U.S. patent application number 12/138915 was filed with the patent office on 2008-12-25 for blade for a horizontal-axis wind generator.
Invention is credited to Manuel Torres Martinez.
Application Number | 20080317599 12/138915 |
Document ID | / |
Family ID | 39824386 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080317599 |
Kind Code |
A1 |
Martinez; Manuel Torres |
December 25, 2008 |
BLADE FOR A HORIZONTAL-AXIS WIND GENERATOR
Abstract
The invention relates to a blade for a horizontal-axis wind
generator consisting of two flattened bodies which are arranged
opposite one another in longitudinal convergence towards the tip
without making contact with one another, said bodies being attached
by means of an intermediate latticework formed by ties (3) with an
aerodynamic profile, which ties are joined to the flattened bodies
by means of hinged attachments providing flexibility to the
structural assembly for preventing fatigue fractures.
Inventors: |
Martinez; Manuel Torres;
(Torres De Elorz (Navarra), ES) |
Correspondence
Address: |
LUCAS & MERCANTI, LLP
475 PARK AVENUE SOUTH, 15TH FLOOR
NEW YORK
NY
10016
US
|
Family ID: |
39824386 |
Appl. No.: |
12/138915 |
Filed: |
June 13, 2008 |
Current U.S.
Class: |
416/182 |
Current CPC
Class: |
F03D 80/00 20160501;
Y02E 10/721 20130101; Y02E 10/74 20130101; F03D 9/25 20160501; F03D
3/062 20130101; Y02E 10/72 20130101; F03D 1/0633 20130101; F03D
1/0675 20130101 |
Class at
Publication: |
416/182 |
International
Class: |
F01D 5/22 20060101
F01D005/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2007 |
ES |
200701720 |
Claims
1. A blade for a horizontal-axis wind generator of the type formed
by a biplane assembly, characterized in that it consists of two
essentially equal aerodynamic flattened bodies (1) and (2) which
are arranged opposite one another, which bodies longitudinally
extend in convergence from the blade root to the tip without making
contact with one another, with an intermediate latticework for the
attachment between said bodies (1) and (2) formed by ties (3) also
having an aerodynamic profile, the attachments of said ties (3) of
the intermediate latticework to the flattened bodies (1) and (2)
being formed by means of hinged attachments providing
flexibility.
2. The blade for a horizontal-axis wind generator according to
claim 1, characterized in that the oblique ties (3) of the
intermediate latticework are oriented such that the resultant of
the aerodynamic forces thereof collaborates in extracting energy
from the wind acting on the blade.
3. The blade for a horizontal-axis wind generator according to
claim 1, characterized in that according to an embodiment, the
attachments between the ties (3) of the intermediate structure and
the flattened bodies (1) and (2) are formed with a support (4)
fixed on the central structural case (6) of the corresponding
flattened body (1) or (2), and a screw (7) coupled to the
respective tie (3), said screw (7) having a ring-shaped head (8),
by means of which a hinged attachment is formed with the
corresponding support (4) by means of a pin (9).
4. The blade for a horizontal-axis wind generator according to
claim 1, characterized in that the flattened bodies (1) and (2) are
attached at the end of the blade by means of a transverse strut
(10) with an aerodynamic section.
Description
FIELD OF THE ART
[0001] The present invention relates to wind generators which are
used for electricity production by means of using wind energy,
particularly those of the horizontal-axis type having a blade rotor
which is arranged facing the wind to receive a rotating drive,
proposing a blade with a particular structural embodiment for said
wind generators.
STATE OF THE ART
[0002] Horizontal-axis wind generator blades usually have an
aerodynamic configuration in a monoplane embodiment, such that as
the size of said blades increases, drawbacks arise in the following
aspects:
[0003] The maximum length is limited by the transport, which
implies having to renounce a percentage of the output in order to
facilitate moving them to parks for installing the wind
generators.
[0004] The blades structurally need to be very thick, and as a
consequence of the length limitations, the aerodynamic profiles
which are used have a high relative thickness, which makes their
aerodynamic efficiency decrease, thereby reducing energy
efficiency.
