Vertical axis turbine and floating vessel

Abstract

The invention relates to a vertical axis turbine comprising a rotor and a frame for supporting the rotor, said frame comprising: - a top support with a bearing for the rotor, - a base support, and - six rigid legs, wherein the six rigid legs are attached in pairs to three mounting positions on the base support, and wherein the six rigid legs are attached in pairs different from the pairs formed at the base support to three mounting positions on the top support, wherein the three mounting positions on the base support lie on a first virtual circle with a first diameter, wherein the three mounting positions on the top support lie on a second virtual circle with a second diameter, and wherein the first diameter is larger than the second diameter.

Description

[0001] TITLE OF THE INVENTION

[0002] Vertical axis turbine and floating vessel

[0003] BACKGROUND OF THE INVENTION

[0004] The invention relates to a vertical axis turbine such as a wind turbine or underwater turbine and a floating vessel provided with such a vertical axis turbine.

[0005] A turbine in the context of this application is used to extract energy from wind or water current by converting kinetic energy from the wind or water into kinetic energy of a rotor, and then possibly into other forms of energy, for instance electrical energy, although this is not necessary per se, and the turbine may also be used for amusement or promotional purposes. Turbines, e.g., wind turbines, come in two types, namely well-known horizontal axis turbines having the main rotor shaft extending horizontally and vertical axis turbines having the main rotor shaft extending vertically.

[0006] In turn, vertical axis turbines can generally be divided into two types as well, namely those comprising Savonius-type rotors and those comprising Darrieus-type rotors. The Savonius-type works mainly based on a difference in drag, thereby limiting the maximum efficiency. The benefit of this type of turbine, however, is its simplicity in design and the fact that it will start operating automatically once it captures enough wind or water. The Darrieus-type, on the other hand, operates based on lift generated over the blades, which enables higher relative speeds and a higher efficiency.

[0007] It is well-recognized that the rotor of a vertical axis turbine of the Darrieus-type, due to the higher relative speeds, is subjected to higher forces and torques. The blades are subjected to lift and drag forces caused by the relative movement of the blade through the medium, i.e., air or water. Turbulent flows, e.g., the passing of strong wind gusts for a wind turbine, may introduce extreme and potentially destructive, forces on the blades and rotor. Further, the blades are subjected to centrifugal forces that increase with increasing relative speeds. Other drawbacks of vertical axis turbines may include difficult / impossible self-starting, lower output due to operation closer to the ground, and higher level of vibration caused by the inherent torque ripple and dynamic stall of the blades, at least in the "small wind" domain.

[0008] SUMMARY OF THE INVENTION

[0009] In view of the above it is an object of the invention to provide an improved vertical axis turbine.

[0010] According to a first aspect of the invention, there is provided a vertical axis turbine comprising a rotor and a frame for supporting the rotor, said frame comprising: a top support with a bearing for the rotor, a base support, and six rigid legs, wherein the six rigid legs are attached in pairs to three mounting positions on the base support, wherein the six rigid legs are attached in pairs different from the pairs formed at the base support to three mounting positions on the top support, wherein the three mounting positions on the base support lie on a first virtual circle with a first diameter, wherein the three mounting positions on the top support lie on a second virtual circle with a second diameter, and wherein the first diameter is larger than the second diameter.

[0011] An advantage is that due to the construction of the frame, relatively large loads from the rotor can easily be transferred to the ground or foundation without using a relatively large and heavy frame. A further advantage is that the construction of such a vertical axis turbine is scalable (even highly scalable compared to other types of vertical axis turbines) and is both suitable for small configurations (with small induced forces) and large configurations (with large induced forces) without resulting in an unrealistic increase of dimensions to withstand the larger forces.

[0012] It is to be noted here that the terms "base" and "top" refer to an orientation in which the base support is arranged below the top support, or in other words, the top support is located at a higher level than the base support. All references in this description, e.g. top view, side view, etc., are related to this orientation, which will be referred to as the normal orientation when necessary. However, as will also be explained below in more detail, it is also envisaged that the vertical axis turbine is used upside down, which orientation will be referred to as the inverted orientation when necessary.

[0013] In an embodiment, the base support includes a foot per mounting location, wherein the foot can be mounted to a support structure, e.g. a roof of a building, a platform, etc.

[0014] In an embodiment, the base support includes a connecting element between each pair of feet. An advantage thereof may be that loads are more distributed over the feet and thus the peak load per foot reduces. Another advantage may be that no rigid supporting surface is required, thereby eliminating the requirement for the mounting positions to have sufficient rigidity to transfer the forces. This rigidity is then provided by the connecting element.

[0015] In an embodiment, the first diameter is at least 1.5 times, preferably at least twice, as large as the second diameter.

[0016] In an embodiment, the rotor comprises: a blade support structure extending from the bearing at the top support, at least two blades coupled to the blade support structure at a distance from the bearing, wherein the blade support structure comprises an arm for each blade extending between the corresponding blade and the bearing.

[0017] In an embodiment, each arm includes a pair of beams extending between the corresponding blade and the bearing, wherein the pair of beams diverge from the blade towards the bearing.

[0018] In an embodiment, each arm includes a pair of beams extending between the corresponding blade and the bearing, wherein the beams are attached in pairs to respective mounting positions on or near the bearing, each pair being formed by a beam associated with one blade or arm and a beam associated with another blade or arm.

[0019] In an embodiment, said pair of beams form a substantially V-shape in top view.

[0020] In an embodiment, each arm includes a pair of beams extending between the corresponding blade and the bearing, wherein the pair of beams diverge from the bearing towards the bearing, and wherein said pair of beams form a substantially V-shape in side view.

[0021] In an embodiment, each arm has four beams forming substantially the shape of a tetrahedron with one of its edges extending horizontally at the bearing and an opposite edge extending vertically at the blade. Horizontally at the bearing may alternatively be described as parallel to a plane substantially perpendicular to a vertical rotation axis defined by the bearing. Vertically at the blade may alternatively be described as substantially parallel to a vertical rotation axis defined by the bearing.

[0022] In an embodiment, the vertical axis turbine further comprises a generator having a stator part arranged on the top support and a rotor part arranged on the rotor.

[0023] In an embodiment, the generator has a third diameter that is at least 70%, preferably at least 80%, and more preferably at least 90% of the second diameter. In some embodiments, the third diameter is equal to the second diameter.

