Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Tined or irregular periphery
Reexamination Certificate
2003-02-21
2004-12-14
Nguyen, Hoang (Department: 3748)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Tined or irregular periphery
C416S232000, C416S235000
Reexamination Certificate
active
06830436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wind turbine provided with a nacelle, in which dentation such as serration formed of triangular or trapezoidal teeth is formed in the trailing edge part of each of the blades of the turbine along the length of the blade.
2. Description of the Related Art
Up to now, wind turbine generator equipment having a large electric power generation capacity have been established at high elevations such as on hills and mountains or on the sea where high wind speed can be utilized, the equipment comprising a number of large wind turbine generating units, each wind turbine being provided with a nacelle and generating rotating force by the wind force acting on a plurality of blades attached to the rotor to drive an electric generator connected to the rotor.
An example of a horizontal-axis wind turbine provided with a nacelle will be explained with reference to FIGS.
12
(A) and
12
(B). As shown in the drawings, the wind turbine is mounted on the top of a tapered tube-like tower (support)
4
made of, for example, steel or concrete for revolution in a horizontal plane via a nacelle (box for accommodating apparatuses)
5
, the horizontal drive shaft
3
of a rotor
2
having three blades
1
in front of the nacelle
5
is supported by the nacelle
5
. The horizontal drive shaft
3
is connected to an electric generator(not shown in the drawing) via a speed increasing gearbox (not shown in the drawing) in the nacelle
5
.
The diameter of the surface of revolution of the blades of a conventional large horizontal-axis wind turbine reaches nearly 45 m, and the wind turbine to which the present invention is applied can be composed to have the diameter of the surface of revolution of blade of 10 m to 100 m, not limited to nearly 45 m.
FIGS.
13
(A),
13
(B) and
13
(C) show an example of the blade of prior art of a conventional wind turbine provided with a nacelle, when FIG.
13
(A) is a partial perspective view, FIG.
13
(B) is a sectional view, and FIG.
13
(C) is an enlarged partially plan view of the trailing edge part of the blade.
Referring to FIG.
13
(A), reference numeral
1
is a blade,
11
is the leading edge part,
12
is the trailing edge part,
1
a
is the upper chord surface, and
1
b
is the lower chord surface of the blade
1
. As shown in FIG.
13
(B), the sectional profile of the blade of the wind turbine is a streamlined one, a profile so-called an airfoil, which is tapered off to the rear edge (trailing edge) and less subjected to air resistance, and rotating force results from the lift F effected through the pressure difference arising from the difference between the velocities of air stream S on the lower chord surface
1
b
and upper chord surface
1
a
of the blade
1
.
The blade
1
is made of FRP (fiber reinforced plastic) into a one-piece structure or may be made of porous resin such as foamed polypropylene (polybrene) in the case of a small size blade.
A wind turbine blade consisting of a main blade body part and a rear end part is proposed in Japanese Patent Application Publication 2000-120524, in which the rear end part is formed as a separate member and fixed to the main blade body, and the rear end member constituting the rear end part has a plurality of protrusions of triangular or sawtooth-like tooth formed along the length of the blade in its trailing edge part and extending toward the rear.
According to the disclosure, become the rear end member of the wind turbine blade is formed as a separate member and fixed to the main blade body, the rear end member can be worked separately, and the working thereof becomes easy as the handling of the whole of the large blade is not necessary.
The present invention is directed to forming the rear end member with such high precision that the thickness of the trailing edge can be reduced to a value such that the generation of Karman vortex street is suppressed, and further that vertices which interfere with the generation of the Karman vortex street are generated as a result of the protrusions of triangular or sawtooth-like teeth formed in the trailing edge part along the length of the trailing edge part of the separate rear end member and extending toward the rear, and, as a result, noise level is reduced.
By providing the protrusions of triangular or sawtooth-like teeth in the trailing edge part, the generation of Karman vortex street is suppressed compared with the case in which the trailing edge is straight.
Twisting moment about the longitudinal axis of the blade and bending moment act on the wind turbine blade as a result of its own weight and wind force as it rotates, and shearing and tensile stresses as a result of the moments are easy to concentrate in the leading edge and trailing edge. Particularly, the trailing edge part is liable to be fractured by stress concentration as the thickness thereof is necessary to be thin.
According to the present invention, the front end part and the rear end part of the blade are composed of a plurality of separate members respectively and each separate member can be deformed independently. With this composition, the concentration of stress is alleviated and fracture resulting from stress concentration is prevented.
In this prior art, the rear end part of the wind turbine blade having dentation of triangular or trapezoidal teeth formed in the trailing edge part is formed into a separate member or a plurality of separate members made of hard rubber which is tenacious than the FRP of the main blade body and fixed to the rear end of the main blade body.
When the thickness t of trailing edge part
12
is larger than a certain value, Karman vortex street
19
consisting of a couple of vortex sheets is developed downstream from the trailing edge, the vortex being generated periodically with a cycle proportional to wind speed, and the couple of vortex streets A, A
1
proceed downstream to B, B
1
as shown in FIG.
13
(A). Noise with a frequency proportional to wind speed is generated caused by this phenomenon.
In the case of the blade
1
made of FRP shown in
FIG. 13
, the thickness t of trailing edge of the blade
1
is inevitably relatively large because the sheet of FRP joins at the trailing edge, and it is difficult to suppress the generation of the Karman vortex street
19
completely.
Even when the rear end part (rear end member or members) of the split-type wind turbine blade is made of hard rubber, the thickness t of trailing edge becomes relatively large and as a result the suppression of the noise due to the generation of said Karman vortex street is difficult, so that, in addition to making the rear end part of hard rubber, said dentation is formed in the trailing edge part
12
to allow vertices rotating about the lines parallel to the wind stream passing the tips and roots of the teeth of the dentation to be generated. These vertices suppress the generation of Karman vortex street, and as a result the noise resulting from Karman vortex street is suppressed.
In the prior art as mentioned above, because the main blade body composing most of the blade is made of FRP and the rear end part made of hard rubber is fixed to the rear end of the main blade body, there are problems to be solved such that it is necessary to provide joining part of the FRP sheet in the vicinity of the trailing edge, and that the blade must inevitably be made large in thickness in consideration of the strength of the blade as a whole, which limits blade performance and suppresses improvement of efficiency of the wind turbine.
When the wind turbine provided with a nacelle is in operation, a blade surface boundary layer
21
is formed between air stream S and the surface of the blade
1
, i.e., the upper chord surface
1
a
and lower chord surface
1
b
as shown in FIG.
13
(B) as a result of the construction that an FRP sheet surrounds the vicinity of the trailing edge part. The blade surface boundary layer
21
influences largely upon the performance of the blade
1
. When the thickness &dgr; of the boundary layer
21
Furukawa Toyoaki
Hayashi Yoshiyuki
Kato Eiji
Shibata Masaaki
Armstrong Kratz Quintos Hanson & Brooks, LLP
Mitsubishi Heavy Industries Ltd.
Nguyen Hoang
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