, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation of the invention, and is not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present invention includes such modifications and variations.
FIG. 1 is a schematic view of a typical wind turbine. The wind turbine 100 includes a tower 110 to which a machine nacelle 120 is mounted at its top end. The nacelle houses a drive train to which a main electric generator is connected (not shown). A hub 130 bearing three rotor blades 140 is mounted to a lateral end of the machine nacelle 120. The rotor blades 140 can be adjusted by pitch drives which are typically accommodated inside hub 130.
The basic configuration of a wind turbine blade or rotor blade 140 is shown in FIG. 2. Therein, the wind turbine blade 140 includes a root section 150 which serves for mounting blade 140 to hub 130. Opposite to the blade root 150, the tip end 160 of the wind turbine blade 140 is disposed. A blade body 170 of the blade 140 extends between the blade root 150 and the blade tip 160. The wind turbine blade includes a leading edge 180 and a trailing edge 190. The rotor blade has a total length RL and a chord length CL, which typically varies along the length of the rotor blades 140.
FIG. 3 shows an embodiment of the invention. A wind turbine blade 140 is equipped with a plurality of bristles 300 disposed on an outer surface of the blade body 170. In order to reduce noise which is caused by various effects related to the trailing edge 190 of the blade, the bristles are attached to the blade body in the vicinity of the trailing edge 190. Typically, one end of the bristles 300 is attached to the trailing edge 190, protruding away from the blade body 170 in a rear direction of the blade 140. Typically, the bristles 300 are arranged in at least one row along a longitudinal direction of the blade. The bristles may be disposed in groups along the blade, so as to form areas with bristles and areas without. The bristles can be applied to the blade body by a variety of methods such as gluing, fusing, heat-sealing, etc. or by mechanical insertion into small pinholes provided on the blade body or an intermediate carrier element. In particular, rotor blades of existing wind turbines may be retrofitted with bristles in order to reduce noise emission.
A plurality of rows of bristles may be used in order to achieve a higher noise reduction effect. These rows, as defined by mounting points of the bristles in a longitudinal direction of the blade 140, are located close to each other and disposed in the vicinity of the trailing edge 190. FIG. 4 shows an embodiment with five rows disposed above each other at the trailing edge 190 of the blade body 170. However, the present invention is not limited to bristles disposed in rows. Any arrangements of bristles on a wind turbine blade is regarded to fall into the scope of the present invention, including randomly disposed bristles in various areas of the blade body, typically, but not limited to, the area of the trailing edge.
The length of the bristles 300 lies between 5 mm and 100 mm, typically between 15 mm and 80 mm, more typically between 25 mm and 70 mm, e.g., 30 mm or 50 mm. The diameter varies between 0.1 mm and 4 mm, typically between 0.2 mm and 0.8 mm, more typically between 0.3 mm and 0.6 mm, e.g. 0.3 mm or 0.5 mm. The material of the bristles 300 can be chosen from a variety of materials used for man made fibers, typically polymers like polyolefins, cyclic polyolefins, silicones, acrylic polymers, polyester, polyamides, aromatic polyamides and the like, also metal or quartz are applicable. More typically, the material is polypropylene, polyethylene, polyamide or polyvinyl chloride. Also natural or cellulose-based fibers, for example hemp jute, flax, ramie or sisal are applicable and are regarded to fall into the scope of the invention. The fibers should provide flexibility, fatigue resistance and long term stability when exposed to the ultraviolet component of the sunlight.
FIG. 5 shows a further embodiment of the present invention, according to which a carrier element 500 is located between the blade body 170 and the bristles 300. This carrier element may be, but is not limited to, a lengthy profile of aluminum, steel, plastic or the like. Typically, the thickness of the profile is approximately equal or smaller than the thickness of the trailing edge 190. There may also be a plurality of such elements disposed in a continuous row or intermittently. Such a carrier element has the advantage of facilitating easier mounting, maintenance, etc. For example, for testing or optimization purposes, elements with different bristle configurations may be quickly interchanged. The carrier element may be attached to the blade body by mechanical means such as screws or quick-lock systems etc., by chemical means like gluing or by heat-sealing and the like. The bristles are typically, but not necessarily, mechanically attached to the element. The carrier element with bristles can either be applied during the production process of a blade or in the process of retrofitting an existing wind energy system.
FIG. 6 shows a wind turbine blade 140 according to another embodiment of the present invention. Due to the nature of a rotating airfoil as used in a wind turbine, the speed of the airflow around the airfoil increases with growing distance from the hub 130 of the rotor. Thus, the airspeed is relatively low at the innermost part of a blade and can reach speeds in the magnitude of several 100 meters per second at the tip of the blade. The differences in airspeed lead to variations in the amplitude, spectral composition etc. of the noise generated at different parts of the blade. Accordingly, the noise-reducing measures of the present invention are advantageously applied in different variations along the blade. Main parameters influencing the noise reduction properties of the bristles include the length, diameter and flexibility. In this embodiment, either one or more of these parameters of the bristles are varied depending on the distance of the respective bristles 300, 310, 320 from the blade root 150. The dependency of a chosen parameter from that distance may be determined by a mathematical relation, for example by a linear or