Wind turbine rotor blade

Abstract

A wind turbine rotor blade (20) is described, the rotor blade comprising an inboard region and an outboard region, the outboard region comprising a span section (20UAM) associated with the development of an unstable aeroelastic mode (UAM). The rotor blade of the invention is characterized in that it comprises a leading edge correction mass (1) arranged within the span section (20UAM), said leading edge correction mass (1) being adapted to move the center of mass (22) of the span section (20UAM) towards the leading edge (20LE) in order to suppress the development of an unstable aeroelastic mode (UAM). The invention further describes a method of manufacturing a wind turbine rotor blade (20).

Description

Background Art

[0001] The power output of a wind turbine depends largely on the rotational speed of the aerodynamic rotor (i.e., the rotor blades mounted to the hub). A "large" wind turbine with a rated power output of about 15 MW may have rotor blades that are about 100 meters in length or more. The speed at any point along the rotor blade depends on the distance of that point from the hub, with the outermost tips moving at the greatest speed. For a particular wind turbine type, the relationship between various parameters (such as achievable power output, allowable rotor speed, etc.) can be expressed as an "operating envelope," and the wind turbine is controlled within the range of this operating envelope.

[0002] During the design of wind turbine rotor blades, aeroelastic stability must be considered in order to avoid unstable aeroelastic modes such as linear flutter, stall-induced vibrations, vortex flutter, etc. Flutter modes are particularly problematic because unrestrained vibrations in wind turbine rotor blades can result in severe structural damage and significant repair costs.

[0003] During the design and testing of a wind turbine rotor blade, an optimal combination of geometry, mass, stiffness and aerodynamic profile is determined, and a stability limit for said rotor blade design is determined, preferably taking into account aeroservoelastic aspects. The stability limit for a wind turbine rotor blade may be understood as the maximum rotor speed allowed under a combination of parameters (allowed tip speed, wind speed, pitch angle, generator torque, control response, etc.), above which aeroelastic instabilities are expected to develop. For example, an aeroelastic modal analysis of a rotor blade design for a certain wind turbine type may determine the rotor speed or rpm value at which an aeroelastic mode may become negatively damped, thereby causing flutter.

[0004] However, as wind turbine size and rotor blade length continue to increase, the stability limit approaches the operating envelope, i.e., aeroelastic instabilities will become more likely to occur during normal operation if corrective design measures are not implemented. The damping of the aeroelastic modes depends on instantaneous operating parameters such as pitch angle, rpm, wind speed, etc. With positive damping, vibrations can be damped, but rapid damping is usually at the expense of increased rotor blade mass. Although positive damping is generally desired, if this is achieved by adding a large amount of material in the rotor blade, such positive damping may be at the expense of adversely affecting the dynamic loads on the wind turbine.

[0005] However, insufficient damping or negative damping can cause the amplitude to increase rapidly, leading to structural damage or even catastrophic failure of the rotor blade. Insufficient positive damping can also lead to fatigue damage, structural failure, etc. Additional external damping sources such as tuned mass dampers have shown potential to suppress aeroelastic instabilities, but such damping solutions usually result in increased cost, complexity, and mass.

[0006] Various techniques have been proposed to avoid unstable aeroelastic modes of wind turbine rotor blades. For example, the shape and structure of the rotor blades can be tailored to ensure adequate aerodynamic damping in critical modes. However, the high uncertainty associated with the modeling of static vibrations and flutter means that a large safety margin is required, i.e., additional mass must be added to the body of the rotor blade in the region where the aeroelastic stability is highly sensitive to the airfoil shape. It has also been proposed to provide additional damping mechanisms to help minimize the maximum amplitude of the unstable aeroelastic modes. However, known solutions generally involve some improvements in the structure of the outboard rotor blade region, such as changing the position of the shear webs along the critical section of the rotor blade. Because these improvements are generally associated with mass moment losses, fatigue loading along the edge will increase because this is driven primarily by the cyclic gravity loads as the rotor blade rotates through a full revolution. Furthermore, any additional mass incorporated in the outboard rotor blade region has the effect of increasing the mass moment of the rotor blade, and the length of the moment arm is proportional to the distance of the additional mass from the hub. The higher mass moment in turn increases fatigue loading (due to the downward pull of gravity during each revolution of the rotor) and may require further cost-intensive structural improvements to the rotor blades and hub components to account for this increased loading.

