WO2018177493A1

WO2018177493A1 - Wind turbine including wake flow reducing structures and method of using same

Info

Publication number: WO2018177493A1
Application number: PCT/DK2018/050060
Authority: WO
Inventors: Anurag Gupta
Original assignee: Vestas Wind Systems A/S
Priority date: 2017-03-28
Filing date: 2018-03-28
Publication date: 2018-10-04

Abstract

A wind turbine (30) includes a support structure (12) and at least one energy generating assembly (32) having central structures along an axis of rotation such as a rotor hub (40) and a nacelle (46), which may enclose a generator (44) for transferring rotations of the hub (40) and wind turbine blades (42) extending from the hub (40) and caused by airflow into electrical energy. One of the central structures includes an aft end (50) defining a corrugated profile (34) with a plurality of lobes (36). Airflow over these lobes (36) generates powerful flow vortices which help mix out the wake flows downstream from the wind turbine (30). A method of using the lobes (36) for reducing a wake region downstream of the wind turbine (30) is also disclosed.

Description

WIND TURBINE INCLUDING WAKE FLOW REDUCING STRUCTURES AND METHOD OF USING SAME

Technical Field

The present invention relates generally to wind turbines, and more particularly, to a wind turbine having one or more energy generating assemblies with components added to help mix wake flows downstream from the wind turbine and that are caused by the airflow past the wind turbine.

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 horizontal-axis wind turbine (HAWT). As illustrated in Fig. 1 , an exemplary single rotor HAWT 10 includes a tower 12 defining a support structure, a nacelle 14 located at the apex of the tower 12, and a single rotor 16 having a central rotor hub 18 and one or more blades 20 (e.g., three blades) mounted on the hub 18 and extending radially therefrom. The rotor 16 is supported by the nacelle 14 and positioned at the front of the nacelle 14 so that the rotor 16 faces into the wind upstream of its supporting tower 12. The rotor 16 may be coupled either directly or indirectly with a generator (not shown) housed inside the nacelle 14 and configured to convert the mechanical energy of the rotor 16 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, such as in a linear array that is generally perpendicular to a prevalent or expected wind direction. In this way, wind passing through a particular wind turbine does not significantly disrupt the airflow passing by its adjacent wind turbine. In addition or alternatively, large groups of wind turbines may be arranged in a multi-dimensional array (e.g., a rectangular array) collectively defining what is known as a wind "farm." In such an array or farm of multiple wind turbines, 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 potentially impact the airflow that passes through the downstream wind turbine.

In this regard, it is generally well known that when air flows over a body, a wake region is formed downstream of the body. The wake region is defined by wake flows, which are discontinuous flows of air, typically with high turbulence and velocity fluctuations/deficits. The velocity field in the wake region is changed compared to the free stream velocity, which leads to increases in turbulence intensity. When a wind turbine blade passes through the wake region, the blade will experience different loads as compared to loads experienced when the blade passes through a free stream airflow. Since the velocity field in the wake region is different, the angle of attack of the blade will change. However, the different loading on the blade can introduce aeromechanical issues, instabilities, noise and other undesirable effects. Furthermore, the energy that may be extracted from airflow in a wake region tends to be lower than the energy that may be extracted from airflow in a free stream velocity setting. Thus, passing wind turbine blades through relatively moderate to strong wake regions and wake flows is generally considered undesirable.

Accordingly, the spacing between an upstream wind turbine and a downstream wind turbine of a wind farm may be selected so as to minimize or reduce the impact of wake flows produced by operation of the upstream wind turbine on the downstream airflow that passes through the downstream wind turbine. While there may be several factors in determining the appropriate spacing, one may generally consider the effects of the upstream rotor and upstream support structure on 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. Such spacing is large and limits how many wind turbines can be placed in the wind farm, but it assures that no adverse wake flow effects are applied to downstream wind turbines and their components.

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 the wind turbine blades and the overall size of the wind turbines 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. It should be appreciated that there are different types of multi-rotor wind turbines. For example, one type of multi-rotor wind turbine is a coplanar multi-rotor wind turbine. As illustrated in Fig. 2, in which like reference numbers refer to similar features shown in Fig. 1 , in an exemplary coplanar wind turbine 22, multiple rotors 16 are arranged such that the individual wind turbine blades 20 on each rotor 16 generally lie within the same plane. The support structure includes horizontal support arms 24 connected to the tower 12 in such embodiments to space the coplanar rotors 16 apart sufficiently for simultaneous operation. Another type of multi-rotor wind turbine may include three- dimensional configurations of rotors 16 instead of coplanar, but the construction thereof is highly similar. Each type increases the sweep area of the corresponding wind turbine blades 20, which leads to the development of wake flows over an even larger area.

As such, even though there are generally negligible intra wind turbine effects, the wake region caused by airflow over the coplanar wind turbine may be significant to wind turbine arrangements with upstream and downstream relationships, such as in a wind farm. In this regard, an upstream coplanar wind turbine and a downstream wind turbine (coplanar or otherwise) may be spaced to allow the wake region generated by the upstream rotors and the upstream support structure to passively dissipate prior to the airflow impacting the downstream wind turbine. The provision of multiple rotors on such wind turbines leads to multiple wake flows and wake regions which need to mix together before encountering a downstream wind turbine, at least if the adverse effects of wake flows are to be avoided.

Another particular conventional wind turbine design is shown in U.S. Patent No. 8,308,437, in which the rotor hub is provided with additional aerodynamic fins between the elongated blades. These aerodynamic fins have a shape configured to capture the wind flowing past the wind turbine and thereby impart additional torque input to the electrical-generation portion of the wind turbine. Such designs and additional components improve the lift and torque generation, but additional wake flows are created downstream from the wind turbine as well, exacerbating the problems of the conventional designs. In view of the above, wind turbine manufacturers continually seek improvements that minimize or reduce the impact of the upstream rotor/support structure on the downstream airflow that passes through a downstream rotor, whether that be on a different wind turbine (e.g., such as in a wind farm) or the same wind turbine (such as with three dimensional wind turbines). More particularly, there is a need to minimize or reduce the wake region, or more precisely a need to mitigate the velocity deficits and turbulence increases in the wake region, caused by airflow over an upstream wind turbine and its rotor. This may allow the spacing between adjacent wind turbines in a wind farm to be decreased, thus allowing more wind turbines to be located within a smaller space, while improving the overall energy extraction thereof. In this regard, for three dimensional wind turbines, reducing wake flows may reduce the cost of the load-carrying structures, increase the energy capture efficiencies, and reduce maintenance and repair costs associated with downstream wind turbines and rotors (e.g., gearbox repair costs caused by wake turbulence). It is desired to further advance the efforts and options for such wake flow reduction.

