Blade tip

Abstract

A blade tip adapted to be in spanwise alignment with a main blade is disclosed The blade tip comprises a lower bladelet element, an upper bladelet element and a connecting element joining the lower bladelet element and the upper bladelet element. The connecting element is configured to extend substantially upwards to define a connecting element vertical height. The lower region of the connecting element is connected to the lower bladelet tip end, while the upper region of the connecting element is connected to the upper bladelet tip end. The lower region and upper region twist away from each other, so that the lower bladelet leading edge extends in front of the upper bladelet leading edge, and the lower bladelet trailing edge extends in front of the upper bladelet trailing edge, when viewed in a planform direction. A blade incorporating said blade tip is also disclosed.

Description

BLADE TIPFIELD OF THE INVENTION

[0001] The invention pertains to a blade tip, which can be coupled to an aerodynamic geometric structure such as a wind turbine rotor blade or a wing for an aircraft. The invention also pertains to a blade incorporating said blade tip.BACKGROUND

[0002] Aerodynamic geometric structures such as wind turbine rotor blades and aircraft wings experience blade or wing tip vortices. These tip vortices generate additional drag and create noise. Tip vortices are generated because of a pressure differential when air moves from a surface of higher pressure to a surface of lower pressure For example, when wind turbine blade 100 is moving towards incoming air 105 as shown in Figure 1, air pressure on the bottom surface of blade 100 will be higher than the air pressure on the upper surface of blade 100. At the tip of blade 100, the higher pressure air will roll up towards the lower pressure upper surface of blade 100 in a circular manner, as represented by circular airflow 110. The circular airflow 110 will then result in blade tip vortex trail 120 being generated behind blade 100 (and hence circular airflow 110 can also be called pre-vortex circulatory airflow 110). Wing tip vortices are generated in a similar manner in a wing of an aircraft in motion. These tip vortices create noise and drag, which is undesirable. As such, efforts have been made to reduce the tip vortices.

[0003] Conventional solutions, such as winglets in the aeronautical industry, suppress or eliminate tip vortices by blocking the pre-vortex circulatory airflow that rolls up from the bottom surface of the blade. Winglets may not be suitable for wind turbines because such winglets extend inwards towards the wind turbine tower as shown in Figure 2. This compromises tower clearance requirements, where the rotor blade is required to maintain a specific distance away from the wind turbine tower to prevent a “tower hit” event. To adapt winglets in wind turbines, further adjustments will be needed to increase blade stiffness or rotor tilt. However, these adjustments will increase costs. Furthermore, power extraction may be reduced due to additional rotor tilt.

[0004] As such, there is a need for a solution to suppress or eliminate tip vortices in a cost effective and practical manner.SUMMARY Of INVENTION

[0005] According to a first aspect of the invention, a blade tip adapted to be in spanwise alignment with a main blade is provided. The blade tip comprising: a lower bladelet element, the lower bladelet element having a lower bladelet root end, a lower bladelet tip end, a lower bladelet leading edge and a lower bladelet trailing edge, the lower bladelet root end adapted to be closer to the main blade as compared to the lower bladelet tip end; an upper bladelet element, the upper bladelet element having an upper bladelet root end, an upper bladelet tip end, an upper bladelet leading edge and an upper bladelet trailing edge, the upper bladelet root end adapted to be closer to the main blade as compared to the upper bladelet tip end; and a connecting element, the connecting element joining the lower bladelet element and the upper bladelet element, the connecting element configured to extend substantially upwards to define a connecting element vertical height, the connecting element comprising a lower region and an upper region.

[0006] The lower region of the connecting element is connected to the lower bladelet tip end, and the upper region of the connecting element is connected to the upper bladelet tip end such that the upper bladelet element is higher than the lower bladelet element, when viewed in a root to tip direction.

[0007] The lower region and the upper region of the connecting element twist away from each other such that when the blade tip is coupled to the main blade, the lower bladelet leading edge extends in front of the upper bladelet leading edge, and the lower bladelet trailing edge extends in front of the upper bladelet trailing edge, when viewed in a planform direction.

[0008] Preferably, the connecting element is curved in a convex manner.

[0009] Preferably, the lower region of the connecting element twists away from the upper region such that the lower region extends in a different direction from the upper region.

[0010] Preferably, the upper bladelet trailing edge is higher than the lower bladelet leading edge.

[0011] Preferably, the lower bladelet trailing edge extends in front of the upper bladelet leading edge.

[0012] Preferably, the lower bladelet element has a lower bladelet chord, and the upper bladelet element has an upper bladelet chord, and wherein the lower bladelet leading edge extends in front of the upper bladelet trailing edge by a maximum horizontal distance, wherein the maximum horizontal distance exceeds a sum of the lower bladelet chord and the upper bladelet chord.

[0013] Preferably, the lower bladelet trailing edge intersects the upper bladelet leading edge such that, at the lower bladelet tip end, the upper bladelet leading edge extends in front of the lower bladelet trailing edge, and at the lower bladelet root end, the lower bladelet trailing edge extends in front of the upper bladelet leading edge, when viewed in the planform direction.

