阅读说明：本技术 用于减轻在停顿期间风力涡轮的转子叶片上的涡旋脱落振动或失速诱发振动的系统和方法 (System and method for mitigating vortex shedding or stall induced vibrations on rotor blades of a wind turbine during standstill ) 是由 A·赫里格 B·P·哈利西 M·卡纳尔 J·H·N·范卡尔肯 于 2020-09-18 设计创作，主要内容包括：本发明涉及用于减轻在停顿期间风力涡轮的转子叶片上的涡旋脱落振动或失速诱发振动的系统和方法。具体地,一种用于减轻在停顿期间风力涡轮的一个或多个转子叶片上的涡旋脱落振动或失速诱发振动的设备包括位于叶片尖端区段和其叶片根部区段之间的至少一个定位元件。定位元件适于围绕转子叶片的至少一部分缠绕。该设备还包括至少一个空气流改变元件,其联接到定位元件并且限定相对于转子叶片的表面的高度。另外,该设备包括至少一个固连元件,该至少一个固连元件可操作地联接至定位元件以便将空气流改变元件临时地固连至转子叶片。(The invention relates to a system and a method for mitigating vortex shedding vibrations or stall induced vibrations on rotor blades of a wind turbine during standstill. Specifically, an apparatus for mitigating vortex-shedding or stall-induced vibrations on one or more rotor blades of a wind turbine during standstill comprises at least one positioning element located between a blade tip section and a blade root section thereof. The positioning element is adapted to be wound around at least a portion of the rotor blade. The apparatus also includes at least one airflow altering element coupled to the positioning element and defining a height relative to a surface of the rotor blade. In addition, the apparatus includes at least one securing element operatively coupled to the positioning element for temporarily securing the airflow altering element to the rotor blade.)

1. An apparatus for mitigating vortex shedding or stall induced vibrations on one or more rotor blades of a wind turbine during standstill, the apparatus comprising:

at least one positioning element positioned between a blade tip section and a blade root section thereof, the at least one positioning element being adapted to be wound around at least a portion of the rotor blade;

at least one airflow modifying element coupled to the at least one positioning element, the at least one airflow modifying element defining a height relative to a surface of the rotor blade; and the number of the first and second groups,

at least one securing element operably coupled to the at least one positioning element for temporarily securing the at least one airflow altering element to the rotor blade.

2. The apparatus of claim 1, wherein the at least one positioning element comprises at least one cord member helically wound around a portion of the rotor blade.

3. The apparatus according to claim 2, wherein the helically wound cord element has a pitch greater than or equal to half the chord of the rotor blade and less than or equal to six times the chord of the rotor blade, wherein at least a portion of the helically wound cord element is separated from the surface of the rotor blade by a distance defined by the at least one air flow altering element.

4. The apparatus of claim 1, wherein the at least one airflow modification element comprises at least one of a fascia, a barrier, an inflatable unit, serrations, a vortex generator, and/or a spoiler.

5. The apparatus of claim 1, wherein the at least one airflow altering element comprises a plurality of airflow altering elements distributed along and secured to the at least one positioning element.

6. The apparatus of claim 5, wherein the plurality of airflow altering elements comprises leading edge airflow altering elements and trailing edge airflow altering elements, wherein the leading edge airflow altering elements and the trailing edge airflow altering elements are distributed in an alternating pattern along the at least one positioning element.

7. The apparatus of claim 1, wherein the at least one airflow altering element comprises at least one leading edge airflow altering element and at least one trailing edge airflow altering element disposed opposite thereto, wherein the at least one positioning element is comprised of an elastic cord element coupled between the leading edge airflow altering element and the trailing edge airflow altering element, wherein the elastic cord element limits a spacing between the leading edge airflow altering element and/or the trailing edge airflow altering element at a specified spanwise location of the rotor blade.

8. The apparatus of claim 1, wherein the at least one positioning element comprises a leading edge positioning element arranged parallel to a leading edge of the rotor blade and a trailing edge positioning element arranged parallel to a trailing edge of the rotor blade, the at least one airflow altering element comprising: at least one leading edge airflow altering element coupled to the leading edge positioning element and at least one trailing edge airflow altering element coupled to the trailing edge positioning element, the leading edge airflow altering element defining a leading edge mounting notch corresponding to a leading edge profile and the trailing edge airflow altering element defining a trailing edge mounting notch corresponding to a trailing edge profile.

9. The apparatus of claim 1, wherein the at least one airflow altering element has a mounting edge along which the airflow altering element is coupled to the at least one positioning element, the at least one positioning element oriented perpendicular to a chordwise direction of the rotor blade, the at least one positioning element being temporarily coupled to at least one of a leading edge, a trailing edge, or along a line upstream of a flow separation point on a suction side or a pressure side of the rotor blade.

10. The apparatus of claim 9, wherein the at least one positioning element comprises a spanwise oriented rope along the rotor blade, and wherein the at least one securing element comprises a first securement element coupled to a first end of the positioning element and a second securement element coupled to an opposite second end of the positioning element.

Technical Field

The present disclosure relates generally to wind turbines, and more particularly to systems and methods for mitigating vortex shedding or stall induced vibrations on rotor blades of a wind turbine during a standstill.

Background

Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. Modern wind turbines typically include a tower, generator, gearbox, nacelle, and one or more rotor blades. The nacelle includes a rotor assembly coupled to a gearbox and a generator. The rotor assembly and gearbox are mounted on a deck support frame located within the nacelle. One or more rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

During the lifetime of a wind turbine, there may be periods of rotor blade shutdown or inactivity (or idled) from time to time. For example, during installation or repair of the rotor blade, the wind turbine is typically locked in a fixed position. In another case, the rotor blades may be pitched in order to disable the wind turbine during a maintenance procedure. Typically, during such maintenance or installation procedures, or in response to system failures, the ability to pitch the rotor blades or yaw the nacelle relative to the wind may be lost. Therefore, modern wind turbines risk being subjected to flow induced oscillations caused by the wind when they are shut down or deactivated.

In one case, the flow induced oscillations may be the result of wind mainly impacting the side of the rotor blade opposite the edge. When wind strikes the edge(s) in this manner, the wind attempts to flow around the elongated structure of the rotor blade and forms a vortex (or vortex) at the point where the flow separates from the rotor blade. Depending on the relative angle between the wind and the rotor blades, a vortex shedding phenomenon may occur, wherein vortices are formed on the edges of the blades and shed from alternate edges in a rhythmic pattern. The alternating nature of vortex shedding on the edges can lead to vibration of the rotor blades. When the vortex shedding frequency coincides with or is sufficiently close to the natural frequency of the structure, large and damaging vibrations can result.

