Wind turbine

Abstract

The invention relates to a wind turbine (10) which comprises a mast (11) rotatable about a vertical axis (18), a wing system (12, 14) attached to the mast in order to rotate it, and a generator (17). In this wind turbine: - the mast is retained only by a pivot link (16) having a vertical axis, - the wing system comprises: - a lower stage (14), near the pivot link, comprising two coplanar blades (15) that are symmetrical with respect to the axis of rotation; - an upper stage (12), away from the pivot link, comprising two coplanar blades (13) that are symmetrical with respect to the axis of rotation; - the plane of the blades of the upper stage forms an angle of between 70° and 110° with the plane of the blades of the lower stage; and - the moments, relative to the pivot link, of the maximum forces exerted by a constant wind on the blades of the two stages during one revolution of the mast, are substantially equal.

Description

[0001] DESCRIPTION

[0002] TITLE OF THE INVENTION: WIND TURBINE

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The present invention relates to a wind turbine. It applies, in particular, to the generation of electrical energy at sea ("offshore") or on land.

[0005] STATE OF THE ART

[0006] Today, efforts are underway to install offshore wind turbines because the wind is stronger and more consistent there, as it is less affected by the seabed. At sea, wind turbines are generally anchored to the seabed in shallow water, on the order of a few tens of meters: these are called "fixed-bottom" turbines. However, the number of suitable wind farm sites in shallow waters is limited. Conversely, in most other seas and oceans, the depth increases very rapidly with distance from the coast, making the use of fixed-bottom turbines impractical.

[0007] There are now plans to move wind turbines further from the shore by supporting them on floating platforms. These floating turbines have a virtually no visual impact, allowing for the installation of larger, and therefore more powerful, turbines and larger wind farms, thus avoiding the uncontrolled proliferation of installations and reducing the number of underwater cables needed to bring the electricity produced to the shore.

[0008] For economic reasons, it is preferable to increase the power output of each deployed wind turbine to maximize yields. This creates new technical challenges. Indeed, unlike fixed-bottom turbines, these turbines are larger (two to three times larger), can move relative to the seabed, and are sensitive to, among other things, the horizontal forces of the wind on the sails, the horizontal forces of the current on the floating support structure, the alternating horizontal and vertical forces of waves and currents, the restoring forces of the mooring lines (horizontal and vertical), the buoyant force on the floats, and the forces of gravity on all components. The type of mooring used represents a significant portion of the total investment for a floating offshore wind turbine and also ensures its reliability.Furthermore, technical problems are common to floating platform wind turbines, fixed-bottom wind turbines, and onshore wind turbines. The main types of wind turbines used are horizontal-axis wind turbines (known as HAWT, an acronym for Horizontal Axis Wind Turbine) and vertical-axis wind turbines (known as VAWT, an acronym for Vertical Axis Wind Turbine). VAWT turbines generally have lower performance (efficiency) than HAWT turbines. The significant length of the blades relative to their swept area generally necessitates heavier rotors than those used for HAWT turbines. Moreover, the radial and tangential aerodynamic forces exerted on each blade of a VAWT turbine fluctuate with each revolution of the blade due to the cyclic variation in their angle of attack. These variable forces thus create unsteady loads on the structure.These loads cause fatigue and require oversizing the blades to achieve long service lives.

[0009] PRESENTATION OF THE INVENTION

[0010] The present invention aims to remedy all or part of these drawbacks.

[0011] It proposes a vertical axis wind turbine equipped with a cantilever type rotor with only one support point and a pivot joint located at the lower part of the rotor and a mast supporting the blades up to their upper end.

[0012] BENEFITS PROVIDED

[0013] The invention aims to overcome all or part of the disadvantages of the prior art described above.

