Wind turbine

Abstract

A horizontal axis wind turbine comprising a rotor having a plurality of blades, the rotor having a radius R of at least 80 meters, the blades comprising: a root end and a tip end, the blade extending in a spanwise direction from the root end to the tip end; a leading edge and a trailing edge, the blade extending in a chordwise direction along a chord from the leading edge to the trailing edge; a shoulder between the root end and the tip end, the chord length defined between the leading edge and the trailing edge being at a maximum at the shoulder; the blade being twisted between the root end and the tip end and the twist being defined by a twist profile curve along the spanwise direction of the blade, each blade further comprising: an inboard region between the root end of the blade and the shoulder of the blade; an outboard region between a rotor radius of 0.9R and the tip end of the blade; and an intermediate panel region located between the inboard region and the outboard region; a noise reducing feature in the intermediate panel region of the blade, the noise reducing feature protruding from the trailing edge and extending from a first radial position R1 towards the tip end; wherein the twist profile curve comprises a first inflection point near the first radial position R1.

Description

Technical Field

[0001] This invention relates to a horizontal-axis wind turbine comprising a rotor having multiple blades. In particular, the invention relates to specific blade geometries to reduce aerodynamic noise generated by the rotor. Background Technology

[0002] Wind turbines are used to convert the kinetic energy from wind into electricity. 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 onshore and offshore. 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 resulting noise has become a greater concern. In this respect, wind turbines are now being positioned closer to commercial and residential areas, where various laws and regulations may restrict noise levels.

[0003] There are two main sources of noise in wind turbines: mechanical noise and aerodynamic noise. Mechanical noise can originate from various wind turbine components, such as gearboxes, generators, pitch and yaw controls, hydraulic systems, etc. Aerodynamic noise, on the other hand, is likely due to the interaction between the blades and the air flowing over them. While mechanical noise can be a significant contributor to overall wind turbine noise, some known 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] Several sources of aerodynamic noise may exist, including trailing edge noise and blade tip vortex noise. Trailing edge noise (which may include blunt trailing edge vortex detachment noise and turbulent boundary layer trailing edge noise) has attracted some attention from power companies 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 blades.

[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, comprising a rotor having a plurality of blades, the rotor having a radius R of at least 80 meters, the blades comprising:

[0007] The root end and the tip end; the leaf extends from the root end to the tip end in the wingspan direction.

[0008] Leading and trailing edges; the blade extends from the leading edge to the trailing edge along the chord in the chordal direction.

[0009] The shoulder, located between the root end and the tip end, has the greatest chord length defined between the front and rear edges;

[0010] The leaf blade twists between its root and tip ends, and the twist is defined by a twist distribution curve along the leaf's span direction. Each leaf blade also includes:

[0011] The inner region located between the root end of the leaf and the shoulder of the leaf;

[0012] Located in the outer region between the rotor radius 0.9R and the tip of the blade;

[0013] And the middle plate area, which is located between the inner and outer areas;

[0014] A noise reduction feature is located in the middle plate region of the blade, the noise reduction feature protrudes from the trailing edge and extends from a first radial position R1 toward the tip;

[0015] The torsional distribution curve includes the first inflection point near the first radial position R1.

[0016] 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.

[0017] In the middle plate 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 this disclosure, 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.

[0018] 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 the lift generated by the blade and / or increase the 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 this lift loss from the noise reduction feature.

[0019] Preferably, the noise reduction feature includes a serrated trailing edge. The serrated trailing edge has a serrated shape and is used to reduce trailing edge noise.

[0020] Preferably, the torsion decreases towards the outer region in the middle plate area of ​​the blade. This reduction in torsion provides a suitable angle of attack along the blade length.

[0021] When the torsional distribution includes a first inflection point near the first radial position, the distance from the first radial position to the first inflection point can be less than 15% of the rotor radius, preferably less than 10%, and more preferably less than 5%. Preferably, the first inflection point is located at the root of the first radial position. This allows the blades to be set at the desired torsional angle at the beginning of the noise reduction feature.

[0022] Preferably, the torsional distribution curve includes a second inflection point located between the first inflection point and the distal end.

[0023] 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-reducing features (such as serrated trailing edges) only in the outer third of the blade, as this location is the main source of aerodynamic noise.

