DE102013006203B4 - rotor blade for a wind turbine - Google Patents

Abstract

Rotor blade with a profile (1) which has a suction side (2), a pressure side (3), a profile nose (4), a profile trailing edge (5) and a profile chord (6) with a profile depth (T), wherein the pressure side (3) is convexly curved with a fixed radius (RD), characterized in that the suction side (2) is convexly curved only in a central section (Zb) with a fixed radius (RS).

Description

The present invention relates to a rotor blade having the features of the preamble of claim 1.

Wind turbines are characterized by particularly complex rotor aerodynamics. In addition to the blade rotation, the rotor is also exposed to external influences such as atmospheric turbulence and temporal and spatial fluctuations in the flow velocity. Many of these fluid mechanics problems in wind turbines are closely related to those in helicopter rotors and are therefore directly transferable.

In order for the aerodynamic lift of a rotor blade to fully develop its lift force, the wind flow must remain in contact with the profile of the rotor blade for as long as possible. The longer the flow remains in contact with the rotor blade, the noise emissions from the rotor tip are also reduced.

From the DE 10 2008 052 858 A1 is a family of aerodynamic profiles designed to optimize the performance of wind turbines. These profiles are characterized by the fact that the skeleton line runs at least partially below the chord in the direction of the pressure side.

Furthermore, the DE 36 40 780 A1 Wing profiles are known for fluid-technical systems such as aircraft, air and water propellers or power plants. The wing profiles have pointed leading and trailing edges, whereby the flow path from the leading to the trailing edge should be the same on both sides of the wing profile. Furthermore, the flow resistance should be reduced by the largest possible radii of the wing sides.

It is an object of the present invention to provide a rotor blade which has good aerodynamic properties and reduces the noise emission emanating from the rotor tip.

This object is achieved by a rotor blade having the features of claim 1.

According to this, a rotor blade is provided with a profile that has a suction side, a pressure side, a profile nose, a profile trailing edge and a profile chord with a profile depth, wherein the pressure side is convexly curved with a fixed radius, in which the suction side is only convexly curved in a central section with a fixed radius. The circular shape of the suction side causes the air mass to be applied for a long time.

In the inventive embodiment, it is advantageous if the middle section of the suction side has at least one length whose projection onto the profile chord extends over a range of 10% to 90% of the profile depth from the profile nose. As a result, the flow is particularly long, namely up to 90% of the profile depth from the profile nose.

Furthermore, it is preferably provided that the radius of the pressure side is equivalent to twice the profile depth.

It is advantageous if the radius of the suction side is equivalent to the profile depth.

In addition, it is advantageous if the front and rear sections of the suction side are connected to the circular middle section of the suction side in such a way that the mathematical function of the course is differentiable.

In the inventive embodiment, the twisting and tapering of the profile also has a linear course that is adapted to the diameter of the rotor. This makes it possible to achieve a constant flow speed of the wind on the rotor blade from the blade root to the blade tip, which ensures optimal energy yield and low-noise operation.

• 1: einen Querschnitt eines Rotorblattes,
• 2: schematische Darstellung einer Windkraftanlage,
• 3: Profilansicht einer linearen Profilverdrehung, sowie
• 4: Konstruktionsskizze der linearen Profilverdrehung.

A preferred embodiment of the invention is explained in more detail below with reference to the drawing. It shows:

• 1 : a cross-section of a rotor blade,
• 2 : schematic representation of a wind turbine,
• 3 : Profile view of a linear profile twist, as well as
• 4 : Design sketch of the linear profile twist.

In the 1 a profile 1 of a rotor blade according to the invention is shown. The profile 1 is defined by its suction and pressure side 2,3 and a profile depth T. The profile depth T is defined as the straight connection from the profile nose 4 to the profile trailing edge 5. The curvature of the pressure side 3 is constant with a radius R _D . The radius R _D is equivalent to the profile depth T.

