HORIZONTAL-AXIS TURBINE FOR A WIND GENERATOR, AND WIND GENERATOR COMPRISING SAID TURBINE

Abstract

Horizontal-axis turbine for a wind generator, the turbine comprising a hub and two opposed blades, the turbine being characterized in that:

said hub is adapted to be directly or indirectly connected to a supporting pole (P) of the wind generator, and comprises a rotary part (M2), to which said two blades are connected;
said two blades are elongate in a longitudinal direction operationally orthogonal to the central axis of rotation (A) of the turbine,
each one of said two blades comprises a wing (A1, A2) and a deflector (D1, D2) fixedly connected to said rotary part (M2), the wing and the deflector having a head and a tail, the deflector tail being proximal to the wing head,
the deflector is positioned ahead of the respective wing with respect to the direction of rotation of the turbine, so as to deflect the air flow towards the wing,
the tail of each deflector is spaced apart from the head of the respective wing, so as to define a gap (L1, L2) between the deflector and the wing,
the wing and the deflector of each one of said two blades are connected at their outermost ends by a connection element (F).

Claims

1. Horizontal-axis turbine for a wind generator, the turbine comprising a hub and two opposed blades, the turbine being characterized in that: said hub is adapted to be directly or indirectly connected to a supporting pole (P) of the wind generator, and comprises a rotary part (M2), to which said two blades are connected; said two blades are elongate in a longitudinal direction operationally orthogonal to the central axis of rotation (A) of the turbine, each one of said two blades comprises a wing (A1, A2) and a deflector (D1, D2) fixedly connected to said rotary part (M2), the wing and the deflector having a head and a tail, the deflector tail being proximal to the wing head, the deflector is positioned ahead of the respective wing with respect to the direction of rotation of the turbine, so as to deflect the air flow towards the wing, the tail of each deflector is spaced apart from the head of the respective wing, so as to define a gap (L1, L2) between the deflector and the wing, the wing and the deflector of each one of said two blades are connected at their outermost ends by a connection element (F).

2. Turbine according to claim 1, wherein said hub has a biconvex shape defined by the revolution of an aerofoil.

3. Turbine according to claim 1, wherein said deflector and said wing have a section defined by a wing profile and a development characterized by a twist, with a chord that defines the profile length having a dimension that is greater at the hub and decreases linearly towards the outside of the turbine, being at its minimum at said connection element (F).

4. Wind generator comprising said turbine according to claim 1, the generator comprising: a rigid supporting tube (S) adapted to be connected, at a first end thereof, to a fixed part (M1) of the hub, said fixed part being connected to said rotary part (M2); an electromagnetic generator (G) directly or indirectly connected to a second end of said supporting tube (S) and to said supporting pole (P); an elastic metal cable inside the supporting tube (S), adapted to transfer the rotation of said rotary part (M2) to said electromagnetic generator (G).

5. Wind generator according to claim 4, comprising an interface (C) between said second end of the supporting tube (S) and said electromagnetic generator (G), said interface (C) being fixedly or rotatably connected to said supporting pole (P), said interface (C) being in a position away from said turbine and cantilevered relative to the supporting pole (P), so as to provide balancing of the weights of said wind turbine generator.

6. Wind generator according to claim 5, wherein said electromagnetic generator (G) has an axis of rotation (E) orthogonal to said axis of rotation (A) of the turbine, and said supporting tube (S) is substantially L-shaped, with a first part aligned with said axis of rotation (A) of the turbine, a second part aligned with said axis of rotation (E) of the electromagnetic generator (G), and a curved central connecting part.

7. Wind generator according to claim 5, wherein said electromagnetic generator (G) has an axis of rotation (E) parallel to said axis of rotation (A) of the turbine, and said supporting tube (S) is substantially U-shaped, with a first part aligned with said axis of rotation (A) of the turbine, a second part aligned with said axis of rotation (E) of the electromagnetic generator (G), and a curved central connecting part.

8. Wind generator according to claim 5, comprising a vane (B) in said curved central part.

9. Turbine according to claim 1, wherein an electromagnetic generator (G) is directly connected to said rotary part (M2).

10. Wind generator comprising said turbine according to claim 2, the generator comprising: a rigid supporting tube (S) adapted to be connected, at a first end thereof, to a fixed part (M1) of the hub, said fixed part being connected to said rotary part (M2); an electromagnetic generator (G) directly or indirectly connected to a second end of said supporting tube (S) and to said supporting pole (P); an elastic metal cable inside the supporting tube (S), adapted to transfer the rotation of said rotary part (M2) to said electromagnetic generator (G).

