DK176357B1 - A wind energy system with extra set of wings - Google Patents

Description

DK 176357 Bl A WINDOW ENERGY INSTALLATION WITH EXTRA SET OF WINGS.

The invention relates to a wind energy system with a first set of blades mounted on a shaft and at least one additional second set of blades of less length than the first set of blades. The at least two sets of blades are mounted on the same shaft and with the same direction of rotation.

Background

The wind is increasingly being used as an energy source, which is why both more and 10 ever larger wind power plants are installed around. In order to achieve greater power output, wind power plants are made more efficient by optimizing the individual components of the system and partly with longer and longer blades.

15 At a wind power plant with a three-blade horizontal axis rotor, the blades on their innermost part towards the hub are relatively narrow, and in this part of the rotor a large part of the wind passes through unexploited or only little use. If this part of the wind can also be utilized optimally by the blades instead, the power output of the turbine can be significantly increased.

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One method of capturing and utilizing this energy is by making the wings very wide at their innermost part at the root. However, this results in very large loads on the blades - especially at larger wind speeds and gusts, whereby the rotor must be stopped or turned out of the wind earlier (at lower wind speeds) than would otherwise be the case with traditionally shaped blades. Furthermore, the very wide wings cause problems partly during production and not least when transporting the finished wings to the installation site.

30 It is also known, inter alia, from DE 10152449 to design the wings so that their inner part towards the root consists of foldable tabs 2 or shells so that the surface of the blade can be changed as a function of, for example, the wind speed. However, such blades involve a considerable complication of the manufacturing process, which is considerably expensive. In addition, the technique involves the use of advanced control mechanisms to regulate and initiate the change of the surface area of the blades.

It is furthermore known from EP 1255931 with wind power plants where the 'hole' in the center of the rotor is covered with a corresponding extra but small rotor which rotates the same path located in front of the first one. The smaller rotor must then rotate faster than the large rotor in order for the two rotors to run equally efficiently. This design with an extra rotor therefore requires either gear exchange between the rotors or two shafts, the output of which must then be connected in some way. The construction of the mill is thus both significantly expensive and complicated. Also, it may be necessary to leave the wings of the small rotor 15 with pitch bearings so that the shorter wings can handle the large differences in angles of incidence.

Objects and Description of the Invention

It is the object of the invention to provide a wind energy system which can utilize all or the wind within the rotor plane optimally or almost optimally and at all wind speeds, so that the above-mentioned problems with partly storm loads and partly complicated and expensive gear exchange are avoided.

The present invention thus relates to a wind energy system having a first set 25 having at least one wing mounted on a shaft and at least a second set having at least one wing mounted on the same shaft. The at least two sets of rotors are mounted such that the blade sets have the same direction of rotation and the same speed, and the second set of wings has a length less than the first set of wings. The second set of blades also has a different optimal tip speed ratio than the first set of blades, so that the two sets of blades are optimized for power output at the same rpm.

3 DK 176357 Bl

The tip velocity ratio is here and hereinafter defined as the ratio of the blade tip velocity to the wind velocity. By optimized in terms of power output, it is meant that each set of blades is optimized to exhibit approximately the maximum power coefficient of the rotor type concerned and thereby utilize the wind's energy optimally.

With a wind power plant according to the aforementioned, it is advantageous that the power output of the wind power plant is considerably increased, since the wind is also utilized at the center of the rotor, where otherwise it smokes between the rotor blades at traditional wind turbines. At the same time, a synergy effect is obtained, since the total wind energy obtained by the wind energy system according to the invention is greater than what can be achieved for each of the two sets of blades combined. This is achieved as the wind near the center of the rotor is not only utilized by the smaller set of blades but is also to a certain extent routed and sent out on the large blades where they make optimal use of the wind. Furthermore, the present invention is advantageous in that the two sets of blades are mounted on the same shaft, whereby no more shafts are to be used, and it is not necessary to use gear exchange between the two sets of blades as these rotate at the same speed.

In one embodiment, the ratio of the lengths of the two sets of wings is approximately determined by the ratio of the optimum tip velocity ratios of the two sets of wings. This achieves that both sets of blades are designed to run optimally at the same speed, with the greatest possible output power.

