Method for optimizing rotor blade of wind turbine and rotor blade of wind turbine

Abstract

The invention relates to a method for optimizing a rotor blade of a wind turbine and a rotor blade of a wind turbine, in which the rotor blade extends from a rotor blade coupling to a rotor blade tip at a rotor blade length in a rotor blade longitudinal direction, the rotor blade having an aerodynamic profile extending between a leading edge and a trailing edge, wherein the method comprises the steps of designing the rotor blade for a design environmental condition comprising at least one design air density wherein the designing comprises providing a sound protection device comprising at least one bristle within a blade outer region of the rotor blade, the blade outer region is defined as 50% of the length of the rotor blade adjoining the rotor blade tip; providing an air density at the installation site of the wind turbine; comparing the air density with the designed air density; and when the air density is lower than the designed air density, increasing an induction factor by increasing a density factor of the sound protection device.

Description

Field of the Invention

[0001] The present invention relates to a method for optimizing rotor blades of a wind turbine, to rotor blades of a rotor of a turbine and to a wind turbine and a wind farm. Background Art

[0002] Wind turbines are generally known and constructed as Figure 1 exemplarily shown therein. The design of the rotor blades is a crucial aspect when it comes to the emissions and efficiency of a wind turbine. The rotor blades of a wind turbine generally have a suction side and a pressure side. The suction side and the pressure side converge along the trailing edge of the rotor blade of the rotor blade, abbreviated as the trailing edge. The pressure difference between the suction side and the pressure side generates eddy currents, which may lead to noise emissions and power reduction, especially at the tip of the rotor blade. In addition, when there is a flow around the blade surface, small eddy currents and pressure variations are caused by the friction effects at the pressure side and the suction side, which may lead to noise emissions when flowing past the trailing edge of the rotor blade.

[0003] Wind turbines and their components are designed respectively according to standardized guidelines (e.g., IEC 61400), and the standardized guidelines stipulate the basic design requirements to ensure the technical integrity of the wind turbine. The purpose of this standard is to provide an appropriate level of protection against dangerous damage during the planned service life of the wind turbine. Herein, when sizing a wind turbine, standard parameters according to standardized loads are considered, but they are independent of the site. Among them, the standard parameters are wind shear, the occurrence of turbulence, climate conditions, air density, reference speeds for wind classes and wind zones. Since the sizing of the rotor blades depends on standardized loads, the rotor blades have a defined profile with fixed parameters, and the fixed parameters include, for example, the profile poles associated therewith, such as the profile depth of the lift / drag poles. This fixed profile is the basis for calculating loads and the annual energy output (AEO).

[0004] The design of the wind turbine and the configuration of the rotor blades resulting from the design of the wind turbine are mainly based respectively on standardized sites and standardized loads, and specific site certifications / loads may also be considered. Thereby, the subsequent geometric configuration of the rotor blades is determined. In particular, the rotor blades have a fixed geometry, which cannot be adjusted in terms of twist or profile depth during later manufacturing. Summary of the Invention

[0005] In this context, the object of the present invention is to allow for site-specific optimization of the rotor blades without changing the fixed geometry.

[0006] In a first aspect, a method for optimizing a rotor blade of a wind turbine is provided, wherein the rotor blade extends from a rotor blade connection to a rotor blade tip in a rotor blade longitudinal direction by a rotor blade length, and the rotor blade has an aerodynamic profile extending between a leading edge and a trailing edge. Thus, rotor blades optimized by the method provided by the present invention are substantially known.

[0007] The method comprises the steps of: designing the rotor blade for design environmental conditions including at least one design air density, wherein the design includes providing a sound protection device within an outer blade region of the rotor blade, the outer blade region being defined as 50% of the rotor blade length adjacent to the rotor blade tip.

[0008] The process of designing a wind turbine is well-known and is widely described in common textbooks. Given basic design conditions, such as design speed and / or design tip speed ratio, the configuration of the rotor blade that is generally desired is not only as efficient and durable as possible but also cost-effective.

[0009] The design conditions also include design environmental conditions, i.e., the conditions that model the environment at the installation site of the wind turbine under the design conditions. Thus, the design environmental conditions are the theoretical environmental conditions on which the design is based, but they do not necessarily prevail at the proper installation site of the wind turbine. Deviations between the design environmental conditions and the environmental conditions prevailing at the installation site of the wind turbine may result in, for example, performance losses. Here, the most important thing to consider is the air density at the installation site that is lower than the design air density. For example, the design air density can be the standard air density, but it can also be a different value.

[0010] For this purpose, according to the present invention, in a further step, the air density at the installation site of the wind turbine is provided. This air density can be determined as an average value or an extreme value or other value representing the air density at the installation site. For example, the air density can be measured or derived from a meteorological model.