One known method for limiting vortex induced vibrations is to feather the rotor blades with respect to the wind so that the wind flows smoothly around the rotor blades. However, without the ability to adjust the position of the rotor blades, the wind direction typically shifts and increases the angle of attack of the rotor blades. At a sufficiently large angle of attack, the flow on the rotor blade separates, resulting in the rotor blade being in a stall condition. The separated, stalled flow is unstable and can cause stall-induced vibration.

In view of the foregoing, new and improved systems and methods for mitigating vortex shedding vibrations or stall induced vibrations are continually being sought in the art. Accordingly, a system and method for mitigating vortex shedding or stall induced vibrations on one or more rotor blades of a wind turbine during standstill would be advantageous.

Disclosure of Invention

Aspects and advantages of the invention will be set forth in part in the description which follows, or may be obvious from the description, or may be learned by practice of the invention.

In one aspect, the present disclosure relates to an apparatus for mitigating vortex shedding or stall induced vibrations on one or more rotor blades of a wind turbine during a standstill. The apparatus may have at least one positioning element located between the blade tip section and the blade root section thereof. The positioning element(s) is adapted to be wound around at least a portion of the rotor blade. The apparatus may also have at least one airflow altering element coupled to the positioning element(s). The airflow altering element(s) may define a height relative to a surface of the rotor blade. In addition, the apparatus may include at least one securing element operably coupled to the positioning element(s) to temporarily secure the airflow altering element(s) to the rotor blade.

In one embodiment, the positioning element(s) may comprise at least one cord member helically wound around a portion of the rotor blade. In an additional embodiment, the helically wound cord element may have a pitch which is greater than or equal to half the chord of the rotor blade and less than or equal to 6 times the chord of the rotor blade. At least a portion of the helically wound cord element may be spaced from the surface of the rotor blade by a distance defined by the airflow altering element(s).

In one embodiment, the airflow altering element(s) may comprise at least one of a fascia, a barrier, an inflatable unit, a serration, a vortex generator and/or a spoiler.

In one embodiment, the airflow altering element(s) may comprise a plurality of airflow altering elements distributed along and secured to the positioning element(s). In another embodiment, the plurality of airflow altering elements may include a leading edge airflow altering element and a trailing edge airflow altering element. The leading edge airflow altering elements and the trailing edge airflow altering elements may be distributed in an alternating pattern along the positioning element(s).

In one embodiment, the air flow altering element(s) may comprise at least one leading edge air flow altering element and at least one trailing edge air flow altering element disposed opposite thereto. The positioning element(s) may be comprised of an elastic cord element coupled between the leading edge airflow altering element and the trailing edge airflow altering element. The elastic cord elements may limit the spacing between the leading edge airflow altering elements and/or the trailing edge airflow altering elements at a specified spanwise location of the rotor blade.

In one embodiment, the positioning element(s) may comprise a leading edge positioning element arranged parallel to the leading edge of the rotor blade and a trailing edge positioning element arranged parallel to the trailing edge of the rotor blade. The airflow altering element(s) may include at least one leading edge airflow altering element coupled to the leading edge positioning element and at least one trailing edge airflow altering element coupled to the trailing edge positioning element. The leading edge airflow modifying element may define a leading edge notch corresponding to the leading edge profile. The trailing edge airflow modifying element may define a trailing edge mounting notch corresponding to the trailing edge profile.

In one embodiment, the air flow altering element(s) may have a mounting edge. The air flow altering element may be coupled to the positioning element(s) along the mounting edge. The positioning element(s) may be oriented perpendicular to the chordwise direction of the rotor blade. The positioning element(s) may be temporarily coupled to at least one of the leading edge, the trailing edge, or along a line upstream of a flow separation point on the suction side or the pressure side of the rotor blade. In an additional embodiment, the locating element(s) may include a cord oriented spanwise along the rotor blade. In such embodiments, the securement element(s) may include a first securement element coupled to a first end of the positioning element and a second securement element coupled to an opposite second end of the positioning element.

In another embodiment, the positioning element(s) may comprise a hollow sleeve configured to enclose a portion of the rotor blade. The hollow sleeve may define at least one inlet air aperture.

In another aspect, the present disclosure is directed to a method for mitigating vortex shedding or stall induced vibrations on one or more rotor blades of a wind turbine during a standstill. The method may include mounting a vibration reduction apparatus on the rotor blade. The mounting of the vibration damping device may comprise positioning the at least one airflow altering element at a desired position along the outer surface of the rotor blade, for example with at least one positioning element, and securing the positioning element(s) to the outer surface of the rotor blade via at least one securing element. The method may further comprise performing maintenance and/or repair operations on the wind turbine with the mounted vibration damping apparatus. Once the maintenance and/or repair operation is complete, the method may include removing the vibration reduction apparatus from the rotor blade.

In one embodiment, the airflow altering element(s) may include a fascia, a barrier, and at least one of an inflatable unit, a serration, a vortex generator, and/or a spoiler.

In another embodiment, the positioning element(s) may comprise a cord element. In such embodiments, positioning the airflow altering element(s) at the desired location may include helically winding a cord element around a portion of the rotor blade so as to disrupt airflow over the chordwise or spanwise section of the rotor blade. At least a portion of the positioning element(s) may be spaced from the outer surface of the rotor blade by a distance defined by the airflow altering element(s).

In an additional embodiment, positioning the airflow altering element(s) at the desired location may include positioning an edge of the airflow altering element(s) adjacent at least one of the leading edge, the trailing edge, or along a line upstream of a flow separation point on the suction side or the pressure side of the rotor blade.

In one embodiment, the positioning element(s) may comprise a hollow sleeve defining an inlet air bore, and the airflow altering element(s) may comprise an inflatable cell. In such embodiments, positioning the airflow altering element(s) at the desired location may include enclosing a portion of the rotor blade within the hollow sleeve and coupling the inflatable unit to the hollow sleeve, and operably coupling the inflatable unit to the air bore. Additionally, the inflatable unit may be disposed adjacent to a pressure side or a suction side of the rotor blade.