polynomial dependency. Typically, an optimum configuration in terms of noise emission is determined by means of testing of the individual wind turbine blade in combination with bristles of different parameters at various distances from the blade root 150. As an example, a long bristle 300 in the vicinity of the rotor blade tip has a length between 50 mm and 100 mm, e.g. 70 mm. A medium-sized bristle 310 in the middle part of the blade body has a length between 30 and 70 mm, e.g. 40 mm. A short bristle 320 in the vicinity of the blade root has a length between 10 nm and 40 mm, e.g. 25 mm. The exact values depend on the choice of the designer depending on test results with the given rotor blade. If a variation in flexibility is desired, this can for example be achieved by means of a variation of the fiber diameter or by a variation of the material or fiber type. Regarding the nature of the airflow around the wind turbine blade, it is obvious that the chord length of the blade will influence the behaviour of the air stream in the vicinity of the trailing edge. Hence, the parameters of the bristles can also be determined by taking into account the actual chord length at their position on the blade.
FIG. 7 shows another embodiment of the present invention, according to which bristles 300, 330, 340, 350 of different lengths and/or diameter and/or flexibility are disposed on the blade body 170 intermittently or in groups. The noise reduction characteristic of bristles varies, for example, with varying length. Experimental data hints to the fact that for reducing trailing edge related noise, shorter bristles achieve better reduction results for lower frequencies, whereas longer bristles tend to be more effective for higher frequencies. Thus, a combination of bristles with significantly different outer dimensions in the same region of the blade contributes to a reduction characteristic with a higher efficiency in a broad frequency spectrum. As an example, bristles 300 and 350 are both from 30 mm to 50 mm long, e.g., 40 mm, and have a diameter of 0.5 mm and 0.3 mm, respectively, bristles 330 and 340 are both 60 mm to 90 mm long, e.g. 70 mm, and have a diameter of 0.5 mm and 0.3 mm, respectively.
FIG. 8 shows an elevational view of a brush 600 according to an embodiment of the present invention. The brush includes a brush body 610 and a plurality of bristles 300 which are disposed on one surface of the latter. In FIG. 9, a front view of the brush 600 is shown.
FIG. 10 shows another embodiment of the present invention, according to which the wind turbine blade 140 is provided with a lengthy brush 600 protruding longitudinally along a percentage between 1 and 100% of the total blade length, typically between 1 and 70%, more typically between 1 and 20%. Typically, one end of the brush is located at a point in the vicinity of the tip 160 of the blade. The brush 600 includes a brush body 610 and a plurality of flexible fibers or bristles 300. The length of the bristles 300 lies between 5 mm and 100 mm, typically between 15 mm and 80 mm, more typically between 25 mm and 70 mm, e.g. 30 mm or 50 mm. The diameter varies between 0.1 mm and 4 mm, typically between 0.2 mm and 0.8 mm, more typically between 0.3 mm and 0.6 mm, e.g. 0.3 mm or 0.5 mm. The material of the bristles 300 can be chosen from a variety of materials used for man made fibers, typically polymers like polyolefins, cyclic polyolefins, silicones, acrylic polymers, polyester, polyamides, aromatic polyamides and the like, also metal or quartz are applicable. More typically, the material is polypropylene, polyethylene, polyamide or polyvinyl chloride. Also natural or cellulose-based fibers, for example hemp jute, flax, ramie or sisal are applicable and are regarded to fall into the scope of the invention. The fibers should provide flexibility, fatigue resistance and long term stability when exposed to the ultraviolet component of the sunlight. The brush may be attached to the blade body by mechanical means such as screws or quick-lock systems etc., by chemical means like gluing or by heat-sealing and the like. The bristles are typically, but not necessarily, mechanically attached to the brush body. Rotor blades of existing wind turbines may be economically and quickly retrofitted with one or more brushes in order to reduce noise emission, or the brushes may be attached during the production process of the blade.
In an embodiment of the present invention, the brush 600 is located in the vicinity of the trailing edge 190.
In a further embodiment of the present invention, the brush 600 includes bristles 300 of different lengths and/or of different diameters and/or different flexibility, which are intermittently or randomly disposed about the brush.
In still another embodiment of the present invention, at least one of the parameters of said bristles 300, chosen from the group consisting of length, diameter and flexibility, is dependent from a chord length of the blade 140, as measured at the position of the respective bristle.
FIG. 11 shows a further embodiment of the present invention, according to which the rotor blade is equipped with at least two brushes, which may differ in length, diameter and length of the bristles etc. In this embodiment, the length of a single brush varies between 0.3 m and 20 m, typically 1 m to 5 m, e.g. 2 m. Discrete brushes provide greater flexibility in a variety of aspects like handling, support and commercial availability of pre-fabricated brushes.
FIG. 12 shows another embodiment of the present invention, according to which a fraction of between 5% to 30% of the rotor blade length, e.g. 15%, is equipped with one brush or a plurality of discrete brushes. The one ore more brushes are typically, but not necessarily located in the tip region of the blade.
FIG. 13 shows an embodiment of the present invention, according to which a wind turbine 140 for use in a wind energy system comprises a rotor blade with a blade body having a trailing edge and a leading edge, and a plurality of bristles 300 disposed on an outer surface of said blade body.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. Especially, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims of they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

