EP1446577A1

EP1446577A1 - Wind turbine diffuser

Info

Publication number: EP1446577A1
Application number: EP02795384A
Authority: EP
Inventors: Pascal Ferracani
Original assignee: Cita
Current assignee: Cita
Priority date: 2001-11-19
Filing date: 2002-11-19
Publication date: 2004-08-18
Also published as: FR2832465A1; US20050069415A1; FR2832465B1; CA2466897A1; WO2003044361A1; AU2002360179A1

Abstract

The invention concerns a diffuser for a wind turbine, in particular a large-dimension wind turbine mounted on a mast (2) and comprising a wind-driven propeller (3) equipped with blades (5) as well as an alternator converting wind kinetic energy into electric power. The invention is characterized in that it consists of a circular element (7) enclosing the ends (9) of the blades (5), and consisting of a skin (14) made of a stretched textile membrane associated with a rigid internal and/or external framework (15) supporting the loads and enabling to stretch the membrane and forming it.

Description

The invention relates to a diffuser for a wind turbine, in particular a large wind turbine mounted on a mast and comprising a wind-driven propeller, as well as an alternator cooperating with the propeller to provide electric energy.

Specialists have long sought to recover wind energy which has the advantage of being clean, that is to say not to generate thermal or chemical pollution and at the same time to be inexhaustible. These advantages are however offset by a series of drawbacks in particular linked to the dispersed and intermittent nature of the wind; it is also well known that wind farm “parks” consume a lot of space and do not operate without noise pollution.

In addition, the wind turbines currently used are most often equipped with propellers with radial blades and with a horizontal axis similar to those allowing the propulsion of airplanes, but as a rule much larger. Such propellers conventionally cooperate with dynamos or industrial alternators with speed multiplier drives, which makes them heavy, expensive and of low efficiency. These drawbacks mean that the wind turbine market has not experienced the growth that one would have expected in recent years and that the development prospects in this field are very broad today.

To overcome these drawbacks, it has recently been proposed in accordance with document FR-2 793 528 a more robust wind turbine, less bulky at equal power and less noisy than the wind turbines previously proposed.

Such a wind turbine is mounted on a vertical mast and comprises a wind-actuated propeller which is equipped with helical blades inclined upstream carried by a hub of horizontal axis as well as an alternator cooperating with the propeller to provide electric power and which is equipped with a magnetic rotor fixed to the hub and a stator with magnetic coils adjacent to the rotor and fixed to a fixed frame.

This wind turbine is furthermore equipped with a static diffuser constituted on the one hand by a fixed circular element of relatively short length mounted concentrically with the hub on arms integral with the chassis and cooperating with little play with the ends of the blades, and comprising both on the other hand a rounded leading edge followed by a thick hull and a thin diverging trailing edge.

Numerous wind tunnel tests have shown that this wind turbine has aerodynamic characteristics far superior to those of previous conventional wind turbines.

This situation is due to the optimized profile of the rotor blades and the presence of the divergent diffuser.

Such a diffuser conventionally consists of a skin which gives it its profile and an internal structure such as to absorb the forces and to receive the end of the support arms allowing the diffuser to be centered around the blades of the wind turbine.

In the case of small wind turbines (up to a few meters in diameter), we can use boilermaking solutions or conventional manufacturing technologies and use, for example, either thin composite skins associated with an internal box to combined structure foam / epoxy glass, ie rigid thick skins in particular in plastic, steel or Duralumin ^® also serving as structure.

However, for wind turbines with larger diameters (up to several tens of meters) these conventional technologies are excluded: indeed, steel skins with a thickness of 1 to 2 mm would generate a mass that is far too significant and too high a cost, and would nevertheless require the presence of a substantial and rigid internal structure.

It is no more conceivable for economic reasons to produce a diffuser in composite material since the costs of the tools and of the raw materials would reach excessive proportions.

Consequently, the known solutions cannot be transposed to the production of diffusers for large-scale wind turbines of the aforementioned type because they would not be viable on an industrial scale.

However, so far no technology has been proposed to limit the weight and cost of such diffusers.

