Cross-flow wind turbine with double blades and tilted rotation axis

Abstract

A wind turbine (1) comprising a cross-flow double-impeller turbine (10, 20) connected to a generator (30) comprising a shaft configured to rotate upon rotation of the turbine, the wind turbine comprising: - a first turbine (10) rotatable about a first axis of rotation (Δ1) and comprising a plurality of blades (11, 12, 13) distributed about said first axis of rotation; a second turbine (20) rotatable about a second axis of rotation (Δ2) and comprising a plurality of blades (21, 22, 23) distributed about said second axis of rotation; - said first axis of rotation and said second axis of rotation being mutually symmetrical with respect to a vertical axis (Z); the wind turbine being characterized in that: - said first axis of rotation and said second axis of rotation are inclined with respect to said vertical axis at an inclination angle of between 25° and 50°.

Description

TECHNICAL FIELD

[0001] The technical field of the present invention is a cross-flow wind turbine. BACKGROUND

[0002] Renewable energy is experiencing a major development. As a consequence, large wind turbine installations on land or at sea have experienced a rapid growth over the last decades. Most of the installed wind turbines are horizontal axis wind turbines (HAWT) whose rotation axis is parallel to the incident wind direction.

[0003] Other types of wind turbines include cross-flow turbines whose rotation axis is perpendicular to the incident wind direction. The rotation axis is generally vertical. This type of wind turbine is commonly called vertical axis wind turbine (VAWT).

[0004] Wind turbines with vertical rotation axis have been described in JP 59190482, FR 2973843 and US 7189051. This concerns Savonius type wind turbines.

[0005] In cross-flow wind turbines, Darrieus type wind turbines can include straight or curved blades. Vertical wind turbines with curved blades include blades extending around a vertical central rotation axis which also forms the tower. This type of wind turbine has experienced a moderate development due to a reputation of fragility, especially for very high wind turbines. Unlike horizontal wind turbines, very high vertical wind turbines are subjected to a steady wind not only at high altitude but also closer to the ground, in a region called "boundary layer" where vortices are liable to appear. This results in a certain sensitivity to fatigue.

[0006] To improve rigidity, very high vertical wind turbines with curved blades can be reinforced by cables extending between the wind turbine apex and the ground. But this results in a significant increase of the footprint, which is particularly detrimental for offshore installations. Moreover, the cables exert a compressive stress towards the ground on the bearings allowing the rotation of the shaft. This requires the use of particularly robust bearings, which increases the complexity and the cost of the wind turbine. Furthermore, the presence of a large rotation axis at the center of each blade generates vortices (Karman vortices) which affect the performance of the wind turbine. Finally, the central rotation axis and the retaining cables can be subjected to vibrations under the action of the periodic aerodynamic forces when the blades rotate, which can cause a resonance instability, especially when the height of the central shaft or the length of the cables is large.

[0007] Currently, most high-power wind turbines are horizontal wind turbines. However, they have several drawbacks: the generator, which generates electricity under the action of the blades, is suspended on the nacelle and raised to a high level. This is also the case for the main speed and control components such as the gearbox, brakes and control systems. The nacelle, arranged at height, therefore supports a large weight, which is detrimental to stability due to the high sensitivity to pitch or roll. To compensate for these drawbacks, the mast supporting the nacelle and the blades is large, as is the foundation of the entire assembly of support on land or at sea. The arrangement of the nacelle at height also complicates maintenance operations. Another drawback of horizontal wind turbines is the very large size of the blades, which, combined with the size of the mast, complicates transport and installation. And, in the case of blades made integrally, even more so. These blades are generally heavy, which results in a high gravitational load of the wind turbine. The blades can also have a complex shape, which increases their cost.

[0008] Vertical wind turbines with straight-bladed Darrieus-type turbines have also been proposed. One significant advantage of vertical wind turbines is that, unlike horizontal-axis wind turbines, it is possible to arrange the generator and the electromechanical transmission chain at a low level. Another advantage is the sensitivity to all directions of the wind, which does not require the use of a wind turbine yaw angle adjustment. Moreover, straight-bladed wind turbines have a reduced footprint and are less sensitive to the difference in height according to the wind speed.

[0009] Document US2020 / 0217297 describes a wind turbine comprising different vertical-axis turbines of Darrieus type with curved blades. The turbines are spaced apart from each other and connected to a generator by means of a horizontal shaft of large length. This results in a large-volume wind turbine with a large footprint.

[0010] Document WO2017153676 describes a wind turbine comprising vertical-axis twin-jumelles turbines of Darrieus type with straight blades, in which the turbines are symmetrical with respect to a median vertical plane. The counter-rotating turbines are supported by a central mast from which two horizontal supports perpendicular to the median plane extend from the upper end of the mast. The vertical blades of each turbine are extended at their ends by horizontal profile arms that rotate around a vertical rotation axis. In general, the high efficiency of the twin-turbine case with respect to the single-turbine case is related to the local transverse confinement effect that is manifested when the blades move in the area between the turbines. Indeed, in this area, the vertical median plane between the counter-rotating turbines prevents the incident flow from moving away from the turbines. However, two conditions must be met: the turbines must rotate at the same speed and in the same angular position relationship. Synchronizing the two turbines requires meeting these two conditions. Conversely, the blades can be diverted against the wind (thrust direction) or with the wind (suction direction) in said area.

[0011] However, this type of design has drawbacks related to the centrifugal forces exerted on the vertical blades of the turbine during rotation. Under the effect of centrifugal forces, the vertical blades are subjected to bending stresses tending to expand the turbine laterally, i.e. to increase the diameter. This results in unwanted vibrations that affect the efficiency. Furthermore, the horizontal arms of large-size turbines are subjected to a downward deformation related to the weight of the vertical blades, which occurs when the turbine is stopped, where the centrifugal forces are no longer compensating the gravity. This results in a fatigue effect at the arm / blade junctions.

[0012] In fact, the periodic aerodynamic forces acting on the vertical part, whether in the wind or against the wind, periodically break the symmetry of each blade. When the vertical blades turn against the wind, the aerodynamic forces are directed towards the inside of the turbine, while when the blades turn in the opposite direction, they are directed towards the outside of the turbine. This results in a periodic asymmetry that generates oscillations during each rotation.

[0013] The twin turbine allows to increase the efficiency of the wind turbine. However, this results in a certain complexity related to the use of two generators, each connected to a turbine. The generators are controlled by an electronic power system to synchronize the turbines, which causes an increase in costs and the necessity of making periodic adjustments.

[0014] Furthermore, the structure for holding the turbine is prone to bending stresses that can cause vibrations to occur. This can also cause premature wear of the structure.

[0015] The present invention proposes a wind turbine aimed at avoiding or reducing the aforementioned drawbacks. SUMMARY

[0016] The object of the present invention is to provide a wind turbine comprising a cross-flow twin turbine connected to a generator comprising a shaft designed to be driven in rotation under the effect of the rotation of the turbine, comprising:

[0017] - a first turbine able to rotate around a first rotation axis and comprising a plurality of blades distributed around the first rotation axis;

[0018] - a second turbine able to rotate around a second rotation axis and comprising a plurality of blades distributed around the second rotation axis;

[0019] - the first rotation axis and the second rotation axis are preferably symmetrical with respect to each other with respect to a vertical axis;

[0020] - the first rotation axis and the second rotation axis are inclined with respect to a vertical axis at an inclination angle, preferably at the same inclination angle of 25° to 50°.

[0021] Advantageously, the wind turbine defines a median plane, the median plane:

[0022] • perpendicular to a downstream plane comprising the first and second rotation axes;

[0023] • passing through the intersection of the first and second rotation axes;

[0024] The median plane can form a plane of symmetry of the wind turbine. The median plane can in particular be vertical. The downstream plane is also such.

[0025] Advantageously, each rotation axis converges on a single generator, so that a preferably horizontal shaft of the generator is driven in rotation by the first and second turbines;

[0026] Preferably:

[0027] - each turbine extends around the rotation axis between a lower end and an upper end, the lower end being closer to the generator than the upper end;

[0028] - the lower and upper ends of each turbine are aligned with the rotation axis of said turbine;

[0029] - each blade of a turbine comprises:

[0030] • a lower portion extending from the lower end;

[0031] • an upper portion extending from the upper end;

[0032] - each blade extends from the lower end to the upper end so that:

[0033] • along the lower portion, the radius of the blade corresponding to the distance between the blade and the rotation axis gradually increases as the distance relative to the lower end increases;

[0034] • along the upper portion, the radius of the blade gradually decreases as the distance relative to the upper end increases.

[0035] Advantageously:

[0036] - at the lower end, the lower portion forms a lower opening angle with the rotation axis, the lower opening angle being acute;

[0037] - at the upper end, the upper portion forms an upper opening angle with the rotation axis, the upper opening angle being acute.

[0038] Preferably, the upper and lower opening angles are equal and form the same opening angle. The opening angle can be between 40° and 60°.

[0039] Preferably, each blade has a straight lower portion and / or a straight upper portion.

