NL2028634B1 - Noise reducing wind turbine and a row of such turbines - Google Patents

Abstract

The present invention pertains to a noise reducing wind turbine, the turbine comprising a support extending in a vertical direction and a vane rotatively connected to said support, the vane comprising an elongated body that extends between a first end and a second end of the vane, the elongated body being spatially limited by a first and a second side line that extend between the first and second end of the vane, wherein at least the first side line has a sinusoidal shape having a wavelength (?) of at least 1.7 cm and an amplitude (A) of at least 0.85 cm.

Description

NOISE REDUCING WIND TURBINE AND A ROW OF SUCH TURBINES

GENERAL FIELD OF THE INVENTION The present invention pertains in general to a wind turbine that is able to convert wind energy into mechanical (and optional electric) energy, and in particular to a wind turbine that at the same time is able to reduce noise, and a row of such wind turbines.

BACKGROUND ART Wind turbines are commonly used since centuries to convert wind into work. A wind turbine typically is an impulse turbine. The turbine changes the direction of flow of the wind and the resulting impulse spins the turbine and leaves the wind with diminished kinetic energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or pumping water, the device is usually called a windmill or wind pump. Developed for over a millennium, today's wind turbines are manufactured in a range of vertical and horizontal axle types. The most common and oldest ones are the horizontal axle turbines, wherein the axles are positioned in line with the direction of the wind (i.e. the direction in which the wind blows). The smallest turbines are used for applications such as battery charging or auxiliary power on sailing boats, while large grid-connected arrays of turbines are becoming an increasingly large source of commercial electric power.

Wind is currently appreciated as one of the most widespread renewable and sustainable energy source in the world. Therefore, the development of wind turbines is currently booming. Despite many advantages of vertical axis wind turbines or vertical wind turbines, horizontal axis wind turbines or horizontal wind turbines are currently the most used and known because of their better efficiency. However, horizontal wind turbines also have many disadvantages, such as noise pollution, visual impacts, dangers linked to the risks of falling structures, collisions with flying objects, the needs of space and the needs of the lamellar wind, etc. Horizontal wind turbines require open environments. This reduces land use efficiency in a horizontal axis wind farm. Horizontal wind turbines are not very suitable in cities, confined spaces and in bird migration corridors.

One of the developments of the last decades is to devise wind turbines that are suitable for low wind velocities (typically below 10 m/s, about 5 Beaufort). In particular at lower heights, above land and in the presence of buildings, wind velocity is often too low to economically extract energy from common wind turbines. Recent developments include the Darrieus (including giromill and cycloturbine) and Savonius wind turbines which may generate mechanical energy even at a wind velocity below 5 m/s (about 3 Beaufort). Unlike the Savonius wind turbine, the Darrieus is a lift-type turbine. Rather than collecting the wind in cups dragging the turbine around, a Darrieus uses lift forces generated by the wind hitting aerofoils to create rotation. With these turbines, the axles are positioned transverse to the wind (as opposed to “in line” with the wind) which has the additional advantage that the vanes do not need to be pointed to the wind. In most cases the axles are positioned vertically (which explains the commonly used acronym VAWT: vertical axle wind turbine), but they may also be positioned horizontally as long as the axle is transverse to the wind (TAWT - transverse axle wind turbine- would thus be a more correct acronym), typically substantially perpendicular to the direction in which the wind blows. The overall rate of conversion of kinetic into mechanical energy of these turbines however is a concern.

