Flow control arrangement for a wind turbine rotor blade

Abstract

A rotor blade for a wind turbine is provided. The rotor blade includes an aerodynamic device for influencing the airflow flowing from the leading-edge section of the rotor blade to the trailing edge section of the rotor blade. The aerodynamic device is mounted at a surface of the rotor blade and includes a pneumatic or hydraulic actuator, such as a hose a cavity, of which the volume depends on the pressure of a fluid being present inside the pneumatic or hydraulic actuator. The rotor blade further includes a control unit for controlling the pressure of the fluid in the hose or the cavity of the aerodynamic device.

Claims

1. A rotor blade for a wind turbine, the rotor blade comprising: an aerodynamic device for influencing an airflow flowing from the leading edge section of the rotor blade to the trailing edge section of the rotor blade, wherein the aerodynamic device is mounted at a surface of the rotor blade and comprises a pneumatic or hydraulic actuator of which the volume depends on the pressure of a fluid being present inside the pneumatic or hydraulic actuator, and a control unit for controlling the pressure of the fluid in the pneumatic or hydraulic actuator of the aerodynamic device, wherein the aerodynamic device is in a first configuration when no pressure application to the fluid in the pneumatic or hydraulic actuator is induced by the control unit, the aerodynamic device is in a second configuration when the control unit induces the application of a positive or negative pressure to the fluid in the pneumatic or hydraulic actuator, in the first configuration, at least a first section of the aerodynamic device protrudes away from the surface of the rotor blade into the airflow flowing from the leading edge section of the rotor blade to the trailing edge section of the rotor blade, and in the second configuration, the first section is positioned closer to the surface of the rotor blade than in the first position.

2. The rotor blade according to claim 1, wherein the lift of the rotor blade in the first configuration is smaller than the lift of the rotor blade in the second configuration.

3. The rotor blade according to claim 2, wherein the aerodynamic device comprises a bending part made of flexible material which allows the change of configuration of the aerodynamic device from the first configuration to the second configuration and vice versa.

4. The rotor blade according to claim 3, wherein the protrusion of the first section away from the surface of the rotor blade is caused, or at least supported, by pretensioning the bending part of the aerodynamic device.

5. The rotor blade according to claim 1, wherein, in the second configuration of the aerodynamic device, the aerodynamic device is at least partially embedded into a shell of the rotor blade.

6. The rotor blade according to claim 1, wherein the aerodynamic device extends in parallel to the length axis of the rotor blade.

7. The rotor blade according to claim 1, wherein the aerodynamic device extends over at least ten percent of the length of the rotor blade.

8. The rotor blade according to claim 1, wherein the aerodynamic device is placed between the leading edge of the rotor blade and fifty percent of the chord length of the rotor blade, as measured from the leading edge.

9. The rotor blade according to claim 1, wherein the rotor blade further comprises a flow regulating unit for influencing the airflow flowing from the leading edge section of the rotor blade to the trailing edge section of the rotor blade.

10. The rotor blade according to claim 9, wherein both the aerodynamic device and the flow regulating unit are mounted on the suction side of the rotor blade.

11. The rotor blade according to claim 9, wherein the flow regulating unit is placed between the aerodynamic device and the trailing edge of the rotor blade.

12. The rotor blade according to claim 11, wherein the chordwise distance between the aerodynamic device and the flow regulating unit is between ten percent and fifty percent of the chord length of the rotor blade.

13. The rotor blade according to claim 9, wherein the flow regulating device is placed between the leading edge of the rotor blade and the aerodynamic device.

14. The rotor blade according to claim 13, wherein the chordwise distance between the aerodynamic device and the flow regulating unit is between one percent and twenty percent of the chord length of the rotor blade.

15. The rotor blade according to claim 9, wherein the aerodynamic device itself is equipped with the flow regulating unit.