[0014] Preferably, the blade tip further comprising a middle bladelet element in between the lower bladelet element and the upper bladelet element, the middle bladelet element having a middle bladelet root end and a middle bladelet tip end, wherein the middle bladelet tip end is connected to the connecting element.

[0015] In another aspect of the invention, a blade is provided. The blade comprising: a main blade, the main blade having a main blade root end and a main blade tip end; and a blade tip according to the first aspect and its embodiments, wherein the blade tip is coupled to the main blade, and the blade tip is in spanwise alignment with the main blade.

[0016] Preferably, the blade tip is directly coupled to the main blade.

[0017] Preferably, the blade tip is coupled to the main blade through a pylon.

[0018] Preferably, the main blade has a main blade thickness, and wherein the connecting element vertical height of the blade tip is at least 0.5 times of the main blade thickness.

[0019] Preferably, the main blade has a main blade span, and the blade tip has a blade tip span, and wherein the blade tip span is at least 2% of the main blade span.

[0020] Preferably, the main blade has a main blade chord, and wherein the sum of the lower bladelet chord and the upper bladelet chord of the blade tip is at least 30% of the main blade chord.

[0021] Preferably, the main blade has f e chord, and wherein the maximum horizontal distance of the blade tip is at leas ; main blade chord.

[0022] Preferably, the main blade is a wind turbine rotor blade.

[0023] Preferably, the main blade is a wing for an aircraft.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to illustrate various embodiments, by way of example only, and to explain various principles and advantages in accordance with a present embodiment.

[0025] Figure 1 is an illustration of tip vortices on a conventional wind turbine rotor blade.

[0026] Figure 2 is an illustration of a conventional winglet attached to a wind turbine rotor blade.

[0027] Figure 3A is a perspective view of a blade tip according to certain embodiments.

[0028] Figure 3B is a side view of a blade tip according to certain embodiments, when viewed in a root to tip direction.

[0029] Figure 3C is a top view of a blade tip according to certain embodiments, when viewed in a planform direction.

[0030] Figure 3D is a side view of a blade tip according to certain embodiments, when viewed in a chord wise plane.

[0031] Figure 4A is perspective view of a blade incorporating a blade tip according to certain embodiments.

[0032] Figure 4B is a side view of a blade incorporating a blade tip according to certain embodiments.

[0033] Figure 4C is a top view of a blade incorporating a blade tip according to certain embodiments

[0034] Figure 5 is a cross section view of a blade incorporating a blade tip according to certain embodiments, when the blade is in motion and is viewed in the cross section along a chord wise plane at interface between blade tip and main blade.

[0035] Figure 6 is an illustration of a blade incorporating a blade tip according to certain embodiments, when the blade is in motion.

[0036] Figure 7 is an illustration of a blade tip according to certain embodiments.

[0037] Figure 8 is an illustration of a blade tip being coupled to a main blade through a pylon according to certain embodiments.

[0038] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been depicted to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements to help improve understanding of the present embodiment.DETAILED DESCRIPTION

[0039] The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description.

[0040] It is the intent of embodiments of the invention to teach a blade tip and a blade incorporating said blade tip. The blade tip can be adapted to be in spanwise alignment with a main blade (for example, a wind turbine rotor blade, or an aircraft wing) Spanwise alignment can mean that the blade tip extends out along span of the main blade (or main blade span).

[0041] The blade tip can comprise a lower bladelet element. The lower bladelet element can have a lower bladelet root end, a lower bladelet tip end, a lower bladelet leading edge and a lower bladelet trailing edge. The lower bladelet root end can be adapted to be closer to the main blade as compared to the lower bladelet tip end, when the blade tip is coupled to the main blade.

[0042] The blade tip can further comprise an upper bladelet element. The upper bladelet element can have an upper bladelet root end, delet tip end, an upper bladelet leading edge and an upper bladelet trailing edge.rladelet root end can be adapted to becloser to the main blade as compared to the upper bladelet tip end, when the blade tip is coupled to the main blade.

[0043] The blade tip can further comprise a connecting element. The connecting element can join the lower bladelet element and the upper bladelet element. The connecting element can extend substantially upwards (for example, vertically or in a gradient relative to a horizontal surface plane of the lower bladelet element) to define a connecting element vertical height.

[0044] The connecting element can comprise a lower region and an upper region. The lower region can be connected to the lower bladelet tip end, and the upper region can be connected to the upper bladelet tip end such that the upper bladelet element is higher than (or is vertically spaced apart from) the lower bladelet element, when viewed in a root to tip direction (or a side view of the blade tip).

[0045] The lower region and the upper region of the connecting element can twist (or bend) away from each other When the blade tip is coupled to the main blade, the lower bladelet leading edge can extend in front of (or first contact incoming air before) the upper bladelet leading edge, when viewed in a planform direction (or a top view of the blade tip). Similarly, when the blade tip is coupled to the main blade, the lower bladelet trailing edge can extend in front of the upper bladelet trailing edge, when viewed in a planform direction (or a top view of the blade tip).

