Noise reduction device for a wind turbine blade, wind turbine blade, wind turbine and method for noise reduction of a wind turbine blade

Abstract

Noise reduction device for a wind turbine blade, wind turbine blade, wind turbine and method for noise reduction of a wind turbine blade. Noise reduction device for a wind turbine blade (2) comprising an active noise reduction apparatus (8) and a passive noise reduction apparatus (7), wherein the passive noise reduction apparatus (7) comprises at least one serrated edge profile (9) adapted to be fixed to a trailing edge (4) of the wind turbine blade (2), wherein the active noise reduction apparatus (8) comprises at least one unsteady pressure sensor (10) adapted to generate an output signal corresponding to a turbulent flow state during operation of the wind turbine blade (2), at least one actuator (11), and a control unit (12), wherein the sensor (10) is arranged adjacent to a serrated edge (14) of the serrated edge profile (9) and the control unit (12) is adapted to control the actuator (11) in dependence of the output signal of the sensor (10) to emit an anti-noise signal at least partially reducing the noise generated by the wind turbine blade (2).

Description

TECHNICAL FIELD

[0001] The present invention relates to a noise reduction device for a wind turbine blade, the noise reduction device comprising an active noise reduction apparatus and a passive noise reduction apparatus, wherein the passive noise reduction apparatus comprises at least one serrated edge profile adapted to be fixed to a trailing edge of a wind turbine blade. Furthermore, the present invention also relates to a wind turbine blade, a wind turbine and a method for noise reduction of a wind turbine blade. BACKGROUND

[0002] Trailing edge noise emitted from a wind turbine blade during operation of a wind turbine is a major noise generation mechanism of modern industrial scale wind turbines. The noise generated from a wind turbine during operation determines the area in which a wind turbine can be erected, or correspondingly the way in which the machine can be operated, in order to comply with noise limits in the surroundings of the wind turbine.

[0003] The emission of excessive noise during operation of a wind turbine can result in the wind turbine having to be operated in a reduced mode of operation, wherein power generation is sacrificed in order to limit noise emissions. Thus, the noise emissions of a wind turbine can directly affect its economic viability. Therefore, there is a demand for noise reduction technology, in particular for noise reduction technology for onshore wind turbines. One method for limiting the noise emitted by a wind turbine blade is to use serrations at the trailing edge of the wind turbine blade to passively reduce the noise emitted at the trailing edge. In the prior art, further methods have been considered to reduce the noise of a wind turbine, in particular the noise of the wind turbine blades of a wind turbine.

[0004] In EP 3 249 216 A1 a rotor blade with a noise reduction device is described. The rotor blade comprises at least one sensor for detecting flow characteristics of a fluid flowing substantially from a leading edge to a trailing edge of the rotor blade. The rotor blade further comprises at least one actuator for generating an anti-noise signal for at least partially cancelling a flow-induced edge noise of the rotor blade.

[0005] WO 2008 / 043874 A1 discloses a system for suppressing and cancelling noise in a wind turbine, wherein the system comprises a plurality of microphones disposed on a tower and a span of a blade. Microphones on the blade measure near field turbulent pressure fluctuations and microphones on the tower measure the acoustic far field noise generated by the turbulent flow past the trailing edge of the blade. Based on the signals captured by these microphones, loudspeakers located at the blade are activated to cancel the noise generated by the rotor.

[0006] US 2013 / 0164135 A1 discloses a system and method for actively suppressing the noise signature of a noise-emitting component from a wind turbine. Therefore, an active noise measuring device is used which is capable of measuring the original noise signature of the noise-emitting wind turbine component. Based on the measured noise signature, a counter noise signature is created and amplified using an amplifier in order to emit it using at least one loudspeaker. SUMMARY

[0007] It is an object of the present invention to provide an improved noise reduction device for a wind turbine blade.

[0008] According to the invention, this object is solved by a noise reduction device as initially described, wherein the active noise reduction device comprises at least one unsteady pressure sensor adapted to generate an output signal corresponding to a turbulent flow condition during operation of the wind turbine blade, at least one actuator, and a control unit, wherein the sensor is arranged adjacent to the serrated edge of the serrated trailing edge profile and the control unit is adapted to control the actuator depending on the output signal of the sensor to emit an anti-noise signal at least partially reducing the noise generated by the wind turbine blade.

