Serrated trailing edge panel for a wind turbine blade

Abstract

A serrated panel (70) for a wind turbine blade (10) is provided. The serrated panel (70) is configured to be attached to the trailing edge (20) of the wind turbine blade (10) to form a one or more, preferably a plurality of, serrations (80) at the trailing edge (20) of the wind turbine blade (10), The serrated panel comprises a base part (72) for attachment to the trailing edge (20) of the wind turbine blade (10), the base part (72) comprising a first longitudinal end (73) for arrangement nearest a tip end of the wind turbine blade, a second longitudinal end (74) for arrangement nearest a root end of the wind turbine blade, a first side (75) for arrangement nearest a leading edge of the blade, and a second side (76) for arrangement farthest from the leading edge of the blade. One or more serrations (80) extend from the second side (76) of the base part (72), wherein each serration (80) comprises: a base portion (81) proximal to the second side (76) of the base part (72), an apex portion (82) distal to the second side (76) of the base part (72), a first side portion (83) arranged nearest the first longitudinal end (73) of the base part (72), and a second side portion (84) arranged nearest the second longitudinal end (74) of the base part (72). Each of the serrations (80) have a corrugated cross-sectional profile with alternating grooves (85) and ridges (86) as seen in a transverse direction between the first side portion (83) and the second side portion (84) along at least a mid-range portion (87) between the base portion (81) and the apex portion (82), wherein the corrugated cross-sectional profile at the mid-range portion (87) comprises at least one groove (85) and one ridge (86), preferably a plurality of both grooves (85) and ridges (86).

Description

[0001] SERRATED TRAILING EDGE PANEL FOR A WIND TURBINE BLADE

[0002] FIELD OF THE INVENTION

[0003] The present disclosure relates to a serrated trailing edge panel for a wind turbine blade as well as a wind turbine blade provided with serrations at the trailing edge of the wind turbine blade.

[0004] BACKGROUND OF THE INVENTION

[0005] Wind power is increasingly popular due to its clean and environmentally friendly production of energy. The rotor blades of modern wind turbines capture kinetic wind energy by using sophisticated blade design created to maximise efficiency. However, complaints have arisen about the creation of noise associated with the operation of wind power plants. Hence, noise reducing devices and associated blade designs are increasingly desired.

[0006] One of the continued considerations for wind turbine blade design is the operational noise produced when such blades rotate, in particular for onshore wind turbine installations. A portion of such noise is generated from airflow leaving the profile of a wind turbine blade at the blade trailing edge and is often referred to as trailing edge noise.

[0007] As modern wind turbine blades are manufactured at increasingly longer blade lengths, the longer span of the blades results in higher relative wind speeds experienced by the blades. Accordingly, this can lead to relatively large levels of trailing edge noise.

[0008] To this end, modern wind turbine blades are sometimes provided with serrations along the blade trailing edges, in an effort to reduce blade trailing edge noise and / or to improve wind turbine blade efficiency, as can be seen in EP1314885. The serrations are typically provided by attaching a serrated panel at the trailing edge of the wind turbine blade. While the noise mitigating properties of such serrations are advantageous, several drawbacks remain. Often, finding the right serration geometry is a trade-off between noise mitigation performance and structural requirements. This may lead to the need for thick trailing edge regions, especially near the serration base. This increased thickness can become a potential source of additional noise. Further, from both manufacturing purposes and the purpose of minimising noise, it may be beneficial to make the serrations rather thin, whereby inter alia material use can be reduced. This, however, has the drawback that the serrations become too flexible and have eigen frequencies that may cause the serrations to oscillate, which in turn can lead to the serrations breaking off. The low stiffness increases the susceptibility for flow-induced vibrations, both as a response to unsteady forcing and possible resonances involving fluid-structure coupling. Using stiffer materials is an option, but this comes with extra manufacturing costs, which should be avoided.

[0009] WO 2020 / 169540 Al discloses a wind turbine rotor blade assembly comprising a rotor blade and a noise reducer configured on the rotor blade. The noise reducer comprises a plurality of aligned spine members.

[0010] WO 2018 / 130641 Al discloses a wind turbine blade including a noise reducing device in form of a serrated panel, which is provided with protruding fins that have a height being less than two-thirds or a local boundary layer thickness.

[0011] WO 2017 / 137394 Al discloses a serrated panel for a wind turbine blade. The serrated panel comprises a base part for attaching the panel to the trailing edge of the wind turbine blade. An exterior surface of the base part has an undulated surface, which is described in the disclosure as a corrugated surface.

[0012] US 9,841,002 B2 discloses a wind turbine blade provided with a serrated extension at the trailing edge. Furthermore, the wind turbine blade is provided with ridge-shaped protrusions, which may be located on teeth of the serrated extension.

[0013] It is therefore an object of the invention to provide a wind turbine blade having an improved trailing edge configuration as well as a trailing edge serration panel for arrangement at the trailing edge of a wind turbine blade that at least ameliorates some of the drawbacks found in prior art serration designs.

