GB2558232A

GB2558232A - Wind turbine flow modifier device and method of using same

Info

Publication number: GB2558232A
Application number: GB1622028.7A
Authority: GB
Inventors: KUDSK Henrik; Gupta Anurag
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2016-12-22
Filing date: 2016-12-22
Publication date: 2018-07-11
Also published as: GB201622028D0

Abstract

A wind turbine including a support structure 14 and a plurality of energy generating units 12 coupled to the support structure. Each energy generating unit includes a rotor 26 having at least one wind turbine blade 30. The arrangement of the energy generating units on the support structure defines an interstitial region 36 subject to a free stream airflow. An airflow modifier means (AFM) 38 is positioned in the interstitial region. The airflow modifier means may include a flow diverter, for diverting the free stream airflow toward the rotors, or a vortex generator, for generating vortices that mix out the wake region downstream of the rotors. The AFM may be a hybrid flow diverter and vortex generator. The AFM may have an active state and a passive state, it may either expand and collapse, or inflate and deflate between these states. A method of operating a wind turbine with AFM is also claimed. A wind farm using these turbines is also claimed, where the turbines in the farm may have different AFMs.

Description

(54) Title of the Invention: Wind turbine flow modifier device and method of using same Abstract Title: Wind turbine with flow modifier device and method of using same (57) A wind turbine including a support structure 14 and a plurality of energy generating units 12 coupled to the support structure. Each energy generating unit includes a rotor 26 having at least one wind turbine blade 30. The arrangement of the energy generating units on the support structure defines an interstitial region 36 subject to a free stream airflow. An airflow modifier means (AFM) 38 is positioned in the interstitial region. The airflow modifier means may include a flow diverter, for diverting the free stream airflow toward the rotors, or a vortex generator, for generating vortices that mix out the wake region downstream of the rotors. The AFM may be a hybrid flow diverter and vortex generator. The AFM may have an active state and a passive state, it may either expand and collapse, or inflate and deflate between these states. A method of operating a wind turbine with AFM is also claimed. A wind farm using these turbines is also claimed, where the turbines in the farm may have different AFM’s.

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WIND TURBINE FLOW MODIFIER DEVICE AND METHOD OF USING SAME

Technical Field

The present invention relates generally to wind turbines, and more particularly to a airflow modifier device for a wind turbine that utilizes the leakage airflow through the wind turbine in an improved, more productive manner, and to a method of using the leakage airflow through a wind turbine to improve the operation of the wind turbine or wind farm.

Background

Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. Generally, a wind turbine converts kinetic wind energy into mechanical energy and then subsequently converts the mechanical energy into electrical energy. A common type of wind turbine is the single rotor upwind horizontal-axis wind turbine (HAWT). An exemplary single rotor HAWT includes a tower, a nacelle located at the apex of the tower, and a single rotor having a central hub and one or more blades (e.g., three blades) mounted the hub and extending radially therefrom. The rotor is supported by the nacelle and positioned at the front of the nacelle so that the rotor faces into the wind upstream of its supporting tower. The rotor may be coupled either directly or indirectly with a generator (not shown) housed inside the nacelle and configured to convert the mechanical energy of the rotor to electrical energy.

While wind turbines may be configured as stand-alone structures, such that there is no other wind turbine in the immediate vicinity of the wind turbine, often times wind turbines are grouped together. For example, large groups of wind turbines may be arranged in a multi-dimensional array (e.g., a rectangular array). In such an array of wind turbines, which may comprise a wind farm, the wind turbines may be clustered relatively close together such that adjacent wind turbines may have an upstream/downstream relationship to each other, and wherein the upstream wind turbine may impact the airflow that passes through the downstream wind turbine.

Wind turbine manufacturers continually strive to increase power production from a wind turbine or wind farm. In this regard, the particular wind turbine design may play a significant role in the generated power output from the wind. For example, in addition to the increased power from higher wind velocities, energy obtained from the wind is proportional to the sweep area of the wind turbine blades. Thus for single-rotor HAWTs, the sweep area may be increased by using long wind turbine blades. In other words, the longer the blades, the larger the area that is traced by the blade tips, and thus more energy may be extracted from the wind. However, the continued increase in the length of

- 1 the wind turbine blades may have certain practical limits and pose significant design challenges for wind turbine manufacturers.

Accordingly, as an alternative to single-rotor HAWTs, wind turbine manufacturers have looked to multi-rotor wind turbines (such as multi-rotor HAWTs), which generally incorporate multiple rotors on a single support tower, as a potential route to increase energy capture and power production. In this regard, multiplying the number of rotors effectively increases the sweep area of the wind turbine. One type of multi-rotor wind turbine is a coplanar multi-rotor wind turbine, wherein multiple rotors are arranged such that the individual wind turbine blades on each rotor generally lie within the same plane. In order to prevent the blades from adjacent rotors from contacting each other, the rotors must be sufficiently spaced apart from one another. The required spacing of the rotors defines an interior space or interstitial region between the rotors of the wind turbine. This space, which may be relatively large for modern multi-rotor wind turbines, allows uninterrupted, high energy airflow (i.e., the free stream wind) to effectively leak past the wind turbine. The leaked airflow through the interstitial region of the wind turbine represents a lost opportunity to use that wind energy for a productive purpose.

Accordingly, there is a need for improved devices and methods that utilize the high energy airflow in the interstitial region of multi-rotor wind turbines in a more productive manner.

Summary

A wind turbine includes a support structure and a plurality of energy generating units coupled to the support structure. Each of the energy generating units includes a rotor having at least one wind turbine blade. The arrangement of the energy generating units on the support structure defines an interstitial region subject to a free stream airflow. The wind turbine further includes an airflow modifier means coupled to the support structure and positioned in the interstitial region. The airflow modifier means is configured to facilitate the use of energy in the free stream airflow passing through the interstitial region so as to produce a useful result in the operation of the wind turbine or wind farm.

In one embodiment, the airflow modifier means is movably coupled to the support structure. For example, the airflow modifier means may be rotatable about the support structure (e.g., such as a tower). In this regard, the airflow modifier means may be operatively coupled to a yaw mechanism that is configured to yaw at least one of the rotors of the plurality of energy generating units. Alternatively, the airflow modifier means may have its own yaw mechanism for rotating the airflow modifier means about the tower. In a further alternative embodiment, the airflow modifier means may be non-rotatably secured to the support structure. In this embodiment, the airflow modifier means may be

- 2 symmetric about a rotational axis such that a front profile of the airflow modifier means is substantially the same independent of the yaw angle of the rotors of the plurality of energy generating units.