[0009] The noise reduction device according to the invention combines the serrated trailing edge profile as passive noise reduction device with an active noise reduction device comprising at least an unsteady pressure sensor or a corresponding at least one acoustic sensor, a control unit and at least one actuator. By arranging the at least one sensor adjacent to the serrated edge of the serrated trailing edge profile, it is possible to achieve an active noise reduction corresponding to the noise generated by the turbulent flow condition at the serrated edge. In addition, the noise reduction effects of both the active noise reduction device and the passive noise reduction device are combined, so that an improved noise reduction achieved by the noise reduction device is obtainable. The noise reduction device can be regarded as a kind of combined noise reduction system.

[0010] Theories and experimental results have shown that an active noise reduction device can achieve a reduction of approximately 6 dB at its most effective frequency or respectively as maximum attenuation. In order to further increase the reduction of the noise generated by the wind turbine, it can be advantageous to use a combination of the active noise reduction device and the serrated trailing edge profile as passive noise reduction device, because for a serrated trailing edge a noise reduction of up to 10 dB at its most effective frequency is obtainable. Arranging the at least one sensor and the serrated edge of the serrated trailing edge profile allows the anti-noise signal to be specifically adapted to the serrated trailing edge profile and thus creates a synergistic effect which improves the overall noise reduction capability of the noise reduction device.

[0011] When using an active noise reduction device in combination with a serrated edge profile as a passive noise reduction device, the number of sensors required to obtain a certain noise reduction at a given location in the far field can be reduced compared to using only an active noise reduction device. Since the performance of an active noise reduction device depends on both the number of sensors and their spacing, the spacing between the sensors can also be larger in combination with a serrated edge, thereby facilitating the manufacturing of the noise reduction device and reducing its cost.

[0012] The noise reduction device can be attached to a wind turbine to reduce the noise generated by the wind turbine blades during operation, thus in the mounted state of the wind turbine blades when the wind flows over the profile of the wind turbine blades, in particular when the rotor is rotating. The anti-noise signal is in particular generated and emitted in such a way that the noise in the far field, thus in at least one location or area in the surrounding environment of the wind turbine that is affected by the noise of the wind turbine, for example in the downwind direction where the noise propagates most efficiently, is reduced. The far field refers to the area outside the turbulent air flow around the airfoil / blade, where the pressure changes include in particular sound waves that propagate efficiently and are acoustically perceptible as noise. By reducing the far field noise of the wind turbine, the impact of the noise on the surrounding environment of the wind turbine can be minimized.

[0013] The noise reduction device can be included in the wind turbine blade during the manufacturing of the wind turbine blade or it can be provided as an additional kit that can be modified accordingly to an existing wind turbine or its wind turbine blades for reducing the noise generated during its operation. Thus, the serrated edge profile comprising the at least one sensor of the active noise reduction device, the control unit and the at least one actuator can be mounted to the wind turbine blade, wherein the at least one sensor and the at least one actuator are connected to the control unit of the active noise reduction device.

[0014] In a preferred embodiment of the present application, the active noise reduction device comprises a plurality of sensors, wherein the sensors are arranged next to the serrated edge, in particular in one or more rows, wherein each row has a constant or substantially constant distance between the serrated edge and each sensor of the row, and / or in one or more rows, wherein each row has a varying distance between the serrated edge and each sensor of the row. The plurality of sensors is in particular arranged in one or more rows along the spanwise direction of the serrated trailing edge profile, wherein in each row, in particular within the constant or substantially constant distance between each sensor and the serrated edge profile of the serrated edge, the sensors follow the course of the serrated edge. Additionally or alternatively, the sensors can also be arranged in one or more rows, wherein the distance between each sensor of the row and the serrated edge is varying, for example depending on the spanwise position of the sensor, so that the sensors are closer to the serrated edge when the fluid flow at the position of the sensor is lower. The sensors following the serrated edge can be considered to be arranged along a non-linear path at the trailing edge of the wind turbine, wherein the path can accordingly serve as a reference for determining the generated noise or anti-noise signal. By the plurality of unsteady pressure sensors, the unsteady flow conditions at the serrated edge, in particular the pressure of the fluid flowing along the wind turbine blade, can be recorded with a spatial resolution defined by the position of the sensors along the path.

