U.S. patent application number 11/351379 was filed with the patent office on 2007-08-16 for wind turbine rotor.
Invention is credited to Michael Lawrence Serpa.
Application Number | 20070189899 11/351379 |
Document ID | / |
Family ID | 38368690 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070189899 |
Kind Code |
A1 |
Serpa; Michael Lawrence |
August 16, 2007 |
Wind turbine rotor
Abstract
A wind turbine rotor, the rotor blades of which are shaped
generally to resemble the sail of an Oceanic sprit rig sailboat (a
traditional sailing craft with a sail plan having unusual and
significant aerodynamic properties). The rotor blades might be
movably mounted to maximize use of apparent wind. An alternative
embodiment includes a contra-rotating rotor of similar design.
Inventors: |
Serpa; Michael Lawrence;
(Oakland, CA) |
Correspondence
Address: |
MICHAEL L. SERPA
P.O. Box 478
San Francisco
CA
94104
US
|
Family ID: |
38368690 |
Appl. No.: |
11/351379 |
Filed: |
February 10, 2006 |
Current U.S.
Class: |
416/132B |
Current CPC
Class: |
F03D 3/061 20130101;
Y02E 10/74 20130101; F03D 9/25 20160501; F03D 3/005 20130101; F03D
3/02 20130101; F05B 2240/301 20130101 |
Class at
Publication: |
416/132.00B |
International
Class: |
B63H 1/06 20060101
B63H001/06 |
Claims
1) A wind turbine rotor; the wind turbine rotor having at least one
rotor blade shaped to resemble generally the sail of an Oceanic
sprit rig.
2) The wind turbine rotor of claim 1, wherein the at least one
rotor blade shaped to resemble generally the sail of an Oceanic
sprit rig is manufactured from a rigid or semi-rigid material, or
from a pliant fabric material.
3) The wind turbine rotor of claim 1, wherein the at least one
rotor blade shaped to resemble generally the sail of an Oceanic
sprit rig is movably mounted to the wind turbine rotor.
4) The wind turbine rotor of claim 1, wherein the at least one
rotor blade shaped to resemble generally the sail of an Oceanic
sprit rig is attached to a strut or spoke opposite a central
hub.
5) The wind turbine rotor of claim 1, in combination with a second,
contra-rotating, rotor.
6) The wind turbine rotor of claim 1, wherein the at least one
rotor blade shaped to resemble generally the sail of an Oceanic
sprit rig is capable of flexing or folding to increase camber.
7) A wind turbine rotor; the wind turbine rotor having one or more
rotor blades; at least one of the one or more rotor blades
resembling generally the sail of an Oceanic lateen rig.
8) The wind turbine rotor of claim 7, wherein the one or more rotor
blades is/are manufactured from a rigid or semi-rigid material, or
from a pliant fabric material.
9) The wind turbine rotor of claim 7, wherein the one or more rotor
blades is/are movably mounted to the wind turbine rotor.
10) The wind turbine rotor of claim 7, wherein the one or more
rotor blades is/are attached to struts or spokes opposite a central
hub.
11) The wind turbine rotor of claim 7, in combination with a second
rotor that rotates in the opposite direction.
12) The wind turbine rotor of claim 7, wherein at least one of the
one or more rotor blades is capable of flexing or folding for
de-powering.
13) A wind turbine rotor; the wind turbine rotor having rotor
blades; some or all of the rotor blades resembling generally the
sail of a crab claw rig.
14) The wind turbine rotor of claim 13, wherein the rotor blades
are arranged to substantially balance forces when operating in
wind.
15) The wind turbine rotor of claim 13, wherein one or more of the
rotor blades is/are manufacture from a rigid or semi-rigid
material.
16) The wind turbine rotor of claim 13, wherein one or more of the
rotor blades is/are movably mounted to the wind turbine rotor.
17) The wind turbine rotor of claim 13, arranged in combination
with a second, contra-rotating, rotor; the second, contra-rotating,
rotor having one or more rotor blades resembling generally the sail
of a crab claw rig.
18) The wind turbine rotor of claim 13, wherein one or more of the
rotor blades is/are capable of flexing or folding along more or
less a centerline for de-powering.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the rotors of wind-driven
turbines. More specifically, it concerns rotors for those wind
turbines that can produce electrical power when linked to a
generator.