[0014] SUMMARY OF THE INVENTION

[0015] Thus, according to a first aspect, there is provided a serrated panel for a wind turbine blade, wherein the serrated panel is configured to be attached to the trailing edge of the wind turbine blade to form one or more, preferably a plurality of, serrations at the trailing edge of the wind turbine blade, wherein the serrated panel comprises: a base part for attachment to the trailing edge of the wind turbine blade, the base part comprising: a first longitudinal end for arrangement nearest a tip end of the wind turbine blade, a second longitudinal end for arrangement nearest a root end of the wind turbine blade, a first side for arrangement nearest a leading edge of the blade, and a second side for arrangement farthest from the leading edge of the blade, and one or more, preferably a plurality of serrations, extending from the second side of the base part, wherein each serration comprises: a base portion proximal to the second side of the base part, an apex portion distal to the second side of the base part, a first side portion arranged nearest the first longitudinal end of the base part, and a second side portion arranged nearest the second longitudinal end of the base part, wherein each of the serrations have a corrugated cross-sectional profile with alternating grooves and ridges as seen in a transverse direction between the first side portion and the second side portion along at least a mid-range portion between the base portion and the apex portion, wherein the corrugated cross-sectional profile at the mid-range portion comprises at least one groove and one ridge, preferably a plurality of both grooves and ridges.

[0016] Thereby, it is possible to provide relatively thin serrations that are stiffer and reduce the risk of vibrations, which in turn lead to longer fatigue life at still low cost. By letting the cross-sectional profile of the serrations being corrugated, a larger effective plate thickness is achieved. This increases the bending stiffness as well as the eigenfrequencies of the serrations, without using noticeably more material or having to introduce significant changes to the process for manufacturing the serrated panels. Further, it has been found that the corrugated cross-sectional profile may further reduce noise emissions. Accordingly, the design has been found to increase the lifetime of the serrated panels while improving the acoustic properties. The serrations can be manufactured via for instance vacuum forming or thermoforming, e.g. from a flat panel. They can also be manufactured via injection moulding or composite manufacturing like resin infusion or using prepregs.

[0017] It is noted that a corrugated cross-sectional profile entails that the serrations have a number of grooves and ridges, respectively, as seen from one surface side of the serrations, e.g. the pressure side of the serrations, that coincides with corresponding ridges and grooves, respectively, as seen from the opposite surface side of the serrations, e.g. from the suction side of the serrations. In other words, the corrugations are not surface corrugations but for the cross-sectional profile itself.

[0018] It is understood that the at least one groove and at least one ridge is located at a distance or with a spacing from the first side portion and the second side portion of the serration. It is further understood that by having at least one groove and at least one ridge that the cross-sectional profile will have at least two local turning points (at the peaks of the at least one groove and the at least one ridge) along the cross-sectional profile with alternating grooves and ridges. In a preferred embodiment, the corrugated cross-sectional profile at the mid-range portion comprises at least two grooves and one ridge. By having at least two grooves and one ridge, it is also clear that the cross-sectional profile will have at least three local turning points along the cross- sectional profile with alternating grooves and ridges. It is also clear that the at least two grooves and one ridge are thus seen from one side of the serrations. As seen from the other side, the serrations will have at least two ridges and one groove.

[0019] Similarly, according to a second aspect, there is provided a wind turbine blade having a profiled contour including a pressure side and a suction side as well as having a leading edge and a trailing edge with a chord having a chord length extending therebetween, the wind turbine blade extending in a spanwise direction between a root end and a tip end, where the wind turbine blade comprises one or more, preferably a plurality of, serrations extending from the trailing edge of the wind turbine blade, wherein each serration comprises: a base portion arranged nearest the leading edge of the wind turbine blade, an apex portion arranged farthest from the leading edge of the wind turbine blade, a first side portion arranged nearest the tip end of the wind turbine blade, and a second side portion arranged nearest the root of the wind turbine blade, wherein each of the serrations have a corrugated cross-sectional profile with alternating grooves and ridges as seen in a transverse direction between the first side portion and the second side portion along at least a mid-range portion between the base portion and the apex portion, wherein the corrugated cross-sectional profile at the mid-range portion comprises at least two grooves and one ridge, preferably a plurality of both grooves and ridges.

[0020] In the following, various embodiments are described that are applicable to any of the above- mentioned aspects. The embodiments can be combined with each other.

[0021] According to a preferred embodiment, the serrations have a substantially uniform thickness. This provides a simple solution, where the serrations can be made with a limited amount of material and constant thickness material, but where the effective surface area and stiffness can be increased by the corrugated design. Further, this design provides a simple way of manufacturing the serrated panel from a flat panel. Accordingly, each serration may be formed as a corrugated sheet. Although the panel has a uniform or substantially uniform thickness, the edges may according to another preferred embodiment be chamfered or rounded. According to a preferred embodiment, each serration transitions from a flat cross-sectional profile at the base portion of the serration to the corrugated cross-sectional profile at the mid-range portion of the serration. This ensures that the serrated panel can be formed such that it has a substantially planar base part, which is easy to attach to the trailing edge of the wind turbine blade, e.g. by adhering one of the surfaces to an exterior part of the blade or sandwiching it between shell parts of the wind turbine blade. This design ensures that the serrations may extend and transition from the base part, which preferably has a substantially flat cross-sectional profile as seen between the first longitudinal end and the second longitudinal end of the serrated panel.