[0015] According to the present application, the spacing between two adjacent sensors next to the serrated edge is uniform or non-uniform. In a uniform spacing, the distance between two adjacent sensors can be equal or substantially equal for all pairs of adjacent sensors. The uniform spacing of the plurality of sensors enables a uniform measurement of the acoustic properties along a reference path following the serrated edge. In a non-uniform sensor spacing, pairs of adjacent sensors of the plurality of sensors can comprise different distances between the sensors along a path extending next to the serrated edge and following the shape of the serrated edge. The non-uniform sensor spacing can facilitate a spatial filtering of the turbulent flow along the blade surface.

[0016] In a preferred embodiment of the present application, the serrated edge profile comprises a plurality of teeth, in particular a plurality of triangular teeth, forming the serrated edge. The triangular teeth of the serrated edge profile can be positioned directly next to each other, so that a sawtooth profile of the serrated edge is obtained. It is also possible that two adjacent teeth of the serrated edge profile are arranged spaced apart, so that a straight trailing edge section is obtained between the two adjacent teeth. Additionally or as an alternative to the triangular teeth, other shapes of the teeth are also possible.

[0017] Preferably, the serrated edge profile comprises at least one flow traversable structure, in particular a comb structure and / or a porous structure, arranged between two adjacent teeth. These teeth are solid structures which are not traversable by a fluid flow. By providing a flow traversable structure like a comb structure or a porous structure between two adjacent teeth, the noise reduction of the serrated edge profile can be increased, and thus, by using a serrated edge profile with a comb structure, a higher level of noise attenuation can be achieved.

[0018] In a preferred embodiment of the present application, the at least one actuator is arranged on a base plate which can be attached to the wind turbine blade and / or on the arrangement portion of the serrated edge profile. The control unit can for example be arranged on or in the base plate, but also in the hollow cavity of the wind turbine blade and / or in the serrated edge profile. The actuator or a part of the actuator can accordingly be arranged on the arrangement portion of the serrated edge profile. Additionally or alternatively, the actuator or a part of the actuator can be arranged on a separate base plate which can be attached to the wind turbine blade.

[0019] It is possible that the sensors, the control unit and the actuator at the serrated edge profile are connected using a connection means like a cable, a wireless connection, after the noise reduction device has been installed as an add-on to the wind turbine blade or accordingly during the manufacturing process of the wind turbine blade.

[0020] Preferably, the actuator comprises a loudspeaker and / or the sensor comprises a pressure sensor, in particular an unsteady surface pressure sensor, an optical unsteady pressure sensor and / or a microphone. By this sensor, the local pressure, in particular of a fluid like air or wind flowing along the wind turbine blade, is measured, so that information about the turbulent pressure field at the trailing edge can be collected. By providing an output signal of the sensor corresponding to the measured pressure, these pressures can be used to determine the noise generation at the trailing edge in the control unit. An anti-noise signal corresponding to this noise generation can then be determined by the control unit for at least partially reducing the noise generated by the wind turbine blade. The anti-noise signal can be emitted using the loudspeaker as actuator for generating the overall noise signal. It is possible that the one or more actuators and / or the control unit comprise an amplifier for emitting the anti-noise signal with a sufficient signal level.

[0021] Preferably, the control unit is adapted to use a transfer function describing a relationship between the output signal of the sensor at the serrated edge, in particular a filtered combination of the output signals of a plurality of sensors, and a far field noise for determining the anti-noise signal. Since the noise reduction should preferably be applied to a far field in the surrounding of the wind turbine, a transfer function describing a relationship between the output signal of the sensor at the serrated edge, thus in particular the surface pressure measured by the unsteady pressure sensor, can be used to determine the noise generation at the serrated edge, in particular to determine a three-dimensional sound field generated at the serrated edge. Based on this sound field, the anti-noise signal to be emitted by the at least one actuator can be determined in order to provide a desired noise reduction of the far field noise in a feed-forward process. It is possible that a sum of the output signals of the sensors in the vicinity of the actuator or a filtered combination of the output signals is used to determine the anti-noise signal to be emitted by the actuator.

