Windmill blades

Abstract

To suppress decrease in lift due to a thickness of a blade rear edge in a blade for a wind turbine.SOLUTION: A blade 14 for a wind turbine includes: a pressure surface 16 oriented windward and smoothly extending to a rear edge; a suction surface 18 oriented leeward and smoothly extending to the rear edge; and a rear edge surface 20 connecting a rear edge 16r of the pressure surface 16 to a rear edge 18r of the suction surface 18 and defining an acute angle with the suction surface 18.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to wind turbine blades, and in particular to the blade airfoil. [Background technology]

[0002] In an airfoil such as a wind turbine blade, a thin trailing edge is preferable to suppress turbulence in the wake of the blade. On the other hand, a certain degree of thickness is required for the trailing edge to ensure the strength and rigidity of the blade. Patent Document 1 listed below discloses an airfoil in which the radius of curvature of a trailing edge portion (6), which connects the suction surface (2) and pressure surface (3) of a gas turbine rotor blade (1, 21, 31) with a continuous curved surface, gradually decreases toward the rear end portion (7). Note that the reference characters in parentheses above are reference characters used in Patent Document 1 listed below, and are not related to the reference characters used in the description of the embodiments of the present application. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-17290 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned Patent Document 1, the thickness of the blade gradually decreases toward the rear end, and there is room for improvement in terms of strength and rigidity. The present invention aims to suppress the deterioration of the performance of a wind turbine blade even when the rear edge is relatively thick. [Means for solving the problem]

[0005] The blades of the wind turbine according to the present invention face upwind, From the leading edge The pressure surface extends smoothly to the trailing edge, and the leeward side faces downward. From the leading edge The suction surface extends smoothly to the trailing edge, and the pressure surface is connected to the trailing edge of the suction surface, forming an angle with the pressure surface. Angle but 60~70°and a trailing edge surface where

[0006] The angle between the pressure surface and the trailing edge surface Angle of 60~70° By doing so, the vortex generated by the airflow flowing along the positive pressure surface can be moved away from the trailing edge of the negative pressure surface, thereby suppressing the effect of the vortex on the airflow flowing along the negative pressure surface.

[0007] The blade can be made of fiber-reinforced resin. Fiber-reinforced resin products require a certain degree of thickness, but by adopting the above-mentioned shape of the blade trailing edge, the effect of the thickness of the trailing edge can be suppressed.

[0008] Also, the blade can be formed by joining a first part on the pressure side and a second part on the suction side. When two parts are stacked, it becomes difficult to make the blade thin, but by adopting the shape of the trailing edge of the blade described above, the effect of the thickness of the trailing edge can be suppressed. Effect of the Invention

[0009] By making the angle between the pressure surface and the trailing edge surface an acute angle, the reduction in lift caused by the thickness of the trailing edge of the blade can be suppressed. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a front view showing the rotor of the wind turbine. [Diagram 2] FIG. 1 is a diagram showing the cross-sectional shape of a wind turbine blade, i.e., an airfoil. [Diagram 3] FIG. 4 is a diagram showing pressure distribution on a blade surface. [Figure 4] FIG. 1 shows an example of a blade formed in two parts. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a front view of a rotor 10 of a wind turbine. The rotor 10 has a swept area of, for example, 200 m 2The rotor 10 is for a small wind turbine. The rotor 10 includes a central hub 12 and three blades 14 extending in three directions from the hub 12. The blades 14 are gradually tapered toward their tips, and the shapes of the cross sections perpendicular to the longitudinal direction are similar to each other. The blades 14 are made of, for example, resin, and more specifically, fiber-reinforced resin.

[0012] Fig. 2 shows the cross-sectional shape (airfoil) of the blade 14 perpendicular to the longitudinal direction, where (a) shows the entire airfoil and (b) shows an enlarged view of the trailing edge of the airfoil. In Fig. 2, the lower side is the windward side, and the surface facing the windward side is referred to as the positive pressure surface 16, and the surface facing the leeward side is referred to as the negative pressure surface 18. Airflows Fp and Fn shown by arrows in Fig. 2 flow from left to right in Fig. 2 along the positive pressure surface 16 and the negative pressure surface 18, respectively. In the direction along these airflows Fp and Fn, the upstream side is referred to as the "front" and the downstream side is referred to as the "rear".

[0013] The leading edge 16f of the pressure surface 16 and the leading edge 18f of the suction surface 18 are smoothly connected at the leading edge of the blade 14. The pressure surface 16 extends smoothly from the leading edge 16f to the trailing edge 16r. Similarly, the suction surface 18 extends smoothly from the leading edge 18f to the trailing edge 18r. The trailing edge 16r of the pressure surface 16 and the trailing edge 18r of the suction surface 18 are separated from each other, and the blade 14 has a trailing surface 20 that connects the trailing edge 16r of the pressure surface to the trailing edge 18r of the suction surface. The trailing surface 20 appears as a straight line in the cross-sectional shape. If the blade 14 is straight in the longitudinal direction and has no twist, the trailing surface 20 is flat. Even if the blade 14 is curved or twisted, the trailing surface 20 can be considered to be approximately flat.

