|Publication number||WO2001016482 A1|
|Publication date||8 Mar 2001|
|Filing date||1 Sep 2000|
|Priority date||1 Sep 1999|
|Publication number||PCT/2000/614, PCT/NL/0/000614, PCT/NL/0/00614, PCT/NL/2000/000614, PCT/NL/2000/00614, PCT/NL0/000614, PCT/NL0/00614, PCT/NL0000614, PCT/NL000614, PCT/NL2000/000614, PCT/NL2000/00614, PCT/NL2000000614, PCT/NL200000614, WO 0116482 A1, WO 0116482A1, WO 2001/016482 A1, WO 2001016482 A1, WO 2001016482A1, WO-A1-0116482, WO-A1-2001016482, WO0116482 A1, WO0116482A1, WO2001/016482A1, WO2001016482 A1, WO2001016482A1|
|Inventors||G. C. Corten|
|Applicant||Stichting Energieonderzoek Centrum Nederland|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Non-Patent Citations (1), Referenced by (63), Classifications (8), Legal Events (7)|
|External Links: Patentscope, Espacenet|
Blade for a wind turbine
The present invention relates to a blade for a wind turbine or the like, having a part which rotates in a flow of fluid, which blade comprises an attachment end, which is connected to the said wind turbine or such part, and a free end, which is at a distance from the attachment end, the blade comprising, at least in the vicinity of the free end, a profile which is optimized for a flow of fluid (air).
A blade of this type is generally known, and the flow-optimized profile exhibits considerable similarity to the profile of a standard aircraft wing or propeller blade. This means that, in the direction of movement of the blade, the incoming air firstly encounters a rounded part which on one side merges into a convex part and on the other side merges into a convex or concave part, which meet at a sharp point. However, it should be understood that other flow-optimized profiles are also conceivable and the precise design of the optimized profile of the blade is not essential to the invention.
Wind turbines are being designed for increasingly higher outputs. However, it has been found that in wind turbine parks where there are a number of wind turbines there are inexplicable differences in output between the individual wind turbines. Moreover, it has been found that certain turbines sometimes provide a much lower output than ought to be expected on the basis of the prevailing wind. This phenomenon may last for both a very short period (a few hours) and a very long period. This problem has been found to occur in particular in generators designed for a relatively high output, for example from 180 kW and more particularly from 500 kW.
The object of the present invention is to avoid this drawback and to provide a blade with which it is possible to achieve an output from the corresponding wind turbine which can be successfully predicted in advance, without inexplicable falls in the efficiency.
In a blade as described above, this object is achieved in that adjacent to one of the ends, turbulence-generating members are arranged near that side which lies upstream as seen in the direction of movement of the blade.
It is assumed that the fall in efficiency described above results from the fact that the tip, that is to say the free end of the blade and/or the attachment end, under certain circumstances reaches a stable stalled state. When the flow in the vicinity of the tip is released, vibrations are detected. These may be low-frequency vibrations. In an exceptional situation, it has even been observed that the blades begin to vibrate in the plane in which they rotate, which may ultimately lead to the blades breaking in the vicinity of the main shaft of the turbine. However, it should be understood that the question of whether the above explanation is correct is not connected with the validity of the appended claims.
It has been found that arranging vortex generators in the vicinity of the free end and more particularly in the vicinity of the upstream end of the wing, although possibly leading to a slight fall in efficiency, makes it possible to avoid the sometimes sudden fall in output.
The turbulence generators or vortex generators may be arranged on both the pressure side and the suction side of the blade, from the first point of contact between the air flow and the blade. Vortex generators of this type are preferably arranged on the suction side of the blade. In this context, the term suction side is understood as meaning the side extending from the upstream stagnation point to the back edge which is under the low pressure.
Apart from the intended object of preventing sudden changes in output from the wind turbine, the vortex generators in the vicinity of the free end achieve the additional advantage that the noise production is limited. This is because the avoidance of stalling makes it possible to avoid undesirable noise production.
The vortex generators may comprise any part of any shape which is known in the prior art. They are preferably designed as triangular flaps. More particularly, a series of these generators is arranged on the wing profile. This series may have a common base. The length of each generator, that is to say the distance which it has in common with the adjoining surface of the wing profile, is approximately 3% of the chord length of the wing profile at this location. The chord is the distance between the front and rear points (in a straight line) of the curve which runs through the profile and is at an equal distance from the underside and the top side of the blade. However, it should be understood that the length value referred to here is only an example. The same applies to the height. According to a preferred embodiment of the invention, the latter is approximately 1% of the chord length. Height is understood as being the distance over which the flap extends from the surface of the blade. In practice, this will mean that a height of this nature is at most 10 cm. The distance between two vortex generators in a series may be selected as a function of the flow conditions and is, for example, 1/10 of the chord length described above.
