WIND TURBINE BLADE WITH TRIPPING DEVICE AND METHOD THEREOF

Abstract

A wind turbine and a method of reducing extreme loads and fatigue loads on a wind turbine by using a passively activated tripping device arranged on the pressure side of the wind turbine blade. The tripping device is configured to interrupt the passing airflow, when activated, and transform the airflow into a turbulent airflow. The tripping device is positioned close to the leading edge, wherein its dimensions are optimized so that it reduces the maximum lift coefficient as well as increases the minimum lift coefficient which in turn reduces the range of the lift coefficient. The tripping device is activated at both negative and positive angle-of-attacks outside the normal operating range.

Claims

1. A wind turbine comprising: a wind turbine tower, a nacelle arranged on top of the wind turbine tower, a rotatable rotor with at least two wind turbine blades connected to the nacelle, wherein each of the at least two wind turbine blades comprises a tip end, a blade root and an aerodynamic profile, wherein the aerodynamic profile defines a leading edge, a trailing edge, a first side surface which defines a pressure side, and a second side surface which defines a suction side, wherein a chord extends from the leading edge to the trailing edge and has a chord length of 100%, wherein at least one first tripping device is arranged on the pressure side on at least one of the wind turbine blades, the at least one first tripping device is placed at a predetermined position relative to the leading edge, and wherein the at least one first tripping device is configured to passively reduce a maximum lift coefficient when said at least one of the wind turbine blades has a positive AoA outside a normal operating AoA range and to passively increase a minimum lift coefficient when said at least one of the wind turbine blades has a negative AoA outside the normal operating AoA range.

2. The wind turbine according to claim 1, wherein said at least one first tripping device is further configured to transform an airflow passing over the at least one first tripping device from a laminar airflow into a turbulent airflow when the AoA of said at least one of the wind turbine blades is outside the normal operating AoA range in one direction.

3. The wind turbine according to claim 1, wherein the predetermined position of the at least one first tripping device is determined according to a distance along the chord and projected towards the pressure side, wherein the at least one first tripping device is positioned at a distance of 0% to 1% measured along the chord from the leading edge.

4. The wind turbine according to claim 3, wherein the at least one first tripping device is positioned at a distance of 0.2% to 0.6% from the leading edge.

5. The wind turbine according to claim 1, wherein at least one second tripping device is further arranged on the pressure side of the at least one of the wind turbine blades, the at least one second tripping device is placed at another predetermined position relative to the leading edge, wherein the at least one second tripping device is arranged at a distance from the at least one first tripping device.

6. The wind turbine according to claim 5, wherein the predetermined position of the at least one second tripping device is determined according to a distance along the chord and projected towards the pressure side, where the at least one second tripping device is positioned at a distance of 1% to 3% measured along the chord from the leading edge.

7. The wind turbine according to claim 6, wherein the at least one second tripping device is positioned at a distance of 1.5% to 2.5% from the leading edge.

8. The wind turbine according to claim 5, wherein each of the at least two wind turbine blades has a longitudinal length extending from the blade root to the tip end, wherein the at least one second tripping device is offset relative to the at least one first tripping device in the longitudinal direction.

9. The wind turbine according to claim 5, wherein the at least one first tripping device or the at least one second tripping device has a height of 0.05 mm to 1 mm.

10. The wind turbine according to claim 9, wherein the at least one first tripping device or the at least one second tripping device has a height of 0.2 mm to 0.5 mm.

11. The wind turbine according to claim 5, the at least one first tripping device or the at least one second tripping device has a width of 0.5 mm to 5 mm.

12. The wind turbine according to claim 11, wherein the at least one first tripping device or the at least one second tripping device has a width of 1 mm to 3 mm.

13. The wind turbine according to claim 5, wherein one of the at least one first tripping device and the at least one second tripping device have a rectangular shape in the chord-wise direction.

14. The wind turbine according to claim 5, wherein each of the at least two wind turbine blades has a longitudinal length of 100% extending from the blade root to the tip end, wherein one of the at least one first tripping device and the at least one second tripping device is positioned at a distance of at least 33% measured along the longitudinal length from the blade root.

15. The wind turbine according to claim 14, wherein one of the at least one first tripping device and the at least one second tripping device is positioned at a distance of at least 66% from the blade root.

16. The wind turbine according to claim 1, wherein at least one vortex generator unit is arranged on the suction side of said at least one of the wind turbine blades, the at least one vortex generator unit is placed at a predetermined position relative to the leading edge.