Summary A wind turbine and method are described herein to mitigate the effects of wake flows by encouraging faster mixing of the airflow downstream from the wind turbine, to thereby achieve the objectives set forth above including more efficient placement of wind turbines on a wind farm and better energy extraction efficiency for the collective wind turbines on the farm. To this end, a wind turbine in accordance with one embodiment includes a support structure having a tower, and at least one energy generating assembly supported by the support structure. The energy generating assembly further includes central structures such as a rotor hub and a nacelle, each of which is located along an axis of rotation defined by the rotor hub. The energy generating assembly also includes a generator located at the nacelle for converting rotation of the rotor hub into electrical energy, and at least one wind turbine blade coupled to and extending from the rotor hub into an airflow passing the wind turbine. The wind turbine blade(s) rotate with the rotor hub in the airflow and thereby generate wake flows downstream in a wind flow direction from the wind turbine. At least one of the central structures defines an aft end facing downstream in the wind flow direction, with the aft end defining a corrugated profile having a plurality of lobes located along a periphery of the aft end. The corrugated profile advantageously produces flow vortices which enhance mixing together of different velocity and turbulent flows generated by the wind turbine such that these so-called wake flows mix out in a shorter length than would be the case in the absence of the corrugated profile. In one aspect, the nacelle is the element including the aft end with the corrugated profile. The aft end of the nacelle includes a periphery defined by at least one side edge, with at least one of the lobes being located on each of the side edge(s). To further enhance the mixing of flows, the wind turbine can further include at least one exhaust air port at the aft end of the nacelle. The exhaust air port is in communication with a cooling system included at the nacelle and is thereby configured to inject exhaust air (used to carry heat energy from a heat exchanger, for example) from the cooling system into the airflow proximate the plurality of lobes.

In another embodiment, the plurality of lobes of the corrugated profile may also be configured to operate as a heat exchanger coupled to the cooling system in the nacelle, e.g., for the purposes of removing heat from components of the energy generating assembly. To this end, the plurality of lobes may define cooling fins of the heat exchanger, the cooling fins configured to transfer heat energy to the airflow passing the wind turbine. In some embodiments, the lobes include heat exchange passages configured to pass a fluid from the cooling system therethrough to enable the heat exchange between the fluid and the airflow.

In yet another aspect, the lobes of the corrugated profile define cross-sectional shapes adapted to produce multiple different types of flow vortices when the airflow moves past the corrugated profile. For example, the lobes can produce horseshoe vortices, Kelvin- Helmholtz vortices, and streamwise vortices. The plurality of lobes defines a uniform shape and size in some embodiments of the wind turbine. Moreover, the corrugated profile is typically defined by at least 5 lobes making up the plurality of lobes. Each of the plurality of lobes extends inwardly and outwardly from the periphery of the central structure at the aft end when viewed in cross section transverse to the axis of rotation, which allows for these different flow vortices to be produced in the airflow moving past the wind turbine. In another aspect, the rotor hub is the element including the aft end with the corrugated profile. In such embodiments, the aft end of the rotor hub may be larger in cross section transverse to the axis of rotation than a cross section of the nacelle. For example, the rotor hub may be enlarged in size. Each of the plurality of lobes of the corrugated profile on the rotor hub defines a non-lifting cross section (e.g., such as symmetrical) when viewed transverse to the axis of rotation. As a result, each of the plurality of lobes on the rotor hub is sized and shaped to produce tip vortices in the airflow passing the wind turbine, while not producing substantial lift or torque that would assist with the normal wind turbine function of energy extraction from the airflow. In this regard, the intended function and design of the corrugated profile is to produce better mixing of wake flows downstream of the wind turbine without impacting, in a positive or negative manner, the primary wind turbine function of extracting energy from airflow.

The wind turbine may be provided as a single-axis wind turbine with only one energy generating assembly on the support structure. However, in still further embodiments, the wind turbine is provided as a multi-rotor wind turbine with a plurality of energy generating assemblies mounted on the support structure. Each of the plurality of energy generating assemblies includes at least one central structure having an aft end defining a corrugated profile with a plurality of lobes. Such multi-rotor designs typically have smaller scale layers and wake flows, which makes the flow vortices developed by the corrugated profiles even more effective at reducing wake flows in a wind farm.

In another embodiment in accordance with the invention disclosed herein, a method of reducing wake flows downstream from a wind turbine is provided. The wind turbine again includes at least one energy generating assembly having central structures and at least one wind turbine blade as set forth in detail above. The method includes providing a corrugated profile with a plurality of lobes at an aft end of at least one of the central structures, the aft end facing downstream in the wind flow direction. The method also includes operating the wind turbine in the airflow such that the corrugated profile produces flow vortices in the airflow to mix the wake flows downstream from the wind turbine. Further aspects of the method are consistent with the possible variations of the wind turbine described above, including but not limited to, providing the corrugated profile on the nacelle or providing the corrugated profile on the rotor hub.

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 perspective view of an exemplary single-rotor horizontal axis wind turbine that may utilize the corrugated profile of the invention;

Fig. 2 is a front plan view of an exemplary coplanar multi-rotor wind turbine that may also utilize the corrugated profile of the invention;

Fig. 3 is a side view of an energy generating assembly of a wind turbine in accordance with one embodiment of the invention, the energy generating assembly having a corrugated profile on an aft end of the nacelle, which is generally cylindrical in shape; Fig. 4 is a rear perspective view of the energy generating assembly of Fig. 3, showing additional details of the corrugated profile;

Fig. 5 is a rear perspective view of an energy generating assembly in accordance with another embodiment of the invention, the nacelle of this embodiment being similar but the corrugated profile including more lobes than the embodiment shown in Figs. 3 and 4;

Fig. 6 is a side view of an energy generating assembly of a wind turbine in accordance with a further embodiment of the invention, the energy generating assembly having a corrugated profile on an aft end of the nacelle, which is generally rectangular in shape;

Fig. 7 is a rear perspective view of the energy generating assembly of Fig. 6, showing additional details of the corrugated profile;

Fig. 8 is a detailed view of a portion of the corrugated profile used with the embodiment of the wind turbine shown in Figs. 6 and 7, along with flow arrows indicating different types of flow vortices produced by airflow moving past the lobes;

Fig. 9 is a cross-sectional elevation view, taken along line 9-9 in Fig. 8, to reveal additional internal features of the corrugated profile in this embodiment;

Fig. 10 is a side view of an energy generating assembly of a wind turbine in accordance with yet another embodiment of the invention, the energy generating assembly having a corrugated profile on an aft end of the rotor hub;

Fig. 1 1 is a rear perspective view of the rotor hub of Fig. 10, showing additional details of the corrugated profile;

Fig. 12 is a front perspective view of an energy generating assembly of a wind turbine in a further embodiment of the invention, the energy generating assembly including a rotor hub with wake mixing lobes added to the exterior of the rotor hub, and also showing flow arrows indicating production of wake flows and flow vortices which mix together during operation of the wind turbine;

Fig. 13 is a front elevation view of the energy generating assembly of Fig. 12, showing additional details of the wake mixing lobes; and

Fig. 14 is a schematic airflow diagram showing a wake region of wake flows that need to mix out before the airflow encounters another downstream wind turbine, with a comparison of a conventional wind turbine design and the embodiment shown in Figs. 12 and 13 (similar to the beneficial effects of embodiments shown in prior Figures).

