WO2013067916A1

WO2013067916A1 - New blade of composite material for horizontal-axis wind power generator

Info

Publication number: WO2013067916A1
Application number: PCT/CN2012/084155
Authority: WO
Inventors: 张向增
Original assignee: Zhang Xiangzeng
Priority date: 2011-11-11
Filing date: 2012-11-06
Publication date: 2013-05-16
Also published as: CN102434384A

Abstract

A new blade of composite material for a horizontal-axis wind power generator, having an independent pneumatic wing profile (1) and a bearing structure (2). The pneumatic wing profile (1) has an outer longitudinal beam (2) provided on the outside thereof, for improving the longitudinal bending strength of the blade. This design can guarantee power, improve the bending strength of the blade, and significantly increase the efficiency of the material and reduce the cost of the blade.

Description

Novel composite blade for horizontal axis wind turbine

This application claims priority to Chinese Patent Application No. 201120446769.8, entitled "A New Type of Composite Blade of Horizontal Axis Wind Turbine", filed on November 11, 2011, the entire contents of which are incorporated by reference. In this application.

TECHNICAL FIELD The present invention relates to a novel composite blade for a horizontal axis wind turbine. The aerodynamic functional part of the blade and the load-bearing structure are separated from each other, and the load-bearing structure extends beyond the geometrical limitation of the aerodynamic airfoil profile to the outside of the aerodynamic profile. The outer load bearing structure and the aerodynamic structure part work together to construct the main load bearing structure of the blade. The blade formed by this design concept greatly improves the bending rigidity of the blade and greatly reduces the cost of the blade under the premise of ensuring the aerodynamic power, and the material utilization efficiency is greatly improved.

The invention belongs to the field of composite blade manufacturing of horizontal axis wind turbines.

BACKGROUND OF THE INVENTION Modern horizontal-axis wind turbine composite blades, whether using pre-bent structures or carbon fiber-reinforced structures, have optimized the blades to the extent that they cannot be broken again. The root cause is that it is subject to the geometrical constraints of the blade's aerodynamic airfoil profile, making the structural properties of the material unattainable. Specifically, the blade is subjected to the maximum aerodynamic lift in the waving direction to generate a large bending moment, but the thickness of the blade in this direction is limited by the geometry of the airfoil, so that the bending rigidity of the blade in this direction is limited, even if a high modulus is used. The carbon fiber material is reinforced, and it still appears to be insufficiently stiff for large blades. The blade pre-bending technique only changes the initial position of the blade's flexural deformation and does not increase the blade's own bending stiffness.

We know that the "work" beam has the best bending properties and material efficiency. From the analysis of the bending deformation characteristics of the cantilever beam with a rectangular cross section, we know that the bending stiffness of the beam is proportional to the height of the beam and proportional to the square of the material modulus. Therefore, increasing the thickness of the blade structure is more effective than selecting a high modulus material. Therefore, the method of increasing the bending stiffness of the blade is to increase the thickness of the bearing structure of the blade under the premise of ensuring the pneumatic function. The answer is to break through the limits of the blade's aerodynamic airfoil thickness, allowing the load-bearing structure to be external to the aerodynamic airfoil.

The blades used in wind turbines have a maximum flow velocity at the tip of the blade. The level of 65m/s is equivalent to 1/5 sound speed. This is a low-speed aerodynamic range in aerodynamics, which makes it possible to externally position the blade bearing structure relative to the aerodynamic airfoil.

SUMMARY OF THE INVENTION It is an object of the present invention to achieve a lightweight, inexpensive, and reliable design and manufacture of large-scale blades for horizontal-axis wind turbines.

The so-called large-diameter impeller and large-sized blade can be understood as an impeller with a diameter of 80 m or more and a blade length of 40 m or more.

The idea of the invention is to break through the limitation of the thickness of the aerodynamic airfoil of the blade and let the load-bearing structure be external.

