A horizontal axis fan blade

Abstract

The present application relates to a kind of horizontal axis fan blade, comprising: blade body, and winglet connected in the end of the blade body, winglet is extended from the windward surface of the blade body to form rear-swept wing structure or forward to extend and form front-swept wing structure, the outer surface of winglet is provided with the protruding portion of strip shape, which is generally along the chord length direction of the winglet extends.When the blade body rotates, the flow wind generates protruding vortex behind the protruding portion, and part of the flow appears backflow vortex, the two vortexes generate an induced velocity perpendicular to the winglet upward, the induced velocity makes the subsequent flow trajectory further spread in centrifugal direction, so that the flow pipe area behind the fan becomes larger.Using the protruding portion of strip shape as an example, which is generally along the chord length direction of the winglet, the flow wind to the fan generates an induced velocity in centrifugal direction when passing through the protruding portion, so that the flow pipe area behind the fan expands, thereby improving the wind energy utilization coefficient of the fan.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of horizontal axis wind turbine, and particularly relates to a horizontal axis wind turbine blade. BACKGROUND

[0002] Wind energy as a renewable energy, and not affected by geopolitical and energy price fluctuations, can reduce the dependence on traditional chemical energy. On the other hand, wind energy reserves are huge, and the distribution is wide, and there will be no harmful emissions to the environment. Pollution and climate change have a positive effect on environmental pollution and climate change, and meet the needs of our energy policy.

[0003] Wind turbines are divided into horizontal axis wind turbines and vertical axis wind turbines according to the direction of the shaft. Compared with vertical axis wind turbines, the blades of horizontal axis wind turbines can always convert energy, which makes the wind energy utilization rate of horizontal axis wind turbines much higher than that of vertical axis wind turbines. At the same time, the technology of horizontal axis wind turbines is mature, and it has been widely used at present.

[0004] Therefore, researchers are committed to improving the wind energy utilization coefficient of horizontal axis wind turbines. On the one hand, in order to improve the wind sweeping area of the wind turbine, the horizontal axis wind turbine develops towards "large shape": on the other hand, in order to improve the wind energy utilization rate per unit wind sweeping area, researchers change the shape structure of the wind turbine, such as adding a small wing at the end of the wind turbine blade. Adding a small wing at the end of the wind turbine blade is one of the common methods to improve the wind energy utilization coefficient of horizontal axis wind turbines. The principle is to imitate the end of the aircraft wing bending upward by about 90°. Such design can alleviate the separation of the tip flow and the blade, prolong the formation of the tip vortex, thereby reducing the energy loss of the wind turbine, and achieving the purpose of improving the wind energy utilization coefficient of the wind turbine. The current mainstream design scheme is L-shaped wing, MIE-shaped wing designed by Japanese scholars, V-shaped wing, M-shaped wing designed by domestic scholars, etc.

[0005] At present, scholars' design of small wings stays at prolonging the separation of the tip vortex while reducing the resistance brought by the small wing, and does not explore the possibility that other properties of the small wing can bring the wind turbine aerodynamic performance improvement. At the same time, the research on the existing small wings has been mature, and it is difficult to have a breakthrough research. Other optimization methods based on this also cannot be put into actual use due to their high cost. SUMMARY

[0006] Therefore, it is necessary to provide a horizontal axis wind turbine blade to solve the problem of how to further improve the wind energy utilization coefficient of the wind turbine.

[0007] To achieve the above object, the inventors provide a horizontal axis fan blade, comprising: a blade body, and a winglet connected to the end of the blade body, the winglet extending backward from the windward surface of the blade body to form a backward swept wing structure or extending forward to form a forward swept wing structure, the outer surface of the winglet being provided with strip-shaped protrusions extending along the span direction or chord direction of the winglet.

[0008] Further, the protrusions are linear.

[0009] Further, the protrusions extend along the span direction or chord direction of the winglet.

[0010] Further, the protrusions are provided in multiple strips, and the multiple protrusions are parallel to each other.

[0011] Further, the outer surface of the winglet is provided with two protrusions perpendicular to each other, one of the protrusions being parallel to the span direction of the winglet, and the other protrusion being parallel to the chord direction of the winglet.

[0012] Further, the protrusions are linear.

[0013] Further, when the protrusions extend along the span direction of the winglet, the width value L' of the protrusions is 0.05-0.2 times the chord length L of the winglet, the height value H' of the protrusions is 0.05-0.6 times the maximum thickness H of the airfoil of the winglet, and the distance L" from the center of the protrusions to the leading edge of the winglet is 0-0.7 times the chord length L of the winglet.

