Patent Description:
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

The wind turbine hub may be rotatably coupled to a front of the nacelle. The wind turbine hub may be connected to a rotor shaft, and the rotor shaft may then be rotatably mounted in the nacelle using one or more rotor shaft bearings arranged in a frame inside the nacelle. The nacelle is a housing arranged on top of a wind turbine tower that contains and protects e.g. the gearbox (if present) and the generator and, depending on the wind turbine, further components such as a power converter, and auxiliary systems.

A wind turbine may be stopped or may enter in an idle mode of operation for several reasons. For instance, if the electrical grid is receiving too much energy from a wind farm, a setpoint reduction for the wind farm may be received and some of them may start idling until more energy production is required. Also, a wind turbine may be parked, for example, for performing maintenance on it. In addition, a wind turbine may start idling or may be stopped for security reasons, e.g. if wind gusts may damage the wind turbine. Throughout this disclosure, the terms idle or idling refer to the fact that the wind turbine blades are (slowly) rotating but no energy is produced, namely because the generator is not connected to the grid. A stopped or parked wind turbine may be understood as a wind turbine whose rotor has been locked and is therefore not moving. Herein it may be understood that a wind turbine is in operation when its rotor is rotating at a speed high enough to produce energy and the generator of the wind turbine is producing electrical power.

When a wind turbine is parked or idling, the wind may blow against the wind turbine from unusual directions, i.e. different from normal operation. The airflow around the wind turbine may cause the wind turbine to vibrate. Vibrations may stress and even damage one or more wind turbine components, which may compromise the performance of the wind turbine, may increase the need of reparations and may reduce the lifespan of the wind turbine. As an orientation of a wind turbine blade may not be adapted to the direction of the incoming wind, e.g. through yawing as when the wind turbine is operating, the effects of vibrations may be greater or different when the wind turbine is parked or idling than when the wind turbine is operating normally and producing energy.

<CIT> discloses a wind turbine blade including a hub end, a tip end, a leading edge, a trailing edge, a high-pressure side, and a low pressure side. At least one boundary layer fence is located on at least one side of the blade. The fence includes a plurality of passages. Each passage has an inlet on a hub end side of the fence and an outlet on a tip end side of the fence and the cross-section decreases from the inlet to the outlet, oriented to discharge air towards the trailing edge of the blade.

In a first aspect of the present disclosure, according to independent claim <NUM>, a wind turbine comprising a wind turbine blade is provided. The wind turbine blade comprises a blade surface, and one or more deflectors attached to the wind turbine blade surface configured to disturb a spanwise component of air flowing around the wind turbine blade, wherein the deflectors include wing fences, and wherein the wing fences are configured to be removed from the wind turbine blade before starting operation of the wind turbine.

In accordance with this aspect, the deflector attached to the wind turbine disturbs a spanwise component of air flowing which may occur specifically around an idling or stopped wind turbine blade. Such disturbance may mitigate or even stop vibration of one or more components of a wind turbine, e.g. the wind turbine blade and/or a wind turbine tower. Without wishing to be bound by theory, in particular vortex-induced vibrations (VIVs) and/or stall-induced vibrations (SIVs) may be reduced.

In a second aspect of the present disclosure, according to independent claim <NUM>, a method for installing a wind turbine blade to a wind turbine is provided.

Herein, it may be understood that "disturbing" or "perturbing" a spanwise component of an air flow refers to modify a magnitude, spanwise turbulence coherence, or other characteristics (in particular turbulent vs laminar flow) of the spanwise component without destroying it, i.e. without avoiding the spanwise component. Thus, a spanwise component keeps existing after an alteration of the airflow. Modifying a magnitude and/or direction of the air flow may perturbate a spanwise component of such air flow. The resulting air flow may be more turbulent.

Each example is provided by way of explanation of the invention, not as a limitation of the invention.