[0007] In an alternative approach, sensor data may be evaluated by a wind turbine controller to estimate or measure rotor blade vibrations, and if aeroelastic instability is detected, a control algorithm may respond by curtailing wind turbine power output. The occurrence of potentially problematic rotor blade vibrations may force a wind turbine operator to shut down the wind turbine as a precautionary measure in order to perform inspections to identify potential causes. However, curtailment of output power and shutdown results in loss of revenue. Thus, from the perspective of a wind turbine operator, the approach is unattractive.

[0008] It is therefore an object of the present invention to provide an improved rotor blade design which overcomes the above mentioned problems.

[0009] This object is achieved by the claimed wind turbine rotor blade, by the claimed wind turbine, and by the claimed method of manufacturing a wind turbine rotor blade. Summary of the invention

[0010] According to the invention, a wind turbine rotor blade comprises an inner region for connection to a wind turbine hub and an outer region having an airfoil shape. The outer region of the wind turbine rotor blade is generally understood to comprise at least the outer 50% of the rotor blade and to extend to the outermost tip of the rotor blade. In the context of the present invention, the outer region is understood to comprise at least one span section associated with the development of unstable aeroelastic modes, i.e. a span section which is likely to exhibit a significant participation in unstable aeroelastic modes without corrective measures. The rotor blade of the invention comprises a leading edge correction mass arranged within the span section. The leading edge correction mass is adapted to shift the center of mass of the span section towards the leading edge.

[0011] The result of moving the center of mass toward the leading edge is a more favorable dynamic mass balance of the span section and suppresses the development of unstable aeroelastic modes.

[0012] During certain operating conditions, the effect of the leading edge corrective mass is to create a favorable bending-torsion coupling, i.e., when the airfoil in the span section is accelerated "upwards" (in the direction of the flap), the inertia of the corrective mass causes a "downward" pitching moment. This can be described as a "nose-down" pitching moment, since the leading edge is in front of the airfoil.

[0013] In this way, any acceleration of the airfoil in the flap direction or along the edge direction generates a torque which has a corrective effect on the phase and amplitude of the target (i.e., undesired) aeroelastic mode, thereby providing increased aerodynamic damping. By generating a corrective torque from the flap-directed acceleration of the airfoil, the leading edge corrective mass essentially provides a dynamic mass balance in the span section. This advantageous bending-torsion coupling effectively counteracts any tendency of the rotor blade to twist and thereby amplify a flap-directed deflection of the airfoil, i.e., the rotor blade of the invention prevents the development of undesired unstable aeroelastic modes. "Target aeroelastic mode" is to be understood as an unstable aeroelastic mode which is effectively suppressed by the design of the rotor blade of the invention.

[0014] In the context of the present invention, the position of the moved or improved center of mass is relative to the position of the center of mass of the unmodified span segment. In other words, the center of mass position of the unmodified span segment is used as a reference position relative to which the position of the moved center of mass is defined.

[0015] An advantage of the wind turbine rotor blade of the present invention is that undesirable unstable aeroelastic modes can be prevented from developing during certain operating conditions (i.e., unfavorable combinations of rpm, wind speed, and pitch angle) that would lead to the development of such unstable aeroelastic modes in an unmodified rotor blade of the same type. As explained in the background, the undesirable unstable aeroelastic modes may be edge flutter, linear flutter, stall-induced vibrations, etc. The development of such undesirable modes is actively suppressed by the wind turbine rotor blade of the present invention, thereby allowing it to operate under conditions that could potentially damage an equivalent rotor blade. By suppressing the development of unstable aeroelastic modes, the rotor blade of the present invention is less susceptible to fatigue damage, and the life of the rotor blade can be extended. A wind turbine equipped with the rotor blade of the present invention can operate unimpeded under conditions that would lead to fatigue and / or structural damage in conventional blades.

[0016] Furthermore, since operating conditions associated with the development of unstable aeroelastic modes generally involve high rotor speeds and correspondingly high power outputs, suppressing or mitigating unstable aeroelastic modes (which would otherwise develop beyond the stability limits of the rotor blade) may allow the wind turbine to continue operating, i.e., without having to reduce rotor speed to avoid flutter, such that curtailment of power output may be avoided. In this way, the rotor blade of the present invention avoids revenue losses associated with curtailment during unstable aeroelastic modes.