[0022] Preferably, the transfer function is adapted to the serrated edge profile, in particular to the noise generation characteristics of the serrated edge profile. The noise generation at the serrated edge of a serrated edge profile depends on the shape of the serrated edge and can significantly differ from the noise generation at a straight trailing edge, such that the noise radiation characteristics of a trailing edge comprising a serrated edge profile significantly differ from the noise radiation characteristics of a straight trailing edge. By adapting the control unit to the noise generation characteristics of the serrated edge profile, an improved noise reduction can be obtained using the described noise reduction device.

[0023] Preferably, the transfer function is empirically determined by at least one measurement and / or the transfer function is stored in a data storage unit of the active noise reduction device. The data storage unit may, for example, be part of the control unit or it can be connected to the control unit accordingly. Since the noise generation by the fluid flowing over the serrated edge can be difficult to analytically describe, it can be advantageous to empirically determine the transfer function for determining the required anti-noise signal using measurements.

[0024] The transfer function may, for example, be determined using measurements in an acoustic wind tunnel. Advantageously, a modelling of the wind turbine blade and of the physical relationships at the serrated edge in the controller, so-called plant modelling, can be avoided, since it is possible to determine the noise generated by the serrated edge using the empirically determined transfer function. Advantageously, a modelling of the acoustic scattering effects at the serrated trailing edge, which is difficult to analytically describe and can at least partially depend on not fully established physical models, can be avoided or at least partially avoided. The transfer function depends on physical parameters such as flow velocity and local angle of attack, so the transfer function can be empirically determined at a specific operating point and generalized using an analytical model.

[0025] The wind turbine blade according to the present application comprises at least one noise reduction device according to the present application.

[0026] The wind turbine according to the present application comprises at least one wind turbine blade according to the present application.

[0027] All details and advantages of the noise reduction device according to the present application correspondingly apply to the wind turbine blade and the wind turbine according to the present application.

[0028] The method for noise reduction for a wind turbine blade according to the present application uses an active noise reduction device and a passive noise reduction device, wherein the passive noise reduction device comprises at least one serrated edge profile adapted to be fixed to a trailing edge of the wind turbine blade, wherein the active noise reduction device comprises at least one unsteady pressure sensor adapted to generate an output signal corresponding to a turbulent flow state during operation of the wind turbine blade, at least one actuator, and a control unit, wherein the sensor is arranged adjacent to a serrated edge of the serrated edge profile and the control unit controls the actuator depending on the output signal of the sensor to emit an anti-noise signal at least partially reducing the noise generated by the wind turbine blade.

[0029] In a preferred embodiment of the present application, the control unit uses a transfer function describing a relationship between the output signal of the sensor at the serrated edge, in particular a filtered combination of the output signals of a plurality of sensors, and a far-field noise for determining the anti-noise signal.

[0030] Preferably, a transfer function adapted to the serrated edge profile, in particular to noise generation characteristics of the serrated edge profile, and / or a transfer function determined by at least one measurement and / or stored in a data storage unit of the active noise reduction device is used.

[0031] All details and advantages previously described with respect to the noise reduction device according to the present application correspondingly apply to the method for noise reduction for a wind turbine blade according to the present application. BRIEF DESCRIPTION OF DRAWINGS

[0032] Other objects and features of the present application will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the application. The drawings show:

[0033] Figure 1 : an embodiment of a wind turbine according to the present application comprising a plurality of wind turbine blades according to the present application,

[0034] Figure 2 : a first embodiment of a noise reduction device according to the present application,

[0035] Figure 3 : a second embodiment of a noise reduction device according to the present application, and

[0036] Figure 4 Flowchart of a method for noise reduction of a wind turbine blade according to the present invention. DETAILED DESCRIPTION

[0037] In Figure 1 , a wind turbine 1 is shown. The wind turbine 1 comprises a plurality of wind turbine blades 2 which are mounted to a hub 3 of the wind turbine 1. During operation of the wind turbine 1, wind flows along a contour of each wind turbine blade 2, wherein noise is generated, in particular at a trailing edge 4 of the wind turbine blade 2. This can in particular occur when the rotor comprising the wind turbine blades 2 and the hub 3 of the wind turbine 1 is rotating, in particular in order to generate electricity using a generator of the wind turbine 1.