[0022] Thus, according to a preferred embodiment, amplitudes of the grooves and ridge(s) are locally increasing between a point on the base portion of the serration and the mid-range portion of the serration. The grooves and ridge(s) may for instance have their maximum amplitude at the midrange portion of the serration. This design is particularly implemented for the design where each serration transitions from a flat cross-sectional profile at the base portion of the serration to the corrugated cross-sectional profile at the mid-range portion of the serration.

[0023] According to one embodiment, amplitudes of the grooves and ridges are locally decreasing towards the apex portion of the serration, e.g. from the mid-range portion to the apex portion of the serration. In other words, the amplitudes of the ridges and valleys may have a local maximum somewhere between the base portion and the apex portion.

[0024] According to another embodiment, amplitudes of the grooves and ridge(s) are substantially constant along a range towards the apex portion of the serration, e.g. from the mid-range portion to the apex portion of the serration. Thus, the amplitudes may for instance increase from the base portion to a local maximum somewhere between the base portion and the apex portion and then progress with a constant amplitude from this position and towards the apex portion of the serration.

[0025] As already outlined above, a cross-sectional profile at the base portion of the serration is preferably substantially flat. Thus, the amplitudes of the grooves and ridges increase from zero to a given maximum amplitude at a position between the base portion and the apex portion of the serration, e.g. at the mid-range portion of the serration. However, in an alternative embodiment, the grooves and ridges extend to the base part of the serrated panel. Thus, at least the downstream part of the base part may thus also have a corrugated design. This corrugated part of the base part may then form gaps when attached to a surface of the blade, and these gaps can be filled with an adhesive to attach the serrated panel to the surface of the blade. If the downstream part of the base part has a corrugated design, the base portion may advantageously comprise a transition from a substantially flat or planar profile to the corrugated design in order to obtain a smooth aerodynamic transition.

[0026] In yet another embodiment, an envelope to the grooves and ridges are conical in shape along at least a part of the serration from the base portion and towards the apex portion.

[0027] According to a preferred embodiment, the grooves and ridge(s) are substantially parallel. The serrations and valleys may for instance be parallel to a notional line extending between a midpoint of the base portion and an apex of the serration.

[0028] However, according to an alternative embodiment, grooves and ridge(s) are aligned to merge along a line extending between the base portion of the serration to the apex portion of the serration, e.g. wherein the line is aligned between a midpoint of the base portion and an apex of the serration. Thus, the corrugations (i.e. grooves and ridges) have a converging arrangement, where they meet at the line. The grooves and ridges may for instance be aligned parallel with the first side and the second side to merge at said line. Accordingly, the serration may also have a corrugated profile as seen along said line between the base portion and the apex portion of the serration.

[0029] According to one embodiment, the alternating of the grooves and ridges have substantially identical amplitudes as seen in the transverse direction between the first side portion and the second side portion of the serrations. Accordingly, envelopes drawn between tips or the amplitude portions of the grooves and ridges, respectively, are substantially parallel.

[0030] In another embodiment, amplitudes of the grooves and ridge(s) are decreasing in the transverse direction along at least a mid-range portion of the serration from a central position and towards the first side portion and the second side portion, respectively. Accordingly, envelopes drawn between tips or the amplitude portions of the grooves and ridges, respectively, are converging towards the first side portion and the second side portion, respectively.

[0031] According to a preferred embodiment, a maximum amplitude of a groove or ridge is 2-20 times greater, preferably 2-10 times greater, e.g. around 5 times greater than a thickness of the serration. In particular for thinner serrations, the amplitude may be several times larger than the thickness of the serration. These ranges have proven to provide a great trade-off between establishing a sufficient stiffness while still limiting the amount of material for a serration and being able to easily manufacture the serrations or serrated panel. According to another preferred embodiment, the alternating grooves and ridges have a period, which is 3-20 times greater, preferably 4-15 times greater, and more preferably 5-10 times greater than a thickness of the serration. Alternatively, or in addition thereto, the number of periods may be 1-10, preferably 2-5. Accordingly, the alternating grooves and ridges may comprise a plurality of grooves and ridges, e.g. up to 10 of each.

[0032] Further, the thickness of each serration is preferably in the range 0.5 mm - 10 mm, preferably 0.7 mm - 5.0 mm, more preferably 1.0 mm - 3.0 mm. Accordingly, it is seen that the serrations are relatively thin, but that the corrugated design increases the surface area, stiffness and eigenfrequency of the serrations.

[0033] According to a preferred embodiment, the serrations each comprise at least a total of five grooves and ridges, e.g. at least 3 grooves and 2 ridges, or vice versa.

[0034] According to a preferred embodiment, the alternating grooves and ridges may have a wavy design, such as a sinusoidal-like design. However, the corrugated design may also have sharper sides and tip portions.

[0035] The serrations are advantageously substantially triangular shaped with two sides and a single tip or apex. However, it is recognised that the serrations may also deviate from such a design by having slightly curved sides and / or a curved tip. It is also recognised that the sides may have minor serrations, and / or that the apex portion may have more than one tip.

