U.S. patent application number 11/611319 was filed with the patent office on 2007-05-03 for wind turbine comprising elastically flexible rotor blades.
This patent application is currently assigned to AERODYN ENERGIESYSTEME GMBH. Invention is credited to Sonke Siegfriedsen.
Application Number | 20070098555 11/611319 |
Document ID | / |
Family ID | 35431363 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070098555 |
Kind Code |
A1 |
Siegfriedsen; Sonke |
May 3, 2007 |
WIND TURBINE COMPRISING ELASTICALLY FLEXIBLE ROTOR BLADES
Abstract
The invention relates to a wind turbine having a tower, a
nacelle that is mounted on the tower and can be rotated about the
axis of the tower, and a rotor which is carried by the nacelle on
the lee side and having at least one rotor blade. The flexural
strength of the at least one rotor blade permitting the elastic
flexure of said blade by more than half of its extension and
allowing deflection by more than two thirds of its total
length.
Inventors: |
Siegfriedsen; Sonke; (Drage,
DE) |
Correspondence
Address: |
LARSON AND LARSON
11199 69TH STREET NORTH
LARGO
FL
33773
US
|
Assignee: |
AERODYN ENERGIESYSTEME GMBH
Provianthausstrasse 9 D-24768
Rendsburg
DE
24768
|
Family ID: |
35431363 |
Appl. No.: |
11/611319 |
Filed: |
December 15, 2006 |
Current U.S.
Class: |
416/132B |
Current CPC
Class: |
F05B 2240/311 20130101;
F05C 2251/02 20130101; F05C 2253/04 20130101; F05B 2280/6003
20130101; F05B 2240/2213 20130101; F05B 2240/2022 20130101; F05B
2280/5001 20130101; F03D 1/0608 20130101; Y02E 10/72 20130101 |
Class at
Publication: |
416/132.00B |
International
Class: |
B63H 1/06 20060101
B63H001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 5, 2005 |
WO |
PCT/DE05/01547 |
Sep 18, 2004 |
DE |
102004045401.9 |
Claims
1-7. (canceled)
8. A wind turbine having a tower, a nacelle located on the tower
and rotatable about its axis, and a rotor having at least one rotor
blade rotating on the lee side and carried by the nacelle by a hub,
the wind turbine comprising: a) the at least one rotor blade firmly
connected to the hub and fabricated from a high strength material
having a low modulus of elasticity thereby giving the at least one
rotor blade a flexural strength for allowing their elastic flexure
by more than half a total length of said at least one rotor blade
and a constant profile thickness and profile depth over said total
blade length.
9. The wind turbine of claim 8, wherein the flexural strength of
the at least one rotor blade allows for deflection thereof by more
than two-thirds of the total length of said at least one rotor
blade.
10. The wind turbine of claim 8, wherein the constant profile
thickness of said total blade length of said at least one rotor
blade has a relative profile thickness between 5% and 15%.
11. The wind turbine of claim 8, wherein the at least one rotor
blade is made from an extruded composite fiber profile.
12. The wind turbine of claim 11, wherein the at least one rotor
blade is an extruded profile of fiber glass-reinforced plastic.
13. The wind turbine of claim 8, wherein the at least one rotor
blade comprises two rotor blades disposed in outwardly opposed
directions from said hub.
14. The wind turbine of claim 8, wherein the at least one rotor
blade comprises more than two rotor blades disposed in outwardly
directions from said hub.
Description
PRIOR APPLICATIONS
[0001] This application is a continuation-in-part of International
Application No. PCT/DE2005/001547, filed on Sep. 5, 2005, which in
turn bases priority on German Application No. 10 2004 045 401.9,
filed on Sep. 18, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The invention relates to a wind turbine having a tower, a
nacelle mounted on the tower and rotatable about its axis, and a
rotor having at least one rotor blade mounted in a rotary manner in
the nacelle, and rotating on the lee side relative to the
tower.
[0004] 2. Description of the Prior Art
[0005] Over the last few decades, wind power technology has
developed very dynamically, relating only from average size to very
large turbines for main parallel operation. However, there have
been no advances in the last twenty years in the development of
small power systems in the kilowatt range. Therefore, the turbines
are still very expensive and have, consequently, not entered the
market. Wind power use could play an important part in supplying
two billion people without access to electricity. For such cases,
there is a great need for turbines with a power level of 1 to 10
kW, but these must be extremely robust, inexpensive, easy to erect
and largely maintenance-free.
[0006] However, existing small turbines are unable to fulfill these
requirements because they are too expensive and/or too fault-prone.
A particular problem arises in that the turbines must be designed
in such a way as to withstand extremely high wind forces (typhoons,
hurricanes, etc.). The designed wind speeds are up to 70 meters per
second. With such wind speeds, the turbine is decelerated and is at
a standstill.