In another aspect, the present disclosure is directed to a rotor assembly for a wind turbine. The rotor assembly may include a rotor hub and at least one rotor blade at a standstill. The rotor blade(s) may include a leading edge and a trailing edge disposed between the tip portion and the root portion opposite thereto. The root portion may be coupled to the rotor hub. The rotor assembly may also include apparatus for mitigating vortex shedding vibrations and/or stall induced vibrations on the rotor blade(s) during standstill. The apparatus may comprise at least one positioning element between the blade tip section and the blade root section thereof. The positioning element(s) may be adapted to be wound around at least a portion of the rotor blade(s). The apparatus may also include at least one airflow altering element coupled to the positioning element(s). The airflow altering element(s) may define a height relative to a surface of the rotor blade. In addition, the apparatus may include at least one securing element operably coupled to the airflow altering element(s) to temporarily secure the airflow altering element(s) to the rotor blade. It will be appreciated that the rotor blade assembly may also include any of the additional features described herein.

Specifically, the present disclosure also discloses the following technical solutions.

Technical solution 1. an apparatus for mitigating vortex shedding or stall induced vibrations on one or more rotor blades of a wind turbine during a standstill, the apparatus comprising:

at least one positioning element positioned between a blade tip section and a blade root section thereof, the at least one positioning element being adapted to be wound around at least a portion of the rotor blade;

at least one airflow modifying element coupled to the at least one positioning element, the at least one airflow modifying element defining a height relative to a surface of the rotor blade; and the number of the first and second groups,

at least one securing element operably coupled to the at least one positioning element for temporarily securing the at least one airflow altering element to the rotor blade.

Solution 2. the apparatus of solution 1 wherein the at least one positioning element comprises at least one cord member helically wound around a portion of the rotor blade.

Solution 3. the apparatus according to solution 2, characterized in that the helically wound rope element has a pitch which is greater than or equal to half the chord of the rotor blade and less than or equal to six times the chord of the rotor blade, wherein at least a part of the helically wound rope element is separated from the surface of the rotor blade by a distance defined by the at least one air flow changing element.

Solution 4. the apparatus of solution 1 wherein the at least one air flow altering element comprises at least one of a fascia, a barrier, an inflatable unit, serrations, vortex generators and/or spoilers.

Solution 5. the apparatus according to solution 1 wherein the at least one airflow modifying element comprises a plurality of airflow modifying elements distributed along and secured to the at least one positioning element.

Solution 6. the apparatus of solution 5 wherein the plurality of airflow altering elements comprises leading edge airflow altering elements and trailing edge airflow altering elements, wherein the leading edge airflow altering elements and the trailing edge airflow altering elements are distributed in an alternating pattern along the at least one positioning element.

Solution 7. the apparatus according to solution 1, characterized in that the at least one air flow changing element comprises at least one leading edge air flow changing element and at least one trailing edge air flow changing element arranged opposite thereto, wherein the at least one positioning element is constituted by an elastic cord element coupled between the leading edge air flow changing element and the trailing edge air flow changing element, wherein the elastic cord element limits the spacing between the leading edge air flow changing element and/or the trailing edge air flow changing element at a given spanwise position of the rotor blade.

The apparatus of claim 8, wherein the at least one positioning element comprises a leading edge positioning element arranged parallel to a leading edge of the rotor blade and a trailing edge positioning element arranged parallel to a trailing edge of the rotor blade, the at least one airflow modification element comprising: at least one leading edge airflow altering element coupled to the leading edge positioning element and at least one trailing edge airflow altering element coupled to the trailing edge positioning element, the leading edge airflow altering element defining a leading edge mounting notch corresponding to a leading edge profile and the trailing edge airflow altering element defining a trailing edge mounting notch corresponding to a trailing edge profile.

Solution 9. the apparatus of solution 1, wherein the at least one airflow modification element has a mounting edge along which the airflow modification element is coupled to the at least one positioning element, the at least one positioning element oriented perpendicular to the chord direction of the rotor blade, the at least one positioning element being temporarily coupled to at least one of a leading edge, a trailing edge, or along a line upstream of a flow separation point on a suction side or a pressure side of the rotor blade.

The apparatus of claim 9, wherein the at least one positioning element comprises a cable oriented spanwise along the rotor blade, and wherein the at least one securing element comprises a first securement element coupled to a first end of the positioning element and a second securement element coupled to an opposite second end of the positioning element.

The apparatus of claim 1, wherein the at least one positioning element comprises a hollow sleeve configured to enclose a portion of the rotor blade, the hollow sleeve defining at least one inlet air aperture.

Technical solution 12. a method for mitigating vortex shedding or stall induced vibrations on one or more rotor blades of a wind turbine during a standstill, the method comprising:

mounting a vibration damping device on the rotor blade, wherein the mounting of the vibration damping device further comprises:

positioning at least one airflow altering element at a desired location along an outer surface of the rotor blade with at least one positioning element; and the number of the first and second groups,

securing the at least one positioning element to an outer surface of the rotor blade via at least one securing element;

performing installation, commissioning, maintenance and/or repair operations on the wind turbine with the installed vibration reduction apparatus; and the number of the first and second groups,

once the installation, commissioning, maintenance and/or repair operations are completed, the vibration reduction apparatus is removed from the rotor blade.

Solution 13. the method according to solution 12, wherein the at least one air flow altering element comprises at least one of a fascia, a barrier, an inflatable unit, serrations, vortex generators and/or spoilers.

The method of claim 14, according to claim 12, wherein the at least one positioning element comprises a cord element, wherein positioning the at least one airflow altering element at the desired location further comprises: helically winding the cord element around a portion of the rotor blade so as to disrupt airflow in a chordwise or spanwise section of the rotor blade, wherein at least a portion of the at least one positioning element is spaced from the outer surface of the rotor blade by a distance defined by the at least one airflow altering element.

The method of claim 15, the positioning the at least one airflow altering element at the desired location further comprising positioning an edge of the at least one airflow altering element adjacent at least one of a leading edge, a trailing edge, or along a line upstream of a flow separation point on a suction side or a pressure side of the rotor blade.

The method of claim 16, 13, wherein the at least one positioning element comprises a hollow sleeve defining an inlet air bore, and the at least one airflow altering element comprises the inflatable cell, wherein positioning the at least one airflow altering element at the desired location further comprises enclosing a portion of the rotor blade within the hollow sleeve and coupling the inflatable cell to the hollow sleeve, and operably coupling the inflatable cell to the inlet air bore, wherein the inflatable cell is disposed adjacent to a pressure side or a suction side of the rotor blade.

