How to lift wind turbine blades

Abstract

A method for lifting a wind turbine blade 20, the method comprising the steps of: providing a wind turbine blade; providing a blade yoke and connecting the blade yoke 22 to the blade; providing an elongated element connected to the blade adjacent to a negative pressure surface or a pressure surface, wherein the elongated element is positioned along at least 50% of the outer third of the blade, positioned along the longitudinal axis of the blade, and positioned such that the elongated element reduces the coefficient of the lift force CL of the blade by more than 20%; and lifting the blade via the blade yoke. Thus, a simple method for mitigating the lift force of the blade during the lifting operation can be provided, which increases the safety of the procedure and allows the use of a smaller lifting yoke in comparable winds or the same lifting yoke in stronger winds.

Description

Technical Field

[0001] The current invention relates to a method for lifting a wind turbine blade.

Background Art

[0002] When constructing a wind turbine, typically the wind turbine tower is first constructed, and then the nacelle is placed on top of the tower. Next, the rotor hub is mounted on the drive shaft of the turbine, and then the wind turbine blades are individually attached to the hub. During the step of attaching the blade to the hub, the blade needs to be lifted from the ground by a crane. During the lifting operation, a tag line system is often used to hold the blade in a specific position. However, wind affects the position and movement of the blade. As the wind speed increases, the load on the blade increases, and at a certain wind speed, it becomes difficult to safely maintain the blade in a stable position.

[0003] In addition, the wind acting on the blade may result in undesirable movement of the blade. In certain cases, due to the wind, the tip of the blade may be lifted or pushed down. The movement depends on the wind direction and the orientation of the blade. Since the blade is typically suspended from the crane lifting wire in a horizontal position, when the wind force is removed, the blade tips will each descend or rise again to restore the stable horizontal position of the blade. However, this causes a pendulum motion that is difficult to stop. This pendulum motion is very undesirable because it is dangerous for the operator, the crane, and the blades and other components of the wind turbine.

[0004] Furthermore, once the blade is lifted to the rotor hub, it needs to be attached to the rotor hub via a series of bolts. During the bolting process, the blade must be kept very still and in a fixed position. In this case as well, if wind load is applied to the blade, movement will occur, and therefore the blade needs to be held in place via a tag line or other form of position control system. In this case as well, if the wind speed exceeds a certain level, the work needs to be interrupted because an excessively large force will be required to hold the blade in place.

[0005] The expected maximum wind load on the blade is also used to calculate the size and strength of the blade yoke required to suspend the blade. Note that the blade is held in place in the blade yoke via friction pads that press against the blade surface. To firmly hold the blade, the frictional force must be greater than the expected maximum force attempting to move the blade in the blade yoke. The frictional force is increased by increasing the working load (i.e., gripping force) of the friction pads against the blade surface. However, there is an upper limit to the gripping force, as a gripping force exceeding a certain amount may damage the blade and / or blade yoke. Therefore, the limit of the acceptable gripping force establishes the limit of the maximum permissible wind speed, and / or the maximum expected wind speed determines the required gripping force and / or design and strength of the blade yoke. If stronger winds are expected, a larger and stronger blade yoke is required. Procedures for sizing the appropriate blade yoke are known in the art and will not be described in detail here.

[0006] It should be noted that, for the sake of good order, there are proposals in the art that suggest mitigating blade vibrations caused by vortex detachment by placing diagonal elements on the blade while it is being mounted on a wind turbine. See Chinese Patent Application Publication No. 113685311 and Chinese Patent Application Publication No. 114687960 for this. At first glance, these solutions may seem similar to the present invention, but they are only relevant in hindsight. The solutions proposed in these prior art are not very suitable in the real world and have not been practically implemented. The vortex detachment effect caused by wind loads acts only on bluff bodies such as wind turbine towers. However, blades with their aerodynamic shape do not experience much vortex detachment-induced vibration due to wind acting along the chord direction of the blade (as in the case of lifting operations). Blades do experience vortex detachment-induced vibrations, in some cases, due to wind loads acting perpendicular to the chord of the blade. However, this is not very relevant during lifting operations, as wind is typically horizontal and blades are typically lifted so that their chords are positioned horizontally. Therefore, vortex-dissociation vibrations in the blades are essentially nonexistent during lifting operations. Even when mounted on a hub, vortex-induced blade vibrations are not very common, as the blades can have their pitch adjusted and the hub is rotated to position the blades in a position where they receive low vortex dissociation. Therefore, the solutions proposed in the art are not practically applicable and are not implemented in practice. The solutions proposed in the prior art, while not practically applicable, appear to be simply adaptations of methods used to reduce turbine tower vibrations to blades.