In recent development is to combine the energy conversion property of a wind turbine with that of noise reduction. This way the lower rate of energy conversion is of a lesser concern, since the noise reduction is also a main function of the wind turbine. In fact, when compared to a regular sound barrier (typically a wall of 4-7 meters high), not being able to convert any wind energy into work, any energy conversion rate is advantageous. In US 20190085819 (assigned to Techsafe Global; Titled “Multifunctional wind turbine/ hydro turbine and their assembly for multiple applications and uses”) it is proposed to use a row of contiguous VAWTSs not only to convert wind energy into work, but also as a sound barrier. The wind turbine version of this prior art invention is designed and optimized to adapt to any environment, where wind can be present, onshore and offshore as well as along highways, roads, railways, in tunnels, on fields, on hills, on buildings, on roofs, on balconies, on terraces or by the riversides, by the sea, in offshore wind farms, etc. Installed along roads, highways, etc., the wind turbine installations of this invention will provide electricity for lighting and for stations or charging stations for electric vehicles along transport networks. At the same time, the row of wind turbines act as a sound barrier to reduce the noise produced by vehicles such that urban areas at the other side of the barrier are not hindered by the noise as originally generated. As described, the architecture of the wind turbines allows to adsorb or even block sound waves. Thus, the rows of these aforesaid devices will also play the role of noise barriers along and in the middle on the central median of road and rail transport networks (roads, rail networks, etc.), on balconies, on building terraces, etc. The idea of using a row of wind turbines as a sound barrier is also described in US 2018/0003156 (assigned to N.C. Chris and S. Varga; titled “Power producing walls”). A disadvantage of the prior art ideas to combine energy conversion and sound blocking is that one needs a very densely packed row of wind turbines in order to be able and indeed substantially block the noise. Any open spaces between neighbouring turbines are disadvantageous for the blocking capacity of the row of turbines. This makes the solution costly and not suitable for applications other than along highways and rail tracks, in particular, the solution is not suitable for individual back gardens or dense urban areas.

OBJECT OF THE INVENTION It is an object of the invention to mitigate the disadvantages of the prior art and provide an improved way of combining energy conversion and noise reduction in a wind turbine set up.

SUMMARY OF THE INVENTION In order to meet the object of the invention, a wind turbine is provided comprising a support extending in a vertical direction and a vane rotatively connected to said support, the vane comprising an elongated body that extends between a first end and a second end of the vane, the elongated body being spatially limited by a first and a second side line that extend between the first and second end of the vane, characterised in that at least the first side line has a sinusoidal shape having a wavelength (A) of at least 1.7 cm and an amplitude (A) of at least 0.85 cm. It was recognized that sound blocking by using wind turbines is extremely difficult since wind turbines inherently comprise open space that allows sound waves to propagate through the rotors. The current invention is based on the recognition that another option to reduce noise is to alter the sound waves by creating turbulence around the vanes, instead of by attempting to block them. It was found that by providing a side of the body of the blade with a sinusoidal shape that matches a soundwave of a type that needs to be interfered with in order to create a substantial altering of the sound that needs to be reduced, the resulting sound at the other side of the turbine can be perceived as substantially less hindering, even when the amount of energy is hardly reduced. When the sinusoidal shape has a wavelength (A) of at least 1.7 cm and an amplitude (A) of at least 0.85 cm, it matches sound as can be perceived with the human ear (i.e. below 20 kHz and of sufficient amplitude). In the art one strives for preventing any turbulence being created around vanes. This is believed to be necessary in order to reduce the amount of noise created by the wind turbine itself. Hence the fact that the sides of the blad bodies are typically extremely smooth. Against this prior art believe, it was found that creating turbulence may be used to alter the sound that travels along the turbine. This has the concomitant advantage that even a wind turbine on its own can be used to combine energy conversion and noise reduction. It is namely not needed to substantially block the hindering noise, altering hindering sound waves may be sufficient to reduce the perception of hinder substantially. However, along elongated areas that need noise reduction, such as highways, railway tracks and potentially also water ways, it is advantageous to use a row of wind turbines in line with the current invention. So the present invention also pertains to a row of regularly positioned wind turbines, wherein each wind turbine in this row is a wind turbine in line with the invention as described here above and according to any of the further embodiments as described here below.

The exact wavelength to be chosen depends on the type of noise that has to be reduced. Traffic noise has frequencies that differ for example from noise as produced by a train. Even the noise of traffic differs substantially from the type of movement and location of the traffic: along a highway a different type of hindering noise is produced than for example in an urban area at a crossing. So the type of sinusoidal shape can be easily adjusted to match any type of frequency and amplitude de of noise to be altered by traveling along the body of the vane.

DEFINITIONS 5 For a line to extend in a direction means that the line is not perpendicular to that direction, so that the line at least partly extend in the direction. Preferably the line has an angle smaller than 45° with respect to the direction, even more preferably smaller than 40, 35, 30, 25, 20, 15, 10, 5, 4, 3, 2, 1 or 0 degrees.