[0005] There is considerable bending at the tip and this can cause
the blade to hit the wind generator tower, which forces using
shapes affecting the output and complicating the manufacture.
[0006] The manufacture of each blade is expensive since a large
amount of material must be incorporated.
[0007] Long lengths create buckling problems for the structural
skins of the blades, making it necessary to increase the thickness
of the cores of the blades in order to stabilize them.
[0008] The diameter of the bearing for coupling blades on the hub
increases, its cost being raised and there being few manufacturers
of the necessary bearings.
[0009] Access to wind generator installation parks needs expensive
tracks due to the means of transport which must be used.
[0010] Several solutions of constructive implementations of the
blades have been developed in order to cancel out these drawbacks,
for example:
[0011] French patent document FR 2609506 describes a constructive
solution of blades formed according to a ring-shaped
configuration.
[0012] Patent documents WO 03/036082, U.S. Pat. No. 6,902,370 and
U.S. Pat. No. 6,972,498 describe constructive solutions of blades
formed telescopically.
[0013] European patent document EP 0 064 742 describes a
constructive solution of two twin blades arranged in a common
support for coupling to a rotating rotor, each of the blades having
an independent rotational movement for its orientation.
[0014] Patent documents U.S. Pat. No. 1,780,431, U.S. Pat. No.
4,081,221 and WO 2006/128940 describe constructive solutions of two
or more blades fixedly associated on a common support for coupling
to the rotating rotor to be actuated.
[0015] Patent document U.S. Pat. No. 1,820,529 describes a
constructive solution of blades formed by two bodies diverging from
the tip of the blade to the base thereof, said bodies being
attached at the separation part by means of intermediate ties.
[0016] All these solutions have the purpose of providing a blade
surface which allows fulfilling the necessary efficiency of
collecting the action of the wind, with length dimensions making it
possible to overcome the previously mentioned drawbacks as best as
possible. However such solutions do not provide characteristics
properly ensuring the structural strength of the blades for the
working function for which they are intended, having to resort to
constructive forms with expensive materials and very heavy elements
reducing the efficiency of the blades.
OBJECT OF THE INVENTION
[0017] According to the invention a blade intended for
horizontal-axis wind generators is proposed, which blade has been
developed according to a structural configuration effectively
solving the problems derived from an oversized length, providing
characteristics that improve the performance of the blade in its
application function without negatively affecting the transport,
since the maximum length of the structural assembly of the blade is
within normal transport ranges.
[0018] This blade object of the invention is made up of two
essentially equal, independent flattened bodies which extend
opposite one another, converging from the blade root to the tip
without making contact with one another, with an attachment between
said bodies by means of a lattice structure formed with ties having
an aerodynamic profile and an attachment of such ties to the
flattened bodies by means of hinged couplings.
[0019] A blade structure is thus obtained in which the hinged
attachments between the ties of the central latticework and the
flattened bodies provide a flexibility preventing rigid stress
points prone to fatigue fractures as a consequence of the stress
that the blade is subjected to in the work of its application
function.
[0020] Said blade structure thus has the necessary rigidity and
strength, but having a shock load-damping quality, provided by the
attachment between the ties of the central latticework and the
flattened bodies, that the loads transmitted to the hub on which
the blade is coupled and the occasional loads in the areas of the
structural attachments of the blade itself decrease.
[0021] The relative geometric arrangement between the two flattened
bodies of the blade further allows placing the elastic axis in the
desired position, such that with sudden changes in the direction or
intensity of the wind, the system reacts by twisting itself and
lowering the angle of attack even before the pitch control system
reacts. The response time is thus reduced, which thus achieves
decreasing the value of the mechanical load peaks in the wind
generator, the generated power peaks and rotational overspeeds.
[0022] In addition, the use of a biplane blade system attached by
latticework considerably increases rigidity with respect to a
biplane blade attached only at the root and at the tip, which
increases the natural frequency value of the vibration modes of the
blade, and the pitch control system of the wind generator can
therefore be faster.