<FIG> illustrates a perspective view of one example of a wind turbine <NUM>. As shown, the wind turbine <NUM> includes a tower <NUM> extending from a support surface <NUM>, a nacelle <NUM> mounted on the tower <NUM>, and a rotor <NUM> coupled to the nacelle <NUM>. The rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outwardly from the hub <NUM>. For example, in the illustrated embodiment, the rotor <NUM> includes three rotor blades <NUM>. However, in an alternative embodiment, the rotor <NUM> may include more or less than three rotor blades <NUM>. Each rotor blade <NUM> may be spaced about the hub <NUM> to facilitate rotating the rotor <NUM> to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub <NUM> may be rotatably coupled to an electric generator <NUM> (<FIG>) positioned within the nacelle <NUM> to permit electrical energy to be produced.

<FIG> illustrates a simplified, internal view of one example of the nacelle <NUM> of the wind turbine <NUM> of <FIG>. As shown, the generator <NUM> may be disposed within the nacelle <NUM>. In general, the generator <NUM> may be coupled to the rotor <NUM> of the wind turbine <NUM> for generating electrical power from the rotational energy generated by the rotor <NUM>. For example, the rotor <NUM> may include a main rotor shaft <NUM> coupled to the hub <NUM> for rotation therewith. The generator <NUM> may then be coupled to the rotor shaft <NUM> such that rotation of the rotor shaft <NUM> drives the generator <NUM>. For instance, in the illustrated embodiment, the generator <NUM> includes a generator shaft <NUM> rotatably coupled to the rotor shaft <NUM> through a gearbox <NUM>.

It should be appreciated that the rotor shaft <NUM>, gearbox <NUM>, and generator <NUM> may generally be supported within the nacelle <NUM> by a support frame or bedplate <NUM> positioned atop the wind turbine tower <NUM>.

The nacelle <NUM> is rotatably coupled to the tower <NUM> through the yaw system <NUM> in such a way that the nacelle <NUM> is able to rotate about a yaw axis YA. The yaw system <NUM> comprises a yaw bearing having two bearing components configured to rotate with respect to the other. The tower <NUM> is coupled to one of the bearing components and the bedplate or support frame <NUM> of the nacelle <NUM> is coupled to the other bearing component. The yaw system <NUM> comprises an annular gear <NUM> and a plurality of yaw drives <NUM> with a motor <NUM>, a gearbox <NUM> and a pinion <NUM> for meshing with the annular gear <NUM> for rotating one of the bearing components with respect to the other.

Blades <NUM> are coupled to the hub <NUM> with a pitch bearing <NUM> in between the blade <NUM> and the hub <NUM>. The pitch bearing <NUM> comprises an inner ring and an outer ring. A wind turbine blade may be attached either at the inner bearing ring or at the outer bearing ring, whereas the hub is connected at the other. A blade <NUM> may perform a relative rotational movement with respect to the hub <NUM> when a pitch system <NUM> is actuated. The inner bearing ring may therefore perform a rotational movement with respect to the outer bearing ring. The pitch system <NUM> of <FIG> comprises a pinion <NUM> that meshes with an annular gear <NUM> provided on the inner bearing ring to set the wind turbine blade into rotation around a pitch axis PA.

A schematic perspective view of a wind turbine blade <NUM>, e.g. one of the rotor blades <NUM> shown in <FIG>, is illustrated as an example in <FIG>. The rotor blade <NUM> includes a blade root <NUM>, a blade tip <NUM>, a leading edge <NUM> and a trailing edge <NUM>. The blade root <NUM> is configured for mounting the rotor blade <NUM> to the hub <NUM> of a wind turbine <NUM>. The wind turbine blade <NUM> extends lengthwise between the blade root <NUM> and the blade tip <NUM>. A span <NUM> defines a length of the rotor blade <NUM> between said blade root <NUM> and blade tip <NUM>. A chord <NUM> at a given position of the blade is an imaginary straight line joining the leading edge <NUM> and the trailing edge <NUM>, the cross-section generally having airfoil shaped cross-section. As is generally understood, a chordwise direction is substantially perpendicular to a spanwise direction. Also, the chord <NUM> may vary in length as the rotor blade <NUM> extends from the blade root <NUM> to the blade tip <NUM>. The wind turbine blade <NUM> also includes a pressure side <NUM> and a suction side <NUM> extending between the leading edge <NUM> and the trailing edge <NUM>. The rotor blade <NUM> has an aerodynamic profile and thus an airfoil shaped cross-section <NUM>, such as a symmetrical or cambered airfoil-shaped cross-section.