[0007] Furthermore, it should be noted that the vortex-disengagement prevention solution proposed in the cited patent application proposes a structure similar to those used in wind turbine towers. These structures are large elements that increase the drag on the blades while reducing the possibility of vortex-disengagement vibrations. This increases the torque on the blades around the lifting wire during lifting operations. Therefore, while the vortex-disengagement effect is almost negligible during blade lifting, the drag of the cited solution is increased, which is undesirable. Consequently, there is no incentive for a person skilled in the art to use the cited prior art solution in actual lifting operations. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Chinese Patent Application Publication No. 113685311 [Patent Document 2] Chinese Patent Application Publication No. 114687960 [Overview of the project] [Means for solving the problem]

[0009] A first aspect of the present invention provides a method for lifting wind turbine blades in which the position of the blades is more stable during the lifting operation than in the prior art.

[0010] A second aspect of the present invention is to provide a method for lifting wind turbine blades in which the effect of wind on the blades during the lifting operation is reduced.

[0011] A third aspect of the present invention provides a method for lifting wind turbine blades, which allows for the use of specific blade and blade yoke combinations at wind speeds higher than those of prior art methods.

[0012] These embodiments are provided at least in part by the method described in claim 1. In this way, a simple and effective method for mitigating the lift force on the blade is provided. This makes it possible to use the blade yoke at higher maximum wind speeds, to reduce the size of the blade yoke for a given maximum wind speed, and / or to reduce the gripping force on the blade for a given maximum wind speed.

[0013] It should be noted that the order of the steps in the claims of this method should not be limited to the specific order presented in the claims, and that the steps should be allowed to be performed in any logical order. For example, in claim 1 of this method, the step of providing and attaching the blade yoke to the blade is given before the step of providing the elongated member to be connected to the blade. However, the scope of protection should also include the method by which the elongated member is attached to the blade before the blade yoke is attached to the blade.

[0014] It should also be noted that the term "outer" refers to the distance from the base of the blade. For example, the outer third of the blade should be understood as the tip of the blade, extending from the tip to a point one-third of the blade's length away from the base.

[0015] In some embodiments, the elongated element has a height of more than 0.1%, more than 0.2%, or more than 0.3% of the local chord of the blade. In some embodiments, the elongated element has a height of less than 10%, less than 7%, or less than 5% of the local chord of the blade.

[0016] In some embodiments, the elongated elements are positioned along 50% of the outer half of the blade. In some embodiments, the elongated elements are positioned along 75% of the outer half of the blade.

[0017] In some embodiments, the dimensions of the slender elements parallel to the chord of the blade are less than 50%, 40%, or 30% of the local chord length. When comparing the slender elements to the chord, it should be noted that the comparison should be between the dimensions of the slender elements and the chord at the same radial point along the blade. In other words, the dimensions of the slender elements parallel to the chord of the blade at a distance of 50% of the blade length from the base of the blade should be compared to the chord length at a distance of 50% of the blade length from the base of the blade.

[0018] In some embodiments, the elongated elements reduce the lift coefficient by more than 30%, more than 40%, or more than 50%. In some embodiments, the elongated elements increase the blade's drag coefficient by less than 50%, less than 40%, less than 30%, or less than 20%.

[0019] In some embodiments, the elongated elements are positioned such that the distance parallel to the local chord between the centerline of the elongated element and the leading edge of the blade is less than 50%, less than 40%, or less than 30% of the local chord length of the blade.

[0020] In some embodiments, the slender elements are attached to the suction surface or pressure surface of the blade. In some embodiments, the slender elements are attached to the blade by adhesive. In some embodiments, the slender elements are attached to the blade via individual brackets that are attached to the blade and spaced apart from each other along the length of the slender elements. In some embodiments, the slender elements are not attached directly to the suction surface or pressure surface of the wind turbine blade, but are connected to the wind turbine blade only via attachments to the blade yoke and mounting members attached to the wind turbine blade.

[0021] In some embodiments, the method further includes calculating a maximum estimated lift generated by a blade having an elongate member coupled to the blade due to a maximum predicted wind speed, and sizing a blade yoke according to the maximum estimated lift generated by the blade having an elongate member coupled to the blade.

[0022] In some embodiments, the method further includes attaching one end of an elongate element to a blade yoke, providing an attachment member, attaching the attachment member to the blade at a location near the tip of the blade, and attaching the other end of the elongate element to the attachment member.

[0023] In some embodiments, the elongate element is arranged such that a local distance perpendicular to a local chord between an edge of the elongate element facing away from a surface of the blade closest to the elongate element and the surface is less than 10%, less than 7.5%, or less than 5% of the local chord length.