[0036] The serrated panel may be attached to the blade in a number of ways. The serrated panel can for instance be adhered or otherwise attached to the pressure side of the blade. In another embodiment, the serrated panel can be adhered or otherwise attached to the suction side of the blade. In yet another embodiment, the serrated panel is sandwiched between shell parts of the blade. In all the embodiments, the serrations of course must extend from the trailing edge of the blade or more downstream. However, it is also contemplated that the serrations can be formed as an integral part of one of the shell structures of the blade. This can be done by designing the shell part accordingly or embedding a serrated panel in between the shell structures.

[0037] DETAILED DESCRIPTION OF THE INVENTION

[0038] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 shows a wind turbine,

[0039] Fig. 2 shows a schematic view of a wind turbine blade according to the invention, Fig. 3 shows a schematic view of an airfoil profile of the blade of Fig. 2,

[0040] Fig. 4 shows a schematic view of the wind turbine blade of Fig. 2, seen from above and from the side,

[0041] Fig. 5 shows a schematic view of an exemplary serrated panel, seen in perspective, Fig. 6 shows a schematic top view of the exemplary serrated panel,

[0042] Fig. 7 illustrates various examples of amplitudes of grooves and ridges as seen in a length direction of the serrations,

[0043] Fig. 8 illustrates various examples of amplitudes of grooves and ridges as seen in a transverse direction of the serrations, and

[0044] Fig. 9 shows another schematic view of another exemplary serrated panel.

[0045] It will be understood that elements common to the different embodiments of the invention have been provided with the same reference numerals in the drawings.

[0046] Fig. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called "Danish concept" with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8, the blade extending in a spanwise direction between the root 16 and the tip 14. The rotor has a radius denoted R.

[0047] Fig. 2 shows a schematic view of a wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18. An array of trailing edge serrations is provided along a portion of the trailing edge 20 of the blade. In general, flow of air over the wind turbine blade 10 extends from the leading edge 18 to the trailing edge 20 in a generally transverse or chordwise direction. While the serrations in Fig. 2 are depicted as being arranged along an outboard portion of the blade, it is recognised that the serrations may be arranged for instance closer to the root of the blade 10, or that they may be arranged along for instance the entire airfoil region 34 of the blade 10. According to the inventions, the serrations are provided in form of serrated panels 70, 70' that are attached to a surface of the blade 10 at the trailing edge 20 of the blade 10. The serrated panels 70, 70' may comprise serrations having different sizes. The serrations near the tip of the blade 10 may for instance as shown in Fig. 2 have smaller dimensions than serrations closer to the root of the blade 10.

[0048] The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 is typically constant along the entire root area 30. The transition region 32 has a transitional profile 42 gradually changing from the circular or elliptical shape 40 of the root region 30 to the airfoil profile 50 of the airfoil region 34. The chord length of the transition region 32 typically increases substantially linearly with increasing distance / -from the hub.

[0049] The airfoil region 34 has an airfoil profile 50 with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance / ■from the hub.

[0050] It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and / or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and / or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

[0051] Fig. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during use - i.e. during rotation of the rotor - normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

[0052] Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position <7 / of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position dt of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness ( / c is given as the ratio between the local maximum thickness (and the local chord length c. Further, the position dPof the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

[0053] Fig. 4 shows some other geometric parameters of the blade. The blade has a total blade length L. As shown in Fig. 2, the root end is located at position r = 0, and the tip end located at r = L. The shoulder 40 of the blade is located at a position r = Ln, and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. Further, the blade is provided with a pre-bend, which is defined as Ay, which corresponds to the out-of-plane deflection from a pitch axis 22 of the blade.

[0054] The wind turbine blade 10 generally comprises a shell made of fibre-reinforced polymer and is typically made as a pressure side or upwind shell part 24 and a suction side or downwind shell part 26 that are glued together along bond lines 28 extending along the trailing edge 20 and the leading edge 18 of the blade 10. Wind turbine blades are generally formed from fibre-reinforced plastics material, e.g. glass fibres and / or carbon fibres which are arranged in a mould and cured with a resin to form a solid structure. Modern wind turbine blades can often be more than 50 metres, and even 100 metres, in length, having blade root diameters of several metres. Wind turbine blades are generally designed for relatively long lifetimes and to withstand considerable structural and dynamic loading.

[0055] Figs. 5 and 6 show two views of a serrated panel 70, where Fig. 5 illustrates the serrated panel in perspective and Fig. 6 shows a top view of the serrated panel 70. The serrated panel 70 is configured to be attached to the trailing edge 20 of the wind turbine blade 10 to form a plurality of serrations 80 at the trailing edge 20 of the wind turbine blade 10. As illustrated in Figs. 2 and 3, the serrated panel 70 is arranged such that the serrations 80 extend from the trailing edge 20 of the wind turbine blade 10. The serrated panel 70 comprises a base part 72 for attachment to the trailing edge 20 of the wind turbine blade 10. The base part 72 comprises a first longitudinal end 73 for arrangement nearest the tip end 14 of the wind turbine blade 10, a second longitudinal end 74 for arrangement nearest the root end 16 of the wind turbine blade, a first side 75 for arrangement nearest the leading edge 18 of the blade 10, and a second side 76 for arrangement farthest from the leading edge 18 of the blade 10. The serrated panel 70 further comprises a plurality of serrations 80 extending from the second side 76 of the base part 72. Each serration 80 comprises a base portion 81 proximal to the second side 76 of the base part 72, an apex portion 82 distal to the second side 76 of the base part (72), a first side portion 83 arranged nearest the first longitudinal end 73 of the base part 72, and a second side portion 84 arranged nearest the second longitudinal end 74 of the base part 72.