Wind turbine blade <NUM> further includes a deflector <NUM> attached to a suction side <NUM> according to the example of <FIG>. In other examples, a deflector <NUM> may be attached to a pressure side <NUM>. Or a deflector <NUM> may extend along both suction side <NUM> and pressure side <NUM>. The function and structure of this deflector <NUM> will be explained later on.

<FIG> illustrates a schematic example of a cross-section at a spanwise position of a wind turbine blade <NUM>, e.g. the wind turbine blade <NUM> of any of <FIG> and <FIG> shows an air flow <NUM>, which may reach a wind turbine blade <NUM> with an angle of attack <NUM> that is much higher than usual in operation, e. g around <NUM>-<NUM>°. Such an angle of attack may occur e.g. when the wind turbine is parked or idling. In such a situation, a yaw system of the wind turbine may be inoperative, and the blades may be in a vane position. Because yawing of the rotor does not occur, wind may come from any angle at a wind turbine.

The angle of attack <NUM> is measured between the direction of incoming wind and dashed line <NUM>, which indicates a chordwise direction <NUM>. Vibration may happen when a wind turbine <NUM> is parked or idling and in particular when air flow <NUM> may reach a wind turbine blade <NUM> from several directions. Air flow <NUM> reaching a wind turbine blade <NUM> from several directions may be referred to as crossflow. Crossflow may enable angles of attack <NUM> to be high enough to cause one or more wind turbine components to oscillate. The terms vibrating and oscillating may be used interchangeably throughout this disclosure.

It is known in the art that wind may cause oscillations in the wind turbine. It is however generally believed that these oscillations are caused specifically by the nacelle and/or the tower. The present inventors have found that one main cause of the tower and full wind turbine generator oscillations are blade vortex induced vibrations (VIV) and Stall Induced Vibrations (SIV).

At an angle of attack such as the one indicated in <FIG> (e.g. around <NUM>° or <NUM>°), the blade may essentially form a bluff body. Although not visible in the figure, the incoming wind may also have a spanwise component.

Vibrations in wind turbines may for instance be vortex-induced vibrations (VIVs). In this case, as schematically illustrated in the example of <FIG>, wind flowing around a wind turbine blade <NUM> may cause vortex formation and shedding <NUM>, e.g. in the form of a von Karman vortex street <NUM> downstream of the wind turbine blade <NUM>. The vortex shedding may cause one or more wind turbine blades <NUM> and/or the wind turbine tower <NUM> to start oscillating. For example, a wind turbine blade <NUM> may start oscillating in a plane substantially parallel to a chord <NUM> of the wind turbine blade <NUM>, as schematically illustrated by arrow <NUM> in <FIG>. VIVs may stress structural components of the wind turbine <NUM>.

In an example, angles of attack <NUM> which may cause VIVs may be angles between <NUM> and <NUM> °, and specifically between <NUM>° and <NUM>°. In another example, such angles <NUM> may be between <NUM> and <NUM> °. Inflow angles (angle between a chord direction and wind direction in a horizontal plane) between <NUM> and <NUM> ° may also favor VIVs and/or SIVs. As such angles of attack <NUM> may not be encountered when a wind turbine <NUM> is operating normally, e.g. when the wind turbine blades <NUM> may be yawed and/or pitched, VIVs may mainly take place and may become particularly problematic when a wind turbine <NUM> is parked or idling.