Technical solution 17 a rotor assembly for a wind turbine, comprising:

a rotor comprising a rotatable hub at rest;

at least one rotor blade including a leading edge and a trailing edge disposed between a blade tip and an opposite blade root, the blade root coupled to the rotatable hub; and the number of the first and second groups,

apparatus for mitigating vortex shedding vibrations and/or stall induced vibrations on said at least one rotor blade during a standstill, said apparatus comprising:

at least one positioning element positioned between a blade tip section and a blade root section thereof, the at least one positioning element being adapted to be wound around at least a portion of the rotor blade;

at least one airflow modifying element coupled to the at least one positioning element, the at least one airflow modifying element defining a height relative to a surface of the rotor blade; and the number of the first and second groups,

at least one securing element operably coupled to the at least one positioning element for temporarily securing the at least one airflow altering element to the rotor blade.

Solution 18. the rotor assembly according to solution 17, wherein the at least one air flow altering element comprises at least one of a fascia, a barrier, an inflatable unit, serrations, a vortex generator and/or a spoiler.

The rotor assembly of claim 19, wherein the at least one positioning element comprises a cord helically wound around a portion of the rotor blade, wherein the at least one airflow altering element comprises a plurality of airflow altering elements distributed along the at least one positioning element.

The rotor assembly of claim 20-17 wherein the at least one airflow modifying element has a mounting edge along which the airflow modifying element is coupled to the at least one positioning element oriented perpendicular to the chordwise direction of the rotor blade, the at least one positioning element being temporarily coupled to at least one of a leading edge, a trailing edge, or along a line upstream of a flow separation point on a suction side or a pressure side of the rotor blade.

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.

Drawings

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 illustrates a perspective view of an embodiment of a wind turbine having a mounting apparatus for mitigating vortex shedding or stall induced vibrations in accordance with the present disclosure;

FIG. 2 illustrates a perspective view of one of the rotor blades of FIG. 1;

FIG. 3A illustrates a schematic view of a portion of the rotor blade of FIG. 2, particularly illustrating one embodiment of a device for mitigating vortex shedding vibrations or stall induced vibrations mounted thereon, in accordance with the present disclosure;

FIG. 3B illustrates a cross-sectional view of the rotor blade and apparatus of FIG. 3A according to the present disclosure;

FIG. 4 illustrates a schematic view of a portion of the rotor blade of FIG. 2, particularly illustrating an alternative embodiment of a device for mitigating vortex shedding vibrations or stall induced vibrations mounted thereon, in accordance with the present disclosure;

FIG. 5A illustrates a schematic view of a portion of the rotor blade of FIG. 2, particularly illustrating yet another embodiment of a device for mitigating vortex shedding vibrations or stall induced vibrations mounted thereon, in accordance with the present disclosure;

FIG. 5B illustrates a cross-sectional view of the rotor blade and apparatus of FIG. 5A according to the present disclosure;

FIG. 6A illustrates a schematic view of a portion of the rotor blade of FIG. 2, particularly illustrating a further embodiment of a device for mitigating vortex shedding vibrations or stall induced vibrations mounted thereon, in accordance with the present disclosure;

FIG. 6B illustrates a cross-sectional view of the rotor blade and apparatus of FIG. 6A according to the present disclosure;

FIG. 7 illustrates a perspective view of a portion of the rotor blade of FIG. 2, particularly illustrating another embodiment of a device for mitigating vortex shedding vibrations or stall induced vibrations mounted thereon, in accordance with the present disclosure;

FIG. 8 illustrates a perspective view of a portion of the rotor blade of FIG. 2, particularly illustrating another embodiment of a device for mitigating vortex shedding vibrations or stall induced vibrations mounted thereon, in accordance with the present disclosure; and

FIG. 9 illustrates a flow diagram of one embodiment of a method for mitigating vortex shedding vibrations or stall induced vibrations on one or more rotor blades of a wind turbine during a standstill according to the present disclosure.

Detailed Description

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

As used herein, the terms "upstream" and "downstream" refer to directions relative to the air flow. For example, wind will contact upstream features before contacting downstream features.

In general, the present disclosure relates to an apparatus and method for mitigating vortex shedding vibrations or stall induced vibrations in a rotor blade of a wind turbine when the rotor blade is at standstill. The apparatus may be configured to temporarily attach to the rotor blade when the rotor blade is locked or deactivated and removed at the completion of a maintenance, repair or installation procedure. In various embodiments, the apparatus may include at least one airflow altering element coupled to the at least one positioning element. The apparatus may be secured to the rotor blade and positioned so as to disrupt the flow of air over the locked or deactivated rotor blade. The apparatus may disrupt rhythmic shedding of vortices from the edges of the rotor blades by, for example, disrupting the formation of vortices, fixing the location of vortex shedding, or causing a number of vortices to shed at fixed alternating locations, thereby causing an alternation in the phase relationship with each other. Additionally, the device may be placed to increase the drag of the rotor blade, thereby destroying lift and preventing stall induced vibrations. By disrupting the flow of air over the locked or deactivated rotor blades, the apparatus may mitigate the possibility of large and damaging vibrations that result in vibrations that coincide with the natural frequency of the structure.

Referring now to the drawings, FIG. 1 illustrates a perspective view of one embodiment of a wind turbine 100 according to the present disclosure. As shown, wind turbine 100 generally includes a tower 102 extending from a support surface 104, a nacelle 106 mounted on tower 102, and a rotor 108 coupled to nacelle 106. Rotor 108 includes a rotatable hub 110, and at least one rotor blade 112 coupled to and extending outwardly from hub 110. For example, in the illustrated embodiment, rotor 108 includes three rotor blades 112. However, in alternative embodiments, rotor 108 may include more or less than three rotor blades 112. Each rotor blade 112 may be spaced about hub 110 to facilitate rotating rotor 108 to enable kinetic energy to be converted from wind power to usable mechanical energy, and subsequently, electrical energy. For example, the hub 110 may be rotatably coupled to a generator positioned within the nacelle 106 to allow electrical energy to be generated.