[0038] The emitted noise is schematically depicted by a line 5 and in particular affects an environment of the wind turbine 1. In order to at least partially reduce the noise, in particular to reduce a far field noise affecting at least one location and / or area at a distance from the wind turbine 1, a noise reduction device 6 comprising both passive noise reduction equipment 7 and active noise reduction equipment 8 is used for one or more wind turbine blades 2, in particular for each wind turbine blade 2, as described in the following.

[0039] In Figure 2 , a section of a wind turbine blade 2 is shown having a first embodiment of a noise reduction device 6. The noise reduction device 6 comprises passive noise reduction equipment 7 and active noise reduction equipment 8. The passive noise reduction equipment 7 comprises a serrated edge contour 9. The passive noise reduction equipment 7 is adapted to be fixed to the trailing edge 4 of the wind turbine blade 2 such that after the fixing the trailing edge 4 of the wind turbine blade is formed by the serrated edge contour 9. The passive noise reduction equipment 7 can comprise a plurality of serrated edge contours 9 which can in particular be arranged along the entire trailing edge 4 of the wind turbine blade 2, thus from a root end at the hub 3 of the wind turbine blade 1 to a tip end of the wind turbine blade 2. The section of the wind turbine blade 2 is only shown schematically, the shape of the section of the wind turbine blade 2 can be different, in particular the section to which the noise reduction device 6 is mounted can be a tip section of the blade comprising a curved trailing edge 4. The noise reduction device 6 can in particular be mounted to an outer 10% of the blade where the flow speed of the wind on the blade and thus the noise generation is highest during operation of the wind turbine blade 2. However, in order to also reduce the noise generated at an inner section of the wind turbine blade 2, it is also possible that the noise reduction device 6 extends to the inner section of the wind turbine blade 2 and / or that a plurality of noise reduction devices 6 are arranged on the trailing edge 4 are used.

[0040] The active noise reduction device 8 accordingly comprises a plurality of unsteady sensors 10 or acoustic sensors which are adapted to generate output signals corresponding to a state of turbulence during operation of the wind turbine blade 2. The turbulence measured by the sensors 10 leads to a generation of noise during operation of the wind turbine blade 2. Furthermore, the active noise reduction device 8 comprises a plurality of actuators 11 and a control unit 12. The control unit 12 is connected to each actuator 11, as depicted by the connection 13, which can be, for example, an electrical connection. The control unit 12 is also connected to each sensor 10, wherein the connection to the sensors 10 is not shown for the sake of clarity. Besides using one or more cables to connect the sensors 10 and / or the actuators 11 to the control unit 12, a wireless connection is also possible.

[0041] The sensors 10 are arranged adjacent to the serrated edge 14 of the serrated edge profile 9. The sensors 10 are arranged next to the serrated edge 14 with a constant or substantially constant distance between the serrated edge 14 and each sensor 10.

[0042] By each sensor 10, a local pressure of a fluid, such as air or wind, at the position of the sensor 10 is accordingly measured. The sensors 10 each comprise a pressure sensor, such as a surface pressure sensor, an optical unsteady pressure sensor and / or a microphone for measuring the pressure at the serrated edge 14 of the serrated edge profile 9. Furthermore, the sensors 10 are adapted to generate an output signal corresponding to the measured pressure. The fluid pressure measured by the sensors 10 is related to a noise generation at the serrated edge profile 9 during operation of the wind turbine blade 2.

[0043] The output signal of each sensor 10 is transmitted to the control unit 12, wherein the control unit 12 is adapted to determine the noise generated from the wind turbine blade 2, in particular the far-field noise or the three-dimensional noise field, accordingly. In addition, the control unit 12 is adapted to determine an anti-noise signal which at least partially reduces the generated noise and to control the actuators 11 to generate the anti-noise signal. The actuators 11 can be, for example, loudspeakers for emitting the anti-noise signal. The control unit 12 and / or the actuators 11 can comprise an amplifier for generating the anti-noise signal with a sufficient sound level. The anti-noise signal interferes with the noise generated by the wind turbine 2, in particular the noise generated by the trailing edge 4 or the serrated edge profile 9 of the wind turbine blade 2, respectively, in order to at least partially reduce the noise in the far field in the surrounding environment of the wind turbine 1.