BACKGROUND OF THE INVENTION
[0002] Humans have, for a very long time, tried to harness the
kinetic energy in wind and put it to useful purposes. Numerous
successful attempts at this have produced valuable labor saving
devices.
[0003] In modern times, the most sophisticated arrangements for
harnessing wind power have resulted in electricity-producing wind
turbines. This field of development is increasingly important. As
concern about global petroleum supplies and prices continues to
grow, and environmental problems associated with the burning of
fossil fuels in general yield another set of worries, the promise
of renewable and planet-friendly energy sources is immeasurably
attractive.
[0004] Traditional wind turbines derive their power input by
converting some of the wind's energy into a torque, or turning
force, acting on a rotor. Rotor blades deflect the wind in a given
direction and this causes the rotor to rotate. Electrical power is
produced when the turning force is transferred to a generator. The
amount of energy that the wind transfers to the rotor depends upon
the density of the air, the rotor area, and the wind speed.
[0005] A successful and popular present-day wind turbine design is
the three-bladed tower. In this model, a housing, or nacelle, sits
atop a tall support tower. Attached to the front of the nacelle is
a large three-bladed rotor (similar to an airplane propeller).
Housed within the nacelle are typically a gearbox and a generator.
A nosecone covers the center of the rotor. Added features, such as
variable pitch rotor blades, are sometimes included.
[0006] To keep the rotor perpendicular to the wind, a yaw mechanism
is employed. This can be a simple mechanical pivot or it can be a
sophisticated motorized setup. (If the rotor is not perpendicular
to the wind, the wind turbine will be much less effective and "yaw
error" is said to result.)
[0007] The three-bladed rotor type of wind turbine can be costly to
construct. Because taller turbines produce more power than shorter
ones, large support towers must be built to derive the maximum
benefit. In addition, due to the design of the propeller-like
rotor, the rotor blades must be built with enough strength to
handle the stress loads they must endure in high winds, especially
at the point where the three blades are joined inside the
nosecone.
[0008] In this "horizontal axis" design (wherein the rotor rotates
around a horizontal axis), the blades of the rotors face constant
wind energy when wind is present. It is possible, nevertheless,
that an airplane propeller, though good for propelling an aircraft
through the sky, is not the best design for a rotor intended to
extract energy from wind. There are also numerous "vertical axis"
wind turbine rotor designs that can be somewhat less efficient
because some of the rotor blades are shielded from the wind by the
other rotor blades at certain points in the rotation cycle. On the
other hand, these vertical axis turbines are well-suited to be
installed in locations where a horizontal axis design would be
inappropriate. Furthermore, vertical axis turbines typically do not
have yaw error problems because their rotors are not oriented
perpendicular to the wind direction.
[0009] All of these designs have merit and contribute significantly
to the green energy revolution. Yet there remains room for
improvement. Prior art wind turbines utilize merely the true wind
energy acting upon their rotor blades and cannot benefit from the
apparent wind created by their own rotational movement. This is a
considerable limitation on their performance.
[0010] Comparing prior art wind turbines to sailboats illustrates
this point. When sailing off the wind, as on a broad reach or run,
a sailboat can sail no faster than the true wind speed. In theory
it can absorb a substantial portion of the energy from the wind it
is in contact with, but the sailboat still cannot exceed the true
wind speed when sailing downwind (assuming no effect from water
currents, waves, etc.). The sail is simply being pushed by the
wind, similar to the way that the wind pushes the rotors of prior
art turbines.
[0011] When, however, sailing on a beam reach--the fastest point of
sail--the vessel benefits both from the true wind speed and from
the apparent wind generated by the forward motion of the boat. The
apparent wind is added to the true wind to create a stronger diving
force. The sails capture this driving force and generate "lift".
Even when on a close reach the sailboat realizes this
advantage.
[0012] The physics behind a sailboat's ability to sail against the
wind is probably best explained by the concept of "attached flow"
(whereby the airflow over the leeward side of the sail attaches to
the sail and pulls it along to avoid leaving a vacuum). But
regardless of the explanation for the principle, it might be that
sailboats--because of their ability to benefit from apparent
wind--provide a more proper starting point for wind turbine rotor
design. And wind turbine rotors having rotor blades modeled after
the sail plan of one particular type of sailboat potentially could
result in a significant advancement in wind turbine technology. The
present invention provides such an advancement; It is intended to
yield an extremely efficient turbine rotor capable of operating
safely in a variety of wind conditions while incorporating a simple
construction, low production cost, a low maintenance cost, and
sound structural integrity.