Referring now to FIG. 2, illustrated is a perspective view of the rotor blade(s) 112 of the wind turbine 100 shown in FIG. 1. The rotor blade(s) 112 may generally include a blade root 118 configured to be mounted or otherwise secured to the hub 110 of the wind turbine 100 and a blade tip 120 disposed opposite the blade root 118. The body shell 122 of the rotor blade(s) 112 may generally extend along the pitch axis 116 between the blade root 118 and the blade tip 120. The body shell 122 may generally serve as an outer shell or surface or covering for the rotor blade(s) 112. The body shell 122 may define a substantially aerodynamic profile, such as by defining a symmetrical or curved airfoil shaped cross-section. Body shell 122 may also define a pressure side 124 and a suction side 126 extending between a leading edge 128 and a trailing edge 130 of rotor blade(s) 112. In addition, the rotor blade (S) 112 may also have a span (S) that defines a total length between the blade root 118 and the blade tip 120. The rotor blade(s) 112 may also have a chord (C) that defines an overall length between the leading edge 128 and the trailing edge 130. As is generally understood, the chord (C) may vary in length with respect to the span (S) as the rotor blade (S) 112 extends from the blade root 118 to the blade tip 120.

Referring now to fig. 3A-8, illustrated in accordance with the present disclosure are various embodiments of an apparatus 200 for mitigating vortex shedding vibrations and/or stall induced vibrations on rotor blade(s) 112 of wind turbine 100 during standstill. For example, in some cases, rotor blade(s) 112 may be at a standstill when hub 110 of wind turbine 100 is braked, locked, or deactivated. As shown, the apparatus 200 may include at least one positioning element 202 located between the blade tip 120 and blade root 118 sections of the rotor blade(s) 112. More specifically, as shown, the positioning element(s) 202 may be adapted to wrap around at least a portion of the rotor blade(s) 112.

The apparatus 200 may also include at least one airflow altering element 204 coupled to the positioning element(s) 202. The airflow altering element(s) 204 may define a distance (H) relative to the body shell/surface 122 of the rotor blade(s) 112. The apparatus 200 may also include at least one securing element 206 operably coupled to the positioning element(s) 202 to temporarily secure the airflow altering element(s) 204 to the rotor blade(s) 112. It should be appreciated that, in one embodiment, the positioning element(s) 202 may be spaced from the surface of the rotor blade(s) 112 or the body shell 122 by a distance (H) defined by the airflow altering element(s) 204.

In at least one embodiment, the positioning element(s) 202 may be a rope 208 having a plurality of yarns, strands, fibers, or strands braided or twisted together to form a generally circular cross-section. For example, the cord 208 may be a natural or synthetic rope having a single braid, double braid, braided, twisted, hollow, or diamond braid construction. In one embodiment, the tether 208 may include a plurality of buoyant fibers to enable the device 200 to float. In an additional embodiment, maintaining the selected curvature of the positioning element(s) 202 may be facilitated by the inclusion of a ductile core material (e.g., a metal wire). In further embodiments, the positioning element(s) 202 may be, for example, cables, tapes (e.g., woven nylon tapes), straps, pultrudes, or elasticized cords (e.g., bungee cords).

In an additional embodiment, the positioning element(s) 202 may be coil springs. The positioning element(s) 202 may have a coiled length and an installed length. The installation length may be greater than the coil length. The positioning element(s) 202 may have a stationary coil diameter and a mounting coil diameter that is smaller than the stationary coil diameter. It should be appreciated that applying tension to stretch positioning element(s) 202 to its installed length may result in the positioning element(s) 202 being tensioned around rotor blade(s) 112, and releasing the tension may allow positioning element(s) 202 to return to the stationary coil diameter and release rotor blade(s) 112.

In at least one embodiment, positioning element(s) 202 may be helically wound around a portion of blade 112. The helically wound cords 208 may have a pitch greater than or equal to one-half of the chord (C) of the rotor blade(s) 112. The helically wound cord 208 may also have a pitch less than or equal to six times the chord (C).

It should be appreciated that, in additional embodiments, the positioning element(s) 202 may be positioned in different orientations with respect to the rotor blade(s) 112. For example, positioning element(s) 202 may be oriented substantially parallel to pitch axis 116, leading edge 128, and/or trailing edge 130. In at least one such embodiment, such as depicted in fig. 5A and 5B, the positioning element(s) 202 can include at least one leading edge positioning element 222 arranged parallel to the leading edge 128. The positioning element(s) 202 may also include at least one trailing edge positioning element 224 that is parallel to the trailing edge 130.

In alternative embodiments, the cord 208 may be stretched between the blade tip 120 and the hub 110 or between the fastening elements 206. As depicted in FIG. 7, the tethers 208 may be positioned along a line upstream of the expected flow separation point on the suction side 126 or the pressure side 124 of the rotor blade(s) 112.

As depicted in fig. 6A, the positioning element(s) 202 may also be oriented parallel to the chord (C) and generally perpendicular to the pitch axis 116. For example, in at least one embodiment, the positioning element(s) 202 may include an elastic cord element 226 stretched along the chord (C) between the airflow modifying elements 204 positioned along the leading edge 128 and trailing edge 130, respectively.

In an additional embodiment, such as shown in fig. 8, the positioning element(s) 202 may be a hollow sleeve 210. Thus, as shown, the hollow sleeve 210 may enclose a portion of the rotor blade(s) 112. Additionally, as shown, the hollow sleeve 210 may have a first end 212 and a second end 214 disposed opposite thereto. The first end 212 may define an opening corresponding to the airfoil shape at a first designated spanwise location 216. The second end 214 may define an opening that corresponds to the airfoil shape at a second designated spanwise location 218. In an alternative embodiment, such as depicted in FIG. 4, second end 214 may be sealed so as to enclose blade tip 120. In certain embodiments, the hollow sleeve 210 may be a woven fabric, a mesh, a plastic, or a composite material. In at least one embodiment, the hollow sleeve 210 may be configured to be degradable within a specified time interval such that the hollow sleeve 210 may fall off the rotor blade(s) 112 without intervention.

Referring to fig. 3A, 4, 5A, 6, and 8, in various embodiments, the securing element(s) 206 may be configured to encircle a portion of the blade tip 120. Thus, in certain embodiments, the fastening element(s) 206 may be, for example, a strip, a rope, a belt, or a belt. In one embodiment, the fastening element 206 may be a collar having a diameter corresponding to the size of the airfoil at the specified spanwise location of the rotor blade(s) 112. Alternatively, the securing element(s) 206 may be an adhesive strip positioned between the positioning element(s) 202 and the body shell 122. In at least one embodiment, the securing element(s) 206 may be a high friction material, such as rubber, configured to resist rotational movement about the rotor blade(s) 112. It should be appreciated that the securing element(s) 206 may alternatively be a sleeve, bag, or sock (sock) configured to enclose the blade tip 120.

