Vertical Axis Wind Turbine

Abstract

The shaftless vertical axis wind turbine comprises a hub (3) and a plurality of C-shaped blades (20), each blade (20) comprising a lower radial airfoil (221) disposed on the inner frame (120) at a lower radial section (21) of the blade, a vertical airfoil (223) disposed on the inner frame (120) at a vertical section (23) of the blade, and an upper radial airfoil (222) disposed on the inner frame (120) at an upper radial section (22) of the blade, wherein at least a portion of the vertical airfoil (223) of each blade (20) is rotatable about an associated axis of rotation in a manner independent of corresponding portions of the vertical airfoils (223) of the other blades (20) to adjust the angle of attack or curvature of the associated vertical airfoil (223).

Description

[Technical Field]

[0001] The present invention relates generally to vertical axis wind turbines of the shaftless type. [Background technology]

[0002] Vertical axis wind turbines (or VAWTs) have the potential to solve the major problems that limit the widespread use of traditional horizontal axis wind turbines. To date, installing new horizontal axis installations on land or offshore has been extremely difficult. In the first case, the problem lies in the fact that windy regions where installing wind turbines is economically viable are either nearly saturated or difficult to access. In the second case, for offshore installations, the main problem is the high cost, accompanied by an uncompetitive LCOE (Levelized Cost of Energy) compared to other renewable energy sources. In fact, installing offshore wind power plants using conventional foundations requires shallow waters where the turbines can be anchored to the seabed using steel or concrete foundations. An alternative that is becoming increasingly popular in the wind industry is turbines with floating foundations. These horizontal axis turbines have three rotor blades connected to a generator nacelle mounted on top of a tubular tower slightly higher than the blade length, supported by a steel float, which is the main cost component of this type of installation.

[0003] On the other hand, vertical axis turbines have inherent advantages related to the fact that their axis of rotation is vertical.

[0004] The first result is that the generator can be placed lower, lowering the turbine's center of gravity. Furthermore, because VAWTs can receive wind from all directions, there is no need for yaw control and translation systems. Finally, because the angular momentum vector is vertical and aligned with the axis of rotation, gyroscopic stabilization of the wind turbine is achieved, reducing the angular tilt requirements compared to HAWTs.

[0005] These features make VAWTs a potentially ideal solution both for floating offshore fields (where the low center of gravity can significantly reduce foundation costs and at the same time makes it less important to keep the turbine perfectly vertical) and for onshore fields (where conventional HAWTs are not used, e.g. in urban environments with highly turbulent and discontinuous winds).

[0006] However, traditional VAWTs have received little interest from industry to date due to their low efficiency, difficulty in starting, and heavy weight compared to similarly sized HAWTs. Furthermore, they generally suffer from structural fatigue issues associated with cyclic loading on the vertical vanes and cyclic stall, limiting their performance.

[0007] To make VAWTs industrially competitive, efforts have been made both to increase efficiency and reduce periodic stall on the nearly vertical support surfaces, and to reduce mass and create vertical axis turbines without a central shaft.

[0008] An example of such a turbine is described in U.S. Pat. No. 10,054,107 B2. This turbine has a cage structure and lacks a central shaft extending between the axial ends of the cage structure. This known solution proposes the use of interpenetrating prisms to replace the central shaft, restoring the necessary rigidity to the structure. The upper three horizontal airfoils of this structure are rotated 30° in azimuth relative to the lower horizontal airfoil, reducing the shear and torsional stresses resulting from the absence of a shaft. This increases the complexity (and cost) of the vertical airfoil geometry, but does not solve the problems of structural fatigue and periodic airfoil stall that typically plague this type of wind turbine.