[0014] To this end, according to a first aspect, the present invention relates to a wind turbine comprising a mast rotating about a vertical axis of rotation, a sail fixed to the mast to drive it in rotation, and a generator powered by the rotation of the mast, in which:

[0015] - the mast is held around its axis solely by a pivot joint with a vertical axis,

[0016] - the sail area includes:

[0017] - a lower stage, close to the pivot joint, comprising two coplanar blades symmetrical with respect to the axis of rotation, - an upper stage, far from the pivot joint, comprising two coplanar blades symmetrical with respect to the axis of rotation,

[0018] - the plane of the upper stage blades forms an angle between 70° and 110° with the plane of the lower stage blades,

[0019] - the moments, with respect to the pivot joint, of the maximum forces exerted by a constant wind on the blades of the two stages during one revolution of the mast, are substantially equal, the sum of these moments being substantially constant during the rotation of the wind turbine.

[0020] Thus, during a complete revolution of the mast around its axis, the moment of the forces exerted by the action of a constant wind on the blades of the two stages passes through four approximately equal maxima and four minima less than 30% lower than the maxima. Fatigue in the pivot joint is therefore limited, as is fatigue in the mechanical interface between this pivot joint and the wind turbine support, for example, a floating platform.

[0021] In optional embodiments, the plane of the upper stage blades is perpendicular to the plane of the lower stage blades.

[0022] Thanks to these arrangements, the forces related to wind action are better distributed between the floors.

[0023] In optional embodiments, the wind turbine also includes a means for orienting and maintaining the blades of the lower stage and / or the blades of the upper stage in a plane perpendicular to the direction of the wind.

[0024] By locking the blades of the lower or upper stage in a plane perpendicular to the wind, the drag of these blades is minimized.

[0025] In optional embodiments, the wind turbine also includes a means of orienting and maintaining the upper stage blades in the same plane perpendicular to the wind direction.

[0026] By locking the blades of the two stages in a plane perpendicular to the wind, the drag of the entire wing is minimized.

[0027] In optional embodiments, the ratio of the chord of each blade to the radial extension of that blade is between 0.1 and 0.5.

[0028] Because each stage is two-bladed, the chord of the blades can be increased, which reduces their internal mechanical stresses and therefore makes them lighter.

[0029] In optional embodiments, the pivot joint includes two ball bearings, the ratio of the height of the center of thrust on the blades of the lower stage to the distance between the ball bearings is between 10 and 15.

[0030] The lightness of the sail that the characteristics of the invention allow and the relative uniformity of the moment of forces applied to the pivot joint make it possible to reduce the stresses on the pivot joint, and therefore to reduce its elongation.

[0031] In optional embodiments, each blade has a "U" shape comprising two radial straight segments, one end of which is connected to the mast, and a coplanar straight segment with the axis of rotation connected to the radial straight segments by quarter-circle segments.

[0032] These quarter-circle segments form winglets and reduce induced drag, i.e., the vortices at the ends of the straight blade segments.

[0033] In optional embodiments, the mast has a conical shape whose horizontal section has a decreasing surface area as it moves away from the pivot joint.

[0034] The wind turbine's design results in the bending forces exerted on the tower decreasing with distance from the pivot point. The conical shape of the tower therefore allows it to withstand these decreasing forces, while simultaneously reducing its weight and drag.

[0035] In optional embodiments, the mast has a truncated cylindrical shape.

[0036] In optional embodiments, the blades of the different stages have the same radial extension perpendicular to the axis of rotation.

[0037] The aerodynamic response of the different stages is therefore similar.

[0038] According to a second aspect, the present invention relates to a wind turbine installation comprising a foundation and at least one wind turbine, the subject of the invention, as briefly described above, mounted on this foundation.

[0039] This foundation is suitable for being positioned in deep sea, in shallow waters near the coast, or on land.

[0040] In optional embodiments, the wind turbine installation comprises at least two wind turbines mounted on the foundation, with the directions of rotation of these turbines being opposite. In optional embodiments, the wind turbine installation includes a means for synchronizing the turbine blades configured to maintain these blades symmetrical with respect to the median plane separating their axes of rotation.

[0041] By synchronizing the blades, we reduce interference between them and the turbulence that the sail of one of the wind turbines could cause on the sail of the other.

[0042] In some embodiments, the foundation is a floating platform.

[0043] In some embodiments the foundation is configured to be placed on a surface.

[0044] In some embodiments, the foundation is configured to be at least partially buried in a surface.

