WO2014019034A2

WO2014019034A2 - Wind turbine

Info

Publication number: WO2014019034A2
Application number: PCT/BE2013/000040
Authority: WO
Inventors: Frans MONDELAERS
Original assignee: Mondelaers Frans
Priority date: 2012-07-30
Filing date: 2013-07-29
Publication date: 2014-02-06
Also published as: BE1020851A3; WO2014019034A3

Abstract

Wind turbine of the horizontal axis turbine type, comprising a central housing connected to a set of blades such that the blades are rotatable around the central housing in a swept area, characterized in that the blades have a combined area greater than said swept area.

Description

Wind turbine

The invention relates to a wind turbine of the

horizontal axis turbine type comprising a central housing connected to a set of blades such that the blades are rotatable around the central housing in a swept area.

Wind turbines of the horizontal axis turbine type are known and are frequently applied to generate electricity. The most common wind turbines have three blades which lie displaced 120° relative to each other and which convert the kinetic energy of the wind to a rotating movement of a shaft. This shaft is then coupled to a generator which generates electricity.

In order to increase the output of the wind turbines the length of the blades of commercial wind turbines has

increased greatly over the years. The reason for this is that it is not the number of blades but the length of the blades which has the greatest influence on the potential capacity of the wind turbine. Wind turbines are currently being manufactured with a rotor diameter of 127 metres. Such rotors are mounted on towers with a height of 135 metres. They have a capacity of 7500 kW at wind velocities of 28 m/s (= 100 km/h) .

It is an object of the invention to provide a wind turbine with a small diameter which can generate a high output .

The invention provides for this purpose a wind turbine of the horizontal axis turbine type comprising a central housing connected to a set of blades such that the blades are rotatable around the central housing in a swept area, characterized in that the blades have a combined area greater than said swept area.

The blades rotate in a swept area. This swept area is defined by an annular area perpendicularly of the rotation axis, this being the main shaft of the wind turbine on which the blades are mounted, wherein the annular shape is bounded by two concentric circles. The outer concentric circle has a radius equal to the length of the blade as measured from the centre of the main shaft around which the blade rotates to the tip of the blade. The inner of the two concentric circles has a radius equal to the distance between the centre of the main shaft around which the blades rotate and the beginning of the blade. The swept area is hereby equal to the frontal area where a wind turbine assembly can capture wind with the blades over a complete rotation around the main shaft.

The blades typically have a surface with a complex geometry comprising curvatures in multiple directions. The surface of a blade is therefore- defined as the sum of N sub- surfaces, wherein the surface of the blade is divided into (theoretically preferably an infinite number of) N subsurfaces. The greater N is chosen, the more accurate the surface will be here. When a blade has a front side and a rear side, the surface of the blade will preferably be defined as the surface of the front side of the blade. The front side is here the side facing toward the wind, and so the wind-capturing side of the blade.

Blades are typically tilted relative to the wind

direction in order to be able to convert the wind to a rotation movement. The combined area of the blades can hereby be greater than the swept area, this without the blades colliding with each other. Providing the blades with a combined area which is greater than the swept area makes it possible to nevertheless achieve very high capacities with a wind turbine of a relatively small diameter, for instance a diameter of 3 metres. An additional advantage is that high capacities can already be achieved at low wind velocities, i.e. wind velocities of about 20 km/hour.

Conventional wind turbine assemblies typically only reach their maximum output at wind velocities of about 80 km/hour. A surprising advantage is that the visibility of the wind turbine assemblies to birds is much better, whereby birds are less likely to be taken by surprise, and fewer are therefore struck by a wind turbine assembly. The visually discernible surface is large due to the large combined surface area of the blades, so that they can be seen more easily by birds.

