Wind turbine

Abstract

A horizontal axis wind turbine comprising a rotor having a plurality of blades, the rotor having a radius of at least 80 metres, the blades comprising: a root end and a tip end; a leading edge and a trailing edge; a shoulder between the root end and the tip end, at which shoulder a chord length defined between the leading edge and the trailing edge is at a maximum; wherein: Sol r is at least 0.0140 at 0.7R;Sol r is at least 0.0116 at 0.8R;Sol r is at least 0.0090 at 0.9R;Sol r is a combined radius specific solidity of the blades.

Description

Technical Field

[0001] This invention relates to a horizontal axis wind turbine comprising a rotor having multiple blades. In particular, this invention relates to the specific geometry of the blades for reducing aerodynamic noise generated by the rotor. Background Technology

[0002] Wind turbines are used to convert the kinetic energy from wind into electrical energy. In recent years, wind power has become a more attractive alternative energy source, and the number of wind turbines, wind farms, and the like has increased significantly both on land and at sea. Traditionally, wind turbines have been located in relatively remote areas where noise from them was not a significant problem. However, with the increase in the number of wind turbines, the noise they generate has become a greater concern. In this regard, wind turbines are now being located closer to commercial and residential areas where various laws and regulations may impose noise level restrictions.

[0003] Wind turbines have two main noise sources: mechanical noise and aerodynamic noise. Mechanical noise can originate from various turbine components, such as the gearbox, generator, pitch and yaw control, hydraulic systems, etc. Aerodynamic noise, on the other hand, is likely caused by the interaction between the blades and the air flowing over them. While mechanical noise is likely a significant contributor to overall wind turbine noise, several techniques exist for reducing it, including the use of vibration dampers and sound-absorbing materials. In contrast, aerodynamic noise is often more difficult to mitigate and is considered the primary source of wind turbine noise. As wind turbine size continues to increase, blade tip speeds also increase. With increased tip speeds, aerodynamic noise also increases.

[0004] Aerodynamic noise can have several sources, including trailing edge noise and blade tip vortex noise. Trailing edge noise (which can include blunt trailing edge vortex noise and turbulent boundary layer trailing edge noise) has received some attention from power producers and manufacturers. For example, various trailing edge designs, such as serrated or sawtooth designs, have been used to reduce trailing edge noise. While such solutions for trailing edge noise are known in the art, serrated or sawtooth designs can only mitigate noise to a certain extent, and they may affect the aerodynamic performance of the blade.

[0005] Therefore, the object of the present invention is to provide a wind turbine rotor with reduced aerodynamic noise. Summary of the Invention

[0006] According to the present invention, a horizontal axis wind turbine is provided, the horizontal axis wind turbine comprising a rotor having a plurality of blades having a radius of at least 80 meters, the blades comprising:

[0007] Root tip and shoot tip;

[0008] Leading edge and trailing edge;

[0009] The chord length defined at the shoulder between the root end and the tip end, between the leading edge and the trailing edge, is the greatest.

[0010] in:

[0011] ·Sol r At least 0.0140 at 0.7R;

[0012] ·Sol r At least 0.0116 at 0.8R;

[0013] ·Sol r At least 0.0090 at 0.9R;

[0014] Sol r It is the combined radius specific solidity of the blade and is defined by the following formula:

[0015]

[0016] Where n = number of leaves, C r = chord length at a specific radius, and R = rotor radius.

[0017] The solidity of a wind turbine blade is the area of ​​the wind turbine blade projected onto the rotor plane (A). blade ) and the total area covered by the rotating blades (πR) 2 The ratio between ) . Therefore, the combined fullness, that is, the sum of the fullness of the leaves, is:

[0018]

[0019] Where n is the number of wind turbine blades (e.g., 3), and R is the rotor radius. Therefore, solidity is a measure of the slenderness of the blades, because the lower the solidity, the slenderer the blades.

[0020] A realism can also be established for a specific radius r from the rotor center. The radius-to-realism of the wind turbine rotor (i.e., the combined radius-to-realism of the blades) is given by the following formula (where C... r (This refers to the chord at a specific radius):

[0021]

[0022] It is known that in the design of wind turbine blades, reducing the solidity of the blades reduces the load on the wind turbine. This is because reduced solidity results in a smaller chord, thus reducing fatigue and extreme loads on the wind turbine blades. (This is described, for example, in WO2006 / 090215.) However, the present invention is not intended for longer blades, but rather for higher solidity values ​​in the outer half of the blade.

