Rotor Blade of a Wind Power Plant with a Particle Damping Device and Method for Producing Same

Abstract

A rotor blade of a wind turbine with a particle damping device having at least one cavity (3) with inner walls (4) delimiting an interior and with a medium arranged in the interior so as to be movable with respect to the inner walls (4). Additionally, a rotor blade is provided with a vibration-damping mechanism, and a method for manufacture of such a rotor blade.

Claims

1. Rotor blade of a wind turbine with at least one particle damping device having at least one cavity (3) with inner walls (4) delimiting an interior, and with a medium arranged in the interior so as to be movable with respect to the inner walls (4).

2. Rotor blade according to claim 1, characterised in that the particle damping device has a plurality of cavities (3) each with an inner wall (4), each of which contains the medium which is arranged movably with respect to the inner wall (4) in each case.

3. Rotor blade according to claim 1, characterised in that the medium comprises separate particles (2).

4. Rotor blade according to claim 3, characterised in that the particles (2) are balls.

5. Rotor blade according to claim 1, characterised in that the particles (2) are arranged in a viscous fluid.

6. Rotor blade according to claim 1, characterised in that the cavities (3) extend along a width (B) of the rotor blade (1) and are arranged next to one another along a thickness of the rotor blade.

7. Rotor blade according to claim 1, characterised in that the cavities (3) extend along a thickness (D) of the rotor blade (1) and are arranged next to one another along the width of the rotor blade.

8. Rotor blade according to claim 1, characterised in that the plurality of cavities (3) are arranged between webs.

9. Rotor blade according to claim 1, characterised in that the plurality of cavities (3) in cross-section have a recurrent pattern, in particular a honeycomb structure.

10. Rotor blade according to claim 1, characterised in that a trimming mass has particles (2) which are arranged so as to be movable in the cavity (3).

11. Method for manufacture of a particle-damped rotor blade (1), by an interior of the rotor blade (1) being fitted with at least one cavity (3) having inner walls (4) delimiting the interior, a medium which is movable with respect to the inner walls (4) being filled in the at least one cavity (3).

12. Method according to claim 11, characterised in that separate particles (2) are used as the medium.

13. Method according to claim 9, characterised in that a plurality of cavities (3) are arranged in the interior and each of the cavities (3) is filled with the medium.

14. Method according to claim 9, characterised in that the weights of particles (2) of different rotor blades (1) of a wind turbine are matched in their weights such that all rotor blades (1) have the same weight.

15. Method according to claim 11, characterised in that a trimming mass is determined and used as particles (2) of the particle damping device.

Description

[0032] The invention is described below with reference to four exemplary embodiments in thirteen figures. The drawings show:

[0033] FIG. 1 a sectional view of a rotor blade according to the invention with a flap particle damping in a first embodiment,

[0034] FIG. 2 a sectional view of a rotor blade according to the invention in a second embodiment with a flap particle damping,

[0035] FIG. 3 a perspective view of the cavities used in FIG. 1 and FIG. 2 of a honeycomb arrangement,

[0036] FIG. 4 a rotor blade according to the invention in a third embodiment with particles used as a trimming mass,

[0037] FIG. 5 a sectional view of a rotor blade according to the invention in a fourth embodiment, also with particles used as a trimming mass,

[0038] FIG. 6 a graphic illustration of a vibration amplitude of the particle depending on a coefficient of friction and a vibration amplitude of the rotor blade at a first rotation speed,

[0039] FIG. 7 a graphic illustration of a vibration amplitude of the particle depending on a coefficient of friction and a vibration amplitude of the rotor blade at a second rotation speed,

[0040] FIG. 8 a graphic illustration of a dissipated power per mass unit depending on a coefficient of friction and a vibration amplitude of the rotor blade at a first rotation speed,

[0041] FIG. 9 a graphic illustration of a dissipated power per mass unit depending on a coefficient of friction and a vibration amplitude of the rotor blade at a second rotation speed,

[0042] FIG. 10 an illustration of a damping δ over the amplitude y.sub.0 for various coefficients of friction μ at a rotation speed of U-6.30 rpm,

[0043] FIG. 11 an illustration of a damping δ over the amplitude y.sub.0 for various coefficients of friction μ at a rotation speed of U-9.60 rpm,

[0044] FIG. 12 an illustration of a damping δ over the amplitude y.sub.0 for various coefficients of friction μ at a rotation speed of U-6.30 rpm,

[0045] FIG. 13 an illustration of a damping δ over the amplitude y.sub.0 for various coefficients of friction μ at a rotation speed of U-9.60 rpm.

[0046] In the damping of vibrations of a rotor blade 1, we distinguish between vibrations in a flap direction F which runs along a thickness D of the rotor blade 1, and vibrations in an edge direction E which runs along a width B of the rotor blade 1. The two vibration directions are shown in FIG. 1.

[0047] Vibrations in a longitudinal direction L of the rotor blade 1 are ignored here. Particle damping is based on the principle that particles 2 are arranged in a cavity 3 so as to be movable with respect to the inner walls 4 of the cavity 3. A cavity 3 is here a closed space of fundamentally arbitrary size and inner extent. The internal form of the cavity 3 may in principle be arbitrary in any cross-section.

[0048] The cavities 3 may be provided only between two main chords according to FIG. 1, or be arranged next to one another along the entire width B according to FIG. 2.