The set of blades preferably comprises a maximum of seven blades. The set of blades preferably comprises a maximum of five blades, the set of blades more preferably comprises four blades. When the combined area of the blades is greater than the swept area, and only a limited number of blades are provided, the technical result is that the blades have a low length/width ratio. The blades will therefore be relatively wide. A wide blade is found to be ideal for guiding the wind and achieving a high efficiency at

relatively low wind velocities. Tests with a wind turbine with four blades have shown that, at a wind velocity of 20 km/hour, an output of about 270 W can be obtained with a wind turbine with a diameter of 3 "metres. At wind velocities of 40 km/h outputs of about 1900 W can be obtained with the same wind turbine. At wind velocities of 60 km/h outputs of about 6300 W can be obtained with the same wind turbine. At wind velocities of 80 km/h outputs of about 14700 W can be obtained with the same wind turbine. At wind velocities of 100 km/h outputs of about 28700 W can be obtained with the same wind turbine. The tests and simulations hereby indicate that exceptionally high outputs can be obtained from a wind turbine with a blade diameter of only 3 metres.

Each of the blades preferably comprises a protruding edge at the position of the outer edge of the swept area. A protruding edge at the position of the outer of the two concentric circles defining the swept area guide the wind over the blades and thereby provide for a higher output.

Surprisingly, it is also found that the sound which is produced by the blades, and which is perceived as noise pollution, greatly decreases due to the protruding edge. The wind turbine assembly becomes much quieter as a result of the protruding edge. Owing tq_ the protruding edge the wind captured by the blade cannot flow off the blade via the outer edge. The wind is thus caught on the blade and an overpressure is held in place on the blade. Tests and simulations have demonstrated that the output of the wind turbine increases appreciably as a result.

Each of the blades preferably^* comprises a protruding edge at the position of the inner edge of the swept area. This protruding edge guides the wind along the blades. This protruding edge is placed at the position of the inner of the two concentric circles of the swept area. The inner wall also has the effect that a higher output is obtained and that the blades produce less noise during rotation.

The protruding edge preferably forms an angle to the blade greater than 90°, preferably greater than 100°, and less than 160°, preferably less than 150°, more preferably less than 140°. By placing the protruding edge at an angle of more than 90° to the blade the protruding edge as it were lies tilted outward on the blade. Tests have demonstrated that such a configuration of the protruding edge maximizes the output and the sound-damping . ^*

The protruding edge is preferably formed on the front side and on the rear side of the blade. By forming the protruding edge on the front and rear sides the wind- capturing surface (the front side of the blade) is not only streamlined by the edge so as to guide the wind better, the rear side (where a vacuum zone, a zone of lower pressure, occurs) is also provided with edges, whereby the airflow is guided on both sides. The overpressure on the front side can thus be held in place on the blade and the underpressure can be held in place on the rear side of the blade. The escape of overpressure and underpressure on the upper and lower sides of the blade is hereby made more difficult, this increasing the output .

The swept area preferably has an outer diameter of less than 5 metres, preferably less than 4 metres, more

preferably of about 3 metres . The wind turbine according to the invention is most suitable for application in a small wind turbine assembly, this being a wind turbine assembly with a blade diameter of abou^'fc "3 metres. Tests have

demonstrated that the specific construction and features of the wind turbine according to the invention produce a high efficiency at a blade diameter of less than 5 metres, preferably less than 4 metres, more preferably of about 3 metres. The blade diameter is preferably less than 3 metres. Depending on the application, wind turbines of 1 metre blade diameter or less can also be provided.

Each blade preferably has a length-width ratio of less than 3, preferably less than 2.5, more preferably of about 2. The length is here the distance as measured along the axis of the blade from the beginning of the blade to the end of the blade, and the width is the average width of the blade relative to this axis. A blade with such a length- width ratio has been found from" tests and simulations to have a high output .

The combined frontal area of the blades, at an axial position of the blades between 5 degrees and 30 degrees angular displacement relative to the plane perpendicular to the frontal direction, is preferably equal to the swept area. The frontal area is typically smaller here than the effective area because the frontal area is the projected area in the frontal direction.