17. A method of reducing loads in a wind turbine, comprising a wind turbine tower, a nacelle arranged on top of the wind turbine tower, a rotatable rotor with at least two wind turbine blades arranged relative to the nacelle, wherein each of the at least two wind turbine blades comprises a tip end, a blade root and an aerodynamic profile, wherein the aerodynamic profile defines a leading edge, a trailing edge, a first side surface which defines a pressure side and a second side surface which defines a suction side, wherein a chord extends from the leading edge to the trailing edge and has a chord length of 100%, wherein the method comprising the steps of: arranging at least one tripping device at a predetermined position relative to the leading edge on the pressure side of at least one of the wind turbine blades, operating said at least one of the wind turbine blades within a normal operating AoA range, passively reducing a maximum lift coefficient via said at least one tripping device when said at least one of the wind turbine blades has a positive AoA outside the normal operating AoA range, and passively increasing a minimum lift coefficient via said at least one tripping device when said at least one of the wind turbine blades has a negative AoA outside the normal operating AoA range.

18. The method according to claim 17, wherein said at least one tripping device transforms an airflow passing over said at least one tripping device from a laminar airflow into a turbulent airflow when the AoA of said at least one of the wind turbine blades is outside the normal operating AoA range in one direction.

19. The method according to claim 17, wherein said step of arranging at least one tripping device comprises one of: attaching the least one tripping device to said at least one of the wind turbine blades after manufacture of the at least one of the wind turbine blades, or providing the at least one tripping device during manufacturing of the at least one of the wind turbine blades.

20. The method according to claim 17, wherein the at least one tripping device is positioned on the at least one of the wind turbine blades using an installation tool, wherein said installation tool comprises means for receiving the at least one tripping device and means for aligning the at least one tripping device relative to at least one reference point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 shows an exemplary embodiment of a wind turbine;

[0073] FIG. 2 shows the airflow around the wind turbine blade without a stall device;

[0074] FIG. 3 shows the airflow around the wind turbine blade outfitted with a stall device;

[0075] FIG. 4 shows a first embodiment of a tripping device according to the invention;

[0076] FIG. 5 shows a second embodiment of the tripping device and a stall delaying device according to the invention;

[0077] FIG. 6 shows a third embodiment of the tripping device and the stall delaying device according to the invention;

[0078] FIG. 7a shows an embodiment of a first tripping device installed along approximately the outer 25% of a blade;

[0079] FIG. 7b shows an embodiment of a first tripping device installed along approximately the outer 60% of a blade;

[0080] FIG. 7c shows embodiments of a first and second tripping device according to the invention;

[0081] FIG. 8 shows the airflow around the wind turbine blade without the tripping device;

[0082] FIG. 9 shows the airflow around the wind turbine blade outfitted with the tripping device;

[0083] FIG. 10 shows a first graph of the lift coefficient relative to the angle-of-attack;

[0084] FIG. 11 shows a first graph of the lift coefficient relative to the drag coefficient;

[0085] FIG. 12 shows a second graph of the lift coefficient relative to the angle-of-attack;

[0086] FIG. 13 shows a second graph of the lift coefficient relative to the drag coefficient; and

[0087] FIG. 14 shows a graph of the maximum lift coefficient relative to the position of the tripping device.

DETAILED DESCRIPTION OF THE INVENTION

[0088] In the following text, the figures will be described one by one and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

REFERENCE LIST

[0089] 1. Wind turbine [0090] 2. Wind turbine tower [0091] 3. Nacelle [0092] 4. Wind turbine blades [0093] 5. Pitch mechanism [0094] 6. Tip end [0095] 7. Blade root [0096] 8. Leading edge [0097] 9. Trailing edge [0098] 10. Pressure side [0099] 11. Suction side [0100] 12. Airflow [0101] 13. Stall device [0102] 14. Tripping device, first tripping device [0103] 15. Stall delaying device [0104] 16. Second tripping device [0105] 17. Maximum lift coefficient [0106] 18. Minimum lift coefficient [0107] 19. Normal operating range [0108] 20. Position of tripping device [0109] 21. Chord

[0110] FIG. 1 shows an exemplary embodiment of a wind turbine 1 comprising a wind turbine tower 2. A nacelle 3 is arranged on top of the wind turbine tower 2 and connected to the wind turbine tower 2 via a yaw mechanism (not shown). A rotor comprising at least two wind turbine blades 4, here three blades are shown, is rotatably connected to a drive train arranged inside the nacelle 3 via a rotation shaft. The wind turbine blade 4 is rotatably connected to a hub via a pitch mechanism 5 controlled by a pitch control system.

[0111] Each wind turbine blade 4 has a tip end 6, a blade root 7 and a body having an aerodynamic profile which defines a leading edge 8 and a trailing edge 9. The side surfaces of the aerodynamic shaped body define the pressure side 10 and the suction side 11 respectively.