16. The rotor blade according to claim 9, wherein the flow regulating unit comprises a vortex generator.

17. A wind turbine for generating electricity comprising at least one rotor blade according to claim 1.

18. The rotor blade according to claim 1, wherein the pneumatic or hydraulic activator comprises at least one of a hose and a cavity.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 shows a wind turbine;

(3) FIG. 2 shows a rotor blade of a wind turbine with an aerodynamic device;

(4) FIG. 3 shows a rotor blade of a wind turbine with an aerodynamic device and a flow regulating unit;

(5) FIG. 4 shows a first embodiment of an aerodynamic device in its first configuration;

(6) FIG. 5 shows the first embodiment in its second configuration;

(7) FIG. 6 shows a second embodiment of an aerodynamic device in its first configuration;

(8) FIG. 7 shows the second embodiment in its second configuration;

(9) FIG. 8 shows a third embodiment of an aerodynamic device in its first configuration;

(10) FIG. 9 shows the third embodiment in its second configuration;

(11) FIG. 10 shows an alternative of the second embodiment of the aerodynamic device in its first configuration;

(12) FIG. 11 shows the alternative of the second embodiment in its second configuration;

(13) FIG. 12 shows an embodiment wherein an aerodynamic device is combined with a flow regulating unit being located downstream of the aerodynamic device;

(14) FIG. 13 shows an embodiment wherein an aerodynamic device is combined with a flow regulating unit being located downstream of the aerodynamic device;

(15) FIG. 14 shows an embodiment wherein an aerodynamic device is combined with a flow regulating unit being located upstream of the aerodynamic device;

(16) FIG. 15 shows an embodiment wherein an aerodynamic device is combined with a flow regulating unit being located upstream of the aerodynamic device; and

(17) FIG. 16 shows lift curves of a rotor blade with an aerodynamic device in its first and second configuration.

DETAILED DESCRIPTION

(18) Note that the drawings are in schematic form. Similar or identical elements are referenced by the same or different reference signs.

(19) FIG. 1 shows a conventional wind turbine 10 for generating electricity. The wind turbine 10 comprises a tower 11 which is mounted on the ground 16 by one end. At the opposite end of the tower 11 there is mounted a nacelle 12. The nacelle 12 is usually mounted rotatable with regard to the tower 11, which is referred to as comprising a yaw axis substantially perpendicular to the ground 16. The nacelle 12 usually accommodates the generator of the wind turbine and the gear box (if the wind turbine is a geared wind turbine). Furthermore, the wind turbine 10 comprises a hub 13 which is rotatable about a substantially horizontal rotor axis 14. The hub 13 is often described as being a part of the rotor, wherein the rotor is capable to transfer the rotational energy to the generator.

(20) The hub 13 is the part at which the rotor blades 20 are mounted. Each rotor blade 20 is usually mounted pivotable to the hub 13. In other words, the rotor blades 20 can be pitched about pitch axes 15, respectively. This improves the control of the wind turbine and in particular of the rotor blades by the possibility of modifying the direction at which the wind is hitting the rotor blades 20. Each rotor blade 20 is mounted to the hub 13 at its root section 21. The root section 21 is opposed to the tip section 22 of the rotor blade. Note that in the example as shown in FIG. 1, only two rotor blades 20 are depicted. However, most modern wind turbines comprise three rotor blades.

(21) FIG. 2 illustrates a rotor blade 20 comprising an aerodynamic device 30. The rotor blade 20 comprises a root section 21 with a root 211 and a tip section 22 with a tip 221. The rotor blade 20 furthermore comprises an airfoil section which is characterized in that it is able to generate lift and comprising a suction side 25 and a pressure side 26. The airfoil shape of the airfoil portion is symbolized by one airfoil profile which is shown in FIG. 2 and which illustrates the cross-sectional shape of the rotor blade at this spanwise position. Also note that the suction side 25 is divided or separated from the pressure side 26 by a chord line 27 which connects the leading edge 241 with the trailing edge 231 of the rotor blade 20. Also note that the area around the trailing edge 231 is commonly referred to as the trailing edge section 23. Likewise, the area around the leading edge 241 is commonly referred to as the leading-edge section 24.