Apart from a series of vortex generators positioned next to one another, it is also possible to arrange two or more series of generators arranged parallel to one another, i.e. parallel with respect to the longitudinal axis of the blade, on one or both sides of the blade.
It is also possible to optimize the shape of a series of vortex generators. A particularly efficient design is obtained if a series of this type describes a line which extends from the upstream side of the free end in the direction of the attachment end towards the downstream end and then back towards the upstream end again. As a result, a type of U-shaped profile is obtained.
A further advantage involved with positioning the vortex generators in the vicinity of the tip is that it has been found that the installation of vortex generators means that the output does not fall suddenly even at high wind speeds.
In addition to the arrangement of vortex generators, it has been found that it is also possible to reduce a sudden loss in efficiency by allowing the free end of the blade to extend in the upstream direction. The distance over which the free end runs upstream is preferably of the order of magnitude of the chord length of the blade at the location of the bending point. The effect of vortex generators may also be achieved by air jets arranged at an angle; a flow of air is blown outwards through small holes in the profile, at an angle to the principal flow.
The invention will be explained in more detail below with reference to exemplary embodiments illustrated in the drawing, in which: Fig. 1 shows a very diagrammatic view of a very general structure of a wind turbine provided with two blades;
Fig. 2 shows the detail given in Fig. 1 ;
Fig. 3 shows a blade in accordance with Fig. 1 in which the vortex generators are shown positioned on the suction side; and Fig. 4 shows a detailed view, similar to that of Fig. 2, of an amended embodiment of the end of the blade.
In Fig. 1, a wind turbine is denoted overall by 1. It comprises a conventional post on which a machine housing 2 is arranged. From this there extends a shaft (not shown in more detail) which is coupled to a hub 3, to which two blades 4 are attached by means of the associated attachment end 8. The free end of the blades is denoted by 9. The length of the blades provided with a particular flow profile is indicated by L. The attachment part 8 will generally comprise a simple cylindrical pipe which merges smoothly into flow profile L. Naturally, length L is selected as a function of the output to be generated by the wind turbine. An example which may be mentioned is a value of between 5 and 100 metres. According to the invention, particular measures are taken in the encircled region but also outside this region. This region is shown in more detail in Fig. 2. From this figure, it can be seen that the height of this region is 1 and this height is preferably less than 20% of the length L of the blade. The pressure side is indicated by 6, while the suction side is indicated by 5. The upstream side is 10 and the downstream side is 11.
It can be seen from Fig. 2 that in the vicinity of the upstream side there are two series of turbulence-generating generators 12 and 13. In this example, these generators are triangular flaps which have a common base part. They may, for example, be prefabricated as lengths of 1 metre. These vortex generators are preferably in any case arranged on side 5 and may in addition be arranged on side 6. In the example illustrated, a single series is shown each time, but it is also possible to use a number of series which are parallel to one another or even to have an arbitrary arrangement within a defined region. Vortex generators of this type preferably consist of flexible material, so that during transport they can easily be pressed against the corresponding blade without permanent damage occurring while it is ensured that they spring back into the desired position.
Instead of the straight pattern which is known, it is possible to use a U-shaped pattern. This is shown in Fig. 3, and the line followed in this figure bears the reference numeral 14. This pattern increases the output.
Vortex generator patterns of this nature enables the stability of the blade to be improved considerably under different wind conditions, and a more successfully predictable output and improved efficiency can be obtained without a sudden fall in efficiency for a relatively long or short time.
Vortex generators may comprise any material which is known in the prior art. They may, for example, be aluminium parts which are 0.5 mm thick. Fig. 4 shows a further measure which can be used optionally in combination with the measures shown in Figs. 2 and 3. The free end of the blade is bent towards the arriving flow. The length of this bent end is denoted by N and approximately corresponds to the length of the chord C at the location of the said bending point. It should be understood that this measure can be used both in combination with the vortex generators described above and as a stand-alone measure, that is to say without the presence of turbulence-generating generators of this nature in the vicinity of one of the ends.
Although the invention has been described above with reference to preferred embodiments, it will be immediately understood by a person skilled in the art that numerous modifications are possible and lie within the scope of the appended claims.
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|Cooperative Classification||Y02E10/721, F05B2260/96, F05B2240/122, F03D1/0675, F03D1/0633|
|European Classification||F03D1/06C6, F03D1/06B6|
|8 Mar 2001||AL||Designated countries for regional patents|
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