Abstract
Provided is a wind turbine including a tower, a nacelle arranged at an upper end of the tower, a hub connected to the nacelle and a plurality of blades extending from the hub, wherein the wind turbine further includes a drag device for increasing the drag of the wind turbine) in air and/or for increasing the aerodynamic damping, the drag device including a planar surface configured to be directed perpendicular to an air flow.
Claims
1. A wind turbine comprising: a tower; a nacelle arranged at an upper end of the tower; a hub connected to the nacelle; a plurality of blades extending from the hub; and a drag device for increasing a drag of the wind turbine in air and/or for increasing an aerodynamic damping, the drag device comprising a planar surface configured to be directed perpendicular to an air flow.
2. The wind turbine according to claim 1, wherein the drag device further comprises a frame that gives structural stability to the drag device.
3. The wind turbine according to claim 2, wherein the frame comprises a wire rope.
4. The wind turbine according to claim 1, wherein the drag device is attached by an attaching means to ensure that the drag device is not detached and/or that the planar surface is tightened to increase a drag coefficient.
5. The wind turbine according to claim 4, wherein the attaching means comprises a hook attached to a ring.
6. The wind turbine according to claim 4, wherein the attaching means comprises a carabiner attached to a ring.
7. The wind turbine according to claim 1, wherein the drag device is attached to the nacelle.
8. The wind turbine according to claim 1, wherein the drag device is attached to the tower.
9. The wind turbine according to claim 8, wherein a rotating element is mounted on the tower to allow for yawing of the nacelle when the drag device is attached to the tower.
10. The wind turbine according to claim 1, wherein the planar surface extends in a direction parallel to a longitudinal axis of the nacelle.
11. The wind turbine according to claim 1, wherein the planar surface extends in a direction perpendicular to a longitudinal axis of the nacelle.
12. The wind turbine according to claim 1, wherein the drag device is attached to at least two blades, wherein the planar surface extends between the at least two blades.
13. The wind turbine according to claim 12, wherein one drag device is arranged between each pair of blades.
14. The wind turbine according to claim 1, wherein the drag device is a sail.
15. The wind turbine according to claim 1, wherein the drag device is a kite.
Description
BRIEF DESCRIPTION
[0034] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:
[0035] FIG. 1 shows a perspective view of a wind turbine;
[0036] FIG. 2 shows a wind turbine comprising a drag device in a folded position attached to each blade;
[0037] FIG. 3 shows a wind turbine comprising a drag device in an extended position arranged between each pair of blades;
[0038] FIG. 4 shows the attachment of a drag device to a blade by a ring and a wire rope;
[0039] FIG. 5 shows the attachment of a drag device to a blade by a ring and a hook;
[0040] FIG. 6 shows the attachment of a drag device to a blade by a ring and a carabiner;
[0041] FIG. 7 shows a drag device comprising a frame, a planar surface, a carabiner and an opening;
[0042] FIG. 8 shows a plurality of drag devices attached to the nacelle;
[0043] FIG. 9 shows a plurality of drag devices attached to the nacelle, wherein some of the drag devices are attached to the tower as well;
[0044] FIG. 10 shows a top view of a nacelle comprising a plurality of drag devices;
[0045] FIG. 11 shows the aerodynamic effects of using a drag device on an airfoil;
[0046] FIG. 12 shows the aerodynamic effects of using a drag device on an airfoil; and
[0047] FIG. 13 shows the aerodynamic effects of using a drag device on an airfoil.
DETAILED DESCRIPTION
[0048] FIG. 1 shows a wind turbine 1 comprising a tower 2, a nacelle 3 arranged at an upper end of the tower 2, a hub 4 connected to the nacelle 3 and three blades 5 extending from the hub 4.
[0049] FIG. 2 shows the wind turbine 1 of FIG. 1, wherein the wind turbine 1 further comprising a drag device 10 attached to one side of each blade 5. The drag device 10 comprises a planar surface 11, which is this figure is in a folded position and can therefore not be seen. The other side of each blade 5 comprises an attaching means 20 in form of rings 21. The attaching means 20 can be used to attach each drag device 10 between a pair of blades 5 when the drag device is unfolded and extended between the blades 5.
[0050] FIG. 3 shows the wind turbine 1 of FIG. 2, wherein the drag devices 10 are in an unfolded and extended position between each pair of blades 5. The drag devices 10 are sails 14 and comprise each a frame 12, a planar surface 11, a hook 22 and an opening 13. From the folded position shown in FIG. 2, where the drag devices 10 are attached to one blade 5 each, the drag devices 10 can be extended into an extended or unfolded position and securely attached to the rings 21 of a second blade 5 of the pair of blades 5, thereby extending the planar surface 11 between the blades 5. The frame 12 shown in this figure comprises a wire rope 16, which is secured to a ring 21 of the second blade 5 of the pair of blades 5 by passing the wire rope 16 through the ring 21. For this, the ring 21 can be opened so that the wire rope 16 passes through the inner part of the ring 21 and then closed to lock the wire rope 16 at the inner part of the ring 21. The planar surface 11 comprises an opening 13 to allow the ring 21 to close through the opening 13. A further edge of the frame 12 is secured by a hook 22 to another ring 21 of the blade 5. By attaching the drag device 10 to at least two points of the second blade 5, the planar surface 11 can be tightened and wrinkles can be avoided, thereby increasing the effectivity to stop air currents and increasing the drag coefficient.