[0014] Further, when the protrusions extend along the chord direction of the winglet, the width value L' of the protrusions is 0.05-0.2 times the chord length L of the winglet, the height value H' of the protrusions is 0.05-0.6 times the maximum thickness H of the airfoil of the winglet, and the distance d from the center of the protrusions to the trailing edge of the winglet is 0.05-1 times the span D of the winglet.

[0015] Unlike existing technologies, the above technical solution has the following advantages: Taking a strip-shaped protrusion with an overall orientation along the span of the winglet as an example, when the blade body rotates, the incoming airflow generates a protruding back vortex behind the protrusion, and a portion of the incoming airflow forms a backflow vortex. These two vortices generate an induced velocity perpendicular to the winglet and upward. This induced velocity causes the subsequent incoming airflow trajectory to further diffuse in a centrifugal direction, increasing the flow tube area behind the fan. Taking a strip-shaped protrusion with an overall orientation along the chord length of the winglet as an example, the incoming airflow blowing towards the fan generates a centrifugal induced velocity when passing through the protrusion, further expanding the flow tube area behind the fan. According to the continuity theory, an increase in the flow tube cross-section leads to a decrease in flow velocity, which means the fan absorbs more kinetic energy from the wind and converts it into its own mechanical energy, thereby improving the fan's wind energy utilization coefficient. Attached Figure Description

[0016] Figure 1 This is a perspective view of the protrusion in this embodiment, parallel to the spanning direction of the winglet;

[0017] Figure 2 This is a perspective view of the protrusion in this embodiment, parallel to the chord length of the winglet;

[0018] Figure 3 This is a schematic diagram of wind receiving on the blades of a horizontal axis fan in this embodiment;

[0019] Figure 4 This is a schematic diagram illustrating the mechanism by which a horizontal axis fan generates induced velocity in this embodiment.

[0020] Figure 5 This is another mechanism diagram of how a horizontal axis fan generates induced velocity in this embodiment;

[0021] Figure 6 This is a schematic diagram showing that the protrusion in this embodiment is wavy;

[0022] Figure 7 A schematic diagram showing two protrusions parallel to the small wingspan direction for this embodiment;

[0023] Figure 8 for Figure 7 Mechanism diagram of the embodiment;

[0024] Figure 9 A schematic diagram showing two perpendicularly intersecting protrusions for this embodiment;

[0025] Figure 10 Comparison of CP-TSR curves for a standard winglet and a swept T-winglet with a protrusion along the span direction;

[0026] Figure 11 Comparison of CP-TSR curves for a standard winglet and a swept T-winglet with a protrusion along the chord length;

[0027] Figure 12 Comparison of CP-TSR curves for a standard winglet and a forward-swept T-winglet with a protrusion along the span direction;

[0028] Figure 13 Comparison of CP-TSR curves for a standard winglet and a forward-swept T-winglet with a protrusion along the chord length;

[0029] Figure 14 This is a proportional illustration of the dimensions of the protrusion in this embodiment, which are parallel to the spanning direction of the winglet.

[0030] Figure 15 for Figure 14 Sectional view at point AA;

[0031] Figure 16 This is a proportional diagram showing the dimensions of the protrusion in this embodiment, parallel to the chord length of the winglet.

[0032] Figure 17 for Figure 16 A cross-sectional view along the length of the protrusion.

[0033] Explanation of reference numerals in the attached figures:

[0034] a. Lai Liufeng;

[0035] b. Sudden rise of the rear vortex;

[0036] v. Induction speed;

[0037] c. T-winglet incoming flow trajectory;

[0038] d. Ordinary winglet inflow trajectory;

[0039] e. Rotation direction;

[0040] X, the span direction of the winglets;

[0041] Y, the chord direction of the winglet;

[0042] 1. Blade body;

[0043] 11. Guide edge of the blade body;

[0044] 12. The side of the blade body;

[0045] 2. Small wings;

[0046] 21. The guide edge of the winglet;

[0047] 22. The trailing edge of the small wing;

[0048] 23. The folded edge of the winglet;

[0049] 3. Protrusions. Detailed Implementation

[0050] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0051] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0052] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0053] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0054] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order between these entities or operations.