[0023] The power generated by a wind turbine is proportional to the rotor's rotational speed. As blade length increases, the tip speed of the blades also increases for a given rotational speed. However, the increased tip speed leads to higher aerodynamic noise. Furthermore, the higher tip speed results in increased erosion at the leading edge of the wind turbine blades. By providing a wind turbine rotor with the combined radius-to-solidity described above, the tip speed can be reduced without correspondingly reducing the lift generated by the blades. Moreover, aerodynamic noise is reduced due to the lower tip speed. Typically, for a conventional rotor, if the tip speed is reduced by decreasing the rotational speed, the power generated by the wind turbine will decrease accordingly because there will be lower lift generated by the blades.

[0024] With the aforementioned solidity values, this blade has a larger chord in at least the outer 30% of its span compared to conventional blades. Due to the relatively larger chord, the blade will generate more lift in this outer 30%. Therefore, the tip speed can be reduced. Furthermore, due to the increased chord in the outer 30% of the blade, the blade can operate at a reduced angle of attack while still generating sufficient lift. The reduced angle of attack during blade segment operation also means reduced aerodynamic noise, because the boundary layer on the blade will be thinner.

[0025] For long rotor blades, especially those exceeding 80 meters in length, aerodynamic noise becomes a limiting factor in the design. The defined blade geometry advantageously allows for reduction of aerodynamic noise while still providing sufficient aerodynamic performance.

[0026] Preferably, Sol is at least 0.0164 at 0.6R. Preferably, Sol... r At least 0.0199 for 0.5R. By providing an increased solidity value further inside, noise generated by the blades can be further reduced while still maintaining aerodynamic performance.

[0027] In a preferred embodiment, the blade has a combined radius to solidity, wherein:

[0028] ·Sol r At least 0.0146 at 0.7R;

[0029] ·Sol r At least 0.0123 at 0.8R;

[0030] ·Sol r It is at least 0.0099 at 0.9R.

[0031] These solidity values ​​are particularly advantageous for wind turbines with rotor radii exceeding 80 meters (e.g., exceeding 90 meters).

[0032] Sol r At 0.6R, it can be at least 0.0172; and Sol r At 0.5R, it can be at least 0.0200. For long wind turbine blades (where the rotor radius exceeds 80 meters), these solid values ​​allow for a reduction in rotor tip speed while still maintaining aerodynamic performance.

[0033] In a preferred embodiment, the blade has a combined radius to solidity, wherein:

[0034] ·Sol r Below 0.0164 at 0.7R;

[0035] ·Sol r Below 0.0133 at 0.8R;

[0036] ·Sol r It is below 0.0108 at 0.9R.

[0037] Although the addition of 30% chord in the outer section leads to a reduction in noise, the combined radius is preferably lower than these values ​​to prevent excessive fatigue and extreme loads on the rotor.

[0038] Preferably, the shoulder is located between 0.18R and 0.35R, and more preferably between 0.2R and 0.3R.

[0039] At the shoulder position, the combined radius of the blades is greater than the solid Sol. r It can be less than 0.027, and preferably less than 0.026.

[0040] Defined as The ratio can be greater than 0.5, preferably greater than 0.55, and even more preferably greater than 0.58; wherein the ratio is the ratio of the combined radius ratio of the blade at 0.7R to the combined radius ratio of the blade at the shoulder of the blade.

[0041] Compared to conventional blades, the increased rotor solidity in the outer 30% (and preferably the outer half) of the blade due to the increased chord length can lead to higher loads. In particular, the extreme loads experienced by the wind turbine may increase. However, having a relatively lower rotor solidity at the blade shoulder can mitigate these increased loads and help protect the wind turbine from damage.

[0042] It should be noted that the multiple blades are preferably substantially the same in terms of their external geometry, such that the shoulders on each blade will be in the same position and have the same chord length.

[0043] The expression "at the shoulder position" refers to determining the blade radius to solidity at the position of the blade's maximum chord. The blade shoulder does not have to be a sharp angle, so the expression "at the shoulder position" can be interpreted as at the shoulder position + / - 1%R.