11. Wind generator comprising said turbine according to claim 3, the generator comprising: a rigid supporting tube (S) adapted to be connected, at a first end thereof, to a fixed part (M1) of the hub, said fixed part being connected to said rotary part (M2); an electromagnetic generator (G) directly or indirectly connected to a second end of said supporting tube (S) and to said supporting pole (P); an elastic metal cable inside the supporting tube (S), adapted to transfer the rotation of said rotary part (M2) to said electromagnetic generator (G).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0202] These features will become more apparent in the light of the following descriptions of some preferred embodiments, illustrated merely by way of non-limiting example in the annexed drawings, wherein:

[0203] FIGS. 1 and 2 illustrate vectorial graphs showing the trends of the forces involved in prior-art turbines;

[0204] FIGS. 3 and 4 illustrate graphs showing the trends of the most important parameters in prior-art turbines;

[0205] FIG. 5 shows the trends of the Cp parameter as a function of the TSR parameter for different types of known turbines;

[0206] FIG. 6 shows a perspective view of a first variant of a wind turbine according to the invention;

[0207] FIG. 7 shows a perspective view of a second variant embodiment of the wind turbine according to the invention;

[0208] FIGS. 8 and 9 show perspective views of a third variant embodiment of the wind turbine according to the invention;

[0209] FIG. 10 shows vectorial graphs that illustrate the trends of the forces involved in the turbines of the invention.

[0210] In the drawings, the same reference numerals and letters identify the same items or components.

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION

[0211] With reference to FIG. 6, the following will describe a first generic and non-limiting exemplary embodiment of the turbine proposed herein, which has two blades and respective deflectors.

[0212] In FIG. 6, T designates a turbine for a wind generator having its axis parallel to the wind direction (indicated by an arrow), configured for transforming kinetic energy of an air mass in motion (i.e. kinetic energy of the wind) into mechanical energy in the form of output of propulsive torque at a given revolution frequency through a suitably supported shaft.

[0213] The turbine T comprises two opposed blades, elongated in a longitudinal direction operationally orthogonal to its central axis of rotation A.

[0214] The blades are connected to a supporting hub M to rotate about the central axis A.

[0215] Each blade comprises a wing (A1, A2) and a deflector or flap (D1, D2) fixedly connected to the hub.

[0216] The wing and the deflector have a head and a tail. The deflector tail is proximal to the wing head; the deflector is in a position ahead of the wing with respect to the direction of rotation of the turbine, so as to deflect the air flow towards the wing.

[0217] Preferably, the tail of each deflector is spaced apart from the head of the respective wing to define a gap (L1, L2) between the deflector and the wing.

[0218] Preferably, the aerofoil of each wing and each deflector is biconvex. The wing and the deflector of the blade are connected at their outermost ends by a connecting element F, e.g. of the winglet type.

[0219] In the example of embodiment shown in FIG. 6, unlike most prior-art turbines, the electromagnetic generator G is outside the turbine body.

[0220] In this non-limiting example, the electromagnetic generator G is arranged at the base of a rigid supporting tube S, forming a 90-degree bend relative to the supporting pole P, so that it can be moved away from the blades in order to reduce its shadow effect on the turbine.

[0221] The choice of moving the generator away from the turbine body provides multiple advantages: extremely small hub dimensions, resulting in greater wing extension for the same swept area the turbine is very light, and therefore the terminal part of the supporting tube (from generator to turbine) can be very slim and have a curved shape (reduced shadow effect).

[0222] For applications wherein the turbine must rotate about an axis R, e.g. coinciding with the axis of the supporting tube S, in order to align its axis of rotation A with the wind direction, the generator G is connected to the supporting pole P through an interface C that allows the turbine+generator assembly to rotate about the axis R and orient itself in the wind direction. The generator G is cantilevered relative to the supporting pole P.

[0223] The assembly composed of the turbine T, the supporting tube S, the interface C and the electromagnetic generator G constitutes a balanced system in terms of gravitational inertial forces, as far as the rotation about the axis R is concerned, thus ensuring that the system will only rotate because of the effect of aerodynamic actions.

[0224] At its base, the supporting tube S is rigidly fitted to the interface C, which in turn is rigidly fixed to the electric generator G.

[0225] At the upper end, the supporting tube S is rigidly fitted to the front part of the hub M of the turbine T.

[0226] The hub M comprises a fixed part M1, connected to the tube S, and a rotary part M2, to which the blades are connected.