[0017] Another advantage of the rotor blade of the present invention is that it can be constructed with less material than an equivalent rotor blade without the leading edge correcting mass, because the presence of the correcting mass allows the rotor blade of the present invention to be designed without the otherwise necessary safety margins (e.g., additional material) required by conventional rotor blades to avoid the development of unstable aeroelastic modes.

[0018] According to the invention, a wind turbine comprises a plurality of such rotor blades and benefits from an increase in stability margins, an increase in revenue and a reduction in operating costs due to an increase in the life of the rotor blades.

[0019] The invention also describes a method for manufacturing a wind turbine rotor blade. The method comprises the following steps: determining, in an outboard region of the rotor blade, a span section associated with the development of unstable aeroelastic modes; determining the properties (e.g. weight, density, size) and position of a leading edge correction mass which will inhibit the development of unstable aeroelastic modes in the span section; providing such a leading edge correction mass; and arranging the leading edge correction mass in the span section. The span section may be determined on the basis of simulations, for example, before the molding phase of the manufacturing process. The leading edge correction mass may be fitted, for example, during the layup process, or after the rotor blade has been removed from the mold.

[0020] The step of enhancing the rotor blade with leading edge correction mass can be easily incorporated into the manufacturing process, for example in the composite layup stage or in the post-curing stage, as will be explained below. Thus, the performance advantages of the rotor blade of the present invention can be achieved without significant additional cost or effort.

[0021] The dependent claims give particularly advantageous embodiments and features of the invention, as revealed in the following description. Features of different claim categories may be combined as appropriate to give further embodiments not described herein.

[0022] In the following, it may be assumed that the wind turbine is a horizontal axis wind turbine having (usually three) rotor blades mounted to a hub at the front of a nacelle mounted to the top of a tower. Such wind turbines are common both onshore and offshore. Any reference herein to a "large wind turbine" should be understood to mean a wind turbine having a rated power output of about 6 MW and a rotor diameter of about 130 meters or more; any reference to a "long rotor blade" should be understood to mean a rotor blade having a length of about 65 meters or more.

[0023] The correction mass may be referred to as "ballast mass" in the following, since the purpose of the correction mass is to adjust the centre of mass of the airfoil in said section. The expression "centre of mass" in this document may be abbreviated to CoM.

[0024] The present invention is based on the observation that a small amount of additional aeroelastic damping has the potential to reduce large edgewise and fatigue loads. For example, in the case of long rotor blades (e.g., about 50 meters or longer), adding a leading edge correction mass that increases the rotor blade mass moment by only 1.5% may be sufficient to reduce extreme edgewise loading by about 10% and fatigue loads by about 15%. This damping effect may be sufficient to maintain a stable aeroelastic mode throughout the operating envelope of a wind turbine equipped with such a rotor blade.

[0025] In a preferred embodiment of the invention, the leading edge correction mass is arranged on the outside of the rotor blade, i.e. outside the main body of the rotor blade. In such an embodiment, the ballast mass may be considered as an external fairing and may be mounted to the rotor blade using a suitable mounting structure. Such an embodiment may be preferred when the external component is able to withstand the weather conditions prevailing at the wind turbine assembly site.

[0026] The correction mass may be made of any suitable material or combination of materials to obtain a ballast mass of suitable size and shape. Preferably, the ballast mass comprises a density of at least 10 g / cm 3For example, the ballast mass may include a high-density metal, such as one having a density exceeding 11 g / cm 3 Lead (Pb) and / or its density exceeds 19g / cm 3 Alternatively, tungsten (W) with a density of approximately 2.2 g / cm 3 Lighter materials such as clay, granite, etc.

[0027] In another preferred embodiment of the invention, the leading edge correction mass is bonded to the outer surface of the rotor blade. For example, after the molding, curing and trimming stages are completed, the leading edge correction mass can be attached to the rotor blade airfoil in the span section associated with the development of unstable aeroelastic modes. In one method, the correction mass includes one or more curved thin plates made of dense and heavy material, which are fixed around the leading edge in the span section. The size and weight of the correction mass are selected to move or offset the center of mass of the span section towards the leading edge. Such a correction mass can be applied to modify an already operating rotor blade with the aim of improving its stability limit, reducing fatigue and increasing revenue. Preferably, the ballast mass has a shape that enhances the shape of the airfoil in the span section, i.e., the thickness of the ballast mass is largest on the leading edge of the airfoil and gradually becomes thinner as the ballast mass bends around the leading edge onto the pressure side and suction side of the airfoil.