[0045] These methods of implementation make it possible to adapt to the geographical conditions of installation on land or at sea.

[0046] BRIEF DESCRIPTION OF THE FIGURES

[0047] Other advantages, purposes and special features of the invention will become apparent from the following non-limiting description of at least one particular embodiment of the wind turbine that is the subject of the present invention, with reference to the accompanying drawings, in which:

[0048] Figure 1 schematically and in perspective represents a first particular embodiment of the wind turbine that is the subject of the invention,

[0049] Figure 2 schematically represents the forces acting in a wind turbine shown in [Fig. 1].

[0050] Figure 3 schematically represents the drag moments of the two stages of the wind turbine shown in Figures 1 and 2, during one revolution of the blades.

[0051] Figure 4 schematically and in perspective represents a foundation supporting two wind turbines shown in [Fig. 1], and

[0052] Figure 5 schematically and in plan view shows several examples of foundations supporting one or more wind turbines as shown in [Fig. 1], DESCRIPTION OF CONSTRUCTION METHODS

[0053] The present description is given by way of non-limiting attribution, each feature of an embodiment being able to be advantageously combined with any other feature of any other embodiment.

[0054] The expression "and / or," as used in this document and in the claims, shall be understood as meaning "either or both" of the elements thus joined, that is, elements that are present conjunctively in some cases and disjunctively in others. Multiple elements listed with "and / or" shall be interpreted similarly, that is, "one or more" of the elements thus joined. Other elements may also be present, other than those specifically identified by the "and / or" clause, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, a reference to "A and / or B", when used in conjunction with an open language such as "including", may refer, in one embodiment, to A only (possibly including elements other than B); in another embodiment, to B only (possibly including elements other than A); in yet another embodiment, to A and B (possibly including other elements); etc.

[0055] As used herein in the description and in the claims, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" should be interpreted as inclusive, meaning the inclusion of at least one, but also more than one, of a number or list of items, and optionally, additional items not listed. Only terms explicitly stating the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," refer to the inclusion of only one item from a number or list of items.

[0056] As used in this description and in the claims, the expression "at least one," with reference to a list of one or more elements, should be understood as meaning at least one element chosen from one or more elements in the list of elements, but not necessarily including at least one of each element specifically listed in the list of elements and not excluding any combination of elements in the list of elements. This definition also allows for the optional presence of elements other than those specifically identified in the list of elements to which the expression "at least one" refers, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B", or, equivalently, "at least one of A and / or B") may refer, in one embodiment, to at least one, possibly including more than one, A, without B present (and possibly including elements other than B); in another embodiment, to at least one, possibly including more than one, B, without A present (and possibly including elements other than A); in yet another embodiment, to at least one, possibly including more than one, A, and at least one, possibly including more than one, B (and possibly including other elements); etc.

[0057] In the claims, as well as in the description below, all transitive expressions such as "comprising", "including", "carrying", "having", "containing", "implying", "holding", "composed of", and others, shall be understood as open, that is, as meaning "including, but not limited to". Only the transitive expressions "consisting of" and "consisting essentially of" shall be understood as closed or semi-closed transitive expressions, respectively.

[0058] It should be noted from the outset that the figures are not to scale.

[0059] Figure 1 shows a schematic view of a particular embodiment of a wind turbine 10, the subject of the invention. This wind turbine 10 comprises a vertical tower 11, with an axis of rotation 18, supporting an upper blade stage 12 and a lower blade stage 14. Each blade stage 12 and 14 comprises two blades, 13 and 15 respectively. The blades 13 are coplanar and symmetrical with respect to the axis of rotation 18. The blades 15 are coplanar and symmetrical with respect to the axis of rotation 18. The plane of the blades 15 is perpendicular to the plane of the blades 13 (except, as explained below, in the case of immobilization under extreme wind conditions for certain variants of the wind turbine 10). Preferably, and as shown in Figure 11, the turbine is supported by a vertical mast 11 with an axis of rotation 18.[Fig. 1] Each blade 13 and 15 has a U-shaped form comprising two radial straight segments, one end of which is connected to the mast 11, and a straight segment coplanar with the axis of rotation 18, connected to the radial straight segments by quarter-circle segments. These quarter-circle segments form winglets that reduce induced drag, i.e., the vortices at the tips of the straight blade segments. In the embodiment shown in [Fig. 1], the plane of the blades 15 is perpendicular to the plane of the blades 13. The embodiment shown in [Fig. 1] is preferred. However, in the present invention, more generally, the plane of the blades 13 of the upper stage 12 forms an angle between 70° and 110° with the plane of the blades 15 of the lower stage 13.