[0227] The fixed hub portion M1 is connected to the rotary part M2 by means of, for example, a bearing system.

[0228] In one possible embodiment, the rotary motion of the turbine T about the axis A is transferred to the shaft of the generator G, which rotates about an axis E, by means of an elastic metal cable inside the supporting tube S, rigidly fixed at its ends to the turbine T and to the shaft of the electromagnetic generator G. The cable may be a twisted steel-wire cable, a spring cable, etc.

[0229] In this non-limiting example, the axis A and the axis E run in orthogonal directions.

[0230] As a consequence, the axis E and the axis R are parallel to each other and have some eccentricity necessary for balancing the above-mentioned inertial masses.

[0231] The supporting tube S is substantially L-shaped, with a first part aligned with the axis of rotation A of the turbine, a second part aligned with the axis of rotation E of the electromagnetic generator G, and a curved central connecting part.

[0232] Within the connection interface C there are a system, coaxial to R, which allows the rotation of the assembly T-S-C-G about the axis R, and a rotary contact for the electric transfer of the produced current from the electromagnetic generator G to the electronic management system (not shown). The system is, for example, a bearing system.

[0233] In an implementation variant, as shown in FIG. 7, the axes E and A are parallel, and therefore the rigid supporting tube S has two parallel sections joined by a 180-degree central part, one section being connected to the fixed part M1 of the hub and the other section being connected to the interface C. In a preferred embodiment, this variant envisages that the supporting tube S supports the turbine T from behind, not from the front. In this case, the fixed hub portion is the rear one, not the front one, with respect to the wind direction, and the turbine takes the UPWIND configuration. In this case as well, the generator G is cantilevered relative to the supporting pole P.

[0234] The supporting tube S is substantially U-shaped, with a first part aligned with the axis of rotation A of the turbine, a second part aligned with the axis of rotation E of the electromagnetic generator G, and a curved central connecting part. In this variant, the supporting tube S may therefore be equipped with a stabilizer vane B, preferably applied to the curved central part.

[0235] A common feature of all the non-limiting variant embodiments described above is that the electromagnetic generator G, which is the heavy part, is moved away from and positioned lower than the turbine, and is directly connected to the supporting structure.

[0236] In a variant embodiment, the turbine of the invention can be installed in a fixed position, i.e. without the possibility of rotating about an axis R to remain aligned with the wind, and therefore without the connection interface C.

[0237] This solution can be adopted whenever the turbine is inserted in an environment where the flow is strongly characterized by a dominant direction, e.g. in a tunnel, or between two walls channelling the flow; in such a case, the generator may be rigidly fixed to the existing structures, without the necessity of providing rotary contacts and inertial mass balancing.

[0238] In the example described herein, the rotary motion is transferred from the axis A to the axis E directly by means of the flexible cable; such transfer may also be effected by means of bevel gear pairs and a rigid shaft, or by any other per se known means.

[0239] In a further example of embodiment it is possible to decouple the rpm of the turbine T from the rpm of the generator G by adding a transmission connecting the axes A and E, which may be made in any per se known manner, e.g. by using a transmission belt, gears, bevel gear pairs, etc.

[0240] In a further embodiment, as shown in FIGS. 8 and 9, the electromagnetic generator G is in axis with the turbine T, connected to the hub between the fixed part M1 and the rotary part M2. Therefore, the axis of rotation A of the turbine coincides with the axis of rotation E of the generator shaft. The fixed part M1 of the hub is fixed to the supporting pole P, and the rotary shaft of the generator directly supports the turbine T.

[0241] In the above-described variants, the hub preferably has a biconvex shape defined by the revolution of an aerofoil.

[0242] The deflector and the wing preferably have a biconvex section, defined by a wing profile, and a development characterized by a twist, such that the sections of both profiles are rotated, considering two different diametrical positions, in particular, for example, the one proximal to the hub and the terminal one. Also the chord, i.e. the aerofoil length that defines each section of the deflector and of the wing, has a dimension that is greater near the hub and decreases progressively (according to a definite mathematical law) towards the outside of the turbine, being at its minimum at the outermost end (section corresponding to the turbine diameter).

[0243] The shape is determined on the basis of the following considerations.

[0244] With reference to FIG. 1, since Vp (profile speed) is variable with the radius, it is clear that, if the profile chord is kept constant, and assuming that Vv (external wind speed) is constant, the Reynolds number Re (which is directly proportional to both the profile speed and the profile chord) will take all values comprised between 0 (ideally at the axis of rotation of the turbine, where Vp=0) and its maximum value, reached at the wing tip, which is the fastest section (Vp=ωR).