[0051] FIG. 4 shows the attachment of a drag device 10 to a blade 5 by a ring 21 of the blade 5 and a wire rope 16 of the frame 12 of the drag device 10. The wire rope 16 can be secured to one ring 21 of the blade 5 by passing the wire rope 16 through the ring 21. For this, the ring 21 can be opened so that the wire rope 16 passes through the inner part of the ring 21 and then closed to lock the wire rope 16 at the inner part of the ring 21. The planar surface 11 comprises an opening 13 to allow the ring 21 to close through the opening 13, thereby securing the drag device 10 to the blade 5.
[0052] FIG. 5 shows the attachment of a drag device 10 to a blade 5 by a ring 21 of the blade 5 and a hook 22 of the drag device 10. For the attachment, the hook 22 is inserted in the ring 21. Through the tension of the planar surface 11 of the drag device 10, the hook 22 will not detach from the ring 21. To ensure that the hook 22 does not detach, the opening of the hook 22 can be designed just wide enough to be able to insert the hook 22 in the ring 21.
[0053] FIG. 6 shows the attachment of a drag device 10 to a blade 5 by a ring 21 of the blade 5 and a carabiner 23 of the drag device 10. The carabiner 23 comprises a gate member which can be opened by pressing or turning it, which securely attaches the drag device 10 to the blade 5.
[0054] FIG. 7 shows a drag device 10 comprising a frame 12, a planar surface 11, a carabiner 23 and an opening 13. The drag device 10 is a sail 14. The frame 12 comprises a wire rope 16. This kind of drag device 10 can be attached to a blade 5 as seen in FIGS. 3, 4 and 6.
[0055] FIG. 8 shows a plurality of drag devices 10 attached to the nacelle 3. The drag devices 10 are attached to the lateral surfaces of the nacelle 3 to increase the aerodynamic damping of the wind turbine. The planar surface 11 extends in a direction perpendicular to the longitudinal axis of the nacelle 3. The frame 12 comprises an internal structure extending through the planar surface 11 to increase the structural stability of the drag devices 10. This internal structure can be made of stiff elements such as bars.
[0056] FIG. 9 shows a plurality of drag devices 10 attached to the nacelle 3, wherein some drag devices 10 are attached to the tower 2 as well. One drag device 10 is attached to the top of the nacelle 3 in a similar way as shown in FIG. 8. Further drag devices 10 are attached to both the lower part of the nacelle 3 and to the tower 2 by a rotating element 24 to allow for yawing of the nacelle 3. This rotating element 24 is a ring around the tower 2.
[0057] FIG. 10 shows a top view of a nacelle 3 comprising a plurality of drag devices 10. The planar surface 11 of some drag devices 10 extends in a direction perpendicular to the longitudinal axis of the nacelle 3. The planar surface 11 of other drag devices 10 extends in a direction parallel to the longitudinal axis of the nacelle 3.
[0058] FIGS. 11 to 13 show the aerodynamic effects of using a drag device 10 on an airfoil 32. Usually, the shape of the airfoil, in the case of wind turbines 1 the shape of the blade 5, determines the amount of lift force 30 and drag force 31 acting on the body when an air flow 34 flows around the body.
[0059] In FIG. 11, the airfoil has a simplified NACA-like profile. The lift force 30 occurs because the moving fluid, in this case the air flow 34, is turned around the airfoil 32 in a laminar flow. This results in a low-pressure zone above the airfoil 32 and a high-pressure zone below the airfoil 32, resulting in the lift force 30. Additionally, a drag force 31 smaller than the lift force 30 acts on the airfoil 32 due to air resistance of the airfoil 32.
[0060] The drag force 31 is dependent on the effective area of the airfoil facing directly into the air flow 34. Hence, as seen in FIG. 12, a drag device 10 with a planar surface 11 extending perpendicular to the air flow 44 direction has a very high drag coefficient and experiences a high drag force 31. As the air flow 34 separates at the edges of the drag device 10, the air flow 34 cannot turn around the drag device 10. The laminar flow transitions to a turbulent flow and no lift force 30 acts on the body.
[0061] By attaching the drag device 10 to an airfoil 32, as seen in FIG. 13, the lift force 30 is considerably reduced or disappears due to the effects mentioned above.
[0062] 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.
[0063] 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.
REFERENCE NUMBERS
[0064] 1 Wind turbine [0065] 2 Tower [0066] 3 Nacelle [0067] 4 Hub [0068] 5 Blade [0069] 10 Drag device [0070] 11 Planar surface [0071] 12 Frame [0072] 13 Opening [0073] 14 Sail [0074] 15 Kite [0075] 16 Wire rope [0076] 17 Supporting structure [0077] 20 Attaching means [0078] 21 Ring [0079] 22 Hook [0080] 23 Carabiner [0081] 24 Rotating element [0082] 30 Lift force [0083] 31 Drag force [0084] 32 Airfoil [0085] 33 Separation [0086] 34 Air flow