[0060] The mast 11 continues, at its base, with a rotor mounted on a pivot joint in a bearing 16 and then an electric generator 17. The rotor is therefore of the cantilever type. The height of the mast 11 corresponds to the highest point of the upper sail stage 12. Indeed, each sail stage, 12 and 14, is connected at two points to the mast 11. Moreover, any extension of the mast 11 beyond the upper sail stage 12 would imply an increase in mass and wind resistance of the mast 11, which would be detrimental to the performance of the wind turbine 10. Finally, this maximum height results from the absence of guy wires on the mast 11. Preferably, and as shown in [Fig. 1], the mast 11 has a conical shape, the horizontal section of which has a decreasing surface area as it moves away from the pivot joint 16. Indeed, the architecture of the wind turbine results in the bending forces exerted on the mast 11 decreasing as it moves away from the pivot joint 16.The conical shape of mast 11 therefore makes it possible to resist these decreasing forces, while reducing the weight of this mast and its drag.

[0061] In alternative embodiments not shown, the mast 11 has a truncated cylindrical shape. Preferably, the truncated cylinder is a right truncated cylinder with a circular base.

[0062] The horizontal section of blades 13 and 15 is not described here, as it is well known to those skilled in the art. This section is configured to cause the mast 11 to rotate under the effect of the wind. It is characterized by a chord defined as the maximum distance between its leading edge and its trailing edge.

[0063] In some variations, the wind turbine of the invention has more than two blade stages. For example, a third blade stage, supported by the mast (which is then taller than the mast 11), overhangs the upper blade stage 12. Preferably, in this case, the plane of the two blades of this additional stage is the plane of the blades 15 of the lower stage 14.

[0064] Figure 2 shows the forces applied to the mast 11 and the rotor that drives it. In Figure 2, the pivot joint of the bearing 16 is represented as two ball bearings, 19 (upper) and 20 (lower). To facilitate understanding of Figure 2, the blades 13 and 15 are shown in the plane of Figure 2. The lower blade stage 14 has a height 11 and a radial extent I3. The upper blade stage 12 has a height I2 and a radial extent I3. In some variations, the radial extents of the different blade stages are different. The wind turbine 10 is, in Figure 2, mounted on a floating platform 21. In other installations, the wind turbine 10 is fixed to land or placed on the seabed.

[0065] The center of the lower wing stage 14 is at a distance h1 from the center of the ball bearing 19. The center of the upper wing stage 12 is at a distance h2 from the center of the upper ball bearing 19. These wing centers are the points of application of the thrust forces caused by the wind on the blades 13 and 15. The center of the lower ball bearing 20 is at a distance h3 from the center of the upper ball bearing 19.

[0066] The mast 11 is held at its base by a pivot joint 16 in which the center distance h3 of the bearings 19 and 20 is much smaller than the distances h1 and h2 separating the bottom of the mast 11 from the aerodynamic centers of thrust of its two wing stages 12 and 14. Preferably, the ratio of the height h1 of the center of thrust on the blades 15 of the lower stage 14 to the distance h3 between the ball bearings 19 and 20 is between 10 and 15. This ratio allows, for example, the complete incorporation of the pivot joint 16 into a thin platform, which is easier to move at sea.

[0067] The forces applied to the mast, in steady state, are, apart from its weight:

[0068] - A force F1 applied by the wind at the center of the lower floor 14,

[0069] - A force F2 applied by the wind at the center of the upper floor 12,

[0070] - A force R1 applied radially by the lower ball bearing 20 to alternately counterbalance the moments of the forces F1 and F2 on the upper ball bearing 19 and

[0071] - A force R2 applied radially by the upper ball bearing 19 to counterbalance the force R1 and, alternatively, the forces F1 and F2.