SUMMARY OF THE INVENTION
[0013] The present invention comprises a horizontal axis
wind-driven turbine rotor which can be situated atop a tower or
other suitable support structure. The innovation it offers results
from the unique shape of the rotor's blades.
[0014] The blades are shaped to resemble generally the sail of a
traditional sailing craft which is believed to have been developed
by Pacific Islanders many years ago. The native Pacific proa (a
canoe-like boat) employed an exceptionally well-performing sail and
sail support structure called the "Oceanic sprit rig", sometimes
also referred to as the "Oceanic lateen rig" or the "crab claw rig"
(presumably as a result of the sail's resemblance to a crab's
claw). These three terms will be used interchangeably herein.
[0015] The Oceanic lateen rig's sail possesses some unusual
properties and has been shown to be astonishingly effective at
harnessing the wind's energy to propel a sailing craft over water.
This is especially true when the boat is sailing on a beam
reach.
[0016] While the issue is the subject of debate, it is believed by
some that the sail of the crab claw rig develops lift under very
different aerodynamic principles than those of other sailing rigs,
especially as compared to the popular "Bermudan" rig which is used
on most sailboats made today. The Oceanic sprit rig has been shown
to be aerodynamically superior to the Bermudan rig in many
respects. [For a general discussion of the crab claw rig's benefits
and the science behind it, see Sail Performance; Techniques to
Maximize Sail Power, revised edition, by C. A. Marchaj
(International Marine/McGraw-Hill 2003) pages 152 to 176]
[0017] The present invention exploits the remarkable aerodynamic
properties of the Oceanic lateen rig and applies them to wind
turbine technology to provide an alternative wind turbine rotor
design. The crab claw rig's sail provides a model for the rotor
blades of this new rotor. It supplements the prior art, thereby
contributing to the overall effort to produce electricity from wind
power.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a perspective view of an Oceanic sprit rig.
[0019] FIG. 2a is a plan view of a sail from an Oceanic latten
rig.
[0020] FIG. 2b is a plan view of a variation of the Oceanic lateen
rig's sail.
[0021] FIG. 2c is a plan view of another variation of the Oceanic
lateen rig's sail.
[0022] FIG. 3 is a perspective view of a de-powered Oceanic lateen
rig sail.
[0023] FIG. 4 is a front view of a preferred embodiment.
[0024] FIG. 5 is a front view of an alternative preferred
embodiment with contra-rotating rotors.
DETAILED DESCRIPTION AND OPERATION OF THE PREFERRED EMBODIMENTS
[0025] The basic design of the Oceanic sprit rig and its unique
sail is displayed in FIG. 1. A sail 20 of the Oceanic lateen has an
arrowhead-like profile with a deeper camber--or curve to the
sail--at or near a trailing edge 21. The camber gradually
diminishes towards the tip, designated by arrow "A", where it may
disappear entirely. The sail 20 has leading edges 22 forming the
other two sides of the arrowhead, and the leading edges 22 lie
generally in the same plane. Also, the sail 20 is more or less
symmetrical along its longitudinal axis.
[0026] When sailing upwind or on a beam reach, the tip is closer
than the trailing edge 21 to the direction the wind is coming from.
That is, the tip is in general nearer to the front of the boat than
is the trailing edge 21. Also, like other types of sails, the
concave side of the sail 20 always faces the wind. That is, the
windward side of the sail 20 is concave and the leeward side is
convex.
[0027] For a sailboat, the sail of crab claw rig is typically made
of a cloth material, like most other sails. As a result, the
leading edges 22 must be affixed to rigid spars, or "sprits" (not
shown). For purposes of the preferred embodiments of the present
invention, however, the crab-claw-sail-like-rotor-blades can be
manufactured from a rigid or semi-rigid material of sufficient
strength and durability. This might be the most beneficial
construction for many applications.
[0028] For certain embodiments, though, a pliant fabric material
(supported by one or more spars of some sort) might be an
appropriate construction.
[0029] In FIGS. 2a, 2b, and 2c are shown plan views of three
variations of the Oceanic lateen rig sail, all of which are
suitable rotor blade designs for the wind turbine rotor of the
present invention. In FIG. 2a the leading edges 22 are slightly
curved, the trailing edge 21 is curved, and the tip (marked by
arrow "A") is pointed. In FIG. 2b, the leading edges 22 have a
greater curvature and the tip (marked by arrow "A") is rounded.