[0009] European Patent No. 1888917B1 is another example of a VAWT, and in one proposed configuration, two pairs of arms are angled, and there is no central shaft. It describes an aerodynamic rotor brake through the upper horizontal airfoil. Thus, the performance and structural fatigue issues of the VAWT are not solved or addressed. Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is to provide a shaftless vertical axis wind turbine solution that can at least partially overcome the drawbacks of the known art. [Means for solving the problem]

[0011] Accordingly, the present invention relates to a shaftless vertical axis wind turbine, a hub and a plurality of C-shaped blades, the blades being connected at one end to the hub and at the other end to each other by connecting elements; Each blade is a lower radial portion having a radially inner end connected to the hub; an upper radial portion having a radially inner end connected to the connecting element; a vertical portion having opposing ends connected to the radially outer ends of the lower radial portion and the upper radial portion, respectively; Each blade is a lower radial airfoil disposed on the lower radial portion of the blade; a vertical airfoil located on the vertical part of the blade; an upper radial airfoil disposed on the upper radial portion of the blade; At least a portion of the vertical airfoil of each blade is rotatable about an individual axis of rotation in a manner independent of corresponding portions of the vertical airfoils of other blades to adjust the aerodynamic angle of attack or curvature of the associated vertical airfoil.

[0012] In this description, "independently" means that the rotatable / adjustable airfoils of the blades (or rotatable / adjustable parts of the airfoils) are not connected to a single power source (actuator or set of actuators). In other words, the airfoils that are rotatable / adjustable in an independent manner from each other are each driven by an associated power source, and there is no force transmission connection between the airfoils of the different blades or between a single power source and the airfoils of the different blades.

[0013] Thus, two interrelated fronts are addressed. By eliminating the central shaft commonly found in VAWTs, mass is more efficiently redistributed and reduced, while vertical airfoils that can rotate independently about their associated rotational axis are used. The aerodynamic airfoils and associated control systems not only eliminate periodic stall and increase efficiency near the Betz limit (as is well documented in the scientific literature), but also reduce wind pressure on the structure by more than half, making it possible to eliminate the central shaft. At the same time, removing the shaft not only significantly reduces the turbine's overall mass, but also offers aerodynamic benefits, due to the absence of shaft-induced low-frequency oscillatory flow perturbations (i.e., vortex shedding) that actually make power extraction downstream of the shaft extremely inefficient. In fact, the vortex-oscillating wake generated by the shaft often generates a negligible amount of energy during the second part of the vane rotation, especially for high-stiffness turbines.

[0014] This has advantages both in terms of overall mass of the structure and in terms of efficiency and interaction of the blades with the fluid. From a structural point of view, the main role of the shaft is to unload the bending loads acting on the structure at its base. These loads are reduced by control, making the removal of the shaft sustainable. There may be reinforcing elements, such as cables or tie rods, that operate in traction or substantially in traction, and these will have a reduced cross-sectional area that introduces turbulence levels comparable to those inherent in asymptotic flow.

[0015] Structurally, this results in a more efficient use of the available mass, with a reduction in total mass. On the other hand, from the viewpoint of fluid mechanics, there are the following points: Elimination of vortex shedding perturbations downstream of the central axis (removal of wakes generated by the shaft), thereby increasing the energy extracted from the turbine and reducing vibrations (0-2 Hz) (vortices generated when the flow impinges on a cylindrical structure). Reduced vibrations and therefore reduced turbine noise. Continuity of the airfoil at both ends results in reduced losses due to induced drag. [Brief explanation of the drawings]