(22) A feature which distinguishes the rotor blade 20 as illustrated in FIG. 2 from a standard known art rotor blade is the provision of the aerodynamic device 30. The aerodynamic device 30 is arranged substantially along the length axis of the rotor blade, which is defined as the axis from the root 211 to the tip 221 of the rotor blade 20. In the example shown in FIG. 2, the aerodynamic device 30 extends over ca. fifteen percent of the length of the rotor blade.

(23) The aerodynamic device 30 in FIG. 2 is movable by means of a pressure hose which will be shown and described in more detail in the following Figures. A pressure hose is one example of a pneumatic actuator. Another example of a pneumatic actuator is an (inflatable) cavity.

(24) FIG. 2 furthermore discloses the pressure supply system of the aerodynamic device 30 comprising a control unit 51, a pressure supply system 52 and pressure lines 53. The pressure supply system 52 provides pressurized air. In this context, pressurized air not only comprises positive pressure but also negative pressure, wherein air is sucked (or “drawn”) out of the pressure hose of the aerodynamic device 30. The pressure lines 53 could in practice be realized as tubes or pipes which do not significantly change their volume. Finally, the control unit 51 is responsible for setting a specific pressure at the pressure supply system 52 which subsequently leads to a certain predetermined pressure at the aerodynamic device 30.

(25) In the example shown in FIG. 2, the control unit 51 and the pressure supply system 52 are located in the root section 21 of the rotor blade 20. However, the person skilled in the art is well aware that these parts could also be placed elsewhere in the wind turbine, such as e.g. in the hub of the wind turbine.

(26) FIG. 3 shows a variant of the rotor blade shown in FIG. 2. The rotor blade as shown in FIG. 3 additionally comprises a flow regulating unit 40 comprising multiple pairs of vortex generators. Such vortex generators arranged in pairs on wind turbine rotor blades are well-known both from literature and concrete industrial products.

(27) The flow regulating unit 40 is arranged downstream of the aerodynamic device 30. Therefore, the flow regulating unit can be “switched on” and “off” selectively by activating and deactivating the pneumatic actuator of the aerodynamic device 30.

(28) FIGS. 4 and 5 illustrate a first embodiment of a fail-safe aerodynamic device 30 according to embodiments of the invention.

(29) FIG. 4 shows the situation that the aerodynamic device 30 is in its first configuration. This means that in the situation as illustrated in FIG. 4, no pressure is applied to the pressure hose 31 of the aerodynamic device 30. As a consequence, the fluid 62 inside the hose 31 is at a predetermined pressure which may e.g. approach or be equal to the atmospheric pressure.

(30) The aerodynamic device 30 comprises a first portion 34. The first portion 34 is relatively stiff and rigid. It is at least rigid enough to resist and deviate the airflow 61 which is flowing from the leading-edge section to the trailing edge section of the rotor blade. In the first configuration of the aerodynamic device 30, the first portion 34 of the aerodynamic device 30 protrudes. In other words, the first portion 34 projects away from the surface 28 of the rotor blade.

(31) The aerodynamic device 30 further comprises a pneumatic actuator, which is realized as a hose 31 in the first embodiment of the aerodynamic device 30. The hose 31 comprises an elastic outer skin such that it can expand and collapse (or, in other words, inflate and deflate) reversibly and during many cycles.

(32) The aerodynamic device 30 further comprises a bending part 33. The bending part 33 is made of flexible material, such as e.g. rubber or a synthetic material. The bending part 33 functions as a hinge. The bending part 33 enables a change of orientation of the first portion 34 between an upright position (as in FIG. 4) or a flat position (as in FIG. 5).

(33) The reason why without application of pressure the aerodynamic device 30 does project upwards is due to the fact that the aerodynamic device 30 is provided with a pretension. In particular, it is the bending part 33, which is provided with a pretension.

(34) The aerodynamic device 30 in its first configuration—as illustrated in FIG. 4—induces stall. This is visualized with relatively large vortices 63 downstream of the aerodynamic device 30. A consequence of the induced stall is a decrease in lift of the rotor blade and, consequently, a reduced loading of the rotor blade and related components of the wind turbine.