[0046] As the disclosed embodiments of the blade tip describe that the upper bladelet element can be higher than the lower bladelet element, the upper bladelet element will be spaced apart from the lower bladelet element and form a vertical gap between the lower bladelet element and the upper bladelet element.

[0047] Also, as the disclosed embodiments of the blade tip describe that the lower bladelet leading edge can extend in front of the upper bladelet leading edge, the lower bladelet element will be spaced apart from the upper bladelet element and form an angular gap between the lower bladelet element and the upper bladelet element.

[0048] When the blade tip is coupled to the main blade, and the blade incorporating the blade tip is in motion, the vertical gap and the angular gap will allow incoming air to enter the blade tip.

[0049] Advantageously, the arrangement of the lower bladelet element, the upper bladelet element and the connecting element provides an air channel. The air channel will direct (or urge) incoming air towards pre-vortex circulatory airflow that is formed around the main blade (or main blade tip end) coming up towards the lower pressure upper surface. This cancels or disrupts the pre-vortex circulatory airflow. Cancelling or disrupting the pre-vortex circulatory airflow is advantageous since the pre-vortex circulatory airflow eventually sheds into blade tip vortex trail (or tip vortices).

[0050] The blade tip therefore provides an air channel that directs incoming air towards the pre-vortex circulatory airflow, thereby cancelling or disrupting the pre-vortex circulatory airflow. This reduces, suppresses or eliminates tip vortices, which will in turn reduce drag, and reduce noise.

[0051] The connecting element of the blade tip also provides an additional advantage. As the lower region of the connecting element can be connected to the lower bladelet tip end, the connecting element can block any pre-vortex circulatory airflow that is formed at the lower bladelet tip end. As the upper region of the connecting element can be connected to the upper bladelet tip end, the connecting element can block any pre-vortex circulatory airflow that is formed at the upper bladelet tip end. Therefore the connecting element can advantageously suppress or eliminate tip vortices for the lower bladelet element and upper bladelet element.

[0052] Further, as the lower bladelet element can have an aerodynamic profile (or an airfoil cross section), when incoming air flows across the lower bladelet element, air pressure on the bottom surface of the lower bladelet element will be higher than air pressure on the upper surface of the lower bladelet element (creating a suction pressure). This allows the lower bladelet element to provide lift. As the upper bladelet element can have an aerodynamic profile (or an airfoil cross section), the upper bladelet element can provide lift for the same reason. Hence, the blade tip provides additional lift when the blade tip is coupled to the main blade

[0053] Advantageously, due to the suction pressure on the lower bladelet element, the lower bladelet element allows additional incoming air to enter the blade tip (or entrains air) When additional incoming air enters the blade tip, overall air velocity coming through the blade tip will be increased. This results in further additional lift provided to the upper bladelet element (and hence further additional lift provided t p).

[0054] Further, as the blade tip can be in spanwise alignment with the main blade, the blade tip also exhibits lower radar cross section. For the same reason, the blade tip also does not compromise tower clearance requirements, while suppressing or eliminating tip vortices in a cost effective and practical manner. The advantages of the blade tip can be applicable in both wind energy and aeronautical applications.

[0055] In some embodiments, the connecting element can be curved in a convex manner (or outwardly from the lower bladelet element and / or upper bladelet element). Advantageously, the connecting element can provide a streamlined profile to allow for smoother airflow around it. This in turn reduces drag.

[0056] In some embodiments, the upper bladelet trailing edge can be higher than the lower bladelet leading edge. Advantageously, this arrangement enlarges the air channel. The enlarged channel directs more incoming air towards the pre-vortex circulatory airflow, thereby suppressing or eliminating tip vortices.

[0057] In some embodiments, the lower bladelet trailing edge can extend in front of the upper bladelet leading edge. Advantageously, this arrangement enlarges the air channel. The enlarged channel directs more incoming air towards the pre-vortex circulatory airflow, thereby suppressing or eliminating tip vortices.

[0058] In some embodiments, the lower bladelet element can have a lower bladelet chord. The upper bladelet element can have an upper bladelet chord. The lower bladelet leading edge can extend in front of the upper bladelet trailing edge by a maximum horizontal distance, and wherein the maximum horizontal distance exceeds a sum of the lower bladelet chord and the upper bladelet chord. Advantageously, this arrangement enlarges the air channel. The enlarged channel directs more incoming air towards the pre-vortex circulatory airflow, thereby suppressing or eliminating tip vortices.

[0059] In some embodiments, the lower bladelet trailing edge can intersect the upper bladelet leading edge such that, at the lower bladelet tip end, the upper bladelet leading edge extends in front of the lower bladelet trailing edge, and at the lower bladelet root end, the lower bladelet trailing edge extends in front of the upper bladelet leading edge, when viewed in a planform direction. In this configuration, the lower b snt and the upper bladelet element (or their surface planes) do not substantially O' ntageously, this arrangement enlargesthe air channel. The enlarged channel directs more incoming air towards the pre-vortex circulatory airflow, thereby suppressing or eliminating tip vortices.