[0024] In an embodiment, the generator has a third diameter, wherein the rotor has a fourth diameter, and wherein the third diameter is at least 10% of the fourth diameter, preferably at least 15%, more preferably at least 20%, and most preferably at least 25%.

[0025] In an embodiment, the generator is an axial flux generator. In an embodiment, the generator comprises at least two stator parts and / or at least two rotor parts stacked in height direction.

[0026] In an embodiment, in the stack of stator parts and rotor parts, the number of one of the stator parts and the rotor parts is n, and the number of the other one of the stator parts and the rotor parts is n+1, wherein n can be any whole number starting from 1.

[0027] In an embodiment, the at least two blades are pivotally coupled to the blade support structure, wherein the rotor further comprises a pitch regulating mechanism arranged between the blade support structure and a corresponding blade to regulate the pitch of the blade in dependence of fluid dynamic forces acting on the blade, and wherein the pitch regulating mechanism comprises a damper system, wherein the damper system has a first damping coefficient in a first rotational direction of the blade relative to the blade support structure and a second damping coefficient in a second rotational direction of the blade relative to the blade support structure.

[0028] It is noted here that a damper system refers to the function of being able to dissipate energy. The damper system thus refers to the use of one or more dampers and not to the use of one or more springs. It is noted here explicitly that the inventors acknowledge, as will all persons skilled in the art of engineering, that ideal springs and dampers do not exist in practice. Hence, springs will dissipate some energy in practice and thus have a non-zero damping coefficient and dampers or other components of the rotor will not have an infinite stiffness in practice and thus will have a non-zero spring constant.

[0029] Statements as a zero damping coefficient or devoid of springs thus have to be interpreted within this practical context as respectively meaning that energy dissipation is minimal as reasonably can be expected and that no elements have been employed to provide a significant resilient behavior of the pitch of the blade.

[0030] In an embodiment, the damper system may be configured to use or provide the energy dissipated (to) somewhere else in the rotor or vertical axis turbine. The dissipation may only refer to the dissipation of kinetic energy of the blade. For instance, the dissipated energy may be used later for safety purposes to prevent the rotor from exceding a predetermined maximum speed and / or to startup the rotor. It is explicitly noted here that the use of dissipated energy is not to be used directly similar to a spring would do.

[0031] The rotor may define an advancing rotational direction in which the rotor will rotate during operation. The first rotational direction of the blade relative to the blade support may be in the same direction as the advancing rotational direction in which case the second rotational direction of the blade relative to the blade support is in an opposite direction to the advancing rotational direction.

[0032] The damping coefficient is defined as the ratio between a force generated by the damper system by a relative speed between two components of the damper system. The higher the relative speed, the higher the generated force.

[0033] In an embodiment, the first damping coefficient is higher than the second damping coefficient.

[0034] In an embodiment, the second damping coefficient is substantially zero.

[0035] In an embodiment, the first damping coefficient is variable depending on an orientation of the corresponding blade relative to the blade support.

[0036] In an embodiment, the first damping coefficient is increasing when the blade rotates in the first direction.

[0037] In an embodiment, the first and / or second damping coefficient are adjustable. An advantage thereof is that this may allow speed control by aerodynamic braking of the rotor.

[0038] In a practical embodiment, the first and / or second damping coefficient are determined by a size of an aperture in a hydraulic or pneumatic cylinder through which fluid is forced upon movement of the blade. The first and / or second damping coefficient may then by adjustable by making the size of the aperture adjustable. In an embodiment, the aperture is formed by a valve and the valve is regulated by a damping regulating device controlling the size of the aperture of the valve.

[0039] The damping regulating device may be an active device using for instance a speed sensor to determine a rotational speed of the rotor, a control unit to determine a desired size of the aperture of the valve based on the determined rotational speed of the rotor, and an actuator to set the size of the aperture of the valve to the desired value.

[0040] Alternatively, the damping regulating device may be a passive device in which for instance a centrifugal regulator is used to reduce the size of the aperture of the valve when the rotational speed of the rotor increases. Such a passive device typically includes a mass that is arranged on a rotatable arm such that the mass can rotate away from a center of the rotor, and a configuration to provide a force urging the mass to rotate towards a center of the rotor and that is able to increase when the mass rotates away from the center of the rotor. The configuration may be based on gravity or a spring.

[0041] In an embodiment, each blade is pivotally connected to the blade support structure at or near its leading edge, and wherein the pitch regulating mechanism is arranged between the blade support structure and a trailing edge side of the blade.

[0042] In an embodiment, each blade has a plate-like construction that can bend about a vertical axis due to fluid dynamic forces and forces exerted on the blade by the pitch regulating system.

[0043] In an embodiment, each blade comprises strengthening ribs extending substantially horizontally over the plate-like construction.

[0044] In an embodiment, each blade includes a sail.

[0045] In an embodiment, each blade includes a mast and a boom extending from the mast, wherein a sail is arranged between the mast and a free end of the boom, and wherein the corresponding blade support structure is provided between the bearing and the boom. Preferably, the boom is rotatably connected to the blade support structure to allow the blade to pivot relative to the blade support structure.

[0046] In an embodiment, the damper system is arranged between the blade support structure and the boom.

[0047] In an embodiment, each blade includes a pair of booms, wherein the sail is arranged in between the pair of booms.

[0048] In an embodiment, each blade includes two pairs of booms at different height levels of the sail.

[0049] The first aspect of the invention also relates to a floating vessel comprising at least two vertical axis turbines according to the first aspect of the invention, wherein the rotor of one vertical axis turbine is configured to rotate in one rotational direction and the rotor of another vertical axis turbine is configured to rotate in the opposite rotational direction.

[0050] In an embodiment, the two vertical axis turbines are arranged in the normal orientation to extend above water and configured to interact with the wind.

[0051] In an embodiment, the two vertical axis turbines are arranged in the normal orientation to extend in the water and configured to interact with water.

[0052] In an embodiment, the two vertical axis turbines are arranged in the inverted orientation to extend in the water and configured to interact with water.

[0053] In an embodiment, the two vertical axis turbines are arranged in the inverted orientation to extend above water and configured to interact with the wind.

[0054] An advantage of using a plurality of vertical axis turbines rotating in opposite directions is that forces, e.g. torques as a result of power generation by the generator, applied by the vertical axis turbines to a shared or common frame, hull or vessel can be compensated at least partially, but preferably substantially in full, preventing the frame, hull or vessel from being subjected to moments that urge the frame, hull or vessel from rotating about a vertical axis, i.e. reduce or minimize yaw of the floating vessel. Alternatively, or additionally, the gyroscopic effect may be used to stabilise the floating vessel as it will reduce roll and pitch of the floating vessel.