This is also achieved in yet another embodiment of the invention, wherein the second set of blades is designed for an optimal tip velocity ratio determined from the ratio of the length of the two sets of blades to the optimum tip velocity ratio for the one set of blades.

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The invention further relates to a wind power plant according to the above, wherein the at least two sets of blades are placed one after the other on their common shaft, or where the at least two sets of blades form a common rotor plane. This means that 5 each set of wings can optimally utilize the wind energy without disturbing the flow field significantly for the second set of wings. Furthermore, placing the two sets of wings directly in front of each other prevents an aerodynamic gap between the two or more sets of wings. This embodiment is also advantageous in that the extra set of wings or blades can be easily and easily mounted on the wind energy system and correspondingly easily replaced or perhaps completely removed again if needed.

An embodiment of the invention discloses a wind energy plant wherein the second set of blades constitutes a wind rose and the first set of blades constitutes a quick-release. This embodiment is advantageous in that a wind rose is simple and relatively inexpensive to manufacture. In addition, the wind rose at a fixed speed is effective over a relatively wide range of wind speeds.

In yet another embodiment of the invention, the second set of blades hinge 20 is mounted so that they can be rotated about their longitudinal axis. In this way, the loads on these blades can be simply reduced considerably, which can be an advantage of high wind speeds which are not so great that the entire rotor needs to be stopped or turned out of the wind. Thus, one set of wings can be rotated out of the wind independently of the other set of wings.

In yet another embodiment of the invention, the second set of vanes is mounted such that they can be braked independently of the first set of vanes or can be assembled radially into one or more groups. Both embodiments are advantageous in that the storm loads can be reduced on the second set of blades, while the first 30 sets of blades can travel further unaffected.

The present invention also relates to the use of a wind power plant as described by one or more of the aforementioned elements. The benefits here are as mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention is described with reference to the figures, in which figure 1 shows schematic curves of the different coefficients of wind turbines as a function of their tip velocity ratio, 10 figures 2-3 show a wind energy system according to the invention with two sets of wings Fig. 4-5 shows another embodiment according to the invention of a wind energy insert with two sets of blades located in the same rotor plane, viewed diagonally from the front and side, Fig. 6 shows a wind energy system according to the invention. Figure 7 shows a wind power plant according to the invention where the second set of blades can be assembled in groups, and Figures 8-11 show various embodiments of the second set of blades.

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DESCRIPTION OF EMBODIMENTS Figure 1 shows the various power factors or power coefficients Cp, 102 of various types of wind rotors outlined as a function of their tip velocity ratio X, 101.

The tip velocity ratio X is given as the ratio of the blade tip velocity 30 to the velocity of the wind and thus varies proportionally to the length of the blade and inversely proportional to the wing turn-around time (the time a revolution takes). From the curves in Figure 1 it can be read at which tip velocity ratio 101 a rotor of a particular type will operate optimally (having maximum power factor). The curve 103 is for an ideal propeller rotor which, among other things due to the friction in real rotors, will always be above the realizable. Curve 104 shows the coefficient of power of a fast runner, which is the term for a rotor whose tip speeds are several times greater than the wind speed. Modern wind turbines with three blades are fast runners. A multifaceted slow-motion inverter, such as a wind rose, has characteristics as outlined by curve 105. A 10-year-old wind turbine power coefficient curve is given at 108, and curves 106 and 107 are for a Savonius and a Darrieus mill, respectively, both of which are vertical rotation axes. Thus, in order to obtain the maximum power output from a rotor, its turnaround time must be aligned with the diameter of the rotor, so that a larger rotor should rotate more slowly around 15 a little. These power coefficient curves are used below to design a wind power plant with optimum utilization of the wind.

Figure 2 shows a wind power plant 200 according to the invention, in which the wind turbine generally comprises a rotor 201 and a nacelle 202 on a barrel 203. Here, the rotor 20 201 is a three-blade or blade 204. Quickly in front of this primary rotor is mounted a further a small rotor 205 having a much smaller diameter covering the innermost of the large rotor 201. Thus, all the wind within the large rotor area 208 is utilized optimally, with the wind at the innermost of the blades 204 partly utilized by the extra rotor 205 25 instead. in order to smoke directly through the hole in the rotor and partly to a certain extent are routed out on the widest part of the large wings 204 where the wind is optimally utilized.