As particularly depicted in fig. 6A, in one embodiment, the securement element(s) 206 may be a rigid securement element 220. The rigid fastening element 220 may be formed, for example, from wood, metal, foam, plastic, composite, or any other suitable rigid material. The rigid fastening element 220 may define an opening corresponding to a cross-section of the rotor blade(s) 112 at a specified spanwise location.

Still referring to fig. 3A-8, the airflow altering element(s) 204 may be any suitable structure configured to disrupt the airflow over and/or around the rotor blade(s) 112 at standstill. For example, in various embodiments, such as depicted in fig. 7 and 8, the airflow altering element(s) 204 may include at least one of a fascia 242, a barrier, an inflatable cell 258, serrations, vortex generators, spoilers, or a combination thereof. In several embodiments, the airflow altering element(s) 204 may be formed of wood, foam, plastic, composite, metal, fabric, or any other suitable material. Further, the airflow altering element(s) 204 may be buoyant. In further embodiments, the airflow altering element(s) 204 may be a solid structure or a hollow structure. The airflow altering element(s) 204 may have fixed outer dimensions or may be inflatable. In at least one embodiment, the airflow altering element(s) 204 may have a diameter greater than or equal to 5% of the chord (C). In one embodiment, the airflow altering element(s) 204 may have a diameter less than or equal to 15% of the chord (C) when installed.

In further embodiments, the airflow altering element(s) 204 may be any suitable three-dimensional shape in one embodiment. For example, in various embodiments, the airflow altering element(s) 204 may be a sphere, prolate ellipsoid, hemisphere, cube, rectangular prism, frustum, or irregular three-dimensional shape. In additional embodiments, the airflow altering element(s) 204 may be a flexible sheet oriented on a plane having one fixed edge or curved so as to have at least two fixed edges. For example, in one embodiment, the airflow altering element(s) 204 may be a flexible sheet coupled to the trailing edge 130 at between 0.5 and two times the chord pitch and extending to the serrated edge. It should be appreciated that the airflow altering element(s) 204 may be formed so as to establish a face that conforms to (or matches) the curvature of the rotor blade(s) 112.

Referring again to fig. 3A, 4, 5A, and 6, the apparatus 200 may include at least one removal element 228. As shown, the removal element(s) 228 may be configured to act on the securing element(s) 206 in order to initiate removal of the apparatus 200 from the rotor blade(s) 112 upon completion of a maintenance, repair or installation operation. In one embodiment, the removal element(s) 228 may be a rope or wire coupled to the securement element(s) 206 and extending to the support surface 104. In another embodiment, the removal element(s) 228 may be at least one of a separation feature (e.g., a pull tab, perforation, zipper, or other feature configured to facilitate separation at a selected location), a quick-release coupler, or a magnetic fastener (or catch) configured to release the fastening element(s) 206 from the rotor blade(s) 112.

As particularly depicted in fig. 3A-4, the apparatus 200 may include a plurality of airflow altering elements 204 distributed along and secured to the positioning element(s) 202. In one embodiment, as shown in fig. 3A, the airflow altering elements 204 may be distributed at specified intervals (I) along the helically wound cords 208. The designated spacing (I) may be selected to ensure that the airflow altering elements 204 may be distributed across the pressure side 124 and/or the suction side 126 of the rotor blade(s) 112. In an additional embodiment, the plurality of airflow altering elements 204 may include at least one leading edge airflow altering element 230 and at least one trailing edge airflow altering element 232 distributed in an alternating pattern along the positioning element(s) 202, and the specified spacing (I) may be selected to position the airflow altering elements 204 along the leading edge 128 and the trailing edge 130. Thus, the positioning of the airflow altering element 204 relative to the rotor blade(s) 112 may be determined by the specified spacing (I) and the pitch of the helically wound cord 208.

Still referring to fig. 3A-4, in one exemplary embodiment, the airflow altering element 204 may be a sphere or prolate spheroid having cords 208 passing through its center and fixed at designated intervals (I) along the positioning element(s) 202. In such an embodiment, the distance (H) may be the radius of the airflow altering element 204 minus the radius of the cords 208.

Referring specifically to fig. 5A and 5B, another embodiment of an apparatus 200 for mitigating vortex shedding vibrations or stall induced vibrations in rotor blade(s) 112 at standstill is depicted. In such an embodiment, the positioning element(s) 202 may include a leading edge positioning element(s) 222 arranged parallel to the leading edge 128 of the rotor blade(s) 112. Positioning element(s) 202 may also include trailing edge positioning element(s) 224 arranged parallel to the trailing edge of rotor blade(s) 112. The airflow altering element(s) 204 may include a leading edge airflow altering element(s) 230 coupled to a leading edge positioning element(s) 222. The airflow altering element(s) 204 may also include trailing edge airflow altering element(s) 232 coupled to the trailing edge positioning element(s) 224.

Thus, as shown, the leading edge airflow altering element(s) 230 may define a leading edge mounting notch 234 corresponding to a leading edge profile 236, while the trailing edge airflow altering element(s) 232 may define a trailing edge mounting notch 238 corresponding to a trailing edge profile 240. In at least one embodiment, the leading and trailing edge airflow altering elements 230, 232 may extend from the pressure side 124 to the suction side 126 around the respective edges. Accordingly, the apparatus 200 may include additional leading edge positioning elements 222 and trailing edge positioning elements 224.

It should be appreciated that, in at least one embodiment, the leading and trailing edge airflow altering elements 230, 232 may also be distributed at designated locations along the respective positioning elements 202 that are calculated to fix the location of the vortex shedding. The distribution of the leading and trailing edge airflow modifying elements 230, 232 may place the respective modifying elements in-line along a given chord (C), establish an alternating spanwise pattern, or a combination thereof.

6A-6B, the apparatus 200 may include a leading edge airflow altering element(s) 230 and an opposite trailing edge airflow altering element(s) 232 at a specified spanwise location. In at least one embodiment, the leading and trailing edge airflow altering elements 230, 232 may extend from the pressure side 124 to the suction side 126 around the respective edges. The leading and trailing edge airflow altering elements 230, 232 may be coupled by an elastic cord element 226. The elastic cord elements 226 may limit the spacing between the leading edge airflow altering element 230 and the trailing edge airflow altering element 232 at a specified spanwise location. For example, in one embodiment, the length (L) of the elastic cord element 226 may be adjusted to conform to the length of the chord (C) at a specified spanwise location. Thus, in the tapered portion of the rotor blade(s) 112, the length (L) of the elastic cord element 226 may determine the placement of the leading and trailing edge airflow altering elements 230, 232.