[0055] Without further limitations, the use of terms such as “comprising,” “including,” “having,” or other similar open-ended expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0056] As understood in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0057] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0058] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral arrangement; it can be a direct connection or an indirect connection through an intermediate medium; it can be a relationship of two components combined together, an interaction relationship between two components, or a connection within two structures. Those skilled in the art to which this application pertains can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0059] Please see Figures 1-5 This embodiment provides a horizontal axis wind turbine blade, comprising: a blade body 1, and a small wing 2 connected to the end of the blade body 1. The small wing 2 extends backward from the windward side of the blade body 1 to form a swept-back wing structure or extends forward to form a swept-forward wing structure. The outer surface of the small wing 2 is provided with a strip-shaped protrusion 3 that extends along the span direction X or the chord direction Y of the small wing.

[0060] The blade body 1 and the winglet are smoothly connected. The outer surface of the winglet 2 refers to the surface that is away from the rotation axis of the blade body 1.

[0061] The protrusion 3 extends a certain length on the outer surface of the winglet 2, so that the protrusion 3 produces a continuous synergistic effect on the winglet. The width of the protrusion 3 can be designed to be consistent at all points.

[0062] For small wind turbines, the protrusion 3 can be directly glued to the outer surface of the winglet 2 using industrial adhesive, and the winglet 2 with the protrusion 3 can be installed on the tip of the wind turbine blade using a hot-melt method. For large wind turbines, it is recommended to directly bend the end of the blade body 1 backward to form a swept-back wing structure, or directly bend the end of the blade body 1 forward to form a forward-swept wing structure, and then weld the protrusion 3 to the outer surface of the bent winglet 2.

[0063] The winglet structure in this application retains the advantage of traditional winglet-equipped wind turbine blades, which can extend tip vortex separation. For example... Figures 3-5 As shown, taking a strip-shaped protrusion with an overall orientation along the span direction X of the winglet as an example, when the blade body 1 rotates, the incoming airflow a generates a protruding back vortex b behind the protrusion 3, and a portion of the incoming airflow forms a backflow vortex. These two vortices generate an induced velocity v perpendicular to the upward direction of the winglet 2. This induced velocity causes the subsequent incoming airflow trajectory to further diffuse in a centrifugal direction, increasing the flow tube area behind the fan. Taking a strip-shaped protrusion with an overall orientation along the chord direction Y of the winglet as an example, the incoming airflow a blowing towards the fan generates a centrifugal induced velocity v when passing through the protrusion 3, increasing the flow tube area behind the fan. According to the continuity theory, the flow tube cross-section increases, and the flow velocity decreases. This means that the fan absorbs more kinetic energy from the wind and converts it into its own mechanical energy, thereby improving the fan's wind energy utilization coefficient.

[0064] In some embodiments, the protrusion 3 is linear. That is, the protrusion 3 is a straight protrusion structure disposed on the outer surface of the winglet 2. The protrusion height of the protrusion 3 is uniform and continuous throughout.

[0065] In some embodiments, the overall orientation of the protrusion 3 is parallel to the span direction X or chord direction Y of the winglet. The span direction X of the winglet refers to the direction along the length of the winglet, and the chord direction Y of the winglet refers to the direction perpendicular to the length of the winglet. When the protrusion 3 is linear, the overall orientation of the protrusion 3 is its extension direction, and the protrusion 3 is positioned parallel to the span direction X or chord direction Y of the winglet.

[0066] like Figure 1 As shown in the diagram, the straight protrusion 3 extends parallel to the span direction X of the winglet. To obtain a larger area for generating induced velocity, the protrusion 3 extends from the connection between the blade body 1 and the winglet 2 to the tip of the winglet 2. Figure 2 As shown in the diagram, the straight protrusion 3 is parallel to the chord direction Y of the winglet. To increase the effect of the protrusion, it extends from the trailing edge of the winglet to the leading edge of the winglet. The leading edge 21 of the winglet is continuous with the leading edge 11 of the blade body, and the trailing edge 22 of the winglet is continuous with the trailing edge 12 of the blade body.

[0067] In the aforementioned embodiment, the cross-section of winglet 2 resembles the letter T, which the inventors named "T-shaped winglet". The inventors conducted comparative experiments on the different T-shaped winglets and ordinary winglets without protrusions.

[0068] Figure 3 The diagram shows the T-shaped winglet in this application being affected by the incoming airflow a and rotating along the rotation direction e.

[0069] Figure 5 The paper presents a comparison diagram of the T-shaped winglet inlet trajectory c and the ordinary winglet inlet trajectory d in this application. The diagram shows that the T-shaped winglet inlet trajectory will generate an induced velocity v perpendicular to the winglet 2 upward due to the protrusion.