The two rotors 201, 205 are mounted on the same shaft and rotate the same path, 30 as illustrated by the arrows 206. Because of the different lengths of the two rotors wings 204, 207, their blade tip speeds, and thus also their tip speed ratios , correspondingly different if the rotors rotate equally quickly with the same turnaround time. If the 'hole' in a primary rotor is filled with yet another corresponding rotor of the same type only of smaller diameter, the result will be that one of the rotors cannot run as efficiently as possible, or alternatively that the two rotors can not drive just as fast and a gear exchange becomes necessary. This problem is solved according to the present invention by selecting the smaller secondary rotor 205 of a different type or according to a different principle with a different optimal tip speed ratio than the primary rotor 201. Hereby, both rotors can run at the same orbital time and at their respective optimum tip speed ratio with the greatest power output. At the same time, the rotors can sit on the same shaft, and small rotor gear is unnecessary. This is illustrated in Figure 2, where the primary largest rotor 201 is a three-bladed high speed runner, while the smaller secondary rotor 205 is a wind rose, which type of wind rotor is a slow runner with a much lower tip speed ratio, see Figure 1. By designing and constructing the two rotors relative to each other in this way are obtained so that both rotors will provide maximum power output at the same orbital speed. At the same time, the following synergistic effect is obtained that the wind is better utilized than by the sum of the two rotors together, since the wind at the smallest rotor 205 is not only captured and utilized but also to some extent is directed and sent out to the wings of the primary rotor 204, where is the widest and most effective.

In one embodiment of the invention, the ratio of the lengths of the two sets of wings 204, 207 is approximately determined as the ratio of the optimum tip velocity ratios of the two sets of 25 wings. That is, if the two rotor types are selected, and thus their optimum tip speed ratio, their size ratio is dimensioned from here. Similarly, the type of the secondary (primary) rotor can be determined directly from the type of the primary (secondary) rotor and the ratio of the wing lengths of each rotor. This can be illustrated by the following examples: 8 DK 176357 B1

Example 1:

As wind speed, a mean value applies to both rotors.

Primary rotor: The three-blade speed runner with maximum Cp at v.

v _ tip.size n v find

Rotor diameter Dslor =] 00m.

5 Secondary rotor is selected with diameter Dme = 20m.

y - - V X large _ TtDgit ,, · Tstor _ Dy y _ 20m _. .

γ / φ., Μ7 nDstor-Tmc 'A (07 ΪΟΟ »* = where T is the turnaround time.

Thus, as a secondary rotor, according to the invention, a rotor with an optimum tip speed ratio Xulle of approx. 1.4.

Example 2:

Primary rotor as in Example 1.

15 As a secondary rotor, a species of wind rose with X small ~ 1 'is selected

Xmte = ^ ll! Ie · X slor (same calculations as in Example 1), tor

G

Dm, = i-100m * K3m.

large ^ DK 176357 Bl 9

Thus, the diameter of the secondary rotor is selected at about 14.3 m.

The wind energy system according to the invention is also advantageous in that the wind rose is effective over a larger range of wind speeds, which is why the wind rose 5 is not as sensitive to fluctuations in wind speeds. This is a great advantage over, for example, a small three-blade speed runner, which, in order to operate properly at the low tip speeds, would have to operate over a wide range of angles, so pitch control of each blade would be required.

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The two rotors 201,205 are mounted immediately in succession, as can also be seen in Figure 3, where the wind energy system 200 is shown in side view. By installing the rotors 201, 205 just one after the other, an aerodynamic gap is created between the two rotors, whereby the flow field remains optimally 15 and all wind through the rotor plane will be utilized. The secondary smaller rotor 205 can here also be mounted on the main shaft in such a way that it can be disengaged and stopped independently of the rotation of the primary rotor. This is advantageous at high wind speeds where the storm loads can thus be considerably reduced.

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The secondary smaller rotor 205 can also be located in another embodiment immediately behind the primary large rotor 201.

Figure 4 shows another embodiment of a wind energy system according to the invention, in which one set of blades 204 from the larger primary rotor 201 is mounted in the same plane as the additional set of shorter blades 207 from the other rotor 205 and thus constitutes a overall rotor with shorter blades 207 positioned between the larger blades 204. In the sketched embodiment, the total rotor here is constituted by a wind rose and a three-bladed high speed runner. This is also shown from the side in Figure 5.