The object of the present invention is to fill this gap. To this end, it relates to a diffuser for wind turbines, in particular large wind turbines mounted on a mast and comprising a wind-driven propeller equipped with blades, as well as an alternator transforming the kinetic energy of the wind into electricity. According to the invention, such a diffuser is characterized in that it is formed by a circular element surrounding the ends of the blades, and consisting of a skin made of a stretched textile membrane associated with a rigid internal and / or external framework supporting the efforts and allowing the membrane to be stretched and shaped.

It should be noted that the invention advantageously applies to a wind turbine of the aforementioned type but could just as easily adapt to any faired wind system.

According to the invention, the textile membrane preferably has a density of the order of 1 kg / dm ³ .

The implementation of such a textile membrane proves to be particularly advantageous: in fact there are currently membranes of this type on the market having high mechanical properties, good resistance to UN radiation and good weather resistance; in addition, the manufacturers offer maintenance facilities in the event of a tear.

It should also be noted that the tension of this textile membrane, which is produced by the internal framework, can be adjustable over time to compensate for possible creep phenomena in the materials. According to another characteristic of the invention, the textile membrane is equipped with a lattice making it possible to reinforce it in particular in its zone located near the blades.

Over the entire profile of the diffuser, that is to say on the internal and external surfaces of the latter, it can occur locally according to the main direction of the wind relative to the axis of rotation of the blades of the depressions. important that can take off the textile membrane of the internal framework.

However, it is essential that this phenomenon does not occur in the area located near the blades in order to avoid any risk of tearing.

For this reason, it is imperative to provide at this level either a reinforcing lattice or means for fixing the textile membrane to the internal framework.

According to another characteristic of the invention, the rigid framework comprises a series of identical radiating ribs, closed on themselves in a flat curve having a wing-shaped contour corresponding to the profile of the diffuser and materializing the internal surfaces and external of it. These radiating ribs can advantageously be made of a metal such as steel or aluminum or also of wood or a composite material.

According to another characteristic of the invention, the rigid framework also comprises a series of peripheral members allowing the connection of the radiating ribs and if necessary a series of stiffening elements making it possible to keep the thickness of the profile of the diffuser constant.

These members and these stiffening elements can be made of materials similar to the constituent materials of the radiating ribs.

According to a first variant of the invention, the radiating ribs as well as the peripheral members consist of steel tubes. According to this variant, the neighboring peripheral members can advantageously be connected by stiffening elements constituted by steel profiles located in the plane of the radiating ribs along the internal and external faces of the diffuser and / or transverse thereto. Additional steel rods also having a stiffening function can optionally connect the radiating ribs parallel to the peripheral members.

According to a second variant of the invention, the radiating ribs are formed by aluminum profiles having in particular an Ω-shaped section while the peripheral members are constituted by aluminum tubes.

According to this variant, the various aluminum tubes constituting the peripheral members can advantageously be connected to each other by other aluminum tubes acting as stiffening elements.

It should be noted that the framework corresponding to this second variant is largely similar to that corresponding to the first variant of the invention but has the advantage of having a reduced weight, by the nature of the materials used. According to a third variant of the invention, the radiating ribs are constituted by wooden profiles, in particular in the shape of a T and the peripheral members are constituted by carbon beams, in particular of rectangular section connected in pairs. by webs, in particular plywood on both sides of the radiating ribs so as to define boxed beams.

These boxed side members are preferably hollowed out in their middle part so as to limit as much as possible the weight of the rigid frame, and as a rule connected two by two by cables made of stainless steel.

According to a fourth variant of the invention, the radiating ribs are constituted by elements in particular of rectangular section made of a glued laminated composite material and the peripheral members consist of beams, in particular of rectangular section made of a composite material glued laminated laminated in pairs on both sides of the radiating ribs by a series of rings rigidly fixed to each other and also made of glued laminated composite material. According to this variant of the invention, the internal and external faces of each of the radiating ribs are preferably connected by a series of rings rigidly fixed to each other and made of a glued laminated composite material acting as stiffening elements. . It is also advantageous to provide additional wooden strips connecting the radiating ribs parallel to the peripheral members.