The invention will now be further described on the basis of an exemplary embodiment as shown in the drawing.

In the drawing:

figure 1 is a front view of a wind turbine according to an embodiment of the invention; figure 2 is a transverse view of a part of the blade of a wind turbine according to an embodiment of the invention; figure 3 is a transverse view of a set of blades of a wind turbine according to an embodiment of the invention; figure 4 shows a cross-section of a part of a blade of a wind turbine according to an embodiment of the invention; figure 5 is a front view of a wind turbine according to an embodiment of the invention.

The same or similar elements are designated in the drawing with the same reference numeral.

Figure 1 shows a wind turbine with its main components. Wind turbine 1 comprises four blades 2, 3, 4 and 5, each connected via a blade shaft 6 to a main shaft 7 around which the blades can rotate in order to transmit force to main shaft 7. Main shaft 7 is preferably placed in a central housing 8. A generator can further be mounted in this central housing 8 for the purpose of generating electrical energy. According to the invention the blades 2, 3, 4 and 5 can also be connected directly to a generator instead of being connected to a generator via a main shaft 7. The generator is then placed in the central housing. Central housing 8 is preferably mounted on a tower (not shown) so that the wind turbine assembly can be placed at a height in the landscape.

The blades of wind turbine 1 are provided for rotation in a theoretical swept area. This ..theoretical swept area is annular and lies in a plane perpendicular to main shaft 7. The annular form has an inner diameter and an outer

diameter. The inner diameter lies at the position of the inner edge 10 of the blades. The inner edge of the blades is the edge of the blade surface lying closest to the centre of rotation of the blades. In figure 1 the centre of rotation is defined by main shaft 7. The outer circle of the annular swept area lies at the position of outer edge 9 of the blades. The outer edge of the ^'"blades is the edge of the wheel surface furthest removed from the centre of rotation of the blades. The swept area is hereby indicative of the maximum amount of wind which can be captured by the blades of the wind turbine. Another way of defining the swept area is by subtracting the frontal area of the central housing from the circular area defined by the rotation diameter of the blades, whereby an annular swept area is obtained. The frontal area of an object is defined here as the projected area of the object perpendicularly of the direction of movement or wind direction.

Each of the blades 2, 3, 4 and 5 has a surface. The area of a blade is preferably defined as the area on the front side of the blade, being the wind-capturing side of the blade. The surface of the blade is further defined as the sum of N sub-surfaces of the blade (wherein N is a natural number which is preferably as large as possible) . Because a blade often has a complex three-dimensional form, the surface is preferably defined via the sum of the subsurfaces. Blades 2, 3, 4 and 5 of the wind turbine are preferably identical. The combined surface area of the blades is therefore equal to the number of blades times the area of one blade. In the case of figure 1 the combined area of the blades is four times the area of blade 2.

Wind turbine 1 is formed such that the combined area of blades 2, 3, 4 and 5 is greater than the swept area.

Although this is apparently not the case in figure 1 because openings are visible between adjacent blades, the blades are however tilted relative to the wind direction so that the frontal area (the area which is visible in figure 1) is appreciably smaller than the effective area of the blades. This means that in figure 1, where there is a distance between adjacent blades in the front view, the combined surface area of the blades is greater than the annular swept area. It will be apparent that a wind turbine, wherein the above ratio of areas applies for a limited annular segment of the blades, also falls within the scope of protection of the invention. This relates to the fact that it is not inconceivable to further lengthen a blade as shown in figure

1 (for instance with an extension piece in the form of conventional commercial blades) , whereby the swept area becomes larger (via a slender blade end) without appreciably increasing the area of the blades .