In an exemplary embodiment, the airflow modifier means is deployable between an active position wherein the airflow modifier means is operational to produce the useful result in the operation of the wind turbine or wind farm, and a passive position wherein the airflow modifier means is configured to minimize the disruption of the free stream airflow through the interstitial region. By way of example, in one embodiment the airflow modifier means may be inflatable and deflatable so as to transition between the active and passive positions. In an alternative embodiment, the airflow modifier means may be expandable and collapsible so as to transition between the active and passive positions.

In one embodiment, the airflow modifier means includes an airflow diverter and the useful result includes diverting at least a portion of the free stream airflow toward the rotors of the plurality of energy generating units. The airflow diverter may include a relatively large wind-engaging surface that occupies a significant portion of the interstitial region. For example, the airflow diverter may include a spherical portion, the outer surface of which defines the wind-engaging surface. In another embodiment, the airflow modifier means includes a vortex generator and the useful result includes generating vortices for mixing out a wake region downstream of the rotors of the plurality of energy generating units. In an exemplary embodiment, the vortex generator may include a wing assembly having one or more wings, wherein airflow over the one or more wings generates vortices downstream of the rotors. The wind turbine may include three generating units and the wing assembly may include three wings. Similarly, the wind turbine may include four generating units and the wing assembly may include four wings. The four wings may be arranged in an X shape.

In a further embodiment, the airflow modifier means includes a hybrid device, wherein a first portion of the hybrid device is configured as a flow diverter with the useful result of diverting at least a portion of the free stream airflow toward the rotor of the plurality of energy generating units, and a second portion of the hybrid device is configured as a vortex generator with the useful result of generating vortices for mixing out the wake region downstream of the rotors of the plurality of energy generating units. In this regard, the hybrid device includes a central region configured to operate as the flow diverter and a vortex generator is positioned at the periphery of the central region. The vortex generator at the periphery of the central region may include a wing assembly including one or more wings. In this embodiment, the deployment of the flow diverter between its active and

-3passive positions may be independent of the deployment of the wing assembly between its active and passive positions.

In yet another embodiment, a method of improving the operation of a wind turbine or wind farm includes providing a multi-rotor wind turbine having a plurality of energy generating units arranged to define an interstitial region, and positioning an airflow modifier means in the interstitial region so that the interaction between a free stream airflow and the airflow modifier means produces a useful result in the operation of the wind turbine or wind farm.

The wind turbine may include a support structure for carrying the plurality of energy generating units and the method may further include rotating the airflow modifier means about a rotational axis. More particularly, the airflow modifier means may be rotated in registration with the yawing of the rotors of the plurality of energy generating units. The method may further include moving the airflow modifier means between an active position wherein the airflow modifier means is operational to produce the useful result in the operation of the wind turbine or wind farm, and a passive position wherein the airflow modifier means is configured to minimize the disruption of the free stream airflow through the interstitial region. The movement between the active and passive positions may further include inflating and deflating the airflow modifier means. Alternatively, movement between the active and passive positions may further include expanding and collapsing the airflow modifier means.

In one embodiment, the airflow modifier means includes an airflow diverter and the method further includes diverting at least a portion of the free stream airflow toward the rotors of the plurality of energy generating units to produce a useful result. In this embodiment, the flow may be diverted toward the high efficiency region of the blades of the rotors. In another embodiment, the airflow modifier means includes a vortex generator and the method further includes generating vortices to mix out the wake region downstream of the rotors of the plurality of energy generating units to produce a useful result. In one embodiment, the step of generating vortices may include providing a wing assembly having one or more wings, wherein airflow over the one or more wings generates the vortices that mix out the wake region downstream of the rotors of the plurality of energy generating units.

In a further embodiment, the airflow modifier means includes a hybrid device and the method further includes diverting a portion of the free stream airflow toward the rotors of the plurality of energy generating units, and using the energy in another portion of the free stream airflow (e.g., a pass through portion of the free stream airflow) to generate vortices downstream of the rotors of the plurality of energy generating units.

-4In accordance with yet another embodiment, a wind farm includes at least one wind turbine as described above and having an airflow modifier means. Further, at least one wind turbine has an airflow modifier means that is different than an airflow modifier means on at least one other wind turbine. The airflow modifier means may be selected from a flow diverter, a vortex generator, or a hybrid device. In one embodiment, a method of operating a wind farm includes providing at least one wind turbine with an airflow modifier means positioned within an interstitial region of the wind turbine, and selectively moving the airflow modifier means between an active position wherein the airflow modifier means is operational to modify a free stream airflow through the interstitial region, and a passive position wherein the airflow modifier means is configured to minimize the disruption of the free stream airflow through the interstitial region. In another embodiment, a method of operating a wind farm includes selecting at least one of the wind turbines in the wind farm to have an airflow modifier means of a first type, and selecting at least another one of the wind turbines in the wind farm to have an airflow modifier means of a second type. The first and second types of airflow modifier means may be selectively moved between their active and passive positions in accordance with a control strategy.

Brief Description of the Drawings

Various additional features and advantages of the invention will become more apparent to those of ordinary skill in the art upon review of the following detailed description of one or more illustrative embodiments taken in conjunction with the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the general description given above and the detailed description given below, serve to explain the one or more embodiments of the invention.

Fig. 1 is a front view of a multi-rotor wind turbine in accordance with one embodiment of the invention;

Fig. 2 is a front view of another multi-rotor wind turbine in accordance with another embodiment of the invention;

Fig. 3 is a view of the multi-rotor wind turbine shown in Fig. 1 taken along line 3-3 illustrating an airflow diverter according to one embodiment of the invention;

Fig. 4 is a view similar to that shown in Fig. 3 illustrating an airflow diverter according to another embodiment of the invention;

-5Fig. 5A is a top view of an airflow diverter according to an embodiment of the invention in an active position;

Fig. 5B is a top view of the airflow diverter shown in Fig. 5A but in a passive position;

Fig. 6A is a front view of an airflow diverter according to an embodiment of the invention in an active position;

Fig. 6B is a top view of the airflow diverter shown in Fig. 6A but in a passive position;

Fig. 7 is a partial side view of a multi-rotor wind turbine illustrating a vortex generator according to one embodiment of the invention;

Fig. 8 is a partial top view of the multi-rotor wind turbine illustrating the vortex generator shown in Fig. 7;

Fig. 9 is a partial front view of a multi-rotor wind turbine illustrating a vortex generator according to another embodiment of the invention; and

Fig. 10 is a partial top view of a multi-rotor wind turbine illustrating hybrid device that includes both a flow diverter and a vortex generator.