[0007] In order to achieve this, solutions are known in which the
rotor blades are rotated about their longitudinal axis so as to
reduce shear. In other turbine types the entire nacelle is rotated
out of the wind with the aid of a wind vane or by a pivoting device
in which the complete rotor is brought into helicopter mode. It is
a common feature of all these solutions that they are expensive,
and also fault-prone, so that they are unsuitable for more
widespread use. The same applies with regards to turbines which
have to absorb high, extreme loads using very rigid blades, and
transfer the same to the overall turbine and into the
foundation.
[0008] DE 298 80 145 U1 discloses a wind turbine with an
elastically flexible rotor blade.
[0009] The problem of the invention is to provide a wind turbine of
the aforementioned type, where limited loads are applied to the
overall wind turbine structure due to wind pressure under extreme
wind conditions.
SUMMARY OF THE INVENTION
[0010] According to the invention, this problem is solved by the
construction of the at least one rotor blade with a flexural
strength of the blade profile in the force application direction,
allowing the elastic deflection of the rotor blade by more than
half its total length. In a preferred embodiment, the flexural
strength of the rotor blade permits the deflection by more than
twice its length.
[0011] It is particularly advantageous to have a fixed attachment
of the rotor blade to the hub without any adjustability by means of
bearings or joints, so that fault-proneness is minimized.
[0012] As a result of this pronounced deflection there is, firstly,
a considerable decrease in the projected wind application surface,
and secondly, the resistance coefficient is significantly reduced
as a result of the pronounced outward curvature of the blades
associated with the flexure or deflection. As a result of these two
effects, under extreme wind conditions the wind shear on the entire
turbine can be reduced by half compared with those turbines using
rigid blades. This economized materials for the load-transferring
components, such as the rotor shaft, machine casing, vertical
bearing, tower, anchoring and foundation, so that the total turbine
production costs are significantly decreased.
[0013] The considerable deflection is made possible by the use of
thin aerodynamic profiles in conjunction with the use of high
strength materials, and at the same time a low modulus of
elasticity. Thus, even in the case of pronounced deflections, the
permitted material stresses and strains are not exceeded. The
preferably used relative profile thickness, i.e. the ratio of the
absolute profile thickness to the absolute profile depth, is
between 0.05 and 0.15.
[0014] In a preferred embodiment, the profile thickness and profile
depth are constant over the entire blade length. This development
makes it possible for the at least one rotor blade to be an
extruded fiber composite profile. If the fiber composite material
is a glass fiber plastic composite, the requirement for high
strength and, at the same time, relatively low modulus of
elasticity is fulfilled.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Further features and advantages of the present invention can
be gathered from the following descriptions of the preferred
embodiment with reference to the attached drawings, wherein:
[0016] FIG. 1 shows a side view of the wind turbine comprising
elastically flexible rotor blades with the rotor in a non-bent
position and the wind direction indicated by an arrow.
[0017] FIG. 2 shows a side view of the embodiment of FIG. 1 with
the wind turbine in a decelerated state and the rotor blades in a
bent position from extreme winds.
[0018] FIG. 3 shows an exploded view of the rotor blade in an
extruded position directed by the wind force indicated by the
letter S.
[0019] FIG. 4 shows a diagrammatic representation of the deflection
rate of the rotor blade at different wind speeds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] FIG. 1 illustrates the wind power turbine with tower 10 and
tower anchor 12. The nacelle 14 is mounted so as to rotate about
the axis of tower 10. In nacelle 14 is mounted the rotor 16, which
rotates on the lee side, i.e. on the side of tower 10 that is
remote from the wind. When the rotor 16 is stationary because of
limited wind conditions, and with the turbine operating, the blades
are not or only slightly deflected. The blades are fitted to the
hub with a cone angle, i.e. a tilted arrangement in the wind
direction, so that when the turbine is operating the centrifugal
forces and wind shear forces are such that there are roughly no
bending movements on the blade root. For wind speeds above the
cut-out speed, the turbine is decelerated and brought to a
standstill.
[0021] As illustrated in FIG. 2, the wind power turbine of FIG. 1
is shown in the decelerated state under extreme wind speeds. As a
result of the wind shear, the blades are deflected by more than two
thirds of their total length. As a result of this pronounced
deflection, the wind load is significantly reduced because the wind
application surface is reduced. In addition, the resistance
coefficient of the profile is decreased compared with the flow
direction due to the marked inclination of the blade.
[0022] FIG. 3 illustrates a thin aerodynamic profile of the rotor
blade with a relative profile thickness of approximately 8%, i.e.
the value of the greatest profile thickness 20 relative to the
profile depth 22 is 0.08. As a result, the profile cross-section
has a limited rigidity in the force application direction, and the
wind loading can significantly bend the blade in the force
application direction.
[0023] As illustrated in FIG. 4, the deflection of the flexible
rotor blade is determined by the prevailing wind speed. The
flexural strength is chosen in such a way that at wind speeds of 70
meters per second, it allows an elastic deflection of the blades of
70% of the total blade length.
* * * * *