EP3146201A1

EP3146201A1 - Aerodynamic device of a rotor blade of a wind turbine

Info

Publication number: EP3146201A1
Application number: EP15716486.4A
Authority: EP
Inventors: Peder Bay Enevoldsen; Alejandro Gomez Gonzalez; Mogens Nielsen
Original assignee: Siemens AG
Current assignee: Siemens Gamesa Renewable Energy AS
Priority date: 2014-05-23
Filing date: 2015-04-10
Publication date: 2017-03-29
Also published as: WO2015176868A1

Abstract

The invention relates to a rotor blade (20) for a wind turbine (10), the rotor blade (20) comprising a rotor blade body (31) and an aerodynamic device (32). The aerodynamic device comprises a first portion (321) by which the aerodynamic device (32) is attached to the rotor blade body (31), and a second portion (322) which is movable with regard to the rotor blade body (31). The aerodynamic device (32) is configured such that if load on the aerodynamic device (32) exceeds a predetermined value, a torque is generated on the second portion (322) of the aerodynamic device (32) such that the second portion (322) is passively deflected; and due to the deflection of the second portion (322) of the aerodynamic device (32), the airflow flowing from the leading edge section (24) to the trailing edge section (23) of the rotor blade (20) is deviated such that load on the rotor blade (20) is alleviated. The rotor blade (20) is characterized in that the first portion (321) and the second portion (322) of the aerodynamic device (32) are located at different spanwise postions of the rotor blade (20). Furthermore, the invention is related to a wind turbine (10) comprising at least one of such a rotor blade (20).

Description

Aerodynamic device of a rotor blade of a wind turbine The invention relates to a rotor blade of a wind turbine, wherein the rotor blade comprises a rotor blade body and an aerodynamic device.

The design of a wind turbine, in particular the design of a rotor blade of a wind turbine, is influenced by a plurality of factors. One of the most important of these factors is the loading of the rotor blade, in particular the maximum allowable loading of the rotor blade. High loading of the rotor blade typically occurs during extreme operating conditions. These extreme operating situations include situations where the lift of the rotor blade is maximum and the relative speed of the rotor blade is high. These extreme operating conditions may occur at extreme turbulences, occurrence of gusts or emergency events such as a shutdown of the wind turbine at wind speeds which are close to the rated maximum wind speed allowed for the wind turbine.

The maximum allowable load of the rotor blade has a direct impact on the structural requirements, e.g. the design limit, of the rotor blade. Thus, the problem of reducing high loads of the rotor blade is highly relevant and has been addressed in several ways in the past.

One approach for adjusting the loading of a rotor blade of a wind turbine is disclosed in the patent application US

2012/0141268 Al . In this publication, a rotor blade assembly which comprises a spoiler assembly operable to alter a flow past a surface of the rotor blade is disclosed. The spoiler assembly is incrementally deployable from the surface of the rotor blade.

Another approach for reducing the maximum loading of the rotor blade is disclosed in the patent application WO 2007/045940 Al . In this publication, a wind turbine blade which comprises an active elastic member arranged with access to the surface of the wind turbine blade is provided. The active elastic member is deformable from a first shape to a se- cond shape and thus the lift coefficient of the wind turbine blade is advantageously influenced by this active elastic member .

These approaches, however, have the disadvantage that they require complex activation mechanisms and that they require considerable modification of the rotor blade. Consequently, they are expensive and may require significant servicing during the lifetime of the rotor blade. Another approach of alleviating load of a rotor blade is the provision of a flexible flap as disclosed in DK 9 500 009 U3. This flap is able to be designed in a way that it bends downstream and thus alleviates loading of the rotor blade. However, it is desirable to provide a concept with improved load alleviation properties compared to the known prior art.

This objective is achieved by the independent claims. Advantageous developments and modifications are described in the dependent claims.