[0072] Consequently, the mechanical stresses are concentrated in bearing 16. This bearing must absorb the drag of the mast 11. Outside of steady-state conditions, for a floating wind turbine, bearing 16 must also absorb the inertial forces associated with the movements of the floating platform, under the combined effect of swell, wind, and currents. However, this drawback is relatively minor, because in practice, it proves quite simple to build a very rigid pivot joint with two large ball bearings 19 and 20 mounted on a relatively short (a few meters) and very rigid shaft. This compact pivot joint can be achieved at the cost of a reasonable mass concentrated at the base of the rotor, and therefore does not raise the overall center of gravity.Finally, these assemblies can be integrated within the foundation itself (for example, the floating platform) in order to pool the mass of the elements of this platform, to take over both hydrodynamic and aerodynamic and inertial forces.

[0073] Another drawback of this cantilever architecture is the difficulty in designing a rotor that is both rigid and lightweight enough to absorb the stresses it is subjected to, and, more importantly, to have natural mode frequencies significantly higher than the aerodynamic and hydraulic excitation frequencies to which it is subjected. Indeed, for large rotors such as those envisioned for floating offshore wind turbines (diameter and height > 150m), the bending moments on the blades, whether aerodynamic or centrifugal, are very significant. Therefore, it is necessary to use blades with very long chords to withstand these loads. The use of two-bladed rotor stages with a mast makes it possible to obtain a structure rigid enough to meet the natural mode criterion while also withstanding the aerodynamic and centrifugal forces.

[0074] With each revolution of a blade stage, the drag it generates changes from almost zero when the two blades are aligned with the incident wind to a maximum value of approximately twice the average drag when the blades are crosswind. To avoid large variations in drag forces during the rotation of the mast 11, the blades of the blade stages 12 and 14 of the wind turbine 10 are in perpendicular planes.

[0075] It is noted that the reaction forces R1 and R2 at the bearings are determined, to the first order, not by the value of the drag of the wing stages 12 and 14, but by their moment with respect to the pivot joint 16. In the wind turbine 10, the two-stage wing is geometrically defined so that the sum of the aerodynamic moments produced by the two stages of the rotor has the same dynamic behavior as the drag of a single-stage four-bladed rotor.

[0076] To this end, in the wind turbine of the invention, the moments 22 and 23 of the drag forces F1 and F2 alternately exerted at their center of pressure are, although phase-shifted by 90°, substantially equal for two successive stages. [Fig. 3] schematically shows the moment 22 with respect to the ball bearing 19, of the drag forces of the lower blade stage 14 (solid lines), and the moments of the drag forces 23 of the upper blade stage 12 (dashed lines) during one revolution of the blade. It can be observed that the sum 24 of these moments 22 and 23 has a moderate standard deviation, allowing the values ​​of the reactions R1 and R2 to be smoothed. The total mean moment 25 is also shown in [Fig. 3].

[0077] In other words, and as illustrated in [Fig. 3], for a given wind force, for example the average wind force at the location of the wind turbine, the product of the intensity of the maximum force F1 during a rotation of the sail, by the height h1 is thus substantially equal (and preferably equal) to the product of the intensity of the maximum force F2 during a rotation of the sail, by the height h2.

[0078] This feature allows for a "smoothing" of the reactions R1 and R2 during one rotor revolution. It imposes a precise relationship between the heights of the two stages, I1 and I2, in order to compensate for the drag differences between the two stages by an appropriate combination of the respective lever arms h1 and h2.

[0079] Thus, during a complete revolution of the mast around its axis, the moment 24 of the forces exerted by the action of a constant wind on the blades of the two stages passes through four maxima that are substantially equal and four minima that are less than 30% lower than the maxima.

[0080] Thus, this two-stage two-bladed rotor makes it possible to obtain a standard deviation of the fluctuations of the reactions R1 and R2 equivalent to that which would be obtained with a single-stage four-bladed rotor.