[0024] A horizontal axis wind turbine may include a rotor, wherein:

[0025] Sol r At 0.7R, it is at least 0.0140;

[0026] Sol r At 0.8R, it is at least 0.0116;

[0027] Sol r At 0.9R, it is at least 0.0090;

[0028] Sol r It is the ratio of the combined radius of the blades to their density and is defined by the following:

[0029]

[0030] Where n = number of blades, Cr = chord length at a specific radius, and R = rotor radius.

[0031] The compactness of a wind turbine blade is the area of ​​the wind turbine blade projected onto the rotor plane (A). 叶片 ) and the total area covered by the rotating blades (πR) 2 The ratio between ) . Therefore, the density of the combination (i.e., the sum of the density of the leaves) is:

[0032]

[0033] Where n is the number of wind turbine blades (e.g., 3) and R is the rotor radius. Therefore, density is a measure of the thinness of the blade, because the lower the density, the thinner the blade.

[0034] The compaction can also be established from the rotor center for a specific radius r. The radius-to-compactness of the wind turbine rotor (i.e., the combined radius-to-compactness of the blades) is given by (where Cr is the chord at a specific radius):

[0035]

[0036] It is known in the design of wind turbine blades that reducing the density of wind turbine blades reduces the load on the wind turbine. This is because the reduced density results in a smaller chord, thus reducing fatigue and extreme loads on the wind turbine blade (as described in WO2006 / 090215). However, the present invention does not seek longer blades, but rather a higher density value in the outer half of the blade.

[0037] The power generated by a wind turbine is proportional to the rotor's rotational speed. As blade length increases, the tip velocity of the blades also increases for a given rotational speed. However, the increased tip velocity leads to higher aerodynamic noise. Furthermore, higher tip velocities result in increased corrosion at the leading edge of the wind turbine blades. By providing a wind turbine rotor with the combined radius-to-density ratio described above, the tip velocity can be reduced without correspondingly reducing the lift generated by the blades. Additionally, aerodynamic noise is reduced due to the lower tip velocity. Typically, for conventional rotors, if the tip velocity is reduced by decreasing the rotational speed, there will be a corresponding decrease in the power generated by the wind turbine because there will be lower lift generated by the blades.

[0038] Using the density values ​​listed above, the blade has a larger chord in at least the outer 30% of its span compared to conventional blades. With a relatively large chord, the blade in this outer 30% will generate more lift. Therefore, the tip velocity 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 across the blade will be thinner.

[0039] For long rotor blades, especially those exceeding 80 meters in length, aerodynamic noise becomes a limiting factor in the design. The blade geometry defined here advantageously allows for the reduction of aerodynamic noise while still providing sufficient aerodynamic performance.

[0040] Preferably, Sol rAt 0.6R, it is at least 0.0164. Preferably, Sol r At 0.5R, it is at least 0.0199. By further increasing the density value inward, the noise generated by the blades can be further reduced while still maintaining aerodynamic performance.

[0041] In a preferred embodiment, the blades have a combined radius-to-density ratio, thereby:

[0042] Sol r At 0.7R, it is at least 0.0146;

[0043] Sol r At 0.8R, it is at least 0.0123;

[0044] Sol r At 0.9R, it is at least 0.0099.

[0045] This density value is particularly beneficial for wind turbines with rotor radii exceeding 80 meters (e.g., exceeding 90 meters).

[0046] 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), such a compaction value allows for a reduction in the rotor tip speed while still maintaining aerodynamic performance.

[0047] In a preferred embodiment, the blades have a combined radius-to-density ratio, thereby:

[0048] Sol r Below 0.0164 at 0.7R;

[0049] Sol r Below 0.0133 at 0.8R;

[0050] Sol r It is below 0.0108 at 0.9R.

[0051] Although the 30% increase in string length in the outer section leads to a reduction in noise, the radius of the composite is preferably lower than these values ​​to minimize fatigue and extreme loads on the rotor.

[0052] Preferably, the shoulder is located between 0.18R and 0.35R, and more preferably between 0.2R and 0.3R.

[0053] At the shoulder position, the combined radius of the blades is greater than the density Sol. r It can be less than 0.027, and preferably less than 0.026.

[0054] The ratio is defined as:

[0055] The ratio may be greater than 0.5 and preferably greater than 0.55, and even more preferably greater than 0.58; wherein the ratio is the ratio of the radius-to-density of the blade assembly at 0.7R to the radius-to-density of the blade assembly at the shoulder of the blade.