[0024] In some embodiments, the attachment member is located at the outer one-fifth, outer one-sixth, or outer one-seventh of the blade.

[0025] In some embodiments, the step of providing an attachment member and the step of attaching the attachment member to the blade include providing a blade tip clamp, and the step of attaching the attachment member to the blade at a location near the tip of the blade includes attaching a blade tip yoke to the blade near the tip of the blade.

[0026] In some embodiments, a. the step of providing an attachment member includes providing a blade tip clamp, b. the step of attaching the other end of the elongate member to the attachment member includes attaching the other end of the elongate member to the blade tip clamp, c. the method i. Rotating the rotor hub until the blade to which the blade tip gripping portion is attached is oriented so that it extends downward, ii. A step of lowering the blade tip gripping portion along the blade from the blade yoke via an elongated member, iii. The step of controlling the position of the blade tip gripping portion relative to the blade via a tag line attached to the blade tip gripping portion, d. The step of attaching the mounting member to the blade at a point near the tip of the blade includes attaching the blade tip yoke to the blade at a point near the tip of the blade.

[0027] In some embodiments, the step of providing a mounting member includes providing a blade tip gripping portion having one or more controllable lift generating devices, a. The step of attaching the other end of the elongated member to the mounting member includes attaching the other end of the elongated member to the blade tip gripping portion, b. The method further includes the step of using one or more controllable lift generating devices to launch the blade tip gripping portion to a blade position located away from the blade yoke, c. The step of attaching the mounting member to the blade at a point near the tip of the blade includes attaching the blade tip yoke to the blade at a point near the tip of the blade.

[0028] It should be noted that the phrase “one or more controllable lift-generating devices” should be understood as one or more devices capable of controllingly providing lift such that the blade tip gripping section can fly and lift its own weight under control. One example of “one or more controllable lift-generating devices” is a configuration of four pitch-controllable propellers arranged in a square shape, as is well known from the drone technology field. In some embodiments, the blade tip gripping section can also be considered to be coupled to a drone.

[0029] This specification also relates to the use of elongated members connected to wind turbine blades and positioned along the longitudinal axis of the wind turbine blades to reduce the maximum lift force generated by the wind when lifting the wind turbine blades. In this way, the required blade yoke strength and / or size can be reduced compared to lifting the same blade without elongated members in a particular expected wind range. Alternatively, the maximum allowable wind force for the blade, blade yoke, and elongated member combination is increased compared to the same blade and blade yoke combination without elongated members. Naturally, both options may be combined to achieve both a reduction in the required blade yoke size and an increase in the allowable wind speed.

[0030] The elongated member in the use claim may be further characterized according to any feature or combination of features described herein with respect to the elongated member.

[0031] This specification also relates to devices and / or systems for reducing motion and / or forces generated by wind during the lifting of the blades, and / or for reducing the effects of wind on the blades during the lifting of the blades. Specifically, this specification relates to wind turbine blades equipped with such devices or systems.

[0032] In some embodiments, a wind turbine blade is provided having a longitudinal axis, a negative pressure surface, and a pressure surface, the wind turbine blade further comprising an elongated element, the elongated element being connected to the blade and positioned adjacent to the negative pressure surface or pressure surface of the blade, positioned along at least 50% of the outer third of the blade, extending along the longitudinal axis of the blade, and positioned to reduce the lift coefficient of the blade by more than 20%, more than 30%, more than 40%, or more than 50%.

[0033] It should be noted that the phrase "extending along at least 50% of the outer third of the blade" suggests that the elongated elements do not necessarily have to be continuous and may be arranged in multiple independent segments. In some embodiments, the elongated elements extend along more than 75% of the outer third of the blade. In some embodiments, the elongated elements extend along more than 50% of the outer half of the blade.

[0034] In some embodiments, the elongated element has a height of more than 0.1%, more than 0.2%, or more than 0.3% of the local chord length of the blade. In some embodiments, the elongated element has a height of less than 10%, less than 7.5%, or less than 5% of the local chord length of the blade.

[0035] In some embodiments, the elongated elements are positioned along at least 50% of the outer half of the blade. In some embodiments, the elongated elements are positioned along at least 75% of the outer half of the blade. In some embodiments, the dimension of the blade parallel to the chord is less than 50%, less than 40%, less than 30%, or less than 20% of the local chord length.

[0036] In some embodiments, the slender elements are arranged such that the distance between the local center of the slender element and the leading edge of the blade is less than 50%, less than 40%, or less than 30% of the local chord length of the blade.

[0037] In some embodiments, the elongated elements are attached to the pressure or negative pressure surface of the blade by adhesive. In some embodiments, the elongated elements are not attached to the pressure or negative pressure surface of the blade by adhesive.