Sinusoidal means relating to, shaped like, or varying according to a sine curve or sine wave, a mathematical curve that describes a continuous periodic oscillation comprising a pattern of peaks and valleys having a wavelength A and an amplitude A (which both may vary along the length of the curve). A sinusoidal curve can comprise a sine, square, triangle, sawtooth or any other (periodic or aperiodic) pattern of peaks and valleys, and may also be topped up with any other mathematical function such as a polynomial function of any order.

Macroscopic means visible with the naked human eye, typically having dimensions above 0.1 mm, preferably above 1 mm.

A through hole is a hole completely passing through an object, the hole thus being open at both ends thereby forming a channel through the body it is made in.

Colour is the property of an object of producing different sensations on the eye as a result of the way the object reflects or emits light. Colour depends on the wavelength and amplitude of the reflected light (wave).

FURTHER EMBODIMENTS OF THE INVENTION In a first further embodiment of a wind turbine according to the invention the sinusoidal shape comprises at least one period of a sinus, in particular the sinusoidal shape comprises multiple periods of a sinus, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, or even more periods. In this respect, a period of a sinus is the distance between two consecutive peaks, even if the overall sinusoidal curve is aperiodic as such (i.e. not having a truly regular pattern). The number of periods influences the way a sound wave is altered when travelling along a body of the vane. Depending on the type of noise to be reduced (in the present invention in its broadest sense, the reduction takes place by at least altering the noise such that it is perceived as less hindering), and the preference of people that live or stay in the vicinity of the wind turbine for a particular alteration, the number of periods can be varied as desired.

In yet a further embodiment the wavelength is 17 m at maximum. This corresponds to sound having a frequency of 20 Hz, the lowest than can be regarded as hindering by people with normal physical capacities. For many applications, given the fact that noise perceived as hindering typically has a frequency between 1000 and 4000 Hz the wavelength is between 8.5 cm and 34 cm.

In still a further embodiment, in addition to the first side line, the second side line of the elongated body also comprises the said sinusoidal shape. It is not necessary that both side lines have the same sinusoidal shape, it may even be advantageous that they differ in order to create optimal noise interference.

In again a further embodiment the elongated body comprises one or more macroscopic through holes. It was found that such through holes may be used advantageously in altering the noise. Through holes can create additional turbulence, in particular a side line of the through hole has a Ra value (see ISO 4287:1997) above 1 mm, thus being “rough” and not smooth.

In still again a further embodiment the elongated body is provided with a liner (surface coating) having a hardness of 80 Shore A (see ASTM D2240 type A scale) or lower. It was found that tis way hindering noise can be absorbed by the elongated body, thereby further improving the noise reduction and hence perception of the remaining noise. In particular, the elongated body is provided with a liner having a hardness of 60 Shore A or lower, preferably 40 Shore A or lower.

Yet again, in a further embodiment the elongated body comprises a geometrical pattern that has a variable density, i.e. mass per unit of length, between the first and second end. This means that at different positions between the first and second end, the mass per unit of length of the body is different (e.g. by having an irregular shape along the length between the first and second end). It was recognised that during day time, the vane(s) of the turbine will heat up due to absorbing sun light. This way, even when the vane is not rotating, turbulence may be created. In particular, due to the variable density in the pattern (i.e. the amount of material per square meter), different areas of the vane will be warmed up to different temperatures. The difference in temperature will create a difference in speed of the sound waves travelling around the vane while at the same time warmer and colder areas of the vane will cause airflow and turbulence. An example of a vane having a geometrical pattern that has a variable density between the first and second end, is a vane that resembles a natural branch of a tree or bush provided with leaves. In line with the above, in yet a further embodiment the elongated body comprises a colour pattern such that the elongated body has a variable colour between the first end and the second end. For the same reasons as given here above, this may be used to create additional noise reduction, even when the amount of wind is too low to let the turbine turn to create turbulence due to the sinusoidal side of the body of the vane. In again a further embodiment the wind turbine comprises a means to actively create noise having a frequency between 20Hz and 20kHz. Active noise creation to reduce noise that is perceived as hindering is already known form the art. However, it was found that it can be advantageously used in combination with the invention for further improving noise reduction. In a further embodiment of the row of regularly positioned wind turbines, an open space between each pair of neighbouring wind turbines is at least 0.34 m and at maximum 17 m. The open space is the distance between the tips of the vanes of two neighbouring turbines in their closest possible position. By having a deliberate open space between the turbines sound interference can be generated. This can further help the altering of the actual noise to be reduced.