Vibrations may also be stall-induced vibrations (SIVs). In this case, the angle of attack <NUM> is such that it causes air flow to separate from a surface of a wind turbine blade <NUM> and vortex <NUM> formation and flow downstream the wind turbine blade <NUM>. In some examples, the angle of attack <NUM> of an airflow may be between <NUM>° and <NUM> °. A schematic illustration of this effect is illustrated in <FIG>. These vortices <NUM> may cause the wind turbine blade <NUM> to oscillate in a plane substantially parallel and/or inclined with respect to a chord <NUM> of the wind turbine blade <NUM>, as schematically illustrated by arrows <NUM> in <FIG>. Again, such oscillations may cause stress in structural components of the wind turbine <NUM> and cause fatigue damage and even potentially cause catastrophic failure of the wind turbine. As modern wind turbines may rarely encounter stall in operation, SIVs may affect an idling, and more particularly, a parked wind turbine.

Referring back to <FIG>, in an aspect, a wind turbine blade <NUM> comprises a deflector <NUM> attached to the wind turbine blade <NUM> such that the deflector <NUM> perturbates or disturbs a spanwise component <NUM> of air <NUM> flowing around the wind turbine blade <NUM> when the wind turbine blade <NUM> is mounted to a wind turbine <NUM> and the wind turbine <NUM> is parked or idling. An example of such a deflector <NUM> in cross-section may be seen in <FIG>.

Disturbing a spanwise component <NUM> (see <FIG>) of air <NUM> flowing around the wind turbine blade <NUM> may reduce and even stop vibration of one or more components of a wind turbine <NUM>, e.g. the wind turbine blade <NUM>. In some examples, disturbing a spanwise component <NUM> of air <NUM> flowing around a wind turbine blade <NUM> may reduce and even stop vibration of the entire wind turbine <NUM>. In particular, VIVs and/or SIVs may be mitigated.

A direction of air <NUM> flowing around a wind turbine <NUM> may be decomposed into a spanwise component <NUM>, a chordwise component <NUM> and a vertical component <NUM>. The vertical component is perpendicular to the spanwise component <NUM> and to the chordwise component <NUM>. A deflector <NUM> may modify a magnitude and/or direction of air flow <NUM>, and in particular may disturb a spanwise component <NUM> of the air flow <NUM> without destroying, i.e. making disappear, the spanwise component <NUM>, as schematically shown in <FIG>. In general, the chordwise component <NUM>, which mostly dominates in normal turbine operation, may not be destroyed either.

As it can be seen in <FIG>, deflector <NUM> modifies a direction and/or magnitude of air flow <NUM>, and in particular a magnitude of a spanwise component <NUM> of said air flow <NUM>. Passing against and over deflector <NUM>, air flow <NUM> may become more turbulent. A magnitude of a spanwise component <NUM>' of the resulting air flow <NUM> may be enhanced. , spanwise flow <NUM>' after the interaction of an incoming airflow with a deflector <NUM> may be promoted. In the context of interaction with a deflector <NUM>, an incoming air flow may refer to an air flow approaching and surrounding a wind turbine blade <NUM> before meeting the deflector <NUM>. A resulting air flow <NUM> may be understood as the air flow <NUM> remaining after the incoming air flow has met deflector <NUM>.

In some examples, the wind turbine blade <NUM> is configured to make vortex sheddings <NUM> uncoherent along the span of the blade.

As schematically shown in <FIG>, vortex shedding may occur at several positions along a length or span <NUM> of a wind turbine blade <NUM>. In this regard, if in <FIG> wind comes upwards <NUM>, i.e. in a direction substantially parallel to the indicated z axis in this figure, a von Karman street <NUM> may be imagined downstream of all these positions. For instance, and just for illustrative purposes, one could imagine that four von Karman streets S1, S2, S3 and S4 may be formed as schematically illustrated in <FIG>. S1 to S4 may propagate in a plane xz. As illustrated in <FIG>, the z axis is perpendicular to the x and the y axes, wherein the x axis is parallel to a chord <NUM> of the wind turbine blade <NUM> and the y axis is parallel to a length <NUM> of the wind turbine blade <NUM>.

S1 and S2 may be spanwise coherent because the forces F1 and F2 cause to the wind turbine blade <NUM> by S1 and S2, respectively, substantially go in the same direction at the same time. In the example of <FIG>, F1 and F2 go in the +x direction. Therefore, these two forces add up and vibration e.g. of the wind turbine blade <NUM> may be enhanced.