[0060] Figure 3 A is a perspective view of blade tip 200 according to certain embodiments. Figure 3B is a side view of blade tip 200 according to certain embodiments, when viewed in a root to tip direction. Figure 3C is a top view of blade tip 200 according to certain embodiments, when viewed in a planform direction. Figure 3D is a side view of blade tip 200 according to certain embodiments, when viewed along a chord wise plane.

[0061] Referring to Figure 3 A, blade tip 200 can comprise lower bladelet element 310, upper bladelet element 320 and connecting element 330.

[0062] Lower bladelet element 310 can have lower bladelet root end 312 and lower bladelet tip end 314. Lower bladelet root end 312 can be adapted to be closer to a main blade as compared to lower bladelet tip end 314 when blade tip 200 is coupled to the main blade. Lower bladelet element 10 can have lower bladelet leading edge 316 and lower bladelet trailing edge 318.

[0063] Upper bladelet element 320 can have upper bladelet root end 322 and upper bladelet tip end 324. Upper bladelet root end 322 can be adapted to be closer to the main blade as compared to upper bladelet tip end 324 when blade tip 200 is coupled to the main blade. Upper bladelet element 320 can have upper bladelet leading edge 326 and upper bladelet trailing edge 328.

[0064] Lower bladelet element 310 and upper bladelet element 320 can each have an aerodynamic profile (or airfoil cross section). Due to the aerodynamic profile, when incoming air 105 flows across lower bladelet element 310, air pressure on the bottom surface of lower bladelet element 310 will be higher than air pressure on the upper surface of lower bladelet element 310. The pressure differential allows lower bladelet element 310 to provide lift. Similarly, due to the aerodynamic profile, when incoming air 105 flows across upper bladelet element 320, air pressure on the bottom surface of upper bladelet element 320 will be higher than air pressure on the upper surface of upper bladelet element 320. The pressure differential allows upper bladelet element 320 to provide lift.

[0065] Lower bladelet element 310 and t :t element 320 can each have its own twist and angle of attack. Lower bladelet ele d upper bladelet element 320 can eachhave other modifications known to airfoils for improving aerodynamics, such as vortex generators and serrated trailing edges.

[0066] Lower bladelet leading edge 316 can be defined as the region of lower bladelet element 310 where incoming air 105 spilts into an upper streamline and a lower streamline. Lower bladelet trailing edge 318 can be defined as the region of lower bladelet element 310 where the upper streamline and lower streamline leave the lower bladelet element 310 under ideal conditions.

[0067] Upper bladelet leading edge 326 can be defined as the region of upper bladelet element 320 where incoming air 105 spilts into an upper streamline and a lower streamline. Upper bladelet trailing edge 328 can be defined as the region of upper bladelet element 320 where the upper streamline and lower streamline leave the upper bladelet element 320 under ideal conditions.

[0068] Angle of attack can be defined as the angle of the lower bladelet element 310 or upper bladelet element 320 makes with incoming air 105.

[0069] Lower bladelet element 310 and upper bladelet element 320 can be of the same size. Lower bladelet element 310 and upper bladelet element 320 can be of the same shape.

[0070] Connecting element 330 can join lower bladelet element 310 and upper bladelet element 320.

[0071] Lower bladelet element 310, upper bladelet element 320 and connecting element 330 can be discrete components that are joined together. Alternatively, lower bladelet element 310, upper bladelet element 320 and connecting element 330 can be a single integral component. Lower bladelet element 310, upper bladelet element 320 and connecting element 330 can be manufactured using any method known to the skilled person, such as 3D printing.

[0072] Connecting element 330 can comprise lower region 334 and upper region 336.

[0073] Referring to Figure 3B, as shown, connecting element 330 can be configured to substantially extend upwards. As used herein, “upwards” can be a direction relative to a horizontal surface plane of lower bladelet ern,M1t 1 nThe upwards direction can be vertical or substantially vertical. The upwards direc f any gradient.

[0074] Connecting element 330 can be configured to substantially extend upwards such as to define connecting element vertical height 340. Connecting element vertical height 340 can be a maximum vertical distance between lower region 334 and upper region 336, as shown in Figure 3B.

[0075] Connecting element 330 can be curved in a convex manner (or outwardly from lower bladelet element 310 and / or upper bladelet element 320 as shown in Figure 3B). Advantageously, connecting element 330 can provide a streamlined profile to allow for smoother airflow. This can in turn reduce drag.

[0076] Alternatively, connecting element 330 can be curved in a concave manner (or inwardly towards lower bladelet element 310 and / or upper bladelet element 320). Alternatively, connecting element 330 can be substantially vertical.

[0077] Lower region 334 of connecting element 330 can be connected to lower bladelet tip end 314 Upper region 336 of connecting element 330 can be connected to upper bladelet tip end 324. As a result of the connections, upper bladelet element 320 will be higher than (or vertically displaced from) lower bladelet element 310, when viewed in the root to tip direction (as shown in Figure 3B). Therefore, upper bladelet element 320 will be spaced apart from lower bladelet element 310 and form a vertical gap 410 between upper bladelet element 320 and lower bladelet element 310.

[0078] Still referring to Figure 3B, lower bladelet element 310 can have lower bladelet thickness 350. Connecting element vertical height 340 can be greater than lower bladelet thickness 350.