[0023] This allows increasing the band width of the pitch control
system, raising the relative influence of the modification of the
pitch angle (.beta.) control on the rotor speed (O), such that this
allows controlling larger blades in which the increase of the
radius of the blade raises the relative influence of the
modification of the wind speed (V) on rotor speed (O), i.e., the
partial derivatives ratio .differential..OMEGA./.differential.V,
more proportionally than the partial derivatives ratio
.differential..OMEGA./.differential..beta..
[0024] The aerodynamic profile of the ties of the latticework
attaching the flattened bodies to one another in turn allows
optimizing output, since said ties have minimum aerodynamic drag,
slowing the blade down very little in the rotational direction
insofar as the oblique ties can be oriented such that the resultant
of the aerodynamic forces collaborates in extracting energy from
the wind, minimizing the loads on the blade.
[0025] In addition, from the structural point of view, the strong
areas can be further separated and provide greater inertia to each
section without jeopardizing the aerodynamics, since the
aerodynamic function is separate from the structural function,
profiles having little relative thickness and high efficiency being
able to be used, with which profiles great structural rigidity is
achieved in this case.
[0026] Furthermore the manufacture of the component elements of the
blade is simplified and the amount of material necessary is
reduced, less severe buckling conditioners, as well as lower weight
being achieved, which allows decreasing the diameter of the
coupling for fastening the blade in its assembly.
[0027] The transport is equally simplified upon decreasing the
maximum length of the blade, even being able to separately
transport the component elements and assemble them in the
installation site of the wind generators applied.
[0028] The decrease of blade tip losses, and accordingly an extra
output increase, can also be achieved as a secondary effect by
means of aerodynamically placing a transverse strut at the end of
the blade, thereby essentially preventing the circulation of air
between the lower side and upper side of each of the component
flattened bodies, such that the drop of the induction factor is
emphasized in that area, whereby the outer area of the blade
operates better and the global output increases.
[0029] The effect of reducing the generation of marginal vortexes
also decreases the noise caused by the blade, which allows reaching
higher rotational speeds since the main limitation to rotational
speed is currently the noise caused by the blades. The increase of
the rotational speed further involves a savings in the costs of the
generator and other mechanical elements, as well as an increase in
the output by being able to operate at the optimal ratio between
the rotational speed and the wind speed during a longer operating
range.
[0030] From an aerodynamics point of view, the configuration of the
proposed blade has a series of particularities which can be used
such that on one hand the component flattened bodies of the blade
are shorter than the conventional blades with a single body, the
length of this new blade structure depending on the gap between the
flattened bodies and the aerodynamic interference factor between
them.
[0031] On the other hand, the gap between the two flattened bodies
and the stepping between them influences the lift coefficients of
each body and the strength of the assembly, such that the two
flattened bodies can be sufficiently separated so as to perform
like independent profiles or the interference between them can be
positively used bringing them closer to one another. The pressure
fields equally vary, resulting in being able to obtain benefits
such as delaying the stall or obtaining an increase in the lift
coefficients.
[0032] There is an additional degree of freedom which can also be
used, consisting of the possibility of arranging each of the
flattened bodies at different angles of attack, whereby the
performance of the blade can be optimized. The position of the
pressure center can further be varied with the influence that this
represents in the necessary torque in the pitch axis.
[0033] Said configuration of the proposed blade in turn allows
using flattened bodies having little relative thickness to the
blade root with good aerodynamic efficiency, thus overcoming the
main reasons which conventional long blades have for not reaching a
higher output, due to tip stalls and the use of profiles different,
from those which would be necessary, the latter due to the fact
that in approaching the blade root a certain height of the central
case of the blade is necessary for supporting large bending loads
occurring, which forces increasing the relative thickness, and
consequently an efficiency loss occurs, since below approximately
20% of the span, the necessary length greatly complicates
logistics, so the law of optimal length is no longer followed and
cylindrical geometry is used for attaching the blade to the
assembly hub in the wind generator, which makes it necessary to use
profiles having a high relative thickness (greater than 30% having
worse aerodynamic properties.
[0034] Said blade object of the invention therefore has certainly
advantageous features, acquiring its own identity and preferable
character with respect to conventional blades which are being used
in wind generators for the same function.
DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 shows a side view of a wind generator blade
structured according to the invention.