According to the invention there is provided a rotor blade of a wind turbine, wherein the rotor blade comprises a rotor blade body and an aerodynamic device. The aerodynamic device comprises a first portion by which the aerodynamic device is attached to the rotor blade body, and a second portion which is movable with regard to the rotor blade body. The aerodynamic device is configured such that if load on the aerodynamic device exceeds a predetermined value, a torque is gen- erated on the second portion of the aerodynamic device such that the second portion is passively deflected; and due to the deflection of the second portion of the aerodynamic device, the airflow flowing from the leading edge section to the trailing edge section of the rotor blade is deviated such that load on the rotor blade is alleviated. The rotor blade is characterized in that the first portion and the second portion of the aerodynamic device are located at different spanwise positions of the rotor blade.

A wind turbine refers to a device that can convert wind energy, i.e. kinetic energy from wind, into mechanical energy. The mechanical energy is subsequently used to generate elec- tricity. A wind turbine is also denoted a wind power plant.

The aerodynamic device is attached to the rotor blade body at the trailing edge section. Thus, the aerodynamic device is also a part of the trailing edge section of the rotor blade.

The aerodynamic device can be subdivided into the first portion and the second portion. Note that this division may be a purely virtual division and that the border between the first portion and the second portion may be invisible re- garding the aerodynamic device. The division into the first portion and the second portion rather comes from a functional perspective. Namely, the first portion of the aerodynamic device refers to the part of the aerodynamic device by means of which the aerodynamic device is firmly and durably at- tached to the rotor blade body of the rotor blade. Contrary to the first portion, the second portion refers to the part of the aerodynamic device which is aligned to the rotor blade body of the rotor blade but which is misaligned to the rotor blade body due to deflection of the aerodynamic device under certain conditions.

In a first alternative, continuous deflection of the second portion of the aerodynamic device occurs according to the load which is applied to the rotor blade.

In a second alternative, deflection of the second portion of the aerodynamic device occurs if the load which is applied to the rotor blade, in particular to the aerodynamic device, ex- ceeds a predetermined critical load. In other words, a threshold value of the load on the rotor blade is predetermined above which the second portion of the aerodynamic device passively deflects.

The torque, which is generated on the second portion of the aerodynamic device, is also referred to as the moment or moment of force. The torque is understood to be the product of distance of the point where the external loading force ap- plies from the axis of rotation times the external force.

In a particular embodiment, the first portion of the aerodynamic device is firmly attached to the rotor blade body of the rotor blade.

A key aspect of the present invention is that due to the deflection of the aerodynamic device loading of the rotor blade is reduced. In other words, an effect of the described aerodynamic device is that it selectively influences the load of the rotor blade.

An advantage of the described rotor blade is that the aerodynamic device does not need any external energy supply in order to be activated.

Another advantage is that no changes in the structure of the rotor blade and only negligible change of the mass of the rotor blade is required by this purely aerodynamic solution. It is furthermore an advantageous feature of the described rotor blade that the aerodynamic device is particularly activated at high loading, while it does not affect operation of the rotor blade during normal operation conditions. Distinction between normal operation conditions and high loads or extreme conditions can e.g. be made by an appropriate choice of the predetermined critical load above which the second portion of the aerodynamic device passively deflects. Note, however, that the aerodynamic device may also be designed such that it bends at medium loads, e.g. at loads which typically occur at wind speeds where the wind turbine reaches it rated power. Concretely, the aerodynamic device may start being deflected at wind speeds between 8 m/s and 14 m/s .

In particular, the advantage of the inventive flap compared to the flap as e.g. disclosed in DK 9 500 009 U3 is that more design flexibility exists. By varying and optimizing e.g. the extension of the first portion relative to the second portion, further load alleviation potential results.

Another advantage of the proposed solution is that it is in- expensive and durable as it can be manufactured by cheap materials and does not need significant maintenance.

A beneficial result of using such a rotor blade is that also other components of the wind turbine such as the pitch bear- ing tower or the main frame of the wind turbine are less stressed and less loaded, thus allowing for either an up scaling of the wind turbine or a reduction of the costs of the components. Both options are beneficial for a reduction of the cost of energy produced by the wind turbine.

Note that in the unloaded state, where the second portion of the aerodynamic device is aligned along the rotor blade body, the second portion may either be in direct contact with the rotor blade body or be in close proximity to the rotor blade body .