[0016] Further features and advantages of the wind turbine according to the invention will become more apparent from the following detailed description of embodiments of the invention, with reference to the accompanying drawings, which are given purely for illustrative and non-limiting purposes, in which: [Figure 1] 1 is a perspective view of a vertical axis wind turbine according to the present invention; FIG. [Figure 2] 2 is a tangential section along a vertical portion of a blade of the wind turbine of FIG. 1; FIG. [Figure 3] FIG. 3 is an elevational view of the vertical section of the blade of FIG. 2. [Figure 4] FIG. 2 is a perspective view of the hub of the wind turbine of FIG. 1. [Figure 5] FIG. 2 is a longitudinal cross-section of the hub of the wind turbine of FIG. 1. [Figure 6] FIG. 2 is a plan view of the hub of the wind turbine of FIG. 1. [Figure 7] FIG. 2 is a plan view of an upper corner of a blade of a wind turbine. [Figure 8] 2 is a cross-sectional view of an upper connecting element of a blade of the wind turbine of FIG. 1. [Figure 9] 2 is a cross-sectional view of an upper connecting element of a blade of the wind turbine of FIG. 1. [Figure 10] FIG. 2 is a simplified perspective view of the wind turbine of FIG. 1 with a reinforcing tie rod. [Figure 11]FIG. 2 is a simplified plan view of the wind turbine of FIG. 1 with reinforcing tie rods. [Figure 12] FIG. 1 is a perspective view of another vertical axis wind turbine according to the present invention. [Figure 13] FIG. 13 is a cross-sectional view of the airfoil of the wind turbine of FIG. 12. [Figure 14] FIG. 13 is a perspective view showing details of the wind turbine of FIG. 12. [Figure 15] FIG. 10 is a plan view of an additional vertical axis wind turbine according to the present invention. [Figure 16] FIG. 1 is a perspective view of another vertical axis wind turbine according to the present invention. [Figure 17] FIG. 17 is a side view of a detail of the wind turbine of FIG. 16. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1-11, a vertical axis wind turbine is shown and generally designated 1. The wind turbine 1 comprises a hub 3 mounted on a shaft 5, which is rotatable about an axis z that is perpendicular to the shaft 5. The wind turbine further comprises an axial generator 7 configured to convert the mechanical energy of the rotating wind turbine into electrical energy. The axial generator 7 comprises a rotor integrated with the wind turbine hub 3 and equipped with permanent magnets, and a stator with windings (not shown), integrated with the shaft 5, and integrated with the ground. An inclined ball bearing 8 is interposed between the rotor and the stator / shaft (see FIG. 5). The use of an axial generator has the advantage of compactness, but the invention is not limited thereto, and the wind turbine may comprise other systems for converting mechanical energy into electricity.

[0018] The wind turbine hub 3 further comprises a lower connection plate 9, via which the wind turbine blades 20 are connected to the hub 3. The hub 3 further comprises an outer cover 11 (shown in dotted lines in Figure 1) that is attached to the rotor of the generator 7 and encloses the lower connection plate 9 and other components that will be described below.

[0019] The wind turbine 1 further comprises a number of C-shaped blades 20 (three blades in the example shown). The blades 20 are connected at one end to the hub 3 and at the other end to each other by an upper central connecting element 30. The blades 30 together form a cage structure without a central shaft connecting the hub 3 to the connecting element 30. In this sense, the wind turbine 1 is said to be of the "shaftless" type. The centerline of each blade 20 lies in a radial plane. The blades 20 are equally spaced azimuthally relative to the axis z of the wind turbine.

[0020] Thus, each of the blades 20 has a lower radial portion 21 having a radially inner end 21a connected to the hub 3, an upper radial portion 22 having a radially inner end 22a connected to the connecting element 30, and a vertical portion 23 having opposite ends 23a, 23b connected to the radially outer end 21b of the lower radial portion 21 and the radially outer end 22b of the upper radial portion 22, respectively. The radial portions 21, 22 extend substantially along a radial direction relative to the axis z, or more generally, along a direction including a radial component (e.g., the extension direction of the radial portions 21, 22 may include an azimuthal component; see FIG. 15 ). In particular, the radial portions 21, 22 extend along a horizontal radial direction. The vertical portion 23 extends substantially along a vertical direction, or more generally, along a direction including a vertical component. Preferably, the vertical portion 23 extends along a precisely vertical direction.

[0021] Preferably, each of the radial portions 21, 22 and the vertical portion 23 of each blade 20 is straight. The radial portions 21, 22 are connected to the vertical portion 23 via respective corner portions 24, 25.