[0036] FIG. 2 shows a perspective view of an embodiment of a
flattened body for forming the proposed blade.
[0037] FIG. 3 is an exploded perspective view of a detail of the
hinged attachment of ties of the central latticework to one of the
flattened bodies in the proposed blade.
[0038] FIG. 4 is a sectioned frontal view of the assembly of the
previous figure assembled.
[0039] FIG. 5 is a perspective view of the end section of a blade
according to the invention with the ends of the flattened bodies
attached by means of an aerodynamic transverse strut.
[0040] FIG. 6 is a perspective view of a wind generator with blades
structured according to the invention.
[0041] FIG. 7 is an enlarged side view of the upper part of the
wind generator of the previous figure.
[0042] FIG. 8 is an enlarged perspective of the upper part of the
previous wind generator without the casing of the body for housing
the generator.
DETAILED DESCRIPTION OF THE INVENTION
[0043] The object of the invention relates to a blade for
horizontal-axis wind generators with a constructive embodiment
which improves the functional performance and strength of the blade
and allows achieving a high output with a relatively small
longitudinal dimension.
[0044] The proposed blade is formed with two essentially equal,
aerodynamically flattened bodies (1) and (2) which are arranged
opposite one another, longitudinally converging from the blade root
to the tip without making contact with one another at the end.
[0045] In forming the blade said flattened bodies (1) and (2) are
attached to one another by means of an intermediate latticework
formed by ties (3), whereby achieving a strong structural assembly,
the flattened bodies (1) and (2) of which add a wind collection
function allowing a high drive performance by the wind with a
relatively small length, such that the blade can be constructed
with suitable lengths for normal transport means.
[0046] According to a particular feature, the ties (3) of the
intermediate latticework of the blade are formed with profiles that
are also aerodynamic, such that said ties cause minimum drag
slowing down the blade in the direction of its movement, which
accordingly allows optimizing the output of said blade movement in
the function applied in wind generators.
[0047] The oblique ties (3) of the mentioned structural
intermediate latticework of the blade can be further oriented such
that the resultant of the aerodynamic forces thereof collaborates
in extracting energy from the wind, thus reducing the loads which
the blade must support in the function of its application.
[0048] In addition, said ties (3) of the structural intermediate
latticework of the blade are attached to the flattened bodies (1)
and (2) by means of hinged attachments, as shown in FIGS. 3 and 4,
whereby these attachment points offer a flexibility that prevents
stresses which can cause fatigue fractures, such that the
constructive blade structure is certainly strong for supporting the
stresses and loads which the blade must support in the work
function of its application.
[0049] According to one embodiment, the mentioned hinged
attachments between the ties (3) of the intermediate latticework
and the flattened bodies (1) and (2) of the blade are formed with a
support (4) which is fixed by means of screws (5) on the central
structural case (6) of the corresponding body (1) or (2), and a
screw (7) coupled to the respective tie (3), said screw (7) being
attached in a pivoting manner by means of a ring-shaped head (8) it
has at its end, on the support (4) of the attachment by means of a
pin (9) acting as a hinge pin.
[0050] The flattened bodies (1) and (2) are attached to one another
at the end of the blade by means of a transverse strut (10), as
shown in FIG. 5, said strut (10) also having an aerodynamic
section, whereby essentially preventing the circulation of air
between the lower side and upper side of the flattened bodies (1)
and (2) in that area, the drop of the induction factor being
emphasized, and accordingly a decrease in blade tip stalls is
achieved, thus achieving an extra output increase.
[0051] The proposed blade can be applied in horizontal-axis wind
generators having a rotor (11) with blades (12) for being driven by
the wind, for the purpose of providing the rotating operation of
the electric power production generator (13) which is housed in the
body (14) of the wind generator, according to FIGS. 6 to 8.
[0052] The structural formation of the flattened bodies (1) and (2)
forming the blade according to the invention can have any
constructive solution, FIGS. 2, 3 and 4 showing a non-limiting
embodiment of said flattened bodies (1) and (2) comprising a
central case (6) formed by two U-shaped halves fitted together with
an outer coating (15) determining the aerodynamic structural
configuration.
* * * * *