[0070] As shown in Table 1, the table presents the wind energy utilization efficiency (CP) and tip speed ratio (TSR) data of ordinary winglets (winglets are only set at the end of the blade body) and swept T-shaped winglets with protrusions along the span direction (the end of the blade body is bent backward to form a swept wing structure, and a strip-shaped protrusion extending along the span direction is set on the outer surface of the winglet) under the same experimental conditions.

[0071] Table 1 - CP-TSR Relationship of Ordinary Winglets and Swept T-shaped Winglets with Protrusions Along the Span Direction

[0072]

[0073] Based on Table 1, plot the relationship between wind energy utilization efficiency (CP) and tip speed ratio (TSR) for ordinary winglets and swept T-shaped winglets with protrusions along the span direction. Figure 10 As shown, it can be clearly seen that the CP-TSR curve of the swept T-shaped winglet with the protrusion set along the span direction is basically above that of the ordinary winglet. It can be seen that the swept T-shaped winglet with the protrusion set along the span direction in this application can achieve higher wind energy utilization efficiency.

[0074] As shown in Table 2, the table presents the wind energy utilization efficiency (CP) and tip speed ratio (TSR) data of ordinary winglets (winglets are only set at the end of the blade body) and swept T-shaped winglets with protrusions along the chord direction Y (the end of the blade body is bent backward to form a swept wing structure, and strip-shaped protrusions extending along the chord direction Y are set on the outer surface of the winglets) under the same experimental conditions.

[0075] Table 2 - CP-TSR Relationship of Ordinary Winglets and Swept T-shaped Winglets with Protrusions Set Along the Chord Direction Y

[0076]

[0077] Based on Table 2, plot the relationship between wind energy utilization efficiency (CP) and tip speed ratio (TSR) for ordinary winglets and swept T-shaped winglets with protrusions along the chord Y direction. Figure 11 As shown, it can be clearly seen that the CP-TSR curve of the swept T-shaped winglet with the protrusion set along the chord Y direction is basically above that of the ordinary winglet. It can be seen that the swept T-shaped winglet with the protrusion set along the chord Y direction in this application can achieve higher wind energy utilization efficiency.

[0078] Table 3 - CP-TSR Relationship of Ordinary Winglets and Forward-Sweeping T-Shaped Winglets with Protrusions Along the Span Direction

[0079]

[0080] As shown in Table 3, the table presents the wind energy utilization efficiency (CP) and tip speed ratio (TSR) data of ordinary winglets (winglets are only set at the end of the blade body) and forward-swept T-shaped winglets with protrusions along the span direction (the end of the blade body is bent forward to form a forward-swept wing structure, and a strip-shaped protrusion extending along the span direction is set on the outer surface of the winglet) under the same experimental conditions.

[0081] Based on Table 3, plot the relationship between wind energy utilization efficiency (CP) and tip speed ratio (TSR) for ordinary winglets and forward-swept T-shaped winglets with protrusions along the span direction. Figure 12 As shown, it can be clearly seen that the CP-TSR curve of the forward-swept T-shaped winglet with the protrusion set along the span direction is basically above that of the ordinary winglet. It can be seen that the forward-swept T-shaped winglet with the protrusion set along the span direction in this application can achieve higher wind energy utilization efficiency.

[0082] As shown in Table 4, the table presents the wind energy utilization efficiency (CP) and tip speed ratio (TSR) data of ordinary winglets (winglets are only set at the end of the blade body) and forward-swept T-shaped winglets with protrusions along the chord direction Y (the end of the blade body is bent forward to form a forward-swept wing structure, and strip-shaped protrusions extending along the chord direction Y are set on the outer surface of the winglets) under the same experimental conditions.

[0083] Table 4 - CP-TSR Relationship of Ordinary Winglets and Forward-Sweeping T-Shaped Winglets with Protrusions Set Along the Chord Direction Y

[0084]

[0085] Based on Table 4, plot the relationship between wind energy utilization efficiency (CP) and tip speed ratio (TSR) for ordinary winglets and forward-swept T-shaped winglets with protrusions along the chord Y direction. Figure 13As shown, it can be clearly seen that the CP-TSR curve of the forward-swept T-shaped winglet with the protrusion set along the chord Y direction is basically above that of the ordinary winglet. It can be seen that the forward-swept T-shaped winglet with the protrusion set along the chord Y direction in this application can achieve higher wind energy utilization efficiency.

[0086] like Figure 6 As shown, in some embodiments, the end face of the protrusion 3 away from the winglet is wavy. Specifically, the end face of the protrusion 3 away from the winglet is a regular, undulating wave surface, like a sine curve. This effectively reduces the drag generated by the protrusion.

