4 into electrical energy. The generator 5 is an electric machine comprising a rotor and a stator, wherein the rotor is connected to the hub 4 and the stator is connected to the nacelle 3. If the hub 4 is directly connected to the rotor, the wind turbine 1 is referred to as a gearless, direct-driven wind turbine. Such a generator 5 is also referred as direct drive generator 5. As an alternative, if the hub 4 is indirectly connected to the rotor via a gear box, this type of wind turbine 1 is referred to as a geared wind turbine. Embodiments of the present invention are suitable for both types of wind turbines 1.

FIG. 2 shows a perspective half-transparent view of a blade 6 according to an embodiment, and FIG. 3 shows a partial cross-section view of an active member 10 according to an embodiment. The blade 6 comprises a blade body 9, a plurality of active members 10 which are mounted to the blade body 9 and configured to move between a retracted position and an extended position to change an aerodynamic property of the blade 6. In FIG. 2, the active members 10 are positioned in the retracted position, whereas in FIG. 3, the active member(s) 10 is/are positioned in the extended position.

The blade 6 further comprises a bladder 11 which is configured to be connected to a pneumatic or hydraulic system of the wind turbine 1 to move the active member 10 when the bladder 11 is filled by a fluid supplied by the pneumatic or hydraulic system, or when the fluid is removed from the bladder 11 by the pneumatic or hydraulic system. The fluid is supplied or removed to and from the bladder 11 via hoses 16.

In the embodiment of FIG. 3, each active member 10 comprises an airfoil portion 21 which forms part of an airfoil of the blade 6, and a movable portion 22 which is moved by the bladder 11. The blade 6, in this case each active member 10, further comprises a spring which is configured to retract the active member 10, i.e. in particular the movable portion 22 of the active member 10 into the retracted position. In the embodiment of FIG. 3, the spring is implemented by a flexible portion 17 of each active member 10 which connects the airfoil portion 21 to the movable portion 22.

The wind turbine 1 further comprises a retaining means configured to prevent the active member 10 from moving towards the extended position. In the embodiment of FIG. 3, the retaining means comprises a suction means configured to control a predetermined fluid pressure within the bladder 11 which prevents the bladder 11 from inflating due to pressure which builds up inside the bladder 11 to the centrifugal action on the entrapped air in the hoses 16 and the bladder 11 which is created when the hub 4 rotates. In this case, the bladder 11 is not necessarily to be fixed to the active member 10 because the flexible portion 17 is usually configured to move or maintain the active member 10 to or in the retracted position.

FIG. 4 shows a perspective view of an active member 10 and a suction pressure reduction element 12 which is combined with a plurality of vortex generators 120 according to an embodiment, and FIG. 5 shows a perspective view of an active member/bladder arrangement according to the embodiment. In the embodiment of FIGS. 4 and 5, the retaining means is different from that of the previous embodiment. In detail, suction pressure reduction element 12 is provided at the blade body 9 adjacent a trailing edge of the active member 10, wherein the suction pressure reduction element 12 is configured to reduce a suction pressure induced by an air flow on the active member 10 when the active member 10 is in the retracted position. The suction pressure reduction element 12 reduces the suction pressure induced on the active member 10. The local airflow by the trailing edge of the active member 10 is modified, hence reducing the local lift force acting on the active member 10, which is described later in view of FIGS. 6 to 8. The suction pressure reduction element 12 can be shaped as a bulge, a convex bulge.

FIG. 6 shows a graph of an aerodynamic suction pressure behavior according to the prior art, where the blade is not provided with any suction pressure reduction element. The suction pressure exhibits a strong peak P′ near a trailing edge T′ of an active member 10′.

FIG. 7 shows a graph of an aerodynamic suction pressure behavior according to an embodiment of the present invention, where the blade (for example the blade body 9 or also a baseplate) is provided with suction pressure reduction element 12. The suction pressure does substantially not exhibit any peak near a trailing edge T of the active member 10. Reference sign R designates an area of a suction pressure reduction which is achieved by the suction pressure reduction element 12 compared to FIG. 6.