[0055] When similar vertical axis turbines are used, the number of vertical axis turbines attached to the same frame, hull or vessel is preferably even, but an odd number of vertical axis turbines is also possible, for instance by using one larger vertical axis turbine and two smaller vertical axis turbines wherein the loads of the two smaller vertical axis turbines may be substantially compensated by the loads of the larger vertical axis turbine.

[0056] An advantage of the inverted orientation (mainly, but not only, for the floating vessel) may be that the center of mass of the vertical axis turbine is located below its support such that gravity aids in stabilizing the orientation of the vertical axis turbine during operation.

[0057] In an embodiment, each base support of the vertical axis turbines is arranged on one or more buoyancy members.

[0058] According to a second aspect of the invention, there is provided a vertical axis turbine comprising a rotor, a frame for supporting the rotor, and a generator having a stator part arranged on the frame and a rotor part arranged on the rotor so that the rotor part rotates along with the rotor of the vertical axis turbine, wherein the generator has a generator diameter, wherein the rotor has a rotor diameter, and wherein the generator diameter is at least 10% of the rotor diameter, preferably at least 15%, more preferably at least 20%, most preferably at least 25%.

[0059] In an embodiment, the generator is an axial flux generator.

[0060] In an embodiment, the generator comprises at least two stator parts and / or at least two rotor parts stacked in height direction. In an embodiment, in the stack of stator parts and rotor parts, the number of one of the stator parts and the rotor parts is n, and the number of the other one of the stator parts and the rotor parts is n+1.

[0061] According to a third aspect of the invention, there is provided a vertical axis turbine comprising a rotor, and a frame for supporting the rotor, wherein the rotor comprises a blade support structure extending from a center of the rotor, and at least two blades pivotally coupled to the blade support structure at a distance from the center, and wherein each blade has a plate-like construction that can bend about a vertical axis due to fluid dynamic forces.

[0062] In an embodiment, the rotor further comprises a pitch regulating mechanism arranged between the blade support structure and a corresponding blade to regulate the pitch of the blade in dependence of fluid dynamic forces acting on the blade, and wherein the pitch regulating mechanism comprises a damper system, wherein the damper system has a first damping coefficient in a first rotational direction of the blade relative to the blade support structure and a second damping coefficient in a second rotational direction of the blade relative to the blade support structure.

[0063] In an embodiment, each blade is pivotally connected to the blade support structure at or near its leading edge, and wherein the pitch regulating mechanism is arranged between the blade support structure and a trailing edge side of the blade, such that the plate-like construction can bend about a vertical axis due to fluid dynamic forces and forces exerted on the blade by the pitch regulating system.

[0064] In an embodiment, each blade comprises strengthening ribs extending substantially horizontally over the plate-like construction.

[0065] It is explicitly noted here that features and / or embodiments in relation to one aspect of the invention may readily be applied as features and / or embodiments to another aspect of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The invention will now be described in a non-limiting way by reference to the accompanying drawings in which like parts are indicated by like reference symbols, and in which:

[0067] Fig. 1 schematically depicts a perspective view of a vertical axis turbine according to an embodiment of the invention,

[0068] Fig. 2 schematically depicts a side view of the vertical axis turbine of Fig. 1,

[0069] Fig. 3 schematically depicts a top view of the vertical axis turbine of Fig. 1,

[0070] Fig. 4 schematically depicts a cross-section of a generator suitable for a vertical axis turbine similar to Fig. 1,

[0071] Fig. 5 schematically depicts a perspective view of a vertical axis turbine according to another embodiment of the invention,

[0072] Fig. 6 schematically depicts a side view of the vertical axis turbine of Fig. 5,

[0073] Fig. 7 schematically depicts a top view of the vertical axis turbine of Fig. 5,

[0074] Fig. 8A schematically depicts a cross-section of a first generator suitable for a vertical axis turbine similar to Fig. 5,

[0075] Fig. 8B schematically depicts a cross-section of a second generator suitable for a vertical axis turbine similar to Fig. 5,

[0076] Fig. 9 schematically depicts a perspective view of a portion of a vertical axis turbine according to a further embodiment of the invention,

[0077] Fig. 10 schematically depicts a bottom view of the portion of the vertical axis turbine of Fig. 9, and

[0078] Fig. 11 schematically depicts a damping regulating device suitable for a vertical axis turbine according to an embodiment of the invention.

[0079] DETAILED DESCRIPTION OF THE INVENTION

[0080] Figs. 1 to 3 schematically depict a vertical axis turbine 1 comprising a rotor 100 and a frame 200 for supporting the rotor 100. Fig. 1 depicts a perspective view, Fig. 2 depicts a side view, and Fig. 3 depicts a top view. The frame 200 comprises a top support 201 with a bearing or bearing construction 202 for the rotor 100, a base support 203, and six rigid legs 211-216.

[0081] The base support 203 comprises three mounting plates 221-223 that are connected to each other using base support beams 224-226. Preferably, as in this embodiment, the three mounting plates and the base support beams form an equilateral triangle with the base support beams corresponding to the sides of the equilateral triangle and the three mounting plates being located at the vertices of the equilateral triangle.

[0082] The three mounting plates form three corresponding mounting positions for the six legs 211-216, which are attached in pairs to the three mounting plates 221-223. Legs 211 and 212 are attached to mounting plate 221, legs 213 and 214 are attached to mounting plate 222, and legs 215 and 216 are attached to mounting plate 223.

[0083] The legs extend between the base support 203 and the top support 201. The pairs attached to the mounting plates on the base support 203 diverge to meet with a leg of an adjacent pair at the top support 201 and form a different pair of legs at the top support 201. The legs are thus attached in pairs different from the pairs formed at the base support to three mounting positions on the top support 201. This results in this embodiment in the following pairs of legs at the top support: legs 212 and 213, legs 214 and 215, and legs 211 and 216.

[0084] The three mounting positions at the top support 201 in this embodiment also form an equilateral triangle, which has an orientation 180 degrees rotated relative to the orientation of the equilateral triangle formed by the three mounting positions on the base support 203.