(35) FIG. 5 shows the same aerodynamic device 30 as in FIG. 4, but in the second instead of the first configuration. The second configuration is different from the first one in that a negative pressure is applied to the fluid 62 inside the hose 31. As a consequence, the first section 34 has moved downwards towards the surface 28 of the rotor blade.

(36) As a consequence, the airflow 61 flowing across the aerodynamic device 30 is influenced differently. In particular, the airflow 61 remains attached to the surface 28 of the rotor blade, thus that no flow separation, i.e. stall, occurs. As a consequence, the lift of the rotor blade increases.

(37) The fail-safe feature of aerodynamic device 30 consists in the fact that if connection between the control unit/pressure supply system and the aerodynamic device 30 is disrupted, the aerodynamic device 30 automatically moves into the first configuration, cf. FIG. 4. As a consequence, the lift and load of the rotor blade is minimized, which is generally desired in the assumed case that connection between the control unit/pressure supply system and the aerodynamic device 30 is disrupted.

(38) FIGS. 6 and 7 show a second embodiment of an aerodynamic device 30. For sake of conciseness, similar or identical elements, which have already been introduced for the first embodiment of the aerodynamic device 30 will not be repeated.

(39) FIG. 6 shows the aerodynamic device 30 in its first configuration, i.e. in its “neutral” position without application of any pressure by the pressure supply system. The airflow 61 is spoiled, stall is induced, and, consequently, lift and load is reduced.

(40) The aerodynamic device 30 of the second embodiment is slightly differently designed compared to the aerodynamic device 30 of the first embodiment. Although both embodiments comprise a first portion 34, which protrude in the first configuration of the aerodynamic device 30 and which is buried (or embedded) in the second configuration, the change of configuration in the second embodiment is not realized by applying a negative pressure, but by applying a positive pressure. Descriptively speaking, in the first embodiment, the first portion 34 of the aerodynamic device 30 is brought downwards by drawing the fluid out of the pneumatic actuator, while in the second embodiment, this is achieved by pressing fluid into the pneumatic actuator.

(41) The fail-safe mechanism is, however, achieved in both embodiments: A pressure (a positive one or a negative one) needs to be actively applied on the pneumatic actuator for achieving a high lift of the rotor blade. If no pressure is applied, the pneumatic actuator makes the first portion 34 move into the “small-lift”, “low-load” configuration.

(42) As a detail, the pneumatic actuator is realized as a hose 31 in the first embodiment and as a cavity 32 in the second embodiment. This is, however, not relevant for the functionality of the fail-safe mechanism. The mechanism would also perfectly work if the aerodynamic device of the first embodiment was realized as a cavity and the aerodynamic device of the second embodiment was realized as a hose.

(43) Finally note that care must be taken during design of the second embodiment, in particular with regard of the hinge mechanism which induces aligning the first portion with the surface 28 of the rotor blade. At the same time, it needs to be ensured that the aerodynamic device 30 in its second configuration is flat enough to not spoil the airflow, although its pneumatic actuator is inflated.

(44) FIGS. 8 and 9 show a third embodiment of an aerodynamic device 30. Again, for sake of conciseness, similar or identical elements, which have already been introduced for the first or second embodiment of the aerodynamic device 30 will not be repeated here.

(45) FIG. 8 shows the aerodynamic device 30 in its first configuration, i.e. in its “neutral” position without application of any pressure by the pressure supply system. The airflow 61 is spoiled, stall is induced, and, consequently, lift and load is reduced.

(46) In contrast to FIG. 8, FIG. 9 shows the aerodynamic device 30 in its second configuration. Here, the first portion 34 of the aerodynamic device 30 is flat such that the airflow 61 flowing across the aerodynamic device 30 is not stalled.

(47) The similarity between the second and the third embodiment consists in that for both embodiments, a positive pressure needs to be applied to the pneumatic actuator of the aerodynamic device 30 to change the aerodynamic device 30 from its first into its second configuration.