The aerodynamic device may be made of elastomeric polymer, in particular rubber. An advantage of manufacturing the aerodynamic device by elastomeric polymer is that elastomeric polymer is a material that is readily available, relatively inexpensive and well proven for the use in components of a wind turbine. Furthermore, elastomeric polymer has the capability to provide a reversible deflection of the second portion of the aerodynamic device over a long time span, even at harsh con- ditions under which the wind turbine may operate.

The rotor blade may comprise a plurality of aerodynamic devices. Exemplarily, the aerodynamic device may have a

spanwise extension between 2 per cent and 15 per cent of the chord length of the rotor blade. The aerodynamic device may have, for instance, a spanwise extension of 20 cm. Having in mind that the total spanwise extension of the rotor blade may easily exceed 50 meters or even 100 meters, it is therefore advantageous to provide a plurality of aerodynamic devices in order to efficiently impact the loading of the rotor blade.

Advantageously, the aerodynamic devices of the plurality of aerodynamic devices are aligned along the spanwise direction of the rotor blade.

Assuming that the trailing edge of the rotor blade is substantially parallel to the spanwise direction of the rotor blade, the aerodynamic devices are beneficially aligned along the trailing edge.

In a first option, two neighboring aerodynamic devices of the plurality of aerodynamic devices are directly adjacent to each other. This has the advantage that the full area along the trailing edge is used and covered by aerodynamic devices. Thus, a maximum benefit can be drawn from the deformable aerodynamic devices . In a second option, two neighboring aerodynamic devices of the plurality of aerodynamic devices are spaced apart from each other. This may be advantageous from a manufacturing point of view. Concretely, it may be easier to integrate the aerodynamic devices to the trailing edge section of the rotor blade if certain spacing between two neighboring aerodynamic devices is present.

In a first embodiment, the aerodynamic device is shaped as a flap . The aerodynamic device may have an elongated shape comprising a long side and a short side.

Advantageously, the aerodynamic device is orientated with its long side along the spanwise direction of the rotor blade.

The second portion of the aerodynamic device advantageously deflects towards the suction side of the rotor blade.

Advantageously, the aerodynamic device, in particular the second portion of the aerodynamic device, is deflected or bent such that the airflow between the leading edge section and the trailing edge section of the rotor blade is disrupted in such a manner that flow separation is caused. Due to the flow separation the lift of the rotor blade is reduced and the load of the rotor blade is reduced as well.

In a second embodiment, the aerodynamic device comprises a serrated trailing edge. A serrated trailing edge which is also referred to as a sawtooth trailing edge or serrated panels are a well-known feature to reduce noise which is generated by the rotor blade and/or to increase the efficiency of the rotor blade. It is beneficial to combine this feature with the deformable aero- dynamic device. In a third embodiment, the aerodynamic device is shaped as a Gurney flap and is situated at the pressure side of the rotor blade . Gurney flaps as such are also well-known for aircraft wings or rotor blades of a wind turbine to increase the lift. However, with conventional Gurney flaps which are mounted on the pressure side close to the trailing edge of a rotor blade the lift of the rotor blade is potentially increased over the whole range of relevant angles of attack of the rotor blade.

The aerodynamic device shaped as a Gurney flap presented here has the advantage that in a loaded state of the rotor blade the Gurney flap is deflected and at least this part of the trailing edge thus bends away from the airfoil in a direction parallel to the airflow, flowing from the leading edge section to the trailing edge section of the rotor blade. As a consequence, the lift enhancing effect of the Gurney flap is lost or at least decreased, thus the load of the rotor blade is decreased, too.

In a fourth embodiment, the aerodynamic device is rotatable mounted . Advantageously, the aerodynamic device has a predetermined rotational stiffness such that rotation of the aerodynamic device is only activated in a loaded state of the rotor blade . Advantageously, the aerodynamic device comprises an axis of rotation which is substantially parallel to the chord line of the airfoil profile of the rotor blade. The aerodynamic device is mounted rotatable about the axis of rotation to the rotor blade body.