[0112] FIG. 2 shows the airflow around the wind turbine blade 4 with no stall devices provided on the pressure side 10. The incoming wind hits the wind turbine blade at an AoA measured relative to the chord extending from the leading edge 8 to the trailing edge 9. The passing airflow 12 develops a plurality of boundary layers over the respective pressure and suction sides 10, 11 as illustrated in FIGS. 2 and 3.

[0113] FIG. 3 shows the passing airflow 12 around the wind turbine blade 4 outfitted with a conventional stall device 13. The stall device 13 is designed to separate the passing airflow 12 along the suction side 11 as illustrated in FIG. 3 and thereby causing the wind turbine blade 4 to stall earlier compared to the wind turbine blade 4 of FIG. 2.

[0114] FIG. 4 shows a first embodiment of a tripping device 14 arranged on the pressure side 10 of the wind turbine blade 4. The tripping device 14 is positioned relative to the leading edge 8 and has a longitudinal length, a transverse width and a height extending outwards from the pressure side 10.

[0115] The tripping device 14 is preferably positioned at a distance of 0% to 1% measured along the chord 21 (indicated by the dashed line) from the leading edge 8. As illustrated, the tripping device 14 has a rectangular cross-sectional profile, however, other cross-sectional profiles may be used depending on the respective aerodynamic profile and dimensions of the wind turbine blade 4. The dimension of the tripping device 14 is designed for transforming the passing airflow 12 from a laminar condition to a turbulent condition. This, in turn, reduces the maximum lift coefficient and also increases the minimum lift coefficient of the wind turbine blade 4. The tripping device 14 has a width between 0.5 mm and 5 mm and a height between 0.05 mm to 1 mm for optimal effect on the maximum and minimum lift coefficients.

[0116] FIG. 5 shows a second embodiment wherein a stall delaying device 15 in the form of a VG-unit is arranged on the suction side 11 of the wind turbine blade 4 shown in FIG. 4. The stall delaying device 15 is designed for a different purpose, i.e., delaying stall, than the tripping device 14. Thus, the cross-sectional profile and dimensions of the stall delaying device 15 differ from those of the tripping device 14. The profile of the stall delaying device 15 causes the overall lift coefficient of the wind turbine blade 4 to increase which in turn compensates for the lift loss due to an increasing surface roughness of the wind turbine blade 4. The dimensions of the stall delaying device are known and will not be described in further details.

[0117] The positions of the tripping device 14 and the stall delaying device 15 is projected onto the chord 21 (dashed line) and measured along the chord 21 relative to the leading edge 8. As illustrated, the stall delaying device 15 is placed at a distance located closer to the trailing edge 9 compared to that of the tripping device 14.

[0118] FIG. 6 shows a third embodiment wherein a second tripping device 16 is further arranged on the pressure side 10 of the wind turbine blade shown in FIG. 5. The first tripping device 14 is positioned at a first distance from the leading edge 8 while the second tripping device 16 is positioned at a second distance from the leading edge 8. As illustrated, the second tripping device 16 is positioned between the first tripping device 14 and the trailing edge 9. The first and second distances are here measured along the chord and projected as illustrated with the dashed line normal to the chord 21.

[0119] The cross-sectional shape and dimensions of the first tripping device 14 is optimized to reduce the maximum lift coefficient. The cross-sectional shape and dimensions of the second tripping device 16 is optimized to increase the minimum lift coefficient. The first and second tripping devices 14, 16 of FIG. 6 are aligned relative to each other in the chord-wise direction.

[0120] FIG. 7a shows an embodiment of a first tripping device 14 installed along approximately the outer 25% of a blade 4 seen from the pressure side 10. In this embodiment, the stall delaying device 15 may be omitted.

[0121] FIG. 7b shows an embodiment of a first tripping device 14 installed along approximately the outer 60% of a blade 4 seen from the pressure side 10. In this embodiment, the stall delaying device 15 may be omitted.

[0122] FIG. 7c shows embodiments of a first and second tripping device according to the invention, where the second tripping device 16 is offset relative to the first tripping device 14 in a longitudinal direction towards the tip end 6. The wind turbine blade 4 has a longitudinal length extending from the blade root 7 to the tip end 6. The first tripping device 14 is placed at a first distance between approximately 25% to 65% measured along the longitudinal length from the blade root 7. The second tripping device 16 is placed at a second distance of approximately 65% to 100% measured along the longitudinal length from the blade root 7. The offset between the first and second tripping devices 14, 16 may be determined according to the aerodynamic profile and dimensions of the respective wind turbine blade 4. Here, the offset is approximately 0%.