[0028] The ballast mass at the exterior of the rotor blade is preferably protected from exposure to the elements. Therefore, in a preferred embodiment of the invention, a protective cover is applied to the leading edge correction mass. For example, if the leading edge correction mass is implemented as a curved body arranged on a curved leading edge, the protective cover may be a leading edge protector (LEP) of said rotor blade. LEPs are generally required to protect the leading edge of a wind turbine rotor blade from impact damage, for example from hail, sand or other objects.

[0029] In a preferred embodiment of the invention, the leading edge correction mass is embedded in the rotor blade body, for example during the composite material layup phase during rotor blade manufacturing. Here, the ballast mass can also be in the form of one or more curved thin plates made of a heavy and dense material, such as lead. By incorporating the ballast mass into the rotor blade body, no corrosion protection needs to be provided. Such an embodiment may be preferred if the prevailing weather conditions at the installation site are very severe.

[0030] The design of a wind turbine rotor blade typically involves a design phase in which the structural parameters of the rotor blade are established. A prototype rotor blade is then manufactured and thoroughly tested. In order to meet the manufacturer's requirements for structural stability and life, multiple design and test iterations may be required. According to the present invention, the rotor blade may be developed by testing the prototype on an already assembled wind turbine. During the testing process, it is desirable to cover as many "real life" situations as possible in order to evaluate the performance of the prototype rotor blade. Initially, the prototype rotor blade may or may not include a leading edge correction mass.

[0031] As described above, different unstable aeroelastic modes may develop under different sets of conditions, such that while several parameters may be held constant (e.g., pitch angle and rpm), another parameter may vary (e.g., wind speed), leading to the development of unstable aeroelastic modes. However, wind conditions associated with unstable aeroelastic modes may not naturally occur during the testing process. Therefore, in order to simulate conditions that would promote the development of unstable aeroelastic modes, a ballast mass is preferably attached along a suitable spanwise section of the rotor blade at the leeward or rearward end of the trailing edge so as to change the dynamic aeroelastic properties of the rotor blade during the test sequence. The role of the trailing edge ballast mass is to induce unstable aeroelastic modes in the prototype rotor blade. In this way, the spanwise section of the prototype rotor blade that is most susceptible to the development of unstable aeroelastic modes may be determined, i.e., the trailing edge ballast mass may assist in collecting information data regarding the conditions under which unstable aeroelastic modes may develop for the rotor blade design.

[0032] The trailing edge correction mass may be in the form of a wedge arranged on the trailing edge in the span section of the rotor blade. Alternatively or additionally, the trailing edge correction mass may be attached to the trailing edge end of a fixture arranged around the airfoil. The trailing edge ballast mass is preferably sized to ensure that the test sequence always remains within a safe operating mode.

[0033] A series of tests may be performed for a number of different trailing edge corrective masses to cover a wider range of simulation conditions. Similarly, a series of tests may be performed with trailing edge corrective masses located at different positions in the outer side region of the rotor blade to cover a wider range of simulation conditions. In an early design phase, the trailing edge corrective masses may be deployed without any leading edge corrective masses, for example using the example of a rotor blade type that has already been deployed in an existing wind turbine installation.

[0034] Using the information gathered from the test program, the characteristics of the corrective leading edge ballast mass can be determined, and a suitable leading edge corrective mass can then be constructed and attached to a sample rotor blade in the determined span segment. Likewise, the information gathered from the test process can allow the analytical model to be validated with greater confidence. The wind turbine is run again to replicate the previously simulated conditions, with the goal of validating the effect of the leading edge corrective mass on the prototype rotor blade. Once the physical characteristics and location of a promising leading edge corrective mass have been determined for the rotor blade type, production of the rotor blade series can begin.

[0035] During simulations of a model of the rotor blade of the present invention, the inventors have observed that even a only slight shift of the CoM towards the leading edge in the critical span section can increase the stability limit or upper rotation speed threshold by an amount of approximately 10% compared to a prior art wind turbine rotor blade. This is a significant increase of the upper rotation speed threshold, allowing the wind turbine of the present invention to operate safely under conditions that would require preventive curtailment of a wind turbine equipped with a prior art rotor blade. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It should be understood, however, that the drawings are designed only for purposes of illustration and not as a definition of the limits of the present invention.

