Note: Descriptions are shown in the official language in which they were submitted.
CA 02606927 2007-10-18
CURVED BLADE FOR WIND TURBINES
Field of the Invention
[0001]The present invention generally pertains to horizontal wind turbines,
and in
particular to a blade suitable for use on wind turbines in which the blade
comprises a
concave curved trailing edge and a convex curved leading edge.
Background of the Invention
(0002] Wind is a powerful renewable energy source that civilizations have
harnessed to
varying degrees for several thousand years. Historians accredit ancient
Mesopotamia
and Egypt as giving rise to sail-based propulsion systems for boats, while
most
accounts accredit ancient Persia as having developed and implemented windmills
in
500 to 900 AD. In around 1390, the Dutch began to refine the windmill,
eventually
implementing thousands for various applications such as irrigation, land
drainage, grain-
grinding, saw-milling and the processing of commodities.
[0003]With the current awareness of global warming and the human impact upon
the
environment, there is an increasing shift towards greener, ecologically-
friendly
technologies. While fossil fuel-fired and nuclear power plants have been
standard
methods of power generation for the last century, alternative methods for
power
generation, particularly from renewable energy sources such as the sun and
wind have
been attracting increasing attention from industry, governments and the
general public.
[0004]Modern windmills for power generation, or wind turbines, are growing in
popularity, with wind farms being established in many countries around the
world.
Modern windmills come in a variety of sizes and configurations, but many
people
associate them with the large horizontal wind turbines used for large scale
energy
generation. These large turbines can stand as tall as 90 meters, with
generally three
equidistantly spaced blades measuring upwards of 30 meters each.
[0005]At the same time, there is growing interest for smaller turbine units
that are 3kW
to 99 kW that are better suited to farm and residential application.
Unfortunately, these
smaller units are subject to less than optimal wind characteristics as they
are generally
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located on lower towers for aesthetic, economic, and practical reasons. As
such, there
is a need for smaller turbine units having wind capturing characteristics that
are suited
for the conditions under which these smaller turbine units are operated.
Summary of the Invention
[0006]According to an aspect of an embodiment, provided is a curved blade for
use on
horizontal wind turbines, the blade comprising a substantially semicircular
tip portion; a
substantially semicircular counter-tip portion opposite the tip portion; and a
body portion
extending between the tip portion and the counter-tip portion, the body
portion being
further defined by a concave curved trailing edge and a convex curved leading
edge.
[0007]According to a further aspect of an embodiment, provided is a curved
blade for
use in a blade rotor assembly, said blade comprising a substantially
semicircular tip
portion; a substantially semicircular counter-tip portion opposite the tip
portion; and a
body portion extending between the tip portion and the counter-tip portion,
the body
portion being further defined by a concave curved trailing edge and a convex
curved
leading edge.
Brief Description of the Drawings
[0008]Embodiments of the present application will now be described, by way of
example only, with reference to the attached Figures, wherein
Figure 1 is a front perspective view of an embodiment showing a complete wind
turbine;
Figure 2 is a perspective view of the wind assembly of the embodiment shown in
Figure
1;
Figure 3a is a front view of a wind turbine blade according to a first
embodiment,
wherein the chord is constant throughout the body portion;
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Figure 3a is a front view of a wind turbine blade according to a first
embodiment, wherein the
chord is constant throughout the body portion;
Figure 3b is a front view of a wind turbine blade according to a second
embodiment wherein
maximum chord occurs at a intermediate region between the tip and counter-tip
portions;
Figure 4 is a side view of the wind turbine blade, shown mounted on a stem;
Figure 5a is a rear view of the wind turbine blade, schematically shown
mounted on a rotor.
Figure 5b is a sectional view of the wind turbine blade of Figure 5a, shown
though section a-a;
Figure 6 is a perspective view of a first stem/mounting block arrangement for
mounting the wind
turbine blade to a rotor;
Figure 7 is a perspective view of an alternate stem/mounting block arrangement
for mounting the
wind turbine blade to a rotor.
Figure 8a is a front view of an alternate wind turbine blade arrangement on a
stem, wherein the
blades are of substantially the same dimension; and
Figure 8b is a front view of a further alternate wind turbine blade
arrangement on a stem,
wherein the distal blade is smaller than the proximal blade.
Description of the Preferred Embodiments
100091 The curved blade having a curved convex leading edge and a curved
concave trailing
edge described below is suitable for use on a wide range of horizontal wind
turbines, such as the
horizontal dual-rotor wind turbine described in Applicant's U.S. Patent No.
8002526 entitled
"ROTOR DRUM".