[0044] To determine the anti-noise signal, the control unit 12 uses a transfer function describing a relation between an output signal of the sensor 10 or a respective measured pressure at the serrated edge 9 and a far-field noise. In particular, a filtered combination of output signals of multiple sensors 10, in particular of sensors 10 in the vicinity of the actuator 11, can be used. Further, the anti-noise signal can depend on a positioning of the sensor 10 and the actuator 11 on the wind turbine 2. The transfer function used by the control unit 12 is adapted to the serrated edge profile 9, such that a noise generation by the serrated edge profile 9 can be taken into account. The noise generation can for example depend on a shape of the serrated edge profile 9, in particular of the serrated edges 14 of the serrated edge profile 9.

[0045] In this embodiment, the serrated edge profile 9 comprises a plurality of teeth 15 arranged directly adjacent to each other, forming the serrated edges 14. In addition to the active noise reduction by the active noise reduction device 8, the serrated edge profile 9 also generates a noise reduction during operation of the wind turbine blade 2. The noise can in particular be generated by a fluid flowing along the profile of the wind turbine blade 2, in particular by wind flowing from the leading edge 16 to the trailing edge 4 of the wind turbine blade 2, as indicated by arrows 17.

[0046] The actuator 11 is arranged on a base plate 18, which is attached to a surface of the wind turbine blade 2. The serrated edge profile 9 is also adapted to be fixed to the trailing edge 4 of the wind turbine blade 2, such that an existing wind turbine blade 2 can be modified using the noise generation device 6 by attaching the base plate 18 and the serrated edge profile 9 to the wind turbine blade 2. For the fixation, the serrated edge profile 9 can comprise a fixation section, for example adapted to a shape of a trailing edge portion of the wind turbine blade 2. Alternatively, the serrated edge profile 9 can be fixed to the trailing edge 4 during a manufacturing process, in particular a casting process, of the wind turbine blade 2.

[0047] The control unit 12 can for example be arranged inside the wind turbine blade 2. Alternatively, the control unit 12 can be integrated into the serrated edge profile 9 and / or in the base plate 18 carrying the actuator 11.

[0048] The sensors 10 can be arranged at a uniform distance or a non-uniform distance between each pair of adjacent sensors 10 along the serrated edges 14 of the serrated edge profile 9. The uniform or non-uniform arrangement of the sensors 10 can influence the filtered or output signals generated by the plurality of sensors 10 in the control unit 12 and can be chosen according to a shape of the serrated edge profile 9.

[0049] The transfer function used in the control unit 12 can be stored in a data storage unit of the active noise reduction device 8, in particular in a data storage unit of the control unit 12. The transfer function can be determined empirically by at least one measurement, for example by a measurement performed in an acoustic wind tunnel using the serrated edge profile 9 and / or a part of the wind turbine blade 2.

[0050] In Figure 3 , a second embodiment of the noise reduction arrangement 6 is shown. In this embodiment, the actuator 8 is arranged on the arrangement portion 19 of the serrated edge profile 9. This allows the noise reduction arrangement 6 to be provided as a single piece part, thereby facilitating the modification of the noise reduction arrangement 6 to an existing wind turbine blade 2. In this embodiment, the serrated edge 14 comprises a comb structure as flow-traversable structure 20 arranged between two adjacent teeth 15 of the serrated edge profile 9. It is also possible that, instead of at least a part of this comb structure, a porous structure is arranged between some or all pairs of adjacent teeth 15 as flow-traversable structure. By using flow-traversable structures 20 between the teeth 15 of the serrated edge profile 9, which are solid structures and thus not traversable by a fluid flow, the noise reduction achieved by the serrated edge profile 9 can be further improved. The control unit 12 of the noise reduction arrangement 6 can use a transfer function adapted to the serrated edge profile 9 in view of the noise generating properties of the serrated edge profile 9 as passive noise reduction device 7 of the noise reduction arrangement 6.

[0051] In both the first embodiment depicted in Figure 2 and the second embodiment depicted in Figure 3 , the serrated edge 9 can have different geometrical shapes. It is possible that the teeth have a shape different from the depicted triangular shape and / or that the teeth are not arranged directly adjacent to each other such that, for example, a straight trailing edge section is provided between two adjacent teeth 15. It is also possible that in each embodiment the sensors 10 are arranged in one or more rows along the serrated edge 14, wherein the distance between the sensors 10 of each row and the serrated edge 14 is constant or substantially constant. The sensors 10 or a part of the sensors 10 can also be arranged in one or more rows with a different distance between the sensors 10 of the row and the serrated edge 14 in the row. The distance between the sensors 10 can for example depend on the spanwise position of the sensors 10 such that the sensors 10 are closer to the serrated edge 14 when the fluid flow at the position of the sensors 10 is lower.