[0044] Preferably, the design Reynolds number at the tip of the blade is at least 1.1 × 10⁻⁶. 6 More preferably, it is at least 1.2 × 10⁻⁶. 6 The design Reynolds number at the maximum chord position on the blade can be at least 9 × 10⁻⁶. 6 And preferably at least 10×10 6 .

[0045] As is well known in the art, the lift and drag coefficients of an airfoil or blade depend on the Reynolds number. The Reynolds number is defined as:

[0046]

[0047] Where w is the relative wind speed of the blade segment, ρ is the air density, and μ is the dynamic viscosity of the air. For a local blade segment, the Reynolds number will be determined based on the chord length C. r And change.

[0048] The dimensions of wind turbine blades can be described by length. However, they can also be described with reference to the Reynolds number, and longer blades result in higher Reynolds numbers. The solid values ​​of this invention are particularly suitable for wind turbine blades operating at the aforementioned Reynolds numbers. The Reynolds number provided herein is the "design Reynolds number" taken at the design point of the wind turbine. The design point is when the rotor operates at its optimal tip speed ratio, as understood by those skilled in the art. The values ​​for air density and aerodynamic viscosity are taken at sea level.

[0049] The leaf blade can extend from the root tip to the tip in the leaf spread direction, and extend along the chord from the leading edge to the trailing edge in the chord direction;

[0050] The leaf blade twists between its root tip and its tip, and the twist is defined by a twist distribution curve along the leaf span direction. Each leaf blade includes:

[0051] The inner region between the root tip of the leaf and the shoulder of the leaf;

[0052] The outer region between 0.9R and the tip of the leaf; and

[0053] A middle region, which is located between the inner region and the outer region;

[0054] The noise reduction feature in the middle region of the blade protrudes from the trailing edge and extends from the first radial position R1 toward the tip;

[0055] The torsional distribution curve includes a first inflection point near the first radial position.

[0056] Wind turbine blades are twisted along their span to account for the fact that the outer regions of the blades move faster than the inner regions during operation. This results in a twisted distribution along the blade's span length.

[0057] In the middle region of the blade, the torsion decreases towards the blade tip to maintain a relatively constant angle of attack along the blade, which is the angle between the blade chord and the relative wind direction. According to the invention, as the torsion "decreases," the leading edge of the blade rotates upward to increase the local angle of attack. At the inflection point on the torsion distribution curve, the second derivative of the torsion distribution is zero.

[0058] The location of the first inflection point corresponds to the start of the noise reduction feature at the radial position R1. In operation, the noise reduction feature at the trailing edge reduces the aerodynamic performance of the blade. Specifically, the noise reduction feature can reduce lift and / or increase drag generated by the blade at the radial position where the noise reduction feature is located. To compensate for this lift loss, the inflection point in the torsion profile provides a decrease in the torsion angle and an increase in the angle of attack. The increase in the angle of attack will compensate for the lift loss from the noise reduction feature.

[0059] Preferably, the noise reduction feature includes a serrated trailing edge. The serrated trailing edge includes a serrated shape for reducing trailing edge noise.

[0060] Preferably, the torsion decreases from the middle region of the blade towards the outer region. This reduction in torsion provides a suitable angle of attack along the blade length.

[0061] When the torsional distribution includes a first inflection point near a first radial position, the first inflection point can be less than 15% of the rotor radius from the first radial position, preferably less than 10% of the rotor radius, and more preferably less than 5% of the rotor radius. Preferably, the first inflection point is located in the root direction of the first radial position. This allows the blades to be positioned at the desired torsional angle at the start of the noise reduction feature.

[0062] Preferably, the torsional distribution curve includes a second inflection point located between the first inflection point and the tip.

[0063] The first radial position R1 can be located between 0.6R and 0.8R. In particular, the first radial position R1 can be located at approximately 0.7R. It is advantageous to use noise reduction features such as a serrated trailing edge only in the outer third of the blade, as this location is the primary source of aerodynamic noise. Attached Figure Description

[0064] To facilitate a clearer understanding of the invention, embodiments of the invention will now be described by way of example only and with reference to the following figures, wherein:

[0065] Figure 1 This is a view of a horizontal axis wind turbine.

[0066] Figure 2a It is a 3D diagram of a wind turbine blade. Figure 2b This is a cross-sectional view of a wind turbine blade.