In yet a further embodiment, in a pair of neighbouring wind turbines, the first turbine has a first vertical footprint, and the second turbine has a second vertical footprint, the first vertical footprint differing from the second vertical footprint. It was recognised that the rotation of the (VAWT) blades causes a so called Doppler effect on the incoming and outgoing sound wave. By setting up the turbines such that neighbouring turbines have different vertical footprints (i.e. different diameters when viewed from above), a difference in doppler effect of the re-directed sound waves can be created. This can further help the altering of the actual noise to be reduced. In again a further embodiment, in a pair of neighbouring wind turbines, the first turbine has a vane of which the elongated body has a first minimal height above surface, and the second turbine has a vane of which the elongated body has a second minimal height above surface, the first minimal height differing from the second minimal height. This creates a difference in height of the vanes above the surface which has an effect on the noise disturbance which may further help the altering of the actual noise to be reduced.

Correspondingly, in a pair of neighbouring wind turbines, the first turbine has a vane of which the elongated body has a first length, and the second turbine has a vane of which the elongated body has a second length, the first length differing from the second length. Also this difference has an effect on the noise disturbance which may further help the altering of the actual noise to be reduced. The invention will now be further explained using the following figures.

EXAMPLES Figure 1 is a schematic view of three types of vertical axis wind turbines Figure 2 schematically depicts a vane of a wind turbine Figure 3 schematically depicts various types of bodies for a vane Figure 4 schematically depicts a tree-like vane Figure 5 shows a row of wind turbines Figure 6 shows an alternative row of wind turbines Figure 7 shows yet a further alternative of a row of wind turbines Figure 1 Figure 1 is a schematic view of three types of vertical axis wind turbines, indicated with 1, 1’and 1” in Figure 1A, 1B and 1C respectively. Each of the turbines comprises a vertical support 2 and multiple vanes 3. Each vane comprises an elongated body that extends between a first end and a second end of the vane, which elongated body being is spatially limited by a first side line 4 and a second side line 5 that extend between the first and second end of the vane.

Figure 2 Figure 2 schematically depicts a vane 3 of a wind turbine, showing both side lines 4 and 5 ofthe elongated body.

In figure 2A a part P of the first side line 4 is cut out and shown in Figure 2B in detail.

It is shown that the side line 4 at the cut out has a sinusoidal shape having a wavelength (A) and an amplitude (A), both varying along the length of the vane.

Depending on the type of turbulence to be created the wavelength and amplitude may vary, not only between different turbines, but also between different blades on the same turbine or even along the length of one particular vane.

Figure 3 Figure 3 schematically depicts various types of bodies for a vane 3. In Figure 3A it is shown that the elongated body which in essence is the vane is provided with multiple macroscopic through holes 6 to create additional turbulence and therewith noise reduction.

In Figure 3B the side lines of each through hole are roughened, having an Ra value of 3.5 mm.

Figure 3C is a side view of the vane 3 as depicted in Figure 3A, individually depicting the basic elongated body 3’ and a liner 8 that is provided on this body.

The liner 8 in this case consist of a layer of felt, having a ShoreA hardness of 30. Figure 4 Figure 4 schematically a spotted vane 3, showing the individual spotted like elements 9. By constituting a vane this way, it can be provided that the side line 4 (partly indicated in Figure 4) has a sinusoidal shape, but also that viewed in the direction X, the geometrical pattern provides for a variable density between the first and second end (which direction is indicated with an X), and in a direction perpendicular thereto (indicated with a Y), as well as (by having spots with different colour), a colour pattern is provided for such that the vane has a variable colour.

In particular the constitution by which the body is build up form individual or sets of spots, while at the same time having a variable width along the direction X, makes sure that there is a geometrical pattern that has a variable density in both direction X and Y.

The reason for this variation is twofold: the varying width along the length of the body in combination with the discontinuities in the body due to open spaces between the spots.