[0079] Referring to Figure 3C, as shown, lower region 334 and upper region 336 of connecting element 330 can twist away from each other. Twist away can mean that lower region 334 extends in a different direction from upper region 336 (or upper region 336 extends in a different direction from lower region 334).

[0080] Twist away can mean that lower region 334 can be bent away from upper region 336 to form a V shape profile. Twist away can mean that lower region 334 can be bent away from upper region 336 at an angle (or upper region 336 can be bent away from lower region 334 at an angle). The angle can be an angle more e and less than 180 degree. The angle can be 10 degree, 20 degree, 25 degree, 30 c -gree, 40 degree, 50 degree, 60 degree,70 degree, 80 degree, 90 degree, 100 degree, 110 degree, 120 degree, 130 degree, 140 degree, 150 degree, 160 degree or 170 degree.

[0081] The twist away can be such that when blade tip 200 is coupled to the main blade, lower bladelet leading edge 316 extends in front of upper bladelet leading edge 326, and lower bladelet trailing edge 318 extends in front of upper bladelet trailing edge 328, when viewed in a planform direction (as shown in Figure 3C).

[0082] As lower bladelet leading edge 316 extends in front of upper bladelet leading edge 326 (that is, lower bladelet leading edge 316 contacts incoming air 105 first, before the upper bladelet leading edge 326, as shown in Figure 3C), lower bladelet element 310 will be spaced apart from upper bladelet element 320 and form an angular gap 420 between lower bladelet element 310 and upper bladelet element 320.

[0083] Lower bladelet leading edge 316 can extend in front of upper bladelet trailing edge 328 by a maximum horizontal distance W, as shown in Figure 3C. Maximum horizontal distance W can refer to the largest possible horizontal distance between lower bladelet leading edge 316 and upper bladelet trailing edge 328. The largest possible horizontal distance between lower bladelet leading edge 316 and upper bladelet trailing edge 328 can be at the lower bladelet root end 312 and / or upper bladelet root end 322.

[0084] Lower bladelet element 310 can have lower bladelet chord CL Lower bladelet chord Cl can be defined by the distance between lower bladelet leading edge 316 and lower bladelet trailing edge 318.

[0085] Upper bladelet element 320 can have upper bladelet chord C2. Upper bladelet chord C2 can be defined by the distance between upper bladelet leading edge 326 and upper bladelet trailing edge 328.

[0086] Still referring to Figure 3C, as shown, lower bladelet trailing edge 318 can intersect upper bladelet leading edge 326 such that, at the lower bladelet tip end 314, upper bladelet leading edge 326 extends in front of lower bladelet trailing edge 318, and at the lower bladelet root end 312, lower bladelet trailing edge 318 extends in front of upper bladelet leading edge 326. In this arrangement, lower bladelet element 310 and upper bladelet element 320 (or their surface planes thereof) do not substantially

[0087] In some embodiments, lower bladelet trailing edge 318 can extend in front of upper bladelet leading edge 326. That is, lower bladelet trailing edge 318 do not intersect upper bladelet leading edge 326. In this arrangement, lower bladelet element 310 and upper bladelet element 320 (or their surface planes thereof) do not overlap, and lower bladelet element 310 will be spaced apart from upper bladelet element 320 and form angular gap 420.

[0088] In some embodiments, lower bladelet trailing edge 318 and upper bladelet leading edge 326 can define a V-shape profile. That is, lower bladelet trailing edge 318 can be at an angle from upper bladelet leading edge 326. The angle can be an angle more than 0 degree and less than 180 degree. The angle can be 10 degree, 20 degree, 25 degree, 30 degree, 35 degree, 40 degree, 50 degree, 60 degree, 70 degree, 80 degree, 90 degree, 100 degree, 110 degree, 120 degree, 130 degree, 140 degree, 150 degree, 160 degree or 170 degree. In this arrangement, lower bladelet element 310 will be spaced apart from upper bladelet element 320 and form angular gap 420.

[0089] Referring to Figure 3D, vertical gap 410 between lower bladelet element 310 and upper bladelet element 320 is shown. Angular gap 420 between lower bladelet element 310 and upper bladelet element 320 is also shown.

[0090] Figure 4A is a perspective view of blade 600 incorporating blade tip 200 according to certain embodiments. Figure 4B is a side view of blade 600 incorporating blade tip 200 according to certain embodiments. Figure 4C is a top view of blade 600 incorporating blade tip 200 according to certain embodiments.

[0091] Referring to Figure 4A, blade 600 can comprise main blade 400 and blade tip 200. Blade tip 200 can be coupled to main blade 400. Blade tip 200 can be retrofitted to an existing main blade 400. Blade tip 200 can be a cost-effective and practical way to improve an existing main blade 400. Alternatively, blade tip 200 can also be integrated into a design of new main blade 400. Blade tip 200 can be pre-fabricated together with main blade 400.

[0092] Main blade 400 can comprise main blade root end 612 and main blade tip end 614. Main blade 400 can be an aerodynamic geometric structure such as but not limited to a wind turbine rotor blade, a rotor blade for a helicopter, or a wing for an aircraft.