The characteristics of the wind turbine diffuser which is the subject of the invention will be described in more detail with reference to the nonlimiting configuration examples shown in the accompanying drawings in which:

FIG. 1 is a perspective view of a wind turbine fitted with a static diffuser according to the invention,

FIG. 2 is a partial axial section view of this wind turbine, FIG. 3 is a partial perspective view illustrating the installation of the static diffuser,

FIG. 4 is an axionometric view showing a detail of the framework of a diffuser according to the first variant of the invention,

FIG. 5 is an axionometric view similar to FIG. 4 but showing the framework of a diffuser according to the second variant of the invention, FIG. 6 is an axionometric view similar to FIG. 4 but showing the framework of a diffuser according to the third variant of the invention,

- Figure 7 is an axionometric view similar to Figure 4 but showing the framework of a diffuser according to the fourth variant of the invention

According to Figures 1 and 2, the wind turbine 1 is mounted on a vertical mast 2 and comprises a propeller 3 actuated by the wind which is equipped with helical blades 5 inclined upstream. The blades 5 are carried by a hub 4 with a horizontal axis.

The wind turbine 1 also includes an alternator not shown in the figures which cooperates with the propeller 3 to supply electrical energy.

This alternator is equipped with a magnetic rotor fixed to the hub 4 and a stator with magnetic coils adjacent to the rotor and fixed to a fixed frame 6.

The rotor and the stator are not shown in the figures. The wind turbine is also equipped with a static diffuser 7 constituted by a fixed circular element of relatively short length. This diffuser 7 is mounted concentrically with the hub 4 on arms 8 integral with the chassis 6 and cooperates with low clearance with the ends 9 of the blades 5.

According to FIG. 2, the static diffuser 7 has an aerodynamic profile and has a rounded leading edge 10 followed by a thick hull 11 and a thin diverging trailing edge 12.

According to Figure 1, the diverging trailing edge 12 is supported by gussets 13 distributed in radial planes.

According to FIG. 2, this configuration makes it possible to create a divergence of the air flow downstream of the diffuser according to the arrows F and F '.

The configuration of the static diffuser which is the subject of the invention will now be described with reference to FIGS. 3 to 6.

It should be noted that in these figures, the blades 6 of the propeller 3 are not shown but are simply shown diagrammatically by their axis XX '.

According to Figure 3, the diffuser 7 consists of a skin 14 made of a textile material of very low density. This skin 14 is stretched on a rigid frame 15 allowing it to be shaped and centered around the blades 6.

The frame 15 is essentially constituted on the one hand by a series of radiating ribs 16 all identical and on the other hand by a series of peripheral members 17 having the function of allowing the connection of the radiating ribs 16 and receiving the end of the arm 8 on which the diffuser 7 is mounted.

According to FIG. 3, the radiating ribs 16 are constituted by elements closed in on themselves in a plane curve having a wing-shaped contour corresponding to the profile of the diffuser 7 as shown in FIG. 2.

These radiating ribs 16 thus materialize the internal surface 18 and the external surface 19 of the diffuser 7.

According to Figure 4, the radiating ribs 16ι and the peripheral members 17ι are constituted by steel tubes.

The constituent tubes of the peripheral members 17ι are interconnected by different stiffening elements to allow the thickness of the profile of the diffuser 7 to be kept constant.

According to Figure 4, these elements include steel profiles 20 located in the planes of the radiating ribs 16ι as well as cables 21 made of stainless steel which are located transverse to these planes.

These different stiffening elements 20, 21 also cooperate with annexed steel rods 22 connecting the radiating ribs 16ι parallel to the peripheral members 17ι.

According to FIG. 5, the radiating ribs I62 are constituted by aluminum profiles having a section in the shape of an Ω while the peripheral members 172 are constituted by aluminum tubes. The various neighboring tubes 172 on the internal surface 18 or on the external surface 19 of the diffuser 7 or on either side of the radiating ribs I62 are connected by aluminum tubes 23 situated in the plane of the radiating ribs I62 or transversely with respect to to these in a pyramidal configuration so as to make it possible to stiffen the internal framework 15 of the diffuser 7.

According to FIG. 6, the radiating ribs I6 ₃ are formed by T-shaped wooden profiles while the members peripherals 17 ₃ are constituted by carbon beams of rectangular section.