Detailed Description

With reference to Figs. 3 through 14, several embodiments of a wind turbine are shown for reducing wake flows downstream from the wind turbine. In this regard, corrugated profiles or lobes are provided on one or more of the structures of the wind turbine, which result in flow vortices being generated when airflow moves past the wind turbine. The flow vortices act to promote rapid mixing of wake flows and all discontinuous air flows following the separation and turbulence added by the operation of the wind turbine and its blades. Consequently, the length of a wake region defined by these wake flows is reduced in size, allowing for downstream wind turbines to be placed much closer to upstream wind turbines than in conventional wind farm designs. Furthermore, the likelihood of inefficient energy extraction or wind turbine damage caused by such wake flows is reduced when using these wind turbine designs. Turning with specific reference to Figs. 3 and 4, a first embodiment of a wind turbine 30 in accordance with the invention is shown. More particularly, the energy generating assembly 32 of the wind turbine is shown in detail to focus on the added features for reducing wake flows, as the support structure in the form of a tower 12 is the same as described above for Figs. 1 and 2. It will be appreciated that the energy generating assembly 32 may be the only one provided in a single-rotor wind turbine arrangement, or alternatively, one of a plurality of such assemblies in a multi-rotor wind turbine arrangement, such multiple rotors being coplanar or in a three dimensional arrangement, depending on the particular type of wind turbine design. Likewise, it will be understood that the support structure for the energy generating assembly 32 may include additional features such as the horizontal support arms 24 described with reference to Fig. 2, but not shown in the drawings for the following embodiments. For example, the wind turbine 30 will include one or more yaw mechanisms for turning the rotor(s) into the direction of the wind flow, but these elements are not shows because they are largely unrelated to the aspects of the invention described in further detail throughout this document. As described in further detail below, at least one of the components in the energy generating assembly 32 includes a corrugated profile 34 defining a plurality of lobes 36 which the airflow must pass when flowing through and around the wind turbine 30. The corrugated profile 34 advantageously enhances the mixing out of wake flows downstream from the wind turbine 30 by generating flow vortices in the airflow. As used herein, an "energy generating assembly" 32 means the part of the wind turbine 30 which actually transforms the kinetic energy of the wind into electrical energy. In accordance with this meaning, the energy generating assembly 32 of this and other embodiments includes a rotor 38 having a central rotor hub 40 and one or more wind turbine blades 42 (e.g., three blades) mounted to the hub 40 and extending radially therefrom, and a generator 44 (shown schematically in Fig. 3) located within a nacelle 46. In addition, the energy generating assembly 32 typically includes a drive train (not shown), including a gear arrangement, interconnecting the rotor 38 and the generator 44. The generator 44 and a substantial portion of the drive train may be positioned inside of the nacelle 46. Likewise, one or more cooling systems 48 (shown schematically in Fig. 3) are also typically provided with other control equipment in the nacelle 46, the cooling system(s) 48 capable of removing heat energy generated by components of the energy generating assembly 32 during operation of the wind turbine 30. Additional components may be included in each energy generating assembly as well understood in the wind turbine field, but for the purposes of this invention, these primary elements described above are the most pertinent ones for discussion.

The wind turbine blades 42 are sized and shaped to capture the kinetic energy of the airflow passing the wind turbine 30 and transform that energy into rotation of the hub 40. As shown in Fig. 3, the hub 40 and the blades 42 therefore rotate about an axis of rotation A_R defined through a center of the hub 40. The rapid movement of the blades 42 during this rotation causes velocity deficits due to energy extraction and turbulence in the air flow passing the wind turbine 30, these effects being summarized as one part of the wake flows generated downstream in the wind flow direction from the wind turbine 30, within the context of this disclosure. Wake flows are also generated by airflow over largely stationary wind turbine components such as the tower 12 or other support structures and the nacelle 46, as such flow is disturbed by having to move around these structures (e.g., the generation of turbulence, deficits, and/or flow separation caused by such movements).

The wind turbine 30 of the embodiment shown in Figs. 3 and 4 includes a plurality of central structures located along this axis of rotation A_R defined through a center of the hub 40. More specifically, the central structures include at least the rotor hub 40 and the nacelle 46. Additional structures which may be located along the axis of rotation A_R can also be included in other embodiments. The corrugated profile 34 is located along one of these central structures in this and other embodiments of the presently-described invention. Airflow over these central structures causes turbulence and flow inconsistencies, just like the airflow over the rotating wind turbine blades 42 and the tower 12 which extend outwardly away from the central structures. However, the generation of wake mixing flow vortices (caused by airflow over the corrugated profile 34) in a centralized location at the central structures is advantageous because such vortices are placed in the middle of the wake flows generated downstream from the components of the wind turbine 30. As a result, the flow vortices have maximized effect within a central portion of the wake flows, thereby rapidly mixing those wake flows out before the airflow encounters a downstream wind turbine.

The corrugated profile 34 of this embodiment is shown in perspective in Fig. 4 and in side elevation view in Fig. 3. In this regard, these Figures illustrate that the corrugated profile 34 is provided at an aft end 50 of the nacelle 46, which is one of the central structures as defined above. The nacelle 46 defines a generally cylindrical shape in this embodiment, which defines an outer periphery 52 proximate the aft end 50. The lobes 36 defining the corrugated profile 34 project radially, e.g., relative to the axis of rotation A_R, inwardly and outwardly from the periphery 52 of the nacelle 46, such as when viewed in cross section transverse to the axis of rotation A_R (not shown). Consequently, the airflow passing over the nacelle 46 is forced to move in a manner which produces rotational flow vortices of different types, as set forth in further detail below in the description of a flow diagram at Fig. 8. The aft end 50 of the nacelle 46 (and the periphery 52 proximate this aft end 50) is larger in transverse cross sectional size than a transverse cross section of the rotor hub 40. Therefore, the lobes 36 and corrugated profile 34 extend outwardly beyond the outermost periphery or extent of the central structures, so as to maximize air flow and vortex generation in airflow over the central structures such as the nacelle 46. To this end, the lobes 36 project outwardly into the surrounding airflow to enable the generation of multiple flow vortices in the airflow.

In view of the cylindrical cross sectional profile of the nacelle 46 in this embodiment of Figs. 3 and 4, the periphery 52 defines a single, circular side edge 54. The lobes 36 are provided along an entirety of this single side edge 54. More specifically, a total of six lobes 36 are provided to define the corrugated profile 34 in this embodiment of the wind turbine 30. As set forth in further detail below, other embodiments may include differing numbers of lobes 36, such as more than six. Each of the lobes 36 may generate a separate set of different flow vortices to help mix the wake flows downstream in the wind flow direction from the wind turbine 30. The flow vortices generated may vary depending on the particular shape, size, and profile of the lobes 36 in the corrugated profile 34. In the embodiment of Figs. 3 and 4, each of the lobes 36 in the corrugated profile 34 defines a uniform shape and size, thereby to produce similar flow vortices for wake mixing along an entirety of the periphery 52 and aft end 50 of the nacelle 46. As shown in Fig. 4, each of the lobes 36 of the corrugated profile 34 is defined by a pair of lobe walls 56 connected at a radially outward end by a curved terminal wall 58 to define the U-shape which is uniform with the other lobes 36. The lobe walls 56 are separately connected to adjacent lobes 36 at the radially inward end with additional curved walls 60. As set forth above, the curved terminal wall 58 may be located radially outside the periphery 52 of the reminder of the nacelle 46, while at least a portion of the additional curved walls 60 connecting adjacent lobes 36 is located generally radially inside the periphery 52 of the remainder of the nacelle 46. The size of the lobes 36, and particularly at the lobe walls 56 and the curved terminal wall 58, increases from an intersection with the periphery 52 to a distal end 64 of the corrugated profile 34 or "skirt" like structure, so as to be largest at the distal end 64.