FIG. 8 shows a cross-section of parts of a blade according to an embodiment of the present invention, where the blade (for example the blade body 9 or also a baseplate) is provided with a suction pressure reduction element 12 which is combined with at least one vortex generator 120. The vortex generator(s) 120 is/are shaped like fins. The suction pressure behavior is substantially similar like that of FIG. 7, and the vortex generator(s) 120 additionally generate vortices.

The operating principle of the suction pressure reduction element 12 is to reduce local aerodynamic suction on the spoiler due to its own outer contour, in particular towards the trailing edge T of the active member 10, which is embodied as a spoiler here. The effect of this is that the total suction on the active member 10, i.e. the aerodynamic force trying to lift it from the surface, is reduced. By using such a suction reduction element 12, part of the suction pressure distribution is transferred from the active member 10 onto the suction reduction element 12. This is done by an appropriate adjustment of the outer contour of the active member 10 and of the suction reduction element 12. The suction reduction element 12 can either be configured such that the active members' trailing edge T rests on it, as shown in FIGS. 7 and 8, or be configured to butt-joint with a thicker spoiler trailing edge. Additionally, the suction reduction element 12 can be combined with the vortex generator(s) 120 or any other type of flow regulating devices.

FIG. 9 shows a cross-section view of parts of a blade 6 according to an embodiment. In this embodiment, the active member 10 further comprises a baseplate 20. The airfoil portion 21 is connected by a clip-connection 23 (see also FIGS. 10 to 12) or any other force-fit or form-fit connection to the baseplate 20, wherein the clip-connection 23 can act as a fulcrum. The bladder 11 is arranged and/or fixed between the baseplate 20 and the movable portion 22 of the active member 10. The baseplate 20 in turn is fixed to the blade body 9, for example by gluing. In this embodiment, the active member 10 and the bladder 11 are implemented in a single module which can readily be mounted to the blade body 9, for example by gluing.

FIG. 10 shows a cross-section view of an active member 10 according to an embodiment, where the bladder 11 is inflated, and FIG. 11 shows a cross-section view of the active member 10, where the bladder 11 is deflated. The blade 6 comprises a plurality of abutment members 13 which are arranged at the active member 10, strictly speaking at the airfoil portion 21 and at the movable portion 22, i.e. at portions in front and behind of the flexible portion 17. The abutment members 13 define the retracted position of the active member 10 when the abutment members 13 abut on or are pressed to the blade body 9. The abutment members 13 can directly abut on the blade body 9, or they can be pressed towards the blade body 9, for example when a baseplate 20 or another intermediate element is arranged between the abutment members 13 and the blade body 9.

The abutment members 13 can fulfill several functions. First, the abutment members 13 define the final shape of the active member 10 when the abutment members 13 abut on the blade body 9 or are pressed towards the blade body 9. Second, the abutment members 13 can form a fulcrum so that, given a certain suction level in the bladder 11, the contact force between the active member's trailing edge and the blade 6 is increased, and the required pressing force of the bladder 11 for down-pressing the active member 10 can be reduced. Each abutment members 13 can be shaped as a leg or a rib.

The embodiment of FIGS. 10 and 11 can be used together with the suction means which configured to control a predetermined fluid pressure within the bladder 11 which prevents the bladder 11 from inflating due to a centrifugal force which is created when the hub 4 rotates. In this case, the bladder 11 is not necessarily to be fixed to the active member 10. In a modification, the embodiment of FIGS. 10 and 11 can use the bladder 11 as shown in FIG. 13 (described later) together with the suction means which is configured to apply a negative pressure in the bladder 11 in order to actively press or retain the active member 10 to/in the retracted position. In this case, the bladder 11 is mechanically fixed to the active member 10 and (directly or indirectly) to the blade body 9.