[0040] According to one embodiment:

[0041] - each blade comprises an equatorial portion connecting a lower portion and an upper portion;

[0042] - in the equatorial portion, the radius of the blade reaches a maximum radius.

[0043] According to one embodiment:

[0044] - the height of each blade corresponds to the distance between the lower end and the upper end parallel to the rotation axis;

[0045] - each blade has a shape factor corresponding to the ratio of the height of the blade to twice the maximum radius of the blade;

[0046] - the shape factor of each blade is between 1.3 and 1.5.

[0047] Preferably:

[0048] - the equatorial portion is curved;

[0049] - along the equatorial portion, the radius gradually increases from the lower portion until it reaches the maximum radius of the blade, then gradually decreases until the upper portion.

[0050] According to one possibility, for each turbine:

[0051] - the equatorial plane extends perpendicularly to the rotation axis, the equatorial plane passing through the maximum radius of each blade of the turbine;

[0052] - the equatorial plane forms a plane of symmetry of the turbine.

[0053] Each blade can comprise:

[0054] - a lower junction corresponding to the junction between the lower portion and the equatorial portion;

[0055] - an upper junction corresponding to the junction between the upper portion and the equatorial portion;

[0056] Each blade is such that:

[0057] - the distance between the lower junction and the upper junction parallel to the rotation axis forms the height of the equatorial portion;

[0058] - the relative height of the equatorial portion corresponds to the ratio between the height of the equatorial portion and the height of the blade;

[0059] - the relative height of each blade is greater than 0.5 and less than 0.8.

[0060] According to one embodiment:

[0061] - two blades belonging to two different turbines are separated by a minimum separation during their rotation around their respective rotation axis;

[0062] - the shape factor of the wind turbine corresponds to the ratio between the minimum clearance and twice the maximum radius;

[0063] - the shape factor of the wind turbine is comprised between 0.1 and 0.3.

[0064] According to one embodiment, each turbine comprises two blades, each blade being symmetrical to the other with respect to the rotation axis of the turbine. According to another embodiment, each turbine comprises three blades uniformly distributed around the rotation axis of the turbine.

[0065] Preferably:

[0066] - the first turbine:

[0067] • at its lower end, is connected to the first lower rotation axis;

[0068] • at its upper end, is connected to the first upper rotation axis;

[0069] • the first lower rotation axis, the first upper rotation axis and the first rotation axis are coaxial;

[0070] - the second turbine:

[0071] • at its lower end, is connected to the second lower rotation axis;

[0072] • at its upper end, is connected to the second upper rotation axis;

[0073] • the second lower rotation axis, the second upper rotation axis and the second rotation axis are coaxial;

[0074] - the wind turbine comprises a holding structure, the holding structure comprising:

[0075] • a nacelle supporting the electric generator;

[0076] • a mast extending vertically from the nacelle and centered with respect to the median plane, the mast being set back with respect to the downstream plane along a longitudinal direction perpendicular to the downstream plane;

[0077] • a first upper arm extending from the mast to the first upper support, the first upper support holding the first upper rotation axis;

[0078] • a second upper arm extending from the mast to the second upper support, the second upper support holding the second upper rotation axis;

[0079] • the first upper arm and the second upper arm are inclined with respect to the vertical axis.

[0080] According to one possible implementation:

[0081] - the first upper support comprises a bearing in which the first upper rotation axis is inserted;

[0082] - the second upper support comprises a bearing in which the second upper rotation shaft is inserted.

[0083] The holding structure can further comprise:

[0084] - a king post extending away from the downstream plane from the mast;

[0085] - a first shroud extending between the king post and the first upper arm;

[0086] - a second shroud extending between the king post and the second upper arm.

[0087] According to one possible solution:

[0088] - the first shroud extends between the king post and the first upper support;

[0089] - the second shroud extends between the king post and the second upper support.

[0090] According to one embodiment, the first upper arm and the second upper arm comprise successive base arms extending respectively towards the first upper support and the second upper support, each base arm being more inclined with respect to the vertical direction the closer it is to the first upper support or to the second upper support.

[0091] According to one embodiment, at least one strut extends between the mast and the nacelle, the strut being inclined with respect to the vertical direction and extending from the mast towards the downstream plane.

[0092] According to one embodiment, the nacelle is rotatable about a vertical rotation axis so that, in the presence of a wind blowing in a direction, the wind, under the effect of the thrust exerted by each turbine, causes the turbines to be arranged spontaneously downstream of the mast in said direction, wherein the mast extends about this vertical rotation axis. According to another embodiment, the nacelle is fixed in terms of rotation, the wind turbine being such that the turbines are arranged downstream of the mast in a direction corresponding to the prevailing wind direction.

[0093] According to one embodiment, each lower rotation shaft is connected to the shaft of the generator by means of a bevel gear.

[0094] According to one embodiment, a brake is arranged between each bevel gear and each respective lower end of each turbine. Each brake can comprise a disc rigidly connected to the turbine and a shoe rigidly connected to the bevel gear.

[0095] According to one embodiment, at least one crossbar extends between two different blades of the same turbine. The junctions between the crossbar and the two blades can form connection angles. According to one possible solution, the two different blades of the same turbine are connected by an upper crossbar and a lower crossbar arranged respectively closer to the upper end and to the lower end of the turbine than to the equatorial plane.

[0096] According to one embodiment, the mast has a horizontal section extending parallel to the median plane P a between the convex upstream end and the downstream end close to the downstream plane P m The horizontal section of the mast can advantageously taper between the upstream end and the downstream end.

[0097] According to one embodiment, each arm has a vertical profile section extending between a leading edge and a trailing edge, the trailing edge facing the downstream plane.

[0098] The application will be better understood upon reading the following description of an embodiment shown on the attached drawings. BRIEF DESCRIPTION OF DRAWINGS

[0099] Figure 1A is a general view of an exemplary embodiment of a wind turbine comprising two blades.

[0100] Figure 1B is a side view of the wind turbine shown in Figure 1A

[0101] Figure 1C is a downstream view of the wind turbine shown in Figure 1A

[0102] Figure 2A is a view of the turbine of the wind turbine shown in the preceding figures.

[0103] Figure 2B is a view of the turbine extending in the downstream plane of the wind turbine.

[0104] Figure 2C is a detail of Figure 2B

[0105] Figure 3A is a top view of the wind turbine described in connection with the preceding figures.

[0106] Figures 3B to 3C shows the upper support structure of the wind turbine.

[0107] Figure 3D is similar to Figure 3A Figure 3D shows the forces exerted in the horizontal plane at the upper support.

[0108] Figure 4 is an upstream view of the wind turbine described in the preceding figures.

[0109] Figure 5A shows one configuration of the wind turbine, wherein each turbine comprises three blades.

[0110] Figure 5B and Figure 5C ​​​​Possible profiles of the arms forming the holding structure of the wind turbine are shown.

[0111] Figure 5D are Figure 5A Another view of the wind turbine is shown.

[0112] Figure 5E and Figure 5F Variations are shown, according to which the mast has a horizontal section adapted to operate according to an upwind Figure 5E ) or downwind Figure 5F ) mode.

[0113] Figure 6A A crossbar adapted to turbines each comprising three blades is shown.

[0114] Figure 6B are Figure 6A details.

[0115] Figure 6C A crossbar adapted to turbines each comprising two blades is shown.

[0116] Figure 6D and Figure 6E The use of interface parts for assembling the crossbar with the blades is shown.

[0117] Figure 7A and Figure 7B The mechanical transmission between each blade and the generator is shown.

[0118] Figure 8A and Figure 8B are other embodiments of the wind turbine. DETAILED DESCRIPTION

[0119] Figures 1A to 1C A view of one example of a wind turbine according to the invention is shown. The wind turbine comprises a first turbine 10 of the Darrieus type with curved blades and a second turbine 20 of the cross-flow type. The first turbine 10 is able to rotate around a first rotation axis Δ1. The second turbine 20 is able to rotate around a second rotation axis Δ2. The first and second rotation axes are coplanar. They lie in the same vertical plane P a called downstream plane. The term "downstream" should be interpreted with reference to the flow of the wind through the wind turbine. In the downstream plane, the first rotation axis Δ1 and the second rotation axis Δ2 are inclined with the same inclination angle a with respect to a vertical axis Z. The downstream plane P a is vertical.

[0120] "Cross-flow turbine" means that the turbine rotates under the action of the wind blowing transversely to each rotation axis. In the present example, the downstream plane P aPreferably, it is arranged perpendicular to the wind direction W. Figure 1B It is with the downstream plane P a Vertical side view. Figure 1C It is the wind turbine and the downstream plane P a Parallel upstream view.

[0121] The first rotation axis Δ1 and the second rotation axis Δ2 converge at the intersection point Ω, which is equidistant from each turbine. This is in relation to the downstream plane P. a The plane perpendicular to and passing through the intersection point Ω forms the mid-plane P of the wind turbine. m The first turbine 10 and the second turbine 20 are symmetrically arranged in the mid-plane P. m On both sides, this mid-plane forms a plane of symmetry. Therefore, the first and second turbines are twins, meaning they are symmetrical about each other with respect to the mid-plane. Mid-plane P m It is a vertical plane. The mid-plane P will be discussed below. m It also forms a symmetrical plane that holds the retaining structure 50 for each turbine.