[0038] In some embodiments, a wind turbine blade lifting system is provided which includes a wind turbine blade as described above, the system further comprising a blade yoke attached to the blade near the center of gravity of the blade, and a blade tip gripping portion attached to the blade near the tip of the blade, wherein an elongated element is positioned between the blade yoke and the blade tip gripping portion.

[0039] This specification also discloses a second independent invention which may form the basis for a divisional application. The second independent invention relates to attaching a blade tip gripper to a wind turbine blade. In the figures described in more detail below, the second invention is used to attach an elongated element to the blade to act as a lift-reducing element. However, the method described herein may also be used in other applications where the primary objective is not to obtain a lift-reducing effect but simply to attach a blade tip gripper to the blade. The second invention is described in more detail below with reference to Examples 1 to 3.

[0040] Example 1 A method for attaching a blade tip gripping portion to a wind turbine blade, wherein the method is a) Rotating the rotor hub until the blade to which the blade tip gripping portion is attached is oriented to extend downward, b) A step of lowering the blade tip gripping portion along the blade via an elongated element connected to the blade tip gripping portion, c) A method comprising the step of attaching a blade tip yoke to a blade.

[0041] Example 2 The method according to Example 1, wherein the method further includes the step of attaching the blade yoke to the blade, and the step of lowering the blade tip gripping portion along the blade includes lowering the blade tip gripping portion from the blade yoke.

[0042] Example 3 The method according to Example 1 or Example 2, further comprising the step of controlling the position of the blade tip gripping portion relative to the blade via a tag line.

[0043] This specification also discloses a third independent invention which may form the basis for a divisional application. In many cases, it is desirable to attach a tag line or other attachment to the blade tip via a blade tip gripper. Blade tip grippers are known in the art and are typically attached while the blade is on the ground. If the blade is already mounted on a wind turbine, a crane is required to lift the blade tip gripper to the blade, where it is manually attached to the blade tip. This is a complex operation. Furthermore, positioning a crane tall enough to attach a prior art blade tip gripper to a blade mounted on a wind turbine is costly. Similarly, removing a prior art blade tip gripper after the blade has been installed on the turbine is complex and time-consuming.

[0044] Therefore, the first aspect of the third invention is to provide a blade tip gripping portion that is easier to attach to blades already installed on a wind turbine.

[0045] A second aspect of the third invention is to provide a blade tip gripping portion that is easier to remove from the blade while the blade is installed in a wind turbine.

[0046] These embodiments are provided in accordance with the third invention by a blade tip gripping unit as described below by the following examples 10 to 13 of the third invention.

[0047] Example 10 A blade tip gripping portion arranged to be attached to a wind turbine blade, wherein the blade tip gripping portion comprises a gripping mechanism suitable for attaching the blade tip gripping portion to the blade near the tip of the blade, the gripping mechanism having a first configuration in which the gripping mechanism is spread and not attached to the blade when the blade tip gripping portion is positioned on the blade, and a second configuration in which the gripping mechanism is retracted and attached to the blade when the blade tip gripping portion is positioned on the blade, the blade tip gripping portion further comprises at least one controllable lift generating device suitable for lifting the blade tip gripping portion from the ground to the blade under controlled conditions.

[0048] Example 11 The blade tip gripping portion according to Example 10, further comprising mounting elements for attaching one or more tag lines and / or one or more other accessories to the blade tip gripping portion.

[0049] Example 12 A method for attaching a blade tip gripping portion to a wind turbine blade, wherein the method is a) Providing a blade tip gripping section having at least one controllable lift generating device, b) A step of using at least one controllable lift generating device to propel the blade tip gripping portion to a position close to the tip of the wind turbine blade, c) A method comprising the step of attaching a blade tip gripping portion to a blade.

[0050] Example 13 The above method, a. Steps to attach the blade yoke to the blade, b. The method according to Example 12, further comprising the steps of attaching a first end of an elongated element to the blade yoke and attaching a second end of an elongated element to the blade tip grip before the step of launching the blade tip grip to a position close to the tip of the wind turbine blade.