[0245] As previously explained, in order to maximize the efficiency of wind turbines it is necessary to keep Re as constant as possible throughout the profile sections, and therefore the blades of HAWTs cannot have a constant chord along the radius, but must have a chord that increases from the tip towards the root, for the purpose of keeping Re as constant as possible in the various profile sections (Vv being equal).

[0246] Moreover, for a HAWT to express its best aerodynamic efficiency, its blade should ideally maintain, in every section and for any value of Vr (apparent wind vector), the optimal angle of attack α of the chosen profile for that fluid speed (identified by vector Vr).

[0247] However, the speed triangle of FIG. 1 shows that the angle of attack α, assuming that Vv is constant, decreases linearly from the centre towards the periphery as Vp increases.

[0248] This is the reason why the blades of horizontal-axis wind turbines are twisted, i.e. their cross-sections are rotated, considering two different diametrical positions, forming angles with the direction of incidence of the external wind Vv which decrease from the centre to the periphery, so as to follow the rotation of the vector Vr and keep the value of α as close as possible to the optimal one.

[0249] The above-described non-limiting examples may be subject to further variations without however departing from the protection scope of the present invention, including all equivalent embodiments known to a man skilled in the art.

[0250] The elements and features shown in the various preferred embodiments may be combined together without however departing from the protection scope of the present invention.

[0251] From the above description, those skilled in the art will be able to produce the object of the invention without introducing any further construction details.

[0252] The following will describe the behaviour of the system in physical terms with reference to FIG. 10.

[0253] In FIG. 10, speeds and forces are described in vectorial terms.

Symbols:

[0254] Vp blade advance speed
Vv absolute external wind speed
Vrf apparent wind on the flap
Vva absolute speed of the wind on the wing after the deviation generated by the flap
Vra apparent wind on the wing
Flf aerodynamic lift of the flap
Fdf aerodynamic drag of the flap
Ff resultant of the aerodynamic forces on the flap
F∥f propulsive component of the aerodynamic force of the flap, parallel to Vp
F⊥f detrimental component of the aerodynamic force of the flap, orthogonal to Vp
Fla aerodynamic lift of the wing
Fda aerodynamic drag of the wing
Fa resultant of the aerodynamic forces on the wing
F∥a propulsive component of the aerodynamic force of the wing, parallel to Vp
F⊥a detrimental component of the aerodynamic force, orthogonal to Vp
αf angle of attack of the apparent wind on the flap
αa angle of attack of the apparent wind on the wing
δ angle of deviation of the actual wind produced by the flap

[0255] For each blade section (wing+flap), it is possible to draw speed and force triangles similar to this, with different values of Vp (increasing from the root towards the tip of the blade), but always, assuming that Vv is constant, with the same αf and αa.

[0256] Vv is the actual wind speed. The blade section taken into consideration is moving at a speed Vp. By vectorially summing up such speeds, one obtains the apparent speed of the wind on the flap Vrf. Such speed, according to the known aerodynamics principles, generates on the flap a force Ff that is the vectorial resultant of the lift Flf (orthogonal to Vrf) and the drag Fdf (parallel to Vrf).

[0257] As regards the operation of the turbine, it is of interest to break up the resultant of the aerodynamic forces in two other directions: [0258] F∥f component parallel to Vp, and therefore propulsive and usable for energy production; [0259] F⊥f component orthogonal to Vp, useless for propulsive purposes and detrimental to the structures.

[0260] The aerodynamic forces are generated through the effect of the angle of attack αf.

[0261] The aerodynamic forces generated by the wing are made possible also with a low TSR due to the fact that the angle of attack αa is smaller than αf, through the effect of the deviation of the flow generated by the flap, and takes values smaller than the profile stall values.

[0262] The angle αa assumes aerodynamically optimal values in all sections of the wing.

[0263] CFD simulations and experimental wind tunnel tests have shown that the wind having an absolute vectorial speed Vv is deviated, through the effect of the presence of the flap, by an angle δ and takes the vectorial value Vva. The wing that follows the flap therefore meets the air flow at the apparent speed Vra, which is the vectorial summation of Vva and (−Vp). The angle of attack of Vra on the wing is αa. This angle is smaller than it would without the presence of the flap. On the other hand, if the angle αa exceeds the stall value, the wing profile will produce no lift and will lose propulsive force. Therefore, two components are consequently generated for the wing as well: [0264] F∥a component parallel to Vp, and therefore propulsive and usable for energy production; [0265] F⊥a component orthogonal to Vp, useless for propulsive purposes and detrimental to the structures.