[0037] Figure 1 and Figure 2 Exemplary embodiments of rotor blades of the present invention are explained;

[0038] Figure 3 and Figure 4 Another exemplary embodiment of a rotor blade of the present invention is explained;

[0039] Figure 5 and Figure 6 Explains the prototype development phase;

[0040] Figure 7 and Figure 8 Another exemplary embodiment of a rotor blade of the present invention is explained;

[0041] Fig. 9 The behavior of the rotor blade of the present invention during an unstable aeroelastic mode is explained;

[0042] Fig.10 shows a curve of the rpm of the rotor blades varying with time;

[0043] Fig.11 A prior art rotor blade is shown.

[0044] In the drawings, like reference numerals refer to like objects throughout. Objects in the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0045] Figure 1 and Figure 2 An exemplary embodiment of a wind turbine rotor blade 20 of the present invention is illustrated. Figure 1 The rotor blade is shown in cross section, and Figure 2 2 shows a rotor blade 20 mounted to the hub of a wind turbine 2. Figure 1 As indicated in the figure, at the leading edge 20 LE The leading edge correction mass 1 is arranged at a position offset from the center of mass (CoM) of the airfoil. Figure 1 As indicated in FIG. 1 , the leading edge correction mass 1 is added to the critical section 20 UAM As mentioned above, the critical section 20 UAM It can be any outer section of the rotor blade that is most susceptible to unstable aeroelastic modes such as edge flutter, vortex flutter, etc. The leading edge correction mass 1 can be implemented as a curved thin plate of heavy material such as lead, tungsten, etc., shaped to surround the curved leading edge 20 of the rotor blade 20. LE Fitted on surface 200. One or more such heavy curved bodies may be incorporated or otherwise applied to critical section 20 UAM Leading edge 20 LE , and protective cover 20 LEP can be applied to the correction mass 1. The function of the leading edge correction mass 1 is to move the CoM 22 forward, i.e., towards the leading edge 20 as indicated by the arrow. LE . Slightly increase the critical section 20 UAM The total mass of the airfoil and the new or offset CoM 24 obtained (in the span section 20 UAM The combined effect of the above (i.e., the addition of the leading edge correction mass 1) is to reduce or eliminate the possibility of the development of unstable aeroelastic modes. In other words, the wind turbine can be operated without any need to reduce the rotor speed (i.e., cut the output power) even during unfavorable combinations of operating parameters that would lead to the development of unstable aeroelastic modes for an equivalent conventional rotor blade (i.e., a rotor blade without the addition of the leading edge correction mass 1).

[0046] Figure 3 and Figure 4 Another exemplary embodiment of a wind turbine rotor blade 20 of the present invention is illustrated. Figure 3 The rotor blade is shown in cross section, and Figure 4 is a front view of rotor blade 20 .

[0047] like Figure 3As indicated, in critical section 20 UAM Inside, the leading edge correction mass 1 is set at the leading edge 20 LE The ballast mass 1 is mounted to the rotor blade 20 by means of a sturdy frame 12. Here, the function of the leading edge correction mass 1 is also to move the CoM 22 forward as indicated by the arrow, i.e. to obtain a closer position to the leading edge 20. LE The offset center of mass CoM 24.

[0048] Figure 5 A test procedure is shown in which a prototype rotor blade 20 test To simulate as many "real life" situations as possible, each prototype rotor blade 20 test By having a trailing edge ballast mass of 30 TE In the exemplary embodiment, the blade clamp 30 is positioned on the sample rotor blade 20. test Alternatively or additionally, each blade fixture 30 may have a different trailing edge ballast mass 30. TE Initially, the prototype rotor blade 20 test The leading edge correction mass may or may not be included. As described above, the trailing edge ballast mass 30 TE The role is to promote the prototype rotor blade 20 test This allows the determination of the wing span segments most susceptible to the development of unstable aeroelastic modes. UAM During the test procedure it was observed that the “control” rotor blade 20 c (eg a prototype rotor blade without any correction mass or a prior art rotor blade as described in the background).

[0049] When the unstable aeroelastic mode was successfully simulated, the prototype rotor blade 20 test The nature of the oscillations in the wing can be observed and evaluated in order to determine the nature of the leading edge correction mass required to suppress or damp the oscillations. Using the information collected from the sensors and observations during the test program, the critical span section 20 can be targeted. UAM The leading edge correction mass in determines an optimum arrangement such that a desired high stability limit can be achieved for a rotor blade of said type when it is mounted on a wind turbine.