[0051] The terms “comprises,” “comprising,” and “composed of,” as used herein, are employed to indicate the presence of a described feature, integer, step, or component, but it should be emphasized that they do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0052] The present invention will be described in more detail below with reference to the embodiments shown in the enclosed figures. It should be emphasized that the embodiments shown are for illustrative purposes only and should not be used to limit the scope of this disclosure. [Brief explanation of the drawing]

[0053] [Figure 1] This is a schematic cross-sectional view seen through a wind turbine blade having a lift-relieving elongated element according to the present invention attached to the blade. [Figure 2] This is a detailed cross-sectional view of the region defined by the circle labeled II in Figure 1. [Figure 3] This is a schematic cross-sectional view seen through a wind turbine blade having a second embodiment of the lift-relieving elongated element according to the present invention attached to the blade. [Figure 4] This figure shows the results of a computational fluid dynamics (CFD) analysis of a typical wind turbine blade airfoil. [Figure 5] This figure shows the results of a CFD analysis of a wind turbine blade, Figure 4, which has a lift-relieving elongated element, as shown in Figure 1, attached to the negative pressure surface of the blade near the leading edge. [Figure 6] This figure shows the results of a CFD analysis of a wind turbine blade, as shown in Figure 4, which has a lift-relieving elongated element, as shown in Figure 3, positioned on the negative pressure surface of the blade near the leading edge. [Figure 7] This is a schematic top view of a wind turbine blade suspended by a blade yoke, illustrating an alternative embodiment of the elongated lift-relieving element according to the present invention. [Figure 8] This is a schematic front view of a wind turbine blade suspended by a blade yoke, illustrating an alternative embodiment of the elongated lift-relieving element according to the present invention. [Figure 9] This figure schematically illustrates one embodiment of a method for attaching elongated lift-relieving elements to wind turbine blades, showing two different stages of the method. [Figure 10] This figure schematically illustrates one embodiment of a method for attaching elongated lift-relieving elements to wind turbine blades, showing two different stages of the method. [Figure 11] This figure schematically illustrates another embodiment of a method for attaching a lift-relieving elongated element to a wind turbine blade, showing two different stages of the method, and also illustrates a second invention which provides a method for attaching a blade tip gripping portion to the blade. [Figure 12] This figure schematically illustrates another embodiment of a method for attaching a lift-relieving elongated element to a wind turbine blade, showing two different stages of the method, and also illustrates a second invention which provides a method for attaching a blade tip gripping portion to the blade. [Figure 13] This figure schematically illustrates another embodiment of a method for attaching elongated lift-relieving elements to wind turbine blades, at one stage of the method. [Figure 14] This is a schematic side view of a first embodiment of a blade tip gripping portion attached to the blade together with a lift-reducing elongated element to provide blade lift reduction. [Figure 15] This is a schematic side view of an example of a blade tip gripping part according to the third invention, which is attached to the blade. [Modes for carrying out the invention]

[0054] Figures 1 and 2 schematically show cross-sections of a wind turbine blade 1 and an elongated lift-relieving element 2 according to the present invention. In this embodiment, the elongated lift-relieving element is an elongated element having a cross-section with a base 4 positioned to be attached to the negative pressure surface 6 of the wind turbine blade by adhesive 8, and an upwardly projecting projection 10. In this embodiment, the upwardly projecting projection is semicircular in shape. The elongated element 2 is mounted along the length of the blade. In this embodiment, the element extends from a position close to the base of the blade to a position close to the tip of the blade. It can also be said that the elongated element is positioned from a position 10% of the length to a position 90% of the length. However, in other embodiments, the elongated lift-relieving member is mounted in varying amounts along the blade, typically along at least the outer half of the blade. Note that instead of having one long elongated element, it is conceivable that multiple shorter elongated elements be positioned along the blade, with each of the shorter elongated elements spaced apart from one another. However, several shorter, elongated elements may still be considered elongated members that extend along the blade but do not cover the entire length of the blade.

[0055] In this embodiment, the elongated elements are attached to the blades while they are still on the ground, before the blades are lifted. If the blades are already attached to the wind turbine rotor hub, the elongated elements may be attached by a worker descending along the blades. Other options are also possible.

[0056] The adhesive is of a type that provides a firm engagement between the blade and the base of the elongated element, but also allows the elongated element to be pulled away from the blade without damaging the blade itself during removal. Those skilled in the art of adhesives may be able to suggest suitable adhesives. It should be noted that the load on the elongated element is not significant, and therefore the adhesive does not need to be particularly strong.

[0057] Figure 3 shows an alternative embodiment in which a round elongated element 12 is positioned adjacent to the blade instead of an elongated element attached to the blade with adhesive. This round elongated element may be attached to the blade via point attachments offset from each other along the longitudinal axis of the blade, for example, via point adhesive applied between the blade and the elongated element. In another embodiment, the elongated element may be attached to the blade via adhesive applied along the entire length of the round elongated element. In yet another embodiment, the round elongated element may be attached to the blade via brackets that are individually attached to the blade and spaced apart along the length of the blade. In yet another embodiment, the round elongated element may be attached to the blade at only two points: a first point closer to the base of the blade and a second point closer to the tip of the blade. To ensure that the elongated element is positioned closer to the blade surface, the actual locations of the attachment points may be determined according to the curvature of the blade.