However, S3 and S4 may not be spanwise coherent because in this example the forces F3 and F4 caused to the wind turbine blade <NUM> by S3 and S4, respectively, substantially go in opposite directions at the same time. In this example, F3 goes in the +x direction and F4 goes in the +x direction. This may be due to the fact that an offset <NUM> between S3 and S4 may exist. As indicated in <FIG>, an offset <NUM> may be measured in a direction substantially perpendicular to a length <NUM> and a chord <NUM> of the wind turbine blade <NUM>, i.e. in a z direction. In this particular example, the offset <NUM> is such that F3 and F4 go in opposite directions with a same magnitude. Thus, force F3 may be cancelled by force F4, and vibrations, e.g. of the wind turbine blade <NUM>, may be reduced.

Hence, making two or more vortex sheddings <NUM> to be spanwise uncoherent may be understood as decorrelating the vortex sheddings <NUM>, e.g. by increasing an offset among the vortex sheddings <NUM>. Accordingly, a deflector <NUM> attached to a wind turbine blade <NUM> may make vortex sheddings <NUM> spanwise uncoherent by decorrelating them, e.g. by making them less similar in the vicinity of a same point in the y-axis of <FIG>. This may cause an offset <NUM> between them. Vibrations, e.g. VIVs, may be accordingly reduced.

It is noted that decorrelating two or more vortex sheddings <NUM> may not necessarily cause forces in opposite directions to arise. For instance, forces may still act in a same direction as before decorrelation, but a magnitude and/or a phase matching of one or more of the forces may have decreased. Thus, a force exerted by the plurality of vortex sheddings <NUM> acting on a wind turbine blade <NUM> may be lower than before the decorrelation. In such a case, vibrations may also be reduced.

According to the invention, the deflectors of the wind turbine blade <NUM> are configured to promote a turbulent air flow <NUM>, resulting from the crossflow component in idling or parked condition, along a length <NUM> of the wind turbine blade <NUM>. Herein, promoting a turbulent air flow <NUM> along a <NUM> length of the wind turbine blade <NUM> may refer to the fact that air flow <NUM> after passing over deflector <NUM> is more turbulent than an incoming air flow and/or the air flow without the deflector. If air flow becomes more turbulent after meeting deflector <NUM>, in particular in a spanwise direction, oscillations in a wind turbine (particularly a parked or idling wind turbine) may be reduced. In normal operation, the spanwise component <NUM> is relatively small or negligent, and the deflector <NUM> does not disturb the normal flow allowing the blade operate as designed at optimal conditions.

For instance, if a surface, e.g. a portion of a suction side <NUM> of the wind turbine blade <NUM>, is suffering from the effects of crossflow, a turbulent air flow <NUM> occurring over this surface may modify the air flowing over it and vibrations of the blade <NUM> may be reduced. This may reduce vibrations of the wind turbine <NUM>, in particular VIVs and/or SIVs.

In some examples, the deflector <NUM> may be an elongated deflector <NUM> attached to the wind turbine blade <NUM> such that a length of the deflector <NUM> follows a perimeter of the wind turbine blade <NUM> in cross-section and the deflector <NUM> protrudes from a surface of the wind turbine blade <NUM>. An example of an elongated deflector <NUM> may be seen in <FIG>. Deflector <NUM> may be substantially a flat plate extending both along the pressure side and the suction side and from the leading edge to the trailing edge.

In some examples, as e.g. as illustrated in <FIG>, the elongated deflector <NUM> protrudes substantially perpendicular to a local surface of the wind turbine blade <NUM>. A local surface may be understood as a surface to which the elongated deflector is attached to. Such perpendicularity, or in other words, a plane of symmetry defined by a length <NUM> and a height <NUM> of the deflector <NUM>, may enable homogenizing an action by the deflector <NUM> on an incoming air flow independently of its direction. In some other examples, the elongated deflector <NUM> may not protrude substantially perpendicular to a local surface. For example, it may happen that an angle of inclination between the deflector <NUM> and a local surface of the wind turbine blade <NUM> to which deflector <NUM> is attached to may be selected according to particularities of air flowing in the region where a wind turbine <NUM> is located.