DK 176357 B1 10

At high wind speeds it may be necessary to limit the loads on the blades. The loads on a wind rose become critical at lower wind speeds than on a fast runner, so it may be advantageous to be able to reduce the wind rose area against the wind without changing the speed of the speed runner. One way to do this is to mount the blades 207 on the smaller secondary rotor in hinges or pivot joints 601, as outlined in Figure 6, where only a portion of the rotor is shown. In this way, the blades 207 can be turned out of the wind direction 602 and the storm loads are greatly reduced. At very short blades, shorter than the distance from the rotor plane to the tower, the blades 207 can also be mounted hinged in such a way that at critical wind speeds they can be completely or partially lowered in the wind direction along the nacelle.

Another method of reducing the loads on the secondary rotor blades 207 at high wind speeds is outlined in Figure 7. Here, the blades 15 are also hinged mounted 701, but in this embodiment in such a way that the blades 207 can be assembled in groups 702 by sliding. or are brought together and partially or partially radially over one another. The outlined proposals in Figures 6 and 7 for limiting storm loads on the second set of shorter blades 207 can also be used on several other types of rotors 20 than for the wind rose shown.

Figures 8-11 show various other embodiments of the smaller secondary rotor 205. In Figure 8 is illustrated a rotor 205 of a type in which the blades or blades 207 are designed as vanes equal to a fan.

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The rotor 205 outlined in Fig. 9 also has vane barrel and a relatively large number of tightly seated blades 207. Due to the vane shape of the blades, the rotor is not as sensitive to small tip speeds and will be more or less equally effective over a relatively large wind speed range. For example, the blades on the rotor shown in Figure 9 can be made by bending thin sheets.

In Figure 10, a rotor 205 is sketched, the blades of which are manufactured according to the same principle as in the previous figure, but with only a few blades 207 (here 4 blades), which is why the optimum tip speed ratios of the two rotors will be different.

Finally, in Figure 11, another rotor principle 205 for use as a secondary rotor on a wind power plant according to the invention is shown. Here, the individual wings 207 are formed of stretched sail cloth or thin sheets.

The blades of the various rotor principles shown in the preceding Figures 8-11 can also be placed in the same rotor plane as the larger primary rotor 201 between the longer blades and in this way fill the center of the rotor and utilize the wind optimally.

It is to be understood that the invention, as disclosed in the present disclosure and figures, may be modified or altered and continue to be included in the scope of protection of the claims below.

Claims (10)

A wind energy system having a first set of at least one blade mounted on a shaft, and at least a second set of at least one blade mounted on the same shaft and mounted such that the blade sets will have the same direction of rotation and the same speed, which second set of wings has a length less than the first set of blades, and which second set of blades has a different optimal tip velocity ratio than the first set of blades, such that two sets of blades are optimized for power output at the same rpm number. A wind energy system according to claim 1, characterized in that the ratio of the lengths of the two sets of wings is approximately determined by the ratio of the optimum tip velocity ratios of the two sets of wings. 15 A wind energy system according to claim 1, characterized in that the second set of blades is designed for an optimum tip velocity ratio determined from the ratio of the length of the two sets of blades to the optimum tip velocity ratio for the one set of blades. 20 A wind power plant according to one or more of claims 1 to 3, characterized in that the at least two sets of blades are placed one after the other on their common shaft. A wind power plant according to one or more of claims 1-4, characterized in that the at least two sets of blades form a common rotor plane. A wind power plant according to one or more of claims 1 to 5, characterized in that the second set of blades constitutes a wind rose and the first set of blades constitutes a 30 runner. A wind power plant according to one or more of claims 1-6, characterized in that the second set of blades are hingedly mounted so that they can be rotated about their longitudinal axis. DK 176357 Pg 13 A wind power plant according to one or more of claims 1-7, characterized in that the second set of wings is mounted so that they can be braked independently of the first set of wings. A wind power plant according to one or more of claims 1-8, characterized in that the second set of blades is mounted so that they can be radially assembled into one or more groups. Use of a wind power plant as claimed in one or more of claims 1-9. 15