The latter, when having dimensions that correspond to the wavelength of sound, is a further means for causing turbulence to reduce (hindering) noise. Figure 5 Figure 5 shows in a top view, a row 20 that consist out of multiple wind turbines 1. The turbines do not form a closed wall, as known from the prior art for any row of wind turbines used to reduce noise, but deliberately there is an open space D between each pair of neighbouring wind turbines. In this embodiment the open space is 1 meter. The open space may be different for consecutive pairs of turbines, but in the shown embodiment it is a fixed distance D along the length of the row. The effect on a propagating sound wave 10 is schematically depicted in Figure 5B. The wave 10 moves forward through the row 20 in the indicated direction Z. Due to the open spaces sound interference is generated creating an altered wave 11 causing less hindrance.

Figure 6 Figure 6 shows, again in a top view, an alternative row 200 that consists of multiple wind turbines 1 and 1’. In this particular embodiment, in each pair of neighbouring wind turbines, the first turbine has a different vertical footprint than the second turbine. This way a difference in doppler effect of the re-directed sound waves can be created. This further helps altering the actual noise to be reduced. Figure 7 Figure 7 shows yet a further alternative of a row 2000 of wind turbines 1, 1’and 1”. In this particular case each wind turbine is a tree-like turbine resembling the appearance of a Cypress. Pairs of neighbouring turbines have different vertical footprints (see Figure 6). There are openings D between each pair of the turbines. The turbines 1 and 1” have vanes with a (half) length 11, which differs from the length 12 of the vanes of turbine 1’.

The minimal height above surface is h1 for turbines 1 and 1”, and h2 for turbines 1'. This way, a further noise reducing effect can be created.

Claims (18)

CONCLUSIONS A wind turbine comprising a strut extending in a vertical direction and a vane pivotally connected to the strut, the vane comprising an elongate body extending between a first end and a second end of the vane, the elongate body is spatially confined between a first and a second lateral line extending between the first and second ends of the vane, characterized in that at least the first lateral line has a sinusoidal shape with a wavelength (A) of at least 1.7 cm and an amplitude (A) of at least 0.85 cm. A wind turbine according to claim 1, characterized in that the sinusoidal shape comprises at least one period of a sinus. A wind turbine according to claim 1 or 2, characterized in that the sinusoidal shape comprises several periods of a sinus. A wind turbine according to any one of the preceding claims, characterized in that the wavelength is a maximum of 17 m. A wind turbine according to any one of the preceding claims, characterized in that the wavelength is between 8.5 cm and 34 cm. A wind turbine according to any one of the preceding claims, characterized in that in addition to the first lateral line, the second lateral line also comprises said sinusoidal shape. A wind turbine according to any one of the preceding claims, characterized in that the elongate body comprises one or more macroscopic through-holes. 8. A wind turbine according to claim 7, characterized in that a lateral line of each through hole has a Ra value above 1 mm. A wind turbine according to any one of the preceding claims, characterized in that the elongated body is provided with a top layer having a hardness of 80 Shore A or lower. A wind turbine according to claim 9, characterized in that the elongated body is provided with a top layer having a hardness of 60 Shore A or lower, preferably 40 Shore A or lower. A wind turbine according to any one of the preceding claims, characterized in that the elongate body comprises a geometric pattern having a variable density between the first and second ends. A wind turbine according to any one of the preceding claims, characterized in that the elongate body comprises a color pattern such that the elongate body has a variable color between the first and second ends. A wind turbine according to any one of the preceding claims, characterized in that the wind turbine comprises means for creating active sound with a frequency between 20Hz and 20kHz. A row of regularly positioned wind turbines, characterized in that each wind turbine in this row is a wind turbine according to one of the preceding claims. An array of wind turbines according to claim 14, characterized in that an open space between each pair of adjacent wind turbines is at least 0.34 m, and at most 17 m. An array of wind turbines according to claim 14 or 15, characterized in that in a pair of adjacent wind turbines, the first turbine has a first vertical footprint, and the second turbine has a second vertical footprint, the first vertical feed footprint differing from of the second vertical footprint. An array of wind turbines according to any one of claims 14 to 16, characterized in that in a pair of adjacent wind turbines, the first turbine has a vane whose elongate body has a first minimum height above a ground surface, and the second turbine has a vane whose elongate body has a second minimum height above a ground surface, the first minimum height being different from the second minimum height. An array of wind turbines according to any one of claims 14 to 17, characterized in that in a pair of adjacent wind turbines, the first turbine has a vane whose elongate body has a first length, and the second turbine has a vane the elongate body of which has a second length, the first length being different from the second length.