[0058] While the examples above were shown in semicircular and full-circular forms, numerous other possible shapes are also available. In one embodiment, the elongated element has an inverted T-shaped cross-section. In this case, the base of the T may be positioned adjacent to the blade surface. In one embodiment, the two T-shaped flanges may be attached to the blade surface by tape attached to the two T-shaped flanges.

[0059] Figure 4 shows some results from a computational fluid dynamics (CFD) analysis of a blade with no "slender elements" attached. As can be seen from the figure, the flow across the negative pressure surface of the blade is smooth and adheres to the negative pressure surface of the blade. In this way, the blade generates lift as desired for a typical blade. However, it will be understood that this lift is undesirable because, while lifting the blade itself and while mounting the blade, it results in unwanted blade motion, and / or pendulum motion, and / or extra force.

[0060] Figure 5 shows the results of a CFD analysis of the same blade shown in Figure 4, but with an elongated element attached near the leading edge of the blade, as shown in Figures 1 and 2. As can be seen, the flow across the negative pressure surface is extremely turbulent here and no longer adheres to the negative pressure surface of the blade. In this way, the lift generated by the blade and the resulting blade motion are significantly reduced. In an actual CFD analysis using a cross-section of a real blade with a chord length of 1 m and an angle of attack of 10°, the reference lift coefficient was approximately 1.59, while in the case of an elongated element with a semicircular cross-section of radius 10 mm, the lift coefficient was approximately 0.75. This represents a lift reduction of approximately 53%. Here, the blade can be lifted in stronger winds than before the elongated element was installed, using the same blade yoke, or a smaller blade yoke can be used in winds of the same magnitude.

[0061] Figure 6 again shows the results of the CFD analysis of the same blade as in Figures 4 and 5, in this case with the elongated element from Figure 3 attached to the blade. In this case as well, as with the analysis results shown in Figure 5, the flow still becomes turbulent across the negative pressure surface and moves away from it. In this case as well, the lift is reduced, and the blade can be lifted in stronger winds. In an actual CFD analysis using the cross section of a real blade with a chord line of 1 m and an angle of attack of 10°, the reference lift coefficient was approximately 1.59, while in the case with the elongated element having a full-circle cross section with a radius of 5 mm, the lift coefficient was approximately 1.01. This represents a lift reduction of approximately 37%. In this case as well, with such an elongated member attached to the blade, the blade can be lifted in stronger winds than before the elongated element was installed, or using a smaller lifting yoke.

[0062] Figures 7 and 8 show one method for connecting elongated elements to a blade to provide the lift-reducing effect described above when it is difficult to attach the elongated elements with adhesive. This corresponds to a situation such as that shown in Figure 3. In this case, the blade 20 is lifted by a crane (not shown) via a blade yoke 22. A blade tip gripper 24 is attached near the tip of the blade, and a rope 26 is positioned between the blade yoke and the blade tip gripper. This type of configuration may be connected to the blade while the blade is on the ground, or while the blade is attached to the rotor hub. Several different examples of how to attach the elongated elements to the blade via the blade yoke and blade tip gripper are described below.

[0063] One method for attaching an elongated element, as shown in Figures 7 and 8, to a blade is described with reference to Figures 9 and 10. In this case, the blade yoke 30 is attached to the blade 32, and the blade tip grip 34 is supported by the blade yoke. The blade tip grip is provided with a drive mechanism 36 having a wheel 38 supported on the blade itself. When the blade yoke is attached to the blade, the drive mechanism of the blade tip grip is also attached to the blade at a point close to the blade yoke. The drive mechanism then "drives" the blade tip grip outward along the blade, pulling the rope 40. When the blade tip grip is near the tip of the blade, the blade tip grip engages more firmly with the blade, and the rope is taut. In this way, an elongated element that has a lift-reducing effect on the blade is provided. When the lifting operation is complete, the blade tip grip can be "driven" back along the blade until it reaches the blade yoke.

[0064] In one embodiment (not shown), a pressure-applying mechanism is provided in a blade tip gripping section similar to those schematically illustrated in Figures 9 and 10, which can apply pressure to an elongated element, such as a rope, as the blade tip gripping section is driven outward along the blade. In this way, the blade tip gripping section can press the rope against the blade, and an adhesive applied to the "rope" can engage the rope with the blade surface. In such an embodiment, instead of a blade tip gripping section that engages with the blade tip itself, a pressure-applying robot may be provided that drives along the blade so as it drives along the blade, it presses the elongated element against the blade surface, thereby attaching the elongated element to the blade surface.