[0085] The three mounting positions on the base support 203 lie on a first virtual circle shown in Fig. 3 having a first diameter DI. The three mounting positions on the top support 201 lie on a second virtual circle having a second diameter D2 as shown in Fig. 2. The first diameter DI is larger than the second diameter D2. In this example, the first diameter is at least twice as large as the second diameter D2. With the configuration of the frame 200 as described above it is possible to effectively transfer horizontal forces, vertical forces, moments and torques from the rotor (and thus the top support) to the base support without overdetermining the construction and introducing undesired tensions in the construction.

[0086] The mounting plates 221-223 of the base support 203 have been provided with corresponding feet 230 allowing to stably support the frame 200 and transfer the forces to the ground or any corresponding foundation. It is also conceived that the mounting plates are each connected to separate floats or together to a floating vessel. The feet 230 may also be used to level the frame 200.

[0087] The rotor 100 comprises a blade support structure 110 extending from the bearing 202 at the top support 201 and at least two blades coupled to the blade support structure 110. It is explicitly noted here that the invention also works using one blade, but that it is preferred to use a more symmetrical design to avoid introducing a too large asymmetrical load applied to the frame 200.

[0088] In this example, the rotor includes three blades 120 coupled to the blade support structure 110 at a distance from the bearing 202. The blade support structure 110 includes a pair of beams for each blade 120 extending between the corresponding blade 120 and the bearing 202. Hence, three blades 120 results in six beams 111-116 forming three pairs (111 and 112, 113 and 114, and 115 and 116) at the blades 120.

[0089] The beams 111-116 are attached in pairs to respective mounting positions 117-119 on or near the bearing 202, wherein each pair is formed by a beam associated with one blade and a beam associated with another blade, e.g. an adjacent blade 120. This results in the following pairs:

[0090] Mounting position 117: beams 111 and 116

[0091] Mounting position 118: beams 112 and 113

[0092] Mounting position 119: beams 114 and 115 The beams that form a pair at a blade 120 may form an integrated arm by being connected to each other along a length of the arm, e.g. via cross-beams 121 or plates 122.

[0093] The blades 120 are pivotally coupled to the blade support structure 110 to pivot about a pivot axis 130. The rotor further comprises a pitch regulating mechanism arranged between the blade support structure 110 and a corresponding blade 120 to regulate the pitch of the blade in dependence of fluid dynamic forces acting on the blade 120. The pitch regulating mechanism comprises a damper system, in this embodiment including two dampers 140 (although one could also be used) per blade 120, to provide a first damping coefficient in a first rotational direction of the blade relative to the blade support structure and a second damping coefficient in a second rotational direction of the blade relative to the blade support structure. An advantage of the different damping coefficient for different rotational directions is that the pitch behavior of a blade during a complete 360 degrees rotation of the rotor can be optimized to deal with different drawbacks and operating conditions of this type of vertical axis wind turbine. For instance, the first damping coefficient may be optimized to deal with the passing of strong wind gusts and / or centrifugal forces, while the second damping coefficient may be optimized to deal with easy self-starting and torque generation.

[0094] Each blade 120 has a leading edge LE and a trailing edge TE. The rotor 100 defines an advancing rotational direction, in this case a rotational direction indicated by arrow RD in which blade 120 will move in a direction parallel to a direction from trailing edge TE to leading edge LE. Each blade 120 can pivot in two rotational directions about respective pivot axis 130 relative to the blade support structure 110. The rotational direction corresponding to the advancing rotational direction RD will be referred to as the first rotational direction FRD, and the rotational direction in opposite direction to the advancing rotational direction will be referred to as the second rotational direction SRD.

[0095] In an embodiment, the first damping coefficient is larger than the second damping coefficient. The second damping coefficient is preferably substantially zero. In the example of Figs. 1-3, each blade 120 is pivotally connected to the blade support structure 110 at or near its leading edge LE, and the pitch regulating mechanism is arranged between the blade support structure and a trailing edge TE side of the blade 120.

[0096] Although other locations are possible as well, the vertical axis turbine 1 of Figs. 1-3 may include a generator having a stator part arranged on the top support 201 and a rotor part arranged on the rotor 100. An advantage thereof is that the rotor 100 can be directly connected to the generator without requiring a transmission thereby reducing the number of moving parts. Another advantage is also that an impedance of the generator does not increase with the same transmission factor which would limit the available generator power.

[0097] Fig. 4 schematically depicts a cross-sectional view of a generator 300 suitable for a vertical axis turbine similar to Fig. 1. Schematically indicated are a portion of a rotor 100 and a top support 201 of a frame for supporting the rotor. Between the rotor 100 and the top support 201, a bearing is provided comprising a first bearing portion 202a and a second bearing portion 202b allowing the rotor 100 to rotate about a vertical axis VA and transferring at least a portion of the horizontal and vertical loads to the top support 201.

[0098] The generator 300 here includes three stator parts 310 mounted to a central column 201a of the top support 201 and extending in radial direction from the central column 201a. The stator parts preferably have an arrangement of stator windings, which can either have separate coils or separate connected spools, or an integral woven arrangement of windings. The stator parts 310 are stacked in height direction.

[0099] Generator 300 further comprises a rotor part 320 per stator part 310. Each rotor part 320 comprises a plurality of magnets 321 (only indicated for the top rotor part 320) providing a magnetic flux direction between the rotor part 320 and the stator part 310 that is parallel to the vertical axis VA. Such a generator may thus be referred to as axial flux generator. To reduce the number of components, some portions of one rotor part 320 may also be part of an adjacent rotor part 320. For instance, magnets used to provide a flux between a rotor part 320 and a stator part 310 may also be used to provide a flux between another rotor part 320 and another stator part 310. In such a case, when these shared components are viewed as a single rotor part, the number of rotor parts is the number of stator parts plus one.

[0100] The possibility to stack rotor parts 320 and stator parts in the generator 300 allows to match the generator to the expected generated torque by the vertical axis turbine and / or provides the possibility to maximize the generator diameter allowing to maximize the number of pole pairs on the rotor and the length of stator windings. Another advantage may be that a more homogenic magnetic field can be provided between the rotor parts 320 and the stator parts 310 reducing the need for electrical steel and thus reduces the required torque for startup.

[0101] The coils in the stator parts 310 may be fabricated using PCB's and / or corresponding production methods such as automated stator winding production methods, or coil bending machinery, which may provide the advantage that the coils and / or the production process can be more easily optimized.