Figure 2 shows a transverse view (transversely of main shaft 7) of a blade 2 mounted on a central shaft 7 via a blade shaft 6. The blade has an inner edge 11 and an outer edge 12. Inner edge 11 is the edge of the blade lying closest to the central rotation point, in this case being main shaft 7. Outer edge 12 is the edge of the blade lying furthest from the central rotation point of the wind

turbine, in this case main shaft 7. The figure shows the wind direction 13, as a result of which the blade as shown in figure 2 will generate a force to the left. This force is generated as a result of the three-dimensional form of blade

2 and the rotated position of the blade relative to axis 7 (the blade is not at right angles^' to axis 7 but is rotated relative to this right-angled position) . The three- dimensional form is substantially defined by a combination of a preferred form in the direction of rotation (the left- right direction in the figure) and a preferred form in the radial direction of the blade (radial relative to central shaft 7; visible in the figure as the difference between inner edge 11 and outer edge 12 of the blade) . In the rotation direction the front side of the blade has a concave form, wherein the radius increases from the edge cutting into the wind (the edge shown on the left in the figure) to the opposite edge (edge on the right in the figure) . The blade is twisted in the radial direction such that the average angular displacement relative to the swept area (which lies perpendicularly of axis 7) is greater close to axis 7 and decreases in a direction away from the axis. Figure 2 thus shows that edge 11, which forms the inner edge of the blade, has a greater angular displacement relative to the plane perpendicularly of axis 7 than outer edge 12. A torsion in this direction is generally applied in the case of blades of wind turbine assemblies, since the absolute speed during rotation of an inner point on the blade is lower than the absolute speed of a point on the outer side of the blade .

Figure 3 shows a transverse view of two adjacent blades 2 and 3 and shows the effect of the angular displacement of the blades relative to the plane perpendicularly of axis 7 (due to rotation of the blades around their longitudinal axis (not shown) ; this is the axis typically extending radially from the main shaft 7) . In figure 3A blades 2 and 3 are rotated relative to the main shaft so as to form an angle a to the plane lying perpendicularly of the main shaft. In order to define the, angle a a theoretical plane 16 is determined which is equal to the average of the tangent planes of N sub-surfaces of the blade (wherein N is a natural number which is preferably as large as possible) in order to thus determine an average direction of the blade. In figure 3A the average direction is indicated with line 16. The angle a is chosen in figure 3A such that in the frontal direction, being the direction perpendicularly of the swept area 15, there is no overlap and no opening visible between adjacent blades 2 and 3. As seen from the front, blades 2 and 3 connect closely together as indicated with line 14. In figure 3B the selected angle at which the blades are placed is smaller, angle β, indicated as the angle between swept area 15 and the average theoretical plane 17 of the blades. An overlap 18 is hereby visible in the front direction between adjacent blades. This is the result of the larger combined area of the blades of the swept area. In figure 1 a larger angle is chosen and an opening is visible in the front view between adjacent blades. Different mechanisms can be provided in the central housing to rotate the blades around their longitudinal axis. It is thus possible to take varying wind velocities into account (by making the angle to the rotation plane smaller at lower wind velocities and larger at higher wind

velocities) . The blades can preferably be rotated from an operative position to a feather position, and vice versa.

The blades preferably have a protruding edge at the position of the outer and inner^" edges, being respectively the edges 9 and 10 in figure 1. It is understood here that the edge protrudes relative to the plane of the blade. Such protruding edges are shown in figure 4. Figure 4A shows a cross-section of blade 2 and shows a protruding edge 9 on the edge of the blade. Figure 4A shows the wind direction 13 and shows how protruding edge 9 takes a two-part form on both the front side, designated with reference 19, and the rear side, designated with reference numeral 20. The