FIG. 12 shows a partial cross-section view of an active member 10 according to an embodiment, and FIG. 13 shows a cross-section view of a bladder 11 according to an embodiment. In the embodiment of FIGS. 12 and 13, the retaining means is different from that of FIG. 3. In the embodiment of FIGS. 12 and 13, the retaining means is implemented in that the bladder 11 is fixed to the blade body 9 and the active member 10, in particular to the movable portion 22 of the active member 10, wherein the active member 10 is pressed and/or retained in the retracted position by a suction means configured to apply a negative pressure in the bladder 11. In the embodiments, a control means (not shown) can be provided which is configured to control a fluid pressure within the bladder 11.

In FIG. 12, the bladder 11 is drawn inside a recess of the blade body 9 or a support element/baseplate 20 of the active member 10; however, this recess is not essential, and the bladder 11 could also be installed on a nominal (smooth, no recessed) surface of the blade body 9 or the support element/baseplate 20 of the active member 10.

FIG. 14 shows a cross-section view of a bladder 11 according to an embodiment. Limiting members 14 are arranged within the bladder 11, wherein the limiting members 14 define a minimum deflated state of the bladder 11. The limiting members 14 are particularly advantageous in the retaining means of option a) which uses partial suction pressure, because the limiting members 14 prevent the bladder 11 from closing airtightly under vacuum and potentially prevents a portion of the bladder 11 to deflate completely. The limiting members 14 can be an extruded rib inside the bladder 11 or an additional member placed inside the bladder 11, for example a mesh or a foam.

Several modifications and combinations are conceivable. For example the embodiment of FIG. 12 can be modified by the features of the embodiment of FIG. 9.

Attachment portions 18, 19 of the bladder 11 (see FIGS. 11 to 14) provide for a form-fit or force-fit connection between bladder 11 and baseplate 20 on the one hand, and between the bladder 11 and the active member 10 (movable portion 22) on the other hand. For example, the bladder 11 can be slid in a longitudinal direction of the blade into corresponding receiving portions of the baseplate 20 and the active member 10 (movable portion 22).

The embodiments can be modified in that the active member 10 is hinged to the blade body 9 by a hinge such as a hinge 24 in FIG. 12, wherein a separate spring presses the active member 10 into the retracted position.

The embodiments can structurally be modified by features from the embodiments of FIGS. 15 to 32:

The adaptable spoiler 100 as schematically illustrated in FIG. 15 along a longitudinal axis 101 of a rotor blade 103 in a sectional side-view comprises a base element 105 which is adapted to be connected at or integrated with a rotor blade surface 107 of the rotor blade 103 which is partly illustrated in FIG. 15. The adaptable spoiler 100 further comprises an airfoil element 109 which is (e.g. reversibly or permanently) attachable to the base structure 105 (for example illustrated in FIG. 17) and having an airfoil shaped surface 111 to be exposed to an air flow 113 during operation of a wind turbine. The airfoil element 109 comprises an encapsulated core 110 providing enforcement.

The rotor blade 103 has a longitudinal axis 101 which is substantially perpendicular to the flow direction 113 of the air during operation of the wind turbine. The base element 105 comprises at least one attachment portion 115 and also the airfoil element 109 comprises at least one attachment portion 117. Thereby, the attachment portions 115 and 117 of the base element 105 and the airfoil element 109 are engageable with each other, as is for example illustrated in FIG. 17.

As can be taken from FIG. 15, the attachment portion 115 of the base element 105 is arranged in an upstream region 119 of the base element 105, in particular in a region between 5% and 50% of the entire extent lbe of the base element along the flow direction 113. Furthermore, the attachment region 117 of the airfoil element 109 is also arranged within an upstream region 121 of the airfoil element 109, in particular in a region between 0% and 50% of an entire extend lae of the airfoil element.

FIG. 15 illustrates a disassembled state, in which the airfoil element 109 is not attached to the base element 105. As can be appreciated from FIG. 15, the airfoil element 109 is pre-bent such that upon attaching the airfoil element 109 at the base element 105 (as illustrated in FIG. 17) the rear edge 123 of the airfoil element 109 presses upon the surface 107 of the rotor blade 103. Thus, the airfoil element 109 presses in a downstream region 125 towards the rotor blade surface 107 or in other embodiments towards the base element 105.