It will be understood that these curved terminal walls 58 and additional curved walls 60 could be modified and repositioned relative to the lobe walls 56 and/or the periphery 52 in other embodiments of a wind turbine without departing from the scope of this invention. Moreover, the lobe walls 56 are shown as generally parallel to one another in each lobe 36, but this could be modified in other embodiments of the invention such that the lobe walls 56 are converging or diverging. As will be readily understood by those skilled in the art, such modifications can still result in each of the lobes 36 having uniform cross sectional shapes, but the flow vortex generation would change in the different embodiments. One such example of the vortex generation applicable to the embodiments shown in this application is provided below at the description of Fig. 8.

Even though the lobes 36 of the corrugated profile 34 do not rotate or move within the airflow as a result of being formed in the aft end 50 of the nacelle 46, airflow passing over the central structures of the wind turbine 30 is forced to move in different directions at the lobes 36. This movement generates powerful small flow vortices of air rotation which can act as stirring or mixing activators for the wake flows downstream from the wind turbine 30. The flow vortices grow out in size as they travel away from the wind turbine 30 and then interact with the wake flows to break those wake flows down by mixing them out with one another. To explain the vortex generation another way, airflow over the corrugated profile 34 reacts in a similar manner to airflow over a generalized lobed mixer (for aircraft engines and the like) or airflow over vortex generators, which are sometimes added to wind turbine blades. The vortices are effective at forcing mixing together of airflows with differing velocity profiles and gradients, thereby removing deficits and/or turbulence that naturally occur in those conditions. It will be appreciated that producing flow vortices with the corrugated profile 34 at the central structures may be even more effective at rapidly mixing wake flows when used on each energy generating assembly 32 of a multi-rotor wind turbine. This higher effectiveness with multi-rotor arrangements is present because there are several "edges" between streamtubes of the individual rotors and the gap flow which can be more easily manipulated thanks to the smaller scale disparities between the rotor wake and adjacent atmospheric flow, e.g., smaller velocity gradients to mix out. However, the production of flow vortices also works to reduce wake flows in the single rotor type turbines as well, despite the larger velocity and scale disparities involved with those embodiments. The mixing effects caused by the flow vortices resulting from airflow over the corrugated profile 34 can be further enhanced in some embodiments with additional features as shown in Figs. 3 and 4. In this regard, the nacelle 46 of the wind turbine 30 houses many components that generate heat during operation, including the generator 44, the drive train, and similar elements. To avoid heat damage and maintain the operational state of these components, one or more cooling systems 48 are typically incorporated into the nacelle 46 to exhaust heat energy into the ambient environment of airflow moving past the wind turbine 30. Although such cooling systems 48 can operate with various refrigerant fluids and structural layouts, airflow is often used in some embodiments to transport heat energy in the cooling system 48. That airflow can be captured from the ambient airflow, but then must be exhausted from the wind turbine 30 after picking up heat energy, such as at a heat exchanger (not shown).

The wind turbine 30 may therefore incorporate at least one exhaust air port 62 at the aft end 50 of the nacelle 46 for the dual purposes of removing the heat energy from the cooling system 48 and injecting additional flow jet effects into the wake flows downstream from the wind turbine 30. The exhaust air port 62 may be located inside the space delimited by the plurality of lobes 36 as shown in Fig. 4, with each exhaust air port 62 directed to provide additional flow under the "skirt" structure defined by the corrugated profile 34 and along one or more of the lobes 36. It will be understood that the exhaust air ports 62 can be moved to other locations in other embodiments as well, including the alternative shown in Fig. 5 and discussed below. When positioned as shown in Fig. 4, the exhaust flow jets of air from the cooling system 48 help move the normally "still" air located directly behind the aft end 50 for mixing with the faster airflows moving around the nacelle 46. This configuration is capable of enhancing the mixing via the flow vortices generated by the corrugated profile 34.

Regardless of whether the heat exchange exhaust air is injected from the exhaust air ports 62, the corrugated profile 34 of the nacelle 46 in the wind turbine 30 of this embodiment generates multiple types of flow vortices as a result of fluid dynamics effects in airflow moving over such a bluff body and the lobes 36 provided on the body. The flow vortices encourage faster mixing of wake flows with different velocities and deficits downstream from the wind turbine 30, with the effect being the mixing out of wake flows in a shorter lateral distance than conventional designs without the corrugated profile 34 (or corrugated profiles 34, when one is added to each nacelle 46 of a multi rotor wind turbine as set forth above). This difference can be viewed schematically in Fig. 14, which is described in further detail below.

The provision of a corrugated profile is not limited to the example shown in Figs. 3 and 4, as several modifications can be made to the design without departing from the scope of the invention. To this end, Fig. 5 illustrates another embodiment of a wind turbine 70 including a corrugated profile 72 with a plurality of lobes 74 for generating flow vortices to mix wake flows downstream in the wind flow direction from the wind turbine 70. The wind turbine 70 of this embodiment includes many similar or identical components as the previous embodiment of the wind turbine 30, and these elements have been marked with the same reference numbers where they are essentially unchanged. For example, the wind turbine 70 again includes an energy generating assembly 32 mounted on top of a tower 12 or support structure, the energy generating assembly 32 including the rotor 38 with hub 40 and wind turbine blades 42, the nacelle 46, and internal components within the nacelle 46 which are not shown in Fig. 5. The nacelle 46 of the wind turbine 70 is once again cylindrical in shape, defining an aft end 50 and an outer periphery 52 with one single, circular side edge 54 at the aft end 50. The corrugated profile 72 extends from this aft end 50 as with the previous embodiment.

The corrugated profile 72 is modified in this embodiment, as are the location(s) of the at least one exhaust air ports 76. Starting with the corrugated profile 72, in this embodiment a higher number of lobes 74 are provided in the corrugated profile 72 as compared to the six lobes of the previous embodiment. More specifically, ten lobes 74 are shown in Fig. 5, with the lobes 74 having a smaller size compared to the lobes 36 of the Fig. 3 embodiment, so that these lobes 74 can fit along the single side edge 54 and the outer periphery 52 of the aft end 50 of the nacelle 46. It will be understood that the number of lobes in a corrugated profile of these types may be modified to have anywhere from 5 to 60 lobes, for example, depending on the preferences of the wind turbine operator. A higher number of smaller lobes such as in Fig. 5 will produce a higher number of flow vortices, but these flow vortices may have lesser rotational strength or mixing capability than the smaller number of flow vortices produced in the Fig. 3 embodiment. The intent of reducing wake flows by encouraging mixing effects with the flow vortices remains the same in both types of example, so the corrugated profile 72 can be modified to have a different number of lobes 74 as shown in Fig. 5 without departing from the scope of the invention.

Even though the lobes 74 in the corrugated profile 72 of this embodiment are smaller in size, the general layout and components thereof are largely the same as previously described. To this end, each of the lobes 74 again defines a uniform U-shaped cross section which expands or increases between an intersection with the periphery 52 of the nacelle 46 and a distal end 64 of the corrugated profile 72. The lobes 74 each include a pair of lobe walls 56 connected together at radially outward ends by a curved terminal wall 58, with the lobe walls 56 each separately connected to adjacent lobes 74 via additional curved walls 60 at the radially inner end. The lobes 74 project radially outwardly into the airflow relative to the periphery 52 of the nacelle 46 and relative to the axis of rotation A_R through the hub 40 and central structures of the wind turbine 70. The lobes 74 may also project inwardly (at the additional curved walls 60 connecting adjacent lobes 74) from the periphery 52 of the nacelle 46 at the aft end 50, but it will be understood that these portions may also remain about the same size as the periphery 52 of the nacelle 46 in other embodiments.