The course of the suction side 2, however, can be divided into three sections: a front, a middle and a rear section Z _a ,Z _b ,Z _c . To describe the sections Z _a ,Z _b ,Z _c , two points A,B are defined on the profile chord 6: the first point A is located from the profile nose 4 starting at a depth of 10% of the profile depth T, the second point B is located from the profile nose 4 at a depth of 90% of the profile depth T. The front section Z _a of the suction side 2 is then defined as the piece from the profile nose 4 to the first intersection point at which the perpendicular from the first point A of the profile chord 6 intersects the suction side 2. The section from this first intersection point to the second intersection point at which the perpendicular from the second point B of the profile chord 6 intersects the suction side 2 is referred to as the middle section Z _b . Furthermore, the rear section Z _c is given as the section between the second intersection point and the profile trailing edge 5. The course of the middle section Z _b has a constant curvature with a radius R _s , which is equivalent to twice the profile depth T. The front and rear sections Z _a , Z _c connect the middle section Z _b of the suction side 2 with the profile nose 4 and profile rear side 5 in such a way that the descriptive mathematical function is differentiable at every point and a convex course of the suction side 2 is maintained.

The circular course of the middle section Z _b of the suction side 2 results in a longer flow and thus largely reduces the noise emission.

The setting angle shown between the rotor plane and the profile chord 6 is at the position at the blade root. The twisting and tapering of the profile is linear and depends on the diameter of the rotor. Preferably, the profile has a taper from the blade root to the blade tip in the profile depth and the profile height perpendicular to this by half.

2 shows a wind turbine which has a rotation axis d of the rotor, a hub 7 and rotor blades 8 extending from the hub 7 with blade root 9 and blade tip 10. Here, r _s is the distance between the rotation axis d of the rotor and the blade tip 10, r _{m is} the distance between the rotation axis d of the rotor and the rotor blade center and r _{w is} the distance between the rotation axis d of the rotor and the blade root 9.

3 shows a rotor blade twist. Since the blade tip 9 has a higher speed than the blade root 10, the profile 1 of the rotor blade must become flatter from the blade root to the blade tip. This is preferably achieved by twisting the profile, whereby a twist angle α(r), which describes the angle of the profile chord at a distance r from the axis of rotation d of the rotor to the profile chord at the blade root 61, changes linearly.

3 shows profile 1 at the blade root with profile chord 61 and the profile at the blade tip with profile chord 62. For the sake of completeness, the direction of the wind flow is designated W and D indicates the direction of rotation of the rotor. The diameter of the rotor in this special embodiment is 5 m. The pitch S, the distance the wind travels along the rotor that is required for one rotation of the rotor, is 2.50 m. The greater the pitch S, the more wind flow through the rotor, greater torque, easier starting of the rotor and lower speed with less noise. The desired revolutions per minute of the rotor are achieved by adjusting the pitch S to the wind speed. Since the pitch S along the rotor from the blade root to the blade tip is preferably constant, the twist angle α between the blade root and blade tip in this specific example is 38.84°.

In general, the angle of rotation α(r) for a constant slope S is given by the following equation: $$\alpha \left(r\right)={\text{tan}}^{-1}\left(\frac{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="DE102013006203B4\_0003.png"\; state="\{\{state\}\}">S</figure-callout>}}{2\mathrm{\pi }r}\right)-{\text{tan}}^{-1}\left(\frac{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="DE102013006203B4\_0003.png"\; state="\{\{state\}\}">S</figure-callout>}}{2\mathrm{\pi }{r}_w}\right).$$

4 shows the geometric construction of the angle of rotation α(r) for the embodiment of the 3 . The slope S is plotted on the vertical axis and the circumference of the rotor at the blade tip is plotted on the horizontal axis. These two axes form the legs of a right-angled triangle, where the angle α(r _s ) between the hypotenuse and the adjacent side is the sum of the twist angle α _s to be determined and the angle α(r _w ) = α _w , and where the angle α _w is determined by plotting the circumference of the rotor at the blade root on the horizontal axis and reading off the angle between the new hypotenuse and the new adjacent side with the slope S remaining the same. To also determine the twist angle α _m of the center of the rotor blade, plot the circumference of the rotor at the center of the rotor blade on the horizontal axis and read off the angle α(r _m ) between the new hypotenuse and the new adjacent side with the slope S remaining the same and subtract α _w .