100101 Referring now to FIGURE 1, shown for exemplary purpose is a
horizontal dual-rotor
wind turbine, indicated by reference numeral 10. The dual rotor wind turbine
10 generally
comprises a wind assembly 12 rotatably mounted on a tower 14.
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[0011]The wind assembly 12 generally comprises a rotor assembly having
arranged
thereon a plurality of a equidistantly spaced-apart blades. In the example
shown in
Figure 2, a dual rotor assembly is provided comprising a primary rotor
assembly 16 and
an auxiliary rotor assembly 18, each rotor assembly having mounted thereon a
plurality
of blades 20, the blades being circumferentially equidistantly spaced on
respective
rotors 22, 24. As shown, both the primary rotor assembly 16 and the auxiliary
rotor
assembly 18 comprise four blades each, and both assemblies work cooperatively
to
rotate a common generator shaft 26 from a generator 28 affixed to a rotatable
tower hub
30 (generator shown detached from rotor assemblies for clarity). To enable the
wind
assembly 12 to rotate relative to the tower 14, and in particular towards the
incurrent air
(upwind orientation), the tower hub 30 is provided with a rotatable yaw
bearing surface
32. Rotation of the wind assembly 12 about tower hub 30 is facilitated by a
tail
assembly mounted downwind of the wind assembly, the tail assembly generally
comprising a tail boom 34 and vane 36.
[0012]As shown in Figure 3a and 4, the blade 20 is generally planar and
comprises a
curved configuration. Each blade 20 comprises a tip portion 42 at the distal
end of the
blade, and a counter-tip portion 40 closest the rotor, defining an opposite
end of the tip
portion 42. A body portion 44 extends between the tip portion 42 and the
counter-tip
portion 40, defining a concave curved trailing edge 46 and a convex curved
leading
edge 48. As such, for the purposes of the following description, the blade is
generally
referred to as a convex/concave curved blade 20. Overall, the convex/concave
curved
blade 20 further defines a windward side 50 upon which the incurrent air
exerts a force,
and a leeward side 52 opposite the windward side 50, upon which suitable
mounting
hardware is located, as shown in Figure 4, and described below. As shown, the
counter-tip portion 40 and tip portion 42 are rounded, generally defining a
semicircular
configuration that connects the convex curved leading edge 48 to the concave
curved
trailing edge 46.
[0013] In a preferred embodiment, the chord (A) of each convex/concave curved
blade
20, defined as the distance from the leading edge 48 to the trailing edge 46,
is
substantially constant through the body portion 44, thereby defining a
constant-chord
configuration. Alternatively, as shown in Figure 3b, the convex/concave curved
blade
,
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20 may be configured with a maximum chord at a midpoint M between the counter-
tip
portion 40 and the tip portion 42, with the chord decreasing towards each of
the
counter-tip 40 and tip portions 42, the chord at each of the counter-tip 40
and tip
portions 42 being identified as point T. Preferably, the decrease in chord is
symmetrical
on either side of the midpoint, towards each of the counter-tip and tip
portions.
[0014]In one embodiment, for a convex/concave curved blade 20 having a maximal
chord at a midpoint M, the differential in chord at midpoint M and the tip and
counter-tip
portions (identified as point T) is approximately 0 to approximately 10%
relative to the
overall length of the convex/concave curved blade 20. In further embodiments,
the
differential range is at least one of approximately 1% to approximately 8%,
approximately 1.5% to approximately 6%, and approximately 2% to approximately
4%.
In a preferred embodiment, the differential range is approximately 2.5% to
approximately 3.5%, as presented in Table I. As will be appreciated, the
dimensions
provided in Table I are merely exemplary, and should not be interpreted or
used to
dimensionally limit the convex/concave curved blade described herein. One may
implement convex/concave curved blades having dimensions that are larger or
smaller
than those mentioned in Table I. One may also implement convex/concave curved
blades that comprise a chord differential that falls outside the above-noted
ranges,
depending on the implementation.
Table I: Sample dimensions for convex/concave curved blade.
Overall Lengtha Chord at point Tb Chord at point Mc
Differential'
50 10.5 12 3%
37 7.875 8.875 2.7%
32 7 8 3.1%
Note: a Length from tip to counter-tip
measurement at T; see Figure 3b
measurement at M; see Figure 3b
differential = (chord at point M ¨ chord at point T)/overall length x 100
[0015]With the above-noted blade configuration, the surface area of the
convex/concave curved blade 20 is increased relative to comparable tapered
blades
normally found on conventional wind turbines. The increased surface area
increases
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the overall torque produced by the convex/concave curved blade 20, with
increased
contribution of torque from the tip portion 42 and midpoint region of the body
portion 44,
as compared to conventional tapered blades. In other words, for any given
blade
length, the above-noted convex/concave curved blade exhibits a greater overall
surface
area and resulting torque compared to a similarly dimensioned tapered blade.