(48) The modification of the third embodiment with regard to the second embodiment is that in the third embodiment the aerodynamic device 30 is predominantly embedded into the shell 29 of the rotor blade. This has the advantage that drag of the aerodynamic device 30 is minimized. This is especially advantageous in the second configuration of aerodynamic device 30, when an increase as high as possible of the lift of the rotor blade is generally desired. The third embodiment of the aerodynamic device 30 proposes an attractive solution to this desire, as the aerodynamic device 30 is almost flush with the surface 28 of the rotor blade in its second configuration.

(49) FIGS. 10 and 11 show a variant of the second embodiment of an aerodynamic device 30 according to embodiments of the invention. The sole difference between the aerodynamic device 30 as shown and described in FIGS. 6 and 7 is that the embodiment of the aerodynamic device 30 shown in FIGS. 10 and 11 additionally comprises a flow regulating unit 40 at its first portion 34. The flow regulating unit may be shaped as a pair of vortex generators.

(50) The flow regulating unit 40 does not have a significant influence on the airflow 61 in the first configuration of the aerodynamic device 30. The airflow 61 is spoiled, i.e. stalled, anyway and the flow regulating unit 40 does not change this.

(51) In the second configuration of the aerodynamic device 30, however, the airflow 61 is not only not spoiled by the aerodynamic device 30, but the boundary layer is even re-energized by re-energizing vortices 64, which are typically induced by vortex generators under suitable flow conditions. The effect is that the lift of the rotor blade is even further increased. In summary, the equipment of the aerodynamic device 30 by a flow regulating unit 40 is in principle capable to even further increase the lift of the rotor blade in the second configuration of the aerodynamic device 30.

(52) FIGS. 12 and 13 shows a combination of the first embodiment of the aerodynamic device 30 as shown in FIGS. 4 and 5 with a flow regulating unit 40, such as a vortex generator. As known to the person skilled in the art, a vortex generator is in principle able to increase the lift of a rotor blade due to re-energizing vortices 64 which it may induce in the boundary layer.

(53) Notably, the combination of a fail-safe aerodynamic device 30 with a flow regulating unit 40 results in a particularly powerful tool for, on the one hand, maximizing the lift of a rotor blade without, on the other hand, compromising safety issues in case of a failure of the system.

(54) Looking first at FIG. 13, which is the situation where a lift of the rotor blade as high as possible is aimed for. This is achieved by the arrangement disclosed here, as the aerodynamic device 30 is made as flat as possible (by e.g. drawing air out of the pressure hose of the aerodynamic device 30) for not spoiling the airflow 61 flowing across it, and, at the same time, the flow regulating unit 40 ensures an additional increase in the lift due to the generation of re-energizing vortices 64. Thus, a lift of the rotor blade as high as possible is achieved.

(55) In the case of a failure of the system, e.g. in a situation wherein the pneumatic actuator cannot be controlled, the aerodynamic device 30 automatically moves into the first configuration, which is depicted in FIG. 12. In the situation of loss of control over the pneumatic actuator, the aim is to minimize the lift of the rotor blade as much as possible because this involves a reduction of the load of the rotor blade and related components of the wind turbine as much as possible.

(56) This maximum reduction of the lift is achieved by the arrangement disclosed in FIG. 12, as the aerodynamic device 30 induces a stall of the airflow 61 (symbolized in FIG. 12 by the generation of large-scale stall-inducing vortices 63). At the same time, the flow regulating unit 40 is simply “switched off”, in other words deactivated. As the flow regulating unit 40 is arranged behind, i.e. downstream of the aerodynamic device 30, and the airflow 61 is deviated such by the protruding first portion 34 of the aerodynamic device 30 that it does not impinge suitably onto the flow regulating unit 40, the flow regulating unit 40 is not capable to generate re-energizing vortices for enhancing the lift of the rotor blade. Thus, the lift of the rotor blade is reduced as much as possible.