[0056] Due to the increased blade length compared to conventional blades, the increased rotor density in the outer 30% (and preferably the outer half) of the blade can lead to higher loads. In particular, this can increase the extreme loads experienced by the wind turbine. However, providing a rotor with a relatively low rotor density at the blade shoulder can mitigate these increased loads and help protect the wind turbine from damage.

[0057] It should be noted that the multiple blades are preferably substantially identical in their external geometry, such that the shoulders on each blade will be in the same position and have the same chord length.

[0058] The expression "at the shoulder position" means that the blade radius is determined at the position of the maximum chord of the blade. The shoulder of the blade may not be a sharp point, so the expression "at the shoulder position" can be interpreted as at the shoulder position + / - 1%R.

[0059] Preferably, the design Reynolds number at the tip of the leaf is at least 1.1 × 10⁻⁶. 6 And more preferably at least 1.2 × 10 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 .

[0060] 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:

[0061]

[0062] Where w is the relative wind speed at the blade section, ρ is the air density, and μ is the dynamic viscosity of the air. For a local blade section, the Reynolds number will vary depending on the chord length Cr.

[0063] The dimensions of wind turbine blades can be described in terms of length. However, they can also be described with reference to the Reynolds number, with longer blades resulting in higher Reynolds numbers. The density values ​​of this invention are particularly applicable to wind turbine blades operating at the aforementioned Reynolds numbers. The Reynolds number provided herein is the "design Reynolds number" obtained at the design point of the wind turbine. As will be understood by those skilled in the art, this design point is when the rotor operates at its optimal tip speed ratio. The values ​​for air density and dynamic viscosity are obtained at sea level. Attached Figure Description

[0064] To facilitate a clearer understanding of the invention, examples of the invention will now be described by way of illustration 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 perspective view of a wind turbine blade, and Figure 2b It is the cross-section passing through the wind turbine blade.

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

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

[0069] Figure 5 and Figure 6 The radius-to-density 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 that supports 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 example, 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 end 20 to a tip end 22 in the longitudinal spanwise direction and extends between a leading edge 24 and a trailing edge 26 in the transverse chordwise direction. 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 rotor 16 has a radius such that the tip of the blade is at position r = R, and the axis of rotation is at r = 0.

[0073] As the blade moves from the root end 20 towards the shoulder 25, the blade 18 transitions from a circular profile to an airfoil profile. The shoulder 25 is the widest part of the blade 18, where it has its maximum chord. The blade 18 has an airfoil profile with a thickness that gradually decreases from the shoulder towards the tip of the blade.

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

[0075] Figure 2b This is a diagram of the airfoil profile of a wind turbine blade in the mid-plate blade region. A chord connects the leading edge 24 and the trailing edge 26.

[0076] Figure 2a The blade is shown to include a noise-reducing feature 27, which in this example is a serrated trailing edge. The serrations are used to reduce noise caused by the blade 18 in use. In one example, the serrations are provided as an attachment that is adhesively bonded to the blade at the trailing edge and may be formed, for example, from injection-molded plastic. The serrations, in a triangular form (e.g., serrated shape), are understood to reduce aerodynamic trailing edge noise by interacting with the turbulent boundary layer flowing over the blade surface. In another example, the noise-reducing feature may include bristles and / or combs 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 the trailing edge noise is most pronounced. The noise reduction feature begins at a radial position R1 and extends towards the tip of the blade. In the example, the radial position R1 may be 0.7R. In particular, the noise reduction feature has a proximal end located in the middle plate region of the blade (closest to the root end 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 the example, the pitch axis of the blade is aligned with the blade's span direction. The Y-axis is perpendicular to the X-axis and Z-axis.

[0079] As is well known in the art, wind turbine rotor blades can rotate about a pitch axis to regulate the power output of the wind turbine and the load experienced by the wind turbine components. In the case of a wind turbine, where the blades are not tapered and have no pre-bending, the blade spanwise axis is aligned with the pitch axis. In this case, the blade will pitch about the Z-axis. However, if the blades are pre-bending or tapered, the pitch axis does not coincide with the blade spanwise axis.

[0080] The airfoil profile of a wind turbine blade is twisted along its span to account for the fact that, during operation, the outer region of a wind turbine blade moves faster than the inner region. As the blade twists along its length, the chord rotates about the blade's spanwise axis. (As in...) Figure 3 As can be seen, the cross-section of the leaf is taken along the length of the leaf. 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 example, the twist angle typically decreases from the root of the blade to the tip.