As initially described above, the exhaust air port 76 (one or more) for injecting exhaust air flow from the cooling system 48 inside the nacelle 46 is moved to a different location in the wind turbine 70 of Fig. 5. In this regard, the exhaust air port 76 is still positioned adjacent to the aft end 50 and the plurality of lobes 74, but on an exterior side of the lobes 74 or the "skirt" like structure defined by the corrugated profile 72. In this position, the injected air from the exhaust air port 76 increases a velocity ratio between airflow moving around the nacelle 46 and the corrugated profile 72 and the "still" air located directly downstream from the aft end 50. That increase in velocity ratio is believed to further enhance the mixing effectiveness of the flow vortices developed at the distal end 64 of the corrugated profile 72, while also providing an outlet path for heat exchanger air that needs to be discharged to remove heat energy from the nacelle 46 and the components therein. The mixing effects caused by generating flow vortices with the corrugated profile 72 are still effective, however, regardless of whether the exhaust air ports 76 are located as shown in Fig. 5 or in other locations of the wind turbine 70.

Another similar embodiment of a wind turbine 80 with still further revisions to the design and layout of a corrugated profile 82 is shown in Figs. 6 and 7. Once again, the same reference numbers are used in this embodiment as in prior embodiments where components of the wind turbine 80 are effectively unchanged from the prior description, including at the tower 12 and the rotor 38. Although the central structures of the energy generating assembly 32 in this wind turbine 80 continue to include the rotor 38 and a nacelle 84, the shape of the nacelle 84 is modified from the cylindrical versions shown in the previous embodiments. To this end, the nacelle 84 defines a rectilinear shape with a generally rectangular cross section when viewed transverse to the axis of rotation AR. Accordingly, the nacelle 84 includes an outer periphery 86 defining a plurality of side edges 88 at an aft end 90 thereof, with the corrugated profile 82 including lobes 92 positioned along each of the side edges 88 at the aft end 90. For example, Figs. 6 and 7 specifically show that three lobes 92 are positioned along each of the four side edges 88, thereby providing the corrugated profile 82 at the aft end 90 with twelve lobes 92 overall. It will be appreciated that the specific number and size of lobes, as well as the number of lobes per side edge, may vary in other embodiments with similar nacelles and other components.

Although the nacelle 84 is shown with a generally constant cross section between the rotor 38 and the aft end 90, it will be appreciated that the nacelle 84 may also vary in cross- sectional size in other similar embodiments. To this end, the nacelle 84 of this or other embodiments may gradually increase in size towards the aft end 90, or even be egg-shaped so as to taper some amount towards the aft end 90 in other embodiments without departing from the scope of the invention. In tapering or egg-shaped designs, the aft end 90 may need to be designed to overcome the unfavorable flow geometry for maximizing flow vortex generation at the aft end 90 (such as by making the corrugated profile 82 significantly larger than the remainder of the aft end 90). The corrugated profile is configured for the geometry of the nacelle and the airflow around the nacelle, as will be readily understood from the examples in the embodiments described. Regardless of the particular shape and cross- sectional profile of the nacelle 84, the lobes 92 on the corrugated profile 82 should project outwardly into the airflow to assure that a maximum amount of airflow will move over the structure of the lobes 92 to produce the flow vortices as set forth above.

Even though the lobes 92 in the corrugated profile 82 of this embodiment may differ in layout and size compared to previous embodiments with cylindrical nacelles, the shape and components thereof are largely the same as previously described. To this end, each of the lobes 92 again defines a uniform U-shaped cross section which expands or increases between an intersection with the periphery 86 of the nacelle 84 and a distal end 64 of the corrugated profile 82. The lobes 92 each include a pair of lobe walls 56 connected together at radially outward ends by a curved terminal wall 58, with the lobe walls 56 each separately connected to adjacent lobes 92 via additional curved walls 60 at the radially inner end. The lobes 92 project radially outwardly into the airflow relative to the periphery 86 of the nacelle 84 and relative to the axis of rotation A_R through the hub 40 and central structures of the wind turbine 80. The lobes 92 may also project inwardly (at the additional curved walls 60 connecting adjacent lobes 92) from the periphery 86 of the nacelle 84 at the aft end 90. When airflow moves over the plurality of lobes 92, a number of different types of flow vortices are generated as described in further detail below with reference to Fig. 8. These flow vortices assist with mixing together the wake flows generated downstream from the wind turbine 80, in a similar fashion as the prior embodiments. Thus, the corrugated profiles added to nacelle(s) of a wind turbine in accordance with this invention function to provide the same beneficial mixing of wake flows regardless of the particular shape and size of the lobes, the shape and size of the nacelle, and/or the layout of any exhaust air ports. In each of the embodiments of the wind turbine 30, 70, 80 described above and in some of those described below, a corrugated profile is formed at the aft end of an element, so as to generally provide a series of crests and troughs (alternatively described as peaks and valleys) along the periphery of an aft end. As schematically illustrated in Figs. 8 and 9, an end view of the corrugated profile may show lobes that are relatively smooth and wavy. Alternatively, the corrugated profile may define lobes that are more sharp or jagged in cross section or when viewed from the end thereof, so long as the lobes still generate a plurality of flow vortices for mixing wake flows downstream from the wind turbine. In a further alternative embodiment, the corrugated profile may include further corrugations on a smaller, finer scale (not shown), so as to provide so-called macro corrugations and micro corrugations. Additionally, and by way of example, the wavelength and amplitude of the corrugations or lobes may vary in other embodiments. In short, the corrugated profile added to central structures of the wind turbine should not be deemed limited to the specific cross- sections shown in the Figures, as alternative designs of the corrugated profile would also generate the desired flow vortices. With continued reference to Fig. 8, a portion of a corrugated profile 82 similar to that shown in the embodiment of the wind turbine 80 in Figs. 6 and 7 is shown in further detail. This portion of the corrugated profile 82 would be located along one of the generally linear side edges 88 at the aft end 90 of the nacelle 84. Airflow over the lobes 92 in the corrugated profile 82 results in the generation of multiple different types of flow vortices, as indicated schematically with flow arrows downstream from the lobes 92. More particularly, in the example provided in Fig. 8, at least three different types of flow vortices are generated in the airflow. At the terminal ends of the curved terminal walls 58 and of the additional curved walls 60, horseshoe vortices are formed as shown by horseshoe vortex flow arrows 100. In the middle of the lobe walls 56, streamwise vortices are formed as shown by streamwise vortex flow arrows 102. Both of these types of vortices result from changes in geometry that the airflow has to flow over, which leads to pinch off effects and rotation that defines the vortex and its mixing capabilities downstream from the wind turbine. The flow over the entirety of the corrugated profile also collectively leads to development of Kelvin-Helmholtz vortices, also referred to as normal vortices, as shown by normal vortex flow arrows 104. Each of these distinctive types of flow vortices provides a different mixing effect on wake flows downstream from the wind turbine, which enhances the overall mixing caused by this design.

Of course, these flow vortex types shown in Fig. 8 are but one example, as it will be readily understood that the corrugated profile may develop additional or different types of flow vortices when arranged differently as alluded to above for other embodiments. For example, designs of the corrugated profile with more jagged lobe shapes or macro and micro corrugations will develop different types of powerful vortices, which will nevertheless lead to the desired result of mixing wake flows. Likewise, in embodiments where each of the lobes is not provided with a uniform shape and size contrary to the examples described above, the flow vortex formation may also vary in different parts of the corrugated profile based on these differences in the lobes of the corrugated profile.