[0011] In a further step, the present invention provides comparing the air density with the design air density and increasing the induction factor by increasing the density factor of the sound protection device when the air density is lower than the design air density.

[0012] Thus, when the air density obtained at the installation site of the wind turbine is lower than the design air density, the density factor of the sound protection device is creatively increased to increase the induction factor and thus improve the performance.

[0013] The basic finding of the inventors of the present invention is based on the fact that the density factor of the sound protection device also increases the lift generated at the site where the sound protection device is attached.

[0014] The density factor of the sound protection device is a parameter indicating the ratio of the imaginary rectangular plane with the length of the sound protection device as one side and the length in the longitudinal direction of the rotor blade where the trailing edge of the attached sound protection device is located as the other side, and this imaginary rectangular plane is covered by the sound protection device.

[0015] In other words, the density factor indicates how much of this imaginary plane spanned around the sound protection device at the trailing edge of the rotor blade is covered by the sound protection device. The remaining part of the imaginary plane is preferably not covered so that air can flow through.

[0016] The higher the density factor, the higher the lift generated by the rotor blade, resulting in improved performance.

[0017] When the air density is lower than the design air density, two effects occur. First, the generated noise is lower, thus providing the possibility of also making the aerodynamic-acoustic compromise that leads to higher noise emissions. In addition, the induction is lower, resulting in lower performance, and therefore it is desirable to improve the performance.

[0018] In this case, an increase in the density factor of the sound protection device allows for on-site optimization, and in particular allows for optimizing the performance of the rotor blade without changing the geometry of the rotor blade.

[0019] The sound protection device can include, for example, bristles or serrations arranged at the trailing edge of the rotor blade or at the solid plate attachment.

[0020] There can also be a combination of various types of sound protection devices arranged on the rotor blade.

[0021] Bristles and serrations are known types of sound protection devices arranged at the trailing edge and modifying the effective profile of the trailing edge, i.e., the overflow edge. Therefore, the acoustic effect of the air turbulence at the trailing edge of the rotor blade is reduced, and the wind turbine can operate at a lower noise level.

[0022] The most common shape of the bristles is a cylindrical shape, but conical bristles or pyramidal bristles can also be considered within the scope of the present invention. For the bristles, the density factor can be increased by adding additional bristles to the trailing edge or reducing the gap between the bristles.

[0023] The material of the bristles can be, for example, plastic, carbon, some fiber-reinforced materials, or fiberglass.

[0024] The saw teeth are most commonly shaped as triangles, but multi-angle saw teeth or saw teeth with concave and / or convex profiles can also be considered within the scope of the present invention. In the triangular shape, the saw teeth occupy more than fifty percent of the area beyond the trailing edge, i.e., fifty percent of the area with the saw tooth profile. Modifying the edge profile, for example by shaping the edge into a convex shape or by modifying the shape into multi-angles, can increase the share of the area covered by the saw teeth relative to the total area beyond the trailing edge, thus increasing the density factor and thereby the induction factor.

[0025] The density factor can also be adjusted by changing the porosity of the sound protection device. To increase the density factor, the porosity can be reduced.

[0026] Porosity or void fraction is a measure of the void (i.e., "empty") space in a material and is the fraction of the void volume to the total volume, ranging from 0 to 1, or between 0% and 100% in percentage form. Strictly speaking, some tests measure "accessible voids" - the total amount of void space accessible from the surface (see closed-cell foams). There are many methods for testing the porosity of substances or parts, such as industrial CT scans.

[0027] Preferably, in the context of the present invention, it is aerodynamic permeability in the sense of potential flow through. This will vary between 100% permeable, i.e., a material that actually offers no obstruction to flow, and 0% permeable, i.e., a completely dense material that does not allow any flow through. Aerodynamic permeability is determined in an experimental setup in which the mass or volume flow rate is determined by a test sample in a closed channel under a given pressure difference. In this case, 100% permeability would be an empty channel, and 0% permeability would be a 100% closed channel.

[0028] The sound protection device can be attached to the blade, for example, by lamination, gluing, or adding it to the blade during the manufacturing process of the rotor blade. Specifically, the bristles and saw teeth can be laminated or glued to the surface of the rotor blade in one working step.

