Abstract
A rotor blade of a wind turbine is provided, wherein the rotor blade has a flow deflection device for influencing an airflow flowing from the leading edge section of the rotor blade to the trailing edge section of the rotor blade. The flow deflection device passively changes its configuration depending on the bending of the rotor blade. Furthermore, the airflow is influenced such that load on the rotor blade is reduced. Furthermore, a method to reduce load on a rotor blade of a wind turbine is provided.
Claims
1. A rotor blade of a wind turbine, wherein the rotor blade comprises a flow deflection device for influencing an airflow flowing from a leading edge section of the rotor blade to a trailing edge section of the rotor blade, wherein the flow deflection device passively changes its configuration depending on the bending of the rotor blade, wherein the airflow is influenced such that load on the rotor blade is reduced, wherein the flow deflection device comprises a base plate disposed atop and secured to a surface of the rotor blade, and a lid comprising a first surface portion and a second surface portion, the lid disposed atop and secured to the base plate, and wherein the first surface portion and the second surface portion fold up when bending of the rotor blade is above a pre-determined threshold bending value, thereby forming a gap between the base plate and the first and the second surface portions, such that the first and the second surface portions form a ramp that guides the airflow away from the surface of the rotor blade.
2. The rotor blade according to claim 1, wherein the flow deflection device is arranged on a suction side of the rotor blade.
3. The rotor blade according to claim 2, wherein the flow deflection device is arranged upstream with regard to a vortex generator mounted to the surface of the rotor blade.
4. The rotor blade according to claim 2, wherein the flow deflection device is a part of a retrofit kit for an existing rotor blade of a wind turbine.
5. The rotor blade according to claim 1, wherein the flow deflection device continuously changes its configuration depending on the bending of the rotor blade.
6. A method to reduce load on a rotor blade of a wind turbine, wherein an airflow flowing from a leading edge section of the rotor blade to a trailing edge section of the rotor blade is passively influenced by a flow deflection device, the method comprising: inducing a change of the configuration of the flow deflection device by bending of the rotor blade, and influencing the airflow with the flow deflection device such that the load on the rotor blade is reduced, wherein the flow deflection device comprises a base plate disposed atop and secured to a surface of the rotor blade, and a first surface portion and a second surface portion both disposed atop and secured to the base plate, and wherein the first surface portion and the second surface portion fold up when bending of the rotor blade is above a pre-determined threshold bending value, thereby forming a gap between the base plate and the first and the second surface portions, such that the first and the second surface portions form a ramp that guides the airflow away from the surface of the rotor blade.
7. The method according to claim 6, wherein the flow deflection device is retrofitted to the wind turbine.
8. The method according to claim 6, wherein, the flow deflection device continuously changes its configuration depending on the bending of the rotor blade.
9. A rotor blade of a wind turbine, wherein the rotor blade comprises: a flow deflecting device comprising a base plate disposed atop and secured to a surface of the rotor blade, and a lid disposed atop the base plate; wherein during deflection of the rotor blade the lid translates relative to the base plate to an unstowed configuration; wherein in the unstowed configuration airflow is redirected to reduce a load on the rotor blade; and wherein the lid comprises two panels, each panel individually secured to the base plate at a first end and not secured to the base plate at a second end, wherein the translation comprises the second ends moving relative to the base plate and apart from each other, thereby forming a flow channel therebetween into which the airflow is redirected.
10. A rotor blade of a wind turbine, wherein the rotor blade comprises: a flow deflecting device comprising a base plate disposed atop and secured to a surface of the rotor blade, and a lid disposed atop the base plate; wherein during deflection of the rotor blade the lid translates relative to the base plate to an unstowed configuration; wherein in the unstowed configuration airflow is redirected to reduce a load on the rotor blade; and wherein the lid is secured to the base plate in two locations, wherein the two locations are separated by a region of the lid, wherein the translation comprises the region lifting off the base plate to form a ramp that redirects the airflow.