1. A rotor blade for use in a wind energy system, comprising:

a blade body having a trailing edge and a leading edge, and

a plurality of bristles disposed on an outer surface of said blade body.

2. The rotor blade of claim 1, wherein said bristles are attached to said blade body in the vicinity of said trailing edge.

3. The rotor blade of claim 1, wherein said bristles are arranged in at least one row along a longitudinal direction of said blade.

4. The rotor blade according to claim 3, wherein said at least one row of bristles has a length between 5 and 100% of the total rotor blade length.

5. The rotor blade of claim 1, further comprising a carrier element, wherein said carrier element is attached to said blade body, and said bristles are attached to said carrier element.

6. The rotor blade according to claim 1, wherein the length of said bristles lies in a range between 10 mm and 100 mm.

7. The rotor blade according to claim 1, wherein said bristles are flexible.

8. The rotor blade according to claim 1, wherein the diameter of said bristles lies in a range between 0.1 mm and 4 mm.

9. The rotor blade according to claim 1, wherein the blade comprises bristles of different lengths and/or of different diameters.

10. The rotor blade according to claim 1, wherein at least one of the parameters chosen from the group consisting of length, diameter and flexibility of the bristles varies depending on the distance of said bristle from the blade root.

11. A rotor blade for use in a wind energy system, comprising:

a shell having a trailing edge and a leading edge,

a brush comprising a plurality of bristles,

wherein said brush is disposed on said shell in the vicinity of said trailing edge.

12. The rotor blade according to claim 11, wherein said brush has a length between 1 and 100% of the total rotor blade length.

13. The rotor blade according to claim 11, wherein the length of said bristles lies in a range between 10 mm and 100 mm.

14. The rotor blade according to claim 11, wherein said bristles are flexible.

15. The rotor blade according to claim 11, wherein the material of the bristles is chosen from the group consisting of synthetic polymer, silicone, metal, quartz or natural fiber.

16. The rotor blade according to claim 11, wherein the diameter of said bristles lies in a range between 0.1 mm and 4 mm.

17. The rotor blade according to claim 11, wherein a blade comprises bristles of different lengths and/or of different diameters.

18. The rotor blade according to claim 11, wherein at least one of the parameters of said bristles, chosen from the group consisting of length, diameter and flexibility, varies in accordance with a chord length of said blade.

19. The rotor blade according to claim 11, wherein a plurality of discrete brushes are disposed about the rotor blade.

20. A wind turbine for use in a wind energy system, comprising:

a rotor blade comprising a blade body having a trailing edge and a leading edge, and

a plurality of bristles disposed on an outer surface of said blade body.