Below it is referred to a chordwise direction 113 that is a direction that points from the leading edge towards the trailing edge of the rotor blade. During normal operation the chordwise direction 113 is along an airflow direction. In the following the airflow direction is meant to be equal to the chordwise direction.

The attachment portion 115 of the base element 105 comprises in the illustrated embodiment two noses 127, 129 being spaced apart in the chordwise direction or airflow direction 113 and pointing according to the flow direction 113 downstream. Also the attachment portion 117 of the airfoil element 109 comprises two noses 131, 133 also being spaced apart in the flow direction 113 but pointing towards upstream. When the airfoil element 109 is attached to the base element 105 (see FIG. 171), the noses 131, 133 of the attachment region 117 of the airfoil element 109 engage below the noses 127, 129 of the base element 105. Furthermore, an elastic tongue 137 of the attachment region 117 of the airfoil element 109 is bent in the assembled state and contacts a protrusion 139 comprised in the attachment portion 115 of the base element.

The adaptable spoiler 100 illustrated in FIGS. 15 to 17 further comprises an inflatable, expandable container 141, for example configured as a bag or a hose and made from elastic deformable material. The container is illustrated in FIG. 15 in a disassembled and deflated state and in FIG. 17 in an assembled state. The expandable container 141 comprises a lumen 143 which is fillable with a fluid, such as air. Filling the lumen 143 of the container 141 to a different agree will expand the container 141 to a different degree thereby touching and pushing a back-surface 145 of the airfoil element 109 for flexing upwards the airfoil shaped surface 111 of the airfoil element, thereby achieving different states of the adaptable spoiler 100.

The container 141 is fixable at or to the base element 105. Therefore, the container 141 comprises an engagement portion 147 and the base element comprises a respective engagement portion 149 in particular in a downstream region 151 of the base element 105. The engagement portions 147 and 149 of the container 141 and the base element 105, respectively, are engageable with each other. In particular, also the engagement portion 147 of the container comprises noses which latch or catch below noses of the engagement portion 149 of the base element.

FIG. 16 schematically illustrates in more detail a portion of the airfoil element 109 showing the attachment region 117.

When the inflatable container 141 is inflated to a different degree, a state sketched in dashed lines in FIG. 17 is achieved. In particular, the container is now labelled with reference sign 141′ and the airfoil shaped surface of the airfoil element 109 is labelled with reference sign 111′. It can be seen from FIG. 17 that the position and/or orientation and/or shape of the downstream portion 125 of the airfoil element 109 is changed, while the position and/or orientation and/or shape of the airfoil element 109 is substantially unchanged in the upstream region 121.

As can be seen in FIG. 15, the rotor blade surface has in the region of the attached base element 105 a slight depression as indicated with Δ. Thus, the base element 105 is slightly submerged into the rotor blade 103.

FIGS. 18 to 20 illustrate in a sectional side-view an adaptable spoiler 200 according to another embodiment of the present invention, wherein FIGS. 19 and 20 illustrate partial views. Similar to the embodiment of the adaptable spoiler 100 illustrated in FIGS. 15 to 17, also the base element 215 of the spoiler 200 comprises an attachment portion 215 in an upstream region 219. Thereby, the attachment portion 215 comprises hook-like protrusions 227, 229 which engage with an attachment portion 217 of the airfoil element 209 having the airfoil shaped surface 211. Thereby, the attachment portion 217 comprises a front nose 231 pointing downstream and a further nose 235 (or hook) pointing upstream. In contrast, the nose 227 of the base element 205 points upstream engaging with the downstream directed nose 231 of the airfoil element 209. The downstream directed nose or hook 229 of the base element 205 engages with the upstream pointing nose 235 of the airfoil element 299.

Also the adaptable spoiler 200 comprises an inflatable, expandable container 241 between a downstream portion 225 of the base element 205 and the airfoil element 209 (see FIG. 20). Also, the container 241 is attached via an engagement portion 247 via an engagement portion 249 to the base element 205