[0081] like Figure 3 As shown, twisting involves the rotation of the blade about the spanwise direction or the Z-axis. When the blade twists so that the leading edge points downwards, as... Figure 3 As the curved arrows in the diagram indicate, twist increases, and conversely, the leading edge rises as twist decreases. The twist 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 the 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 of the blade. As will be appreciated, for a given number of blades, the radius is more important than the compaction (Sol). r It is directly proportional to the local chord length on the blade.

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

[0084] Figure 5 The diagram shown extends to 90% of the rotor radius. The final 10% of the rotor radius is not included because the chord length can rapidly decrease to zero at the tip.

[0085] have Figure 5 The rotor with the improved blades shown has the following combination of radius-to-density values: where

[0086] Sol r At 0.7R, it is 0.0140;

[0087] Sol r At 0.8R, it is 0.0116;

[0088] Sol r It is 0.0090 at 0.9R.

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

[0090]

[0091] Where n = number of blades, Cr = chord length at a specific radius, and R = rotor radius.

[0092] When these density values ​​are combined with rotors with a radius of at least 80 m, there are several advantages compared to conventional blades. Specifically, the higher density value (which is generated by the increased chord length in the outer 30% of the blade) means that this part of the blade will generate more lift, allowing for a reduction in the rotor's tip speed. The operating angle of attack of the rotor blades can also be reduced, which will result in a decrease in aerodynamic noise.

[0093] Figure 6 An improved blade (represented by solid line 42) is shown compared to a conventional blade (represented by dashed line 40), which has radius-to-density ratio values ​​on the X-axis and Y-axis. As can be seen on the improved blade, the density value at the shoulder of the blade (where the chord is at its maximum) is lower than that of the conventional blade. This feature, combined with the improved blade having higher density in at least the outer 30% of the blade, helps to reduce the extreme loads experienced by the blade in use due to the reduced chord length at the shoulder.

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

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

[0096] In particular, the ratio of the combined radius density of the blade at 0.7R to the combined radius density of the blade at the blade 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 7 The torsional distribution of a conventional blade, identified by dashed line 50, is shown. The torsional distribution of an improved blade is identified by line 52. As is standard in the art, due to structural reasons, the torsion initially increases in the root region of the blade before decreasing towards the tip. Blade torsion is necessary because the effective flow at the blade in use includes the rotor rotational speed and the incoming wind speed. As the circumferential velocity 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 leaves are also "de-twisted" to reduce the resistance caused by the tips of the leaves. This is in Figure 7 The figure shows a starting point at approximately 0.95R, but this feature is not relevant to this disclosure.

[0099] When comparing Figure 7 When comparing the conventional torsion distribution line 50 and the improved torsion distribution line 52, it can be seen that a "bulge" exists in the torsion distribution line at approximately 0.7R. For clarity, in Figure 8 This feature has been exaggerated and amplified.

[0100] exist Figure 8 In the torsional distribution shown, as the movement proceeds from the middle plate 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 seen from a viewpoint above the torsional distribution line. The typical torsional distribution curves in this region (e.g., from 0.4R to 0.9R) have a purely concave shape.

[0101] The first and second concave regions C1 and 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] Concave regions C1 and C3 join 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 beginning of the noise reduction feature 27 at the radial position R1 (the "beginning" 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 and / or increase the drag generated by the blade at the radial position where the noise reduction feature is located. To compensate for this lift loss, the improved blade exhibits a "bulge" in the torsional distribution as just described. In particular, the torsional value is reduced, causing the leading edge of the airfoil to rotate upward. Rotating the airfoil section in this direction will increase the local angle of attack and thus increase the lift generated by the blade at that radial position.

[0104] In other words, by reducing the twist angle near the noise reduction feature, that portion of the blade is placed at a higher angle of attack to compensate for the reduced 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 example, the noise reduction feature is a serrated trailing edge 27 starting at a radial position of 0.7R. To achieve effective torsional reduction at the serrated trailing edge, a first inflection point I1 will be located on the root side 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 located near the radial position R1 where the noise reduction feature begins. For example, the distance from the inflection point to R1 is less than 15% of the rotor radius, preferably less than 10%, and more preferably less than 5%.

[0107] As the movement moves toward the tip, there is a second inflection point I2 after the first inflection point I1. The purpose of the second inflection point is to increase the twist angle so that the angle of attack decreases toward the tip.