[0029] In a preferred embodiment, the sound protection device is configured as a plurality of bristles, each bristle having a bristle length, a cross-section perpendicular to the direction in which the bristle extends with the bristle length, and an effective diameter of the cross-section, where the effective diameter provides the diameter of an imaginary circular cross-section having the same cross-sectional area. Each bristle is arranged side by side in the longitudinal direction of the rotor blade, and the density factor of the sound protection device is based on the number of bristles, the bristle diameter, and the normalized bristle density factor per unit span, where the unit span is the distance in the longitudinal direction of the rotor blade from the bristle closest to the rotor blade joint to the bristle closest to the rotor blade tip, and a normalized bristle density factor of 1 means that the bristles are arranged adjacent to each other without gaps.

[0030] It has been found that bristles provide better aeroacoustic performance compared to serrations. Specifically, the bristles provide broadband noise reduction without specific peaks and in particular reduce trailing edge noise. In addition, compared to serrations, the bristles can change the direction of the emitted noise, resulting in a more diffused emission and an overall reduction in noise.

[0031] Another advantage compared to serrations is that the bristles are lighter, thus reducing the load on the blade.

[0032] In addition, the bristles do not include sharp edges that could pose a danger to workers or other persons near the wind turbine.

[0033] The normalized bristle density factor is introduced as an indication of aerodynamic permeability and is calculated by the following formula:

[0034]

[0035] This formula assumes that each bristle has exactly the same diameter.

[0036] However, the present invention is not limited to this case. In the case of using bristles arranged to have varying diameters, the value "bristle diameter" is replaced by the average value of the diameters of the bristles.

[0037] A bristle density factor of 1 means that the bristles are arranged adjacent to each other without gaps. A bristle density factor greater than 1 means that the bristles are arranged at least partially in more than one layer.

[0038] Thus, a layer includes bristles arranged side by side in the longitudinal direction of the rotor blade, and an additional layer is arranged at a position different from the first layer between the leading edge and the trailing edge. For example, a second layer of bristles can be attached adjacent to the first layer on the surface of the rotor blade. Preferably, in the case of multi-layer bristles, the bristles of the multi-layers are arranged in parallel. In the case where the direction of the bristles of the first layer changes in the longitudinal direction of the rotor blade, the bristles of the additional layer are preferably attached parallel to the direction of the local bristles of the first layer. Thus, the local bristles can include the two closest bristles of the first layer.

[0039] In the case where the bristles have a non-circular cross-section different from a circular shape, an effective diameter can be defined. The non-circular cross-section can be a square-shaped cross-section, a multi-angular-shaped cross-section, a rectangular-shaped cross-section. In order to define the effective diameter, the cross-sectional area of the non-circular bristle must be determined. The effective diameter of the bristle is the diameter of an imaginary circular cross-section having the same cross-sectional area. Regarding the normalized bristle density factor, "bristle diameter" is then replaced by the effective diameter.

[0040] Due to the cross-section, the bristles can also include directional flexibility.

[0041] In the case of using non-circular bristles with different effective diameters, the average effective diameter is used instead of the "bristle diameter" in order to calculate the normalized bristle density factor.

[0042] For sites with reduced air density, the normalized bristle density factor can be increased by increasing the amount of bristles per unit span, or by keeping the amount of bristles per unit span constant but increasing the average bristle diameter or the average effective diameter. Additionally, the number of bristles and the bristle diameter can be increased simultaneously.

[0043] For cases where the bristle density factor varies along the blade span, such as a stepwise or sinusoidal variation of the bristle density factor, the average normalized bristle density factor of the rotor blade can be determined and used as a reference. When the induction factor is increased, the average normalized bristle density factor increases.

[0044] In another preferred embodiment, the normalized bristle density factor is in the range between 0.5 and 10. The inventors have found that for each possible situation occurring at the construction site of a wind turbine, there is a normalized bristle density factor within this range at which the wind turbine can be beneficially operated.

[0045] Another finding of the inventors is that for locations with reduced density, it is beneficial to increase the normalized bristle density factor by a factor greater than 1 compared to the designed setting, as through this increase, significant performance optimization can be achieved.

[0046] The positive effect of increasing the bristle diameter can be increased bristle stiffness, which results in a higher effective camber of the airfoil when applying aerodynamic loads. The bristle diameter is preferably between 0.3 mm and 0.5 mm.

[0047] Increasing the number of bristles more effectively reduces the aerodynamic permeability.

[0048] To achieve an even better aerodynamic effect, it is beneficial to increase the length of the bristles, such that the effective chord length of the rotor blade increases.

[0049] When the material of the bristles is selected such that the low-density setting of the bristles is harder than the normal-density setting, another aerodynamic effect can be achieved even when using the same bristle diameter. For this purpose, the fiber density in the epoxy resin of the bristles can be adjusted.

[0050] In another embodiment, a plurality of bristles includes a curvature perpendicular to the longitudinal direction of the rotor blade. This ensures optimized air flow and increases the lift. The bristles can be pre-bent before being attached to the rotor blade.