[0052] The different noise generation characteristics describing the noise generated at the serrated edge profile 9 depend accordingly on the shape of the serrated edge 14 or of its teeth 15. The noise generation characteristics used in connection with the active noise reduction device 8 can be taken into account by providing a transfer function in the control unit 12 corresponding to the serrated edge profile 9 used for determining the anti-noise signal generated by the actuator 11.

[0053] In all embodiments, the noise reduction device 6 can be formed as part of the wind turbine blade 2, in particular as a component of the wind turbine blade 2 included during the casting process of the wind turbine blade 2, or the noise generation device 6 can be retrofitted to an existing wind turbine blade 2 as an add-on similar to passive serrations or vortex generators. The fixation can occur for example by gluing or other fixation means, adhering the noise generation device 6 to the surface of the wind turbine blade 2 as an upgrade and / or retrofit procedure.

[0054] In Figure 4 , a flow chart of a method for noise reduction of a wind turbine blade is shown. The method can be performed using the noise reduction device 6 as described before.

[0055] In a first step S1, a plurality of sensors 10 arranged adjacent to the serrated edges 14 of the serrated edge profile 9 are used to generate output signals corresponding to the state of turbulence at the serrated edge profile 9 mounted to the trailing edge 4 of the wind turbine blade 2. Thus, the sensors 10 can measure for example the surface pressure of the fluid at the position of each sensor 10 and provide output signals corresponding to the measured pressure. The output signals of all sensors 10 are transmitted to the control unit 12.

[0056] In step S2, the control unit 12 receives the output signals of the sensors 10 and uses these output signals together with a transfer function describing the noise generation at the serrated edge 9 to determine for example a three-dimensional sound field generated at the serrated edge profile 9 in the current operating state of the wind turbine blade 2 described by the output signals of the sensors 10. Based on these sound fields determined by the control unit 12, an anti-noise signal is determined by the control unit 12 which can at least partially reduce the noise generated by the wind turbine blade 2 by interfering with this sound field.

[0057] In step S3, the control unit 12 controls the actuator 11 to emit this anti-noise signal for partially reducing the noise generated by the wind turbine blade 2. The method can in particular be performed as a feed-forward process by repeating steps S1 to S3 for example at regular time intervals to generate an anti-noise signal corresponding to the current noise generation conditions at the serrated trailing edge 9 described by the output signals of the sensors 10.

[0058] Although the present application has been described in detail with reference to preferred embodiments, the application is not limited to disclosed examples, and other variants will be apparent to those skilled in the art in the light of the disclosed examples, without departing from the scope of the application.

Claims

1. A noise reduction device for wind turbine blades (2), comprising an active noise reduction device (8) and a passive noise reduction device (7), wherein, The passive noise reduction device (7) includes at least one serrated edge profile (9) adapted to be fixed to the trailing edge (4) of the wind turbine blade (2), wherein the active noise reduction device (8) includes: at least one unstable pressure sensor (10) adapted to generate an output signal corresponding to a turbulent state during operation of the wind turbine blade (2); at least one actuator (11); and a control unit (12), wherein the sensor (10) is arranged adjacent to the serrated edge (14) of the serrated edge profile (9), and the control unit... The element (12) is adapted to control the actuator (11) according to the output signal of the sensor (10) to emit an anti-noise signal that at least partially reduces the noise generated by the wind turbine blade (2), wherein the active noise reduction device (8) includes a plurality of unstable pressure sensors (10), wherein the unstable pressure sensors (10) are arranged in one or more rows next to the serrated edge (14), wherein each row has a constant or substantially constant distance between the serrated edge (14) and each sensor (10) in the row.

2. The noise reduction device according to claim 1, characterized in that, The spacing between two adjacent sensors (10) next to the serrated edge (14) is uniform or non-uniform.

3. The noise reduction device according to claim 1 or claim 2, characterized in that, The serrated edge profile (9) includes a plurality of teeth (15) to form the serrated edge (14).

