Low-Reynolds-number vertical axis fan adopting KFm stepped airfoil profile, blade of low-Reynolds-number vertical axis fan and blade forming method

Abstract

The invention belongs to the technical field of vertical-axis wind turbines, and particularly relates to a low-Reynolds-number vertical-axis fan adopting a KFm step wing section, a blade of the low-Reynolds-number vertical-axis fan and a blade forming method. According to the airfoil, eddy current reattachment is induced through the step design at the position of 50%-60% of the chord length, flow separation is delayed, the lift force performance and the stall resistance characteristic under the low Reynolds number are improved, and the lift-drag ratio is optimized. Meanwhile, the invention provides a segmented manufacturing method of the aluminum alloy blade, the blade is divided into the front edge and the rear edge, the front edge and the rear edge are independently formed through an aluminum pultrusion process and then are riveted and assembled, the problem of high mold cost is solved, the technological process is reduced to single riveting, and the production cost is remarkably reduced. During installation, aiming at the periodic windward / leeward working condition of the vertical axis fan, an installation positioning strategy that the blade steps face the outside of the circumference is specifically designed, and separation flow deterioration is avoided. The vertical axis wind turbine has the advantages of aerodynamic efficiency optimization, low cost and easiness in manufacturing, and is suitable for vertical axis wind power equipment in low-wind-speed and high-turbulence environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of vertical-axis wind turbines, and particularly relates to a low Reynolds number vertical-axis wind turbine adopting a KFm stepped airfoil, its blades, and a blade forming method. Background Art

[0002] The problems faced by small wind turbines are mainly that due to the reduction in size and the effect of turbulence, the Reynolds number of small wind turbines is relatively low. The low Reynolds number leads to laminar separation, resulting in a decrease in the lift-to-drag ratio of the airfoil, thereby directly reducing the power coefficient of the wind turbine. Since vertical-axis wind turbines do not require a yaw device and are more adaptable to high-turbulence environments, they have great advantages in the application scenarios of small wind turbines.

[0003] KFm (Kline-Fogleman) series airfoils: Full name: Kline–Fogleman airfoil. A step appears at 50% - 60% of the chord length of the KFm airfoil, and the step height is 9% - 12% of the airfoil thickness. As Figure 2 shown, when the air flow passes over the KFm airfoil, a rotating attached vortex is formed behind the step. The vortex and the KFm airfoil form the shape of a traditional airfoil. Since the resistance between the air and it is very small, the resistance suffered by the airfoil is reduced. The position where the lift of the traditional airfoil is generated is approximately around 25% - 30% from the leading edge to the chord length, and the lift generated by the rest of the airfoil is relatively small. There is a 50% step on the upper surface of the KFm airfoil, and vortices (stagnation vortices) are generated at the trailing edge. The pressure on the suction surface is reduced due to the generation of the vortices. Even at a high angle of attack, lift is generated on most of the chord length of the KFm airfoil, which results in the center of gravity of the KFm airfoil being closer to the trailing edge than that of a common airfoil.

[0004] Due to its unique stepped design, the KFm airfoil exhibits the advantages of stall resistance and easy manufacturability in low-speed, low Reynolds number scenarios (such as small wind turbines and model aircraft). However, the shortcoming of its lift-to-drag ratio and high-speed performance limits its application in large high-speed aircraft. For low Reynolds number wind turbines, this airfoil can effectively balance the aerodynamic efficiency and cost requirements through optimized design, and is a potential choice for medium and small-sized wind power generation equipment. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the purpose of the present invention is to provide a low Reynolds number vertical-axis wind turbine adopting a KFm stepped airfoil, its blades, and a blade forming method.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The blade of a low Reynolds number vertical axis wind turbine adopting a KFm stepped airfoil includes a blade leading edge, which includes a connecting end and a smoothly transitioning guiding surface. The connecting end is connected to a blade trailing edge, and at least one side between the blade leading edge and the blade trailing edge is provided with a first step.

[0008] The present invention utilizes the stepped design of the KFm airfoil to form a vortex behind the first step at a low Reynolds number (Re < 10 5 ), stabilizing the flow separation, delaying the stall, enhancing the lift-drag ratio and the anti-turbulence ability, thereby improving the problem of the "dead zone" with a low tip speed ratio of small vertical axis wind turbines.