[0022] From a structural point of view, each blade 20 comprises an inner frame 120 extending along the entire extension of the blade 20, i.e., along the lower radial section 21, the vertical section 23 and the upper radial section 22 of the blade 20. In particular, the inner frame 120 comprises a part of the lower radial frame 121, a part of the vertical frame 123 and a part of the upper radial frame 122. The lower radial frame section 121 extends from the radially inner end 21a of the lower radial section 21 of the blade to the lower corner section 24 of the blade. At the radially inner end 21a of the lower radial section 21 of the blade, the lower radial frame section 121 is hinged to a lower connecting plate 9 arranged inside the hub 3. In particular, it is hinged along a horizontal hinge axis oriented in the tangential direction. At the lower corner 24 of the blade, the lower radial frame section 121 is hinged to the vertical frame section 123 (note that the hinge 24a between the lower radial frame section 121 and the vertical frame section 123 is configured to prevent rotation of the vertical frame section 123 relative to the lower radial frame section 121 towards the turbine inboard side, or at most allows rotation within a very small angular range (see Figure 3)). The vertical frame section 123 extends from the lower corner 24 to the upper corner 25 of the blade. At the upper corner 25, the vertical frame section 123 is hinged to the upper radial frame 122 (note that the hinge 25a between the upper radial frame section 122 and the vertical frame section 123 is configured to prevent rotation of the vertical frame section 123 relative to the upper radial frame section 122 towards the turbine inboard side, or at most allows rotation within a very small angular range (see Figure 3)). The upper radial frame part 122 extends from the upper corner part 25 to the radially inner end 22a of the upper radial section 22 of the blade. At the radially inner end 22a of the upper radial section 22 of the blade, the upper radial frame part 122 is hinged to an upper connecting plate 39 arranged within the connecting element 30. In particular, it is hinged along a tangentially oriented horizontal hinge axis. An outer cover 39a is fixed to the upper connecting plate 39 and encloses control components as described below.

[0023] Each blade 20 of the wind turbine further comprises a number of airfoils arranged on the inner frame 120. In particular, it comprises a lower radial airfoil 221 arranged on the lower radial section 21 of the blade, a vertical airfoil 223 arranged on the vertical section 23 of the blade, and an upper radial airfoil 222 arranged on the upper radial section 22 of the blade. Additional airfoils 224, 225 are arranged on the corner sections 24, 25 of the blade. In Figure 1, one airfoil of the blade 20 has been removed.

[0024] The lower radial airfoil 221 is rotatable about an axis of rotation extending in the longitudinal direction of the lower radial airfoil, i.e., in the radial direction. In the illustrated example, this axis of rotation is defined by the lower radial frame portion 121. The vertical airfoil 223 is rotatable about an axis of rotation zP extending in the longitudinal direction of the vertical airfoil 223, i.e., in the vertical direction (see Figures 2, 3, and 7). In the illustrated example, this axis of rotation is defined by the vertical frame portion 123. Referring to Figure 2, in the illustrated example, the central portion of the vertical frame portion 123 is tubular, and bearings 123a supporting individual rotation pins 123b are disposed inside thereof, which are rigidly connected to the vertical airfoil 223 via connecting members 123c. The connecting members 123c are disposed through individual slots cut into the wall of the tubular vertical frame portion 123. This method of connection between the frame portion and the airfoil portion is merely an example and is not essential to the present invention.

[0025] The upper radial airfoil 222 is rotatable about an axis of rotation extending in the longitudinal direction, i.e., the radial direction, of the upper radial airfoil 222. In the illustrated example, this axis of rotation is defined by the upper radial frame portion 122. The airfoils 224, 225 located at the corner portions 24, 25 of the blade are fixed.

[0026] The wind turbine 1 is provided with control mechanisms on-board for moving the movable airfoils and adjusting their trim according to operating conditions.

[0027] The first control mechanism 40, shown in Figures 4-6, is attached to the blade's lower radial airfoils 221 and is operable to adjust the aerodynamic angle of attack of these airfoils to stabilize bending moments at the bearing or connection joint between the airfoils. Adjusting the aerodynamic angle of attack of the lower radial airfoils can induce aerodynamic loads adapted to counteract wind-induced drag moments on the structure. In the illustrated example, the first control mechanism 40 includes an eccentric plate 41 that rotates integrally with the lower connection plate 9. A plurality of L-shaped control arms 42, one for each lower radial airfoil 221, are hinged at one end to the eccentric plate 41 about respective vertical hinge axes. Each of the control arms 42 is also hinged to the lower connection plate 9 about an associated vertical axis located at 43 (see Figure 6). The opposite end of each control arm 42 is articulated to the associated lower radial airfoil 221 via a connecting rod 44. The connecting rod 44 is connected to the associated lower radial airfoil 221 eccentrically with respect to the adjustment axis y1 of the lower radial airfoil 221. Rotation of the eccentric plate 41 about the vertical axis z relative to the connecting plate 9 thus results in rotation of the lower radial airfoil 221 about the respective adjustment axis y1 relative to the respective lower radial frame part 121. In the illustrated example, a servo motor 45 configured to drive the eccentric plate 41 in rotation relative to the connecting plate 9 is arranged inside the hub 3. The eccentricity of the eccentric plate 41 about the vertical axis z is also adjustable. For this purpose, the eccentric plate 41 is arranged to be translatable along a guide relative to the connecting plate 9, and a second servo motor 46 is arranged inside the hub 3 and drives the eccentric plate 41 in translation relative to the connecting plate 9. The two servo motors 45, 46 allow the eccentricity and position of the eccentric plate to be set, thereby adjusting the amplitude and phase of the sine wave describing the respective lower radial airfoil according to the wind speed and direction.