[0049] The plurality of cavities 3 are arranged in a recurrent pattern according to FIG. 3, e.g. in the form of a honeycomb pattern, wherein the cavities 3 are formed elongate and in each case run along the thickness D or width B, and present the regular pattern shown in FIG. 3, e.g. the honeycomb pattern, in a cross-section perpendicularly to the thickness D or width B.

[0050] According to FIGS. 4 and 5, a trimming mass of the rotor blade 1 is formed as a medium. The trimming mass is preferably also arranged so as to be movable in the interior of the cavity 3. In FIG. 4, the trimming mass is provided between the two main webs, and in FIG. 5 between the one main web and a rotor blade trailing edge.

[0051] At low rotation speeds, only a low centrifugal force forms in the cavity 3. The particles 2 move freely in the cavity 3 and vibration damping takes place in that the particles 2 hit the inner wall 4 and the other particles, and thus absorb the vibration energy of the rotor blade 1.

[0052] For the case that the rotation speed and hence a centrifugal force F.sub.c=a.sub.c*m increases, the particles 2 are pressed against the radially outer wall 4a of the cavity 3. There they become arranged next to one another and, due to the vibration of the rotor blades 1, slide to and fro on the radially outer wall 4a of the cavity 3. This creates friction which absorbs energy and damps the vibration. In the present case, primarily the second dissipation mechanism is concerned, i.e. the friction of the particles 2 on the inner wall 4 of the rotor blade 1.

[0053] For the sake of simplicity, as stated initially, the friction of the particles 2 on the inner wall 4 of the cavity 3 is regarded as the main contribution to the damping system in operation when the wind turbine is turning. The movement equation of the particle 2 is as follows:

m[ÿ(t)+{umlaut over (x)}(t)]+μF.sub.n.Math.sign({dot over (x)}(t))=0.

[0054] Here, y is the deformation (vibration) of the rotor blade 1 at the position at which the system is arranged, and x is the relative position of the particle 2 in the rotor blade 1. This means that when the particle 2 also moves, i.e. for example if the coefficient of friction μ is high, the relative movement is x=0. This the coefficient of friction is low, i.e. the particle 2 does not move with the rotor blade 1 but remains stationary in space, then x=−y.

[0055] μ is the coefficient of friction, m the mass of the particle and F.sub.n the normal force. The normal force is approximately

F.sub.n=m.Math.c.sub.c=m.Math.(ω.sup.2R±g)

[0056] The equation is thus independent of the mass.

[0057] It is assumed that the vibration of the blade is

y(t)=y.sub.0.Math.sin(2πf.sub.et)

wherein f.sub.e is the first natural frequency in the vibration direction (edge or flap). The graphs in FIG. 6 and FIG. 7 show that the amplitude of the particles 2 is small in the case of high friction and low amplitude of the rotor blade vibration; in other words, the particles 2 vibrate with the rotor blade 1. No dissipation by friction takes place here.

[0058] The conservative estimate performed by ourselves shows that the dissipation arises only from the friction between the particles 2 and the inner wall 4 of the cavity 3. In fact, there are further mechanisms such as the mutual impact between the particles 2, and the additional friction of the particles 2 in a viscous medium etc.

[0059] The dissipation energy per rotor revolution per unit mass is:

[00001]$\frac{E_d}{m}=4x_{\mathrm{ampl}}.Math.\mu a_c$

[0060] The dissipative power per mass unit is calculated as:

[00002]$\frac{W_d}{m}=\frac{E_d}{m.Math.f_e}=\frac{4x_{\mathrm{ampl}}.Math.\mu a_c}{f_e}$

[0061] The results are shown in the graphs in FIGS. 8 and 9.

[0062] The vibration energy for the natural mode is:

[00003]$U=\frac{1}{2}{\left(2\pi f_e\right)}^2{u}_e^2=\frac{1}{2}{\left(2\pi f_e\right)}^2{\left(\frac{y_{sys}}{q_{esys}}\right)}^2,$

wherein y.sub.tip is the amplitude of the rotor blade vibration and q.sub.i the amplitude of the natural mode, evaluated at the position of the damping system.

[0063] The damping factor may be defined as a logarithmic decrement

[00004]$\delta =\ln \frac{y\left(t\right)}{y\left(t+T\right)}$

wherein y is the amplitude of the rotor blade vibration and T the vibration duration.

[0064] The logarithmic decrement also amounts to:

[00005]$\delta =\ln \sqrt{\frac{U}{U-E_d}}=\frac{1}{2}\ln \frac{U}{U-E_d}$

[0065] The graphs in FIG. 10 and FIG. 11 illustrate the damping δ with respect to the amplitude y.sub.0 for various coefficients of friction μ and rotation speeds U. The damping δ is a measure of the ratio between the dissipative energy E.sub.d of the particle damping mechanism and the quantity of energy contained in the rotor blade vibration. The graphs in FIG. 10 and FIG. 11 show the correlation for an arrangement of the particle damping mechanism which is provided over 100% of the length of the rotor blade 1. In the graphs in FIGS. 12 and 13, the particle damping mechanism is arranged over 80% of the length of the rotor blade 1.

[0066] According to the present results, a few kilogrammes of particles 2 may, depending on rotor blade type, achieve a doubling of the edge damping of the rotor blades.

LIST OF REFERENCE SIGNS

[0067] 1 Rotor blade [0068] 2 Particle [0069] 3 Cavity [0070] 4 Inner wall [0071] 4a Radially outer wall [0072] B Width [0073] D Thickness [0074] E Edge direction [0075] F Flap direction [0076] L Longitudinal direction