The elongated deflector <NUM> may be attached to a wind turbine blade <NUM> at any distance from the tip <NUM> of the wind turbine blade <NUM>. In some examples, the body <NUM> is attached to the wind turbine blade <NUM> at <NUM>% to <NUM>% of the span, and specifically between <NUM> and <NUM>% of the span. This range of distances enables achieving a balance between mitigating vibrations and affecting the performance of the wind turbine <NUM> in normal operation. For instance, if a deflector <NUM> is placed outside this range, e.g. close to the root <NUM> or close to the tip <NUM>, the deflector <NUM> may miss a lot of incoming airflow or may cause excessive noise, respectively. Thus, in this range vibrations may be reduced while the performance of the wind turbine <NUM> may not, or may barely be, negatively affected. In an example, a wind turbine blade <NUM> may have a length <NUM> or span <NUM> of <NUM> and a deflector <NUM> may be attached <NUM> away from the blade root <NUM>. More than one deflector may be installed in some cases, especially for very long blades.

One way of determining a suitable location for deflectors according to the present disclosure is to use an aeroelastic analysis of a blade along its length to calculate or estimate which portions of the blade contribute positively to a vibration (i.e. the wind transfers energy to the blade) and which portion of the blade reduce a vibration (i.e. these portions transfer energy from the blade to the wind). One measure to determine such a contribution is the aerodynamic work per cycle. The deflectors may be placed particularly in areas of the blade where the contribution of the blade to a vibration is positive.

Such a process may be reiterative, i.e. a simulation or aeroelastic analysis is made on a simulated blade having one or more deflectors.

In some examples, a height <NUM> of the deflector <NUM> is between <NUM> and <NUM> times of the local (maximum) thickness of the airfoil of the wind turbine blade <NUM>. In this range, a balance between vibration reduction and affecting the performance of the wind turbine <NUM> may be achieved. If the height <NUM> of the deflector <NUM> is too small, e.g. less than <NUM> times the local thickness of the wind turbine blade <NUM>, vibrations may not be sufficiently attenuated, since the deflector may not sufficiently disturb a spanwise flow. If the height <NUM> of the deflector <NUM> is too big, e.g. more than twice the local thickness of the wind turbine blade <NUM>, the performance of the wind turbine <NUM> may be excessively affected in a negative way. Also, a relatively large deflector might add significant weight to the blade. In an example, a height <NUM> of deflector <NUM> may be <NUM>.

A length <NUM> of the deflector <NUM> may extend partially or totally over a local chord of the blade. In <FIG>, a length <NUM> of the deflector <NUM> extends partially along the profile of the local cross-section of the blade, i.e. only a portion of a blade between the leading edge and the trailing edge is covered. In some examples, the deflector <NUM> covers, at least in part, at least one of: a leading edge <NUM> and a trailing edge <NUM> of the wind turbine blade <NUM>.

In some other examples, a length <NUM> of the deflector <NUM> may extend from the local leading edge to the local trailing edge, and follow the entire local profile.

The dimensions of the deflector <NUM> and its position on the wind turbine blade <NUM> may be chosen depending e.g. on shape and dimensions of the wind turbine blade. In this regard, computer simulations may be performed in order to optimize the dimensions and location of the deflector <NUM> on a wind turbine blade <NUM>.

In some examples, a top <NUM> of the deflector <NUM> comprises irregularities <NUM>, i.e. along its length, the deflector may have a non-constant height. A top <NUM> may be understood as a side of the deflector <NUM> opposed to the side of the deflector <NUM> which is attached to the wind turbine blade <NUM>. <FIG> shows an example of a deflector <NUM> having a top <NUM> including irregularities <NUM>. Irregularities <NUM> may include protrusions and/or recesses. The irregularities <NUM> may extend over the entire top <NUM> of the deflector <NUM>, as shown in <FIG>, or may extend over a portion of it. <FIG> shows an undulated top <NUM> of the deflector <NUM>, but irregularities <NUM> having a different shape, e.g. a triangular or rectangular shape, are possible. Irregularities <NUM> may facilitate disturbing a spanwise component of air flowing around the wind turbine blade as disclosed herein.