[0087] like Figure 7 , Figure 8 As shown, in some embodiments, multiple protrusions 3 are provided, and these protrusions 3 are arranged parallel to or intersecting each other. This design can increase the area for generating induced velocity, thus generating a higher induced velocity v. In this embodiment, the cross-section of the winglet structure resembles two side-by-side letter "T", i.e., a Π-shaped winglet.

[0088] like Figure 9 As shown, in some embodiments, the outer surface of the winglet is provided with two mutually perpendicular protrusions 3. One protrusion 3 is parallel to the span direction X of the winglet, and the other protrusion 3 is parallel to the chord direction Y of the winglet. In this embodiment, a cross-shaped protrusion 3 is formed on the outer surface of the winglet. This design combines the advantages of both protrusion 3 being oriented parallel to the span direction X of the winglet and protrusion 3 being oriented parallel to the chord direction Y of the winglet, and can simultaneously generate induced velocity due to rotation and induced velocity due to the incoming airflow a.

[0089] like Figure 14 , Figure 15 As shown, in some embodiments, when the strip-shaped protrusion is oriented along the span direction X of the winglet, the width L´ of the protrusion is 0.05-0.2 times the chord length L of the winglet, the height H´ of the protrusion is 0.05-0.6 times the maximum thickness H of the winglet airfoil, and the distance L″ from the center of the protrusion to the leading edge of the winglet is 0-0.7 times the chord length L of the winglet.

[0090] like Figure 16 , Figure 17As shown, in some embodiments, when the strip-shaped protrusion is oriented along the chord Y of the winglet, the width L' of the protrusion is 0.05-0.2 times the chord L of the winglet, the height H' of the protrusion is 0.05-0.6 times the maximum airfoil thickness H of the winglet, and the distance d from the center of the protrusion to the folded edge 23 of the winglet is 0.05-1 times the winglet span D. The folded edge of the winglet refers to the connection point between the blade body 1 and the winglet.

[0091] Finally, it should be noted that although the above embodiments have been described in the text and drawings of this application, this should not limit the scope of patent protection of this application. Any technical solutions that are based on the essential concept of this application and utilize the content described in the text and drawings of this application, resulting in equivalent structural or procedural substitutions or modifications, as well as the direct or indirect application of the technical solutions of the above embodiments to other related technical fields, are all included within the scope of patent protection of this application.

Claims

1. A horizontal axis fan blade, characterized in that, include: Blade body; And a small winglet connected to the end of the blade body, the small winglet extending backward from the windward side of the blade body to form a swept-back wing structure or extending forward to form a swept-forward wing structure, the outer surface of the small winglet is provided with a strip-shaped protrusion extending along the span direction of the small winglet, so that when the blade body rotates, it will generate an induced velocity perpendicular to the small winglet upward; or the outer surface of the small winglet is provided with a strip-shaped protrusion extending along the chord length direction of the small winglet, so that when the blade body rotates, it will generate an induced velocity in the centrifugal direction.

2. The horizontal axis fan blade according to claim 1, characterized in that: The protrusion is straight.

3. The horizontal axis fan blade according to claim 2, characterized in that: The overall orientation of the protrusion is parallel to the span or chord direction of the winglet.

4. The horizontal axis fan blade according to claim 3, characterized in that: The protrusions are provided in multiple ways, and the multiple protrusions are parallel to each other.

5. The horizontal axis fan blade according to claim 3, characterized in that: The outer surface of the winglet is provided with two mutually perpendicular protrusions, one of which is parallel to the span direction of the winglet, and the other of which is parallel to the chord direction of the winglet.

6. The horizontal axis fan blade according to any one of claims 1-5, characterized in that: The end face of the protrusion away from the winglet is wavy.

7. The horizontal axis fan blade according to any one of claims 1-5, characterized in that: When the strip-shaped protrusion is oriented along the span of the winglet, the width L´ of the protrusion is 0.05-0.2 times the chord length L of the winglet, the height H´ of the protrusion is 0.05-0.6 times the maximum thickness H of the winglet airfoil, and the distance L″ from the center of the protrusion to the leading edge of the winglet is 0-0.7 times the chord length L of the winglet.

8. The horizontal axis fan blade according to any one of claims 1-5, characterized in that: When the strip-shaped protrusion is oriented along the chord length of the winglet, the width L´ of the protrusion is 0.05-0.2 times the chord length L of the winglet, the height H´ of the protrusion is 0.05-0.6 times the maximum thickness H of the winglet airfoil, and the distance d from the center of the protrusion to the folded edge of the winglet is 0.05-1 times the span D of the winglet.

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