As such,
the convex/concave curved blade described here is well suited for use on
smaller-sized
wind turbines, in particular on turbines comprising multiple rotors, each of
which are
fitted with a plurality of convex/concave curved blades.
[0016]As shown in Figures 3a and 3b, the counter-tip 40 and tip 42 portions,
as well as
the leading 48 and trailing 46 edges are curved, thereby eliminating corners
and angular
transitions along the circumference of the blade. During operation, it was
been found
that the convex/concave curved blade exhibits reduced noise characteristics
when used
under normal operating conditions. The noted reduction in the overall noise is
particularly important when the unit is located in close proximity to a
residential setting.
[0017]As mentioned previously, and as shown in Figure 4, the convex/concave
curved
blade is generally planar. The convex/concave curved blade is preferably made
of any
suitable metal, for example but not limited to aluminium and stainless steel.
The
convex/concave curved blade may be manufactured from metal plate having a
thickness in the range of about 1/8 inch to about 3/4 inch, but smaller or
larger
dimensioned materials may also be used, depending on the implementation. In a
preferred embodiment, the blades are formed of 1/8 inch aluminium plate. The
convex/concave curved blade may also be made of any suitable polymeric or
fibreglass
material. For example, the blades could be manufactured of glass fibre
reinforced
plastic. Carbon fibre or Kevlar may also be used as reinforcement materials.
The
simple and straightforward design of the blades makes them economical to
produce
using a range of production technologies such as, but not limited to stamping,
moulding,
protrusion and extrusion, as deemed appropriate for the material being used.
[0018]As shown in Figure 5a, the leeward side 52 of the convex/concave curved
blade
20 is supported by a suitable stem 54 that generally spans the convex/concave
curved
blade 20 from the tip portion 42 through to the counter-tip portion 40. The
stem 54 is
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affixed to the convex/concave curved blade 20 using suitable rivets, but other
fastening
systems including, but not limited to threaded fasteners and welds are also
possible.
An extension portion 56 of the stem 54 extends past the counter-tip portion 40
so as to
fixedly engage the respective rotor. The extension portion exposes the stem
and
creates a space between the counter-tip of the blade and the rotor drum,
allowing the
wind to flow unimpeded over the body of the wind turbine. The space can be
lengthened or shortened, as required, by using a stem having a longer or
shorter
extension portion 56. In general, the convex/concave curved blade 20 is
mounted such
that the longitudinal axis of the stem perpendicularly intersects the chord at
the midpoint
of the body portion. As shown, the extension portion 56 is received by a
corresponding
mounting block 58 on the rotor, and is fixed in position using at least one
suitable
fastener (e.g. bolts, hex bolts, etc.). A variety of configurations for the
stem and
corresponding mounting block are possible. For example, as shown in Figure 6,
the
stem 54, and in particular the extension portion 56 may comprise a square
cross
section, wherein the extension portion 56 is received by a mounting block 58
having a
similarly configured receptacle 60. In such an embodiment, blade pitch is
fixed relative
to the mounting block. Blade pitch variations may be achieved by using
alternate
mounting blocks having preset receptacle orientations. Alternatively, the
mounting
block itself may be adjustable relative to the rotor, so as accommodate a
range of
desired blade pitches. In an alternate embodiment shown in Figure 7, the
extension
portion 56 of the rectangular stem 54 is circular in cross-section, the
extension portion
being received in a corresponding mounting block 58 having a similarly
configured
circular receptacle 60. With a circular configuration, to achieve a particular
blade pitch,
the extension portion 56 is rotated within the mounting block receptacle 60
and
subsequently locked in place using at least one suitable fastener 62. For
example, the
extension portion 56 may be locked in a desired pitch configuration using
threaded
fasteners (bolts, hex bolts, etc.) that engage the extension portion 56 at one
or more
intermediate positions along the axis defined by the mounting block receptacle
60.
Alternate means to maintain the extension portion 56 fixed in the mounting
block 58
may be implemented, as will be apparent to one skilled in the art.
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[0019]To improve the overall characteristics of the convex/concave curved
blade 20,
the stem 54 on the leeward side 52 of the convex/concave curved blade 20 is
preferably
covered by a housing 64. In particular, it is preferred that the housing is a
tapered
housing that directs the wind over the stem. An example of the stem housing is
shown
in Figure 5b.