Another potential feature to be combined with the corrugated profiles of the different embodiments is shown in Fig. 9, which is a cross section taken through a portion of the corrugated profile 82 in Figs. 6 through 8. In this alternative embodiment, the lobes 92 are further integrated to operate as a heat exchanger for the cooling system 48 located within the nacelle 84. More particularly, the lobes 92 define flow passages and/or cooling fins positioned to help heat transfer from a fluid passing through the cooling system 48 and typically delivered by a cooling pump (not shown). As shown in Fig. 9, one example of this arrangement is provided by using 3D printing or similar manufacturing techniques to form heat exchange passages 1 10 within the interior of the walls 56, 58, 60 defining the lobes 92. The heat exchange passages 1 10 receive a heated fluid, refrigerant, or the like from the cooling pump of the cooling system 48 and pass that heated fluid therethrough so as to put the heated fluid into position for heat discharge to the airflow surrounding the lobes 92. The lobes 92 are formed from a material which enables this heat exchange in such embodiments.

Alternatively, or in addition to providing the heat exchange passages 1 10, all or a portion of the interior side 1 12 of the lobes 92 is enclosed (not specifically shown in Fig. 9) so that a fluid from the cooling pump of the cooling system 48 can flow underneath the lobes 92. This arrangement essentially makes the lobes 92 into cooling fins that operate in the manner of a heat exchanger, with the heat energy in the fluid being transferred through the lobes 92 to the airflow moving past the wind turbine. Other mechanisms for operatively coupling the lobes 92 to the cooling system 48 as cooling fins may also be provided to establish this functionality. By incorporating such additional heat exchange features in the corrugated profile 82, separate and independent cooling fins or passages do not need to be provided at the wind turbine as normally would be the case, and the added manufacturing cost of including the corrugated profile 82 could be offset at least to some extent by removing the need for duplicative structures associated with the cooling system(s) 48.

Instead of placing the corrugated profile on a non-moving central structure like the nacelles of the wind turbine embodiments described above, the corrugated profile may instead be located on the so-called spinner portion of the wind turbine, e.g., the rotor hub 40 (which is also a central structure located along the axis of rotation A_R). One such embodiment of the invention is shown at the wind turbine 130 in Figs. 10 and 1 1 . The wind turbine 130 includes a rotor hub 132 that has an aft end 134 defining the corrugated profile 136 with a plurality of lobes 138, which are highly similar to the corrugated profiles and lobes described in the embodiments above. The corrugated profile 136 and its lobes 138 therefore produce the flow vortices for mixing the wake flows at the rotor hub 132 in this embodiment instead of at the nacelle 140, which is again connected to the rotor hub 132 as part of the central structures of the energy generating assembly at the wind turbine 130. In all other respects, the components and elements of the wind turbine 130 are similar to previously-described embodiments and therefore are not described again in detail here.

Typically, such placement of the corrugated profile 136 on the rotor hub 132 is used when the rotor hub 132 is enlarged in size, which is often the case when the energy generating assembly of the wind turbine 130 is configured to generate at least 10 MW or more of electrical energy from the airflow, or in other circumstances like in multi-rotor wind turbines as well. In this regard, the aft end 134 of the hub 132 (and a periphery 142 of the hub 132 proximate this aft end 134) is equal to or larger in transverse cross sectional size than a transverse cross section of the nacelle 140. Therefore, the lobes 138 and corrugated profile 136 extend outwardly beyond the outermost periphery or extent of the central structures, so as to maximize air flow and vortex generation in airflow over the central structures such as the hub 132. To this end, the lobes 138 project outwardly into the surrounding airflow to enable the generation of multiple flow vortices in the airflow. The nacelle 140 is shown with an exaggerated tapering cross section towards the downstream direction (similar to egg- shaped type nacelles), but it will be appreciated that the placement of the corrugated profile 136 on an enlarged size version of the rotor hub 132 can also be used with other nacelles having different shapes and profiles, including those with uniform cross section or increasing in size, without departing from the scope of the invention.

The specific arrangement and shape of the lobes 138 in the corrugated profile 136 of this embodiment are shown in further detail in the Fig. 1 1 perspective view. In this regard, the lobes 138 are similar to those described above in that they define a generally smooth or wavy profile, with each of the lobes 138 having a generally uniform shape and size. Of course, more jagged or macro/micro corrugation designs could also be used in other similar embodiments on the rotor hub 132. There are about ten lobes 138 included in the corrugated profile 136 of this embodiment, but it will be appreciated that the number of lobes and their corresponding size may be varied as with the nacelle-based embodiments (e.g., 5 to 60 lobes could be provided). The lobes 138 are defined by walls which converge towards one another to form a smooth sine-wave type overall profile as the lobes 138 extend radially outwardly from the rotor hub 132, although a U-shaped design more similar to what is shown in Figs. 3 through 9 with generally parallel lobe walls 56 and curved connecting walls 58, 60 could also be used without changing the operation of this embodiment. As with the previous embodiments positioned on nacelles, the lobes 138 project outwardly at an outermost end thereof into the air flow so as to be larger than the cross section of a single, circular side edge 144 defined by the periphery 142 at the aft end 134, and the innermost end of the lobes 138 may be the same size or project slightly inwardly from the periphery 142 at the aft end 134. Airflow over this type of structure, even when rapidly spinning as the hub 132 typically does in operation, causes generation of rotational flow vortices which help mix out the wake flows downstream from the wind turbine 130.

The lobes 138 in the corrugated profile 136 in Figs. 10 and 1 1 are also formed so as to each define a non-lifting (e.g., non lift generating) cross section when viewed transverse to the axis of rotation A_R. To this end, the lobes 138 are not shaped in a manner to capture the airflow moving past the rotor hub 132 and add additional torque input to the rotor hub 132. In the specific examples shown in this application, the non-lifting cross section is also symmetrical with a zero angle of attack, but other configurations are possible for the lobes 138. On the contrary, the non-lifting cross section of the lobes 138 minimizes any lift or torque generating effects (or similar detrimental effects) because the purpose of the lobes 138 is to create powerful flow vortices, not to generate any substantial additional amount of torque. The cross section of the lobes 138 is effectively like a wing tip or a large vortex generator rather than a torque-producing element. In the context of this disclosure, a generation of a "substantial" amount of lift or torque is that which contributes 1 % or more of the total torque input by the blades 42 and any other elements attached to the spinning rotor hub 132. In summary, the airfoil shape and the overall size of the lobes 138 in the corrugated profile 136 serve the sole purpose of creating flow vortices in a similar manner and for similar purposes as the corrugated profiles included on non-spinning elements like the nacelles described in embodiments above, and thus the functionality and benefits of this embodiment will not be separately described again here in a duplicative fashion. Although the enlarged rotor hub 132 is typically used on single rotor wind turbines, it will be appreciated that the corrugated profile 136 on a hub helps mix out wake flows and velocity gradients due to various flow structures, from any different type of wind turbine this embodiment is incorporated upon, including multi rotor wind turbines of all varieties. In the various embodiments described above, the lobes and corrugated profiles may be formed from the same material as the central structure they are attached to, e.g., the nacelle or the rotor hub. Of course, in alternative embodiments, materials different than the central structures may be used and then separately coupled to the central structure(s). To this end, the corrugated profile may be integrally formed as a unitary piece or separately formed and coupled to the central structure(s). By way of example, the lobes may be formed from a polymeric material such as rubber, styrene or the like. The materials may be solid or have a cellular structure (e.g., such as foam). Other non-polymeric materials for forming the lobes may also be used, including wood, plastics, or metals for example. Additionally, the lobes may be formed through various molding processes, such as an injection molding process. Such a process may be conducive to relatively quick manufacturing and high volume output. Accordingly, the lobes in accordance with embodiments of the invention may be manufactured at a relatively low cost.