[0093] Lower bladelet root end 312 of blac i be coupled to main blade tip end 614.Upper bladelet root end 322 of blade tip 20< pled to main blade tip end 614.

[0094] Referring to Figure 4B, main blade 400 can have main blade span 630. Main blade span 630 can be defined by the distance between main blade root end 612 and main blade tip end 614.

[0095] Again referring to Figure 4B, as shown, blade tip 200 can have blade tip span 640. Blade tip span 640 can be the distance between outermost surface of connecting element 330 to an interface between blade tip 200 and main blade 400. Blade tip span 640 be at least 2% of main blade span 630. Blade tip span 640 can be less than 30% of main blade span 630.

[0096] Again referring to Figure 4B, as shown, blade tip 200 can be in spanwise alignment with main blade 400. Spanwise alignment can mean that blade tip 200 extends out along main blade span 630. As blade tip 200 can be in spanwise alignment with main blade 400, blade tip 200 exhibits lower radar cross section. As blade tip 200 can be in spanwise alignment with main blade 400, blade tip 200 does not compromise tower clearance requirements. The aforementioned advantages are applicable when blade tip 200 is applied to an aircraft wing, and when blade tip 200 is applied to a wind turbine rotor blade.

[0097] Again referring to Figure 4B, as shown, main blade 400 can have main blade thickness 620. Main blade thickness 620 can refer to the thickness of main blade 400 at the interface between the blade tip 200 and main blade 400.

[0098] Connecting element vertical height 340 of blade tip 200 can be at least 0.5 times of main blade thickness 620. The connecting element vertical height 340 can be increased until such that lower bladelet element 310 and upper bladelet element 320 are no longer working together to provide an air channel to direct incoming air 105.

[0099] Referring to Figure 4C, as shown, main blade 400 can have main blade chord 650. Main blade chord can be defined by the distance between main blade leading edge 616 and main blade trailing edge 618 at the interface between blade tip 200 and main blade 400.

[0100] Maximum horizontal distance W of blade tip 200 can be at least 80% of main blade chord 650.

[0101] Advantageously, blade tip 200 according to certain embodiments can reduce, suppress or eliminate tip vortices, as explained belov nee to Figure 4A and Figure 5.

[0102] Referring to Figure 4A, as shown, when blade 600 is in motion, at main blade tip end 614, higher pressure air from the bottom surface of main blade 400 will roll up towards the lower pressure upper surface of main blade 400 in a circular manner. This circular airflow is pre-vortex circulatory airflow 110.

[0103] As blade tip 200 is coupled to main blade 400, incoming air 105 will flow towards gap (defined by bladelet separation angle and height) in blade tip 200.

[0104] Figure 5 shows in more detail the manner in which incoming air 105 interacts with blade tip 200 and pre-vortex circulatory airflow 110. Figure 5 is a cross section view of blade tip 200 that is coupled to main blade 400, when viewed in the cross section along a chord wise plane at the interface between blade tip 200 and main blade 400. Blade tip 200 can comprise lower bladelet element 310 and upper bladelet element 320 Connecting element 330 is not shown in Figure 5 for clarity.

[0105] Referring to Figure 5, vertical gap 410 and angular gap 420 allow incoming air 105 to enter blade tip 200.

[0106] The arrangement between lower bladelet element 310, upper bladelet element 320 and connecting element 330 provides an air channel. The air channel directs (or urges) incoming air 105 towards pre-vortex circulatory airflow 110 formed around main blade 400 (or specifically main blade tip end 614) Incoming air 105 will then disrupt or cancel pre-vortex circulatory airflow 110. Cancelling or disrupting pre-vortex circulatory airflow 110 is advantageous since pre-vortex circulatory airflow 1 10 eventually sheds into tip vortices or tip vortex trail (circular flow when left behind due to forward motion). Therefore, the use of blade tip 200 as described to disrupt or cancel pre-vortex circulatory airflow 110 will therefore suppress or eliminate or at the very least reduce tip vortices. Suppressing tip vortices will reduce noise, and reduce drag.

[0107] Again referring to Figure 5, as air pressure on the upper surface of lower bladelet element 310 will be lower than the bottom surface (creating a suction pressure), vertical gap 410 and angular gap 420 will allow additional incoming air 430 to enter blade tip 200 (or in other words, additional incoming air 430 is entrained into vertical gap 410 and angular gap 420 of blade tip 200). The air channel (as provi rrangement of lower bladelet element310, upper bladelet element 320 and conne it 330) directs additional incoming air430 towards pre-vortex circulatory airflow i IU. / vuuiuonal incoming air 430 will then disruptor cancel pre-vortex circulatory airflow 110, thereby suppressing or eliminating or reducing tip vortices.