[0102] The generator design described above may also allow the use of weaker (flux density) magnets compared to Neodymium permanent magnets.

[0103] The generator 300 defines a generator diameter D3, which will alternatively be referred to as third diameter D3. A larger diameter D3 is preferred. A main advantage thereof is that there is more space for coils and magnets. Another advantage is that a relative speed between rotor parts and stator parts gets larger resulting in quicker flux changes and thus higher voltages. A further advantage may be that the larger the third diameter D3, the more the movement of the rotor part relative to a stator part resembles a linear movement which increases efficiency. The third diameter D3 may, in an embodiment, be at least 90% of the second diameter D2. The rotor 100 may define a fourth diameter, e.g. twice the distance between a pivot axis 130 of a blade 120 and the vertical axis VA of the rotor 100. In an embodiment, the third diameter D3 is at least 10% of the fourth diameter, preferably at least 15%.

[0104] Figs. 5 to 7 schematically depict a vertical axis turbine 1 comprising a rotor 100 and a frame 200 for supporting the rotor 100. Fig. 5 depicts a perspective view, Fig. 6 depicts a side view, and Fig. 7 depicts a top view.

[0105] The frame 200 comprises a top support 201 with a bearing or bearing construction for the rotor 100, a base support 203, and six rigid legs 211-216. The bearing construction will be explained in more detail below by reference to Figs. 8A and 8B.

[0106] Referring back to Figs. 5-7, the base support 203 comprises three mounting plates 221- 223 that are connected to each other using base support beams 224-226. Preferably, as in this embodiment, the three mounting plates and the base support beams form an equilateral triangle with the base support beams corresponding to the sides of the equilateral triangle and the three mounting plates being located at the vertices of the equilateral triangle.

[0107] The three mounting plates form three corresponding mounting positions for the six legs 211-216, which are attached in pairs to the three mounting plates 221-223. Legs 211 and 212 are attached to mounting plate 221, legs 213 and 214 are attached to mounting plate 222, and legs 215 and 216 are attached to mounting plate 223.

[0108] The legs extend between the base support 203 and the top support 201. The pairs attached to the mounting plates on the base support 203 diverge to meet with a leg of an adjacent pair at the top support 201 and form a different pair of legs at the top support 201. The legs are thus attached in pairs different from the pairs formed at the base support to three mounting positions on the top support 201. This results in this embodiment in the following pairs of legs at the top support: legs 212 and 213, legs 214 and 215, and legs 211 and 216. The three mounting positions at the top support 201 in this embodiment also form an equilateral triangle, which has an orientation 180 degrees rotated relative to the orientation of the equilateral triangle formed by the three mounting positions on the base support 203.

[0109] The three mounting positions on the base support 203 lie on a first virtual circle having a first radius R1 indicated in Fig. 7. The three mounting positions on the top support 201 lie on a second virtual circle having a second radius R2 as shown in Fig. 6. The first radius R1 is larger than the second radius R2. In this example, the first radius R1 is at least twice as large as the second radius R2.

[0110] With the configuration of the frame 200 as described above it is possible to effectively transfer horizontal forces, vertical forces, moments and torques from the rotor (and thus the top support) to the base support without overdetermining the construction and introducing undesired tensions in the construction. The loads applied to the construction mainly result in tension and pressure forces in the legs and minimizes the torques and moments applied to the legs.

[0111] The mounting plates 221-223 of the base support 203 have been provided with corresponding feet 230 allowing to stably support the frame 200 and transfer the forces to the ground or any corresponding foundation. It is also conceived that the mounting plates are each connected to separate floats or together to a floating vessel. The feet 230 may also be used to level the frame 200.

[0112] The rotor 100 comprises a blade support structure 110 extending from the bearing 202 at the top support 201 and at least two blades coupled to the blade support structure 110. It is explicitly noted here that the invention also works using one blade, but that it is preferred to use a more symmetrical design to avoid introducing a too large asymmetrical load applied to the frame 200. In this example, the rotor includes three blades 120 coupled to the blade support structure 110 at a distance from the bearing 202. The blade support structure 110 includes a pair of arms for each blade 120 extending between the corresponding blade 120 and the bearing 202. Hence, three blades 120 results in six arms 111-116 forming three pairs (111 and 112, 113 and 114, and 115 and 116) at the blades 120.

[0113] The arms 111-116 are attached in pairs to respective mounting positions 117-119 on or near the bearing 202, wherein each pair is formed by an arm associated with one blade and an arm associated with another blade, e.g. an adjacent blade 120. This results in the following pairs:

[0114] Mounting position 117: arms 111 and 116

[0115] Mounting position 118: arms 112 and 113

[0116] Mounting position 119: arms 114 and 115

[0117] In this embodiment, all arms 111-116 have the same construction. For simplicity reasons, the construction of the arms is described in relation to arm 111 and by reference to Fig. 6 only. The same applies mutatis mutandis to the other arms 112-116.

[0118] In this embodiment, the arm 111 includes three beams Illa, 111b and 111c. Beams Illa and 111c are connected at one end to the bearing construction 202 at mounting position 117 and are connected at the other end to the blade 120. The beams Illa and 111c diverge towards the blade 120 so that a distance between the mounting positions of the beams Illa and 111c at the blade 120 is larger than a distance between the mounting positions of the beams Illa and 111c at the bearing construction. The beam 111b extends horizontally from the blade to the bearing construction and is part of a connecting structure between the beams Illa and 111c. In this case, the connecting structure has a lattice structure of which beam lib is part of.

[0119] The blades 120 are pivotally coupled to the blade support structure 110 to pivot about a pivot axis 130. The rotor further comprises a pitch regulating mechanism arranged between the blade support structure 110 and a corresponding blade 120 to regulate the pitch of the blade in dependence of fluid dynamic forces acting on the blade 120. The pitch regulating mechanism comprises a clamper system, in this embodiment including four dampers 140 (although one, two or three could also be used) per blade 120, to provide a first damping coefficient in a first rotational direction of the blade relative to the blade support structure and a second damping coefficient in a second rotational direction of the blade relative to the blade support structure. An advantage of the different damping coefficient for different rotational directions is that the pitch behavior of a blade during a complete 360 degrees rotation of the rotor can be optimized to deal with different drawbacks and operating conditions of this type of vertical axis wind turbine. For instance, the first damping coefficient may be optimized to deal with the passing of strong wind gusts and / or centrifugal forces, while the second damping coefficient may be optimized to deal with easy self-starting and torque generation.