11. The rotor blade of claim 10, wherein the base plate conforms to a curvature of the surface of the rotor blade during the deflection.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, of which:
(2) FIG. 1 shows a wind turbine;
(3) FIG. 2 shows a rotor blade of a wind turbine in an unloaded state;
(4) FIG. 3 shows a set of flow deflection devices on the unloaded rotor blade of FIG. 2;
(5) FIG. 4 shows the rotor blade of FIG. 2 in a loaded state;
(6) FIG. 5 shows the flow deflection devices of FIG. 3 in the loaded state of the rotor blade of FIG. 4;
(7) FIGS. 6a-6c show advantageous locations of the flow deflection device on a rotor blade;
(8) FIG. 7 shows a first embodiment of a flow deflection device;
(9) FIG. 8 shows a detailed view of the components of the flow deflection device shown in FIG. 7;
(10) FIGS. 9a and 9b show the flow deflection device of the first embodiment in two different configurations;
(11) FIGS. 10a and 10b show the airflow flowing along the flow deflection device in a first configuration and a second configuration;
(12) FIGS. 11a-11c show advantageous locations of a flow deflection device of a second embodiment;
(13) FIGS. 12a and 12b show the influence of a flow deflection device on the airflow flowing across the rotor blade;
(14) FIGS. 13a and 13b show a flow deflection device in a second embodiment; and
(15) FIG. 14 shows the flow deflection device of FIG. 13b in another view.
DETAILED DESCRIPTION OF INVENTION
(16) The illustration in the drawings is in schematic form. It is noted that in different figures, similar or identical elements may be provided with the same reference signs.
(17) In FIG. 1, a wind turbine 10 is shown. The wind turbine 10 comprises a nacelle 12 and a tower 11. The nacelle 12 is mounted at the top of the tower 11. The nacelle 12 is mounted rotatable with regard to the tower 11 by means of a yaw bearing. The axis of rotation of the nacelle 12 with regard to the tower 11 is referred to as the yaw axis.
(18) The wind turbine 10 also comprises a hub 13 with one or more rotor blades 20. Advantageously, the wind turbine 10 comprises three rotor blades 20. The hub 13 is mounted rotatable with regard to the nacelle 12 by means of a main bearing. The hub 13 is mounted rotatable about a rotor axis of rotation 14.
(19) The wind turbine 10 furthermore comprises a main shaft, which connects the hub 13 with a rotor of a generator 15. If the hub 13 is connected directly to the rotor of the generator 15, the wind turbine is referred to as a gearless, direct drive wind turbine. Alternatively, the hub 13 may also be connected to the rotor of the generator 15 via a gearbox. This type of wind turbine is commonly referred to as a geared wind turbine.
(20) The generator 15 is accommodated within the nacelle 12. It comprises the rotor and a stator. The generator 15 is arranged and prepared for converting the rotational energy from the rotor into electrical energy.
(21) In the concrete example of FIG. 1, the wind turbine 10 comprises three rotor blades 20 (of which two rotor blades 20 are depicted in FIG. 1). The rotor blades 20 are mounted rotatable with regard to the hub 13 by means of a pitch bearing. The rotor blades 20 may thus be pitched about a pitch axis 16 in order to optimize the orientation with regard to the wind flow impinging on the wind turbine 10. Each of the rotor blades 20 comprises a root section 23 and a tip section 21. The root section 23 refers to the section of the rotor blade 20 which is closest to the hub 13. The tip section 21 refers to the section of the rotor blade 20 which is furthest away of the hub 13, thus being opposite to the root section 23.
(22) FIG. 2 shows some selected components of a wind turbine. A tower 11, a nacelle 12 and a hub 13 is shown. The nacelle 12 is mounted on the top of the tower 11 and the hub 13 is mounted rotatable with regard to the nacelle 12. One rotor blade 20, which is mounted to the hub 13 is illustrated in FIG. 2. A clearance 33 between a tip section 21 of the rotor blade 20 and the surface of the tower 11 can be assigned to the wind turbine. In FIG. 2 the clearance 33 is relatively large which is due to the fact that the rotor blade 20 is relatively straight.