[0108] Blade tip 200 can have an additional advantage. As lower bladelet element 310 can have an aerodynamic profile, this allows lower bladelet element 310 to provide additional lift 440 (or lift in addition to those provided by main blade 400). As upper bladelet element 320 can have an aerodynamic profile, this allows upper bladelet element 320 to provide additional lift 440. Furthermore, when additional incoming air 430 enters blade tip 200 due to the suction pressure provided by lower bladelet element 310, overall air velocity passing through blade tip 200 will be increased, thereby providing further additional lift on upper bladelet element 320 (and hence further additional lift on blade tip 200). Due to the entrainment of additional incoming air 430, overall lift force acting on upper bladelet element 320 will be sum of additional lift 440 and the further additional lift.

[0109] In some embodiments, upper bladelet trailing edge 328 can be higher than lower bladelet leading edge 316. Advantageously, this arrangement enlarges the air channel. The enlarged channel directs more incoming air 105 towards pre-vortex circulatory airflow 110, thereby suppressing or eliminating tip vortices.

[0110] In some embodiments, lower bladelet trailing edge 318 can extend in front of upper bladelet leading edge 326. Advantageously, this arrangement enlarges the air channel. The enlarged channel directs more incoming air 105 towards pre-vortex circulatory airflow 110, thereby suppressing or eliminating tip vortices.

[0111] In some embodiments, maximum horizontal distance W of blade tip 200 can exceed the sum of lower bladelet chord Cl and upper bladelet chord C2. Advantageously, this arrangement enlarges the air channel. The enlarged channel directs more incoming air 105 towards pre-vortex circulatory airflow 110, thereby suppressing or eliminating tip vortices.

[0112] Figure 6 further illustrates that blade tip 200 can suppress tip vortices 120. Figure 6 is an illustration of blade 600 incorporating blade tip 200, when blade 600 is in motion. Main blade 400 can be a wind turbine rotor blade as illustrated in Figure 6, and Figure 6 illustrates how blade tip 200 can be coupled to the wind turbine rotor blade. Incoming air 105 will flow towards blade tip 200 when blade 600 is in

[0113] Figure 7 illustrates blade tip 200 in accordance with certain embodiments. Blade tip 200 can further comprise middle bladelet element 510. Middle bladelet element 510 can be in between lower bladelet element 310 and upper bladelet element 320.

[0114] Middle bladelet element 510 can be arranged such that lower bladelet element 310, upper bladelet element 320, middle bladelet element 510 and connecting element 330 can provide an air channel. The air channel can direct incoming airflow 105 towards pre-vortex circulatory airflow 110, thereby disrupting or cancelling pre-vortex circulatory airflow 110.

[0115] Middle bladelet element 510 can have middle bladelet root end 512 and middle bladelet tip end 514. Middle bladelet tip end 514 of middle bladelet element 510 can be connected to the connecting element 330 as shown in Figure 7.

[0116] Figure 8 illustrates blade tip 200 that is coupled to main blade 400 through pylon 810.

[0117] Pylon 810 can comprise main body 820. Main body 820 can have channel 830 configured to receive main blade tip end 614. Channel 830 can correspond to the cross section of main blade tip end 614. Main blade tip end 614 can be attached to channel 830 through adhesive means. Pylon 810 can have an aerodynamic profile.

[0118] Main body 820 of pylon 810 can be attached to the lower bladelet root end 312 and upper bladelet root end 322 of blade tip 200.

[0119] When blade tip 200 is attached to main blade 400 through pylon 810, blade tip 200 can be wider than main blade 400 (or main blade tip end 614). When blade tip 200 is attached to main blade 400 through pylon 810, maximum horizontal distance W of blade tip 200 can be greater than main blade chord 650 at the interface between main blade 400 and blade tip 200.

[0120] Pylon 810 and / or blade tip 200 can be modular components. Pylon 810 and / or blade tip 200 can be portable. Pylon 810 and / or blade tip 200 can be installed on-site. For example, pylon 810 and / or blade tip 200 can be attached to an existing wind turbine rotor blade. For example, pylon 810 and / or blade tip 200 can be attached to an existing aircraft wing. Advantageously, this attachment method is a cost-effective and practical approach to improve or “upgrade” an existing wind turbine blade or aircraft wing in order to reduce, suppress or eliminate tip vortices. Alternatively, Pylon blade tip 200 can be prefabricated on new main blade 400.

[0121] In some embodiments, lower bladelet element 310 can have a bladelet twist such that lower bladelet leading edge 316 is higher than lower bladelet trailing edge 318 in reference to incoming flow (or incoming air 105). In some embodiments, lower bladelet element 310 can have an angle of attack that is equal or higher than an angle of attack of main blade 400. This configuration allows lower bladelet element 310 to urge incoming air 105 into blade tip 200 and provide additional lift. In some embodiments, upper bladelet element 320 can have a bladelet twist such that upper bladelet leading edge 326 can be higher than upper bladelet trailing edge 328 in reference to incoming air 105. In some embodiments, upper bladelet element 320 can have an angle of attack that is equal or higher than an angle of attack of main blade 400. This configuration allows upper bladelet element 310 to urge incoming air 105 into blade tip 200 and can change gap airflow angle.

[0122] In some embodiments, main blade 400 can be a wind turbine rotor blade. In some embodiments, main blade 400 can be a wing for an aircraft. In some embodiments, main blade 400 can be a rotor blade for a helicopter.