[0051] The inventors have found that attaching the bristles at a first angle between the direction in which the bristles extend in the bristle length direction and the local chord of the rotor blade improves the lift of the blade, the local chord being defined as the direct connection from the leading edge to the trailing edge, and this first angle is non-zero. The specific value for this first angle can be determined according to the local conditions at the construction site of the wind turbine, such as, for example, the air density.

[0052] To counteract the radial force acting on the bristles due to rotation, the bristles can be attached to the profile of the trailing edge at an angle different from 90°, such that the direction in which the bristles extend in the bristle length direction is not perpendicular to the profile of the trailing edge. This can reduce or eliminate the curvature of the bristles caused by the radial force.

[0053] Additional improvements in the operation of the wind turbine are observed when the normalized bristle density factor increases in the longitudinal direction of the rotor blade. The maximum value of the normalized bristle density factor can be reached at the tip of the rotor blade or at the bristles closest to the tip of the rotor blade.

[0054] However, the present invention is not limited to this distribution of the normalized bristle density factor. The distribution of the normalized bristle density factor can also be optimized according to the local parameters and requirements at the construction site of the wind turbine.

[0055] It has also been found that the operation of the wind turbine benefits from the diameters of a plurality of bristles varying in the direction in which the bristles extend in the bristle length direction, specifically when the diameters of the plurality of bristles decrease in the direction in which the bristles extend in the bristle length direction. The bristles can, for example, be of a conical shape.

[0056] The diameter of the bristles can also vary in the longitudinal direction of the rotor blade, specifically decreasing in the longitudinal direction.

[0057] Regarding the structure of the bristles, it has been found that preferably, the bristles comprise a flexible part and a non-flexible part. To increase the induction factor, the non-flexible part of the bristles can be increased. Specifically, the ratio of the non-flexible part to the flexible part can be increased. Preferably, the bristles are attached to the trailing edge of the rotor blade by the non-flexible part.

[0058] As an additional measure to increase the induction factor, the area in which the sound protection device extends in the longitudinal direction of the rotor blade can be increased. Specifically, this extended area can be increased in the rotor blade connection direction, which results in an increase in lift and thus optimized performance.

[0059] In another embodiment, the method further comprises the steps of: determining the influence of the air density on the propagated sound, and optimizing the performance while taking into account the air density and the guaranteed sound power level, and in particular optimizing the performance by increasing the size of the sound protection device.

[0060] Optimizing performance specifically includes maximizing the electricity generated by a wind turbine. At the same time, the improvement in performance must not result in excessive sound emissions.

[0061] The guaranteed sound power level is a measure that describes the maximum emitted sound power level of a wind turbine. In other words, for example, when maximizing electricity, the wind turbine controller includes the emitted sound level as a boundary condition. In some cases, the operation of the wind turbine is then limited or constrained by the guaranteed sound power level. This may apply temporarily, for example, at night or during a specific wind direction.

[0062] As another example, the installation angle of the sound protection device can be changed to optimize power while taking into account air density and the guaranteed sound power level.

[0063] Generally, a lower air density is associated with a lower sound power, such that there is also "reserve sound" that can be increased, for example, by additional power. According to the invention, the additional power is achieved not only by adjusting the operation management, but first and foremost by increasing the induction in the blade tip region, i.e., by increasing the density factor.

[0064] In another embodiment, the sound protection device includes a first type of sound protection device - a plurality of bristles, and a second type of sound protection device other than the bristles, such as triangular-shaped serrations, and the share factor indicates the relationship between the combined length of the trailing edge region to which the first type of sound protection device is attached in the longitudinal direction of the rotor blade and the combined length of the trailing edge region to which the second type of sound protection device is attached in the longitudinal direction of the rotor blade, and the method includes the step of increasing the induction factor by adjusting the share factor.

[0065] Adjusting the share factor also affects the induction factor because different sound protection devices have different effects on the lift of the blade. The induction factor can be increased by adjusting the share factor, increasing the amount of the sound protection device that has a greater impact on the lift, or replacing some of the sound protection devices with other sound protection devices that have a greater impact on the lift.