Similar to the principle of bending deformation of a general beam, when the blade is longitudinally bent and deformed, the material on one side of the curved mandrel is subjected to compressive stress, and the material on the other side is subjected to tensile stress. The ability to withstand compression and stretching is different for different materials and structural shapes. This patent is designed to withstand the compressive stress on the side of the aerodynamic airfoil, while the external longitudinal beam is subjected to tensile stress. While increasing the bending stiffness, the airfoil geometry is fully utilized to improve the bending stability of the blade. For the aerodynamic airfoil section, it is naturally possible to use a pultrusion process to produce a profiled profile to combine the aerodynamic airfoil. Theoretically, from the blade root to the tip of the blade, the chord length of the blade airfoil is required to be different. The solution of the present invention is to adopt a segmented combination approximation treatment method, that is, a constant cross-section blade segment combination formed by a pultrusion process with different chord lengths and thicknesses. The aerodynamic airfoil that forms the entire blade. For the external longitudinal beam section, the longitudinal beam is subjected to tensile stress. The unidirectional fiber reinforced resin composite is the most ideal choice. Since there is no buckling stability problem, the section size can be small, to reduce wind resistance and wind disturbance, and to improve The overall aerodynamic efficiency of the blade, the geometry of the longitudinal beam also requires aerodynamic characteristics, and the flat shape of the axisymmetric profile is preferred. Moreover, it is more suitable to use a carbon fiber composite material for the longitudinal beam.

Of course, the joint structure between the external longitudinal beam and the aerodynamic airfoil should also have aerodynamic characteristics to reduce windage and wind disturbance. It can be a sandwich foam sandwich structure.

Each blade must be able to achieve independent pitch control, which is a must for modern horizontal axis fans. The pitch shaft of the blade of the present invention substantially coincides with the aerodynamic center axis formed by the aerodynamic airfoil, so that when the blade is converted into the paddle, the pneumatic angle of attack adjustment of the blade at different positions can be fully realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing the overall structure of a blade; Figure 2 is a cross-sectional view of a middle portion of a blade;

In Fig. 1, 1 - aerodynamic airfoil, 2 - external longitudinal beam, 3 - upright strut, 4 - diagonal rib, 5 - blade tip, 6 - leaf 艮 connecting section, FL - distributed lift, PX1 - change Paddle axis

Figure 2, 1 - aerodynamic airfoil, 2 - external longitudinal beam, 3 - riser, 7 - leading edge, 8 - trailing edge, 9 - web, XI - wing type string, X2 - external longitudinal Beam string, X3 - bending section centroid axis, PS - pneumatic pressure surface, SS - pneumatic suction surface, Lc - clearance distance, T-wing thickness.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In Fig. 1, a blade body carrying structure is composed of an aerodynamic airfoil 1 portion and an outer longitudinal beam 2; The two are combined by a joint structure to become a load-bearing structure that can effectively resist the bending deformation of the blade. The joint structure may be a lattice structure composed of the riser 3 and the diagonal stay 4.

As can be seen from Figure 1, the outer longitudinal beam 2 breaks through the geometric profile of the aerodynamic airfoil 1 and is placed outside the aerodynamic airfoil 1. The aerodynamic distribution lift FL is distributed longitudinally along the blade on the outer surface of the aerodynamic airfoil 1 .

Of course, the blade structure must also have a tip 5 and a joint portion of the blade joint 6 . The blade root connection section 6 completes the function of connecting the hub and is capable of carrying a large moment load of the blade root.

The pitch axis of the blade and the aerodynamic center axis formed by the aerodynamic airfoil substantially coincide. When the aerodynamic airfoil 1 is a pre-bent blade, the two are mainly coincident at the blade root segment.

Along the longitudinal length of a blade, the aerodynamic airfoil 1 contains at least a segment of a constant cross-section of the blade, a blade consisting of a plurality of segments of the blade, each segment of the blade having a constant cross-section of a particular chord length, for each segment of constant cross-section The blade segments of the section, from the blade root to the tip of the blade, each of the differential cross-sections are continuously twisted by a certain angle around the central axis of the pitch. The magnitude of this angle is determined by the design of the pneumatic angle of attack. Figure 1 illustrates a blade form consisting of a three-section fixed-section aerodynamic airfoil. On the right side of Figure 1, a constant cross-section aerodynamic airfoil with different chord lengths is used at different locations on the ABC, with a rule that the chord length decreases from blade root to tip and the blade thickness decreases. This is a consideration of the stability of the blade structure.

Of course, the aerodynamic airfoil 1 of the blade can be in the form of a continuous change in chord length and thickness, that is, the geometrical shape of the blade with different blade chord lengths at different radial positions obtained according to the theoretical calculation of the leaf, still conforming from the blade root to The law of the length of the tip chord is reduced. The aerodynamic airfoil 1 must conform to a specific pneumatic twist angle.

Pneumatic airfoil 1 with a constant cross-section segmentation technology can be used by the pultrusion process The blade profiles are combined to achieve automated continuous production, while blades with continuously varying chord lengths and thicknesses need to be fabricated intermittently with split molds. The former has higher reliability and lower manufacturing costs, and the technical and economic advantages are obvious.