[0056] Each of the serrations 80 have a corrugated cross-sectional profile with alternating grooves 85 and ridges 86 as seen in a transverse direction between the first side portion 83 and the second side portion 84 along at least a mid-range portion 87 of the serration 80. The mid-range portion 87 is arranged between the base portion 81 and the apex portion 82. The corrugated cross-sectional profile at the mid-range portion 87 comprises at least one groove 85 and one ridge 86, preferably a plurality of both grooves 85 and ridges 86. In the illustrated example in Fig. 6, the corrugated design comprises four grooves 85 and three ridges 86 along the mid-range portion 87 of the serrations 80, which is aligned along the line B-B. It is noted that the corrugated cross-sectional profile entails that the serrations 80 have a number of grooves 85 and ridges 86, respectively, as seen from one surface side of the serrations, e.g. the pressure side of the serrations, that coincides with corresponding ridges and grooves, respectively, as seen from the opposite surface side of the serrations, e.g. from the suction side of the serrations. Accordingly, the design has four ridges and three grooves as seen from the other side of the serrated panel 70.

[0057] In the shown example, the grooves 85 and valleys 86 are aligned parallel to each other, which means that the number of grooves 85 and valleys 86 are fewer near the apex portion 82 of the serration 80 than at the base portion 81 of the serration.

[0058] It is noted that the base part 72 of the serrated panel 70 is preferably substantially flat or planar, such that a surface of the base part 72 of the serrated panel can be attached to a surface of the wind turbine blade 10, e.g. on the suction side or the pressure side of the blade 10. Alternatively, the base part 72 may be sandwiched between shell parts of the blade 10 at the trailing edge. However, it is also recognised that other variations for attaching the serrated panel may be employed. The base part 72 may for instance have a substantially V-shaped or U-shaped part, such that it can be attached to both the pressure side and suction side of the blade 10. It is noted that the base part may alternatively be partially covered with grooves and ridges (preferably of a smaller amplitude) and that gaps between base part and the blade surface be filled with glue for employing the full surface for adhesion.

[0059] The serrations 80 may be generally aligned in the same plane as the base part 72 of the serrated panel 70, or the serrations 80 may be angled compared to a plane of the base part 72 of the serrated panel 80.

[0060] By using the corrugated design, it is possible to provide relatively thin serrations 80 that are stiffer and reduce the risk of vibrations, which in turn lead to longer fatigue life. By letting the cross- sectional profile of the serrations being corrugated, a larger effective plate thickness is achieved. This increases the bending stiffness as well as the eigenfrequency of the serrations without using noticeably more material or having to introduce significant changes to the process for manufacturing the serrated panels. Further, it has been found that the corrugated cross-sectional profile can further reduce noise emissions. Accordingly, the design has been found to increase the lifetime of the serrated panels while improving the acoustic properties. Further, the serrated panel 70 may easily be manufactured via for instance vacuum forming or thermoforming, e.g. from a flat panel, or be injection moulded.

[0061] Preferably, the serrations 80 are designed with a substantially uniform thickness, although the edges of the serrations 80 may be chamfered or rounded.

[0062] In a preferred embodiment, each serration 80 transitions from a flat or planar cross-sectional profile at the base portion 81 of the serration 80 to the corrugated cross-sectional profile at the mid-range portion 87 of the serration 80. This ensures that the serrated panel can be formed such that most of the base part 72 is substantially planar, thereby facilitating attachment to the trailing edge 20 of the wind turbine blade 10. Accordingly, the amplitudes of the grooves 85 and ridges may vary in the length direction (as seen in direction from the base portion 81 to the apex portion 82) of the serration 80. Fig. 7 illustrates examples of how the amplitude of a groove 85 or ridge 86 may vary in the length direction. In the example illustrated in Fig. 7 (a), the amplitude transitions from a zero amplitude at the base portion 81 of the serration to a local maximum amplitude at a middle portion, e.g. at the mid-range portion 87, and back to a zero amplitude at the distal end of the groove 85 or ridge 86, e.g. at the apex portion 82 of the serration. In a second example, illustrated in Fig. 7 (b), the amplitude transitions from a zero amplitude at the base portion 81 of the serration to a local maximum amplitude at a middle portion, e.g. at the mid-range portion 87, of the serration. From the middle portion and towards the distal end, e.g. at the apex portion 82 of the serration 80, the amplitude is substantially constant. In a third example, illustrated in Fig. 7 (c), the amplitude transitions from a zero amplitude at the base portion 81 of the serration to a local maximum amplitude at a middle portion, e.g. at the mid-range portion 87, of the serration, and then decreases to a finite amplitude at the distal end, e.g. at the apex portion 82 of the serration 80.