Also in FIG. 2b, the trailing edge 21 is straight. In FIG. 2c, the
sail has a "delta wing" shape with straight leading edges 22, a
pointed tip (marked by arrow "A"), and a straight trailing edge
21.
[0030] Any combination of these features are appropriate for the
preferred embodiments of the present invention (i.e., straight
leading edges/rounded tip, or curved leading edges/pointed tip;
curved trailing edges, straight trailing edges, or some mixing of
the two). Specific operating conditions, though, might dictate a
preferred combination. What is important is that the blades for the
rotor of the present invention have an arrowhead-like profile with
maximum camber at or near the trailing edge (corresponding to the
trailing edge of a crab claw rig's sail) and camber decreasing
towards the tip of the rotor blade (which corresponds to the tip of
the sail of the crab claw rig), where the camber can disappear
entirely. Also, the leading edges (corresponding to the leading
edges of the crab claw rig's sail) of the rotor blades preferably
lie in the same plane.
[0031] When sailing in strong winds, sailboats sometimes can be
"overpowered" if they have too much sail area exposed to the wind
or have sails trimmed too tight for the conditions. This situation
is usually remedied by easing lines to spill wind from the sail (or
sails) and, in extreme situations, by reducing total sail area. On
an Oceanic sprit rigged-craft, the sail is "de-powered" by
permitting the rigid spars at the leading edges to move closer
together, thus increasing the camber of the sail along more or less
a centerline (the centerline extending from the tip of the sail to
the trailing edge 21). The dramatic increase in the camber of the
sail resulting from this action apparently disrupts the attached
flow on the leeward side of the sail and moderates the lifting
power of the sail.
[0032] This is illustrated in FIG. 3. The leading edges 22 of the
sail 20 have moved towards one another, resulting in increased
camber which will de-power the rig. Indicative of the de-powering
is the dramatic curvature of the trailing edge 21. In FIG. 3, the
concave side of the sail 20 is indicated by arrow "B".
[0033] If a rotor blade of the rotor in this disclosure is capable
of flexing, or folding, along more or less a centerline, it could
mimic the de-powering of an Oceanic lateen rig's sail and thus
de-power the wind turbine rotor. This would be a valuable safety
feature for handling extreme winds.
[0034] A preferred embodiment of the present invention is depicted
in FIG. 4 (the side depicted being that which will face the wind).
A wind turbine rotor 23 consists of struts or spokes 24 extending
from a central hub 25. Rotor blades 26 are situated at the end of
each of the struts or spokes 24 opposite the central hub 25. The
rotor blades 26 are shaped generally like the sail of a crab claw
rig. The rotor blades 26 are also oriented such that their tips are
pointed somewhat towards the direction of rotation for the wind
turbine rotor 23 (this direction of rotation is indicated in FIG. 4
as arrow "C"; i.e., counter-clockwise). Also, the concave side of
the rotor blades (corresponding to the concave side of the Oceanic
sprit rig sail) substantially face the wind.
[0035] Because the lift generated by a Oceanic lateen rig's sail
comes from the leeward--or convex--side of the sail, the rotor
blades 26 are preferably mounted to the struts or spokes 24 by
their concave sides only so as to ensure that the leeward side of
each of the rotors blades 26 remains unobstructed. This will result
in the cleanest air flow over the convex leeward surfaces.
[0036] [NOTE: the size of the rotor blades 26 relative to the
struts or spokes 24 and the wind turbine rotor 23 may vary from the
depiction of FIG. 4. The rotor blades 26 can be larger or smaller,
depending upon the particular adaptation.]
[0037] Any number or combination of struts or spokes 24 can be
included. For example, multiple struts or spokes 24 can support
each of the rotor blades 26. To provide a stronger structure, the
struts or spokes 24 can be connected to one another by suitable
means. Alternatively, a rim (not shown) can encircle the struts or
spokes 24 and the rotor blades 26 can be attached to the rim for
added structural integrity.
[0038] Returning to FIG. 4 each of the rotor blades 26 have two
leading edges 27, and each of the rotor blades 26 is set such that
one of their leading edges 27 is closer than the other to the
central hub 25.
[0039] In operation, as the wind turbine rotor 23 starts to rotate
it will begin to generate apparent wind which will increase the
driving force (i.e., lift) produced by the rotor blades 26.