[0009] As a preferred embodiment of the present invention, in the direction from the blade leading edge to the blade trailing edge, a second step is provided at 50% - 60% of the blade trailing edge, and the second step and the first step are arranged on the same side of the blade trailing edge. The blade leading edge forms a first-level stepped surface, the front section of the blade trailing edge forms a second-level stepped surface, and the rear section of the blade trailing edge forms a third-level stepped surface, so that the blade of the present invention forms a three-level stepped surface.

[0010] As a preferred embodiment of the present invention, first steps are provided on both sides between the blade leading edge and the blade trailing edge, and second steps are provided on both sides between the front section and the rear section of the blade trailing edge. When the first steps and the second steps are provided on both sides, any two surfaces can be used as installation surfaces during installation.

[0011] As a preferred embodiment of the present invention, only one side between the blade leading edge and the blade trailing edge is provided with a first step. The blade has a pressure side and a suction side, and the first step is provided on the suction side of the blade.

[0012] As a preferred embodiment of the present invention, the vertical height of the first step is 9% - 12% of the maximum thickness of the blade leading edge.

[0013] As a preferred embodiment of the present invention, a middle support structure is further connected between the blade leading edge and the blade trailing edge, and the first step is provided between the middle support structure and the blade trailing edge. By providing a middle support structure between the blade leading edge and the blade trailing edge in the present invention, the stability of the long blade can be enhanced.

[0014] A low Reynolds number vertical axis wind turbine adopting a KFm stepped airfoil includes the blade of a low Reynolds number vertical axis wind turbine adopting a KFm stepped airfoil, and further includes a generator. A plurality of brackets are connected to the rotor of the generator, and the blade of the low Reynolds number vertical axis wind turbine adopting a KFm stepped airfoil is installed on the brackets.

[0015] As a preferred embodiment of the present invention, a support rod is connected between adjacent brackets.

[0016] As a preferred embodiment of the present invention, a first step is provided only on one side between the leading edge and the trailing edge of the blade, and the first step is located on the side of the blade facing away from the generator. When installing on the vertical-axis wind turbine as a whole, it should be noted that due to the special power generation principle of the vertical-axis wind turbine, the blade will alternately become the pressure surface and the suction surface, but the main working area is in the windward azimuth angle of 0° to 180°. When installing the blade, pay attention to facing the first step outward of the circumference.

[0017] A method for forming the blade of a low Reynolds number vertical-axis wind turbine using the KFm stepped airfoil includes the following steps:

[0018] S1: Divide the blade into a leading edge and a trailing edge along the span direction, and perform pultrusion molding respectively;

[0019] S2: Then dock and assemble the leading edge and the trailing edge of the blade through a high-precision positioning tooling.

[0020] The present invention proposes a manufacturing method for a split aluminum alloy blade. The blade is divided into a leading edge and a trailing edge, and after being formed in segments by the pultrusion aluminum process, it is riveted and assembled, simplifying the production process of complex curvature airfoils and reducing the mold cost and assembly time.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. The present invention utilizes the stepped design of the KFm airfoil to form eddy currents behind the first step at a low Reynolds number (Re < 10 5 ), stabilizing the flow separation, delaying stall, and enhancing the lift-drag ratio and anti-turbulence ability, thereby improving the problem of the "dead zone" of the low tip speed ratio of small vertical-axis wind turbines.

[0023] 2. The present invention proposes a manufacturing method for a split aluminum alloy blade. The blade is divided into a leading edge and a trailing edge, and after being formed in segments by the pultrusion aluminum process, it is riveted and assembled, simplifying the production process of complex curvature airfoils and reducing the mold cost and assembly time.

[0024] 3. The present invention can enhance the stability of long blades by providing a middle support structure between the leading edge and the trailing edge of the blade. Description of the Drawings

[0025] Figure 1 is a schematic structural diagram of a low Reynolds number vertical-axis wind turbine using the KFm stepped airfoil;

[0026] Figure 2 is a schematic diagram of the KFm airfoil principle;

[0027] Figure 3 is a schematic diagram of the finished KFm airfoil blade;

[0028] Figure 4 is a schematic cross-sectional view of the KFm-3 aluminum profile blade;

[0029] Figure 5 It is a schematic cross-sectional view of the blade of KFm-6 aluminum profile;

[0030] Figure 6 It is a schematic cross-sectional view of the enhanced blade of KFm-6 aluminum profile;

[0031] Figure 7 It is a schematic operation view of the blade of KFm-3 aluminum profile;

[0032] Figure 8 It is a schematic operation view of the blade of KFm-6 aluminum profile.