Detailed Description

Referring to the figures, and to Figs. 1 and 2 in particular, a wind turbine 10 includes a plurality of energy generating units 12 and a support structure 14 for supporting or carrying the plurality of energy generating units 12. In an exemplary embodiment, the wind turbine 10 may be configured as a coplanar multi-rotor wind turbine having a plurality of energy generating units 12. However, aspects of the present invention may benefit other multirotor arrangements and should not be limited to the exemplary embodiments shown and described herein. The support structure 14 includes a tower 16 and one or more support arms 18 mounted to the tower 16 for carrying one or more energy generating units 12. As is conventional, the tower 16 may be coupled to a foundation 20 at a lower end thereof and defines a generally vertical tower axis 22. The foundation 20 may be a relatively large mass, e.g., concrete, steel, etc. embedded in the ground and through which forces on the wind turbine 10 may be ultimately transferred. The one or more support arms 18 have a proximal end adjacent the tower 16 and extend generally outwardly from the tower 16 to a distal or tip end spaced from the tower. The one or more support arms 18 may include various beams and/or lattice structure sufficient to accommodate the one or more energy generating units 12 at a distance from the tower 16 and tower axis 22.

-6By way of example, in one embodiment the one or more support arms 18 may include generally cylindrical beams (e.g., tubular beams having a generally circular cross section) extending outwardly from the tower 16 for at least about 20 m, for at least about 40 m, or for at least about 70 m depending on the size of the wind turbine. Beams having different cross-sectional shapes are also possible. In one embodiment, the one or more support arms 18 may be formed from steel, but it should be realized that other materials may also be possible. Moreover, the support arms 18 may extend from the tower 16 in a substantially perpendicular manner in one embodiment. However, in alternative embodiments, the support arms 18 may extend from the tower at angles other than about 90 degrees. For example, the support arms 18 may extend in a generally upward direction, downward direction or forward direction. The support arms 18 may each extend from the tower 16 at substantially the same angle. Alternatively, the support arms 18 extend from the tower 16 may be different for different support arms. This may depend, for example, on the particular design of the multi-rotor wind turbine.

In an exemplary embodiment, preferably each of the support arms 18 is rotatably mounted to the tower 16 via a yaw mechanism 24 that allows the support arms 18, and the energy generating units 12 attached thereto, to rotate about the tower axis 22 and thereby direct the energy generating units 12 into the wind. As is generally know in the art, the yaw mechanism 24 generally includes one or more yaw bearings and one or more yaw actuators (not shown) that provide rotation of the support arms 18 relative to the tower 16 about tower axis 22. In one embodiment, for example, two or more support arms 18 may be coupled to the same yaw mechanism 24, and the wind turbine 10 may include one or more yaw mechanisms 24 vertically distributed along the height of the tower 16.

As illustrated in Fig. 1, for example, the multi-rotor wind turbine 10 includes a first, lower yaw mechanism 24a having a first support arm 18a and a second support arm 18b coupled thereto and extending from opposing sides of the tower 16. An energy generating unit 12a, 12b is respectively coupled to each of the support arms 18a, 18b adjacent a tip end of the support arms 18a, 18b. Wind turbine 10 may also include a second, upper yaw mechanism 24b having a first support arm 18c and a second support arm 18d coupled thereto and extending from opposing sides of the tower 16. Similarly, an energy generating unit 12c, 12d is respectively coupled to each of the support arms 18c, 18d adjacent a tip end of the support arms 18c, 18d. Thus, in this exemplary embodiment, there are four energy generating units 12a, 12b, 12c, 12d supported on the same tower 16.

The invention, however, is not limited to such an arrangement. For example, Fig. 2, in which like reference numbers refer to like features in Fig. 1, illustrates a multi-rotor wind

- 7 turbine 10' having three energy generating units 12a, 12b, 12c. In this embodiment, the wind turbine 10' includes a first yaw mechanism 24a having a first support arm 18a and a second support arm 18b coupled thereto and extending from opposing sides of the tower 16. An energy generating unit 12a, 12b is respectively coupled to each of the support arms 18a, 18b adjacent a tip end of the support arms 18a, 18b. A third energy generating unit 12c is mounted to a top of the tower 16 via a second yaw mechanism 24b.

As illustrated in these figures, each support arm 18 is configured to carry at least one energy generating unit at a distance from the tower 16. As used herein, an energy generating unit means the part of the wind turbine which actually transforms the energy of the wind into electrical energy. In accordance with this meaning, an energy generating unit typically includes a rotor 26 having a central hub 28 and one or more blades 30 (e.g., three blades) mounted to the hub 28 and extending radially therefrom, and a generator (not shown). In one embodiment, the energy generating unit may further include a drive train (not shown), including a gear arrangement, interconnecting the rotor 26 and the generator. The generator and a substantial portion of the drive train may be positioned inside of a nacelle 32 of the wind turbine 10. As noted above, in one embodiment, an energy generating unit 12 may be positioned adjacent a tip end of each of the support arms 18. It should be recognized, however, that an energy generating unit 12 may be positioned at other locations along the support arm 18, and that each support arm 18 may carry more than one energy generating unit 12. The wind turbine blades 30 are configured to interact with a free stream air flow (the wind) to produce lift that causes the rotors 26 to spin or rotate generally within a plane defined by the wind turbine blades 30. Thus, the energy generating units 12 are able to generate power from the airflow that passes through the swept area 34 of each of the rotors 26.

The arrangement of the energy generating units 12 on the tower 16 must be configured so as to prevent the blades 30 from adjacent rotors 26 from contacting each other during use. Accordingly, the energy generating units 12 must be sufficiently spaced from one another to avoid such contact. This spacing of energy generating units 12 generally defines an interior space or interstitial region 36 generally between the energy generating units. The size of the interstitial region 36 may be appreciable. By way of example and without limitation, the interstitial region 36 may be between about 10% and about 20% of the swept area 34 of each rotor of the energy generating units 12, or greater than about 5% of the collective swept area of all the rotors 26. Moreover, the airflow through the interstitial region is substantially that of the free stream, and thus constitutes a high energy flow field. In a conventional sense, the airflow in this region is simply permitted to leak or pass therethrough without any energy extraction or useful work for producing a desired result or

-8outcome. In short, the energy in that airflow, although being in the immediate vicinity of the wind turbine, is essentially wasted.

Aspects of the present invention are configured to extract some useful work or result from the leakage airflow in the interstitial region 36. In this regard, aspects of the invention position an airflow modifier means or device 38 in the interstitial region 36 for the purpose of converting the energy in the free stream airflow into something useful in the operation of the wind turbine or in the operation of a wind farm having, for example, a plurality of wind turbines. By way of example and without limitation, in one exemplary embodiment, the airflow modifier means 38 may include an airflow deflector or diverter. In this embodiment, the air flow diverter is configured to block at least a portion of the free stream airflow through the interstitial region 36, and preferably a significant portion of the free stream airflow, and accelerate the high energy airflow toward the swept area 34 of one or more of the rotors 26 of the energy generating units 12. In this way, the free stream airflow that would have otherwise leaked past the wind turbine is now redirected so as flow over the blades 30 of one or more of the energy generating units 12, and thereby have energy extracted from that airflow to produce electrical energy via the generator. Accordingly, there is an increase in efficiency, as more of the energy in the free stream airflow in the vicinity of the wind turbine is used to produce power. In this embodiment, the useful result is the redirection and the acceleration of the free stream airflow toward the rotors of the energy generating units so as to increase the efficiency and/or power production of the wind turbine to which the airflow modifier means is associated.