[0063] The alternating grooves 85 and ridges 86 may also have various designs as illustrated in Fig. 8. It is seen that the amplitude A (as seen as a ridge-to-groove amplitude) may vary in the transverse direction. It is also seen that the serrations 80 may be designed with different periods A for the alternating grooves 85 and ridges 86. The illustrated designs may for instance be at the mid-range portion 87 of the serrations 80.

[0064] As illustrated in Fig. 8 (a) and Fig. 8 (c), the grooves 85 and ridges 86 may have substantially identical amplitudes as seen in the transverse direction between the first side portion 83 and the second side portion 84 of the serrations. As illustrated in Fig. 8 (a), the corrugations (i.e. grooves 85 and ridges) may have a relatively small period or equivalently a high spatial frequency, or they may as shown in Fig. 8 (c) have a relatively large period or equivalently a small spatial frequency. In the two shown examples, envelopes drawn between tips or the amplitude portions of the grooves and ridges, respectively, are substantially parallel.

[0065] As illustrated in Fig. 8 (b) and Fig. 8 (d), amplitudes of the grooves 85 and ridge 86 are decreasing in the transverse direction from a central position and towards the first side portion and the second side portion, respectively. Accordingly, envelopes (illustrated with the dashed lines) drawn between tips or the amplitude portions of the grooves and ridges, respectively, are converging towards the first side portion 83 and the second side portion 84, respectively.

[0066] As illustrated in Fig. 8 (e), the corrugated design may also have a non-symmetrical design. In the shown embodiment, the corrugated design has only a single groove and a single ridge.

[0067] According to a preferred embodiment, the maximum amplitude of a groove 85 or ridge 86 is 2-20 times greater, preferably 2-10 times greater, e.g. around 5 times greater than the thickness t of the serration 80. Further, the alternating grooves 85 and ridges 86 preferably have a period A, which is 3-20 times greater, preferably 4-15 times greater, and more preferably 5-10 times greater than the thickness t of the serration 80. The thickness t of each serration 80 is preferably in the range 0.5 mm - 10 mm, more preferably 0.7 mm - 5.0 mm, and even more preferably 1.0 mm - 3.0 mm. In the illustrated example in Figs. 5 and 6, the grooves 85 and ridges 86 are aligned parallel to each other, e.g. along a notional line extending between a midpoint of the base portion 81 and the apex portion 82 of the serration. When mounted to the blade, they may thus be aligned parallel to the local chord or substantially normal to the local trailing edge. However, other designs may also be contemplated. The serrations may for instance be aligned in other directions or have a converging design as illustrated in Fig. 9. In the shown example, the grooves and ridges are aligned parallel to the first side portion and the second side portion, such that they meet or merge at a notional line extending between a midpoint of the base portion and the apex portion or tip of the serration. However, other designs are also be contemplated.

[0068] In the previous embodiments, the serrations 80 are provided as part of a serrated panel 70. However, it is also contemplated that the serrations 80 can be formed as an integral part of the blade 10, e.g. by having the serrations formed as part of e.g. a suction side or downwind shell part of the blade 10 or a pressure side or upwind shell part of the blade 10.

[0069] Exemplary embodiments of the present disclosure are set out in the following items:

[0070] 1. A serrated panel (70) for a wind turbine blade (10), wherein the serrated panel (70) is configured to be attached to the trailing edge (20) of the wind turbine blade (10) to form one or more, preferably a plurality of, serrations (80) at the trailing edge (20) of the wind turbine blade (10), wherein the serrated panel comprises: a base part (72) for attachment to the trailing edge (20) of the wind turbine blade (10), the base part (72) comprising: a first longitudinal end (73) for arrangement nearest a tip end of the wind turbine blade, a second longitudinal end (74) for arrangement nearest a root end of the wind turbine blade, a first side (75) for arrangement nearest a leading edge of the blade, and a second side (76) for arrangement farthest from the leading edge of the blade, and one or more, preferably a plurality of, serrations (80) extending from the second side (76) of the base part (72), wherein each serration (80) comprises: a base portion (81) proximal to the second side (76) of the base part (72), an apex portion (82) distal to the second side (76) of the base part (72), a first side portion (83) arranged nearest the first longitudinal end (73) of the base part (72), and a second side portion (84) arranged nearest the second longitudinal end (74) of the base part (72), wherein each of the serrations (80) have a corrugated cross-sectional profile with alternating grooves (85) and ridges (86) as seen in a transverse direction between the first side portion (83) and the second side portion (84) along at least a mid-range portion (87) between the base portion (81) and the apex portion (82), wherein the corrugated cross-sectional profile at the mid-range portion (87) comprises at least one groove (85) and one ridge (86), preferably a plurality of both grooves (85) and ridges (86).

[0071] 2. A serrated panel (70) according to item 1, wherein each serration (80) has a substantially uniform thickness.

[0072] 3. A serrated panel (70) according to any of items 1-2, wherein each serration (80) is formed as a corrugated sheet.