A deflector <NUM> may be made from (light) metals or composite materials such as fiberreinforced polymers. In some examples, a deflector <NUM> may be made of carbon fiber or glass fiber. A deflector <NUM> may be strong and lightweight accordingly.

According to the invention, a deflector <NUM> is a wing fence and may in some examples be similar to a flat plate, and is generally similar to boundary layer fences or vortilons on a wing plane. they may be relatively thin and extend from both the pressure surface and suction surface of a blade.

It is however noted that the purpose and functioning of such wing fences and vortilons differ from the purpose and functioning of a deflector <NUM> described herein. In particular, wing fences on an aircraft wind aim at stopping or destroying an air flow spanwise component, whereas in the present disclosure the objective is not to eliminate a spanwise component (this would in any case hardly be possible depending on the wind direction). Rather, the objective is to disturb an air flow spanwise component, e.g. by making it more turbulent. Herein an air flow spanwise component may be enhanced. Thus, the functioning and objective of the devices on plane wings are distinct, and even rather opposite, than the ones of deflectors <NUM>.

Although one deflector <NUM> is shown in <FIG>, more than one deflector <NUM> may be placed on a wind turbine blade <NUM>. Computer simulations may be performed to optimize a number of deflectors <NUM> to be attached to a wind turbine blade <NUM>.

According to the invention, a wind turbine <NUM>, e.g. the wind turbine <NUM> of <FIG>, comprises a wind turbine tower <NUM>, a nacelle <NUM> on top of the tower <NUM>, a rotor <NUM> mounted to the nacelle <NUM> and one or more wind turbine blades <NUM> comprising one or more wind turbine blades <NUM> including one or more deflectors <NUM> as described herein.

According to another aspect, a wind turbine blade is provided, which comprises a blade surface extending from a blade root to a blade tip, and having a pressure surface and a suction surface, wherein a span of the blade is defined by a distance between the blade root and the blade tip. The blade comprising a deflector attached to the blade surface may is configured to promote turbulence of a spanwise flow along the wind turbine blade. In particular, the deflector may promote turbulence of a spanwise flow along a span of the wind turbine blade in idling or parked conditions in presence of crossflow wind.

As explained above, a wind turbine blade <NUM> comprising one or more of such a deflectors <NUM> may reduce vibrations of one or more components of a wind turbine <NUM>, e.g. by disturbing a spanwise component <NUM> of air flowing around the wind turbine blade <NUM>. Similarly, in some examples, the wind turbine blade <NUM> may be configured to make two or more vortex sheddings <NUM> to be spanwise uncoherent. In these or other examples, the wind turbine blade <NUM> may be configured to create a spanwise-uncorrelated turbulent air flow along a length <NUM> of the wind turbine blade <NUM>. Accordingly, VIVs and/or SIVs may be in particular reduced.

In some examples, the elongated deflector <NUM> is attached to the wind turbine blade <NUM> between <NUM> and <NUM> times of a length <NUM> of the wind turbine blade <NUM> from the tip <NUM> of the wind turbine blade <NUM>. This range of distances may provide for a more effective oscillation mitigation as explained above.

In some examples, a height <NUM> of the elongated deflector <NUM> is between <NUM> and <NUM> times of a local wind turbine blade <NUM> thickness. Also as indicated above, a height <NUM> in this range may provide for vibration reduction without excessively affecting a wind turbine <NUM> performance in a negative way.

Any of the features commented for the deflector <NUM> above may also be applied to the elongated deflector <NUM> of this aspect. For instance, the elongated deflector <NUM> may cover, at least in part, a leading edge <NUM> and/or a trailing edge <NUM> of the wind turbine blade <NUM>. In some examples, a top <NUM> of the deflector <NUM> comprises irregularities <NUM>.