In another exemplary embodiment, the airflow modifier means 38 includes a vortex generator for the purpose of mixing out the wake region downstream of the rotors 26 of the wind turbine 10. It is generally well known that when air flows through the swept area 34 of a rotor 26, a wake region is formed downstream of the rotor 26. The velocity field in the wake region is changed compared to the free stream velocity and the turbulence intensity in the wake region is increased. This may have some significance in the context of a wind farm, where the spacing between an upstream wind turbine and a downstream wind turbine may be selected so as to minimize or reduce the impact of the upstream wind turbine on the downstream airflow that passes through the downstream wind turbine. In current wind farm designs, for example, upstream and downstream wind turbines may be separated by a distance on the order of several rotor diameters in order to allow the wake region generated by the upstream rotor and the upstream support structure to passively dissipate prior to the airflow impacting the downstream wind turbine.

By positioning a vortex generator in the interstitial region 36 of the wind turbine 10, the energy in the free stream airflow through this region may be used to generate large

-9structure vortices downstream of the rotors 26 of the wind turbine 10. It is believed that the vortices produced from a vortex generator positioned in the interstitial region 36 interact with the wakes/vortex systems of the rotors, essentially mixing out the wake region downstream of the rotors 26. More particularly, it is believed that the vortex generator creates vortices in the rotor wake region that act like fluid dynamic stirrers to enhance mixing in the wake region and entrain more high energy fluid from the surrounding free stream. This reduces the wake deficit downstream of the rotors 26 and allows the energy in the wake region to recover. In this way, the disruptions in the airflow as a result of the rotors 26 are minimized or reduced downstream of the wind turbine 10, thus providing a more uniform airflow for interacting with, for example, a downstream wind turbine. This may allow, for example, wind farms having one or more multi-rotor wind turbines to be spaced closer together and thus provide an increase in energy production per unit area of occupied space. Accordingly, in this embodiment, the useful result is the generation of vortices that diffuse or mix out the downstream wake region from the rotors more quickly so as to increase the collective efficiency and/or power production from a wind farm.

In yet another exemplary embodiment, the airflow modifier means 38 may include a hybrid diverter/vortex generator device positioned in the interstitial region 36 of the wind turbine 10. The hybrid device is configured to block at least a portion of the free stream airflow through the interstitial region 36 and accelerate the high energy airflow toward the swept area 34 of one or more of the rotors 26 of the energy generating units 12. As there may be a portion of the free stream airflow that still leaks through the interstitial region 36, the hybrid device may include a vortex generator that uses that leaked airflow to generate large structure vortices downstream of the rotors 26 of the wind turbine 10 so as to essentially mix out the downstream wake region caused by the rotors 26. Thus in this embodiment, the useful result is a combination of the two useful results described above.

Aspects of the present invention should not be limited to that described above. From a broad perspective, an aspect of the present invention is to locate a structure or device in the interstitial region 36 of the wind turbine 10 that utilizes the high energy airflow through that region to achieve a desired useful result. This may include an energy conversion process that converts the kinetic energy of the free stream airflow into useful work, such as turning a shaft of an electrical generator, or mixing out wake regions through aerodynamic interactions. In any event, aspects of the invention seek to use the energy in the leaked airflow for a useful result. The useful result may be to increase the efficiency and/or power production of an individual wind turbine, or to increase the collective efficiency and/or power production of a group or cluster of wind turbines, such as at a wind

- 10 farm. More particularly, the useful result may include modifying the flow around the rotors or in the wake region to improve the efficiency of the wind turbine or wind farm.

Figs. 1-6B illustrate embodiments of the present invention wherein the airflow modifier means 38 is configured as a flow diverter 40. As noted above, the flow diverter 40 is configured to block the free stream airflow W through the interstitial region 36 and redirect the high energy airflow toward the swept area 34 of one or more of the rotors 26 of the energy generating units 12. Additionally, the flow diverter 40 may also accelerate the diverted flow toward the rotors 26 of the energy generating units 12. In this regard, the flow diverter 40 includes a relatively large wind-engaging surface 42 configured to face into or toward the oncoming free stream airflow W. The size and shape of the windengaging surface 42 is configured to block the passage of the tree-stream airflow W through the interstitial region 36 and redirect at least a portion of the free stream airflow W toward the rotors 26. By way of example and without limitation, the wind-engaging surface 42 may be spherical in shape (e.g., being a portion of a sphere). Such a shape includes a central, forward most aspect that then extends radially outward from the central region. The invention is not limited to such a shape, however, and a wide variety of shapes are possible so long as the shape of the wind-engaging surface 42 facilitates the redirection of the airflow toward the rotors 26.

The wind-engaging surface 42 defines a frontal projected area A_d that occupies a relatively large percentage of the frontal projected area A, of the interstitial region 36. These areas are best illustrated in Figs. 1 and 2, when viewing the wind turbine 10 in a direction generally parallel to the direction of the free stream airflow W. By way of example and without limitation, the frontal projected area A_d of the wind-engaging surface 42 may be between about 60% and about 99.5% of the frontal projected area A of the interstitial region 36. In this way, a significant portion of the free stream airflow W may be redirected by the presence of the flow diverter 40. Depending on the design of the wind turbine, and as discussed below, it may be possible for the frontal projected area A_d of the flow diverter to be greater than the frontal projected area A, of the interstitial region 36.

In an exemplary embodiment, the flow diverter 40 may be movably mounted to the wind turbine 10. More particularly, the flow diverter 40 may be rotatably coupled to the tower 16 via one or more beams or support arms 44 extending away from the tower 16 and coupled to the wind-engaging surface 42. The support arms 44 may also be coupled to one or more collars 46 movably mounted on the tower 16 (Fig. 3). The flow diverter 40 may be configured to rotate about the tower axis 22 in coordination with the yawing of the rotors 26 of the wind turbine 10. For example, in one embodiment, the flow diverter 40 may be operatively coupled to at least one of the yaw mechanisms 24 associated with the wind

- 11 turbine 10. Alternatively, the flow diverter 40 may be provided with its own yaw mechanism that provides rotational movement of the flow diverter 40 about the tower axis 22 independent of yaw mechanisms 24. In any event, when the rotors 26 of the wind turbine 10 are yawed about the tower axis 22 as illustrated by arrow A, the flow diverter 40 may also be rotated about the tower axis 22 such that the flow diverter 40 has a substantially fixed relationship relative to the interstitial region 36 of the wind turbine 10. This aspect is illustrated in phantom in Fig. 3.