[0122] Each turbine includes at least two blades, preferably two or three blades. Figures 1A to 1C In the example shown, each turbine includes two blades: the first turbine 10 includes a first blade 11 and a second blade 21, while the second turbine 20 includes a first blade 21 and a second blade 22. Preferably, the blades are arranged such that the first turbine 10 and the second turbine 20 rotate in opposite directions. (This will be discussed in conjunction with...) Figure 5D This section illustrates an example of a turbine with three blades.

[0123] The first turbine 10 has a first lower end 10 located on the first rotation axis Δ1 i With the second upper end 10 s Extending between. The second turbine 20 is located at its second lower end 20 on the second rotation axis Δ2. i With the second upper end 20 s Extending between.

[0124] The wind turbine includes a generator 30 configured to generate electricity under the action of turbine rotation. First and second rotational axes converge on the same generator 30. The generator 30 includes a rotor simultaneously driven by a first turbine 10 and a second turbine 20. In the illustrated example, the generator includes first driven rotational shafts A extending on both sides of the generator 30. r,1 Second driven rotating shaft A r,2 The first and second driven rotating shafts A r,1 A r,2The rotation of the first turbine 10 and the second turbine 20 is transmitted to the rotor of the generator 30 respectively. The turbines can also be upwind (i.e. turning into the wind when the blades approach the mast) or downwind (i.e. turning into the wind when the blades approach the mast).

[0125] The first turbine 10 is connected, through a bevel gear, first to a first lower end 10 i extending to a first driven rotation shaft A r,1 of the generator 30 i,1 . Symmetrically, the second turbine 20 is connected, through a bevel gear system, to a second lower end 20 i extending to a second driven rotation shaft A r,2 of the generator i,2 of the second lower end 20 i,1 , A i,2 is held at each lower end by a pivotal connection respectively. Each lower rotation shaft has a driving action transmitted to a driven shaft A r,1 , A r,2 of the generator through a bevel gear. The driven shaft of the generator is mechanically coupled to a single engine shaft of the generator, which extends on both sides of the generator. The driving shaft of the generator is thus driven in rotation simultaneously by the two turbines 10, 20, which constitutes a significant aspect of the invention. The details of the mechanical transmission chain between each lower end and the generator are explained in Figures 7A to 7B

[0126] The design of the wind turbine aiming at driving a single generator simultaneously by two turbines 10, 20 rotating around converging two rotation axes allows to obtain a mechanical synchronization of the turbines. Driving the same generator by multiple turbines allows to reduce the cost of the wind turbine by reducing the number of generators needed. Moreover, this avoids using an electronic synchronization system to synchronize multiple generators, as described in the background art, which requires regular readjustments.

[0127] The generator can be an asynchronous squirrel cage generator, a geared variable speed generator, a geared reluctance synchronous generator (without rare earth permanent magnets) or a direct drive synchronous generator. It can also concern other types of generators.

[0128] In addition to the mechanical synchronization, the convergence of the rotation axes on the generator allows to use a compact generator centered with respect to the median plane.

[0129] Description of the turbine

[0130] ​As mentioned above, the angle of inclination a of each rotation axis with respect to the vertical is preferably comprised between 25° and 50°, preferably between 30° and 40°, for example 35°. Such an angle range allows to obtain a good compromise between the height H of the turbine extending along the vertical direction (Z axis) and the width L of the turbine extending in the horizontal direction. The width L of the turbine is defined parallel to the median plane P m The vertical transversal axis Y is defined. According to the application, the height H of the turbine extending along the vertical direction must be optimized so as to be sufficient to increase the wind- facing area but small enough to exploit a wind layer in which the wind speed can be considered uniform. Moreover, the limitation of the height allows to keep the center of gravity of the wind turbine at a sufficiently low level. The height H is usually comprised between a few meters and more than a hundred meters, for example between 5 m and 150 m. The height H and the width L are related by the angle of inclination a.

[0131] The inclination of the rotation axis increases the width L of the wind turbine. In order to maximize the wind-facing area of the wind turbine, it is preferable to optimize the surface area occupied by each turbine within a rectangular range R having a height H and a width L. In Figure 1C The range R is shown with a dashed rectangular profile. The range R does not actually exist (virtual rectangle). In order to optimize the filling, i.e. the area covered by each turbine within the range, the shape of the blades can be optimized as described below.

[0132] Figure 2A A first blade 11 and a second blade 12 of the first turbine 10 are shown. In Figure 2A It can be seen that the leading edge 12 a of the second blade 12 and the trailing edge 11 f of the first blade 11 are not aligned. The first blade comprises an upper crossbar 14 s and a lower crossbar 14 i . The crossbars are perpendicular to the first rotation axis Δ1 and extend between each blade. The role of the crossbars is to reinforce the turbine. The use of crossbars is optional. It can be used only in the case of large turbines. Similarly, the second turbine 20 comprises a lower crossbar 24 i and an upper crossbar 24 s . The preferred form of the crossbars is explained in connection with Figures 6A to 6E The preferred form of the crossbars is explained in connection with

[0133] Each blade is shaped in such a way that it approximates a troposkine curve, i.e. a curve formed by a line rotating around a rotation axis with constant angular velocity, at the lower end 10 i of the turbine 10 and at the upper end 10 sThe twisted rope shape increases the tensile stress applied at each blade, which minimizes the bending stress. As mentioned in the background section, bending stress applied to a turbine blade causes unwanted vibrations, which are detrimental to the operation and performance of the wind turbine. By preferentially applying tensile stress, the risk of unwanted vibrations occurring when the blades rotate around their rotation axis is reduced or even eliminated. When the turbine rotates, each blade is subjected to centrifugal forces, which tend to increase the width of the turbine. This results in a tensile stress applied along each blade between the two lower ends 10 i , 20 i and the upper end 10 s , 20 s .

[0134] When the shape of each blade tends towards a twisted rope curve, each turbine formed by the combination of a plurality of identical blades uniformly spaced apart has a tapered shape.

[0135] Unlike the turbines built in the prior art with a twisted rope shape, it can be noted that each turbine does not comprise a central axis located between the upper end 10 s and the lower end 10 i coaxial with the rotation axis.

[0136] Figure 2B is a detail of the first turbine 10. In this example, the first blade 11 is symmetrical about the first rotation axis Δ1 with the second blade 12. In the following of the present description, the distance between a point of a blade and the rotation axis is referred to as "radius". Each blade comprises a lower portion 11 i , 12 i extending along a lower height h i measured parallel to the rotation axis, from the lower end 10 i . Along the lower portion 11 i (or 12 i ), the radius, i.e. the distance between the blade and the rotation axis, gradually increases as the distance from the lower end 10 i increases. Preferably, the radius of each blade is maximum at a middle point (parallel to the rotation axis), i.e. at a position equidistant from the lower end and the upper end. Each blade comprises an upper portion 11 s , 12 s extending along an upper height h s measured parallel to the rotation axis, from the upper end 10 s . Similarly, along the upper portion 11 s (or 12 s ), the radius decreases as the upper end 10 s is approached.

[0137] In the illustrated example, the lower and upper parts of each blade are straight. The lower and upper parts are inclined with respect to the first rotation axis at the same lower and upper opening angle. In the illustrated example, the lower opening angle is equal to the upper opening angle, which corresponds to a preferred embodiment. In the following, the lower and upper opening angles will be referred to indistinctively as opening angle Φ. The opening angle Φ is an acute angle. When the lower and upper parts of each blade are straight, the radius increases linearly as a function of the distance with respect to the lower (or upper) end and of sin(Φ). In Figure 2B and Figure 2C the opening angle Φ is illustrated.

[0138] According to an alternative, the upper opening angle is greater than the lower opening angle. According to this option, the lower opening angle is smaller to save space. The upper opening angle is greater to increase the moment of force in the upper part of the blade.

[0139] In the illustrated example, each blade 11, 12 comprises an equatorial part 11 e , 12 e extending between the lower and upper parts of said blade. In the illustrated example, the equatorial part is curved. From the lower junction 11 i with the lower part 11 ei , along the equatorial part 11 e , the radius r of the blade gradually increases until it reaches a maximum radius r max , then decreases until the junction 11 s with the upper part 11 es . The succession of a straight lower part, a curved equatorial part, and a straight upper part corresponds to a so-called SCS (which is an acronym for Straight Curved Straight) structure.

[0140] An equatorial plane can be defined which is perpendicular to the rotation axis and passes through the point of maximum radius on each blade. The turbine is preferably symmetrical with respect to the equatorial plane. In Figure 2B a depiction of the equatorial plane P e,1 of the first turbine 10 is illustrated. The point of maximum radius of each blade is then located at the middle height h e / 2 of the equatorial part, determined parallel to the rotation axis. In the illustrated example, due to the symmetry of each blade with respect to the equatorial plane, the point of maximum radius of each blade is located at the middle height h / 2 of the blade, determined parallel to the rotation axis.