[0120] Each blade 120 has a leading edge LE and a trailing edge TE. The rotor 100 defines an advancing rotational direction, in this case a rotational direction indicated by arrow RD in which blade 120 will move in a direction parallel to a direction from trailing edge TE to leading edge LE. Each blade 120 can pivot in two rotational directions about respective pivot axis 130 relative to the blade support structure 110. The rotational direction corresponding to the advancing rotational direction RD will be referred to as the first rotational direction FRD, and the rotational direction in opposite direction to the advancing rotational direction will be referred to as the second rotational direction SRD.

[0121] In an embodiment, the first damping coefficient is larger than the second damping coefficient. The second damping coefficient is preferably substantially zero.

[0122] In the example of Figs. 1-3, each blade 120 is pivotally connected to the blade support structure 110 at or near its leading edge LE, and the pitch regulating mechanism is arranged between the blade support structure and a trailing edge TE side of the blade 120.

[0123] Although other locations are possible as well, the vertical axis turbine 1 of Figs. 5-7 may include a generator having a stator part arranged on the top support 201 and a rotor part arranged on the rotor 100. An advantage thereof is that the rotor 100 can be directly connected to the generator without requiring a transmission thereby reducing the number of moving parts. Another advantage is also that an impedance of the generator does not increase with the same transmission factor which would limit the available generator power.

[0124] Figs. 8A and 8B schematically depict a cross-sectional view of two different embodiments of a generator 300 suitable for a vertical axis turbine similar to Fig. 5. Schematically indicated are a portion of a rotor 100 and a top support 201 of a frame for supporting the rotor. Between the rotor 100 and the top support 201, a bearing is provided comprising a first bearing portion 202a and a second bearing portion 202b allowing the rotor 100 to rotate about a vertical axis VA and transferring at least a portion of the horizontal and vertical loads to the top support 201.

[0125] Referring to Fig. 8A, the generator 300 here includes one stator part 310 mounted to the top support 201 and extending in radial direction from the top support 201. The stator part preferably has an arrangement of stator windings, which can either have separate coils or separate connected spools, or an integral woven arrangement of windings.

[0126] Generator 300 further comprises two rotor parts 320 connected to each other via a connecting element 320a. Each rotor part 320 comprises a plurality of magnets 321 providing a magnetic flux direction between the lower rotor part 320 and the upper rotor part 320 that is parallel to the vertical axis VA. Such a generator may thus be referred to as axial flux generator.

[0127] Referring to Fig. 8B, the generator 300 here includes two stator parts 310 mounted to the top support 201 and extending in radial direction from the top support 201. The stator parts preferably have an arrangement of stator windings, which can either have separate coils or separate connected spools, or an integral woven arrangement of windings. The stator parts 310 are stacked in height direction.

[0128] Generator 300 further comprises three rotor part 320, wherein the upper rotor part 320 and the middle rotor part 320 are connected to each other via a connecting element 320a, and wherein the middle rotor part 320 and the lower rotor part 320 are connected to each other via a connecting element 320b. Each rotor part 320 comprises a plurality of magnets 321 providing a magnetic flux direction between the rotor parts 320 that is parallel to the vertical axis VA. Such a generator may thus be referred to as axial flux generator.

[0129] The middle rotor part 320 is shared by both the upper stator part 310 and the lower stator part 310, meaning that the magnets are used to provide a flux between the upper rotor part 320 and the middle rotor part 320, and to provide a flux between the middle rotor part 320 and the lower rotor part 320. In such a case, the number of rotor parts is the number of stator parts plus one, but it is also conceivable to use a configuration wherein the number of stator parts is the number of rotor parts plus one.

[0130] The possibility to stack rotor parts 320 and stator parts 310 in the generator 300 allows to match the generator to the expected generated torque by the vertical axis turbine and / or provides the possibility to maximize the generator diameter allowing to maximize the number of pole pairs on the rotor and the length of stator windings. Another advantage may be that a more homogenic magnetic field can be provided between the rotor parts 320 and the stator parts 310 reducing the need for electrical steel and thus reduces the required torque for startup.

[0131] The coils in the stator parts 310 may be fabricated using PCB's and / or corresponding production methods such as automated stator winding production methods, or coil bending machinery, which may provide the advantage that the coils and / or the production process can be more easily optimized.

[0132] The generator design described above may also allow the use of weaker (flux density) magnets compared to Neodymium permanent magnets.

[0133] The generator 300 defines a generator diameter D3, which will alternatively be referred to as third diameter D3. A larger diameter D3 is preferred. A main advantage thereof is that there is more space for coils and magnets. Another advantage is that a relative speed between rotor parts and stator parts gets larger resulting in quicker flux changes and thus higher voltages. A further advantage may be that the larger the third diameter D3, the more the movement of the rotor part relative to a stator part resembles a linear movement which increases efficiency.

[0134] The third diameter D3 is here at least 90%, preferably at least 95%, more preferably at least 100% of the second diameter D2. The rotor 100 may define a fourth diameter, e.g. twice the distance R4 between a pivot axis 130 of a blade 120 and the vertical axis VA of the rotor 100. In an embodiment, the third diameter D3 is at least 10% of the fourth diameter, preferably at least 15%.

[0135] The vertical axis turbine using a generator as described above allows to optimize the size of the generator and the size and characteristics of the rotor and blades to the wind conditions at a specific location. High wind locations may need a relatively small rotor and / or blades in combination with a larger generator (e.g. more stator and rotor parts stacked on top of each other), as for instance of the type disclosed in Figs. 1-3, while low wind locations may need a relatively large rotor and / or blades in combination with a smaller generator, as for instance of the type disclosed in Figs. 5-7. This shows that this type of vertical axis turbine is easily scalable and suitable for all kind of use-cases.

[0136] As shown in Figs. 1-3, the blades 120 of the vertical axis turbine may have a plate-like construction that can bend about a vertical axis due to fluid dynamic forces and forces exerted on the blade by the pitch regulating system. This allows to temporarily have a wing-shaped blade, i.e. a positive or negative cambered air foil which may increase the generated lift forces by a factor of e.g. 2, during some portions of the rotation thereby allowing to optimize the generated lift forces in dependence of wind speed and rotation speed of the rotor.