[0081] For the wind turbine 10, the blades 15 of the lower two-bladed stage 14 have a chord equivalent to that of the blades 13 of the upper stage 12. For a conventional four-bladed rotor of a size similar to that shown in [Fig. 1], the blades would have a chord half that of the lower stage 14 of the wind turbine 10. Preferably, the ratio of the chord of each blade 13 and 15 to the radial extension I3 of that blade is between 0.1 and 0.5.

[0082] Thus, by using blades 13 and 15 with larger chords than those of a four-bladed rotor, the stress level in the blades can be significantly reduced. This allows the blade walls to be thinned considerably, and consequently, the rotor to be lightened. It should be noted that this weight reduction occurs in a region far from the rotor's axis of rotation, resulting in a significant reduction of inertia around this axis, which in turn leads to an increase in the torsional natural mode frequency. Compared to a four-bladed rotor of the same dimensions as the lower stage 14, a mass reduction of approximately 40% is achieved, along with an increase in the torsional natural mode frequency of approximately 30%.

[0083] This increases the natural frequency of the torsional mode beyond the aerodynamic excitation frequency, and lightens the blades without changing the rigidity that, to a first approximation, defines the rotor's performance and mass. Recall that the rigidity Sigma is defined by the formula:

[0084] Sigma = Nc / D, where N is the number of rotor blades, D its diameter, and c the blade chord. Thus, by lightening the rotor in this way, we enter a virtuous circle in which mass and stiffness are optimized to increase the natural frequencies of the system.

[0085] It is noted that the wind turbine 10 does not preferentially include an intermediate reinforcement connecting the middle of the vertical blades to the mast 11.

[0086] To minimize the drag of the blades 15 under extreme conditions in which these blades are stationary, the wind turbine 10 preferably includes a means for actively orienting and holding (not shown) the blades 15 of the lower stage 14 or the blades 13 of the upper stage 12 in a plane perpendicular to the wind direction. Thanks to this active holding means, the drag of the oriented and held blade stage is minimized.

[0087] To further reduce the drag of the sail, the wind turbine 10 preferably includes an additional means for actively orienting and holding (not shown) the blades 13 of the upper stage 12 and the blades 15 of the lower stage 14 of the sail in the same plane perpendicular to the wind direction. For example, this second active holding means includes a system for rotating the upper stage 12 of the sail relative to the lower stage 14 of the sail. Thus, under these extreme wind conditions, all the blades are positioned to be in a feathered configuration in a plane perpendicular to the wind direction. This minimizes windage, drag, and drag moment with respect to the pivot joint 16.

[0088] The present invention makes it possible to achieve the same "smoothing" qualities of forces as a conventional single-stage, four-bladed rotor while significantly reducing mass, inertia around the main axis of rotation, and drag and its moment with respect to the pivot joint under extreme conditions. The reduction in rotor mass also has a very beneficial effect on the foundation.

[0089] Figure 4 illustrates the association of two wind turbines on the same foundation 31

[0090] 26 and 27 equipped with two generators 28 and 29. Foundation 31 is preferably a floating platform.

[0091] Preferably, as indicated by the arrows in [Fig. 4], wind turbines 26 and

[0092] The turbines 27 are counter-rotating and synchronized to remain symmetrical with respect to the median plane separating them. This synchronization reduces the effects of drag from one turbine on the other. To achieve this synchronization, a computer 30, equipped with sensors for the position of the turbine blades 26 and 27, modulates the electrical power and applies different torques to the turbine towers on the generators 28 and 29.

[0093] Figure 5 schematically illustrates the association of different types of foundations supporting at least one wind turbine 10, the generators not being shown.

[0094] On the left of Figure 5, the foundation 31 is a floating platform supporting two wind turbines 10. Of course, such a floating platform can support a single wind turbine 10 or more than two wind turbines 10. The floating platform 31 is anchored to the seabed 33 by anchoring means 32, such as chains or other synthetic lines, known to those skilled in the art. The water surface is represented by the curved line 35. These embodiments are suitable for offshore use.