[0141] As mentioned above, the shape thus obtained is close to a twisted cord curve. When the blade rotates around its rotation axis, the main stress applied to it is in Figure 2BThe tensile stress is illustrated by the double arrow along the blades 11. Under the effect of rotation, each blade is kept stretched between the upper and lower ends, hence the name of the twisted rope curve. The greater the angular velocity of the blade, the greater the stretching of the blade. Thus, the tensile stress is used to reduce the bending stress that affects the wind turbine as described in the background art.

[0142] In order to optimize each turbine in combination Figure 1C with the opening angle Ф, it is preferable that the opening angle Ф be sufficiently large. Preferably, the opening angle Ф is between 40° and 50°, for example 45°. This allows to obtain an optimized "filling" of each turbine. The filling corresponds to the surface area defined by each turbine with respect to the surface area of the range R.

[0143] The turbines 10 and 20 are symmetrical with respect to the median plane P m . During each rotation, the two blades of each turbine approach each other until a minimum separation U illustrated in Figure 1C and Figure 2B is reached. In order to optimize the filling defined above, it is desirable to minimize the separation U in order to reduce the free space between the two turbines. However, safety or performance considerations require that the separation U should not be less than a minimum value: this notably involves a structural risk or one turbine impacting the other too much, leading to undesirable oscillations. The greater the opening angle Ф, the smaller the minimum separation U. If d i corresponds to the distance between the two lower ends 10 i , 20 i parallel to the transverse axis Y, then U = d i when a = Ф. When Ф > a, then U < d i : thus reducing the minimum separation U. It can be understood that the minimum separation U depends on d i and the angles a and Ф. In general, it is preferable that: 0.6 Ф ≤ a ≤ Ф. In the example illustrated, a = 35° and Ф = 45°, thus a = 0.78 Ф.

[0144] The separation U quantifies the free space between the turbines, characterized by the distance between two points P u called approach points, respectively located on the blades of each turbine. When the respective two blades of each turbine are opposed, the approach point of the blade of one turbine corresponds to the closest point of the blade of the other turbine. The distance between the respective two approach points of the respective two blades of the two turbines corresponds to the separation U. Preferably, the approach point P u of one turbine is arranged at the equatorial portion 11 e of this turbine. Indeed, it is in the equatorial portion of the blade that the effect is considered to be the most effective. The approach points P u,12 and P u,21 of the blades 12 and 21 respectively are illustrated in Figure 2B .

[0145] r u is the radius of the blade at the point P u . The radius r u corresponds to the distance between the rotation axis and the point P Figure 2B perpendicular to the rotation axis of the blade. In the example shown in u , the radius r u is the same for all the blades of the two turbines.

[0146] To optimize the filling and improve the performance of the wind turbine, it is desirable to minimize the separation U while reducing the distance d i . However, safety considerations require that the separation U should not be less than a minimum value. This is intended to avoid structural problems, especially after a whole holding structure resonance phenomenon caused by a sudden change in the wind, or a longitudinal vibration of the blades caused by a local array of vortices of the wind. The inventors consider that:

[0147]

[0148] In the example shown in Figure 2B , the half separation U / 2 corresponds to the closest distance between the blades of the turbines and the median plane P m .

[0149] As shown in Figure 2C , the half separation U / 2 corresponds to the closest distance between the blades of the turbines and the median plane P m .

[0150] Thus, for the opening angle Ф and the tilt angle a, the following equation must be satisfied:

[0151] a < Ф

[0152] To move away from a configuration in which the turbine axis is vertical and which is not optimized in terms of filling as defined above, it is preferable that 0.6Ф≤a.

[0153] In addition to better filling of the rectangular area R, reducing the free space between the turbines is accompanied by a blocking of the incident flow on both sides of the median plane P m . By "incident flow" is meant the flow of air upstream of each turbine. Thus, this blocking effect on the incident flow is exploited in the particularly effective part of the blade located at the minimum separation U separating the two equatorial parts of the two blades as shown in Figure 2B . It is estimated that the proximity of the blades of the two different turbines against the wind leads to an efficiency improvement of 10% that can be achieved with respect to the case in which each turbine is isolated from each other.

[0154] To improve the efficiency of each turbine, the invention considers that each equatorial part 11 e , 12 ethe height h of each blade relative to the height of each blade e Each equatorial portion can thus be characterized by a relative height Γ as follows:

[0155]

[0156] wherein:

[0157] -h e is the height of each blade equatorial portion parallel to the rotation axis of the blade;

[0158] -h is the height of each blade, i.e. the distance between the lower end and the upper end parallel to the rotation axis of the blade.

[0159] As described in the publication W. Tjiu, T. Marnoto, S. Mat, M. H. Ruslan, K. Sopian, Darrieus vertical axis wind turbine for power generation I: Assessment of Darrieus VAWT configurations, Renewable Energy 75 (2015) 50-67, it is preferred that Γ≥ 0.5.

[0160] It is preferred that 0.5≤Γ≤0.8. For example, Γ=0.6.

[0161] The relative height Γ defines the relative proportion of the curved equatorial portion of each blade.

[0162] The shape factor δ of each blade can also be defined as follows:

[0163]

[0164] wherein:

[0165] -h is the height of each blade parallel to the rotation axis;

[0166] -r max is the maximum radius of the blade.

[0167] The quantity 2r max corresponds to the diameter through which the turbine is turned in the equatorial plane.

[0168] It is preferred that 1.3≤δ≤1.5.

[0169] When Γ=0.6 and Ф=45°, it can be proven that δ=1.4 by using the following equation:

[0170]

[0171] The shape factor δ increases with Γ. When Γ is constant, the shape factor decreases as Ф increases, because r max also increases.

[0172] The shape factor Λ of the wind turbine can be defined as follows:

[0173]

[0174] This shape factor is the ratio between the minimum separation U between two blades of two different turbines and twice the maximum radius defined by each blade. Preferably, 0.05 < Λ < 0.3, or 0.1 < Λ < 0.3. In the example shown, Λ = 0.12.

[0175] From the above, it can be understood that the geometry of each blade results from the optimization of the relative height Γ (ratio ) of the equatorial portion, the shape factor δ (ratio ) of each blade and the shape factor Λ (ratio ) of the wind turbine, in order to optimize the efficiency of the wind turbine.

[0176] Description of the retaining structure

[0177] The wind turbine comprises a holding structure 50 for supporting the blades described above. As Figures 1A to 1C shown in the figures, the holding structure extends from the nacelle 40 of the generator 30. In the embodiment shown in the figures, the nacelle 40 is able to rotate around a fixed support 60. The support 60 is arranged at the top of a pylon 61. Figures 1A to 1C

[0178] ​The pillars 61 extend vertically from a base on which the wind turbine is rested. The base can be set on land. The base can also be set at sea by being mounted on a floating barge. In not deep waters, the base can be connected to the sea bottom. The pillars 61 allow to place the turbines 10, 20 at a height above the boundary layer as described in the background art. The "boundary layer" refers to the layer extending from the base in which the wind is not uniform and can be subject to irregularities due to the topography around the base. The boundary layer promotes the formation of eddies which can cause fatigue phenomena. The pillars 61 allow to lift the turbines 10, 20 above the boundary layer. The turbines are thereby exposed to a more uniform wind. In a maritime environment, to which the wind turbine according to the application is particularly suitable, the height of the pillars 61 can be comprised between 5 m and 50 m. The use of the tapered turbine shape described above facilitates lifting the most efficient equatorial portion so that it is located above the boundary layer while limiting the height of the pillars 61. The particular shape of the turbine allows to reduce the height of the pillars 61 and of the elements located around the nacelle 40. Thereby, the maintenance operations requiring access to the base or to the nacelle located on the base are not performed at great heights. The risk of the wind turbine toppling is also reduced. The proposed structure thereby allows to exploit the wind located above the boundary layer without the need of very high pillars.

[0179] The holding structure 50 comprises a mast 50 extending vertically from the nacelle 40 i . The median plane P m is formed by the mast and, more generally, by the symmetry plane of the whole holding structure. Along a horizontal longitudinal axis X parallel to the median plane, the mast 50 i is located upstream with respect to the downstream plane P a . The mast is thereby located upstream of the downstream plane P a when the wind direction is taken into account. As described hereafter, the setback distance d is adjusted to allow each blade to pass in the vicinity of the mast 50 i to create a yawing effect. The setback distance can be comprised between 0.75 r max and 1.25 times r max .

[0180] The holding structure 50 comprises an upper portion 50 s formed by:

[0181] - a first upper arm 51 extending from the mast 50 i to a first upper support 50 s adjacent to the upper end 10 s of the first turbine 10;

[0182] - a second upper arm 52 extending from the mast 50 i to a second upper support 52 adjacent to the upper end 20 s of the second turbine 20.s .