[0014] From the viewpoint of fluid dynamics, it is preferable that the trailing edge of the blade 14 gradually becomes thinner toward the rear and that the positive pressure surface and the negative pressure surface meet at one point, but a certain thickness is also required at the trailing edge to ensure strength and rigidity. In addition, when the blade 14 is produced by resin molding, a certain thickness is required at the trailing edge in order to fill the mold with resin. In particular, in the case of fiber-reinforced resin, a sheet of reinforcing fiber is placed in the mold and filled with resin, so it is necessary to ensure a sufficient thickness at the trailing edge. Thus, when producing an actual blade 14, the trailing edge does not have an ideal shape from the viewpoint of fluid dynamics, and it is necessary to consider the effect of vortices generated at the trailing edge on the performance of the blade 14, especially on lift.

[0015] In the blade 14 of this embodiment, as shown in FIG. 2B, the angle θ between the pressure surface 16 and the trailing surface 20 (hereinafter, referred to as the trailing edge angle θ) is an acute angle. The angle θ may be, for example, 30 to 80° or 60 to 70°. In a wind turbine, the blade advances in a direction transverse to the wind direction, so that the airflow passes the blade and then bends to the leeward side. As shown in FIG. 2, the airflow Fp that flows along the pressure surface 16 bends to the suction surface 18 side after passing the trailing edge 16r of the pressure surface, and generates a wake vortex T. When the trailing edge angle θ is an acute angle, the starting point of the wake vortex T is farther rearward (to the right in FIG. 2) from the suction surface 18 than when the trailing edge angle θ is a right angle, and the position P where the wake vortex T separates from the suction surface airflow Fn flowing on the suction surface 18 is shifted rearward. This reduces the effect on the negative pressure surface airflow Fn, and suppresses the reduction in lift caused by the thickness of the trailing edge of the blade 14.

[0016] Fig. 3 is a diagram showing pressure distribution on the surface of the tip portion of the blade 14. (a) shown on the left side shows the pressure distribution of the blade 14 of this embodiment in which the trailing edge angle θ is an acute angle, and (b) shown on the right side shows the pressure distribution of the blade 114 shown for comparison in which the trailing edge angle θ is a right angle. In each of (a) and (b) of Fig. 3, the upper side shows the pressure distribution of the suction surfaces 18, 118, and the lower side shows the pressure distribution of the pressure surfaces 16, 116.

[0017] In FIG. 3, for the negative pressure surfaces 18, 118, the darker the color, the lower the pressure. It can be seen that the blade 14 of this embodiment has a lower overall pressure than the blade 114 of the comparative example. For the positive pressure surfaces 16, 116, the darker the color, the higher the pressure. It can be seen that the blade 14 of this embodiment has a higher overall pressure. It can be seen that the blade 14 of this embodiment has a higher lift force than the blade 114 of the comparative example, because the pressure is lower on the negative pressure surface 18 and higher on the positive pressure surface 16.

[0018] 4 is a diagram showing an embodiment in which a blade is configured from two parts. The airfoil shape of the blade 34 is the same as that of the blade 14 described above. The blade 34 has a pressure surface 36 and a suction surface 38 that extend smoothly from the leading edge to the trailing edge, and a trailing surface 40 that connects the trailing edges 36r, 38r of the pressure surface 36 and the suction surface 38. The trailing edge angle formed by the trailing surface 40 and the pressure surface 36 is an acute angle, for example, 30 to 80° or 60 to 70°.

[0019] The blade 34 is formed by bonding a first part 42 arranged on the pressure surface 36 side and a second part 44 arranged on the suction surface 38 side with an adhesive 46. The first part 42 and the second part 44 are made of resin, particularly fiber-reinforced resin. The trailing edge of the blade 34 is formed by overlapping the first part 42 and the second part 44. As described above, resin products have a minimum thickness required for molding. When the blade 34 is manufactured by overlapping the first part 42 and the second part 44, the two parts 42, 44 each have a minimum thickness, so that the trailing edge may be thicker than an integrally molded blade. However, by making the angle between the pressure surface 36 and the trailing edge surface 40 an acute angle, the reduction in lift caused by the thickness of the trailing edge can be suppressed. [Explanation of symbols]

[0020] 10 rotor, 12 hub, 14,34 blade, 16,36 pressure side, 16r pressure side trailing edge, 18,38 suction side, 18r suction side trailing edge, 20,40 trailing edge surface, 42 first part, 44 second part, 46 adhesive, Fp (pressure side) airflow, Fn (suction side) airflow, T wake vortex, θ trailing edge angle.

Claims

1. A pressure surface that faces the windward side and extends smoothly from the leading edge to the trailing edge; a suction surface that faces the leeward side and extends smoothly from the leading edge to the trailing edge; a trailing edge surface that connects the trailing edge of the pressure surface and the trailing edge of the suction surface and forms an angle of 60 to 70 degrees with the pressure surface; The blade of a wind turbine.

2. 2. The wind turbine blade according to claim 1, which is made of fiber reinforced resin.

3. 3. A wind turbine blade according to claim 1 or 2, formed by joining the first part on the pressure side and the second part on the suction side.

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