Regarding the riser 3 and the diagonal ribs 4, there are also more techniques. The riser 3 should also have a suitable aerodynamic shape to minimize air resistance and reduce disturbance to airflow. The riser 3 can be sandwiched with a foam sandwich. From the blade root to the tip of the blade, the height of the riser 3 is reduced and the thickness is reduced. The diagonal rib 4 is entirely a unidirectional fiber reinforced resin composite. Since the distributed lift FL load generated on the aerodynamic airfoil of the blade is distributed over the entire length of the blade, the diagonally inclined ribs 4 at different positions can be assigned a suitable cross-sectional area according to the size of the distributed load.

Since the air velocity of the tip is the highest, in order to reduce the resistance and noise, the external longitudinal beam 2 does not necessarily start to be generated at the tip position, for example, it can start at a position 1/5 of the blade tip length until the end of the blade root.

The outer longitudinal beam 2 and the diagonal rib 4 can be integrally formed. In one embodiment, the continuous fibers of each of the diagonal ribs 4 extend from the surface of the aerodynamic airfoil, across the riser 3, to the root of the blade. Thus, all of the diagonal ribs 4 extend the bundle of fibers into an outer longitudinal beam 2. As a result, the outer longitudinal beam 2 is progressively increased in cross section from the tip to the root. Assuming a blade length of 45 m, every 3 m - a riser 3 and a diagonal rib 4, each fiber composite diagonal rib 4 has a cross-sectional area of 5 cm 2 and can withstand a tensile force of more than 50 tons, then, the external longitudinal The cross-sectional area of the beam 2 from the tip of the blade to the root of the blade is increased by 5 square centimeters, in order of 5 square centimeters, 10 square centimeters, 15 square centimeters, and 75 square centimeters. External longitudinal beam 2 The tip position of the blade is equivalent to 50mm 10mm, and the blade root position is equivalent to 300mm x 25mm.

Figure 2 is a cross-sectional view showing a section of a position in the middle of the blade. The figure is used to analyze the bending resistance of the section. The figure shows the bending section centroid axis X3. On the left side of the X3 axis, the external longitudinal beam 2 is subjected. Tensile stress, on the right side of the X3 axis, the aerodynamic airfoil 1 is subjected to compressive stress. Since the aerodynamic airfoil 1 is a hollow structure, the outer envelope has a large geometric area, so that it has strong resistance to longitudinal compression stability; and the outer longitudinal beam 2 carries tensile stress, so the cross-sectional area can be small. It can be a solid structure, such as the variable cross-section solid structure of the above example. Considering the structural efficiency of the material, the wall thickness of the aerodynamic suction surface SS on the outer side of the aerodynamic airfoil 1 is much larger than the wall thickness of the inner pneumatic pressure surface PS. Considering the bending stiffness requirement of the blade shimmy direction, the bearing structure cannot break the limitation of the aerodynamic airfoil in the direction of the shimmy. The concept of the invention is not applicable to the direction of the shimmy, so at the leading edge of the aerodynamic airfoil 1 And the trailing edge 8 are assigned A sufficient amount of longitudinal fiber reinforcement. In order to improve the buckling stability, the blade aerodynamic airfoil 1 has a web 9 connected to the aerodynamic suction surface SS of the aerodynamic airfoil 1 and a pneumatic pressure surface PS. The numerical examples are used to describe and understand this phase, such as a section of the blade, aerodynamic airfoil 1 with a chord length of 1.6 m, a wall thickness of the outer aerodynamic suction surface SS of 3 mm, and a wall thickness of the inner aerodynamic pressure surface of the PS of 1.5 mm. 7 The inner reinforcement increases the cross-sectional area by 10 square centimeters, the inner edge of the trailing edge 8 increases the cross-sectional area by 20 square centimeters, and the web 9 has a thickness of 2 mm. Of course, on the pneumatic suction surface SS, the pneumatic pressure surface PS and the web 9 of the blade, it is surely necessary to arrange and design a longitudinal reinforcing rib, and the reinforcing rib may be a foam sandwich structure.

For the blade of the present invention, if a carbon fiber material is to be used to increase the bending rigidity of the entire blade, then only the outer longitudinal beam 2 is a carbon fiber reinforced resin composite. Although the modulus of carbon fiber is more than 4 times higher than that of glass fiber, the elongation at break is very low, and the flexibility of blade deformation is limited. If high-strength S-type fiberglass is used to improve the flexibility of the whole blade, then it is only outside. The longitudinal beam 2 is made of a high-strength S-type glass fiber reinforced resin composite material.