[0067] Figure 3 A cross-section along the blade's span is shown.

[0068] Figure 4 The chord distribution of the blades is shown.

[0069] Figure 5 and Figure 6 The radius ratio of the two blades is shown.

[0070] Figure 7 and Figure 8 The torsional distribution of the blades is shown. Detailed Implementation

[0071] Figure 1 A horizontal axis wind turbine 10 is shown. The wind turbine 10 includes a tower 12 supporting a nacelle 14, to which a rotor 16 is mounted. The rotor 16 includes a plurality of wind turbine blades 18 extending radially from a central hub 19. In this embodiment, the rotor 16 includes three blades 18.

[0072] Figure 2a This is a view of one of the blades 18 of a wind turbine 10. The blade 18 extends from a generally circular root tip 20 to a tip tip 22 in the longitudinal span direction and extends in the transverse chord direction between a leading edge 24 and a trailing edge 26. The blade 18 comprises a shell formed primarily of fiber-reinforced plastic (FRP). The blade 18 includes a suction surface 28 and a pressure surface 29. The radius of the rotor 16 is such that the tip tip of the blade is located at position r = R, and the axis of rotation is located at r = 0.

[0073] The blade 18 transitions from a circular profile to an airfoil, which moves from the root tip 20 of the blade 18 toward the shoulder 25 of the blade 18, where the blade 18 has its widest chord. The blade 18 has an airfoil with a thickness that gradually decreases from the shoulder toward the tip of the blade.

[0074] The wind turbine blade 18 includes an inner region between the root tip and the shoulder 25 of the blade; a tip region between the rotor radius 0.9R and the tip tip of the blade; and an intermediate region between the inner region and the tip region.

[0075] Figure 2b This is a diagram of the airfoil of a wind turbine blade in the middle blade region. The chord connects the leading edge 24 and the trailing edge 26.

[0076] Figure 2a The blade is shown to include a noise reduction feature 27, which in this embodiment is a serrated trailing edge. The serrations are used to reduce noise caused by the blade 18 in use. In one embodiment, these serrations are provided as an add-on that is adhesively bonded to the blade at the trailing edge and may be formed from, for example, injection-molded plastic. The triangular shape (e.g., serrated) of the serrations is understood to reduce aerodynamic trailing edge noise by interacting with a turbulent boundary layer flowing on the blade surface. In another embodiment, the noise reduction feature may include bristles and / or a comb extending from the trailing edge.

[0077] The noise reduction feature may cover only a given length of the blade span, specifically towards the tip where trailing edge noise is most dominant. The noise reduction feature originates at a radial position R1 and extends towards the tip of the blade. In one embodiment, the radial position R1 may be 0.7R. In particular, the noise reduction feature has a proximal end located in the middle region of the blade (closest to the root tip 20 of the blade).

[0078] refer to Figure 2a A blade coordinate system can be defined. The origin of the coordinate system is aligned with the rotor's rotation axis at r = 0. The X-axis extends parallel to the rotor axis. The Z-axis extends along the blade's pitch axis. Figure 2a In this embodiment, the pitch axis is aligned with the blade's span direction. The Y-axis is perpendicular to the X-axis and Z-axis.

[0079] As is known in the art, wind turbine rotor blades can rotate about a pitch axis to adjust the power output of the wind turbine and the loads experienced by the wind turbine components. In wind turbines without tapered or pre-bent blades, the blade spanwise axis is aligned with the pitch axis. In this case, the blade will pitch about the Z-axis. However, if the blade is pre-bent or tapered, the pitch axis does not coincide with the blade spanwise axis.

[0080] Wind turbine blades have airfoils that twist along their span to accommodate the fact that the outer regions of a wind turbine blade move faster than the inner regions during operation. As the blade twists along its length, the chord rotates about the blade's span axis. For example... Figure 3 As shown, a cross-section of the blade is cut along its length. The cross-sectional profiles are adjacent to the root (profile 30), 0.25R (profile 32), 0.5R (profile 34), and 0.95R (profile 36). The twist angle of each profile is... Figure 3 As shown in the figure, and as can be seen in this embodiment, the twist angle typically decreases from the root of the blade to the tip of the blade.