[0028] An induction coil 47 (through which electrical energy is transported from the outside to the rotating part) is located inside the hub 3 for powering and controlling the servo motors 45, 46 (and any other electrical or electronic devices on board the wind turbine). Alternatively, brushing contacts can be used. The hub 3 also houses the microprocessor and electronics required to control the trim of the moving surfaces (not shown). According to an alternative embodiment, trim adjustment of the lower radial vanes 221 may be manual, in which case the servo motors 45, 46 and associated controls and power supplies may be absent.

[0029] 3 and 7, a second control mechanism 50 is attached to each of the blade's vertical airfoils 223 and is operable to rotate (aerodynamic angle of attack adjustment) each vertical airfoil 223 independently of the other in order to maximize power extraction and minimize fatigue loads. In the illustrated example, the second control mechanism 50 comprises a stepper motor 51 integrally disposed with the vertical frame portion 123 and a connecting rod crank linkage 52 having one end 52a integral with the output shaft of the stepper motor 51 and the other end 52b hingedly connected to the vertical airfoil 223. The adjustment axis is designated y2 in FIGS. 8 and 9.

[0030] 8 and 9, a third control mechanism 60 is attached to each of the blade's upper radial airfoils 222 and, similar to the first control mechanism 40, is operable to adjust the angle of attack of these airfoils to stabilize bending moments at the bearings and connection joints. Adjusting the angle of attack of the upper radial airfoils can also induce aerodynamic loads adapted to significantly reduce wind-induced drag moments on the structure. In the illustrated example, the third control mechanism 60 is disposed within the upper connection element 30 and includes, for each upper radial airfoil 222, an associated servo motor 61 integrated with the upper connection plate 39 and an associated slot-crank assembly 62 having an end 62a integrated with the output shaft of the servo motor 61 and an opposite end 62b integrated with the upper radial airfoil 222.

[0031] The two types of trim control for the upper and lower radial airfoils, i.e., fully electronic control using actuators and mechanical control using two actuators to adjust phase and amplitude, may be combined as needed. For example, in one embodiment (not shown), the upper radial airfoils are rotatable independently of each other, and the lower radial airfoils are also rotatable independently of each other. In another embodiment (not shown), the upper radial airfoils are rotationally controlled by the same pair of actuators, and the lower radial airfoils are rotationally controlled by another pair of actuators.

[0032] The stepper motors mentioned above are merely examples and in general any type of actuator can be used.

[0033] The wind turbine 1 described above has an internal structure provided by the union of multiple hinged components, which minimizes shear, bending and torsional stresses on the frame, allowing it to operate in compression as much as possible, thereby increasing the operational life of the wind turbine.

[0034] Each blade 20 has hinges at its connection points to the hub 3 (more precisely, the lower connection plate 9), the connection points to the connection element 30 (more precisely, the upper connection plate 39), and the corners 24 and 25. This creates a truss equivalent to an articulated quadrilateral with a carriage at the upper end of the blade. Six degrees of freedom are thus calculated, two for each arm. However, this structural instability is compensated for by the addition of traction elements 70, specifically cables / tie rods, connecting the diagonally positioned hinges at the corners or in the center (see Figures 10 and 11). Various figures show the pins for attaching these cables or tie rods, specifically pin 39b attached to the upper connection plate 39, pins 24b and 25b attached to the hinges 24a and 25a, respectively, and pin 3b attached to the hub 3. Alternatively, the actual hinge may be replaced by a hinge constructed of a cylindrical cross section with lower bending stiffness, which behaves as a plastic hinge once it reaches its yield strength and transfers bending loads between the two parts, reducing the need for cables or tie rods.

