Abstract
A rotor blade of a wind turbine including at least one vortex generator is provided. The vortex generator is attached to the surface of the rotor blade and is located at least partially within the boundary layer of the airflow flowing across the rotor blade. The vortex generator is exposed to a stagnation pressure, which is caused by the fraction of the airflow passing over the vortex generator and of which the magnitude depends on the velocity of the fraction of the airflow passing over the vortex generator. The vortex generator is arranged and prepared to change its configuration depending on the magnitude of the stagnation pressure acting on the vortex generator. Furthermore, an aspect relates to a wind turbine for generating electricity with at least one such rotor blade.
Claims
1. A rotor blade of a wind turbine comprising at least one vortex generator, wherein the vortex generator is attached to the surface of the rotor blade, the vortex generator is located at least partially within the boundary layer of the airflow flowing across the rotor blade, the vortex generator is exposed to a stagnation pressure, which is caused by the fraction of the airflow passing over the vortex generator and of which the magnitude depends on the velocity of the fraction of the airflow passing over the vortex generator, wherein the vortex generator is arranged and prepared to change its configuration depending on the magnitude of the stagnation pressure acting on the vortex generator, such that, with increasing stagnation pressure in the boundary layer, the ability of the vortex generator to generate vortices decreases.
2. The rotor blade according to claim 1, wherein the vortex generator is situated in the outboard half, in particular in the outboard third, of the rotor blade.
3. The rotor blade according to claim 1, wherein the vortex generator comprises an inflatable element, such as a hose or a pressure chamber.
4. The rotor blade according to claim 3, wherein the rotor blade comprises a pressure tube extending substantially upstream from the vortex generator for guiding a portion of the fraction of the airflow flowing across the rotor blade to the inflatable element.
5. The rotor blade according to claim 3, wherein the vortex generator is at least partially embedded into the surface of the rotor blade.
6. The rotor blade according to claim 5, wherein the portion of the vortex generator, which is embedded into the surface of the rotor blade, increases with increasing stagnation pressure.
7. The rotor blade according to claim 1, wherein the vortex generator is able to bend depending on the value of the stagnation pressure acting on the vortex generator.
8. The rotor blade according to claim 1, wherein the vortex generator is able to straighten relative to the direction of the airflow depending on the value of the stagnation pressure acting on the vortex generator.
9. The rotor blade according to claim 7, wherein the vortex generator comprises an elastic portion for realizing the ability to bend or straighten, respectively.
10. A wind turbine for generating electricity with at least one rotor blade according to claim 1.
Description
BRIEF DESCRIPTION
[0036] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:
[0037] FIG. 1 shows a rotor blade of a wind turbine;
[0038] FIG. 2 shows a cross sectional view of the rotor blade at a certain spanwise position;
[0039] FIG. 3 shows a perspective view of a first embodiment of vortex generators;
[0040] FIG. 4 shows a cut-away view of a first embodiment of a thick embodiment of a vortex generators;
[0041] FIG. 5 shows a cut-away view of a first embodiment of a thin embodiment of a vortex generators;
[0042] FIG. 6 shows a side view of a second embodiment of vortex generators having a deflated pressure chamber;
[0043] FIG. 7 shows a side view of a second embodiment of vortex generators having an inflated pressure chamber;
[0044] FIG. 8 shows a third embodiment of vortex generators with a slightly inflated pressure chamber;
[0045] FIG. 9 shows a third embodiment of vortex generators with an inflated pressure chamber;
[0046] FIG. 10 shows a fourth embodiment of vortex generators;
[0047] FIG. 11 shows a fourth embodiment of vortex generators with a thick boundary layer;
[0048] FIG. 12 shows a fourth embodiment of vortex generators with a thin boundary layer;
[0049] FIG. 13 shows a fifth embodiment of vortex generators; and
[0050] FIG. 14 shows a fifth embodiment of vortex generators wherein adjacent vortex generators comprise a significant angle relative to each other.
[0051] Note that the following drawings are only schematically. Similar or identical reference signs are used throughout the drawings.