[0137] A bending stiffness of such a blade can be adjusted using substantially arranged strips on the blade 120, which strips may extend horizontally. To prevent disruption of the air flow around the blades 120, the beams 112, 114 and 116 may be provided with an air flow guide 150 to improve the aerodynamic behavior.

[0138] Although the blades 120 have a substantially semi-circular shape, other shapes, e.g. rectangular, are also envisaged.

[0139] The vertical axis turbine may be used on a floating vessel or floating construction. When a plurality of vertical axis turbines are arranged on such a floating vessel or construction, it is possible to allow some vertical axis turbines to rotate in one direction and to allow other vertical axis turbines to rotate in an opposite direction, so that the torques applied to the floating vessel or construction at least partially cancel and it may for instance be easier to maintain a predetermined orientation with the floating vessel or construction. Preferably, half the vertical axis turbines are configured to rotate in one direction and the other half of the vertical axis turbines are configured to rotate in opposite direction provided they are all identical in size and thus in principle all generate the same amount of torque. Other ratios may apply when the vertical axis wind turbines do not generate the same torque when subjected to the same conditions or are not subjected to the same conditions and therefore do not generate the same torque.

[0140] In an embodiment, varying respective torques generated by the plurality of vertical axis turbines can be used to navigate the floating vessel by means of torque vectoring.

[0141] In an embodiment, to maintain the floating vessel in a position, a floating anchor or static anchor or controlled mobile anchor can be arranged at the upwind direction of the floating vessel.

[0142] Although in the above-described advantages only one rotor is shown for a vertical axis turbine, it is also envisaged that at least two rotors 100 are arranged above each other and supported by the frame 200. Each rotor may have its own generator or rotors may be coupled to each other to share a generator. Figs. 9 and 10 schematically depicts a portion of a rotor of a vertical axis turbine according to a further embodiment of the invention. Fig. 9 depicts a perspective view and Fig. 10 depicts a bottom view. It is noted that although the rotor of Figs. 9 and 10 is described as a further embodiment, the rotor may also be used to replace the rotor in the vertical axis turbine of Fig. 1 or the rotor in the vertical axis turbine of Fig. 5.

[0143] Shown in Figs. 9 and 10 are a rotor part 202c of a bearing, a blade support structure 110 and a blade 120. The blade support structure 110 extend from the rotor part 202c of the bearing to the blade 120 to connect the blade 120 to the rotor part 202c of the bearing.

[0144] The blade 120 in the embodiment of Figs. 9 and 10 includes a mast 120a, two pairs of curved booms 120b arcuately connected athwart of the mast 120a, and a sail 120c secured therebetween. An advantage of this configuration is that the booms 120b can be used to connect the blade 120 to the blade support structure 110 and the sail 120c is relatively free to deform under dynamic fluid loads similar to a sail used for surfing.

[0145] The sail 120c includes two openings 120d allowing a connection to be made between the respective booms 120b of each pair of booms 120b, and to connect this connection to the blade support structure 110 while defining a pivot axis 130 for the blade 120 relative to the blade support structure 110. An advantage of the openings 120d is that the pivot axis 130 may then be located close to or coincide with the sail 120c without interfering with deformation / motion of the sail 120c.

[0146] A further advantage of the openings 120d is that the blade support structure 110 can extend through these openings to reach the opposite side of the blade 120 thereby allowing to provide a respective damper 140 between the blade support structure 110 and both respective booms 120b of each pair of booms 120b.

[0147] In this embodiment, four dampers 140 are provided in total as part of damper system of a pitch regulating mechanism arranged between the blade support structure 110 and the blade 120 to regulate the pitch of the blade 120 in dependence of fluid dynamic forces acting on the blade 120. The damper system is configured to provide a first damping coefficient in a first rotational direction of the blade relative to the blade support structure and a second damping coefficient in a second rotational direction of the blade relative to the blade support structure.

[0148] The mast 120a of the blade 120 forms the leading edge LE of the blade 120. The edge of the sail 120c opposite the mast 120a forms the trailing edge TE of the blade 120. In this embodiment, the mast 120a, and thus the leading edge LE, has a curved shape and the trailing edge TE extends substantially vertical. As a result, a width of the sail 120c at the upper and lower ends of the sail 120c is smaller than at a center of the sail 120c.

[0149] The rotor defines an advancing rotational direction, in this case a rotational direction indicated by arrows RD in which blade 120 will move in a direction substantially parallel to a direction from trailing edge TE to leading edge LE. The blade 120 can pivot about the pivot axis 130 in a first rotational direction and a second rotational direction that is opposite to the first rotational direction. The first rotational direction is in the same direction as the advancing rotational direction RD, such that upon a rotation in the first rotational direction the trailing edge TE moves away from the center of the rotor.

[0150] The first damping coefficient is larger than the second damping coefficient. The second damping coefficient may even be substantially zero.

[0151] The blade support structure 110 includes in this embodiment four beams or rods Illa, 111c, 112a, and 112c. The beams Illa and 111c together form an arm portion 111 and the beams 112a and 112c together form an arm portion 112. The arm portions 111 and 112 together form an arm extending between the rotor part 202c of the bearing and the blade.

[0152] The arm portion 111 extends from a mounting position 117 on the rotor part 202c of the bearing to the pivot axis 130 of the blade 120. The arm portion 112 extends from a mounting position 118 on the rotor part 202c of the bearing to the pivot axis 130 of the blade 120. Hence, seen in bottom view (or top view), e.g. as shown in Fig. 10, the arm portions 111, 112 are mounted at a distance from each other to the rotor part 202c of the bearing and converge towards the blade 120.

[0153] Beams Illa and 112a extend from the rotor part 202c of the bearing to the upper pair of booms 120b. Beams 111c and 112c extend from the rotor part 202c of the bearing to the lower pair of booms 120b. Hence, beams Illa and 111c diverge from the rotor part 202c towards the blade 120. Similarly, the beams 112a and 112c diverge from the rotor part 202c towards the blade 120. The arm formed by arm portions 111 and 112 substantially has the shape of a tetrahedron with one of its edges, in this embodiment the edge from mounting position 117 to mounting position 118, extending horizontally, and an opposite edge, in this embodiment the edge between the two openings 120d, extending vertically.

[0154] In order to increase the rigidity of the arm, cross beams CB1, CB2 may be directly or indirectly provided between the beams forming the arm. In this embodiment, a cross beam CB1 is provided between beams Illa and 112a, and a cross beam CB1 is provided between beams 111c and 112c. These cross beams CB1 provide a direct link between the beams. In addition, two cross beams CB2 are provided between the cross beams CB1 thereby providing an indirect link between the beams Illa and 112a on the one hand and the beams 111c and 112c on the other hand.