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

[0109] • The combined radius of the blades is increased in at least the outer portion of the blade (particularly the last third). This is achieved through a larger chord, which allows for a reduction in tip velocity and a decrease in local angle of attack, both of which contribute to a reduction in noise.

[0110] • When the blade is equipped with a noise reduction feature 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 feature.

[0111] These features can be used individually or in combination. When used in combination, the increased density provides a larger chord in the outer portion of the blade. This means that the angle of attack can be reduced, and therefore localized sections of the blade are twisted, causing the leading edge to rotate downwards (i.e., the twist angle increases). This can... Figure 7 As can be seen, the improved blade (shown by solid line 50) has a larger twist angle after approximately 0.6R. Advantageously, with a higher twist angle (compared to conventional blades), there is a capability to reduce twist to compensate for the loss of aerodynamic performance caused by the noise reduction feature.

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

[0113] When torsion “decreases,” the leading edge of the blade rotates upward to increase the local angle of attack. However, this is purely conventional, and torsion can be measured in the opposite sense, 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 may be made to the above examples 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 R of at least 80 meters, the blades comprising: a root end and a tip end, the blade extending in a spanwise direction from the root end to the tip end; a leading edge and a trailing edge, the blade extending in a chordwise direction along a chord from the leading edge to the trailing edge; a shoulder between the root end and the tip end, the chord length defined between the leading edge and the trailing edge being at a maximum at the shoulder; the blade being twisted between the root end and the tip end, and the twist being defined by a twist profile along the spanwise direction of the blade, each blade further comprising: an inboard region between the root end of the blade and the shoulder of the blade; an outboard region between a rotor radius of 0.9R and the tip end of the blade; and an intermediate panel region between the inboard region and the outboard region; a noise reducing feature in the intermediate panel region of the blade, the noise reducing feature protruding from the trailing edge and extending from a first radial position R1 towards the tip end; wherein the twist profile comprises a first inflection point near the first radial position R1, the first inflection point being less than 15% of the rotor radius from the first radial position.

2. A wind turbine according to claim 1, wherein, the noise reducing feature comprises a serrated trailing edge.

3. Wind turbine according to claim 1 or 2, wherein the twist decreases in the intermediate panel region of the blade towards the outboard region.

4. Wind turbine according to claim 1 or 2, wherein the first inflection point is less than 10% of the rotor radius from the first radial position.

5. A wind turbine according to claim 1 or 2, wherein, the twist profile comprises a second inflection point between the first inflection point and the tip end.

6. A wind turbine according to claim 1 or 2, wherein, the first radial position R1 is between 0.6R and 0.8R.

7. The wind turbine of claim 1, wherein: Sol r at least 0.0140 at 0.7 R; Sol r at least 0.0116 at 0.8 R; Sol r at least 0.0090 at 0.9R; Sol r is the combined radius-specific density of the blades and is defined by: where n = number of blades, Cr = chord length at a particular radius, and R = rotor radius.

8. The wind turbine of claim 7, wherein: Sol r At 0.6 R is at least 0.0164.

9. The wind turbine of claim 7 or 8, wherein: Sol r at least 0.0199 at 0.5 R.

10. The wind turbine of claim 7 or 8, wherein: Sol r at least 0.0146 at 0.7 R; Sol r at least 0.0123 at 0.8 R; Sol r At 0.9R is at least 0.0099.

11. The wind turbine of claim 7 or 8, wherein, Sol r At 0.6 R is at least 0.0172.

12. The wind turbine of claim 7 or 8, wherein, Sol r At 0.5 R is at least 0.0200.

13. A wind turbine according to claim 7 or 8, wherein, At said shoulder position, the combined radius of the vane is greater than the solidity Sol r less than 0.

027.

14. A wind turbine according to claim 7 or 8, wherein, a ratio greater than 0.5; where the ratio is a ratio of a combined radius-to-density of the blade at 0.7R to a combined radius-to-density of the blade at the shoulder of the blade.

15. 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 .

16. 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 .

17. A wind turbine according to claim 1 or 2, wherein, the first inflection point is less than 5% of the rotor radius from the first radial position.

18. A wind turbine according to claim 7 or 8, wherein, At said shoulder position, the combined radius of the vane is less than the solidity Sol r less than 0.

026.

19. A wind turbine according to claim 7 or 8, wherein, a ratio greater than 0.55; where the ratio is a ratio of a combined radius-to-density of the blade at 0.7R to a combined radius-to-density of the blade at the shoulder of the blade.

20. 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 .

21. 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 .

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