[0095] In the middle of Figure 5, foundation 34 is a foundation placed on the seabed 33. Such a foundation can be a gravity foundation, a monopile foundation, in which the mast forms a continuous structure with the foundation, or a jacket foundation; these types of foundations are familiar to those skilled in the art. These embodiments are suitable for marine use and shallow seabeds.

[0096] On the right of Figure 5, foundation 37 is positioned on a ground surface 36. Foundation 37 can be any type of foundation known in the field of civil engineering, for example, a reinforced concrete structure or a footing. These embodiments are suitable for land use.

Claims

DEMANDS 1. Wind turbine (10) comprising a mast (11) rotating about a vertical axis of rotation (18), a blade (12, 14) fixed to the mast to drive it in rotation, and a generator (17) driven by the rotation of the mast, characterized in that: - the mast is held around its axis solely by a pivot joint (16) with a vertical axis, - the sail area includes: - a lower stage (14), close to the pivot joint, comprising two coplanar blades (15) symmetrical with respect to the axis of rotation, - an upper stage (12), located away from the pivot joint, comprising two coplanar blades (13) symmetrical with respect to the axis of rotation, - the plane of the blades of the upper stage forms an angle between 70° and 110° with the plane of the blades of the lower stage, - the moments (22, 23), with respect to the pivot joint, of the maximum forces exerted by a constant wind on the blades of the two stages during one revolution of the mast, are substantially equal, the sum of these moments being substantially constant during the rotation of the wind turbine.

2. Wind turbine (10) according to claim 1, wherein the plane of the blades (13) of the upper stage (12) is perpendicular to the plane of the blades (15) of the lower stage (14).

3. Wind turbine (10) according to any one of claims 1 or 2, further comprising a means for orienting and holding the blades (15) of the lower stage (14) and / or the blades (13) of the upper stage (12) in a plane perpendicular to the direction of the wind.

4. Wind turbine (10) according to claim 3, wherein the orientation and holding means is configured to orient and hold the blades (13, 15) of the two stages (12, 14) in the same plane perpendicular to the wind direction.

5. Wind turbine (10) according to any one of claims 1 to 4, wherein the ratio of the chord of each blade (13, 15) to the radial extension (I3) of that blade is between 0.1 and 0.

5.

6. Wind turbine (10) according to any one of claims 1 to 5, wherein the pivot joint (16) comprises two ball bearings (19, 20), the ratio of the height (h1) of the center of thrust on the blades (15) of the lower stage (14) to the distance (h3) between the ball bearings is between 10 and 15.

7. Wind turbine (10) according to any one of claims 1 to 6, wherein each blade (13, 15) has a "U" shape comprising two radial straight segments, one end of which is connected to the mast (11), and a straight segment coplanar with the axis of rotation (18) connected to the radial straight segments by quarter-circle segments.

8. Wind turbine (10) according to any one of claims 1 to 7, wherein the mast (11) has a conical shape whose horizontal section has a decreasing surface area as it moves away from the pivot joint (16).

9. Wind turbine (10) according to any one of claims 1 to 8, wherein the mast (11) has a truncated cylindrical shape.

10. Wind turbine (10) according to any one of claims 1 to 9, wherein the blades of the different stages have the same radial extension perpendicular to the axis of rotation.

11. Installation of wind turbines (40, 50) comprising a foundation (21, 31, 34, 37) at least one wind turbine (10, 26, 27) according to one of claims 1 to 10, mounted on this foundation.

12. Installation of wind turbines (40, 50) according to claim 10, which comprises at least two wind turbines (26, 27) mounted on the foundation (31), the directions of rotation of these wind turbines being opposite.

13. Installation of wind turbines (40, 50) according to claim 11, which further comprises a means (30) for synchronizing the blades of the wind turbines configured to maintain these blades symmetrical with respect to the median plane separating their axes of rotation. 16 14. Installation of wind turbines (40, 50) according to any one of claims 11 to 13, wherein the foundation (31) is a floating platform.

15. Installation of wind turbines (50) according to any one of claims 11 to 13, wherein the foundation (34) is configured to be placed on a surface (33).

16. Installation of wind turbines (50) according to any one of claims 11 to 13, wherein the foundation (37) is configured to be at least partially buried in a surface (36).

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