[0065] It should be noted that a blade tip gripper having a drive mechanism that allows the blade tip gripper to be displaceably connected to the blade so that the blade tip gripper can move along the blade from a position closer to the base of the blade to a position closer to the tip of the blade can form the basis for a separate divisional application.

[0066] Similarly, a basis for a separate divisional application can be provided for a pressure-applying robot configured to drive along the blade from the base to the tip of the blade while pressing an elongated element against the blade surface. In one embodiment of such a pressure-applying robot, a method may be provided in which a rotor hub is rotated to place the blade in a horizontal position, and then the blade is rotated so that the chord of the blade is essentially horizontal. The pressure-applying robot may then be driven along the surface of the blade while pressing an elongated member against the blade surface. In one embodiment, for a blade having a highly curved surface, the method may include the step of actively rotating the blade around its longitudinal axis while the robot is driving along the blade, so as to ensure that the robot can be essentially horizontal at any time during the drive. In this way, the robot does not come off the blade.

[0067] Figures 11 and 12 provide an alternative method for attaching a rope 50 to a blade 52 for the purpose of reducing blade lift. In this case, the blade is positioned vertically, and the blade tip grip 54 is suspended from the blade yoke 56 via the rope 50. A tag line 58 connected to the blade tip grip extends to the ground and to a worker, and / or an automatic winch connected to the tag line controls the position of the blade tip grip relative to the blade. When the blade tip grip is in the desired position, the gripping mechanism on the blade is engaged, and the blade tip grip engages with the blade. The rope 50 between the blade yoke and the blade tip grip is then stretched taut to provide the lift reduction effect described above.

[0068] Figure 13 shows another embodiment of a configuration for attaching the rope 60 to the blade 62 to provide the blade lift reduction effect described above. In this embodiment, a blade yoke 64 is attached to the blade oriented in a downward position, and a weighted belt 66 is suspended from the blade yoke via the rope 60. The weighted belt is arranged to wrap around the blade. When the rope is stretched to the desired amount, the weighted belt is tightened by a belt tightening mechanism 68 to secure the belt to the blade at a designated position. When the belt is tightened, the rope is held in place on the blade.

[0069] Figure 14 shows one embodiment of a blade tip gripper 70 that can be used to "launch" a rope 72 from a blade yoke (not shown, but similar to the configuration in Figure 8) to the tip of a blade 74. In this embodiment, the blade tip gripper comprises a gripping mechanism 76 suitable for firmly gripping the blade. The blade tip gripper also comprises four controllable lift generating devices 78, such as four independently controllable variable-pitch propellers known in the field of drones. The blade tip gripper 70 in this embodiment may be positioned on the blade yoke, and the rope may be attached to the blade tip gripper and blade yoke via a winch mechanism. When the blade yoke is in place, the blade tip gripper can be launched outward to the tip of the blade and can pull the rope as it moves outward. When the blade tip gripper is in the correct position, the blade tip gripper can grip the blade and the rope is taut. The rope then settles into place to provide the blade lift-reducing effect as described above.

[0070] It should be noted that the blade tip gripping portion 70 in Figure 14 may be used in other applications where something is attached to the tip of the blade. For example, one or more tag lines are one example. Thus, this blade tip gripping portion 70 may be the subject of a divisional application and is described above as an independent “third” invention as previously described in this application.

[0071] An additional example of a blade tip gripper 80 having a controllable lift generating device 82 and a gripping mechanism 84 is shown in Figure 15. In this example, the blade tip gripper is attached to a blade 86, and two tag lines 88 are attached to the blade tip gripper. In this case, the blade tip gripper may be located on the ground. The operator connects the ends of the two tag lines to the blade tip gripper. The blade tip gripper is then launched onto the blade and attached to it, where the tag lines are firmly connected to the blade. If it is desired to remove the tag lines from the blade, the gripping mechanism of the blade tip gripper is disengaged from the blade, and the blade tip gripper is launched back to the ground.

[0072] It should be noted that all embodiments shown in the figures, with the exception of the one shown in Figure 15, result in lift reduction. However, embodiments shown in Figures 9 to 14 also illustrate several different methods of attaching the tip grip to the blade tip. These methods are novel and are currently claimed in conjunction with an elongated member that provides a blade lift reduction effect. However, these methods may also form the basis for one or more divisional applications covering methods of attaching the blade tip grip to the blade. In these situations, the solution does not necessarily provide a blade lift reduction effect and is instead used to attach the tip grip to the blade.

[0073] It should be noted that the figures and the above description illustrate illustrative embodiments in a simple and schematic manner. Many specific mechanical details are omitted because those skilled in the art should be familiar with them, and such details would only unnecessarily complicate this specification. For example, specific materials used and specific manufacturing procedures are not described in detail because those skilled in the art are expected to be able to find suitable materials and processes for implementing the methods and devices according to the present invention.