[0081] like Figure 3 As shown, torsion involves the rotation of the blade about its span or Z-axis. When the blade is torsioned so that its leading edge points downwards, as... Figure 3 As the curved arrows in the diagram indicate, torsion increases, and conversely, the leading edge rises as torsion decreases. The torsion angle represents the angle between the local chord and the rotor's plane of rotation.

[0082] Figure 4 The diagram shows the chord distribution of a blade along its span. In this figure, the X-axis represents the radius, and the Y-axis represents the chord length. It can be seen that the chord length initially increases until the shoulder of the blade, and then decreases towards the tip. It can be understood that for a given number of blades, the radius is greater than the solidity (Sol). r It is proportional to the local chord length on the blade.

[0083] Figure 5 This illustrates the combined radius to solidity (Sol) of the outer half of a rotor with improved blades compared to conventional blades. r The X-axis represents the distance along the blade as a radius. The radius-to-solidity value is displayed on the Y-axis. Dashed line 40 indicates a rotor with conventional blades, and solid line 42 indicates a rotor with improved blades that have a higher radius-to-solidity value.

[0084] Figure 5 The diagram shown extends to 90% of the rotor radius. The last 10% of the rotor radius is not included because the chord length decreases rapidly to zero in the tip region.

[0085] Figure 5 The rotor with improved blades shown has the following combined radius-to-solidity values:

[0086] ·Sol r At 0.7R, it is 0.0140;

[0087] ·Sol r At 0.8R, it is 0.0116;

[0088] ·Solr It is 0.0090 at 0.9R.

[0089] As mentioned above, Sol r It is the ratio of the combined radius of the blades to their solidity, and is defined by the following formula:

[0090]

[0091] Where n = number of leaves, C r = chord length at a specific radius, R = rotor radius.

[0092] When these solidity values ​​are used in conjunction with rotors with a radius of at least 80 m, they offer numerous advantages compared to conventional blades. In particular, the higher solidity value (caused by the increased chord length in the outer 30% of the blade) means that this portion of the blade will generate more lift, thus allowing for a reduction in rotor tip speed. The operating angle of attack of the rotor blades can also be reduced, resulting in a decrease in aerodynamic noise.

[0093] Figure 6 An improved blade (represented by solid line 42) compared to a conventional blade (represented by dashed line 40) is shown, where the radius is on the X-axis and the radius-to-solidity value is on the Y-axis. It can be seen on the improved blade that the solidity value at the blade shoulder (where the chord is greatest) is lower than that of the conventional blade. This feature, combined with the improved blade having higher solidity in at least the outer 30% of the blade, helps reduce the extreme loads the blade experiences during use because of the reduced chord length at the shoulder.

[0094] At the shoulder position, the combined radius of the blades is greater than the solidity Sol. r It can be less than 0.027, and preferably less than 0.026.

[0095] Compared to conventional blades, the increased rotor solidity in at least the outer 30% of the blade due to the increased chord length can lead to higher loads. In particular, the extreme loads experienced by the wind turbine may increase. However, having a relatively lower rotor solidity at the blade shoulder can mitigate these increased loads and help protect the wind turbine from damage.

[0096] Specifically, the ratio of the combined radius of the blade at 0.7R to the combined radius of the blade at the shoulder is greater than 0.5 and preferably greater than 0.55.

[0097] As mentioned above Figure 3 The twist angle of the blade decreases in the direction toward the tip of the blade. Figure 7The diagram illustrates the torsional distribution of a conventional blade, represented by dashed line 50. Line 52 represents the torsional distribution of an improved blade. As is standard in the prior art, torsion initially increases in the root region of the blade due to structural reasons before decreasing towards the tip. Blade torsion is necessary because the effective flow of the blade in use includes both rotor speed and oncoming wind speed. As the circumferential speed of the blade increases along the blade span, the angle of attack of the blade segment also varies along the blade span. To maintain the angle of attack and lift along the blade, the blade therefore has a torsional distribution from root to tip.

[0098] The tips of the blades are also "untwisted" to reduce drag caused by the blade tips. This is in Figure 7 The figure shows a start at approximately 0.95R, but this feature is not relevant to this disclosure.

[0099] When Figure 7 When comparing the traditional torsion distribution line 50 with the improved torsion distribution line 52, a "bulge" can be seen in the torsion distribution line at approximately 0.7R. For clarity, in Figure 8 The article exaggerates and amplifies this feature.