[0066] According to a second aspect of the present invention, there is provided a rotor blade of a wind turbine, wherein the rotor blade extends in a rotor blade longitudinal direction by a rotor blade length from a rotor blade connection portion to a rotor blade tip, the rotor blade having an aerodynamic profile extending between a leading edge and a trailing edge, wherein the rotor blade has a sound protection device in a blade outer region, the blade outer region being defined as 50% of the rotor blade length adjacent to the rotor blade tip, wherein the sound protection device is configured as a plurality of bristles, each bristle having a bristle length, a circular cross-section perpendicular to the direction in which the bristle extends by the bristle length, and a bristle diameter of the cross-section, each bristle being arranged side by side in the rotor blade longitudinal direction, wherein a design normalized bristle density factor is defined for the sound protection device, at which design normalized bristle density factor the rotor blade complies with a guaranteed sound power level when the rotor blade is used at a design air density, wherein the design normalized bristle density factor is based on the number of bristles, the bristle diameter, and the unit span, wherein the unit span is the distance in the rotor blade longitudinal direction from the bristle closest to the rotor blade connection portion to the bristle closest to the rotor blade tip, and a normalized bristle density factor of 1 means that the bristles are arranged adjacent to each other without gaps, characterized in that when the air density is lower than the design air density, the normalized bristle density factor of the rotor blade is greater than the design normalized bristle density factor.

[0067] According to a third aspect of the present invention, there is provided a wind turbine having one or more rotor blades according to the second aspect of the present invention.

[0068] According to another aspect of the present invention, there is provided a wind farm having one or more wind turbines according to the third aspect of the present invention. Description of the Drawings

[0069] In the following, other advantages and preferred embodiments are described with reference to the drawings. In the drawings,

[0070] Figure 1 a wind turbine is schematically and exemplarily shown;

[0071] Figures 2 to 6 a rotor blade having a sound protection device is schematically and exemplarily shown;

[0072] Figure 7 a flowchart of a method is schematically and exemplarily shown, and

[0073] Figure 8 an example of determining a bristle density factor is shown. Detailed Description

[0074] Figure 1Shows a schematic view of a wind turbine according to the present invention. The wind turbine 100 has a tower 102 and a nacelle 104 located on the tower 102. On the nacelle 104, an aerodynamic rotor 106 is provided, which has three rotor blades 108 and a spinner 110. When the wind turbine is operated, the aerodynamic rotor 106 is put into rotational motion by the wind, and thus also rotates an electric rotor or runner of a generator directly or indirectly coupled to the aerodynamic rotor 106. The generator is arranged within the nacelle 104 and generates electrical power. The pitch angle of the rotor blades 108 can be changed by pitch motors located at the rotor blade roots 109 of the respective rotor blades 108.

[0075] Here, the wind turbine 100 has a generator 101 shown in the nacelle 104. Electrical power can be generated using the generator 101. To feed the electrical power, a feeding unit 105 is provided, which can in particular be implemented as an inverter. Here, a three-phase feeding current and / or a three-phase feeding voltage can be generated according to amplitude, frequency, and phase to be fed to a mains supply point PCC. This can be done directly or in cooperation with other wind turbines in a wind farm. To control the wind turbine 100 and also to control the feeding unit 105, a turbine controller 103 is provided. The turbine controller 103 can also obtain default values from the outside, in particular from a central farm computer.

[0076] Figure 2 Schematically and exemplarily shows an outer blade region 120 of the rotor blade 108. The outer blade region 120 is defined as the outer 50% of the rotor blade 108, which is arranged closer to the blade tip 114 and thus further away from the rotational axis of the rotor 106. In the outer blade region 120, the rotor blade 108 has a sound protection device 130 that extends beyond the trailing edge 112. At the trailing edge 112, the suction side and the pressure side of the aerodynamic profile that diverges at the leading edge 110 converge again.

[0077] The sound protection device 130 is preferably implemented as bristles. In the drawings, the bristles are shown as having a serrated profile with serrations formed by edges arranged at an angle to the longitudinal direction of the rotor blade, having alternating tips and notches connected by the edges. Thus, the trailing edge profile is formed by the bristles in the region of the sound protection device 130.

[0078] However, in other embodiments, the bristles can also all have the same length, such that the profile is linear instead of serrated as shown. The shown serrated profile facilitates the identification of the sound protection device compared to the rest of the rotor blade and is therefore only for illustrative purposes.

[0079] The bristles can in particular be described by their length, width, cross-section and mounting angle. The relationship between the length and the width defines an angle relative to the longitudinal direction of the rotor blade. The mounting angle describes the angle of the saw teeth relative to the chord of the rotor blade at the mounting position of the saw teeth, where the chord is the shortest and most direct connection between the leading edge and the trailing edge.

[0080] Although the following description uses bristles as an example of a sound protection device, this also applies to saw teeth or other known examples of sound protection devices. As described above, for example, a combination of saw teeth and bristles is also advantageous in some embodiments.

[0081] The invention relates to a geometry of a rotor blade 108 in an outer blade region 120 for optimizing the induction factor of a wind turbine 100 at low air density sites.