[0183] Figure 3A A top view of the wind turbine is shown. The retaining structure 50 and the downstream plane P are visible. a The distance between them varies depending on the different components of the retaining structure: vertical mast 50 i With downstream plane P a The distance between them is constant and equal to the aforementioned retreat distance d. Each upper arm 51, 52 is connected to the downstream plane P. a The distance between them increases as they approach the upper support member 51 s and 52 s And decrease. Figure 3A The wind direction W is shown, and the displacement of each turbine is indicated by dashed lines. The wind turbines are configured such that the mast is 50... i Located upstream of each turbine, the term "upstream" is relative to the wind direction. Because the longitudinal axis X-orientation is from mast 50... i The upper arm extends towards the downstream plane, thus extending simultaneously along both the vertical axis Z and the X-axis. The further it extends along Z, the closer the upper arm is to the downstream plane P. a The downstream plane includes the upper end of each turbine 10 s and 20 s .

[0184] Mast 50 i Connected to an angle relative to the vertical axis and from the mast 50 i Starting from the downstream plane P a A central column 53 extends from the ground. The inclination of the central column 53 relative to the vertical axis is thus relative to the inclinations of the upper arms 51 and 52 relative to the vertical direction, respectively. The retaining structure includes:

[0185] -At the central column 53 and the first upper support member 51 s The first branch cable 54 extends between them;

[0186] -At the central column 53 and the second upper support member 52 s The second branch 55 extends between them.

[0187] The first upper arm 51 extends to the first upper support member 51 s First upper support member 51 s Configured to accommodate the first upper end portion 11, which is coaxial with the first rotation axis Δ1 and connected to the first turbine 10. s First upper axis A s,1 Similarly, the second upper arm 52 extends to the second upper support 52. s Second upper support member 52 s Configured to accommodate the second upper end portion 21, which is coaxial with the second rotation axis Δ2 and connected to the second turbine 20. s The second upper axis As,2 "Upper shaft" refers to a rotating mechanical element having an upper end and connecting the upper end to the upper support. Each upper arm 51, 52 is in the mid-plane P. m On both sides, from the mast 50 i The retaining structure, formed by the mast, cables, and struts described below, is positioned relative to the mid-plane P. m symmetry.

[0188] First upper support component 51 s Second upper support member 52 s A retaining structure 50 is formed, pivotally connected to the first turbine 10 and the second turbine 20 respectively. The lower end of each turbine is pivotally connected to the nacelle 40. As described below, this pivotal connection ensures that the rotation of each turbine is transmitted to the generator 30. Upper support member 51 s 52 s Forming the upper axis A s,1 A s,2 A freely rotating pivotal connection. The blades are held in place at each (upper) end by a pivotal connection, allowing for a degree of rigidity and preventing deformation of the blades under tension during rotation. Each upper support includes a ball or roller bearing 56, which allows the upper shaft (A) s,1 Or A s,2 It rotates around the axis of rotation (Δ1 or Δ2) within each upper support.

[0189] Figure 3B The second upper support member 52 is shown. s A cross-sectional view. This figure shows the second rotation axis Δ2, and the second turbine 20 and the second upper support member 52. s The mechanical connection between the second upper rotating shaft A s,2 Second upper support member 52 s Includes an upper support 20 extending around the rotation axis Δ2 and allowing insertion of the upper support. s Axis A s,2 Rotating annular bearing 56.

[0190] Each upper arm 51, 52 serves as a support connecting the struts 54, 55 of the central column 53 to the turbines 10, 20, which are held in place by the upper support 51. s 52 s Stretching between the nacelle and 40. In the vertical plane, as... Figure 3C As shown, the forces applied at 51s and 52s to each upper support are of the type of gravity and centrifugal force. Figure 3C The diagram shows the second upper support 52 in the vertical plane YZ. sThe force applied at point S. Force F1 corresponds to gravity in a vertical orientation, and force F2 corresponds to centrifugal force pointing along the rotation axis Δ2. The centrifugal force originates from the tension exerted by the turbine under rotation. When the turbine 20 rotates, due to the centrifugal force, the blades 21 and 22 tend to move apart from each other, which is reflected in the upper support 52. s A resultant force F2 is generated at this point. Force F3 corresponds to the compressive resistance on the upper arm 52. Force F4 is the tensile force originating from the tension applied by the support cable 55. Figure 3B The diagram shows forces F1 to F4, and the resultant force:

[0191] -F 1+2 =F1+F2: This is the tension applied by the turbine;

[0192] -F 3+4 =F3+F4: This is the force applied to the retaining structure (upper arm 52 and support cable 55).

[0193] Thus, the upper arm 52 acts as a support, with two supports extending from its sides: a support cable 55 in the strict sense, and a turbine 20 that acts like a support cable by applying tensile stress to the upper arm during rotation. This results in force triangulation, which allows the upper arm 52 to withstand stress under the tension of the supports and the turbine. This type of structure, analogous to the structure of a suspension bridge, is particularly robust. As for the first upper support member 51 connected to the support cable 54 and the first turbine 10 that acts like a support cable during rotation... s The situation is naturally symmetrical. This type of triangular mesh is beneficial for force triangulation, tensile / compressive stress, and minimizing bending stress.

[0194] In the horizontal XY plane, the force applied to the retaining structure originates from thrust. Balance is ensured by a downstream (i.e., X-axis-oriented) "V" shape formed by the cables 54, 54 extending from the central column 53 and the two upper arms 51, 52. In the horizontal plane, the upper arms 51, 52 and the central column 53 act as braces, resisting compression. Each is connected to two cables that exert a tensile force that can be considered symmetrical on both sides of each brace thus formed. Different triangular grids are used for force triangulation.

[0195] This particularly involves:

[0196] - Connected to the central column 53 of the support cables 54 and 55;

[0197] - Second upper arm 52, which is connected to the support cable 55 and as combined Figure 3B The second turbine 20, which applies a tensile force;

[0198] - A first upper arm 51, which is connected to a support cable 54 and a first turbine 10 that applies a tensioning action similar to a turbine 20.

[0199] existFigure 3D The image shows the upper support member 52. s At this point, the triangulation of the forces applied in the horizontal plane: forces F5, F6, and F7 correspond to the compressive resistance applied by the upper arm 52, the tension applied by the support cable 55, and the tension applied by the turbine 20 under rotation (more specifically, the horizontal component of the centrifugal force applied to each blade). Force F 6+7 This corresponds to F6+F7.

[0200] Established on the downstream plane P a Parallel vertical plane YZ Figure 1C In the diagram, another triangular mesh is visible, formed by the support cable 54, the central column 53, and the upper arm 51. The central column 53 and the upper arm 51 are kept under compression by the support cable 54, which is subjected to tensile stress. This again minimizes the formation of bending stress. Symmetrically, the support cable 55, the central column 53, and the upper arm 52 define another triangular mesh.

[0201] The wind turbine's retaining structure also includes struts 41 to ensure anti-tipping reinforcement. Two struts 41 are located on the mast 50. i Starting from the mast 50, it extends towards the nacelle 40 supporting the generator 30. The strut is arranged in a V-shape, opening as it approaches the nacelle 40. Here, this involves reducing the force applied to the mast 50. i The struts are subjected to bending forces, and compressive stresses are exerted by the thrust applied to each turbine parallel to the wind direction. The only part of the structure that withstands bending stress is the section of the mast that extends between strut 41 and upper arms 51, 52.

[0202] According to this V-shape, as the strut approaches the nacelle 40, it separates from each other on both sides of the longitudinal axis X, and this V-shape ensures an anti-rolling effect. Thus, the strut 41 provides anti-tipping protection for the wind turbine (in the mid-plane P). m (rotation around the Y-axis) and anti-roll (in the mid-plane P) m The effect of rotation about the X-axis in a vertical plane. Due to the mast 50 i Located upstream of the turbine, strut 41 can be used. Thus, mast 50... i The location upstream of the turbine allows for the placement of struts, which reduces the bending stress applied to it.

[0203] The arrangement of struts 41 and, in particular, the inclination of each strut relative to the longitudinal axis X are configured to allow the blades to rotate.

[0204] like Figures 1A to 1C As shown, the cabin 40 can rotate freely about the vertical axis of rotation O relative to the support 60, and the mast 50 i Extending about this vertical axis of rotation. The nacelle 40 allows the assembly formed by the retaining structure 50, turbine, and generator 30 to rotate about the vertical axis of rotation O.Figure 1B The vertical axis O is shown in Figure 3A The rotation axis O corresponds to the center of the raceway 62.