[0155] Fig. 11 depicts a damping regulating device 400 to regulate a first damping coefficient and / or a second damping coefficient of a damper system of a vertical axis turbine according to an embodiment of the invention.

[0156] Fig. 11 depicts the damping regulating device 400 as part of a vertical axis turbine identical or similar to the vertical axis turbine shown partially in Figs. 9 and 10. Depicted in Fig. 11 are a portion of the blade support structure 110 extending through an opening 120d in the sail 120c, a boom 120b extending at a side of the sail 120c that is opposite the rotor part 202c of the bearing, and a damper 140 extending between the blade support structure 110 and the boom 120b. The damping regulating device 400 includes a valve 401, a mass 402, an arm 403, and a spring 404. The arm 403 is rotatably attached to the blade support structure 110 to rotate about a rotation axis 405. The mass 402 is arranged at a free end of the arm 403 to rotate along with the arm 403. The spring 404, in this embodiment embodied as a torsion spring 404 urges the arm 403 to a rest position as shown in Fig. 11. From the rest position, the arm 403 is able to rotate in a direction indicated by arrow AR such that the mass 402 is at a larger distance from a center of the corresponding rotor of the vertical axis turbine. When the mass 402 rotates in the direction indicated by arrow AR, the spring force applied by the spring 404 to the arm 403 will increase. Hence, when the rotational speed of the rotor increases, a larger force is required to keep the mass 402 in a circular motion. When the force applied by the spring 404 is not sufficient to keep the mass 402 in a circular motion synchronous to the rotor, the mass 402 will rotate outwards resulting in an increase of the force applied by the spring 404 until the force applied by the spring 404 is sufficient or until a maximum rotation of the mass 402 is reached or until the arm has rotated to a horizontal orientation and the required force is provided through other components. Hence, the rotational position of the mass 402 is dependent on the rotational speed of the rotor.

[0157] The valve 401 is connected to the arm 403 and thus controlled in dependency of the rotational position of the mass 402. The damping regulating device 400 is configured such that the aperture of the valve 401 is reduced with increasing speed of the rotor thereby increasing the first and / or second damping coefficient of the damper system. This allows to control the behavior of the vertical axis turbine with increasing speed and may prevent damage to the vertical axis turbine when a predetermined rotational speed is exceded by adjusting the damper system to provide maximum damping.

[0158] Although maybe not explicitly mentioned, the vertical axis turbine according to the invention may be used with air as flowing medium and may then be referred to as a vertical axis wind turbine, and with water or other liquid as flowing medium and may then be referred to as vertical axis water turbine or vertical axis hydro turbine. Although in the above described embodiments reference is made to arms and subarms as part of the blade support structure, it is explicitly noted here that embodiments described by using a single arm per blade with subarms may be similar to embodiments described by using multiple arms per blade.

[0159] It is noted that alternatively the frame of the vertical axis turbine may be described as comprising: six legs, a top support with three mounting positions for the six legs, and - a base support with three mounting positions for the six legs, wherein the three mounting positions of the base support, the three mounting positions on the top support and the six legs form a prismatoid with all faces being triangles, and wherein the area of the top face is smaller than an area of the bottom face.

Claims

C L A I M S1. A vertical axis turbine comprising a rotor and a frame for supporting the rotor, said frame comprising: a top support with a bearing for the rotor; a base support; and six rigid legs, wherein the six rigid legs are attached in pairs to three mounting positions on the base support, wherein the six rigid legs are attached in pairs different from the pairs formed at the base support to three mounting positions on the top support, wherein the three mounting positions on the base support lie on a first virtual circle with a first diameter, wherein the three mounting positions on the top support lie on a second virtual circle with a second diameter, and wherein the first diameter is larger than the second diameter.

2. A vertical axis turbine according to claim 1, wherein the first diameter is at least twice as large as the second diameter.

3. A vertical axis turbine according to claim 1, wherein the rotor comprises: a blade support structure extending from the bearing at the top support, at least two blades coupled to the blade support structure at a distance from the bearing, wherein the blade support structure includes a pair of beams for each blade extending between the corresponding blade and the bearing, and wherein the beams are attached in pairs to respective mounting positions on or near the bearing, each pair being formed by a beam associated with one blade and a beam associated with another blade.

4. A vertical axis turbine according to claim 1, further comprising a generator having a stator part arranged on the top support and a rotor part arranged on the rotor.

5. A vertical axis turbine according to claim 4, wherein the generator has a third diameter that is at least 90% of the second diameter.

6. A vertical axis turbine according to claim 4, wherein the generator has a third diameter, wherein the rotor has a fourth diameter, and wherein the third diameter is at least 10% of the fourth diameter, preferably at least 15%.

7. A vertical axis turbine according to claim 4, wherein the generator is an axial flux generator.

8. A vertical axis turbine according to claim 7, wherein the generator comprises at least two stator parts and at least two rotor parts stacked in height direction.

9. A vertical axis turbine according to claim 3, wherein the at least two blades are pivotally coupled to the blade support structure, wherein the rotor further comprises a pitch regulating mechanism arranged between the blade support structure and a corresponding blade to regulate the pitch of the blade in dependence of fluid dynamic forces acting on the blade, and wherein the pitch regulating mechanism comprises a damper system, wherein the damper system has a first damping coefficient in a first rotational direction of the blade relative to the blade support structure and a second damping coefficient in a second rotational direction of the blade relative to the blade support structure.

10. A vertical axis turbine according to claim 9, wherein each blade is pivotally connected to the blade support structure at or near its leading edge, and wherein the pitch regulating mechanism is arranged between the blade support structure and a trailing edge side of the blade.

11. A vertical axis turbine according to claim 10, wherein each blade has a plate-like construction that can bend about a vertical axis due to fluid dynamic forces and forces exerted on the blade by the pitch regulating system.

12. A vertical axis turbine according to claim 11, wherein each blade comprises strengthening ribs extending substantially horizontally over the plate-like construction.

13. Floating vessel comprising at least two vertical axis turbines according to claim 1, wherein the rotor of one vertical axis turbine is configured to rotate in one rotational direction and the rotor of another vertical axis turbine is configured to rotate in the opposite rotational direction.

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