[0082] By default, the bristles are mounted in the outer blade region 120 for noise reduction. Simulation and experimental studies by the inventors of the present invention have clearly shown that by extending the bristles and / or increasing the bristle density factor, i.e., the number of bristles per unit span, the lift at the rotor blade 108 can be increased and thus the induction factor can be increased.

[0083] By extending the bristles, i.e., by providing larger or more bristles, an effective increase in the local blade depth, i.e., the local distance between the leading edge 110 and the trailing edge 112, is achieved because the saw teeth affect the profile of the trailing edge 112. Thereby, the surface area generating lift is increased.

[0084] Air density depends on temperature and atmospheric pressure. At sea level, at a temperature of 15 °C and an atmospheric pressure of 1,013.25 hPa (which is the standard atmospheric pressure), the air density is 1.225 kg / m 3 . The air density decreases with increasing altitude. The air density has a strong influence on the power of the wind, i.e., the wind force, where a higher air density is associated with a higher wind force and thus also with a higher achievable electrical power of the wind turbine 100.

[0085] The wind turbine 100 is designed for certain environmental parameters, i.e., boundary conditions are defined during the planning process, for example, the design air density for which the wind turbine 100 will later be optimized. To achieve the design air density, an optimal operation of the wind turbine is possible, where a change in the design air density usually results in a situation where the wind turbine 100 cannot operate at the optimal operation site determined during the planning process.

[0086] At the same time, it is not possible to design and test a separate wind turbine for each site, such that a wind turbine 100, and in particular a rotor blade 108, with as wide an application range as possible is required.

[0087] At a site where the air density is significantly lower than the design air density, when standard operation management is carried out, the induction factor will generally decrease. A decrease in the induction factor means that the wind turbine 100 collects less energy from the wind, and thus the performance of the wind turbine 100 decreases.

[0088] Previous efforts to improve performance have focused on adjusting operation management (e.g., increasing speed and / or decreasing the pitch angle to increase the local angle of attack) to compensate for induction losses. However, this results in an increase in the service life load in the pivot direction caused, for example, by the increased speed. In addition, the increase in the local working angle may cause the flow to stall at the blade (small stall margin), which may result in larger loads and noise exposure.

[0089] According to the present invention, a solution is proposed that has a sound protection device of increased size and, in particular, uses extended bristles, which allows the induction factor to be adjusted without having to accept larger pivot loads and smaller stall margins.

[0090] The advantage of the present invention described herein is that by using bristles that are longer / greater than the design bristles for a standardized site and / or by increasing the bristle density, a significant power increase and thus an output increase can be achieved at a site with reduced density.

[0091] Figure 3 The rotor blade 108 is schematically and exemplarily shown, wherein Figure 2 the sound protection device 130 has been replaced by a sound protection device 140 with geometrically similarly scaled bristles. The bristles of the sound protection device 140 are geometrically scaled, i.e., the aspect ratio of the bristle tip from length to width remains the same. Thus, the number of tips is less than that of the sound protection device 130; however, the surface area is larger and thus the influence on induction is greater.

[0092] The increase in the size of the bristles used can be achieved either by geometrically similar scaling (the aspect ratio of the bristle tip from length to width remains the same) or by extending the tip geometry without changing the original width (the ratio of the serrated tip from length to width becomes larger). In other examples, increasing the size can simply include making some or all of the bristles in the bristle longer and / or increasing the number of bristles per unit span.

[0093] In Figure 4 the sound protection device 150, a second alternative of extending the tip geometry without changing the original width can be schematically and exemplarily seen.

[0094] In addition to increasing the bristle size, the installation angle (not shown) can also be adjusted to further increase the lift. The installation angle is the angle between the bristles and the chord of the rotor blade 108. A positive installation angle can be defined as being towards the pressure side, and a negative installation angle can be defined as being towards the suction side. Due to the increased curvature, the adjustment towards the pressure side results in an increase in lift.

[0095] A particular advantage of the site with reduced density is that when the air density is low, the wind turbine 100 also transmits less sound. Therefore, an aerodynamic-acoustic optimization design of the bristles is generally no longer necessary at such a site.

[0096] An aerodynamic-acoustic compromise in favor of performance can be accepted without exceeding the guaranteed sound power level.

[0097] Figure 5 Another embodiment of the sound protection device 160 is schematically and exemplarily shown. The scaling of the bristles, i.e., Figure 3 the geometrically similar scaling shown in Figure 4 and / or the scaling of the spike length shown in

[0098] does not necessarily have to be the same along the entire radial extension. Instead, depending on the location, a scaling factor different from the standard density design can also be used. For example, in the aerodynamic-acoustically important region at the blade tip, an acoustically quite optimized design can be used, while in the more internal part of the rotor blade, a performance-optimized bristle scaling can be used. Figure 5 This is shown in

[0099] Figure 6 Another embodiment of the sound protection device 170 is schematically and exemplarily shown. Another way to improve performance at a site with reduced density is to also extend the area where the sound protection device 170 is to be installed, for example, the area where additional bristles are to be installed. Additional bristles installed further inwards at the rotor blade can effectively increase the induction factor in this area.