[0073] 4. A serrated panel (70) according to any of items 1-3, wherein the corrugated cross-sectional profile is formed such that grooves and ridges, respectively, as seen from one surface side of the serrations, e.g. a pressure side of the serrations, coincides with corresponding ridges and grooves, respectively, as seen from the opposite surface side of the serrations, e.g. from a suction side of the serrations.

[0074] 5. A serrated panel (70) according to any of items 1-4, wherein each serration (80) transitions from a flat cross-sectional profile at the base portion (81) of the serration to the corrugated cross- sectional profile at the mid-range portion (87) of the serration.

[0075] 6. A serrated panel (70) according to any of items 1-5, wherein amplitudes of the grooves (85) and ridge(s) are locally increasing between a point on the base portion (81) of the serration and the mid-range portion (87) of the serration.

[0076] 7. A serrated panel (70) according to any of items 1-6, wherein amplitudes of the grooves (85) and ridge(s) are locally decreasing towards the apex portion (82) of the serration. 8. A serrated panel (70) according to any of items 1-6, wherein amplitudes of the grooves (85) and ridge(s) are substantially constant between the mid-range portion (87) of the serration and the apex portion (82) of the serration.

[0077] 9. A serrated panel (70) according to any of items 1-8, wherein a cross-sectional profile at the base portion (81) of the serration is substantially flat.

[0078] 10. A serrated panel (70) according to any of items 1-9, wherein the grooves (85) and ridge(s) are substantially parallel.

[0079] 11. A serrated panel (70) according to any of items 1-10, wherein grooves (85) and ridge(s) are aligned to merge along a line extending between the base portion (81) of the serration to the apex portion of the serration, e.g. wherein the line is aligned between a midpoint of the base portion (81) and an apex of the serration.

[0080] 12. A serrated panel (70) according to any of items 1-11, wherein the alternating of the grooves (85) and ridges have substantially identical amplitudes as seen in the transverse direction between the first side portion (83) and the second side portion (84) of the serrations.

[0081] 13. A serrated panel (70) according to any of items 1-11, wherein amplitudes of the grooves (85) and ridge(s) are decreasing in the transverse direction along at least a mid-range portion of the serration from a central position and towards the first side portion (83) and the second side portion (84), respectively.

[0082] 14. A serrated panel (70) according to any of items 1-13, wherein a maximum amplitude of a groove or ridge is 2-10 times greater, preferably 2-5 times greater, e.g. around 3 times greater than a thickness of the serration.

[0083] 15. A serrated panel (70) according to any of items 1-14, wherein the alternating grooves (85) and ridges have a period, which is 3-20 times greater, preferably 4-15 times greater, and more preferably 5-10 times greater than a thickness of the serration.

[0084] 16. A serrated panel (70) according to any of items 1-15, wherein a thickness of each serration is in the range 0.5 mm - 10 mm, preferably 0.7 mm - 5.0 mm, more preferably 1.0 mm - 3.0 mm. 17. A wind turbine blade (10) having a profiled contour including a pressure side and a suction side as well as having a leading edge (18) and a trailing edge (20) with a chord having a chord length extending therebetween, the wind turbine blade (10) extending in a spanwise direction between a root end and a tip end, where the wind turbine blade (10) comprises one or more, preferably a plurality of, serrations (80) extending from the trailing edge (20) of the wind turbine blade (10), wherein each serration (80) comprises: a base portion (81) arranged nearest the leading edge (18) of the wind turbine blade, an apex portion (82) arranged farthest from the leading edge (18) of the wind turbine blade (10), a first side portion (83) arranged nearest the tip end of the wind turbine blade (10), and a second side portion (84) arranged nearest the root of the wind turbine blade (10), wherein each of the serrations have a corrugated cross-sectional profile with alternating grooves (85) and ridges (86) as seen in a transverse direction between the first side portion (83) and the second side portion (84) along at least a mid-range portion (87) between the base portion (81) and the apex portion (82), wherein the corrugated cross-sectional profile at the mid-range portion comprises at least one groove (85) and one ridge (86), preferably a plurality of both grooves (85) and ridges (86).

[0085] 18. A wind turbine blade (10) according to item 17, wherein the plurality of serrations exhibits any of the characteristics according to any of items 2-16.

[0086] 19. A wind turbine blade (10) according to item 17, wherein the plurality of serrations is provided by one or more serrated panels according to any of items 1-16, attached to the wind turbine blade.

Claims

CLAIMS1. A serrated panel (70) for a wind turbine blade (10), wherein the serrated panel (70) is configured to be attached to the trailing edge (20) of the wind turbine blade (10) to form one or more, preferably a plurality of, serrations (80) at the trailing edge (20) of the wind turbine blade (10), wherein the serrated panel comprises: a base part (72) for attachment to the trailing edge (20) of the wind turbine blade (10), the base part (72) comprising: a first longitudinal end (73) for arrangement nearest a tip end of the wind turbine blade, a second longitudinal end (74) for arrangement nearest a root end of the wind turbine blade, a first side (75) for arrangement nearest a leading edge of the blade, and a second side (76) for arrangement farthest from the leading edge of the blade, and one or more, preferably a plurality of, serrations (80) extending from the second side (76) of the base part (72), wherein each serration (80) comprises: a base portion (81) proximal to the second side (76) of the base part (72), an apex portion (82) distal to the second side (76) of the base part (72), a first side portion (83) arranged nearest the first longitudinal end (73) of the base part (72), and a second side portion (84) arranged nearest the second longitudinal end (74) of the base part (72), wherein each of the serrations (80) have a corrugated cross-sectional profile with alternating grooves (85) and ridges (86) as seen in a transverse direction between the first side portion (83) and the second side portion (84) along at least a mid-range portion (87) between the base portion (81) and the apex portion (82), wherein the corrugated cross-sectional profile at the mid-range portion (87) comprises at least one groove (85) and one ridge (86), preferably a plurality of both grooves (85) and ridges (86).