[0035] The wind turbine 1 may also have wind direction and speed or pressure sensors (e.g., pitot anemometers, hot wire anemometers, cup anemometers, ultrasonic anemometers, LIDAR, weather vanes, temperature and humidity sensors, etc.) on the rotating blades and in the rest of the turbine, allowing for the collection of wind or pressure distribution data.

[0036] To aid in wind prediction and active control of dynamic loads, there may be accelerometers that estimate wind forces and dynamic loads on the structure.

[0037] Finally, accelerometers can be used to monitor product wear, allowing predictive maintenance to be implemented. Temperature and humidity sensors can be used to monitor material condition, along with capacitance or conductivity sensors to estimate corrosion, and strain gauges for thermal deformation and expansion.

[0038] Each controlled airfoil may have a position sensor (e.g., encoder, reed, etc.) to measure relative or absolute angular position, and there may be at least one position sensor on the generator shaft.

[0039] Each controlled airfoil may have a speed sensor (e.g., a tachometer dynamo, a differential speed sensor, etc.) to measure its angular velocity, and there may be at least one speed sensor on the generator shaft.

[0040] There may be a control system that independently controls the moving surface based on sensor information. If necessary, the turbine receives data from the outside (another turbine, the power grid), stores and processes it, uses it for the control system of the moving surface, and transmits it for statistical and monitoring purposes. A communication system with the Internet or satellite networks may thus be built into the electronics.

[0041] There may also be control over the rotational speed of the entire turbine, for example via the generator.

[0042] There may be an emergency braking system that uses a mechanical emergency brake to stop the turbine from rotating.

[0043] Strain gauges may be present to detect deformation of the blade.

[0044] 12 to 14, a second vertical axis wind turbine is shown, which differs from the previous embodiment in that it has a monocoque structure and does not have hinges at the corners or at the connection joints between the radial airfoils and the connection elements. Elements corresponding to the previous embodiment are given the same reference numerals and will not be described again.

[0045] As an example, Figure 13 shows a cross section of one of the lower radial airfoils 221. This structure reflects that of a typical semi-monocoque airfoil (note that this cross section is of an airfoil with no moving parts). Thus, the lower radial airfoil 221 includes an active skin 221a, stringers 221b, and a stiffening beam 221c joined to the skin 221 to relieve loads on the central hub. Although not shown, it is understood that the upper radial airfoil 222 and vertical airfoil 223 have a similar structure.

[0046] The above description of the turbines of Figures 1-11 also applies to semi-monocoque turbines, except that there is no frame and the adjustable airfoils are not rotatable as a whole, but only portions of these airfoils. In particular, in the illustrated example, only half of the chord 223' of each vertical airfoil 223 is rotatable about the longitudinal axis of the associated vertical airfoil 223 relative to the remainder of the associated vertical airfoil 223. This makes it possible to adjust the aerodynamic angle of attack and curvature of the vertical airfoil 223. Furthermore, at the trailing edge of each radial airfoil 221, 222, the radial airfoil 221, 222 has one or more portions 221', 222' that are rotatable about the longitudinal axis (or individual longitudinal axes) of the associated radial airfoil 221, 222 (see Figures 12 and 14). It is thus possible to adjust the aerodynamic angle of attack and curvature of the radial airfoils 221, 222 in the longitudinal section of the radial airfoils 221, 222 in which the rotatable portions 221', 222' are arranged.

[0047] Referring to Figure 15, an additional vertical axis wind turbine is shown, having a structure resulting from a combination of frame and semi-monocoque construction. In particular, in the example shown, radial airfoils 221, 222 have a monocoque structure similar to the embodiment of Figure 12 (but without adjustable parts, although adjustable parts may be present in alternative embodiments), and vertical airfoil 223 has a frame structure similar to the embodiment of Figure 1. Elements corresponding to those of the preceding embodiments are given the same reference numerals and will not be described again. What has been discussed above with respect to the turbines of Figures 1-11 and the semi-monocoque turbines of Figures 12-14 also applies to the turbine of Figure 15.