[0205] Due to the symmetry of the wind turbine with respect to the median plane P m , the rotation of the nacelle allows to obtain a wind turbine self-regulating with respect to the wind direction. Under the action of the wind, forces are exerted on each turbine aiming at orienting these turbines in front of the mast so that the downstream plane P a tends to be passively oriented perpendicularly to the wind direction W. By "passively" it is meant without electric servo-control. This involves a passive yaw orientation. According to such an orientation, due to the symmetry of the whole with respect to the median plane P m , the thrusts exerted by each turbine respectively along the longitudinal axis X are symmetrical and balanced. In case of wind direction variation, an unbalance of thrusts occurs which leads to a self-regulation of the wind turbine so that the thrusts are balanced: the orientation of the wind turbine is self-regulating so that the downstream plane P a is always oriented perpendicularly to the wind. The self-regulation results from the symmetry of the wind turbine with respect to the median plane. In the example shown in Figures 1A to 1C , the nacelle is able to rotate on the rollers 41 along a circular raceway 62 provided on the fixed support 60. In Figure 3A , the raceway 62 and the orientation of the mast with respect to the downstream plane are shown schematically. The raceway extends along a horizontal rolling plane P r . The rolling plane is shown in Figure 1B and Figure 2C .

[0206] Alternatively, the nacelle 40 can be fixed with respect to the support 60. In this case, the orientation of the mast and turbines is predetermined according to the most frequent wind direction. This type of construction is suitable for maritime applications where the prevailing wind direction of the wind can be known. The form of contact between the nacelle and the support can then be an embedding.

[0207] Whatever the construction employed (fixed or able to rotate), the mast is located upstream of the blades, the term "upstream" being considered with respect to the wind direction.

[0208] The setback distance d of the mast 50 i with respect to the downstream plane P a can be optimized. The smaller d is, the radius r max of each blade must be reduced accordingly to allow the rotation of the blades between the rotation axis and the mast 50 i behind. The reduction of r max reduces the wind- facing area of the wind turbine. The larger the setback distance d is, the radius r max can be increased accordingly, which is detrimental to the sensitivity to increased rolling and to increased bulk. According to the invention, it is preferred that the ratio d / rmax is 0.4 to 0.6, for example around 0.5.

[0209] In addition to the reduction of the bending stress and the feasibility of a passive biased orientation, the mast 50 i arranged upstream of each turbine has the further advantage of a shadowing effect of the mast on the blades. This beneficial effect is for example generated when the blades are set to move downwind along the path closest to the mast (downwind mode). As Figure 4 indicated in Fig. 6, this shadowing effect can be ensured not only by the mast 50 i but also by a part of the upper arms. Figure 4 An upstream view of the wind turbine is shown. The mast 50 i can be dimensioned to shadow the wind affecting the part of the equatorial portion of each blade. The upper arms 51 and 52 can also contribute to the shadowing effect. This shadowing effect is generated when the blades move downwind in the vicinity of the arms in a region where the blades are not driven, i.e. the blades are not considered active. The shadowing effect thus contributes to increase the efficiency of the wind turbine.

[0210] The shadowing effect can be enhanced in a configuration as shown in Fig. 7, in which each upper arm comprises successive base arms. Thus, the first upper arm 51 comprises a first base arm 511 extending from the mast 50 i and a second base arm 512 extending between the first base arm 511 and the upper support 51 s . The second upper arm 52 comprises similarly arranged base arms 521 and 522. The further a base arm is from the mast 50 i , the greater the inclination of each base arm with respect to the vertical direction. Figure 5A

[0211] The use of base arms also allows to enhance the reinforcement of the holding structure. This also allows to avoid a buckling effect of each upper arm. The holding structure can comprise a reinforcement leg 581, 582 extending from the central column 53 to each junction between successive two base arms. The reinforcement legs are arranged to form a triangular grid, which is favorable to the appearance of tensile and / or compressive stresses. According to a variant, the number of successive base arms can be greater than 2.

[0212] The beneficial effects of the mast according to the upwind mode and according to the downwind mode are detailed in the variants described in connection with Figure 5E and Figure 5F .

[0213] Profile of the arm

[0214] Preferably, the upper arms 51 and 52 each have a vertical section whose profile corresponds to the profile of a so-called low camber wing section as shown in Figure 4 and Figure 5A and Figure 5B . In​Figure 5A The specific airfoil shape of the base arms composed of the wing sections is shown in Figure 5B The leading edge A is visible in the section, as well as the trailing edge F, opposite the leading edge. The leading edge and the trailing edge are connected to each other by the side wing surface V.

[0215] In a plane parallel to the median plane P m The profiles of these arms are traditionally defined by their vertical sections in a plane also parallel to the wind direction W. These profiles are the profiles of so-called thick wing sections, with a convex upper surface and a lower surface that is also convex but with a local concavity towards the trailing edge. In Figure 5C The local concavity of the lower surface is represented by the symbol C in the section. Its main role is to participate in the structural support of the turbine against the wind. The profile can be characterized by the relative thickness defined as the ratio between the maximum thickness of the profile and the chord length of the profile. The relative thickness can in particular approach a value of 0.5 to ensure a high structural strength. However, this relative thickness should approach 0.35 to obtain a high and therefore advantageous lift / drag ratio: the effect of the lift is to reduce the pressure exerted on the mast 50 i , then on the nacelle 40 by the struts 41. The drag generates an adverse overturning moment. The compromise value consists in setting the thick wing section profile so that the value of its angle of attack is in the lower range of its angle of stall, i.e. a value of 10° to 20°, for example 15°.

[0216] The "angle of attack" refers to the angle with respect to the horizontal direction formed by the straight line AF connecting the leading edge to the trailing edge, which is usually called the term "chord line".

[0217] The arms 51 and 52 thus defined, which are intended to provide lift, have a third advantage. Said arms can be likened to a pair of wings that thus emit an air flow in the direction of the ground to generate this lift. Part of this air flow is emitted in the vicinity of the upper support 51 s and 52 s . In this area, the turbine is impacted along a straight upper portion that is less efficient, which has no significant impact. By travelling along the leading edge of the arms towards the equatorial portion, the air flow reaches the most efficient portion of the blades.

[0218] Such a structure can contribute to the structural support of the turbine against the wind in a plane perpendicular to the downstream plane P aThe rectification of the wind and the increase in the intensity of the wind impacting the turbine are obtained by the rectification of the wind by the arms and by the rectification of the wind by the turbine. The rectification of the wind by the arms requires the rectilinear line AF connecting the leading edge A and the trailing edge F to be arranged according to a specific form depending on whether the turbine is in the wind direction or against the wind direction. The documents on the deflector for increasing the efficiency of a Darrieus turbine with isolated straight blades demonstrate that, in the case of against the wind direction, the angle of attack of the airfoil shape must be such that, after the blade has passed approximately 2 / 3 of its against the wind path, the rectilinear line AF preferably crosses the path of the blade. In the case of in the wind direction, the angle of attack of the airfoil shape must be such that, after the blade has passed half of its in the wind path, the rectilinear line AF crosses the path of the blade.

[0219] Furthermore, under certain conditions, the airfoil shape confers a certain lift on the upper arm, which tends to lighten the holding structure under the action of the wind. This allows the mast 50 i to be reduced. The pressure exerted by the struts 41 on the nacelle 40.

[0220] Generally, according to the combination Figures 5A to 5D of the variants discussed, each arm has a shaped vertical section extending between a leading edge and a trailing edge, the trailing edge being oriented towards the downstream plane P a . The line connecting the leading edge and the trailing edge can advantageously be inclined with respect to the horizontal direction at an angle of attack of 10° to 20°.

[0221] In Figure 5A , each turbine comprises three blades angularly spaced 120° from one another. Such a configuration is also shown in Figure 5D : the first turbine 10 comprises three blades 11, 12, 13. The second turbine 20 comprises three blades 21, 22, 23. According to the application, it is preferred that the turbine comprises either two blades angularly spaced 180° from one another or blades angularly spaced 120° from one another. Increasing the number of blades to more than three is not considered to be advantageous.

[0222] Profile of the mast

[0223] Figure 5E and Figure 5F variations are shown, according to which the mast 50 i has a horizontal section with an optimized profile. According to these variations, the mast extends around a central axis O. When the mast is able to rotate, the central axis O corresponds to the axis of rotation. The central axis O is arranged at a distance l with respect to the downstream plane P a . Thus, in consideration of the direction of the wind, the mast is upstream of the downstream plane P a . The mast is perpendicular to the median plane P mThe central axis O is at a distance l from the downstream plane. Depending on whether the turbine is configured in upwind or downwind direction, the distance l and the width w and the shape of the cross section of the mast in a plane perpendicular to the axis O (horizontal plane) can be adjusted to confer to the mast the positive effects on the turbine performance described below.

[0224] In considering the upwind direction, in addition to its supporting role in the retaining structure 50, the mast 50 i can also play the role of aerodynamic deflector as described in the publication Jin X, Wang Y, Ju W, He J, Xie S. Investigation into parameter influence of upstream deflector on vertical axis wind turbines output power via three-dimensional CFD simulation. Renew. Energ. 2018; 115: 41-53. The deflector combination in this study has two positive effects for improving efficiency:

[0225] - a braking effect in the inter-turbine region, resulting from the pressure drop downstream of the deflector which is subjected to a large pressure resistance;

[0226] - a fairing effect on the incident flow on the blades, which is reflected in an increase in their driving force. The fairing effect is felt in the section of the upstream half-ellipse swept by the blades, between the point most upstream included in this half-disk and the inter-turbine region, i.e. the region located between the two turbines.