In Figure 2, the aerodynamic airfoil 1 around the string XI necessarily meets the aerodynamic characteristics. The outer longitudinal beam 2 around the string X2 also has an aerodynamic profile to minimize air resistance and reduce disturbance to the airflow. The outer longitudinal beam (2) may be a thin plate having a symmetrical aerodynamic profile structure with a reduced cross-sectional area from the blade root to the tip. Moreover, the clearance distance Lc between the outer longitudinal beam 2 and the aerodynamic airfoil 1 is preferably greater than the airfoil thickness T of the aerodynamic airfoil 1 in order to effectively reduce the disturbance to the air flow. The smaller the clearance distance between the external longitudinal beam 2 and the aerodynamic airfoil 1, the smaller the bending stiffness of the blade and the worse the aerodynamic efficiency.

The lift characteristics of the blade deteriorate or even stall, which is usually due to the separation of the airflow on the SS side of the pneumatic suction side. Since the external longitudinal beam 2 is located on the PS side of the aerodynamic airfoil 1 rather than the aerodynamic suction surface SS, and maintains the clearance distance Lc, the presence of the external longitudinal beam 2 may cause local airflow disturbance, but the blade is pneumatically The impact of lift is limited.

According to the analysis of the embodiment, it is known that when the conventional blade is subjected to aerodynamic bending, the suction side of the aerodynamic suction surface SS is subjected to compressive stress and the side of the pneumatic pressure surface PS is subjected to tensile stress, and the height of the curved section is the airfoil thickness T. In the blade of the present invention, substantially the entire section of the aerodynamic airfoil 1 is subjected to compressive stress and the outer longitudinal beam 2 is subjected to tensile stress, and the height of the curved section is Lc + T. Roughly calculated, if Lc+T=2T, the bending stiffness will increase by 23 times. In other words, if the bending stiffness is kept constant, the bending section can be reduced to 1/8 of the original; if the amount of material is kept constant, the bending stiffness is increased by 23 times, meaning that the blade can be extended at least twice. To achieve the manufacture of large blades. It can be seen that material and cost savings are reflected here. The blade of the present invention is obviously completely detachable at the segmented joint of the aerodynamic airfoil 1, and is connected and assembled by a flange bolt structure. In this way, the entire blade can be segmented and transported over long distances, reassembled and joined together at the fan installation site, reducing the length, difficulty and cost of blade transport.

The invention adopts the technical idea of letting the blade bearing structure externally with respect to the aerodynamic airfoil. Although there is a loss in aerodynamic efficiency, the blade can be easily extended, the large diameter impeller is realized, and the sweeping area is significantly increased to ensure the wind catching. Power, a low-cost, highly reliable, lightweight large-size horizontal-axis wind turbine blade.

Claims

Rights request

1. A new composite blade of a horizontal-axis wind turbine with independent aerodynamic airfoil and load-bearing structure, characterized in that: the blade has an externally located outside the aerodynamic airfoil (1) and the longitudinal bending stiffness of the lifting blade is externally placed. Longitudinal beam (2).

2. A composite blade according to claim 1, characterized in that the external longitudinal beam (2) is located on the aerodynamic pressure surface (PS) side of the aerodynamic airfoil (1).

3. A composite blade according to claim 1 wherein: along the longitudinal length of the blade, the aerodynamic airfoil (1) comprises at least one segment of the blade having a constant cross section, the blade consisting of a plurality of segments of the blade, each blade The segments all have a constant cross-section of a particular chord length, and for each segment of the constant cross-section of the blade, from the blade root to the tip of the blade, each differential cross-section is continuously twisted at an angle about the central axis of the pitch.

4. A composite blade according to claim 1 wherein the aerodynamic airfoil of the blade (1) has a geometry of different chord lengths and thicknesses at different radial locations obtained from the theory of the leaf element, from the root to the leaf. The chord length and thickness of the sharp blade aerodynamic airfoil (1) continuously decrease.

5. A composite blade according to claim 1 wherein: the outer longitudinal beam (2) is a thin plate having a symmetrical aerodynamic profile structure with a progressively reduced cross-sectional area from the root to the tip.

The composite material blade according to claim 1 or 5, wherein the external longitudinal beam (2) against bending deformation is a carbon fiber reinforced resin composite material.

7. The composite blade according to claim 1, wherein: the pitch axis of the blade and the aerodynamic center axis formed by the aerodynamic airfoil (1) substantially coincide, when the aerodynamic airfoil (1) is a pre-bent blade The two are mainly coincident in the root segment.

8. A composite blade according to claim 1, characterized in that it is naturally disconnected at the segmented joint of the aerodynamic airfoil (1) and is connected by a flange bolt structure.