Claims

1. In a method for lifting wind turbine blades, the method is a. The step of providing wind turbine blades, b. Providing a blade yoke and connecting the blade yoke to the wind turbine blade, c. Providing an elongated element connected to the wind turbine blade adjacent to a negative pressure surface or pressure surface, wherein the elongated element is i. Displaced along at least 50% of the outer one-third of the wind turbine blade, ii. Arranged along the longitudinal axis of the wind turbine blade, iii. The slender element is arranged such that it reduces the lift coefficient of the wind turbine blade by more than 20%, d. A method comprising the step of lifting the wind turbine blade via the blade yoke.

2. The method described above is a. A step of calculating the maximum estimated lift force generated by the wind turbine blade, which has an elongated member connected to the wind turbine blade, due to the maximum predicted wind speed, b. The method according to claim 1, comprising the step of determining the size of the blade yoke in accordance with the maximum estimated lift generated by the wind turbine blade having the elongated member connected to the wind turbine blade.

3. The method according to claim 1 or 2, further comprising the steps of: attaching one end of the elongated element to the blade yoke; providing a mounting member; attaching the mounting member to the wind turbine blade at a point near the tip of the wind turbine blade; and attaching the other end of the elongated element to the mounting member.

4. a. The step of providing the mounting member includes providing the blade tip gripping portion, b. The step of attaching the other end of the elongated member to the mounting member includes attaching the other end of the elongated member to the blade tip gripping portion, c. The above method, i. A step of rotating the rotor hub until the wind turbine blade to which the blade tip gripping portion is attached is oriented to extend downward, ii. A step of lowering the blade tip gripping portion along the wind turbine blade from the blade yoke via the elongated member, iii. The step of controlling the position of the blade tip gripping portion relative to the blade via a tag line attached to the blade tip gripping portion, d. The method according to claim 3, characterized in that the step of attaching the mounting member to the wind turbine blade at a point near the tip of the wind turbine blade includes attaching the blade tip yoke to the wind turbine blade at a point near the tip of the wind turbine blade.

5. a. The step of providing the mounting member includes providing a blade tip gripping portion having one or more controllable lift generating devices, b. The step of attaching the other end of the elongated member to the mounting member includes attaching the other end of the elongated member to the blade tip gripping portion, c. The method further includes the step of using one or more controllable lift generating devices to launch the blade tip gripping portion to the position of the wind turbine blade, which is located away from the blade yoke, d. The method according to claim 3, characterized in that the step of attaching the mounting member to the wind turbine blade at a point near the tip of the wind turbine blade includes attaching the blade tip yoke to the wind turbine blade at a point near the tip of the wind turbine blade.

6. The use of an elongated member connected to the wind turbine blade and positioned along the longitudinal axis of the wind turbine blade, for reducing the maximum lift force generated by the wind when the wind turbine blade is being lifted.

7. The use of the elongated member according to claim 6, characterized in that the elongated member is connected to the wind turbine blade via a blade yoke attached to the wind turbine blade and a blade tip gripping portion attached to the wind turbine blade near the tip of the wind turbine blade.

8. In a wind turbine blade having a longitudinal axis, a negative pressure surface, and a pressure surface, the wind turbine blade further comprises an elongated element, and the elongated element is a. Connected to the wind turbine blade and positioned adjacent to the negative pressure surface or the pressure surface of the wind turbine blade, b. Displaced along at least 50% of the outer one-third of the wind turbine blade, c. Extending along the longitudinal axis of the wind turbine blade, d. A wind turbine blade characterized by being arranged to reduce the lift coefficient of the wind turbine blade by more than 20%.

9. The wind turbine blade according to claim 8, characterized in that the elongated element is arranged such that the distance between the local center of the elongated element and the leading edge of the wind turbine blade is less than 50% of the local chord length of the wind turbine blade.

10. The wind turbine blade according to claim 8 or 9, characterized in that the elongated element is attached to the pressure surface or the negative pressure surface of the wind turbine blade by adhesive.

11. The wind turbine blade according to claim 8 or 9, characterized in that the elongated element is not attached to the negative pressure surface of the wind turbine blade with an adhesive.

12. A wind turbine blade lifting system comprising a wind turbine blade according to any one of claims 8 to 11, wherein the system further comprises a blade yoke attached to the wind turbine blade near the center of gravity of the wind turbine blade, and a blade tip gripping portion attached to the wind turbine blade near the tip of the wind turbine blade, and the elongated element is disposed between the blade yoke and the blade tip gripping portion.

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