The flow diverter 40, and in particular the wind-engaging surface 42 may be variably positioned relative to the rotor plane defined by the rotors 26 of the plurality of energy generating units 12. By way of example, the flow diverter 40 may be positioned such that when viewed from above (e.g., see Fig. 3) the wind-engaging surface 42 is generally aligned with the rotor plane. In an alternative embodiment, however, the flow diverter 40 may be positioned such that the wind-engaging surface 42 extends in front of or to the rear of the rotor plane. In an exemplary embodiment, the flow diverter may be located even with or behind the rotor plane. In any event, given a fixed size of the wind-engaging surface 42, movement of the flow diverter 40 relative to the rotor plane may impact the portion of the free stream airflow W that is diverted toward the rotors 26, and the portion that passes through the interstitial region 36. For example, the wind-engaging surface 42 may be coupled to the support arm 44 in a manner that allows movement of the windengaging surface 42 toward or away from the rotor plane. This may be achieved, for example, via a pneumatic or hydraulic actuator. In an alternative embodiment, such as with a downwind wind turbine design, the flow diverter 40 may be positioned in front of the rotor plane. In this embodiment, it is possible for the flow diverter to have a frontal projected area A_d that is substantially the same or even greater than the frontal projected area A, of the interstitial region 36.

Fig. 4, in which like reference numerals refer to like features in Fig. 3, illustrates an alternative embodiment wherein the flow diverter 48 does not rotate about the tower axis 22, but instead has a fixed position relative to the yawing of the rotors 26. In this embodiment, for example, the flow diverter 48 may be fixedly secured to the wind turbine, such as to the tower 16. According to this embodiment, the flow diverter 48 is preferably symmetric about the tower axis 22. In this way, the shape of the wind-engaging surface 42 is the same independent of the yaw angle of the rotors 26. In other words, in a preferred embodiment, the free stream airflow W sees the same wind-engaging surface 42 independent of the yaw angle. By way of example and without limitation, the flow diverter 48 may be a spheroid or an ellipsoid. Other geometries may also be possible and within the scope of the present invention.

- 12 In one embodiment, the flow diverter may be a fixed structure such that the flow diverter is always in an operational position. In an exemplary embodiment, however, the flow diverters 40, 48 may be deployable between a first active position and a second passive position. In the first active position, the flow diverters 40, 48 are configured to be operational and thus divert and accelerate the free stream airflow W toward the rotors 26 of the wind turbine 10. In the second passive position, the flow diverters 40, 48 are configured to minimize the disruption of the free stream airflow W and allow the airflow to leak through the interstitial region 36 and past the wind turbine 10. In this regard, it should be realized that there may be times when wind turbine operators may not want the flow diverters to be operational. For example, during high wind conditions it may be desirable to minimize the flow diverters in order to reduce the mechanical loading on the wind turbine 10, such as on the tower 16. Furthermore, in the context of a wind farm, depending on the amount of wind, it may be desirable to have more free stream airflow pass through upstream wind turbines so as to more readily activate downstream wind turbines. In any event, in the passive position, the frontal projected area A_d of the flow diverters 40, 48 may be significantly less than frontal projected area A_d of the flow diverters 40, 48 when in the active position. By way of example and without limitation, the frontal projected area A_d of the flow diverters 40, 48 in the passive position may be less than about 10%, preferably less than about 5%, and more preferably less than about 2% of the frontal projected area A_d of the flow diverters 40, 48 when in the active position.

In this regard, Figs. 5A and 5B illustrate a flow diverter 50 similar to flow diverter 40 in an active position (Fig. 5A) and in a passive position (Fig. 5B). To achieve such a deployable configuration, the flow diverter 50 may have an umbrella-like construction including a central shaft, a number of hinged arms, and a number of spines that support a pliable outer cover that defines the wind-engaging surface 42. The hinged arms are coupled to a collar that is slidable along the central shaft. In a lower position of the collar, the flow diverter 50 is in the passive folded position. However, with movement of the collar outwardly along the shaft, such as by a motor and suitable controller, the hinged arms expand outwardly to locate the splines such that the outer cover has a spherical configuration. Similarly, Figs. 6A and 6B illustrate a flow diverter 52 similar to flow diverter 48 in an active position (Fig. 6A) and a passive position (Fig. 6B). To achieve such a deployable configuration, the flow diverter 52 may have a construction similar to that of a Chinese lantern, in which movement of two collars 54 away from each other causes the flow diverter to expand and movement of the two collars toward each other causes the flow diverter to collapse.

- 13 It should be recognized that in various alternative embodiments, a flow diverter may be moved between an active position and passive position in a different manner. By way of example and without limitation, the flow diverters may be inflatable/deflatable so as to be deployable between an active and passive position. In this regard, the flow diverters may include a pump for pressurizing an enclosed body such that when fully pressurized, the flow diverter is in the active position and has the desired size and shape. To move to a passive position, a release of the fluid (e.g., air) inside the body may take place. Alternatively, a vacuum pump may be provided to withdrawn the fluid from the enclosed body. Additionally, there may be further ways to move a flow diverter between its active position and passive position and the present invention is not limited to that described above.

As best illustrated in Fig. 3, when the flow diverter 40 is in its active position, the free stream airflow W is not permitted to simply pass through the interstitial region 36. Instead, at least a portion of the free stream airflow W is blocked causing a local high pressure region at the front of the flow diverter 40. As the free stream airflow W approaches the high pressure region, the airflow diverts radially outward away from the flow diverter 40 and is accelerated toward the rotors 26 that are outboard of the centralized flow diverter 40. The increase in net wind velocity increases the amount energy which may be extracted from the airflow by the wind turbine. This airflow then flows over the blades 30 of the rotors 26. In a particularly advantageous aspect of the present invention, the accelerated diverted airflow is configured to flow over the outer portion of the blades 30 adjacent a tip region of the blades. For example, the diverted airflow may be configured to flow over the outer 50% to about the outer 20% of the blades 30. It is appreciated in the industry that the efficiency of a wind turbine blade is relatively poor along the root region of the blade and is significantly better along the outer region of the blade toward the blade tip. Thus in one aspect, the flow diverter is configured to divert the high energy free stream airflow W toward the high efficiency region of the blades 30 on the rotors 26. This represents a high efficiency improvement to the operation of the wind turbine 10 as high energy airflow is diverted to the high efficiency section of the blades.