In other words, the orientation of the aerodynamic device can also be described such that the axis of rotation of the aerodynamic device is substantially parallel to the wind, i.e. the airflow, flowing from the leading edge section to the trailing edge section of the rotor blade. Although the wind flow is substantially parallel to the axis of rotation, there are still some components in the wind flow which induce a ro- tation of the aerodynamic device if e.g. the load exceeds a predetermined threshold value, namely the critical load.

Advantageously, the aerodynamic device is rotationally symmetric about an axis of rotational symmetry, and the axis of rotation is different from the axis of rotational symmetry. Consequently, this leads to a preferred rotational direction of the aerodynamic device if the aerodynamic device is deflected . Note that contrary to the previous embodiments, the fourth embodiment does not necessarily involve a structural change of the aerodynamic device. In other words, while in the previous embodiments the shape of the aerodynamic device changes due to the deflection above a certain load, in the fourth em- bodiment the structure of the aerodynamic device may remain unchanged. However, an orientation of the aerodynamic device with regard to the rotor blade body of the rotor blade occurs. Thus, the first portion of the aerodynamic device which is firmly attached to the rotor blade body can be referred to the area around the axis of rotation, in other words around the hinge where the aerodynamic device is connected to the rotor blade body. Likewise, the remaining part of the aerodynamic device can be referred to as the second portion. In a first option, the arrangement of the axis of rotation and the axis of rotational symmetry of the aerodynamic device can be chosen such that in a loaded state of the rotor blade, e.g. for loads exceeding the critical load, two neighboring aerodynamic devices are rotated, i.e. deflected in the same direction of rotation.

In a second option, the axis of rotation and the axis of rotational symmetry of two neighboring aerodynamic devices are chosen such that in the loaded state of the rotor blade the two neighboring aerodynamic devices are rotated in opposite directions of rotation. Which one of the two options is advantageous depends on the specific design of the rotor blade body of the rotor blade as well as the operational mode of the rotor blade.

In another advantageous embodiment, the rotor blade body comprises an airfoil profile which has a flatback profile at its trailing edge section.

In other words, the trailing edge section does not comprise a sharp trailing edge but features rather a blunt trailing edge .

Advantageously, the described aerodynamic device is applied to an aeroelastically tailored rotor blade. These type of rotor blades are also referred to as swept or curved rotor blades .

Finally note that the aerodynamic device may also have a cascading functionality. This includes a first passive bending of the aerodynamic device for a first load applied to the rotor blade and a second passive bending of the aerodynamic de- vice.

Embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, of which :

Figure 1 shows a wind turbine;

Figure 2 shows a rotor blade of a wind turbine; Figures

3A and B show a first embodiment of an aerodynamic device in an unloaded state and a loaded state of the rotor blade, respectively; Figures

4A and 4B show a second embodiment of an aerodynamic device in an unloaded state and a loaded state of the ro- tor blade, respectively;

Figures

5A and 5B show a third embodiment of an aerodynamic device in an unloaded state and a loaded state of the rotor blade, respectively;

Figures

6A to 6C show a fourth embodiment of an aerodynamic device in an unloaded state and loaded states of the rotor blade, respectively;

Figures

7A to 7C show preferred positions of the aerodynamic device on a rotor blade; and

Figure 8 shows the influence of the aerodynamic device on the curve of the lift coefficient with regard to the angle of attack. The illustration in the drawings is in schematic form. It is noted that in different figures, similar or identical elements may be provided with the same reference signs.

In Figure 1, a wind turbine 10 is shown. The wind turbine 10 comprises a nacelle 12 and a tower 11. The nacelle 12 is mounted at the top of the tower 11. The nacelle 12 is mounted rotatable with regard to the tower 11 by means of a yaw bearing. The axis of rotation of the nacelle 12 with regard to the tower 11 is referred to as the yaw axis.

The wind turbine 10 also comprises a hub 13 with three rotor blades 20 (of which two rotor blades 20 are depicted in Figure 1) . The hub 13 is mounted rotatable with regard to the nacelle 12 by means of a main bearing. The hub 13 is mounted rotatable about a rotor axis of rotation 14.