[0048] It should also be noted that the radial sections 21, 22 of the blade 20 extend along a direction that includes a radial component and an azimuthal component relative to the axis z. In this case, the axes of the radial airfoils 221, 222 are not straight, but have a helical cross section.

[0049] 16 and 17, an additional vertical axis wind turbine is shown. Elements corresponding to elements of the above-described embodiments are given the same reference numerals and will not be described further.

[0050] Similar to the embodiments described above, the turbine of Figures 16 and 17 comprises, for each blade 20, a lower radial section 21 having a radially inner end 21a connected to the hub 3, an upper radial section 22 having a radially inner end 22a connected to the connecting element 30, and a vertical section 23 having opposite ends connected to the radially outer end 21b of the lower radial section 21 and the radially outer end 22b of the upper radial section 22, respectively. Each of the sections 21, 22, 23 is fitted with an individual airfoil 221, 222, 223 and has a structure (frame, monocoque or semi-monocoque) similar to those described above, with the adjustment options described above.

[0051] Unlike the previous embodiment, the turbine of Figures 16 and 17 further comprises, for each blade 20, a second lower radial section 21' on which an associated airfoil 221' is mounted. This second lower radial section 21' has a radially inner end 21a' connected to the hub 3 and a radially outer end 21b' connected to an associated vertical section 23, possibly via an associated lower corner section 24 (if present).

[0052] As can be seen particularly in Figure 17, the second lower radial portion 21' is positioned at a different height than the (first) lower radial portion 21 and is angled relative to the first lower radial portion 21 to form a triangular or square structure rigidly connecting the hub 3 to the vertical portion 23 or, if present, the lower corner portion 24. In such a triangular or square structure, the vertical distance d between the radially outer ends 21b, 21b' of the lower radial portions 21, 21' is less than the vertical distance D between the radially inner ends 21a, 21a' of the lower radial portions 21, 21'.

[0053] In the embodiment of Figures 16 and 17, the airfoils 221, 221' of the first lower radial section 221 and the second lower radial section 221' are fixed, ie non-adjustable.

[0054] The above approach reduces shear and bending stresses, which would generally make a central shaft-less approach impractical. Thus, it is a mechanical approach that operates similarly to the embodiment involving adjusting the lower radial airfoil to stabilize the rotor and its rotational dynamics. This approach, when coupled with the towing member 70 described in connection with Figures 10-12, for example, results in full restoration of the bending stiffness of the structure. A triangular or quadrangular structure forms a truss with equivalent stiffness to two lower radial airfoil sections and with appropriate spacing between them. Thus, a structure is obtained that resists bending in a direction perpendicular to the rotation axis z, thereby significantly increasing the rotor's natural frequencies in the excited modes, without affecting the rotor's aerodynamic performance. In addition to the obvious aerodynamic advantages, this approach saves material compared to an approach using a single lower radial section with equivalent bending stiffness. Furthermore, this approach is significantly simpler to implement and control than a similar approach involving cyclical movement of the lower radial airfoil.

[0055] According to an alternative embodiment not shown, the second lower radial portion 21' may be provided with a traction member (in particular a cable or tie rod) having a radially inner end connected to the hub 3 and a radially outer end connected to the associated vertical portion 23, this being possible via the associated lower corner portion 24 (if present).

Claims

1. A shaftless vertical-axis wind turbine, The device comprises a hub (3) and a plurality of C-shaped blades (20), the blades being connected to the hub (3) at one end (21a) and connected to each other at the other end (22a) by a connecting element (30), Each blade (20) - A lower radial portion (21) having a radially inward end (21a) connected to the hub (3), - An upper radial portion (22) having a radially inward end (22a) connected to a connecting element (30), - A vertical section (23) having opposing ends connected to the radially outer end (21b) of the lower radial section and the radially outer end (22b) of the upper radial section (22), respectively. Each blade (20) - A lower radial airfoil (221) is positioned on the lower radial section (21) of the blade, - A vertical airfoil (223) positioned on the vertical section (23) of the blade, - The blade comprises an upper radial airfoil (222) positioned on the upper radial portion (22) of the blade, A shaftless vertical-axis wind turbine in which at least a portion of the vertical airfoil (223) of each blade (20) is rotatable around a related axis of rotation in a manner independent of the corresponding portion of the vertical airfoil (223) of other blades (20), and the angle of attack or curvature of the related vertical airfoil (223) can be adjusted.