[0100] Of course, the sound protection device 170 with an increased size in the longitudinal direction of the rotor blade can also be scaled in size and width according to the site requirements, i.e., combined with the embodiments shown in Figure 3 、 Figure 4 and Figure 5 。

[0101] Figure 7 The flow of a method 200 for optimizing the rotor blade 108 of the wind turbine 100 is schematically and exemplarily shown.

[0102] Method 200 includes step 210 of designing rotor blade 108 for design environmental conditions including at least a design air density, wherein the design includes providing a sound protection device 130 within an outer blade region of the rotor blade, the outer blade region being defined as 50% of the rotor blade length adjacent to the rotor blade tip.

[0103] Additionally, method 200 includes step 220 of providing the air density at the installation site of wind turbine 100, and step 230 of comparing the air density with the design air density.

[0104] Finally, method 200 includes step 240 of increasing the induction factor by increasing the size of sound protection device 130, for example, by moving it towards sound protection devices 140, 150, 160 or 170, when the air density is lower than the design air density.

[0105] Although the foregoing has been described with reference to air density as an environmental parameter, the same solution, i.e., modifying the induction by changing the bristles, can be applied to turbulence intensity as an environmental parameter, wherein the greater lift induced by the sound protection device is then used for lower turbulence intensities.

[0106] Figure 8 Two examples of the bristle density factor as described above are schematically and exemplarily illustrated. In the upper figure, a bristle density factor of 1.0 is illustrated. This corresponds to a plurality of bristles 500 aligned adjacent to each other in a single row.

[0107] A bristle density factor of 2.0 is achieved by adding a second row of bristles 500 in the thickness direction of the rotor blade, i.e., perpendicular to the indicated span direction and perpendicular to the image, as seen in the lower part of the drawing.

Claims

1. A method (200) for optimizing a rotor blade (108) of a wind turbine (100), wherein, The rotor blade (108) extends in the longitudinal direction of the rotor blade by a rotor blade length from a rotor blade connection part (109) to a rotor blade tip (114). The rotor blade (108) has an aerodynamic profile extending between a leading edge (110) and a trailing edge (112). Wherein, the method comprises the following steps: Design (210) the rotor blade (108) for a design environmental condition including at least one design air density. Wherein, the design includes providing a sound protection device (130, 140, 150, 160, 170) in an outer blade region (120) of the rotor blade (108). The sound protection device (130, 140, 150, 160, 170) includes at least one bristle. The outer blade region (120) is defined as 50% of the rotor blade length adjacent to the rotor blade tip; Provide (220) the air density at an installation site of the wind turbine (100); Compare (230) the air density with the design air density; and When the air density is lower than the design air density, increase (240) an induction factor by increasing a density factor of the sound protection device (130, 140, 150, 160, 170).

2. The method (200) according to claim 1, wherein The sound protection device (130, 140, 150, 160, 170) is configured as a plurality of bristles (500), and each bristle: Has a bristle length, A cross-section perpendicular to the direction in which the bristle extends by the bristle length, and The effective diameter of the cross-section, wherein, The effective diameter provides a hypothetical circular cross-section diameter having the same cross-sectional area, Are arranged side by side in the longitudinal direction of the rotor blade, and The density factor of the sound protection device (130, 140, 150, 160, 170) is a normalized bristle density factor based on the following Number of bristles, Bristle diameter, and Unit span. Wherein, the unit span is the distance from the bristle closest to the rotor blade connection part to the bristle closest to the rotor blade tip in the longitudinal direction of the rotor blade, and A normalized bristle density factor of 1 means that the bristles are arranged adjacent to each other without gaps. Wherein, without gaps means that each bristle is in direct contact with at least one other bristle.

3. The method (200) according to claim 2, wherein A normalized bristle density factor greater than 1 means that the plurality of bristles are at least partially arranged in more than one layer. Wherein, a layer includes bristles arranged side by side in the longitudinal direction of the rotor blade, and the more than one layer is arranged at a position different from the first layer between the leading edge and the trailing edge.

4. The method (200) according to any one of claims 2 or 3, wherein The bristle diameter varies among the plurality of bristles, and the normalized bristle density factor is based on the average value of the bristle diameters.