The wind turbine 10 furthermore comprises a main shaft, which connects the hub 13 with a rotor of a generator 15. The hub 13 is connected directly to the rotor, thus the wind turbine 10 is referred to as a gearless, direct driven wind turbine. As an alternative, the hub 13 may also be connected to the rotor via a gearbox. This type of wind turbine is referred to as a geared wind turbine.

The generator 15 is accommodated within the nacelle 12. It comprises the rotor and a stator. The generator 15 is arranged and prepared for converting the rotational energy from the rotor into electrical energy.

Figure 2 shows a rotor blade 20 of a wind turbine. The rotor blade 20 comprises a root section 21 with a root 211 and a tip section 22 with a tip 221. The root 211 and the tip 221 are virtually connected by the span 26 which follows the shape of the rotor blade 20. If the rotor blade were a rectangular shaped object, the span 26 would be a straight line. However, as the rotor blade 20 features a varying thickness, the span 26 is slightly curved or bent as well. Note that if the rotor blade 20 was bent itself, then the span 26 would be bent, too.

The rotor blade 20 furthermore comprises a leading edge section 24 with a leading edge 241 and a trailing edge section 23 with a trailing edge 231.

The trailing edge section 23 surrounds the trailing edge 231. Likewise, the leading edge section 24 surrounds the leading edge 241.

At each spanwise position, a chord line 27 which connects the leading edge 241 with the trailing edge 231 can be defined. Note that the chord line 27 is perpendicular to the span 26. The shoulder 28 is defined in the region where the chord line comprises a maximum chord length.

Furthermore, the rotor blade 20 can be divided into an in- board section which comprises the half of the rotor blade 20 adjacent to the root section 21 and an outboard section which comprises the half of the rotor blade 20 which is adjacent to the tip section 22. Figures 3A and 3B show a first embodiment of an aerodynamic device 32 which is mounted and attached to a rotor blade body 31 of a rotor blade. Specifically, in Figures 3A and 3B two aerodynamic devices 32 are shown, which are spaced apart. Figure 3A shows the rotor blade in an unloaded state. In other words, the rotor blade is loaded by a load which is smaller than the critical load. Note that the critical load is defined as the threshold value where parts of the aerodynamic device 32 are deflected. In Figure 3A no deflection of the aerodynamic device 32 occurs.

The aerodynamic devices 32 are mounted at the trailing edge section 23 of the rotor blade. Figures 3A and 3B show a perspective view on a part of the rotor blade regarding at the suction side 252 of the rotor blade. Note that the pressure side 251 of the rotor blade is opposite to the suction side 252.

Figure 3B shows the same rotor blade as in Figure 3A but in a loaded state, i.e. in a state where the rotor blade is loaded with a load that exceeds the critical load. Now, a first portion 321 of the aerodynamic device 32 is still firmly attached and connected with the rotor blade body 31 of the rotor blade. However, a second portion 322 now is misaligned with the rotor blade body 31 thus the aerodynamic device 32 is partly deflected. This deflection of the aerodynamic device 32 has the consequence that the wind flow is deflected in such a manner that the lift and the load of the rotor blade are decreased.

Figures 4A and 4B show a second embodiment of an aerodynamic device 32. The difference to the first embodiment is that serrations 35 are added to the flap which incorporates the aerodynamic device 32. The serrations 35 have the advantage that noise which is generated by the rotor blade is reduced and/or efficiency of the rotor blade is increased.

In a loaded state above the critical load, as it is shown in Figure 4B, the second portion of the aerodynamic device 322 is deflected. Note that the serrations 35 are deflected or bent, similarly.

Figures 5A and 5B show a third embodiment of an aerodynamic device 32. The aerodynamic device 32 which is shaped as a Gurney flap is attached to the trailing edge section 23 of the rotor blade at the pressure side 351.

Figure 5A shows four aerodynamic devices 32 which are aligned adjacent to each other along the trailing edge of the rotor blade. Each of the aerodynamic devices comprises a first portion 321 and a second portion 322. In an unloaded state of the rotor blade, the aerodynamic device 32 is fully aligned with the trailing edge of the rotor blade. Thus, wind flow that is flowing from the leading edge section 24 to the trailing edge section 23 on the pressure side 251 is deflected such that lift of the rotor blade is increased.