[0020]The pitch of a mounted blade will generally be in the region of 30 to
45 , but
angles above or below this range may be useful for certain operating
conditions.
[0021]In a further embodiment, the convex/concave curved blade and stem may be
integral, wherein the stem is formed into the convex/concave curved blade,
particularly
upon the leeward side. This is particularly suitable for blades made of a
suitable metal,
wherein the corresponding stem and extension portion are dimensioned to have
sufficient strength to withstand the stresses experienced by these components
during
normal operation use.
[0022]As shown in the examples above, in an assembled and operational state,
each
stem 54 located about a rotor is provided with a single convex/concave curved
blade
20. In an alternate embodiment, it is possible to place a plurality of
convex/concave
curved blades on each support beam, for example as shown in Figures 8a and 8b.
On
any one stem 70, the convex/concave curved blades 20 may be adjusted to the
same or
different pitches, thereby enabling the wind turbine to be tuned to more than
one optimal
wind velocity. For example, on any one stem, the distal blade 20a may have a
pitch
that operates more efficiently during low velocity winds, while the proximal
blade 20b
may have a pitch that operates more efficiently during higher velocity winds.
Alternatively, the convex/concave curved blades may be tuned to have the same
pitch,
thereby optimizing operation at one predetermined wind velocity. In addition,
in any
implementation where a plurality of convex/concave curved blades is being used
on a
single stem, the blades may or may not be of equal dimension. For example,
while the
distal and proximal blades may be equally dimensioned, it may be advantageous
to use
smaller distal blades and larger proximal blades, as shown in Figure 8b, or
visa versa.
In addition, the spacing between the distal blades and the proximal blades may
be
adjustable. For example, in one implementation, the spacing may be minimal,
with the
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tip portion of the proximal blade being immediate adjacent the counter-tip
portion of the
distal blade. Alternatively, the spacing may be increased as deemed
appropriate for a
particular implementation. In further embodiments, it may be useful to place
the
convex/concave curved blade 20 in closer or further proximity from the rotor
assembly
by using a shorter or longer extension portion 56, respectively.
[0023]While described and shown as generally planer, the convex/concave curved
blade may be configured with a slight twist as deemed necessary for a
particular
implementation. For instance, the ends of the tip 42 and counter-tip 40 can be
curved
towards the wind to retain more energy from the wind. Further, while the
leading and
trailing edges are shown as comprising a continuous curve, one of both of
these edges
may be shaped. For example, one or both of the trailing/leading edges may be
configured with a wave pattern, castellated, pleated or configured with any
other shape
deemed suitable for a particular implementation. In addition, one or both of
the
windward and leeward sides of the convex/concave curved blade may be textured.
For
example, one or both of the windward and leeward sides of the convex/concave
curved
blade may be provided with dimples, protrusions, ribs or any other texture
affecting the
wind dynamics of the blade.
[0024]The convex/concave curved blade described here is suitable for use on
low
output (3 to 99kWh) up-wind or down-wind wind turbines, as well as variations
thereof,
including both up-wind and down-wind configurations. A typical use will have a
plurality
of blades arranged in balanced fashion about a centralized hub or rotor
assembly. For
example, the blades could be used on rotor assemblies comprising 2 or more
blades
(e.g. rotor assemblies comprising 6, 8 or 10 blades). The blades may also be
used
with rotor assemblies comprising multiple rotors, such as the horizontal dual-
rotor wind
turbine described in applicants co-pending U.S. application "ROTOR DRUM" filed
April
= 13, 2007, which is herein incorporated by reference. The increased
surface area of the
convex/concave curved blade is well suited for use on low output turbines
where limited
wind velocity is often encountered. The increased surface area of the blades
also
permit the overall diameter of a blade assembly to be decreased, permitting
the use of a
lower tower assembly. The convex/concave curved blade may also be used to
retrofit
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the old Dutch windmills, or modern wind turbines of higher output (100 kWh to
750 kWh,
or more).
[0025] The convex/concave curved blade discussed above may find suitable use
in
blade rotor assemblies of a range of other applications, such as for use in a
propeller
assembly for aircraft. The curved blade configuration may also be used with
fans and
the like, such as those installed as ceiling fans in industrial, commercial
and residential
settings.
[0026] It will be appreciated that, although embodiments of the convex/concave
curved
blade have been described and illustrated in detail, various modifications and
changes
may be made. While one embodiment is described above, some of the features
described above can be modified, lengthened, shortened, widened, narrowed,
replaced
or even omitted. Still further alternatives and modifications may occur to
those skilled
in the art. All such alternatives and modifications are believed to be within
the scope of
the invention.