In another embodiment, and as illustrated in Figs. 7-9, the airflow modifier means 38 may be configured as a vortex generator 60. As noted above, the vortex generator 60 is configured to generate large structure vortices downstream of the rotors 26 of the wind turbine 10. It is believed that a vortex generator 60 positioned in the interstitial region 36 essentially mixes out the wake region downstream of the rotors 26 so that the energy in the wake region recovers so as to ensure that a downstream rotor may also extract power in an effective manner. Moreover, disruptions in the airflow as a result of the rotors 26 are

- 14 minimized and a more uniform airflow for interacting with a downstream structure is provided. In other words, the vortex generator 60 may take on a wide variety of forms sufficient to generate large scale vortices. By way of example, in an exemplary embodiment, the vortex generator 60 may include a wing assembly 62 having one or more wings 64, each wing 64 having an airfoil profile defining a leading edge configured to face into or toward the oncoming free stream airflow W and a trailing edge downstream thereof. The one or more wings 64 may be shaped such that when the high energy free stream airflow W flows over the surface of the wing 64, vortex shedding, schematically shown at 66, from the trailing edge or tip of the wings 64 occurs. It is these generated vortices that entrain the high energy airflow from the free stream and mix the air and/or interact with the rotor tip vortices to de-stabilize the helical wake region in order to dissipate that region more quickly. As a result, the wake deficit behind the rotors 26 is reduced more quickly and a more uniform flow field is reestablished in a shorter distance in the downstream direction. This may allow multi-rotor wind turbines to be positioned closer together in a wind farm arrangement, for example.

With further reference to Fig. 8, the vortex generator 60 includes a V-shaped wing assembly 68 having a first wing 70 extending toward a first generating unit 12a and on a first side of the tower 16 and a second wing 72 extending toward a second generating unit 12b and on a second side of the tower 16. Each wing 70, 72 includes an airfoil profile defining a leading edge, a trailing edge and a tip 74. Similar to the above, when the high energy free stream airflow W flows over the surface of the wings 70, 72, large vortices 66 are shed from the tips 74 of the wings 70, 72 that mix out the wake region caused by the rotors 26 of the wind turbine 10. It should be realized that the shape of the wing assembly 68 or wings 70, 72 may be varied to maximize the generation of vortices being shed from the wings. Thus, while trapezoidal wings are shown in Fig. 8, triangular wings (e.g., delta wings) may be used as well. Moreover, the length of the wings and/or other aspects of the wings may be varied in order to alter vortex strength and other vortex characteristics that benefit the dissipation of the wake region downstream of the rotors 26.

In one embodiment according to the invention shown in Fig. 9, the vortex generator 60 may be formed as an X-shaped wing assembly 76 having a first wing 78 extending toward a first generating unit 12a, a second wing 80 extending toward a second generating unit 12b, a third wing 82 extending toward a third generating unit 12c, and a fourth wing 84 extending toward a fourth generating unit 12d. Similar to the above, each wing 78, 80, 82, and 84 has an airfoil profile defining a leading edge, a trailing edge and a tip 74. When the high energy free stream airflow W flows over the surface of the wing assembly 76,

- 15 large vortices 66 are shed from the tips 74 of the wings 78, 80, 82, 84 that mix out the wake region caused by the rotors 26 of the wind turbine 10.

Similar to the flow diverter embodiments described above, the vortex generator 60 may be movably mounted to the wind turbine 10. More particularly, the vortex generator 60 may be rotatably coupled to the tower 16. In one embodiment, the vortex generator 60 may be configured to rotate about the tower axis 22 in coordination with the yawing of the rotors 26 of the wind turbine 10. For example, in one embodiment, the vortex generator 60 may be operatively coupled to at least one of the yaw mechanisms 24 associated with the wind turbine 10. Alternatively, the vortex generator 60 may be provided with its own yaw mechanism that provides rotational movement of the vortex generator 60 about the tower axis 22. In any event, when the rotors 26 of the wind turbine 10 are yawed about the tower axis 22, the vortex generator 60 may also be rotated about the tower axis 22 such that the vortex generator has a substantially fixed relationship relative to the interstitial region 36 of the wind turbine 10.

Again, while the vortex generator 60 may be a fixed structure (e.g., always operational), in an exemplary embodiment, the vortex generator 60 may be deployable between a first active position and a second passive position. In the first active position, the vortex generator 60 is configured to be operational and capable of using the energy in the free stream airflow W to generate large structure vortices downstream of the vortex generator 60. In the second passive position, the vortex generator 60 is configured to minimize the disruption of the free stream airflow W and allow the airflow to leak through the interstitial region 36 and past the wind turbine 10. It should be realized that there may be times when wind turbine operators may not want the vortex generator to be operational.

In this regard, in one embodiment the vortex generator 60 may be inflatable/deflatable so as to be deployable between an active and passive position. To this end, the vortex generator 60 may include a pump for pressurizing an enclosed body such that when fully pressurized, the vortex generator is in the active position. To move to a passive position, a release of the fluid (e.g., air) inside the body may take place. Alternatively, a vacuum pump may be provided to withdrawn the fluid from the enclosed body. Moreover, when the vortex generator is configured as a wing assembly, the elongate nature of the wings may allow the wing assembly to have a telescoping or folding arrangement for transitioning between the active and passive positions. For example, the wing assembly may include a central hub or region that houses the one or more extendable wings. In a passive position, the wings may be positioned in the central hub. When it is desired to move to the active position, the wings may be activated, via a suitable actuator for example, to telescopingly extend radially outward of the central hub. Alternatively, the

- 16 wings may be unfolded so as to be deployed in the active position. Additionally, there may be other ways to move the vortex generator between its active position and passive position and the present invention is not limited to that described above.

In still another embodiment, as best illustrated in Fig. 10, the airflow modifier means 38 may be a hybrid device 90 providing both flow diversion and vortex generation. In this regard, the hybrid device 90 is configured to convert a portion of the energy in the free stream airflow W to electrical energy by diverting and accelerating a portion of the airflow W over the blades 30 of the rotors 26, and is further configured to use a portion of the energy in the free stream airflow W to generate vortices that mix out the wake region downstream of the rotors 26. In this regard, the hybrid device 90 includes a central region 92 that defines a relatively large wind-engaging surface 94 configured to face into or toward the oncoming free stream airflow W. The size and shape of the wind-engaging surface 94 is configured to block the passage of the tree-stream airflow W through the interstitial region 36 and accelerate at least a portion of that flow toward the rotors 26. By way of example and without limitation, the wind-engaging surface 94 may be spherical in shape. However, other shapes are also possible and within the scope of the present invention.