[0100] exist Figure 8 In the torsional distribution shown, as one moves from the middle region toward the tip, there exists a first concave region C1, a convex region C2, and a second concave region C3. The terms "concave" and "convex" are used purely for convenience and are derived from... Figure 8 This is viewed from an angle above the torsional distribution line. The typical torsional distribution curves in this region (e.g., from 0.4R to 0.9R) are purely concave.

[0101] The first concave region C1 and the second concave region C3 are defined by the slope of a torsional distribution with a positive second derivative. The convex region C2 is defined by the slope of a torsional distribution with a negative second derivative.

[0102] The concave regions C1 and C3 connect to the convex region C2 at the first inflection point I1 and the second inflection point I2, respectively. At the inflection points, the second derivative of the torsional distribution is zero.

[0103] The position of the first inflection point I1 corresponds to the starting point of the noise reduction feature 27 at the radial position R1 (the "starting point" of the noise reduction feature is the proximal end closest to the root of the blade 18). Although the noise reduction feature 27 at the trailing edge is used to reduce the trailing edge, it may have a negative impact on aerodynamic performance. In particular, the noise reduction feature can reduce the lift generated by the blade at the radial position where the noise reduction feature is located and / or increase drag. To compensate for this lift loss, the improved blade exhibits a "bulge" in the torsional distribution as described above. In particular, the torsional value is reduced, causing the leading edge of the airfoil to rotate upward. Rotating the airfoil portion in this direction will increase the local angle of attack, thereby increasing the lift generated by the blade at that radial position.

[0104] In other words, the twist angle is reduced near the noise reduction feature to place that part of the blade at a higher angle of attack to compensate for the reduction in lift caused by the noise reduction feature. The reduced twist angle makes the gradient of the twist distribution curve steeper near the noise reduction feature as the blade moves toward the tip.

[0105] In one embodiment, the noise reduction feature is a serrated trailing edge 27 starting at a radial position of 0.7R. To effectively reduce torsion at the serrated trailing edge, a first inflection point I1 will be located in the root direction at a radial position of 0.7R. For example, the first inflection point I1 could be located at 0.65R.

[0106] More generally, the first inflection point I1 is near the radial position R1 where the noise reduction feature begins. For example, the inflection point distance from R1 is less than 15% of the rotor radius, preferably less than 10% of the rotor radius, and more preferably less than 5% of the rotor radius.

[0107] After the first inflection point I1, there is a second inflection point I2 when moving towards the tip. The purpose of the second inflection point is to increase the twist angle so that the angle of attack decreases towards the tip.

[0108] As already described, the improved rotor according to the present invention can exhibit the following characteristics compared to conventional blades:

[0109] • The combined radius of the blades is increased at least on the outer edge of the blade, especially in the last third of the blade. This is achieved through a larger chord, which allows for a reduction in tip speed and a smaller local angle of attack, both of which lead to a reduction in noise.

[0110] • When the blades are fitted with noise reduction features at the trailing edge, the inflection point in the torsional distribution provides a change in local angle of attack to compensate for the loss of aerodynamic performance caused by the noise reduction features.

[0111] These features can be used individually or in combination. When used in combination, the increased solidity provides a larger chord on the outer edge of the blade. This means the angle of attack can be reduced, thus twisting local blade segments, causing the leading edge to rotate downwards (i.e., the twist angle increases). This can be achieved... Figure 7 As seen in the image, the improved blade (shown by solid line 50) exhibits a larger twist angle after approximately 0.6R. Advantageously, due to the higher twist angle (compared to conventional blades), it is possible to reduce twist to compensate for the loss of aerodynamic performance caused by noise reduction features.

[0112] Reference Figure 7 In the leading half of the blade, the improved blade has a smaller twist angle (line 52) than the conventional blade (line 50). As discussed, the lower twist translates into a higher angle of attack, and from... Figure 6 As can be seen, in this blade region, the improved blade (line 42) typically has a reduced chord length compared to the conventional blade (line 40). As previously mentioned, the smaller chord length in the region around the blade shoulder can help reduce the extreme loads the blade experiences during use.

[0113] When torsion “decreases,” the leading edge of the blade rotates upward to increase the local angle of attack. However, this is purely a convention, and torsion can be measured in the opposite direction, such that when torsion decreases, the leading edge rotates downward. In this disclosure, torsion is defined as decreasing when the leading edge of the blade rotates upward.