Except at the front and downstream ends of the radiating ribs I63, the beams 17 ₃ are connected in pairs, on either side of these ribs I63, by plywood cores 24 equipped with recesses 25 at their middle part.

The beams 173 and the plywood cores 24 thus define boxed beams making it possible to maintain the thickness of the profile of the diffuser 7. According to FIG. 6, the neighboring boxed beams are connected together by stiffening cables 26 arranged obliquely to the plan of radiating ribs I63.

According to FIG. 7, the radiating ribs I64 are constituted by elements of rectangular section based on wood made of a glued-laminated composite material while the peripheral members 174 are constituted by beams of rectangular section made of a similar material.

The beams 17 ₄ are connected two by two on either side of the radiating ribs I64 by a series of rings 27 rigidly fixed to each other and also made of a laminated composite material.

According to FIG. 7, the internal 18 and external 19 faces of the radiating ribs I64 are also connected to one another by a series of rings 28 rigidly fixed to each other and also made of a glued laminated composite material.

These rings 28 also cooperate with wooden strips 29 connecting the radiating ribs I64 parallel to the peripheral members 17 ₄ .

It should be noted that in accordance with this configuration, the fixing arms 8 are not directly fixed on the peripheral members 174 at their external ends 81, but mounted at this level on fixing plates 30 themselves fixed on the rings 27, 28.

Claims

CLAIMS 1) Diffuser for wind turbines, in particular large wind turbines mounted on a mast (2) and comprising a propeller (3) powered by the wind equipped with blades (5) as well as an alternator transforming the kinetic energy of the wind in electricity, characterized in that it is formed by a circular element (7) surrounding the ends (9) of the blades (5), and consisting of a skin (14) made of a stretched textile membrane associated with an internal framework and / or rigid external (15) supporting the forces and making it possible to tension the membrane and to shape it.

2) Diffuser according to claim 1, characterized in that the textile membrane (14) has a density of the order of 1 kg / dm ³ .

3 °) Diffuser according to any one of claims 1 and 2, characterized in that the textile membrane (14) is equipped with a lattice making it possible to reinforce it in particular in its zone located near the blades (5).

4 °) diffuser according to any one of claims 1 to 3, characterized in that the rigid frame (15) comprises a series of identical radiating ribs (16), closed on themselves in a plane curve having a contour in wing shape corresponding to the profile of the diffuser (7) and materializing the internal (18) and external (19) surfaces thereof.

5 °) Diffuser according to claim 4, characterized in that the rigid frame (15) comprises: a series of peripheral members (17) allowing the connection of the radiating ribs (16), and if necessary a series of stiffening elements allowing the thickness of the diffuser profile (7) to be kept constant.

6 °) Diffuser according to claim 5, characterized in that the radiating ribs (16ι) as well as the peripheral members (17ι) are constituted by steel tubes.

7 °) Diffuser according to claim 5, characterized in that the radiating ribs (I62) are constituted by aluminum profiles having in particular an Ω-shaped section while the peripheral members (172) are constituted by aluminum tubes.

8 °) Diffuser according to claim 5, characterized in that the radiating ribs (I63) are constituted by wooden profiles in particular in the shape of a T and the peripheral members (173) are constituted by carbon beams, in particular of rectangular section - laire connected two by two by webs (24), in particular plywood on either side of the radiating ribs (I63) so as to define boxed side members.

9 °) Diffuser according to claim 8, characterized in that the boxed beams are provided with recesses (25) at their middle part.

10 °) diffuser according to claim 5, characterized in that the radiating ribs (I64) consist of elements, in particular of rectangular section made of a laminated-glued composite material and the peripheral members (174) consist of beams, in particular of rectangular section made of a glued laminated composite material linked in pairs on either side of the radiating ribs (I64) by a series of rings (27) rigidly fixed to each other and also made of a glued laminated composite material.

11 °) Diffuser according to claim 10, characterized in that the internal (18) and external (19) faces of each of the radiating ribs (I64) are connected by a series of rings (28) rigidly fixed to each other and made of a glued laminated composite material.