(23) The rotor blade 20 in FIG. 2 refers to an unloaded state of the rotor blade 20. Note that the rotor blade 20 in FIG. 2 is drawn as a straight rotor blade 20. Alternatively, the rotor blade 20 may also be pre-bent away from the tower 11 at an unloaded state of the rotor blade 20. The rotor blade 20 comprises flow deflection devices 40 which are positioned close to the tip section 21. A plurality of flow deflection devices 40 are arranged adjacent to each other, resulting in a strip of flow deflection devices 40.
(24) FIG. 3 shows a detailed view of a part of the rotor blade 20 shown in FIG. 2. The strip of flow deflection devices 40 can be discerned. Furthermore it can be seen that the flow deflection devices 40 are closed. FIG. 3 shows a first configuration of the flow deflection devices 40.
(25) FIG. 4 shows the same components of the wind turbine as in FIG. 2. However, in FIG. 4 the rotor blade 20 is shown in a state of considerable loading. As a consequence, the rotor blade 20 is bent along its longitudinal axis thus leading to a deflection of the tip section 21 towards the tower 11. As a consequence the clearance 33 between the tip section 21 and the surface of the tower 11 is reduced. If the rotor blade 20 is further bent towards the tower 11, there is the danger of a collision between the rotor blade 20 and the tower 11. This could result in an undesired stand-still of the wind turbine and in structural damage of components of the wind turbine.
(26) FIG. 5 shows a second configuration of the flow deflection devices 40 which are arranged close to the tip section 21 of the rotor blade 20 as shown in FIG. 4. As a consequence of the changed configuration of the flow deflection devices 40, bending of the rotor blade 20 is reduced. This is due to the fact that the airflow is deflected and load on the rotor blade is decreased.
(27) FIGS. 6a to 6c show a rotor blade 20 in a first embodiment of the invention. The rotor blade 20 comprises a root 24 which is surrounded by a root section 23. Opposite to the root section 23 is a tip section 21 which is surrounding the tip 22 of the rotor blade 20. The rotor blade 20 furthermore comprises a trailing edge 26, surrounded by a trailing edge section 25, and a leading edge 28, surrounded by a leading edge section 27. FIGS. 6a to 6c show a top view onto the pressure side 31 of the rotor blade 20.
(28) A chord 35 can be attributed to each span-wise position of the rotor blade 20, wherein the chord is a straight line between the trailing edge 26 and the leading edge 28. The point of the rotor blade 20 where the chord 35, i.e. the length of the chord 35, is maximum is referred to as shoulder 34 of the rotor blade 20.
(29) FIG. 6a shows a first placement of flow deflection devices 40. Here, the flow deflection devices 40 are placed close to the tip section 21.
(30) In FIG. 6b two regions of the trailing edge section 25 are equipped with flow deflection devices 40. On the one hand a region of the trailing edge section 25 close to the tip section 21 is equipped with flow deflection devices 40; and on the other hand a section of the trailing edge section 25 which is approximately in the middle between the shoulder 34 and the tip section 21 is equipped with flow deflection devices 40.
(31) FIG. 6c shows a third advantageous placement of flow deflection devices 40 on a rotor blade 20. In this embodiment, the trailing edge section 25 almost along its entire length from the shoulder 34 to the tip section 21 is equipped with flow deflection devices 40.
(32) FIG. 7 shows a first specific embodiment of a flow deflection device 40. The flow deflection device 40 comprises a first lid 41, a second lid 42 and a base plate 43. It can be seen that a plurality of flow deflection devices 40 are arranged one after the other with spaces or gaps in between each other along the trailing edge 26 in the trailing edge section 25. In FIG. 7 the flow deflection devices 40 are placed on the pressure side 31 of the rotor blade. FIG. 7 shows a configuration wherein the flow deflection devices comprise a closed flow channel due to closed lids 41, 42. This configuration relates to the scenario of an unloaded rotor blade with a small bending or no bending at all.