DETAILED DESCRIPTION
[0052] FIG. 1 shows a rotor blade 20 of a wind turbine. The rotor blade 20 comprises a root 21 and a tip 22. The root 21 and the tip 22 are connected by a virtual line, which is referred to as the span 25. The span 25 can be described as a virtual line, which is a straight line and which not necessarily exactly connects the root 21 and the tip 22. This would be the case if the rotor blade was a straight rotor blade. If, however, as for example illustrated in the example of the rotor blade of FIG. 1, the rotor blade is a slightly swept rotor blade, the tip may be slightly separate from the span 25. If the rotor blade is designed for a pitchable wind turbine, the span 25 can be associated and coincides with the pitch axis of the rotor blade.
[0053] Another characteristic feature and parameter of rotor blades of a wind turbine are the chords of the rotor blade. The chords 26, which are also referred to as the chord lines, can be defined and assigned for every spanwise position from the root to the tip of the rotor blade. The chord 26 is defined as the straight line being perpendicular to the span 25 and connecting the leading edge 23 of the rotor blade 20 with the trailing edge 24 of the rotor blade 20.
[0054] A particular chord length can be assigned to each chord 26. The maximum chord 261 is understood to be that chord which has the maximum length. The portion of the rotor blade where the maximum chord 261 is present is referred to as the shoulder 262 of the rotor blade. The part of the rotor blade between the shoulder 262 and the tip 22 is also referred to as the airfoil portion of the rotor blade. On the other hand, the part of the rotor blade between the shoulder 262 and the root 21 is referred to a transition and root region of the rotor blade.
[0055] FIG. 2 shows a cross sectional view at a certain spanwise position of the airfoil portion of the rotor blade. Again, the leading edge 23 and the trailing edge 24 can be seen. Additionally, the trailing edge section 241 and the leading edge section 231 are referenced in FIG. 2. The leading edge section 231 is defined as that section surrounding the leading edge 23 reaching from the leading edge 23 to a chordwise position of ten per cent of the chord length as measured from the leading edge 23. Likewise, the trailing edge section 241 of the rotor blade is defined as that section of the rotor blade which extends between ninety per cent chordwise position as measured from the leading edge 23 until the very trailing edge 24.
[0056] FIG. 2 also illustrate the airflow 40 flowing from the leading edge section 231 to the trailing edge section 241 of the rotor blade. As can be seen, the airflow 40 is subdivided into a suction side airflow 41 and a pressure side airflow 42. The separation of the airflow occurs at the stagnation point 29. Typically, the stagnation point 29 is located at the pressure side 28 of the rotor blade, but may also be located at the suction side 27 of the rotor blade. The exact position of the stagnation point 29 depends on a variety of factors, mainly it depends on the angle of attack and the pitch movement of the rotor blade.
[0057] FIG. 3-5 show a first embodiment of the present invention. In particular, a first embodiment of a vortex generator 30 is disclosed, which can be used and which is a part of a first embodiment of an inventive rotor blade.
[0058] FIG. 3 shows a perspective view of four pairs of such vortex generators 30. These vortex generators 30 are attached to a housing 35, which, as a whole, can be attached and mounted onto the surface, e.g. the suction side surface, of the rotor blade. An important feature of the arrangement as illustrated in FIG. 3 is the pressure tube 31. The pressure tube 31 consists of a relatively small diameter tube which is arranged upstream of the vortex generator. The arrangement furthermore comprises an inflatable member, namely a hose 32. This hose 32 is located within the housing 35. The hose 32 is able to push the vortex generator 30 downwards towards the surface of the rotor blade which is exemplarily referenced by the suction side 27. In order to facilitate or enable such a bending of the vortex generator, the vortex generator 30 comprises an elastic portion 34.
[0059] FIG. 4 illustrates the scenario of a thick boundary layer—confer to the shown velocity profile 43 in FIG. 4. In contrast to FIG. 4, FIG. 5 illustrates the scenario of a thin boundary layer—confer to the velocity profile 43 as illustrated in FIG. 5. As it can be seen, depending on the thickness of the boundary layer, the hose 32 is inflated or not which leads to an upwardly projecting vortex generator 30 or a vortex generator which is almost in contact with the suction side 27 of the rotor blade.