5. The method (200) according to any one of claims 2 to 4, wherein The cross-section of the bristle perpendicular to the direction in which the bristle extends by the bristle length is circular, and The effective diameter is the diameter of the bristles, where Non-circular bristles particularly include different effective diameters, and the normalized bristle density factor is based on the average effective diameter.

6. The method (200) according to any one of claims 2 to 5, wherein The step of increasing the normalized bristle density factor includes: increasing the amount of bristles per unit span, and / or increasing the average value of the effective diameter, and / or increasing the normalized bristle density factor by at least 1.

7. The method (200) according to any one of claims 2 to 6, wherein The normalized bristle density factor varies along the longitudinal direction of the rotor blade, and the step of increasing the normalized bristle density factor includes: increasing the average normalized bristle density factor.

8. The method (200) according to any one of claims 2 to 7, wherein, The normalized bristle density factor is between 0.5 and 10.

9. The method (200) according to any one of claims 2 to 8, wherein, The method includes the following steps: when the air density is lower than the designed air density, increasing the induction factor (240) by increasing the bristle length.

10. The method (200) according to any one of claims 2 to 9, wherein The plurality of bristles include bristle hardness based on the material from which the plurality of bristles are made, and the method includes the following steps: when the air density is lower than the designed air density, increasing the induction factor (240) by increasing the bristle hardness, and / or wherein the plurality of bristles include a curvature perpendicular to the longitudinal direction of the rotor blade.

11. The method (200) according to any one of claims 2 to 10, wherein, A first angle between the direction in which the bristles extend at the bristle length and the local chord of the rotor blade is non-zero, the local chord being defined as the direct connection from the leading edge to the trailing edge, and / or wherein the direction in which the bristles extend at the bristle length is not perpendicular to the profile of the trailing edge, and / or wherein the normalized bristle density factor increases in the longitudinal direction of the rotor blade.

12. The method (200) according to any one of claims 2 to 11, wherein, The diameter of the plurality of bristles varies in the direction in which the bristles extend at the bristle length, specifically, the diameter of the plurality of bristles decreases in the direction in which the bristles extend at the bristle length, and / or wherein the plurality of bristles include a flexible part and a non-flexible part, and the method includes the following steps: increasing the induction factor by increasing the non-flexible part of the plurality of bristles.

13. The method (200) according to any one of the preceding claims, wherein, The method includes the following steps: increasing the induction factor by increasing the area of the sound protection device (130, 140, 150, 160, 170) extending in the longitudinal direction of the rotor blade, and / or wherein the method further includes the following steps: determining the influence of the air density on the propagated sound, optimizing the performance while considering the air density and the guaranteed sound power level, and in particular, optimizing the performance by increasing the density factor.

14. The method (200) according to any one of the preceding claims, wherein The sound protection device includes a first type of sound protection device - a plurality of bristles, and a second type of sound protection device other than the bristles, such as triangular-shaped serrations, and the share factor indicates the relationship between the combined length in the longitudinal direction of the rotor blade of the trailing edge region to which the first type of sound protection device is attached and the combined length in the longitudinal direction of the rotor blade of the trailing edge region to which the second type of sound protection device is attached, and the method includes the following steps: increasing the induction factor by adjusting the share factor.

15. A rotor blade (108) of a wind turbine (100), wherein The rotor blade (108) extends in the longitudinal direction of the rotor blade from the rotor blade connection (109) to the rotor blade tip (114) by the length of the rotor blade and has an aerodynamic profile extending between a leading edge (110) and a trailing edge (112), wherein the rotor blade (108) has a noise protection device (130, 140, 150, 160, 170) within a blade outer region (120), which is defined as 50% of the length of the rotor blade adjacent to the rotor blade tip (114), Among them, the noise protection device (130, 140, 150, 160, 170) is configured as a plurality of bristles, each bristle having a bristle length, a circular cross-section perpendicular to the direction in which the bristle extends by the bristle length, and a bristle diameter of the cross-section, and each bristle is arranged side by side in the longitudinal direction of the rotor blade, wherein a design normalized bristle density factor is defined for the noise protection device (130, 140, 150, 160, 170), at which, when the rotor blade (108) is used at a design air density, the rotor blade (108) complies with a guaranteed sound power level, wherein the design normalized bristle density factor is based on the number of bristles, the bristle diameter, and the unit span, wherein the unit span is the distance in the longitudinal direction of the rotor blade from the bristle closest to the rotor blade connection to the bristle closest to the rotor blade tip, and a normalized bristle density factor of 1 means that the bristles are arranged adjacent to each other without gaps, characterized in that when the air density is lower than the design air density, the normalized bristle density factor of the rotor blade (108) is greater than the design normalized bristle density factor.

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