The twist angle α(r) thus indicates the twist of the profile starting from the blade root of the rotor blade.

To regulate the performance, the so-called angle of attack of the rotor, the angle between the direction of the incoming air flow and the profile chord, is changed. The angle of attack is set at the blade root so that this angle rotates the entire rotor blade relative to the incoming air flow. By twisting the rotor blade, the angle of attack always flattens linearly from the blade root to the blade tip.

Using the profile twisting according to the invention, the twisting angle α(r) can be calculated for any point on the rotor blade. The linear profile twisting and its design can be used for all sizes of wind turbines, all pitches and all angles of attack. Using the twisting of the rotor blade profile according to the invention, a constant pitch can be achieved from the blade root to the blade tip, which means that the rotor rotates quietly and energy efficiently.

reference sign

1

profile

2

suction side

3

print page

4

profile nose

5

profile trailing edge

6

profile chord

61

profile chord

62

profile chord

7

hub

8

rotor blade

9

leaf root

10

leaf tip

T

tread depth

RD

Radius print side

RS

radius suction side

Za

front section

Zb

middle section

Zc

rear section

d

axis of rotation rotor

rs

distance d-10

rm

distance d-8

rw

distance d-9

D

direction of rotation of the rotor

W

direction of the wind

αs

angle of twist between the profile chord of the blade root and the profile chord of the blade tip

αw

Angle between the axis of rotation and the profile chord of the blade root

αm

Twist angle between the profile chord of the blade root and the profile chord of the blade center

Claims (8)

Rotor blade with a profile (1) which has a suction side (2), a pressure side (3), a profile nose (4), a profile trailing edge (5) and a profile chord (6) with a profile depth (T), wherein the pressure side (3) is convexly curved with a fixed radius (R _D ), characterized in that the suction side (2) is convexly curved only in a central section (Z _b ) with a fixed radius (R _S ). rotor blade after claim 1 , characterized in that the middle section of the suction side (Z _b ) has at least a length whose projection onto the profile chord extends over a range of 10% to 90% of the profile depth (T) from the profile nose (4). Rotor blade according to at least one of the preceding claims, characterized in that the radius (R _D ) of the pressure side (3) is equivalent to twice the profile depth (T). Rotor blade according to at least one of the preceding claims, characterized in that the radius (R _S ) of the suction side (2) is equivalent to the profile depth (T). Rotor blade according to at least one of the preceding claims, characterized in that the front and rear sections of the suction side (Z _a , Z _c ) are connected to the circular middle section of the suction side (Z _b ) in such a way that the mathematical function of the course is differentiable. Rotor blade according to at least one of the preceding claims, characterized in that a twist and a taper of the profile from a blade root (9) to a blade tip (10) have a linear course which is adapted to the diameter of the rotor. rotor blade after claim 6 , characterized in that the twisting of the profile depends on a pitch (S) and the diameter of the rotor, so that the pitch (S) is constant from the blade root (9) to the blade tip (10). rotor blade after claim 7 , characterized in that the twisting with a twist angle (α(r)), which indicates the angle between a profile chord at the blade root and a profile chord at a distance (r) from a rotation axis (d) of the rotor, and a distance (r _w ) from a rotation axis (d) of the rotor to the blade root (9) by $$\alpha \left(r\right)={\text{tan}}^{-1}\left(\frac{S}{2\mathrm{\pi }r}\right)-{\text{tan}}^{-1}\left(\frac{S}{2\mathrm{\pi }{r}_w}\right)$$

is given.

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