In an additional embodiment, such as depicted in fig. 7, the airflow-altering element(s) 204 may be a fascia 242 (e.g., a flag or other substantially flat flexible sheet). The ribbon 242 may have a surface density greater than 300 g/m. In an additional embodiment, the ribbon 242 may have a surface density less than 750 g/m. Further, as shown, the fascia 242 may have a mounting edge 244 secured to the positioning element(s) 202, e.g., oriented perpendicular to the chordwise direction of the rotor blade(s) 112. In such embodiments, the positioning element(s) 202 may be temporarily coupled to at least one of the leading edge 128, the trailing edge 130, or coupled along a line upstream of the flow separation point 246. Positioning element(s) 202 may be coupled to suction side 126 or pressure side 124 of rotor blade(s) 112. In some embodiments, the fascia 242 may extend from the mounting edge 244 to a length that is three times the length of the chord (C).

Still referring to FIG. 7, in at least one embodiment, the locating element(s) 202 may be a cord or a band oriented spanwise along the rotor blade(s). In one embodiment, the securement element(s) 206 may include a first securement element 248 coupled to a first end 250 of the positioning element(s) 202. The securement element(s) 206 may also include a second securement element 252 coupled to an opposite second end 254 of the positioning element(s) 202. In an alternative embodiment, the securing element(s) 206 may be an adhesive strip positioned between the positioning element(s) 202 and the body shell 122.

Referring now to FIG. 8, yet another embodiment of an apparatus 200 for mitigating vortex shedding vibrations or stall induced vibrations in rotor blade(s) 112 at standstill is depicted. In such an embodiment, the securing element(s) 206 may be a hollow sleeve 210. The hollow sleeve 210 may define at least one inlet air aperture 256. In one embodiment, such as depicted in fig. 8, the airflow altering element(s) 204 may be an inflatable cell 258. The inflatable cell 258 may be a flexible plenum that may be fluidly coupled to the inlet air aperture(s) 256 and inflated by air passing therethrough. The inflatable cells 258 may be positioned adjacent to the pressure side 124 or the suction side 126. It should be appreciated that the inflatable cells 258 may act on the rotor blade(s) 112 in a manner similar to the fascia 242 discussed above when uninflated or partially inflated.

It should be appreciated that in at least one embodiment, device 200 may include various combinations of the embodiments discussed herein. For example, in one embodiment, the device 200 may include an inflatable cell 258 and an airflow altering element(s) 204 distributed along a helically wound cord 208. Alternatively, the apparatus 200 may include leading and trailing edge airflow altering elements 230, 232 in combination with one or more fascia 242. In additional embodiments, the apparatus 200 may include additional combinations of positioning element(s) 202, airflow altering element(s) 204, and securing element(s) 206 as discussed herein.

Referring to FIG. 9, illustrated is a flow diagram of an embodiment of a method 300 for mitigating vortex shedding vibrations and/or stall induced vibrations on one or more rotor blades of a wind turbine during a standstill. The method 300 may be performed using, for example, the apparatus 200 discussed above with reference to fig. 3A-8. For purposes of illustration and discussion, FIG. 9 depicts the steps performed in a particular order. Using the disclosure provided herein, one of ordinary skill in the art will appreciate that the various steps of method 300 or any of the other methods disclosed herein may be adapted, modified, rearranged, performed concurrently, or modified in various ways without departing from the scope of the present disclosure.

As shown at (302), the method 300 includes mounting a vibration reduction apparatus on a rotor blade. As shown at (302 a), the mounting of the vibration damping device includes positioning at least one airflow altering element at a desired location along the outer surface of the rotor blade with at least one positioning element. As shown at (302 b), the mounting of the vibration damping apparatus includes securing at least one positioning element to an outer surface of the rotor blade via at least one securing element. As shown at (304), method 300 includes performing maintenance and/or repair operations on the wind turbine with the installed vibration reduction apparatus. As shown at (306), method 300 includes removing the vibration reduction apparatus from the rotor blade once the maintenance and/or repair operation is complete.

In additional embodiments, positioning the at least one airflow altering element at a desired location may further comprise, in accordance with the present disclosure: the cord element is helically wound around a portion of the rotor blade in order to disturb the air flow over the chordwise section of the rotor blade. In another embodiment, positioning the at least one airflow altering element at the desired location may further include positioning an edge of the at least one airflow altering element adjacent at least one of the leading edge, the trailing edge, or along a line upstream of a flow separation point on the suction side or the pressure side of the rotor blade. In another embodiment, positioning the at least one airflow altering element at the desired location may further include enclosing a portion of the rotor blade within the hollow sleeve and coupling the inflatable unit to the hollow sleeve, and operably coupling the inflatable unit to the inlet air bore.

Furthermore, the skilled person will recognize the interchangeability of various features from different embodiments. Similarly, various method steps and features described, as well as other known equivalents for each such method and feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

For completeness, various aspects of the disclosure are set forth in the following numbered clauses:

clause 1. an apparatus for mitigating vortex shedding or stall induced vibrations on one or more rotor blades of a wind turbine during a standstill, the apparatus comprising:

at least one positioning element positioned between a blade tip section and a blade root section thereof, the at least one positioning element being adapted to be wound around at least a portion of the rotor blade;

at least one airflow modifying element coupled to the at least one positioning element, the at least one airflow modifying element defining a height relative to a surface of the rotor blade; and the number of the first and second groups,

at least one securing element operably coupled to the at least one positioning element for temporarily securing the at least one airflow altering element to the rotor blade.

Clause 2. the apparatus of clause 1, wherein the at least one positioning element comprises at least one cord member helically wound around a portion of the rotor blade.

Clause 3. the apparatus according to any of the preceding clauses, characterized in that the helically wound cord element has a pitch greater than or equal to half the chord of the rotor blade and less than or equal to six times the chord of the rotor blade, wherein at least a portion of the helically wound cord element is separated from the surface of the rotor blade by a distance defined by the at least one air flow changing element.