[0227] The minimum width of the inter-turbine region (perpendicular to the median plane P m ) is the distance U described above. The results of the transplantation of the deflector of the publication to a Darrieus turbine with curved blades confirm, on the one hand, that the ratio w / 2r u = 0.33 constitutes an upper limit of acceptable width, the lower limit according to the invention being 0.25:

[0228] 0.25 < w / 2r u < 0.33.

[0229] And, on the other hand, that the ratio l / 2r u = 0.7 constitutes an upper limit of acceptable width, the lower limit according to the invention being 0.6:

[0230] 0.6 < l / 2r u < 0.7.

[0231] If it is said that the width w of the arrangement parallel to the downstream plane P a can be simply adjusted, the distance l can also be adjusted, the width w and the shape of the cross section of the mast in a plane perpendicular to the axis O (horizontal plane) being adjusted to confer to the mast the positive effects on the turbine performance described below.a The plate at a distance 1 from the mast, which obtains the effect of an aerodynamic deflector, the supporting action of the mast and the constraints imposed by the necessity of letting the turbine blades pass on both sides lead to the introduction of a two-dimensional T-shaped beam or triangular box section. In other words, it is preferable that the horizontal section of the mast have, between the convex upstream end and the downstream end, a horizontal section which extends parallel to the downstream plane P a the component forming the deflector, and which is located downstream of the deflector, extends perpendicular to the downstream plane P a the component extending downstream of the deflector, which performs a fairing of the air flow. By "fairing" it is meant that it tends to straighten the incident flow direction upstream of the deflector. Figure 5E One embodiment of such a section is shown, which is optimized for the turbine in adverse wind direction. In this figure, the horizontal section of the mast extends between a convex upstream end, which is exposed to the wind, and a downstream end. Between the upstream end and the downstream end, the horizontal section of the mast is formed by two concave portions which are symmetrical with respect to the median plane. The concavity provided in the downstream end gives a braking effect to the flow which was previously faired by the upstream end.

[0232] Figure 5F One embodiment of such a section is shown, which is optimized for the turbine in adverse wind direction. In this figure, the horizontal section of the mast extends between a convex upstream end, which is exposed to the wind, and a downstream end. Between the upstream end and the downstream end, the horizontal section of the mast is formed by two concave portions which are symmetrical with respect to the median plane. The concavity provided in the downstream end gives a braking effect to the flow which was previously faired by the upstream end. i may play a positive role in fairing the incident flow in the inter-turbine region. Indeed, in the adverse wind direction, the inter-turbine region is subjected to deep vortex separation. Advantageously, the mast has a thick profile, which comprises a convex upstream end, which is exposed to the wind, and a downstream end, which is located downstream of the median plane P m symmetrical with respect to the median plane P

[0233] 0.15 < w / 2r u < 0.25.

[0234] The aerodynamic center of the mast is located at a distance 1 upstream of the plane Pa as follows:

[0235] 0.6 < 1 / 2r u < 0.7.

[0236] The term "aerodynamic center" is a concept known in the field of aerofoils.

[0237] More generally, it is advantageous that the mast has a horizontal section which extends, between the convex upstream end and the downstream end, parallel to the median plane P m and which is located close to the downstream plane P a It is preferable that the horizontal section of the mast narrows between the upstream end and the downstream end. It is preferable that the horizontal section of the mast is symmetrical with respect to the median plane P mSymmetry. When the turbine is configured to turn in the opposite direction, the horizontal section of the mast has two concave portions disposed symmetrically with respect to the median plane between the upstream end and the downstream end.

[0238] Crossbar

[0239] Figure 6A and Figure 6C are views of shaped rigid crossbars adapted respectively to turbines having 3 blades and 2 blades. As mentioned above, the crossbars extend perpendicularly to the rotation axis and contribute to stiffen each turbine. These crossbars are shaped to reduce the drag. Figure 3A The crossbars shown in Figs. 1 1 and 12 comprise three legs extending at 120° from the center along the rotation axis. Each crossbar can be arranged between the respective two straight portions of a different blade, or near the junction between the equatorial portion and the straight portion of a different blade. Although it is particularly advantageous from a rigidity point of view to arrange the crossbar in the equatorial plane, such an arrangement would seem to cause the formation of vortices, which are sources of energy dissipation. It is preferable to use upper and lower crossbars arranged closer to one end (respectively, the upper end and the lower end) of the turbine than to the equatorial plane.

[0240] Each crossbar is formed according to an aerodynamic profile symmetrical with respect to a plane perpendicular to the rotation axis of the turbine. The junction of each crossbar with the blade can be optimized to form a connection angle 14' as shown in Figs. 1 1 and 12. The connection angle can define a radius decreasing from the leading edge to the trailing edge of the blade. Figure 6C

[0241] Figure 6D An interface part 14 s allowing to connect a crossbar (in this example, the upper crossbar 14 a to a blade (in this example, the blade 12) is shown. The interface part forms a T shape comprising three ends. The interface part is intended to be inserted or to surround the crossbar 14 s , and to be inserted or to surround the two portions 121, 122 of the blade 12. See Figure 6E , the interface part is configured so that the blade curvature has continuity between the two blade portions 121, 122. The interface part is engaged according to a nesting length, either in or around each portion of the crossbar or of the blade. This allows to distribute the forces along the nesting length. Then the fatigue effects that would occur at the junction are limited.

[0242] Electromechanical transmission chain

[0243] Figure 7A and Figure 7B The electromechanical drive chain of the wind turbine driving the generator is shown in detail. At each lower end, each turbine is connected to a lower rotation shaft A extending between each lower end and an angular transmission 31, 32​i,1 A i,2 Each lower rotation axis A i,1 A i,2 Parallel to the rotation axes Δ1 and Δ2 respectively. Each angular transmission device forms a lower rotation axis A that is inclined relative to the horizontal direction. i,1 A i,2 The horizontal driven shaft A of the generator 30 is parallel to the horizontal axis Y. r,1 A r,2 The mechanical connection between them. Each driven shaft drives the through shaft of a single generator 30. The connection between each driven shaft and the through shaft of the generator can be ensured by two flexible connectors, preferably of equal velocity, arranged on both sides of the generator. The flexible connectors allow the driven shaft A to be driven through the through shaft. r,1 A r,2 The through shaft is connected to generator 30. The flexibility of each connector allows for compensation for possible alignment defects, such as those caused by vibration or turbine stalling.

[0244] Figure 7B Details of the stacked elements from turbine 20 to angular transmission 32 are shown. This stack includes blade root flange 38, brake disc 37, brake shoe 36, and plate 35, which form the end of a plate gearbox. A plate gearbox is preferred to minimize dimensions parallel to the axis of rotation. This reduces potential leverage effects. This is achieved by connecting flange 38 to a screw around the periphery of plate 35, and then via a lower shaft A connected to gearbox 34. i,2 This ensures the transmission of rotation. Lower shaft A i,2 This includes connecting splines 33 of the insertion angle transmission 32. This arrangement forms a pivotal connection of a braking stage consisting of a brake disc 37 and brake shoes 36. The brake shoes 36 are supported by the gearbox 34. The brake shoes are configured to press against the brake disc 37, which is rigidly connected to a flange 38. This arrangement allows for a braking stage closest to each turbine, more specifically, between the gearbox and the turbine. This avoids transmitting braking torque through the gearbox. An additional brake disc may be arranged between the generator 30 and the gearbox 34. Such an additional brake disc may be needed during emergency braking. According to a variant, all or part of the gearbox may be partially integrated into the angle transmission. The angle transmission then includes pinions with different numbers of teeth to ensure multiplication.

[0245] Figure 7B The stack shown is compact, which allows for a reduction in the size of the nacelle. Assembly of the stack is simple because it consists of two main components: an angle drive 32 and a gearbox 34. The angle drive is pressed against the nacelle, while the gearbox is sandwiched between the angle drive and the turbine, connected to the turbine via a flange 38.

[0246] The stack forms a self-supporting assembly, without the need for retaining parts for connecting it to the nacelle. This results in a particularly compact nacelle. This allows the free space around the lower end of each turbine to be maximised, thus avoiding the formation of vortices that can be caused by a bulky nacelle or retaining parts.

[0247] The stack also allows the distance between the lower end of the turbine and the nacelle to be minimised. This reduces the lever effect. The inclination of the two axes of rotation allows the bevel gear 32 connected to each turbine on either side of the generator to be brought close together.

[0248] The wind turbine comprises a control unit, not shown, which ensures that the rotational speed of the turbines is continuously optimised.

[0249] Variants

[0250] In combination Figure 2A and Figure 2C The shape of the blades corresponds to the optimised configuration of the application. However, the blades can have other shapes without going beyond the scope of the application. Figure 8A and Figure 8B Examples of blades are shown, which, although not optimised, can be utilised. Such blades have the advantage of being simpler and less costly to manufacture.