Figure 5B shows three aerodynamic devices 32 aligned one next to each other along the trailing edge of the rotor blade. Each of the aerodynamic devices comprises a first portion 321 which is firmly attached to the trailing edge section 23 of the rotor blade. However, the second portion 322 of the aerodynamic device is deflected leading to a misalignment of the second portion 322 with regard to the trailing edge 231. The deflection occurs in parallel with the wind flow flowing from the leading edge section 24 to the trailing edge section 23.

A technical effect of the deflection of the second portion 322 of the aerodynamic device 32 is that the lift enhancement effect of the aerodynamic device 32 is reduced. Thus, the lift enhancement of the rotor blade is reduced, but also the loading of the rotor blade is reduced. Figures 6A to 6C illustrate a fourth embodiment of an aerodynamic device 32.

Figure 6A shows a plurality of aerodynamic devices 32 spaced apart from each other and located at a trailing edge section 23 of a rotor blade. In an unloaded state of the rotor blade, which is shown in Figure 6A, the aerodynamic devices 32 are flush with the rotor blade body 31 of the rotor blade.

Figure 6B shows a loaded state of the rotor blade where the load exceeds the critical load. As a consequence, a rotation of the aerodynamic devices 32 is activated. By activation of the aerodynamic devices 32 these aerodynamic devices 32 are no longer flush with the rotor blade body, in particular with the trailing edge 231. As a consequence, a wind flow flowing from the leading edge section 24 to the trailing edge section 23 is disturbed in such a manner that the lift of the rotor blade is reduced.

Note that the axis of rotation of each aerodynamic device is substantially parallel to the chord line 27 of the rotor blade. If the axis of rotation 33 of the aerodynamic device 32 were coinciding with an axis of rotational symmetry 34 of the aerodynamic device 32, then no direction of rotation would be preferred. However, in Figure 6A the aerodynamic de- vices 32 are arranged such that the axis of rotation 33 and the axis of rotational symmetry 34 do not coincide. This has the effect that a direction of rotation at least a preferred direction of rotation is predetermined. Figure 6A shows a first option where the aerodynamic devices 32 are hinged such that counter-rotating pairs of aerodynamic devices result.

Figure 6C shows another option where all aerodynamic devices 32 are hinged in a similar manner so that they all have the same preferred direction of rotation. Note that in the embodiments of Figures 3A, 3B, 4A, 4B, 6A, 6B and 6C a torque in substantially chordwise direction is generated, while in the embodiments of Figures 5A and 5B a torque in substantially flapwise direction is generated. Figure 7A shows a first preferred location where the aerodynamic device 32 is preferably located on the rotor blade. More specifically, Figure 7A shows a preferred location outboard at the trailing edge section 23 of the rotor blade. Figure 7B shows another preferred location of the aerodynamic devices 32. Additionally to the outboard location a second location approximately in the spanwise center of the rotor blade is disclosed. Finally Figure 7C shows a continuous placement of aerodynamic devices 32 along almost the entire trailing edge section 23, from the shoulder of the rotor blade until almost the tip of the rotor blade.

Figure 8 shows a dependency of the lift coefficient CL with regard to the angle of attack AoA of the rotor blade. A first curve 41 shows a conventional rotor blade without any aerodynamic devices as described in this patent application. It can be seen that during a large range of considered angle of attacks AoA the lift coefficient increases. The point where the lift coefficient has its maximum may be referred to a maximum loading of the rotor blade.

The curve 42 shows a rotor blade with an aerodynamic device as described in this patent application. It can be seen that the lift coefficient is the same for small angle of attacks AoA but deviates from the first curve 41 for high angle of attacks AoA. The second curve 42 deviates in a way that the lift coefficient is reduced for high angles of attack AoA. Particularly, the maximum of the second curve 42 is considerably smaller than the maximum of the first curve 41. This results in a reduced maximum loading of the rotor blade. This is advantageous with regard to for example the structural requirements of the rotor blade or the range in which the wind turbine can be operated.