A wind turbine 170 in accordance with another embodiment is shown in Figs. 12 and 13. The wind turbine 170 includes added elements in the form of vortex generator lobes 172 for the purposes of generating flow vortices that may be useful in mixing out wake flows that occur downstream from a wind turbine, similar to the embodiments described above having corrugated profiles on a central structure to provide such functionality (e.g., the lobes 172 define a different type of profile with lobes or corrugations). Although only one energy generating assembly 174 on a tower 12 is shown in these Figures, it will be understood that this embodiment can also be used on all types of multi rotor wind turbine designs as well as single rotor designs. A sample interaction of flows from the rotating wind turbine blades 42 and from the vortex generator lobes 172 is also shown in Fig. 12 and described in further detail below, for the sake of clarity.

As shown in Fig. 13 in a head-on view, the wind turbine 170 of this embodiment includes the energy generating assembly 174, defined by at least a combination of a plurality of wind turbine blades 42 (same reference numbers used from prior embodiments where the elements remain largely unchanged) extending from a rotor hub 176, and a generator (not shown) within a nacelle 178, these elements being operatively coupled together such that wind energy is captured by rotation of the blades 42 and the rotor hub 176 for conversion to electrical energy. The nacelle 178 is shown to be generally rectangular in transverse cross section, but it will be appreciated that the features added to the rotor hub 176 in this embodiment can be used regardless of the particular nacelle design. Likewise, although the rotor hub 176 is shown to be smaller in cross sectional size than the nacelle 178 in Figs. 12 and 13, the features of this embodiment can be incorporated on enlarged hubs in alternative embodiments similar to what was shown in Figs. 10 and 1 1 .

As initially described above, the rotor hub 176 of this embodiment of the wind turbine 170 is provided with vortex generator lobes 172 projecting from an exterior surface 180 of the rotor hub 176. The lobes 172 are positioned between adjacent pairs of wind turbine blades 42, but it will be understood that the particular placement around the periphery defined by the exterior surface 180 may be modified from the exact arrangement shown in Fig. 13. The lobes 172 are typically constructed separately and coupled to an existing rotor hub 176 to add the flow vortex mixing effects desired downstream from the wind turbine 170. However, the lobes 172 can also be integrally formed as a unitary piece with the rotor hub 176 as well. The lobes 172 in the illustrated embodiment are vane-like or fin-like in shape, which is most clear in the head-on view of Fig. 13. That view also confirms that each of the lobes 172 of this embodiment is formed with a uniform shape and size, as well as with a non-lifting, symmetrical, and/or generally straight (non-curved or twisted) cross section. Consequently, while the vane-like or fin-like lobes 172 are effective (when spinning) at generating powerful flow vortices in the airflow moving past the wind turbine 170, the lobes 172 do not capture airflow in such a manner to produce substantial lift or torque forces to help rotate the rotor hub 176 and produce electrical energy. Instead, the sole purpose of the lobes 172 is the generation of flow vortices. It will be understood that more corrugation-like lobes could alternatively be provided to the rotor hub 176 in other similar embodiments of the wind turbine 170. The factors contributing to this functionality of the lobes 172 are believed to be as follows. The size of the lobes 172 is made sufficient to extend into an airflow at a position radially outward from the central structures of the wind turbine 170, which is shown by the terminal ends 182 of the lobes 172 projecting outwardly beyond the periphery of the nacelle 178 in Fig. 13. However, the terminal ends 182 of the lobes 172 do not extend a significant amount beyond these central structures, unlike the wind turbine blades 42, and that limits the amount of lift-generating or torque-generating wind capture that these elements provide. Likewise, the narrow vane-like or fin-like construction of the lobes 172 is generally straight (non-twisted) in cross section and is therefore distinctive from the somewhat curved and/or impeller-like shapes of blades and other elements which are conventionally added to rotor hubs to help capture energy from the wind. The lobes 172 are configured to produce a tip vortex strength sufficient to define a strong rotational vortex that will propagate mixing effects well into the wake flows downstream from the wind turbine 170. As with the previous embodiment of a corrugated profile on a spinner, any lift or torque provided by the lobes 172 which could be deemed energy-generating is not significant, e.g., less than 1 % of the total torque generated during normal operation of the wind turbine 170 (e.g., the cross section of these elements is intended to be effectively non-lifting).

As the rotor hub 176 of the wind turbine 170 spins with the blades 42 as a result of airflow past the wind turbine 170, the blades 42 are known to produce shed vortex sheets and hub- rollup vortices, along with other flow discontinuities which lead to wake flows downstream from the wind turbine 170 in the wind flow direction. These larger-scale effects are represented by blade flow arrows 184 in Fig. 12. Also during spinning movement, the lobes 172 attached to the rotor hub 176 produce smaller intense flow vortices, such as along the terminal ends 182 and/or downstream ends thereof. These flow vortices from the lobes 172 are represented schematically in Fig. 12 by mix vortex flow arrows 186. As can be seen in Fig. 12, these flow vortices begin interacting with the larger-scale effects caused by the wind turbine blades 42 almost immediately after the airflow moves past these components of the wind turbine 170, which allows the flow vortices to begin mixing uneven velocity flows and turbulent flows together quickly after formation of such wake flows. Such mixing then leads to a more even air velocity field behind the wind turbine, as compared to zones of hot spot velocities and severe deficits which are common in conventional designs not incorporating these vortex generating elements.

The modified wind turbine 170 of Figs. 12 and 13 is shown in a lower portion of Fig. 14 to help illustrate the effects this functionality (and the mixing functionality of the other embodiments described above) have on development of wind farms containing many wind turbines. The upper portion of Fig. 14 shows a wind farm where wind turbines 10 of the conventional design like in Fig. 1 are used. The large-scale shed vortex sheets, hub-rollup vortices, and other velocity gradients defining wake flows caused by airflow over the operating wind turbines 10, 170 are shown by wake flow arrows 200 in Fig. 14. These wake flows eventually mix out to a more uniform airflow which is shown in Fig. 14 by the flow arrows 202. If a downstream wind turbine is placed within the zone where wake flows still exist, the downstream wind turbine will not be efficient in capturing a maximum amount of energy from the airflow, and there is a heightened risk of wind turbine damage when encountering wake flows as identified in the Background section.

Thus, when using conventional designs like wind turbine 10, a large spacing D1 needs to be provided between an upstream wind turbine and a downstream wind turbine to allow for the wake flows to mix out into the uniform airflow. However, when using the wind turbine 170 of Figs. 12 and 13 or one of the other embodiments described herein, flow vortices as shown by vortex flow arrows 204 are produced and expand outwardly to help mix out the wake flows in a more rapid and efficient fashion. The zone of wake flows is reduced in size, as a result, making the generally uniform airflow in a much smaller distance than conventionally, indicated by the shorter wake flow arrows 200 on the bottom portion of Fig. 14. Advantageously, the shorter wake region then allows for downstream and upstream wind turbines of a wind farm to be positioned with a closer or smaller spacing D2, which is less than D1 as shown in Fig. 14. The wake mixing and filling provided by generation of flow vortices improves the efficiency of a wind farm with multiple turbines.