[0123] The first and second tripping devices 14, 16 is in FIG. 7c illustrated as being offset relative to each other in the chord-wise direction. However, the second tripping device 16 may also be aligned in the chord-wise direction with the first tripping device 14 so that both tripping devices are placed at the same distance from the leading edge 8.

[0124] FIG. 8 shows the passing airflow 12 around the wind turbine blade 4 without the tripping device 14, 16. As illustrated, the incoming wind initially forms a stagnation point, S, near the leading edge 8.

[0125] The airflow 12 then passes along the pressure and suction sides 10, 11 towards the trailing edge 9. The airflow 12 on the pressure side 10 then passes a transition point, TP1, where the airflow 12 transforms from a laminar airflow, LF, to a turbulent airflow, TF. Likewise, the airflow 12 on the suction side 11 then passes a transition point, TP2, where the airflow 12 transforms from a laminar airflow, LF, to a turbulent airflow, TF.

[0126] The airflow then further passes towards the trailing edge 9 and finally separates from the respective pressure and suction sides 10, 11 at a separation point (not shown).

[0127] FIG. 9 shows the airflow 12 around the wind turbine blade 4 outfitted with the tripping device 14. As illustrated, the tripping device 14 forms a transition point, TP4, where the airflow 12 transforms from a laminar airflow, LF, to a turbulent airflow, TF. This causes an earlier transformation of the airflow 12 and thus reduces the effect of the laminar airflow compared to the wind turbine blade of FIG. 8.

[0128] FIG. 10 shows a first graph of the lift coefficient, C.sub.L, relative to the angle-of-attack, AoA. A first curve (solid line) shows the lift coefficient of the wind turbine blade 4 where no tripping device 14 is provided on the pressure side 10. A second curve (dashed line) shows the lift coefficient where a tripping device 14 is provided on the pressure side 10 at a distance of 0.25%. A third curve (dotted line) shows the lift coefficient where a tripping device 14 is provided on the pressure side 10 at a distance of 0.5%.

[0129] As illustrated by the second and third curves, the maximum lift coefficient 17 is reduced towards the minimum lift coefficient compared to that of the first curve. Likewise, the minimum lift coefficient 18 is increased towards the maximum lift coefficient compared to that of the first curve. This reduces the extreme loads occurring when the wind turbine blade 4 is pitched outside the normal pitch range.

[0130] FIG. 11 shows a first graph of the lift coefficient, C.sub.L, relative to the drag coefficient, C.sub.d. A first curve (solid line) shows the lift coefficient of the wind turbine blade 4 where no tripping device 14 is provided on the pressure side 10. A second curve (dashed line) shows the lift coefficient where a tripping device 14 is provided on the pressure side 10 at a distance of 0.25%. A third curve (dotted line) shows the lift coefficient where a tripping device 14 is provided on the pressure side 10 at a distance of 0.5%.

[0131] As illustrated by the second and third curves, the tripping device 14 does not adversely affect the lift coefficient in the normal operating range 19. The tripping device 14 reduces the range between the maximum lift coefficient 17 and the minimum lift coefficient 18. This also reduces the fatigue loads occurring when the wind turbine blade 4 is pitched within the normal pitch range.

[0132] FIG. 12 shows a second graph of the lift coefficient, C.sub.L, relative to the angle-of-attack, AoA. This graph differs from the first graph of FIG. 10 by both a stall delaying device 15 and a tripping device being provided on the wind turbine blade 4.

[0133] As illustrated by the second and third curves (dashed and dotted lines), the maximum lift coefficient 17 is increased compared to that of the first curve of FIG. 10. Likewise, the AoA corresponding to the maximum lift coefficient 17 is increased compared to that of the first curve of FIG. 10.

[0134] FIG. 13 shows a second graph of the lift coefficient, C.sub.L, relative to the drag coefficient, C.sub.d. This graph differs from the first graph of FIG. 11 by both a stall delaying device 15 and a tripping device being provided on the wind turbine blade 4.

[0135] As illustrated by the second curve (dashed line), the lift coefficient is increased compared to the third curve of FIG. 11.

[0136] FIG. 14 shows a graph of the maximum lift coefficient 17, C.sub.L-max, relative to the position 20, x/c, of the tripping device 14. The position 20 is defined as the distance from the leading edge 8 along the chord measured in percentage of the total normalised chord length of the wind turbine blade 4.

[0137] As illustrated, the optimal effect of the tripping device 14 is obtained if the tripping device 14 is positioned at a distance between 0% and 1%, preferably between 0.2% and 0.6%. If the tripping device 4 is positioned at a distance greater than 1%, the tripping device has substantially no effect on the maximum lift coefficient 17.