[0050] In another stage, Figure 6 As explained in the prototype rotor blade 20 test This leading edge correction quality 1 is enhanced, for example, as in the above Figure 3 In the embodiment described in (similarly, it is possible to implement Figure 1 The wind turbine was run again to replicate the conditions previously simulated, with the goal of verifying the leading edge correction quality 1 on the prototype rotor blade 20 test Once the effect of the leading edge correction quality has been verified, serial production of rotor blades can begin.

[0051] In order to increase the efficiency of the test phase, or to allow further adjustments to an already assembled rotor blade, the calibration mass may be movably mounted to the inside of the rotor blade or to the outside of the rotor blade. Preferably, the position of the calibration mass may be adjusted in response to a remotely issued command. Such an embodiment allows various test sequences to be performed without requiring a technician to physically access the outside of the rotor blade during the test phase, as these operations are expensive and dangerous and can only be performed under favorable weather conditions. Likewise, such an embodiment allows the performance of an already assembled rotor blade to be further optimized.

[0052] Figure 7 A rotor blade 20, 20 with a movable leading edge correction mass 1 is shown. test The correction mass 1 is mounted to a track 14 on the interior of the airfoil and can be moved back and forth in the chordwise direction in response to commands received via a communication interface, such as the wireless interface 16 indicated here. As described above, the movement of the correction mass 1 is used to adjust the position of the airfoil relative to the leading edge 20 LE Mobile CoM.

[0053] Figure 8 Another rotor blade 20, 20 with a movable leading edge correction mass 1 is shown. test Here, the correction mass 1 is mounted to tracks 14 which allow it to be moved back and forth in the spanwise direction in response to commands received via the communication interface 16. In a similar manner, the leading edge correction mass may be movably mounted to the exterior of the rotor blade if its effectiveness is improved when located upstream of the leading edge.

[0054] The geometry of the rotor blade and the prevailing weather conditions at the wind turbine assembly site may determine whether the leading edge correction mass may be mounted in the interior of the airfoil or upstream of the leading edge.

[0055] Fig. 9 The behavior of the rotor blade 20 of the present invention or of a prototype rotor blade 20 during operating conditions that would otherwise lead to the development of unstable aeroelastic modes is illustrated. Critical Span Section 20 UAM The effect of the initial "upward" or flap motion 91 of the airfoil in the leads results in a corrective reaction "head-down" pitching motion 92 of the leading edge corrective mass 1 so that unstable aeroelastic modes do not develop and the aeroelastic behavior of the entire rotor blade remains stable.

[0056] Fig.10 A graph of rotor speed (rotational frequency, RPM, revolutions per minute) versus time is shown for a rotor blade mounted on an operating wind turbine. The rotor blade may be assumed to operate under a certain set of parameters, for example wind speed and pitch angle may be assumed to be constant. As long as the rotor speed does not exceed a certain threshold or stability limit, the rotor blade remains in a stable aeroelastic mode SAM and does not experience vibrations, such as flutter along the edges. However, if the rotor speed increases above the threshold, the rotor blade enters an unstable aeroelastic mode, in which the vibrations are negatively damped. The amplitude of the oscillations may be such that the rotor blade suffers material fatigue or even direct structural damage, leading to expensive repair procedures. Stability Limit 50 SL The rotor blades of the prior art are suitable and the wind turbine controller must ensure that the rotor speed remains below the limit of 50 SL However, at or above the stability limit of 50 SL Higher rotor speeds are associated with increased power output and valuable revenue. In the rotor blade of the present invention, the leading edge correction mass suppresses the development of unstable aeroelastic modes, resulting in a higher stability limit of 20 SL This is achieved thereby allowing the rotor blade of the invention to be operated at the desired higher rotor speeds without causing fatigue or structural damage. Operators of wind turbines equipped with the rotor blade of the invention may therefore benefit from increased revenue.