[0251] In Figure 8A and Figure 8B each blade comprises a lower part and a straight upper part, which is inclined at an opening angle Ф with respect to the axis of rotation. As mentioned above, the opening angle adjacent the upper end can be different from the opening angle at the lower end. In Figure 8A the blade of the equatorial part is limited to the intersection between the lower part and the upper part.

[0252] In Figure 8B each blade comprises a flat equatorial part, at which the radius is maximum. The equatorial part extends between the lower part and the upper part, parallel to the axis of rotation of the blade.

Claims

1. A Darrieus type wind turbine (1) comprising cross-flow double-rotor turbines (10, 20) connected to a generator (30) comprising a shaft designed to be driven in rotation under the action of the rotation of said turbines, the wind turbine comprising: - a first turbine (10) rotatable about a first axis of rotation (Δ1) and comprising a plurality of blades (11, 12, 13) distributed about said first axis of rotation; - a second turbine (20) rotatable about a second axis of rotation (Δ2) and comprising a plurality of blades (21, 22, 23) distributed about said second axis of rotation; - said first axis of rotation and said second axis of rotation being mutually symmetrical with respect to a vertical axis (Z); wherein: - each turbine (10, 20) extends around an axis of rotation between a lower end (10 i , 20 i ) and an upper end (10 s , 20 s ), the lower end being closer to the generator than the upper end; - the lower end and the upper end of each turbine are aligned with the axis of rotation of said turbine; - each turbine blade comprises: • From the lower end (10) i The lower part extending from (11) i 12 i ); • an upper portion (11 s , 12 s ) extending from said upper end portion (10 s ) - each blade extends from said lower end to said upper end so that: • along said lower portion (11 i , 12 i ), the radius (r) of the blade corresponding to the distance between the blade and the rotation axis gradually increases as the distance from said lower end (10 i ) increases; • along said upper portion (11 s ), the radius of said blade gradually decreases as the distance from said upper end (10 s ) decreases; wherein: - said first axis of rotation and said second axis of rotation are inclined with respect to said vertical axis by the same inclination angle (a) comprised between 25° and 50°; - so that each axis of rotation converges on a single generator so that the horizontal shaft of said generator is driven in rotation by said first turbine and said second turbine; - said wind turbine defines a median plane (P m ), which median plane: • perpendicular to a downstream plane (P a ) containing said first rotation axis (Δ1) and said second rotation axis (Δ2); • through the intersection of said first axis of rotation and said second axis of rotation; - said median plane forms a plane of symmetry of said wind turbine.

2. A wind turbine according to claim 1, wherein, For each blade (11, 12): - at said lower end, said lower portion (11 i , 12 i ) forms a lower opening angle (F) with said rotation axis (Δ1), which is an acute angle; - at said upper end, said upper portion (11 s , 12 s ) forms an upper opening angle (Φ) with said rotation axis, which upper opening angle is an acute angle.

3. A wind turbine according to claim 2, wherein, - said lower opening angle and said upper opening angle are equal and form the same opening angle (Φ).

4. A wind turbine according to claim 3, wherein, - said opening angle is comprised between 40° and 60°.

5. A wind turbine according to claim 3, wherein, Each blade is such that the lower portion (11 i , 12 i ) is straight and / or the upper portion (11 s , 12 s ) is straight.

6. The wind turbine of claim 5, wherein: - each blade has an equatorial portion (11 e , 12 e ) connecting the lower portion and the upper portion; - in said equatorial portion (11 e , 12 e ) the radius of said blades reaches a maximum radius (r max ).

7. The wind turbine of claim 6, wherein: - the height (h) of each blade corresponds to the distance between said lower end and said upper end parallel to said axis of rotation; - each blade has a shape factor corresponding to the ratio between the height of said blade and twice the maximum radius of said blade; - the shape factor (δ) of each blade is comprised between 1.3 and 1.

5.

8. A wind turbine according to claim 7, wherein, For each blade: - said equatorial portion (11 e , 12 e ) is curved; - along said equatorial portion, from said lower portion (11 i , 12 i ), said radius gradually increases until reaching the maximum radius (r max ) of said blade, then gradually decreases until said upper portion (11 s , 12 s ).

9. A wind turbine according to claim 8, wherein, For each turbine: - an equatorial plane (P e,1 ) extending perpendicularly to said rotation axis, said equatorial plane passing through the maximum radius of each blade of said turbine; - said equatorial plane forms a plane of symmetry of said turbine.

10. A wind turbine according to claim 8, wherein, Each blade comprises: - a lower junction (11 ei ) corresponding to the junction between the lower portion and the equatorial portion; - an upper junction (11 es ) corresponding to the junction between the upper portion and the equatorial portion; Each blade so that: - the distance between the lower joint and the upper joint parallel to the axis of rotation forms the height (h) of the equatorial portion e ); - the relative height (Γ) of said equatorial portion corresponds to the ratio between the height of said equatorial portion and the height (h) of said blade; - the relative height (Γ) of each blade is greater than 0.5 and less than 0.

8.

11. The wind turbine of claim 6, wherein: - two blades belonging to two different turbines are spaced apart by a minimum spacing (U) during their rotation about their respective axis of rotation; - the shape factor (Λ) of said wind turbine corresponds to the ratio between said minimum spacing and twice the maximum radius; - the shape factor of said wind turbine is comprised between 0.1 and 0.

3.

12. A wind turbine according to claim 1, wherein, Each turbine (10, 20) comprises two blades, each blade being symmetrical to the other with respect to the axis of rotation (Δ1, Δ2) of said turbine.

13. A wind turbine according to claim 1, wherein, Each turbine has three blades uniformly distributed about the axis of rotation of said turbine.

14. The wind turbine of claim 1, wherein: - said first turbine (10): - said second turbine (20): • at its lower end (10 i ) is connected to a first lower rotation axis (A i,1 ) ; • at its upper end (10 s ) is connected to a first upper rotation axis (A s,1 ); • said first lower rotation axis, said first upper rotation axis and said first rotation axis (Δ1) are coaxial; - said second turbine (20): • at its lower end (20 i ) is connected to a second lower rotation axis (A i,2 ); • at its upper end (20 s ) is connected to a second upper rotation axis (A s,2 ); • said second lower rotation axis, said second upper rotation axis and said second rotation axis are coaxial; - said wind turbine comprises a holding structure (50) comprising: • a nacelle (40) supporting a generator; • a mast (50 i ) extending vertically from the nacelle (40) and centered with respect to the median plane, the mast being set back with respect to the downstream plane by a set back distance (d) along a longitudinal direction perpendicular to the downstream plane; • a first upper arm (51) extending from the mast (50 i ) to a first upper support (51 s ) which holds the first upper rotation axis; • a second upper arm (52) extending from the mast (50 i ) to a second upper support (52 s ) which holds the second upper rotation axis; • said first upper arm and said second upper arm are inclined with respect to a vertical axis.

15. The wind turbine of claim 14, wherein: - said first upper support (51 s ) comprises a bearing in which said first upper rotation shaft (A s,1 ) is inserted; - said second upper support (52 s ) comprises a bearing in which said second upper rotation shaft (A s,2 ) is inserted.

16. A wind turbine according to claim 14, wherein, said holding structure further comprises: - a king post (53) extending from said mast away from said downstream plane; - a first stay (54) extending between said king post and said first upper arm; - a second stay (55) extending between said king post and said second upper arm.

17. The wind turbine of claim 16, wherein: - said first stay (54) extends between said king post and said first upper support; - said second stay (55) extends between said king post and said second upper support.

18. A wind turbine according to claim 14, wherein, Said first and second upper arms comprise successive base arms (511, 512, 521, 522) which extend respectively towards said first (51 s ) and second (52 s ) upper supports, each base arm being more inclined with respect to the vertical direction the closer it is to said first or second upper support.

19. A wind turbine according to claim 14, wherein, At least one strut (41) extends between said mast (50 i ) and said nacelle, said strut being inclined with respect to the vertical and extending from said mast (50 i ) towards said downstream plane (Pa).

20. A wind turbine according to claim 14, wherein, Said nacelle is able to rotate around a vertical rotation axis (O) so that the wind blowing along a direction (W) spontaneously arranges said turbines along said direction downstream of said mast (50 i ) extending around this vertical rotation axis, under the action of the thrust exerted by the wind on each turbine.

21. A wind turbine according to claim 14, wherein, said nacelle is fixed in rotation and wherein said turbines (10, 20) are arranged downstream of said mast along a direction corresponding to a prevailing wind direction.

22. A wind turbine according to claim 14, wherein, Each lower rotation axis (A i,1 , A i,2 ) is connected to the shaft of the generator (30) by means of an angle transmission (32).

23. A wind turbine according to claim 22, wherein, A brake (36, 37) is arranged between each herringbone gear (32) and each respective lower end of each turbine.

24. A wind turbine according to claim 1, wherein, At least one crossbar (14 s , 14 i ) is arranged between two different blades of the same turbine.

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