protruding edge is placed at an angle relative to the blade, preferably an angle of about 120° . Figure 4B shows an alternative protruding edge, and shows a protruding edge with a bend. Figure 4B likewise shows a blade edge with a protruding edge on front side 19 and on rear side 20. Figure 4C shows a curved blade 2 with a curved protruding edge 19, with the purpose of describing how the angle between blade and protruding edge is determined. The angle between the blade and the protruding edge is defined as the angle between the tangent to the edge of the blade and the average direction of the protruding edge. The tangent to the blade at the position of the edge is shown in figure 4C with reference numeral 21 and the average direction of the protruding edge is shown in figure 4C with reference numeral 22. The protruding edge preferably has a length of at least 1 cm, more preferably at least 3 cm, most preferably at least 5 cm. Figure 5 shows an alternative embodiment of a wind turbine according to the invention, wherein a first set of blades 23 rotates in a first direction around central housing 8 and a second set of blades 24 rotates around central housing 8 in a second direction opposite to the first direction. Such configuration of a wind turbine assembly can likewise be embodied in a manner such that the swept area is smaller than the combined surface areas of the blades .

According to one embodiment, the blades are connected to a main shaft or a generator such that their longitudinal axis runs through the centre of rotation. According to a further embodiment, the blades are connected to the main shaft or to a generator such that their longitudinal axis runs along the centre of rotation at a predetermined

distance therefrom.

The housing can preferably be provided on an outer side with protrusions which guide the wind. The housing can comprise a rotatable spherical front head with protrusions which cause the head to rotate so that additional energy can be obtained via the rotating head.

The blades are preferably provided with suitable

amorphous daylight cells. Amorphous daylight cells do not need any direct sunlight and ambient light will be

sufficient to enable generation of energy. During movement

(on the blades) amorphous daylight cells can further produce electricity. The composition of the cells can be modified in accordance with the region where the wind turbine assembly is placed and the strength of.-daylight in this region. The cells can be encapsulated in plexiglass, preferably in light and flexible plexiglass, for mounting on the blades. The daylight cells can function as additional energy source when they are mounted on the blades.

Different variations of a wind turbine can be formed having one or more features according to the wind turbine according to the invention. The above described examples serve only by way of illustration, and the scope of protection is defined by the claims.

Claims

1. Wind turbine of the horizontal axis turbine type, comprising a central housing connected to a set of blades such that the blades are rotatable around the central housing in a swept area, characterized in that the blades have a combined area greater than said swept area.

2. Wind turbine as claimed in claim 1, wherein the combined area is situated on a wind-capturing side of the wind turbine.

3. Wind turbine as claimed in claim 1 or 2 , wherein the set of blades comprises a maximum of seven blades,

preferably a maximum of five blades, more preferably four blades.

4. Wind turbine as claimed in claim 1, 2 or 3, wherein each of the blades comprises a protruding edge at the position of the outer edge of the swept area.

5. Wind turbine as claimed in claim 4, wherein the protruding edge extends on each of the blades at the position of substantially the whole outer edge of the swept area .

6. Wind turbine as claimed in any of the foregoing claims, wherein the protruding edge extends on each of the blades at the position of substantially the whole inner edge of the swept area.

7. Wind turbine as claimed in claim 4, 5 or 6, wherein the protruding edge forms an angle to the blade greater than 90 degrees, preferably greater than 100 degrees, and less than 160 degrees, preferably less than 150 degrees, more preferably less than 140 degrees.

8. Wind turbine as claimed in any of the claims 4-7, wherein the protruding edge is formed on the front side and on the rear side of the blade.

9. Wind turbine as claimed in any of the foregoing claims, wherein the swept area has an outer diameter of less than 5 metres, preferably less than 4 metres, preferably of about 3 metres .

10. Wind turbine as claimed in any of the foregoing claims, wherein each blade has a length-width ratio of less than 3, preferably less than 2.5, more preferably of about 2.

11. Wind turbine as claimed in any of the foregoing claims, wherein the axial position of the blades is

adjustable .

12. Wind turbine as claimed in any of the foregoing claims, wherein the combined frontal area of the blades, at an axial position of the blades between 5 degrees and 30 degrees angular displacement relative to the plane

perpendicular to the frontal direction, is equal to the swept area.

13. Wind turbine as claimed^" in any of the foregoing claims, wherein each blade is formed substantially in the form of a sector of a circle.