[0123] In some embodiments, blade tip 200 can be made of a suitable composite material, metal alloy, or hybrid material system. Suitable composite materials include but is not limited to carbon fibre reinforced composites, fibre glass reinforced composites, or a mixture of carbon fibre and fibre glass reinforced composites.

[0124] In some embodiments, pylon 810 can be made of a suitable material (for example, metal or fibre reinforced composites).

[0125] In some embodiments, pylon 810 and blade tip 200 can be a single integral component. Alternatively, pylon 810 and blade tip 200 can be separate components. Pylon 810 and blade tip 200 can be manufactured separately.

[0126] In the application, unless specified otherwise, the terms "comprising", "comprise", and grammatical variants thereof, intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, non-explicitly recited ele ents.

[0127] It will be apparent that various other modifications and adaptations of the application will be apparent to the person skilled in the iding the foregoing disclosure withoutdeparting from the spirit and scope of the application and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

CLAIMS1. A blade tip adapted to be in spanwise alignment with a main blade, the blade tip comprising: a lower bladelet element, the lower bladelet element having a lower bladelet root end, a lower bladelet tip end, a lower bladelet leading edge and a lower bladelet trailing edge, the lower bladelet root end adapted to be closer to the main blade as compared to the lower bladelet tip end; an upper bladelet element, the upper bladelet element having an upper bladelet root end, an upper bladelet tip end, an upper bladelet leading edge and an upper bladelet trailing edge, the upper bladelet root end adapted to be closer to the main blade as compared to the upper bladelet tip end; and a connecting element, the connecting element joining the lower bladelet element and the upper bladelet element, the connecting element configured to extend substantially upwards to define a connecting element vertical height, the connecting element comprising a lower region and an upper region; wherein the lower region of the connecting element is connected to the lower bladelet tip end, and the upper region of the connecting element is connected to the upper bladelet tip end such that the upper bladelet element is higher than the lower bladelet element, when viewed in a root to tip direction; and wherein the lower region and the upper region of the connecting element twist away from each other such that when the blade tip is coupled to the main blade, the lower bladelet leading edge extends in front of the upper bladelet leading edge, and the lower bladelet trailing edge extends in front of the upper bladelet trailing edge, when viewed in a planform direction.

2. The blade tip according to claim 1 , wherein the connecting element is curved in a convex manner.

3. The blade tip according to any one of the preceding claims, wherein the lower region of the connecting element twists away from the upper region such that the lower region extends in a different direction from the upper region.

4. The blade tip according to any one sding claims, wherein the upper bladelet trailing edge is higher than the lower blads :dge.

5. The blade tip according to any one of the preceding claims, wherein the lower bladelet trailing edge extends in front of the upper bladelet leading edge.

6. The blade tip according to any one of the preceding claims, wherein the lower bladelet element has a lower bladelet chord, and the upper bladelet element has an upper bladelet chord, and wherein the lower bladelet leading edge extends in front of the upper bladelet trailing edge by a maximum horizontal distance, wherein the maximum horizontal distance exceeds a sum of the lower bladelet chord and the upper bladelet chord.

7. The blade tip according to any one of claims 1 to 4 and 6, wherein the lower bladelet trailing edge intersects the upper bladelet leading edge such that, at the lower bladelet tip end, the upper bladelet leading edge extends in front of the lower bladelet trailing edge, and at the lower bladelet root end, the lower bladelet trailing edge extends in front of the upper bladelet leading edge, when viewed in the planform direction.

8. The blade tip according to any one of the preceding claims, further comprising a middle bladelet element in between the lower bladelet element and the upper bladelet element, the middle bladelet element having a middle bladelet root end and a middle bladelet tip end, wherein the middle bladelet tip end is connected to the connecting element.

9. A blade, comprising: a main blade, the main blade having a main blade root end and a main blade tip end; and a blade tip according to any one of claims 1 to 8, wherein the blade tip is coupled to the main blade, and the blade tip is in spanwise alignment with the main blade.

10. The blade according to claim 9, wherein the blade tip is directly coupled to the main blade.

11. The blade according to claim 9, wherein the blade tip is coupled to the main blade through a pylon.

12. The blade according to any one of claim 9 to 1 1 , wherein the main blade has a main blade thickness, and wherein the connecting element vertical height of the blade tip is at least 0.5 times of the main blade thickness.

13. The blade according to any one of claims 9 to 12, wherein the main blade has a main blade span, and the blade tip has a blade tip span, and wherein the blade tip span is at least 2% of the main blade span.

14. The blade according to any one of claims 9 to 13, comprising a blade tip according to claim 6, and the main blade has a main blade chord, and wherein the sum of the lower bladelet chord and the upper bladelet chord of the blade tip is at least 30% of the main blade chord.

15. The blade according to any one of claims 9 to 13, comprising a blade tip according to claim 6, and the main blade has a main blade chord, and wherein the maximum horizontal distance of the blade tip is at least 80% of the main blade chord.

16. The blade according to any one of claims 9 to 15, wherein the main blade is a wind turbine rotor blade.

17. The blade according to any one of claims 9 to 15, wherein the main blade is a wing for an aircraft.

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