[0266] The importance of the present invention lies in the behaviour that will now be described.

[0267] The presence of the flap permits each one of two profiles to mutually benefit from the presence of the other (cooperating profiles).

[0268] Such cooperation is not only fluid-dynamic, but also structural.

[0269] In fact, the two profiles (wing and flap) are connected at their ends by a bridge that, in one possible embodiment, may have winglet characteristics.

[0270] In aerodynamics, a winglet is defined as a wingtip device used for improving the aerodynamic efficiency of a wing by reducing the induced drag caused by wingtip vortices.

[0271] It is an orthogonal or angled extension of the tip, and produces an effect similar to wing elongation, i.e. a reduction in the intensity of wingtip vortices, with a consequent increase in the aerodynamic efficiency of the wing.

[0272] In the proposed turbine, the connection between the wingtips and the deflector creates a closed structure, which considerably improves the blade's capability to withstand the stresses that are generated during the operation of the turbine, thus improving its inherent safety.

[0273] The wing can be efficient (it never enters the stall condition) even at low peripheral speeds when the angles of attack increase, thanks to the presence of the flap that adequately adjusts the angle of attack. By appropriately choosing the best profiles for the wing and the flap, their proportions and their mutual positioning, along with the architecture of the wing and the hub and their cooperation in the central part of the turbine, it is possible to maximize the aerodynamic efficiency of this machine. Such efficiency is always maintained, even in highly variable wind conditions, because the flow that hits the blade has always the same direction, independently of the absolute external wind conditions, due to the deflection generated by the flap.

[0274] The result is a machine with considerable propulsive torque in any wind condition, which can therefore be used at much lower TSRs than any prior-art HAWT, to advantage of quietness and safety. This latter aspect is also guaranteed by the architecture of the machine itself, which is characterized by strong blades having a very large root and therefore firmly connected to the hub, made up of two profiles connected together also at their ends, which ensure a box-like behaviour of the blade and make it stiff and light.

[0275] This latter aspect is of fundamental importance for safety purposes, because light wings hugely reduce the centrifugal forces and hence the stresses undergone by the structure as a whole.

[0276] In order to be able to attain this result in terms of lightness and mechanical performance, it is necessary to adopt an innovative construction technology capable to ensure such a result while at the same time complying with the low production cost requirements imposed by the market of very small micro wind turbines, with an output of the order of hundreds of Watts.

[0277] This is an extremely crowded market, characterized by low production costs and very large volumes, requiring production facilities capable of ensuring such large volumes.

[0278] One technology that could be used to ensure great lightness combined with high mechanical performance is the technology of composite materials.

[0279] Such technology, however, wherein the human labour component is still very important, places strong limitations on productivity.

[0280] On the other hand, given the particular architecture of the turbine, it would also be difficult to implement the classic technology that envisages the injection of charged plastic polymers into moulds, which would be extremely expensive and complex.

[0281] Therefore, a modern technology has been selected, which closely follows the innovation character of the turbine itself.

[0282] 3D printing is, at present, the optimal solution for obtaining complex, biomorphic shapes like those of the turbine proposed herein.

[0283] By means of a powerful computer and software capable of executing parametric modelling operations, it is possible to create a three-dimensional model having sinuous shapes such as those that characterize the turbine, in compliance with all of the above aspects.

[0284] To obtain the turbine, it is then sufficient to print this model in the most appropriate material by using suitable three-dimensional printers.

[0285] This system has no productivity limitations, since it is sufficient to purchase the necessary number of printers to obtain the required number of machines, and ensures full versatility for changing shapes and dimensions at no expense, which would be impossible to do with any other traditional technology, which would inevitably require new physical models and moulds.

[0286] Furthermore, the 3D printing technology offers an additional advantage, which is impossible to obtain, for example, with injection.

[0287] A wing profile printed by 3D technology may have different structures and material in different places to meet variable structural or finishing needs or requirements of any other nature; for example, in order to obtain an extremely light, but strong, wing, a thick and strong skin may be constructed with very high surface finish and a coarser internal honeycomb texture (to speed up the printing process); also, the quantity of material can be dosed at will, e.g. to obtain a texture that is more dense at the root and less dense at the tip, for higher tensile strength.

[0288] A versatile and innovative technology like 3D printing, which is now becoming widespread also for industrial production, and not only for prototyping applications, is currently the best choice for manufacturing the turbine of the present invention.