[0040] As for a still other embodiment, the struts or spokes 24 can
be eliminated entirely and the rotor blades 26 can be affixed
directly to the central hub 25.
[0041] In addition, the rotor blades 26 can be movably mounted such
that, as the rotational speed of the wind turbine rotor 23
increases, the rotor blades 26 will themselves turn so that their
tips face even closer to the direction of the apparent wind. This
would permit the rotor blades 26 to benefit to the fullest extent
from the apparent wind for achieving maximum lift.
[0042] In FIG. 4 the wind turbine rotor 23 has three evenly-spaced
rotor blades 26 arranged to substantially balance forces when
operating. But the number of rotor blades 26 can vary for different
applications. Embodiments of the present invention may have any
number, even or odd, of rotor blades 26 as deemed appropriate.
Experimentation will yield insight as to the arrangement providing
superior performance for a given situation. There might even be an
application where only one rotor blade is appropriate, though the
best designs attempt to balance forces to ensure safety and
stability in high wind situations.
[0043] Furthermore, the rotor of the present invention may also
include rotor blades of other designs in combination with the
Oceanic-sprit-rig-sail-shaped-rotors.
[0044] A significant advantage offered by the FIG. 4 embodiment is
that the turning force is generated as far as possible from the
central hub 25. The turning force the rotor blades 26 generate
therefore benefits from leverage. This results in greater usable
torque at the central hub 25 for producing electrical power if the
present invention is coupled to a generator.
[0045] As for other embodiments, the wind turbine rotor of the
present invention can have a lattice-like structure consisting of
multiple struts or spokes. The advantage of the lattice
construction being that the overall strength of the wind turbine
rotor can be increased by buttressing high stress load areas. The
"airplane propeller" rotor blade cannot increase thickness at the
high stress point near the central hub because to do so would
decrease the aerodynamic efficiency of the rotor blade. But the
wind turbine rotor of the preferred embodiments can work with
struts or spokes with reinforcing support at high stress areas.
[0046] The lattice construction can even take the form of a
crisscrossing spokes "bicycle wheel-like" arrangement, resulting in
a light and strong structure.
[0047] Another advantage of the lattice construction is that a
second wind turbine rotor of the present invention can be housed
within the lattice-like structure of a larger one. The two wind
turbine rotors could then work in combination to generate
electricity. For example, one of the wind turbine rotors could
rotate in a clockwise direction and the second wind turbine rotor
could be arranged to rotate in the opposite direction. If one of
the wind turbine rotors is connected to the rotor of an electrical
generator, and the second of the wind turbine rotors is connected
to the stator of the same generator, then the relative motion of
the generator's rotor relative to its stator would increase. This
would maximize the electricity-generating capacity.
[0048] One example of this contra-rotating embodiment is displayed
in FIG. 5, shown as it will face the wind. A first rotor 30 has a
lattice construction support structure as previously described. The
lattice support structure includes a circular rim 31 for added
strength. The first rotor 30 also has four rotor blades 32. A
second four-bladed wind turbine rotor 33 sits nestled within the
lattice construction support structure of the first rotor 30. In
operation, the first rotor 30, as depicted here, would rotate
counter-clockwise and the second four-bladed wind turbine rotor 33
would rotate clockwise.
[0049] Alternatively, the second four-bladed wind turbine rotor 33
can simply be mounted in front of or behind the first rotor 30,
while still employing the contra-rotating element. Also, the number
of rotors blades for each or the rotors can vary, and rotor blades
of other designs can be included.
[0050] Other alterations to the preferred embodiments are possible.
For example, a wind turbine with a rotor design of the present
invention might be made foldable such that it can be transported to
a variety of locations. Also, many different sizes of rotors are
possible. A smaller rotor might be set up atop the roof of an
electrically-powered automobile to recharge the vehicle's batteries
when it is parked, while larger rotors could be made for permanent
wind turbines that provide electricity for homes or offices.
Furthermore, sensors can be employed to help optimize rotor blade
angle relative to the apparent wind.
[0051] Although the description above contains several
specificities, these should not be construed as limits on the scope
of the present invention. The details given are intended merely to
provide illustrations of some of the presently preferred
embodiments. It is to be therefore understood that many changes and
modifications by one of ordinary skill in the art are considered to
be within the scope of the invention. Thus, the full scope should
be determined by the appended claims and their legal equivalents,
rather than by examples given.
* * * * *