[0057] Fig.11 A prior art rotor blade 50 susceptible to the occurrence of unstable aeroelastic modes is shown, as well as another equivalent prior art rotor blade 50' adapted to avoid the occurrence of said unstable aeroelastic modes by including additional mass in a span section 50UAM in an outboard region. The added mass is obtained by increasing the thickness 510 of the airfoil compared to the thickness 500 of the uncorrected rotor blade 50. The purpose of the added mass is to increase the rotor blade stiffness in said region. However, the added mass also affects the dynamic characteristics of the wind turbine, since it increases the total rotor blade mass, leading to "mass moment losses" (i.e. an undesirable increase in blade loads along the edges), an undesirable increase in loads transmitted to the hub, leading to fatigue damage of the hub and pitch system, etc. Another problem with this known approach is the inherent difficulty in correctly estimating the stability limits of a wind turbine during the design phase, i.e. the difficulty in predicting the performance of a rotor blade as part of an operating wind turbine. Therefore, the added mass in a thicker body wall may not bring the expected benefits and may even have unforeseen adverse effects.

[0058] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0059] For the sake of clarity, it is to be understood that the use of "a" or "an" throughout the application does not exclude a plurality, and "comprising" does not exclude other steps or elements.

Claims

1. A wind turbine rotor blade (20), comprising: - medial area; - an outboard region comprising a span section associated with the development of an unstable aeroelastic mode (UAM) (20 UAM ); The rotor blade is characterized in that - comprising a wing span section (20 UAM ) within a leading edge correction mass (1), the leading edge correction mass being suitable for the span section (20 UAM ) is oriented toward the leading edge (20 LE ) moves in order to suppress the development of unstable aeroelastic modes (UAM).

2. A wind turbine rotor blade according to the preceding claim, wherein: The leading edge correction mass (1) is arranged outside the rotor blade (20).

3. A wind turbine rotor blade according to any one of the preceding claims, comprising a mounting structure (12) for mounting the leading edge correction mass (1) to the rotor blade (20).

4. A wind turbine rotor blade according to any one of the preceding claims, wherein: The leading edge correction mass (1) is bonded to an outer surface (200) of the rotor blade (20).

5. A wind turbine rotor blade according to the preceding claim, comprising a protective cover (20) applied to the leading edge correction mass (1). LEP ).

6. A wind turbine rotor blade according to any one of the preceding claims, wherein: A leading edge correction mass (1) is embedded in the rotor blade body (20).

7. A wind turbine rotor blade according to any one of the preceding claims, wherein: The leading edge correction mass (1) comprises a density of at least 10 g / cm 3 materials.

8. A wind turbine rotor blade according to any one of the preceding claims, wherein: The leading edge correction mass (1) has a curved leading edge (20) aligned with the rotor blade (20) LE )’s shape.

9. A wind turbine rotor blade according to any one of the preceding claims, comprising means for adjusting the leading edge correction mass (1) relative to the span section (20 UAM )'s center of mass (22) is located at a position (14, 16).

10. A wind turbine comprising a plurality of rotor blades (20) according to any one of the preceding claims.

11. A method of manufacturing a wind turbine rotor blade (20), the method comprising the steps of: - determining the span sections (20) associated with the development of unsteady aeroelastic modes (UAM) in the outer regions of the rotor blades (20); UAM ); - Determine the characteristics and location of the leading edge correction mass (1) which will restrain the span section (20 UAM ) development of unsteady aeroelastic modes (UAMs); -Provide this leading edge correction quality (1); as well as - arranging the leading edge correction mass (1) in the span section (20 UAM )Inside.

12. The method according to the preceding claim, comprising a prototype testing phase comprising the following steps: - The trailing edge mass (30 TE ) is attached to the prototype rotor blade (20 test )’s trailing edge; - The prototype rotor blade (20 test ) is mounted to a hub of a previously assembled wind turbine (3); and - adjusting the operating parameters of the wind turbine (3) to achieve the desired performance on the prototype rotor blade (20 test ) of the wingspan section (20 UAM ) develops an unstable aeroelastic mode (UAM).

13. The method according to claim 12, wherein: The characteristics of the leading edge correction quality (1) are determined from information collected during the prototype testing phase.

14. The method according to claim 12 or 13, wherein: The leading edge correction mass (1) is movably arranged on the rotor blade prototype (20 test ) in the chordwise direction of the leading edge, and wherein the position of the leading edge correction mass (1) is adjusted during the prototype testing phase.

15. The method according to any one of claims 12 to 14, wherein: The leading edge correction mass (1) is movably arranged on the rotor blade prototype (20 test ) in the spanwise direction of the wing, and the position of the leading edge correction mass (1) is adjusted during the prototype testing phase.

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