2. The aforementioned lower radial portion (21) is the first lower radial portion (21), Each blade (20) is further provided with an associated airfoil (221') or traction member and comprises a second lower radial portion (21') having a radially inner end (21a') connected to the hub (3) and a radially outer end (21b') connected to the associated vertical portion (23), The second lower radial section (21') is positioned at a different height from the first lower radial section (21) and is angled relative to the first lower radial section (21), thereby forming a triangular or quadrilateral structure that rigidly connects the hub (3) to the associated vertical section (23) or to the lower corner section (24) of the blade interposed between the lower radial sections (21, 21') and the associated vertical section (23). The wind turbine according to claim 1, wherein the vertical distance (d) between the radially outer ends (21b, 21') of the lower radially moving portion (21, 21') is smaller than the vertical distance (D) between the radially inner ends (21a, 21a') of the lower radially moving portion (21, 21').

3. The wind turbine according to claim 1, wherein at least a portion of at least one of the lower radial airfoils (221) and upper radial airfoils (222) of each blade (20) is rotatable around a related axis of rotation as needed, independently of the corresponding portion of the lower radial airfoil (221) or upper radial airfoil (222) of the other blade (20), and the angle of attack or curvature of the related lower radial airfoil (221) or related upper radial airfoil (222) can be adjusted.

4. The lower radial portion (21), vertical portion (23), and upper radial portion (22) of each blade are straight. The lower corner portion (24) of the blade is interposed between the lower radial portion (21) and the vertical portion (23) of each blade. The upper corner portion (25) of the blade is interposed between the upper radial portion (22) and the vertical portion (23) of each blade. The wind turbine according to claim 1, wherein the lower corner portion (24) and the upper corner portion (25) are curved.

5. The wind turbine according to claim 4, wherein each blade further comprises a lower corner airfoil (224) and an upper corner airfoil (225) positioned at the lower corner (24) and upper corner (25) of the blade, respectively.

6. The wind turbine according to claim 4, further comprising a plurality of traction members (70) stretched between related corner portions (24, 25) of different blades, or between at least one of the corner portions (24, 25) of each blade and at least one of the hub (3) and the connecting element (30), or between the hub (3) and the connecting element (30), to increase the rigidity of the wind turbine.

7. The radially outer ends of the lower radial portion (21) and upper radial portion (22) of each blade are connected to the associated vertical portion (23) by individual hinges (24a, 25a) located on the associated lower corner portion (24) and associated upper corner portion (25), respectively. The wind turbine according to claim 4, wherein the radially inner ends of the lower radial portion (21) and upper radial portion (22) of each blade are hinged to the hub (3) and connecting element (30), respectively.

8. The wind turbine according to any one of claims 1 to 7, further comprising a control mechanism (50) associated with each of the vertical airfoils (223) of the blades, which is operable to adjust the angle of attack or curvature of the vertical airfoils (223) independently of each other by the rotation of at least a portion of the vertical airfoils (223) of each blade (20).

9. The blade further comprises a control mechanism (60) associated with each of the upper radial airfoils (222) or lower radial airfoils (221) and located within a connecting element (30) or within a hub (3), The wind turbine according to claim 3, wherein the control mechanism (60) is operable to independently adjust the angle of attack or curvature of the upper radial airfoil (222) or the lower radial airfoil (221) by the rotation of at least a portion of at least one of the lower radial airfoil (221) and the upper radial airfoil (222) of each blade (20).

10. The system further comprises a control mechanism (40) associated with the lower radial airfoil (221) or upper radial airfoil (222) of the blade, and located within the hub (3) or within the connecting element (30), The wind turbine according to claim 3, wherein the control mechanism (40) is operable to adjust simultaneously the angle of attack or curvature of the lower radial airfoil (221) or the upper radial airfoil (222) by the rotation of at least a portion of at least one of the lower radial airfoil (221) and the upper radial airfoil (222) of each blade (20).

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