Finally, a third curve 43 is shown. This third curve 43 represents a rotor blade with an aerodynamic device as described in this patent application. It can be seen that the third curve 43 deviates from the first curve representing a conventional rotor blade in the whole range of considered angles of attack AoA. The third curve 43 has an increased lift coefficient CL for small angles of attack AoA, but a reduced lift coefficient for high angles of attack AoA. This is a highly advantageous behavior as for small loading the lift coefficient is increased while for a high loading of the rotor blade where a further loading due to the aerodynamic device is not desired this lift coefficient is reduced.

Claims

Patent claims

1. Rotor blade (20) for a wind turbine (10), the rotor blade (20) comprising a rotor blade body (31) and an aerodynamic device (32) ,

wherein

- the aerodynamic device comprises a first portion (321) by which the aerodynamic device (32) is attached to the rotor blade body (31) ,

- the aerodynamic device (32) comprises a second portion

(322) which is movable with regard to the rotor blade body (31) , and

- the aerodynamic device (32) is configured such that

- if load on the aerodynamic device (32) exceeds a pre- determined value, a torque is generated on the second portion (322) of the aerodynamic device (32) such that the second portion (322) is passively deflected, and

- due to the deflection of the second portion (322) of the aerodynamic device (32), the airflow flowing from the leading edge section (24) to the trailing edge section (23) of the rotor blade (20) is deviated such that load on the rotor blade (20) is alleviated, characterized in that

- the first portion (321) and the second portion (322) of the aerodynamic device (32) are located at different spanwise positions of the rotor blade (20) .

2. Rotor blade (20) according to claim 1,

wherein the aerodynamic device (32) is attached to the rotor blade body (31) at the trailing edge section (23) of the rotor blade body (31) .

3. Rotor blade (20) according to one of the preceding claims, wherein the value of the predetermined load, at which the second portion (322) of the aerodynamic device (32) is deflected, is greater than 40%, in particular greater than 70% of the design load of the rotor blade (20) at the operational state of the wind turbine (10) when the wind turbine (10) reaches its rated power.

4. Rotor blade (20) according to claim 3,

wherein the aerodynamic device (32) is flush with the rotor blade body (31) for loads which are smaller than the predetermined load, at which the second portion (322) of the aerodynamic device (32) is deflected.

5. Rotor blade (20) according to one of the preceding claims, wherein the second portion (322) of the aerodynamic device (32) is pre-bent.

6. Rotor blade (20) according to one of the preceding claims, wherein the rotor blade (20) comprises a plurality of aerodynamic devices (32) .

7. Rotor blade (20) according to claim 6,

wherein the aerodynamic devices (32) are aligned in spanwise direction along the rotor blade (20) .

8. Rotor blade (20) according to one of the preceding claims, wherein the aerodynamic device (32) is loaded by a force act- ing in substantially flapwise direction of the rotor blade

(20) , such that a torque in substantially chordwise direction of the rotor blade (20) is generated.

9. Rotor blade (20) according to one of the claims 1 to 7 , wherein the aerodynamic device (32) is loaded by a force acting in substantially chordwise direction of the rotor blade (20) , such that a torque in substantially flapwise direction of the rotor blade (20) is generated.

10. Rotor blade (20) according to one of the preceding claims , wherein the first portion (321) of the aerodynamic device (32) extends over at least 10% of the total spanwise extension of the aerodynamic device (32) .

11. Rotor blade (20) according to one of the preceding claims ,

wherein deflection of the second portion (322) of the aerodynamic device (32) is performed by a bending movement of the second portion (322) .

12. Rotor blade (20) according to one of the preceding claims ,

wherein at least the second portion (322) of the aerodynamic device (32) is made of an elastic material, in particular an elastomeric polymer.

13. Rotor blade (20) according to one of the claims 1 to 10, wherein the first portion (321) is a rotational element such that deflection of the second portion (322) of the aerodynam- ic device (32) is performed by a rotational movement of the second portion (322) .

14. Rotor blade (20) according to claim 13,

wherein at least the second portion (322) of the aerodynamic device (32) is stiff up to the maximum load for which the rotor blade (20) is designed for.

15. Wind turbine (10) comprising at least one of the rotor blades (20) according to 1 to 14.