According to the invention, a wind turbine <NUM> comprising a wind turbine tower <NUM>, a nacelle <NUM> on top of the tower <NUM>, a rotor <NUM> mounted to the nacelle <NUM>, and one or more wind turbine blades <NUM> including one or more deflectors <NUM> according to this aspect mounted to the rotor <NUM> is provided.

The present disclosure provides a method <NUM> for installing a wind turbine blade. The method comprises providing a wind turbine blade having one or more deflectors attached to the wind turbine blade, wherein the deflectors are configured to disturb a spanwise component of an air flow along the wind turbine blade,
installing the wind turbine blade to a hub of a wind turbine, and removing the deflectors from the wind turbine blade before starting operation of the wind turbine.

In <FIG>, an example of a method <NUM> for installing a wind turbine blade.

The method includes, at block <NUM>, providing a wind turbine blade <NUM>, one or more deflectors <NUM>. At block <NUM>, one or more deflectors are attached to the wind turbine blade. In other examples, a blade may be provided from a manufacturing facility with the deflectors already attached. The one or more deflectors <NUM> may be as any of the deflectors <NUM> described herein. For instance, a deflector <NUM> may be an elongated deflector, and more in particular an elongated flat plate.

The deflector <NUM> may be formed by a single piece, but in the example of the deflector <NUM> completely surrounding a wind turbine blade <NUM> cross-section, the deflector <NUM> may be formed by more than one piece and the pieces may be attached to one another to form the deflector <NUM>. The assembly of the plurality of pieces may be done before attaching the deflector <NUM> to the wind turbine blade <NUM> or the pieces may be attached to the blade <NUM> then among them to form deflector <NUM>. Alternatively, the deflector <NUM> may be a single piece and it may be slid along the wind turbine blade <NUM> until its final position.

Method <NUM> further comprises, at block <NUM>, mounting the wind turbine blade <NUM> to the wind turbine <NUM>. This step may be performed before attaching one or more deflectors <NUM> to the wind turbine blade <NUM> or after attaching them. In both cases, the wind turbine <NUM> further comprises a nacelle <NUM> on top of the tower <NUM> and a rotor <NUM> mounted to the nacelle <NUM>, and the method may further comprise mounting the wind turbine blade <NUM> to the rotor <NUM> of the wind turbine <NUM>.

The attachment between a deflector <NUM> and a wind turbine blade <NUM> is not permanent. In accordance with the invention, at block <NUM>, one or more deflectors <NUM> are detached from the wind turbine blade <NUM>. In this case, the method further comprises removing one or more deflectors <NUM> from a wind turbine blade <NUM> before starting operation of the wind turbine <NUM>. The deflectors <NUM> are only on the wind turbine blade <NUM> when the wind turbine <NUM> is not in operation and may have a bigger height <NUM>, e.g. more than one time of a local wind turbine blade <NUM> thickness.

A deflector <NUM>, or a piece of a deflector <NUM>, may be attached to a wind turbine blade <NUM> by using at least one of gluing, or mechanically fastening.

In accordance with the example of <FIG>, after removing the deflectors, the operation of the wind turbine may be (re)started at block <NUM>.

Claim 1:
A wind turbine (<NUM>) comprising:
a wind turbine tower (<NUM>);
a nacelle (<NUM>) on top of the tower (<NUM>); and
a rotor (<NUM>) mounted to the nacelle (<NUM>),
wherein the rotor (<NUM>) comprises a hub (<NUM>) and one or more wind turbine blades (<NUM>),
wherein the one or more wind turbine blades (<NUM>) comprise:
a blade surface, and one or more wing fences (<NUM>) attached to the wind turbine blade surface configured to disturb a spanwise component (<NUM>) of air (<NUM>) flowing around the wind turbine blade (<NUM>), and wherein the wing fences (<NUM>) of the wind turbine blade (<NUM>) are configured to promote a turbulent spanwise air flow (<NUM>),
characterised in that
the wing fences (<NUM>) are configured to be removed from the wind turbine blade (<NUM>) before starting operation of the wind turbine (<NUM>).