2. A serrated panel (70) according to claim 1, wherein each serration (80) has a substantially uniform thickness.

3. A serrated panel (70) according to any of claims 1-2, wherein each serration (80) is formed as a corrugated sheet.

4. A serrated panel (70) according to any of claims 1-3, wherein the corrugated cross-sectional profile is formed such that grooves and ridges, respectively, as seen from one surface side of the serrations, e.g. a pressure side of the serrations, coincides with corresponding ridges and grooves, respectively, as seen from the opposite surface side of the serrations, e.g. from a suction side of the serrations.

5. A serrated panel (70) according to any of claims 1-4, wherein each serration (80) transitions from a flat cross-sectional profile at the base portion (81) of the serration to the corrugated cross- sectional profile at the mid-range portion (87) of the serration.

6. A serrated panel (70) according to any of claims 1-5, wherein amplitudes of the grooves (85) and ridge(s) are locally increasing between a point on the base portion (81) of the serration and the mid-range portion (87) of the serration.

7. A serrated panel (70) according to any of claims 1-6, wherein amplitudes of the grooves (85) and ridge(s) are locally decreasing towards the apex portion (82) of the serration.

8. A serrated panel (70) according to any of claims 1-6, wherein amplitudes of the grooves (85) and ridge(s) are substantially constant between the mid-range portion (87) of the serration and the apex portion (82) of the serration.

9. A serrated panel (70) according to any of claims 1-8, wherein a cross-sectional profile at the base portion (81) of the serration is substantially flat.

10. A serrated panel (70) according to any of claims 1-9, wherein the grooves (85) and ridge(s) are substantially parallel.

11. A serrated panel (70) according to any of claims 1-10, wherein grooves (85) and ridge(s) are aligned to merge along a line extending between the base portion (81) of the serration to the apex portion of the serration, e.g. wherein the line is aligned between a midpoint of the base portion (81) and an apex of the serration.

12. A serrated panel (70) according to any of claims 1-11, wherein the alternating of the grooves (85) and ridges have substantially identical amplitudes as seen in the transverse direction between the first side portion (83) and the second side portion (84) of the serrations.

13. A serrated panel (70) according to any of claims 1-11, wherein amplitudes of the grooves (85) and ridge(s) are decreasing in the transverse direction along at least a mid-range portion of the serration from a central position and towards the first side portion (83) and the second side portion(84), respectively.

14. A serrated panel (70) according to any of claims 1-13, wherein a maximum amplitude of a groove or ridge is 2-10 times greater, preferably 2-5 times greater, e.g. around 3 times greater than a thickness of the serration.

15. A serrated panel (70) according to any of claims 1-14, wherein the alternating grooves (85) and ridges have a period, which is 3-20 times greater, preferably 4-15 times greater, and more preferably 5-10 times greater than a thickness of the serration.

16. A serrated panel (70) according to any of claims 1-15, wherein a thickness of each serration is in the range 0.5 mm - 10 mm, preferably 0.7 mm - 5.0 mm, more preferably 1.0 mm - 3.0 mm.

17. A wind turbine blade (10) having a profiled contour including a pressure side and a suction side as well as having a leading edge (18) and a trailing edge (20) with a chord having a chord length extending therebetween, the wind turbine blade (10) extending in a spanwise direction between a root end and a tip end, where the wind turbine blade (10) comprises one or more, preferably a plurality of, serrations (80) extending from the trailing edge (20) of the wind turbine blade (10), wherein each serration (80) comprises: a base portion (81) arranged nearest the leading edge (18) of the wind turbine blade, an apex portion (82) arranged farthest from the leading edge (18) of the wind turbine blade (10), a first side portion (83) arranged nearest the tip end of the wind turbine blade (10), and a second side portion (84) arranged nearest the root of the wind turbine blade (10), wherein each of the serrations have a corrugated cross-sectional profile with alternating grooves (85) and ridges (86) as seen in a transverse direction between the first side portion (83) and the second side portion (84) along at least a mid-range portion (87) between the base portion (81) and the apex portion (82), wherein the corrugated cross-sectional profile at the mid-range portion comprises at least one groove (85) and one ridge (86), preferably a plurality of both grooves(85) and ridges (86).

18. A wind turbine blade (10) according to claim 17, wherein the plurality of serrations exhibits any of the characteristics according to any of claims 2-16.

19. A wind turbine blade (10) according to claim 17, wherein the plurality of serrations is provided by one or more serrated panels according to any of claims 1-16, attached to the wind turbine blade.

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