[0114] Many modifications can be made to the above embodiments without departing from the scope of the invention as defined in the appended claims.

Claims

1. A horizontal axis wind turbine comprising a rotor having a plurality of blades, the rotor having a radius of at least 80 metres, the blades comprising: a root end and a tip end; a leading edge and a trailing edge; a shoulder between the root end and the tip end, at which the chord length defined between the leading edge and the trailing edge is greatest; wherein: • Sol r at least 0.0146 at 0.7R; • Sol r at least 0.0123 at 0.8R; • Sol r at least 0.0099 at 0.9R; • Sol r Below 0.0164 at 0.7R; • Sol r Below 0.0133 at 0.8R; • Sol r Below 0.0108 at 0.9R; Sol r is the combined radius-specific solidity of the blades and is defined by the following equation: where n = number of blades, C r = chord length at a specific radius, and R = rotor radius, and wherein the ratio is greater than 0.5; wherein the ratio is the ratio of the combined radius specific solidity of the blade at 0.7R to the combined radius specific solidity of the blade at the shoulder of the blade.

2. The wind turbine of claim 1, wherein: • Sol r at least 0.0164 at 0.6R.

3. The wind turbine of claim 1 or 2, wherein: • Sol r at least 0.0199 at 0.5R.

4. The wind turbine of claim 1 or 2, wherein: • Sol r at least 0.0172 at 0.6R.

5. The wind turbine of claim 1 or 2, wherein: • Sol r at least 0.0200 at 0.5R.

6. A wind turbine according to claim 1 or 2, wherein, the shoulder is located at a position between 0.18R and 0.35R.

7. A wind turbine according to claim 1 or 2, wherein, the shoulder is located at a position between 0.2R and 0.3R.

8. A wind turbine according to claim 1 or 2, wherein, At the location of the shoulder, the combined radius of the vane is less than solidity Sol r less than 0.

027.

9. A wind turbine according to claim 1 or 2, wherein, At the location of the shoulder, the combined radius of the vane is less than solidity Sol r less than 0.

026.

10. A wind turbine according to claim 1 or 2, wherein, The ratio greater than 0.

55.

11. A wind turbine according to claim 1 or 2, wherein, the design Reynolds number at the tip of the blade is at least 1.1 x 10 6 .

12. A wind turbine according to claim 1 or 2, wherein, the design Reynolds number at the tip of the blade is at least 1.2 x 10 6 .

13. A wind turbine according to claim 1 or 2, wherein, the design Reynolds number at the shoulder of the blade is at least 9 x 10 6 .

14. A wind turbine according to claim 1 or 2, wherein, the design Reynolds number at the shoulder of the blade is at least 10 x 10 6 .

15. The wind turbine of claim 1, wherein, the blade extends in a spanwise direction from the root end to the tip end and in a chordwise direction along a chord from the leading edge to the trailing edge; the blade is twisted between the root end and the tip end and the twist is defined by a twist profile along the spanwise direction of the blade, each blade comprising: an inboard region between the root end of the blade and the shoulder of the blade; an outboard region between 0.9R and the tip end of the blade; and an intermediate region located between the inboard region and the outboard region; a noise reducing feature in the intermediate region of the blade, the noise reducing feature protruding from the trailing edge and extending towards the tip end from a first radial position R1; wherein the twist profile comprises a first inflection point near the first radial position, the first inflection point being less than 15% of the rotor radius from the first radial position R1.

16. A wind turbine according to claim 15, wherein, the noise reducing feature comprises a serrated trailing edge.

17. A wind turbine according to claim 15 or 16, wherein, the twist decreases in the intermediate region of the blade towards the outboard region.

18. A wind turbine according to claim 15 or 16, wherein, the first inflection point is less than 10% of the rotor radius from the first radial position R1.

19. A wind turbine according to claim 15 or 16, wherein, the first inflection point is less than 5% of the rotor radius from the first radial position R1.

20. The wind turbine of claim 15 or 16, wherein, the twist profile comprises a second inflection point located between the first inflection point and the tip end.

21. A wind turbine according to claim 15 or 16, wherein, the first radial position R1 is located between 0.6R and 0.8R.

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