4. The noise reduction device according to claim 1 or claim 2, characterized in that, The serrated edge profile (9) includes a plurality of triangular teeth (15) to form the serrated edge (14).

5. The noise reduction device according to claim 3, characterized in that, The serrated profile (9) includes at least one flow-through structure (20) arranged between two adjacent teeth (15).

6. The noise reduction device according to claim 3, characterized in that, The serrated profile (9) includes a comb-like structure and / or a porous structure arranged between two adjacent teeth (15).

7. The noise reduction device according to any one of claims 1-2 and 5-6, characterized in that, The at least one actuator (11) is arranged on a substrate (18) that can be attached to the wind turbine blade (2) and / or on the arrangement portion (19) of the serrated edge profile (9).

8. The noise reduction device according to any one of claims 1-2 and 5-6, characterized in that, The actuator (11) includes a loudspeaker, and / or the sensor (10) includes a pressure sensor and / or a microphone.

9. The noise reduction device according to claim 8, characterized in that, The pressure sensor is a surface pressure sensor.

10. The noise reduction device according to any one of claims 1-2 and 5-6, characterized in that, The control unit (12) is adapted to use a transfer function describing the relationship between the output signals of the plurality of unstable pressure sensors (10) at the serrated edge (14) and far-field noise to determine the noise immunity signal.

11. The noise reduction device according to any one of claims 1-2 and 5-6, characterized in that, The control unit (12) is adapted to use a transfer function describing the relationship between a filtered combination of the output signals of the plurality of unstable pressure sensors (10) at the serrated edge (14) and far-field noise to determine the noise-resistant signal.

12. The noise reduction device according to claim 10, characterized in that, The transfer function is adapted to the serrated edge profile (9).

13. The noise reduction device according to claim 10, characterized in that, The transfer function is adapted to the noise generation characteristics of the sawtooth edge profile (9).

14. The noise reduction device according to claim 10, characterized in that, The transfer function is determined empirically through at least one measurement, and / or the transfer function is stored in the data storage unit of the active noise cancellation device (8).

15. A wind turbine blade, comprising at least one noise reduction device (6) according to any one of the preceding claims.

16. A wind turbine, comprising at least one wind turbine blade (2) according to claim 15.

17. A method for noise reduction of a wind turbine blade (2) using an active noise reduction device (8) and a passive noise reduction device (7), wherein, The passive noise reduction device (7) includes at least one serrated edge profile (9) adapted to be fixed to the trailing edge (4) of the wind turbine blade (2), wherein the active noise reduction device (8) includes: at least one unstable pressure sensor (10) adapted to generate an output signal corresponding to a turbulent state during operation of the wind turbine blade (2); at least one actuator (11); and a control unit (12), wherein the sensor (10) is arranged adjacent to the serrated edge (14) of the serrated edge profile (9), and the control unit... Unit (12) controls actuator (11) based on the output signal of sensor (10) to emit an anti-noise signal that at least partially reduces the noise generated by the wind turbine blade (2), wherein the active noise reduction device (8) includes a plurality of unstable pressure sensors (10), wherein the unstable pressure sensors (10) are arranged in one or more rows next to the serrated edge (14), wherein each row has a constant or substantially constant distance between the serrated edge (14) and each sensor (10) in the row.

18. The method according to claim 17, characterized in that, The control unit (12) uses a transfer function that describes the relationship between the output signals of the plurality of unstable pressure sensors (10) at the serrated edge (14) and far-field noise to determine the noise immunity signal.

19. The method according to claim 17, characterized in that, The control unit (12) uses a transfer function that describes the relationship between a filtered combination of the output signals of the plurality of unstable pressure sensors (10) at the serrated edge (14) and far-field noise to determine the noise-resistant signal.

20. The method according to any one of claims 17-19, characterized in that, The transfer function used is adapted to the serrated edge profile (9), and / or the transfer function determined by at least one measurement and / or stored in the data storage unit of the active noise cancellation device (8).

21. The method according to any one of claims 17-19, characterized in that, The transfer function uses the noise generation characteristics suitable for the serrated edge profile (9), and / or the transfer function determined by at least one measurement and / or stored in the data storage unit of the active noise cancellation device (8).

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