(33) FIG. 8 shows a detailed view of the components of the flow deflection device 40. For sake of clarity the single components of the flow deflection device 40 are shown separate from each other. It can be seen that the first lid 41 and the second lid 42 are shaped such that they are flush with a base plate 43.
(34) In particular, a configuration where the two lids 41, 42 are flush with the base plate 43 refers to the scenario of a closed flow channel, see FIG. 9a.
(35) In contrast to this, a flow channel 45 is opened when the first lid 41 and the second lid 42 opens up as it is shown exemplarily in FIG. 9b.
(36) The impact of a closed or an open flow channel 45 can be seen in FIGS. 10a and 10b.
(37) In FIG. 10a a trailing edge section 25 of a rotor blade of a wind turbine is shown comprising a flat back trailing edge 26. Airflow 44 is flowing along a suction side 32 and a pressure side 31 of the rotor blade. A flow deflection device 40 is integrated at the pressure side 31 close to the trailing edge 26. As a consequence, the airflow 44 along the suction side 32 is undisturbed, in other words un-deflected; however, the airflow 44 on the pressure side 31 changes with a changing configuration of the flow deflection device 40.
(38) This means that by opening the flow channel 45 in the second configuration of the flow deflection device 40, as shown in FIG. 10b, the airflow 44 along the pressure side 31 is deflected towards the suction side 32. As a consequence load of the rotor blade is reduced.
(39) FIGS. 11a to 11c show a rotor blade 20 with flow deflection devices 40 in a second embodiment of the invention. The rotor blade 20 without the flow deflection devices 40 has a similar shape and design as shown in FIGS. 6a to 6c. However, in FIGS. 11a to 11c a top view on the suction side 32 of the rotor blade 20 is shown. The flow deflection devices 40 in this second embodiment of the invention are located on the suction side 32 of the rotor blade 20, relatively close to the leading edge 28. It can be seen from FIGS. 11a to 11c that the flow deflection devices 40 may either comprise the almost entire length of the leading edge 28 from the shoulder 34 to the tip section 21, or only cover a relatively small section close to the tip section 21, or may comprise several sections along the leading edge section 27. Obviously, other configurations and placements of the flow deflection devices 40 are possible, too.
(40) FIG. 12a shows a flow deflection device 40 located at the suction side 32 of a rotor blade 20. The flow deflection device 40 is placed slightly upstream of a vortex generator 46, wherein upstream refers to an airflow 44 flowing from the leading edge 28 to the trailing edge 26. FIG. 12a represents an unloaded, unbent or slightly bent state of the rotor blade. The flow deflection device does not influence or deflect the airflow 44 thus the vortex generator 46 is located within the boundary layer of the airflow 44, which results in an optimum technical effect of the vortex generator 46 and a delayed stall of the airflow 44.
(41) In FIG. 12b, however, the flow deflection device 40 is in a second configuration, resulting in folding up, in other words away from the surface of the rotor blade. This has the consequence that the airflow 44 is deflected away from the suction side 32 of the rotor blade. Thus, the vortex generator 46 is not within the boundary layer of the airflow 44 anymore, resulting in a premature stall of the airflow 44.
(42) FIGS. 13a and 13b illustrate a second embodiment of the flow deflection device 40. FIG. 13a shows a first surface portion 48 and a second surface portion 49 of the flow deflection device 40. It can be seen that this results in a flat, first configuration of the flow deflection device 40.
(43) In contrast, FIG. 13b shows that the flow deflection device 40 folds up, resulting in a folding up of the first surface portion 48 and a folding up of the second surface portion 49.
(44) This leads to a deflection angle 47, which can be seen in FIG. 14, which is greater than zero degrees. Note that in a rotor blade of a typical dimension exceeding 50 meters and going up until 100 meters, a folding up of the flow deflection device 40 of a few millimeters may be enough to significantly and substantially deflect the airflow and to have a significant impact on the load of the rotor blade.