[0033] In the figure: 1 - blade; 2 - leading edge of the blade; 3 - trailing edge of the blade; 4 - first step; 5 - second step; 6 - middle support structure; 7 - generator; 8 - bracket; 9 - support rod. Specific embodiments

[0034] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0036] Aiming at the problems faced by small vertical-axis wind turbines, such as non-generation at low tip speed ratios and a large "dead zone" range at low Reynolds numbers, an application of a KFm series airfoil on a low Reynolds number vertical-axis wind turbine is proposed in this application.

[0037] In the current vertical-axis wind turbine industry, due to the moderate cost and light weight of aluminum alloy, the blades 1 are basically made of aluminum alloy. However, since the blades 1 generally adopt relatively complex high-curvature airfoils, they cannot be integrally pultruded during aluminum alloy processing and manufacturing. They are usually divided into multiple parts and connected by bolts or rivets, resulting in a long assembly time and a complex process. The forming method of the aluminum alloy blade 1 proposed in this application divides the blade 1 into a blade leading edge 2 and a blade trailing edge 3. The blade leading edge 2 and the blade trailing edge 3 are separately processed using the pultruded aluminum process, which can reduce the forming components of the blade 1 and only requires one riveting process, reducing the production cost of the product and playing a greater positive role in the popularization of vertical-axis wind turbines.

[0038] To improve the power generation performance of small vertical-axis wind turbines, KFm series blades 1 suitable for operating in low Reynolds number scenarios are adopted, and a structure of aluminum profile blades 1 with a simple process is proposed.

[0039] Figure 2 It is a schematic diagram of the KFm airfoil principle. Figure 3 It is a schematic diagram of the finished product of the KFm airfoil blade 1, which explains the influence of the steps on the airflow on the surface of the airfoil blade 1. The steps change the flow separation characteristics at the trailing edge of the airfoil, induce three-dimensional flow, optimize transition, and comprehensively improve the lift performance, lift-to-drag ratio, and stall characteristics. The flow separates in the 1 / 2 chord length region (the flow separation point will change with the change of the angle of attack and Reynolds number), forming an adverse pressure gradient, causing local streamline bending, and generating a counter-rotating vortex structure, forming a recirculation zone. Under the action of the recirculation zone, a corner vortex region is formed. Generally, as the angle of attack decreases, the recirculation region gradually shrinks, and the reattachment region moves forward to the leading edge. The reattachment region is the position where the flow starts to reattach to the airfoil surface. The role of this region is to stabilize the flow after separation, weaken the flow separation, thereby reducing the lift fluctuation and improving the aerodynamic efficiency. As the angle of attack increases, the reattachment line moves backward, forming a larger separation zone. When there are steps on the suction surface of the airfoil, the surface steps cause the flow to transition to turbulence earlier, delaying the large-scale flow separation (i.e., stall). The steps on the pressure surface reduce the flow diffusion region transitioning to turbulence, also playing a role in delaying stall. At Reynolds numbers below 100,000, the flow separation is more easily controlled by geometric steps.

[0040] Figure 1 It is a schematic diagram of the application of the KFm series blades 1 on a vertical-axis wind turbine. The KFm series blades 1, as the key power components of the vertical-axis wind turbine generator set, account for 15% - 25% of the total cost of the whole machine. Currently, most commercial vertical-axis wind turbines adopt high-curvature and high Reynolds number airfoil blades 1, and their aerodynamic layout has technical defects such as a decrease in the lift-to-drag ratio and deterioration of stall characteristics under low Reynolds number conditions, resulting in limited power generation efficiency of the whole machine.