[0060] Note that in the first embodiment of the invention, the housing 35 is designed as a relatively stiff and rigid element. This means that its shape is substantially independent on the state of the hose 32. Whether the hose 32 is inflated (as in FIG. 5) or not (as in FIG. 4)—the housing has the same cross-sectional profile. As a consequence, the airflow, which is passing over the housing 35 is not influenced by the fact whether the hose 32 is inflated or deflated.
[0061] FIGS. 6 and 7 shows a second embodiment of the invention. Here, inflatable element is exemplarily designed as a pressure chamber 33. The pressure chamber may be in a deflated state (confer FIG. 6)—which is the case for a thick boundary layer, i.e. for a low stagnation pressure—or it may be in an inflated state (confer FIG. 7)—which is the case for a thin boundary layer, i.e. for a high stagnation pressure.
[0062] The pressure chamber 33 is accommodated and surrounded by a housing 35. In this embodiment, the housing is made of a flexible material. As a consequence, and contrary to the first embodiment as illustrated in FIGS. 3 to 5, the housing does change its shape depending of the state of the inflatable element.
[0063] Descriptively speaking, the housing 35 represents a “bump” for the airflow passing over it. Note that the airflow, which is passing over the housing 33, is influenced by the fact whether the pressure chamber 33 is inflated or deflated.
[0064] FIGS. 8 and 9 disclose a third embodiment of a vortex generator. This time, the vortex generator 30 is partially embedded into the surface, e.g. into the suction side 27 of the rotor blade. In other words, the rotor blade is provided with a recess or groove at its suctions side 27. In this groove, a device or arrangement comprising a pressure chamber 33 can b seen. This pressure chamber is connected with a pressure tube 31. Depending on the stagnation pressure which is guided through the pressure tube 31, the pressure chamber 33 is either inflated (confer FIG. 9) or it is not or only slightly inflated (confer FIG. 8). As a consequence, the vortex generator 30 is either submerged and embedded into the surface of the rotor blade (confer FIG. 9) or it projects away and sticks out of the surface (confer FIG. 8).
[0065] This third embodiment has the advantage that additional drag from the attachment portion as shown in the first embodiment as illustrated in FIGS. 3-5, is avoided. Thus, additional drag from the attachment portion, but also from the vortex generator as such, is reduced.
[0066] FIGS. 10, 11 and 12 disclose a fourth embodiment of an inventive vortex generator. This time no inflatable element, such as a pressure chamber or a hose, is used. Instead, it is the direct and sole design and configuration of the vortex generator 30 which leads to a changing configuration of the vortex generator in dependence of the velocity profile 43. See FIG. 11 for these scenarios of a thick boundary layer. As a consequence, the stagnation pressure at the position of the vortex generator 30 is small, thus the vortex generator which comprises an elastic portion 34 and which is bent upwards, i.e. away from the surface of the rotor blade, is projecting away and is able to generate vortices to a considerable extent. In contrast to that, FIG. 12 shows these scenarios of a thin boundary layer which can be seen by the velocity profile 43 leading to the bending down of the vortex generator 30 towards the suction side surface of the rotor blade. In the configuration as illustrated in FIG. 12 the ability of generating vortices by the vortex generator is heavily reduced.
[0067] Finally, the FIGS. 13 and 14 disclose a fifth embodiment of the invention. Similar to the fourth embodiment, no inflatable element or the like is present. Instead, the vortex generators themselves again comprise an elastic portion 34. This elastic portion 34 is designed such that for a thin boundary layer, as illustrated in FIG. 13, the vortex generators 30 are almost parallel to each other. They can also be described as being straightened by the high stagnation pressure of the airflow impinging on the vortex generator. In contrast to FIG. 13, FIG. 14 shows this scenario of a thick boundary layer, wherein the relatively small stagnation pressure is not able to overcome the pre-bent of the elastic portion 34 of the vortex generators 30. Thus, the adjacent vortex generators comprise a significant angle relative to each other. In this case, the ability to generate vortices is increased, compared to the straightened scenario as illustrated in FIG. 13.
[0068] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.
[0069] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.