(57) In summary, it can be seen that the combination of a fail-safe aerodynamic device 30 with a flow regulating unit 40 placed downstream of the aerodynamic device 30 represents a particularly useful and advantageous option for optimizing the aerodynamic properties of a rotor blade in a fail-safe manner.

(58) FIGS. 14 and 15 show a different embodiment of combining an aerodynamic device 30 with a flow regulating unit 40.

(59) In this embodiment, the flow regulating unit 40 is placed “before”, i.e. upstream of the aerodynamic device 30. This does not allow the aerodynamic device 30 to directly activate or deactivate the flow regulating unit 40, but may, nevertheless, also represent an attractive option to achieve a high lift of a rotor blade without compromising safety issues in case of a failure of the system.

(60) FIG. 15 represents the situation wherein the aerodynamic device 30 is in its second configuration, i.e. a lift of the rotor blade as high as possible is aimed for. This is effectively achieved by the arrangement as disclosed in FIG. 15, because the flow regulating unit 40 generates re-energizing vortices 64 which pass by the aerodynamic device 30 substantially undisturbed as the aerodynamic device 30 is “flat”. This “flat” configuration of the aerodynamic device 30 may, in the exemplary design of the aerodynamic device 30 as shown in FIGS. 14 and 15, be achieved by applying a negative pressure to the pressure hose of the aerodynamic device 30.

(61) If, for any reason, no pressure is applied to the pressure hose, then the first portion 34 of the aerodynamic device 30 changes its orientation and moves from the “flat” position into an upright position, cf. FIG. 14. This does, however, not directly impact the generation of re-energizing vortices 64 by the flow regulating unit 40, as the flow regulating unit 40 is located upstream of the aerodynamic device 30. When, however, these re-energizing vortices 64 shortly after being generated approach the aerodynamic device 30, in particular the protruding first section 34 thereof, these re-energizing vortices 64 are deviated the same as the remaining airflow 61 and are destroyed. As a consequence, the airflow 61 is separated from the suction side 25 of the rotor blade approximately at the location where the aerodynamic device 30 is situated. In summary, the small lift-enhancing effect of the re-energizing vortices 64 is heavily outweighed by the flow separation induced by the aerodynamic device 30 which is in its first configuration and the overall lift (and load) of the rotor blade is significantly reduced.

(62) As it can be seen, also a combination of a flow regulating unit 40 and an aerodynamic device 30, wherein the flow regulating unit 40 is placed upstream of the aerodynamic device 30, represents an attractive option.

(63) It shall be clear for the person skilled in the art, that any of the aerodynamic devices presented in this disclosure, in particular the three embodiments disclosed in FIGS. 4-9, as well as any obvious variants thereof can be combined with any sort of flow regulating units, in particular with any sort of vortex generators.

(64) Finally, FIG. 16 visualizes the difference between the first and second configuration of the aerodynamic device 30 in terms of its impact on the lift curve.

(65) In FIG. 16, the lift 71 of the rotor blade is shown depending on the angle of attack 72. The first curve 73 represents the lift of the rotor blade when the aerodynamic device is in its first configuration. As usual, the lift 71 increases with increasing angles of attack 72 (at least for angles of attack 72 greater than zero) until a maximum value for the lift is reached. This maximum lift for the first curve 73 is referenced to by the reference sign 731.

(66) The second curve 74 represents the lift of the rotor blade when the aerodynamic device is in its second configuration. Again, the lift 71 increases with increasing angles of attack 72 until a maximum value for the lift is reached. This maximum lift for the second curve 74 is referenced to by the reference sign 741. The lift of the rotor blade is higher when the aerodynamic device is in its second configuration compared to the first configuration. This is—at least in the example shown here—valid for all relevant angles of attack greater than zero, and in particular also for the respective maximum lift values 731, 741. Thus, it can be concluded that the change of configuration of the aerodynamic device from the second into the first configuration effectively reduces the lift (and thus also the load) of the rotor blade.

(67) Although the invention has been illustrated and described in greater detail with reference to the preferred exemplary embodiment, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.

(68) 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.