Clause 4. the apparatus according to any preceding clause, characterized in that the at least one air flow altering element comprises at least one of a fascia, a barrier, an inflatable unit, serrations, vortex generators and/or spoilers.

Clause 5. the apparatus according to any preceding clause, characterized in that the at least one airflow altering element comprises a plurality of airflow altering elements distributed along and secured to the at least one positioning element.

Clause 6. the apparatus of any of clauses 1, 2, 3 or 5, wherein the plurality of airflow altering elements comprises leading edge airflow altering elements and trailing edge airflow altering elements, wherein the leading edge airflow altering elements and the trailing edge airflow altering elements are distributed in an alternating pattern along the at least one positioning element.

Clause 7. the apparatus according to any preceding clause, characterized in that the at least one airflow altering element comprises at least one leading edge airflow altering element and at least one trailing edge airflow altering element disposed opposite thereto, wherein the at least one positioning element is comprised of an elastic cord element coupled between the leading edge airflow altering element and the trailing edge airflow altering element, wherein the elastic cord element limits the spacing between the leading edge airflow altering element and/or the trailing edge airflow altering element at a specified spanwise location of the rotor blade.

Clause 8. the apparatus according to any preceding clause, characterized in that the at least one positioning element comprises a leading edge positioning element arranged parallel to a leading edge of the rotor blade and a trailing edge positioning element arranged parallel to a trailing edge of the rotor blade, the at least one airflow altering element comprising: at least one leading edge airflow altering element coupled to the leading edge positioning element and at least one trailing edge airflow altering element coupled to the trailing edge positioning element, the leading edge airflow altering element defining a leading edge mounting notch corresponding to a leading edge profile and the trailing edge airflow altering element defining a trailing edge mounting notch corresponding to a trailing edge profile.

Clause 9. the apparatus according to any preceding clause, characterized in that the at least one airflow modification element has a mounting edge along which the airflow modification element is coupled to the at least one positioning element, the at least one positioning element being oriented perpendicular to the chordwise direction of the rotor blade, the at least one positioning element being temporarily coupled to at least one of a leading edge, a trailing edge, or along a line upstream of a flow separation point on a suction side or a pressure side of the rotor blade.

Clause 10. the apparatus of clause 9, wherein the at least one positioning element comprises a cord oriented spanwise along the rotor blade, and wherein the at least one securing element comprises a first securement element coupled to a first end of the positioning element and a second securement element coupled to an opposite second end of the positioning element.

Clause 11. the apparatus of any of clauses 1 or 4, wherein the at least one positioning element comprises a hollow sleeve configured to enclose a portion of the rotor blade, the hollow sleeve defining at least one inlet air aperture.

Clause 12. a method for mitigating vortex shedding or stall induced vibrations on one or more rotor blades of a wind turbine during a standstill, the method comprising:

mounting a vibration damping device on the rotor blade, wherein the mounting of the vibration damping device further comprises:

positioning at least one airflow altering element at a desired location along an outer surface of the rotor blade with at least one positioning element; and

securing the at least one positioning element to an outer surface of the rotor blade via at least one securing element;

performing installation, commissioning, maintenance and/or repair operations on the wind turbine with the installed vibration reduction apparatus; and the number of the first and second groups,

once the installation, commissioning, maintenance and/or repair operations are completed, the vibration reduction apparatus is removed from the rotor blade.

Clause 13. the method of clause 12, wherein the at least one air flow altering element comprises at least one of a fascia, a barrier, an inflatable unit, serrations, a vortex generator, and/or a spoiler.

Clause 14. the method of any of clauses 12 or 13, wherein the at least one positioning element comprises a cord element, wherein positioning the at least one airflow-altering element at the desired location further comprises: helically winding the cord element around a portion of the rotor blade so as to disrupt airflow over a chordwise section of the rotor blade, wherein at least a portion of the at least one positioning element is spaced from an outer surface of the rotor blade by a distance defined by the at least one airflow altering element.

Clause 15. the method of any of clauses 12, 13 or 14, wherein positioning the at least one airflow-altering element at the desired location further comprises: positioning an edge of the at least one airflow altering element adjacent at least one of a leading edge, a trailing edge, or along a line upstream of a flow separation point on a suction side or a pressure side of the rotor blade.

Clause 16. the method of any of clauses 12 or 13, wherein the at least one positioning element comprises a hollow sleeve defining an inlet air bore, and the at least one airflow altering element comprises the inflatable unit, wherein positioning the at least one airflow altering element at the desired location further comprises: enclosing a portion of the rotor blade within the hollow sleeve and coupling the inflatable unit to the hollow sleeve, and operably coupling the inflatable unit to the inlet air bore, wherein the inflatable unit is disposed adjacent to a pressure side or a suction side of the rotor blade.

Clause 17. a rotor assembly for a wind turbine, comprising:

a rotor hub at standstill;

at least one rotor blade including a leading edge and a trailing edge disposed between a tip portion and an opposite root portion, the root portion coupled to the rotor hub; and the number of the first and second groups,

apparatus for mitigating vortex shedding vibrations and/or stall induced vibrations on said at least one rotor blade during a standstill, said apparatus comprising:

at least one positioning element positioned between a blade tip section and a blade root section thereof, the at least one positioning element being adapted to be wound around at least a portion of the rotor blade;

at least one airflow modifying element coupled to the at least one positioning element, the at least one airflow modifying element defining a height relative to a surface of the rotor blade; and the number of the first and second groups,

at least one securing element operably coupled to the at least one positioning element for temporarily securing the at least one airflow altering element to the rotor blade.

The rotor assembly of clause 18. the rotor assembly of clause 17, wherein the at least one air flow altering element comprises at least one of a fascia, a barrier, an inflatable unit, serrations, a vortex generator, and/or a spoiler.

The rotor assembly of any of clauses 17 or 18, wherein the at least one positioning element comprises a cord helically wound around a portion of the rotor blade, wherein the at least one airflow altering element comprises a plurality of airflow altering elements distributed along the at least one positioning element.

The rotor assembly of any of clauses 17, 18 or 19, wherein the at least one airflow modification element has a mounting edge along which the airflow modification element is coupled to the at least one positioning element, the at least one positioning element oriented perpendicular to the chordwise direction of the rotor blade, the at least one positioning element being temporarily coupled to at least one of a leading edge, a trailing edge, or along a line upstream of a flow separation point on a suction side or a pressure side of the rotor blade.