The wind-engaging surface 94 defines a frontal projected area A_d that occupies a relatively large percentage of the frontal projected area A, of the interstitial region 36. By way of example and without limitation, the frontal projected area A_d of the wind-engaging surface 94 may be between about 60% and about 95% of the frontal projected area A, of the interstitial region 36. The amount of projected area occupied by the wind-engaging surface 94 of the hybrid device 90 will at least in part dictate how much of the free stream airflow W is diverted toward the rotors 26 and how much passes through so to interact with a vortex generator, such as a wing assembly having one or more wings, associated with the hybrid device 90. Accordingly, the size of the wind-engaging surface 94 may be varied in order to strike a desired balance between flow diversion/acceleration and vortex generation with the purpose of wake mixing and reduced losses. The movement of the wind-engaging surface 94 toward and away from the rotor plane may also be used to strike a desired balance between flow diversion/acceleration and vortex generation with the purpose of wake mixing and reduced losses.

Along a periphery of the central region 92 is one or more wings 96 extending outwardly from the central region. Each wing 96 has an airfoil profile defining a leading edge, a trailing edge, and a tip 98. The wings 96 may be shaped such that when the high energy free stream airflow W flows over the surface of the wings 96, vortex shedding, schematically shown at 66, from the trailing edge or tips 98 of the wings 96 occurs. It is

- 17 believed that these vortices mix the air and/or interact with the rotor tip vortices in the wake region to entrain more kinetic energy from the free stream flow to ensure that the flow behind the wind turbine recovers its energy more quickly. As a result, the wake deficit behind the rotors 26 is reduced more quickly and a more uniform flow field is reestablished in a shorter distance in the downstream direction.

Similar to the embodiments described above, the hybrid device 90 may be movably mounted to the wind turbine 10. More particularly, the hybrid device 90 may be rotatably coupled to the tower 16. In one embodiment, the hybrid device 90 may be configured to rotate about the tower axis 22 in coordination with the yawing of the rotors 26 of the wind turbine 10. For example, in one embodiment, the hybrid device 90 may be operatively coupled to at least one of the yaw mechanisms 24 associated with the wind turbine 10. Alternatively, the hybrid device 90 may be provided with its own yaw mechanism that provides rotational movement of the hybrid device 90 about the tower axis 22. In any event, when the rotors 26 of the wind turbine 10 are yawed about the tower axis 22, the hybrid device 90 may also be rotated about the tower axis 22 such that the hybrid device 90 has a substantially fixed relationship relative to the interstitial region 36 of the wind turbine 10.

In one embodiment, the hybrid device may be a fixed structure. In an exemplary embodiment, however, the hybrid device 90 may be deployable between a first active position and a second passive position. In the first active position, the hybrid device 90 is configured to be operational and capable of converting a portion of the energy in the free stream airflow W to electrical energy by diverting and accelerating a portion of the airflow W over the blades 30 of the rotors 26, and is further configured to use a portion of the energy in the free stream airflow W to generate vortices. In the second passive position, the hybrid device 90 is configured to minimize the disruption of the free stream airflow W and allow the airflow to leak through the interstitial region 36 and past the wind turbine 10. In one embodiment the hybrid device 90 may be inflatable/deflatable so as to be deployable between an active and passive position. In this regard, the hybrid device 90 may include a pump for pressurizing an enclosed body such that when fully pressurized, the hybrid device is in the active position. To move to a passive position, a release of the fluid (e.g., air) inside the body may take place. Alternatively, a vacuum pump may be provided to withdrawn the fluid from the enclosed body. There may be additional ways to move the hybrid device 90 between its active position and passive position and the present invention is not limited to that described above.

In an alternative embodiment, the hybrid device 90 may be configured such that the central region 92 (i.e., the flow diversion portion of the hybrid device) is deployable

- 18 between its active and passive positions independently of the deployment of the wings 96 or other vortex generating devices between their active and passive positions. In this way, for example, the hybrid device 90 may be configured to selectively operate in a flow diversion mode or a dual mode of flow diversion and vortex generation. In regard to the latter, to go from the flow diversion mode to the dual mode, the wings 96 would be activated (e.g., such as by inflation or other means) so as to place the wings in their active position.

As has been discussed above, the use of an airflow modifier means may provide certain benefits to the operation of an individual wind turbine. For example, an airflow diverter may provide an increase in efficiency and/or power production to a wind turbine on which the airflow diverter is installed. The use of an airflow modifier means may also provide certain benefits to the operation of a wind farm. In this regard, it should be realized that the operating strategy to increase the efficiency and/or power production from the collective wind turbines of a wind farm may be different from that of an individual wind turbine. There may be times, for example, when blocking the free stream airflow through the interstitial regions may be beneficial or detrimental to the collective efficiency and/or power production of the wind farm. Similarly, there may be times when generating vortices from the free stream airflow may be beneficial or detrimental to the collective efficiency and/or power production of the wind farm. Moreover, there may be times when it is desired to have minimal disruption of the free stream airflow through the interstitial region (e.g., no impact from an airflow modifier means).

Thus, in accordance with an embodiment of the invention, operators of wind farms may implement a control strategy for operation of the wind farm that uses a plurality of airflow modifier means to increase the efficiency and/or power production of the wind farm as a whole. By way of example, certain of the airflow modifier means in the wind farm may be configured as airflow diverters, certain of the airflow modifier means may be configured as vortex generators, and/or certain of the airflow modifier means may be configured as hybrid devices. By way of example and without limitation, upstream wind turbines of a wind farm may have airflow modifier means configured as vortex generators, mid-section wind turbines of the wind farm may have airflow modifier means configured as hybrid devices, and downwind wind turbines of the wind farm may have airflow modifier means configured as airflow diverters. It should be recognized, however, that other control strategies may also be implemented so as increase the efficiency and/or power production of the wind farm.

Furthermore, in accordance with embodiment of the invention, wind farm operators will also have the option of moving the airflow modifier means between their active and

- 19 passive positions. Accordingly, in instances when the control strategy calls from minimal disruption of the free stream airflow through the interstitial region, the airflow modifier means may be placed in their passive positions. In view of the flexibility afforded by aspects of the present invention as it pertains to modifying the free stream airflow through the interstitial region, wind farm operators will be able to implement a whole host of control strategies that it is believed with improve the overall operation of the wind farm.

While the present invention has been illustrated by the description of various embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail.

Thus, the various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.

Claims

1. A wind turbine, comprising: a support structure;

a plurality of energy generating units coupled to the support structure, each energy generating unit including a rotor having at least one wind turbine blade, wherein the arrangement of the plurality of energy generating units on the support structure defines an interstitial region; and an airflow modifier means coupled to the support structure and positioned in the interstitial region, wherein the airflow modifier means is configured to facilitate the use of energy in a free stream airflow passing through the interstitial region so as to produce a useful result in the operation of the wind turbine or wind farm.