To summarize, the corrugated profiles and lobes shown and described herein are configured to mix out the wake region downstream of a wind turbine. This may provide a number of advantages. By way of example, providing such lobes and profiles on upstream structures may provide downstream wind turbines/rotors with increased energy capture, decreased loads, and decreased capital costs as well as decreased maintenance and repair costs. Moreover, for wind farm arrangements, such profiles and lobes allow the spacing between adjacent wind turbines to be decreased. In addition to mixing out the wake region downstream of a wind turbine, the profiles and lobes described above may have additional advantages. By way of example, this addition may alter the fluid flow regime about the wind turbine so as to decrease the likelihood of approaching vibrations at the natural frequency of the system, thus staving off the negative impact of any vibrations produced in operation.

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, including with any type of single rotor or multi rotor wind turbine. 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 (30) configured to reduce wake flows, the wind turbine (30) comprising:

a support structure (12) including a tower (12); and

at least one energy generating assembly (32) supported by the support structure (12), the energy generating assembly (32) further comprising:

central structures including at least a rotor hub (40) and a nacelle (46), the central structures located along an axis of rotation (A_R) defined by the rotor hub (40);

a generator (44) located at the nacelle (46) and configured to convert rotation of the rotor hub (40) into electrical energy; and

at least one wind turbine blade (42) coupled to and extending from the rotor hub (40) into an airflow passing the wind turbine (30), the at least one wind turbine blade (42) rotating with the rotor hub (40) in the airflow and thereby generating wake flows downstream in a wind flow direction from the wind turbine (30),

wherein at least one of the central structures defines an aft end (50) facing downstream in the wind flow direction, the aft end (50) defining a corrugated profile (34) having a plurality of lobes (36) located along a periphery (52) of the aft end (50).

2. The wind turbine of claim 1 , wherein the nacelle includes the aft end having the corrugated profile.

3. The wind turbine of claim 2, the periphery of the aft end of the nacelle being defined by at least one side edge, wherein at least one of the plurality of lobes of the corrugated profile is located on each of the at least one side edge.

4. The wind turbine of claim 2 or 3, further comprising:

at least one exhaust air port located at the aft end of the nacelle, the at least one exhaust air port being in communication with a cooling system located at the nacelle such that the at least one exhaust air port is configured to inject exhaust air from the cooling system into the airflow proximate the plurality of lobes.

5. The wind turbine of any of claims 2 through 4, further comprising:

a cooling system at the nacelle configured to remove heat from components of the energy generating assembly, the cooling system including a cooling pump for moving a fluid, wherein the plurality of lobes of the corrugated profile are operatively coupled to the cooling pump so as to define a heat exchanger for the cooling system, the cooling fins configured to transfer heat energy from the fluid to the airflow.

6. The wind turbine of claim 5, wherein the plurality of lobes further comprise heat exchange passages configured to pass the fluid from the cooling pump therethrough and thereby enable heat exchange between the fluid and the airflow.

7. The wind turbine of claim 1 , wherein the rotor hub includes the aft end having the corrugated profile.

8. The wind turbine of claim 7, wherein each of the plurality of lobes of the corrugated profile on the rotor hub define a non-lifting cross section when viewed transverse to the axis of rotation.

9. The wind turbine of claim 7 or 8, wherein each of the plurality of lobes of the corrugated profile on the rotor hub are sized to produce tip vortices in the airflow passing the wind turbine, without producing substantial lift or torque that would assist with energy extraction from the airflow.

10. The wind turbine of claim 9, wherein the plurality of lobes of the corrugated profile moving through the airflow generates torque that is 1 % or less of a total torque generated by the rotor hub and the at least one wind turbine blade moving through the airflow during wind turbine operation for energy extraction from the airflow.

1 1 . The wind turbine of any of claims 7 to 10, the rotor hub being enlarged in size such that the aft end of the rotor hub is larger in cross section transverse to the axis of rotation than a cross section of the nacelle.

12. The wind turbine of any of the preceding claims, the corrugated profile being configured to generate flow vortices in the airflow to mix the wake flows downstream from the wind turbine.

13. The wind turbine of claim 12, the plurality of lobes of the corrugated profile defining cross-sectional shapes configured to produce multiple different types of flow vortices when the airflow moves past the corrugated profile.

14. The wind turbine of claim 13, the plurality of lobes being configured to produce horseshoe vortices, Kelvin-Helmholtz vortices, and streamwise vortices when the airflow moves past the corrugated profile.

15. The wind turbine of any of the preceding claims, the plurality of lobes in the corrugated profile having uniform shape and size.

16. The wind turbine of any of the preceding claims, the corrugated profile having at least 5 lobes defining the plurality of lobes.

17. The wind turbine of any of the preceding claims, wherein the plurality of lobes project outwardly and inwardly from the periphery when viewed in cross section transverse to the axis of rotation.

18. The wind turbine of any of the preceding claims, wherein the wind turbine is configured as a multi-rotor wind turbine having a plurality of energy generating assemblies supported on the support structure, wherein each of the plurality of energy generating assemblies includes at least one central structure having an aft end defining a corrugated profile with a plurality of lobes.

19. A method of reducing wake flows downstream from a wind turbine, the wind turbine including at least one energy generating assembly including central structures in the form of at least a rotor hub and a nacelle located along an axis of rotation defined by the rotor hub, and at least one wind turbine blade extending from the rotor hub and rotating with the rotor hub in an airflow, which generates wake flows downstream from the wind turbine in a wind flow direction, wherein the method comprises:

providing a corrugated profile having a plurality of lobes at an aft end of at least one of the central structures, the aft end facing downstream in the wind flow direction; and

operating the wind turbine in the airflow such that the corrugated profile produces flow vortices in the airflow to mix the wake flows downstream from the wind turbine.

20. The method of claim 19, wherein providing the corrugated profile further comprises providing the corrugated profile in the aft end of the nacelle, such that the plurality of lobes remains stationary during operation of the wind turbine.

21 . The method of claim 20, wherein the nacelle includes a cooling system, the aft end of the nacelle includes at least one exhaust air port, and the method further comprises: injecting exhaust air from the cooling system through the at least one exhaust air port and into the airflow proximate the plurality of lobes, the exhaust air configured to further enhance mixing of the wake flows downstream from the wind turbine.

22. The method of claim 20 or 21 , wherein a cooling system located at the nacelle is configured to remove heat from components of the energy generating assembly, the cooling system includes a cooling pump for moving a fluid, and the method further comprises:

flowing the fluid from the cooling pump through heat exchange passages provided at the plurality of lobes of the corrugated profile, thereby to transfer heat between the fluid and the airflow.

23. The method of claim 19, wherein providing the corrugated profile further comprises: providing the corrugated profile in the aft end of the rotor hub, such that the plurality of lobes rotates with rotation of the rotor hub.

24. The method of any of claims 19 through 23, wherein the wind turbine is configured as a multi-rotor wind turbine having a plurality of energy generating assemblies, wherein the method further comprises:

providing a corrugated profile having a plurality of lobes on each of the plurality of energy generating assemblies.