[0041] Figure 4It is a schematic cross-sectional view of the KFm-3 aluminum profile blade 1. The blade of the vertical axis wind turbine with a low Reynolds number adopts the KFm stepped airfoil, including the blade leading edge 2. The blade leading edge 2 includes a connecting end and a smoothly transitioning guiding surface. The connecting end is connected to the blade trailing edge 3. At least one side between the blade leading edge 2 and the blade trailing edge 3 is provided with a first step 4. In the direction from the blade leading edge 2 to the blade trailing edge 3, a second step 5 is provided at 50% - 60% of the blade trailing edge 3. The second step 5 and the first step 4 are arranged on the same side of the blade trailing edge 3. The blade leading edge 2 forms a first-level step surface, the front section of the blade trailing edge 3 forms a second-level step surface, and the rear section of the blade trailing edge 3 forms a third-level step surface. Thus, the blade of the present invention forms a three-level step surface. The KFm-3 series airfoil has a total of three step surfaces including the trailing edge.

[0042] The present invention utilizes the stepped design of the KFm airfoil (such as KFm-3 / KFm-6) to form vortices behind the first step 4 at a low Reynolds number (Re < 10 5 ), stabilize flow separation, delay stall, and improve the lift-to-drag ratio and anti-turbulence ability, thereby improving the problem of the "dead zone" with a low tip speed ratio of small vertical axis wind turbines.

[0043] The production process of the blade 1 adopted in this application is the commonly used aluminum profile pultrusion process. The KFm-3 aluminum profile blade 1 is composed of the KFm-3 blade leading edge 2 and the KFm-3 blade trailing edge 3. In the pultrusion process, the mold cost for a blade 1 with a chord length exceeding 200 mm is relatively high. The split pultrusion forming process is adopted: aiming at the problem of too high mold cost for airfoils with an excessive chord length, the blade 1 is divided into a front section and a rear section along the span direction for separate pultrusion forming, and then butt-assembled through a high-precision positioning tooling. The present invention proposes a manufacturing method for split aluminum alloy blades 1, which divides the blade 1 into the blade leading edge 2 and the blade trailing edge 3 (such as KFm-3) or a symmetric design (such as KFm-6), and is riveted and assembled after segmented forming by the pultrusion aluminum process, simplifying the production process of complex curvature airfoils and reducing the mold cost and assembly time consumption.

[0044] Specifically, the stepped structure is arranged on the pressure side, and its vertical height is 9% - 12% of the maximum thickness of the airfoil. This design controls the boundary layer transition through vortex separation of the first step 4, and can effectively improve the dynamic stall suppression ability under low Reynolds number conditions. When installed on the vertical axis wind turbine 7 as a whole, it should be noted that due to the special power generation principle of the vertical axis wind turbine 7, the blade 1 will alternately become the pressure side and the suction side, but the main working area is in the windward azimuth angle of 0° - 180°. When installing the KFm-3 aluminum profile blade 1, pay attention to facing the "step" outward of the circumference. Figure 7 It is a schematic operation diagram of the KFm-3 aluminum profile blade 1.

[0045] Figure 5This is a cross-sectional diagram of a KFm-6 aluminum profile blade 1. As a symmetrical airfoil, any two surfaces of the KFm-6 airfoil can be used as mounting surfaces during installation. The installation method is as follows: Figure 8 As shown, the KFm-6 aluminum profile blade 1 is composed of a KFm-6 blade leading edge 2 and a KFm-6 blade trailing edge 3.

[0046] use Figure 5 The structure is reasonable for use on shorter blades 1. When using long blades 1, the unstable installation of blades 1 needs to be strengthened. The strengthening method refers to Figure 6 , a cross-sectional diagram of the reinforced KFm-6 aluminum profile blade 1. The difference from the simple version is that the reinforced KFm blade 1 uses a square aluminum profile at the bolt installation position, i.e. Figure 6 The middle support structure 6 of the reinforced version of KFm-6 blade 1. The present invention clarifies the installation rule that the steps are oriented outside the circumference, ensuring that the step design maximizes the aerodynamic efficiency of the blade 1 when the windward side is 0° to 180°, and at the same time, by strengthening the support structure (such as the design of the middle support structure 6 of the reinforced version of KFm-6), the stability of the long blade 1 is enhanced.