2. The wind turbine according to claim 1, wherein the airflow modifier means is movably coupled to the support structure.

3. The wind turbine according to claim 1 or 2, wherein the airflow modifier means is rotatable about the support structure.

4. The wind turbine according to any of the preceding claims, wherein the airflow modifier means is operatively coupled to a yaw mechanism configured to yaw at least one of the rotors of the plurality of energy generating units.

5. The wind turbine according to claim 1, wherein the airflow modifier means is nonrotatably secured to the support structure.

6. The wind turbine according to claim 1 or 5, wherein the airflow modifier means is symmetric about a rotational axis such that a front profile of the airflow modifier means is substantially the same independent of the yaw angle of the rotors of the plurality of energy generating units.

7. The wind turbine according to any of the preceding claims, wherein the airflow modifier means is deployable between an active position wherein the airflow modifier means is operational to produce the useful result in the wind turbine or wind farm, and a passive position wherein the airflow modifier means is configured to minimize the disruption of the free stream airflow through the interstitial region.

- 21

8. The wind turbine according to claim 7, wherein the airflow modifier means is inflatable and deflatable so as to transition between the active and passive positions.

9. The wind turbine according to claim 7, wherein the airflow modifier means is expandable and collapsible so as transition between the active and passive positions.

10. The wind turbine according to any of the preceding claims, wherein the airflow modifier means includes an airflow diverter and the useful result comprises diverting at least a portion of the free stream airflow toward the rotors of the plurality of energy generating units.

11. The wind turbine according to claims 1-4 and 7-9, wherein the airflow modifier means includes a vortex generator and the useful result comprises generating vortices for mixing out a wake region downstream of the rotors of the plurality of energy generating units.

12. The wind turbine according to claim 11, wherein the vortex generator includes a wing assembly including one or more wings, wherein airflow over the one or more wings generates vortices.

13. The wind turbine according to claim 12, wherein the wind turbine includes four energy generating units and the wing assembly includes four wings.

14. The wind turbine according to claims 1-4 and 7-9, wherein the airflow modifier means includes a hybrid device having a first portion configured as an airflow diverter with the useful result of diverting at least a portion of the free stream airflow toward the rotors of the plurality of energy generating units, and a second portion configured as a vortex generator with the useful result of generating vortices for mixing out the wake region downstream of the rotors of the plurality of energy generating units.

15. The wind turbine according to claim 14, wherein the hybrid device includes a central region configured to operate as a flow diverter and a vortex generator at a periphery of the central region configured to generate vortices for mixing out the wake region downstream of the rotors.

16. The wind turbine according to claim 15, wherein the vortex generator at the periphery of the central region includes a wing assembly including one or more wings.

- 22

17. The wind turbine according to claim 16, when dependent from any of claims 7-9, wherein deployment of the flow diverter between its active and passive positions is independent of the deployment of the wing assembly between its active and passive positions.

18. A method of improving the operation of a wind turbine or wind farm, comprising: providing a multi-rotor wind turbine having a plurality of energy generating units arranged to define an interstitial region; and positioning an airflow modifier means in the interstitial region so that the interaction between a free stream airflow and the airflow modifier means produces a useful result in the operation of the wind turbine or wind farm.

19. The method according to claim 18, further comprising rotating the airflow modifier means about a rotational axis.

20. The method according to claim 18, wherein rotation of the airflow modifier means is in registration with yawing of the rotors of the plurality of energy generating units.

21. The method according to any of claims 18-20, further comprising moving the airflow modifier means between an active position wherein the airflow modifier means is operational to produce the useful result in the wind turbine or wind farm, and a passive position wherein the airflow modifier means is configured to minimize the disruption of the free stream airflow through the interstitial region.

22. The method according to claim 21, wherein movement between the active and passive positions further comprises inflating and deflating the airflow modifier means.

23. The method according to claim 21, wherein movement between the active and passive positions further comprises expanding and collapsing the airflow modifier means.

24. The method according to any of claims 18-23, wherein the airflow modifier means includes an airflow diverter and the useful result comprises diverting at least a portion of the free stream airflow toward the rotors of the plurality of energy generating units.

25. The method according to claim 24, further comprising diverting the at least a portion of the free stream airflow toward a high-efficiency region of the blades of the rotors of the plurality of energy generating units.

-2326. The method according to any of claims 18-23, wherein the airflow modifier means includes a vortex generator and the useful result comprises generating vortices to mix out the wake region downstream of the rotors of the plurality of energy generating units.

27. The method according to claim 26, wherein generating vortices further comprises providing a wing assembly having one or more wings, wherein airflow over the wing assembly generates the vortices that mix out the wake region downstream of the rotors of the plurality of energy generating units.

28. The method according to any of claims 18-23, wherein the airflow modifier means includes a hybrid device and the useful result comprises diverting a portion of the free stream airflow toward the rotors of the plurality of energy generating units, and using the energy in another portion of the free stream airflow to generate vortices downstream of the rotors of the plurality of energy generating units.

29. A wind farm comprising at least one wind turbine according to any of claims 1 -17.

30. The wind farm according to claim 29, wherein at least one wind turbine has an airflow modifier means that is different than an airflow modifier means on at least one other wind turbine.

31. The wind farm according to claim 30, wherein the airflow modifier means on the at least one wind turbine and the at least one other wind turbine is selected from an airflow diverter, a vortex generator, and a hybrid device.

32. A method of operating a wind farm, comprising:

providing at least one wind turbine with an airflow modifier means positioned within an interstitial region of the wind turbine; and selectively moving the airflow modifier means between an active position wherein the airflow modifier means is operational to modify a free stream airflow through the interstitial region, and a passive position wherein the airflow modifier means is configured to minimize the disruption of the free stream airflow through the interstitial region.

33. A method of operating a wind farm, comprising:

selecting at least one of the wind turbines in the wind farm to have an airflow modifier means of a first type;

selecting at least another one of the wind turbines in the wind farm to have an airflow modifier means of a second type; and

- 24 operating the wind farm with the first and second types of airflow modifier means.

34. The method according to claim 33, wherein the first and second types of airflow modifier means may be selected from an airflow diverter, a vortex generator, and a hybrid

5 device.

35. The method according to claim 33 or 34, further comprising deploying at least one of the airflow modifier means of the first or second type between an active position wherein the airflow modifier means is operational to modify a free stream airflow, and a

10 passive position wherein the airflow modifier means is configured to minimize the disruption of the free stream airflow.

-2526

Intellectual

Property

Office

Application No: GB1622028.7 Examiner: Adrian Mooney