[0047] like Figure 7 and Figure 8 As shown, a low Reynolds number vertical axis fan using a KFm stepped airfoil includes a low Reynolds number vertical axis fan blade using a KFm stepped airfoil, and also includes a generator 7, a rotor of the generator 7 is connected to a plurality of brackets 8, and the low Reynolds number vertical axis fan blade using a KFm stepped airfoil is mounted on the brackets 8. Support rods 9 are connected between adjacent brackets 8.

[0048] It should be noted that when the first step 4 is only provided on one side between the leading edge 2 and the trailing edge 3 of the blade, the first step 4 is located on the side of the blade 1 facing away from the generator 7. When installing the blade 1 on the vertical axis wind turbine 7, it should be noted that due to the special power generation principle of the vertical axis wind turbine 7, the blade 1 will alternately become a pressure surface and a suction surface, but the main work area is at an azimuth angle of 0° to 180° facing the wind. When installing the blade 1, pay attention to facing the first step 4 outside the circumference.

[0049] The present invention is not limited to the above-mentioned optional implementation modes. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that fall within the scope defined by the claims of the present invention fall within the protection scope of the present invention.

Claims

1. Low Reynolds number vertical axis fan blades with KFm stepped airfoil, characterized by: The blade leading edge (2) comprises a connecting end and a smoothly transitioned flow-guiding surface, the connecting end is connected to the blade trailing edge (3), and a first step (4) is provided on at least one side between the blade leading edge (2) and the blade trailing edge (3).

2. The low Reynolds number vertical axis fan blade using a KFm stepped airfoil according to claim 1, characterized in that: In the direction from the leading edge (2) of the blade to the trailing edge (3) of the blade, a second step (5) is provided at 50% to 60% of the trailing edge (3) of the blade, and the second step (5) and the first step (4) are arranged on the same side of the trailing edge (3) of the blade.

3. The low Reynolds number vertical axis fan blade using the KFm stepped airfoil according to claim 2, characterized in that: A first step (4) is provided on both sides between the leading edge (2) of the blade and the trailing edge (3) of the blade, and a second step (5) is provided on both sides between the front section of the trailing edge (3) of the blade and the rear section of the trailing edge (3) of the blade.

4. The low Reynolds number vertical axis fan blade using a KFm stepped airfoil according to claim 1, characterized in that: A first step (4) is provided on only one side between the leading edge (2) and the trailing edge (3) of the blade, the blade (1) has a pressure surface side and a suction surface side, and the first step (4) is provided on the suction surface side of the blade (1).

5. The low Reynolds number vertical axis fan blade using the KFm stepped airfoil according to claim 1, characterized in that: The vertical height of the first step (4) is 9% to 12% of the maximum thickness of the blade leading edge (2).

6. The low Reynolds number vertical axis fan blade using a KFm stepped airfoil according to claim 1, characterized in that: A middle support structure (6) is also connected between the leading edge (2) and the trailing edge (3) of the blade, and the first step (4) is arranged between the middle support structure (6) and the trailing edge (3) of the blade.

7. A low Reynolds number vertical axis fan using a KFm stepped airfoil, comprising the low Reynolds number vertical axis fan blade using a KFm stepped airfoil according to claim 1, characterized in that: It also includes a generator (7), a rotor of which is connected to a plurality of brackets (8), and low Reynolds number vertical axis fan blades with a KFm stepped airfoil are installed on the brackets (8).

8. The low Reynolds number vertical axis fan using the KFm stepped airfoil according to claim 7, characterized in that: Support rods (9) are connected between adjacent brackets (8).

9. The low Reynolds number vertical axis fan using the KFm stepped airfoil according to claim 7, characterized in that: A first step (4) is provided on only one side between the leading edge (2) and the trailing edge (3) of the blade, and the first step (4) is located on a side of the blade (1) facing away from the generator (7).

10. A method for forming a blade (1) of a low Reynolds number vertical axis fan using a KFm stepped airfoil, used for manufacturing a blade of a low Reynolds number vertical axis fan using a KFm stepped airfoil as claimed in claim 1, characterized in that: The following steps are involved: S1: dividing a blade (1) into a blade leading edge (2) and a blade trailing edge (3) along a span direction, and pultruding each of the two edges; S2: The leading edge (2) and the trailing edge (3) of the blade are then butted and assembled using a high-precision positioning tool.

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