U.S. patent application number 13/108548 was filed with the patent office on 2012-08-23 for horizontal axis airfoil turbine.
This patent application is currently assigned to JET-AGE WIND INC.. Invention is credited to Bertram J. Alexander, Melvin L. Dean, Paul A. Gallant, Louis G. MacDonald.
Application Number | 20120213636 13/108548 |
Document ID | / |
Family ID | 46652875 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120213636 |
Kind Code |
A1 |
Gallant; Paul A. ; et
al. |
August 23, 2012 |
HORIZONTAL AXIS AIRFOIL TURBINE
Abstract
A Horizontal Axis Airfoil Turbine (HAAT) for harnessing wind
power is presented. The horizontal axis airfoil turbine has an
airfoil design configured for low cut-in-speed and operational
speeds, and for high torque operation. Multiple airfoil blade tips
depend inwardly from a structural shroud along the periphery of the
shroud. A number of full airfoil blades depend inwardly from the
shroud along spokes providing mechanical engagement between the
shroud and a central hub. Advantages are derived from a large wind
swept area distributed to maximize leverage in order to enable high
torque operation.
Inventors: |
Gallant; Paul A.;
(Stephenville, CA) ; Alexander; Bertram J.;
(Kippens, CA) ; MacDonald; Louis G.;
(Stephenville, CA) ; Dean; Melvin L.;
(Stephenville, CA) |
Assignee: |
JET-AGE WIND INC.
Stephenville
NL
|
Family ID: |
46652875 |
Appl. No.: |
13/108548 |
Filed: |
May 16, 2011 |
Current U.S.
Class: |
416/182 |
Current CPC
Class: |
F03D 1/0625 20130101;
F05B 2240/33 20130101; Y02E 10/72 20130101; F05B 2240/2211
20130101; Y02E 10/721 20130101 |
Class at
Publication: |
416/182 |
International
Class: |
F01D 5/22 20060101
F01D005/22 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2011 |
CA |
2732543 |
Claims
1. A horizontal axis airfoil turbine for harnessing wind energy to
provide a motive force for use in a power generator, the horizontal
axis airfoil turbine comprising: a ring configured to provide
structural support for an airfoil blade arrangement; a plurality of
airfoil blade tips mechanically connected to, and depending
radially from said ring, said blade tips being configured to
interact with an airflow incident thereon, said airflow causing a
deflection of said blade tips in a direction of rotation of said
ring; a plurality of spokes mechanically connected to, and
depending radially inwardly from, said ring, each spoke extending
from said ring to a central hub, said spokes providing structural
support for said ring and said airfoil blade arrangement; a
plurality of full airfoil blades, each full blade being configured
to provide airfoil characteristics to a corresponding spoke for
reducing turbulent airflow past said spoke, mechanical engagement
between said spokes and said hub providing torsional force transfer
to said hub, said hub transforming said torsional force into the
motive force for use in the power generator.
2. The horizontal axis airfoil turbine as claimed in claim 1, said
ring further comprising an aerodynamically shaped leading edge for
reducing resistance to incident wind.
3. The horizontal axis airfoil turbine as claimed in claim 1, said
ring further comprising a structural shroud preventing radial
airflow spill over distal ends of blades in said airfoil blade
arrangement; and each said airfoil blade tip depending radially
inwardly from said ring.
4. The horizontal axis airfoil turbine as claimed in claim 3, said
structural shroud having an airfoil cross-section for reducing
turbulent airflow around said turbine.
5. The horizontal axis airfoil turbine as claimed in claim 4, said
structural shroud having an airfoil tear shaped cross-section.
6. The horizontal axis airfoil turbine as claimed in claim 2, each
said airfoil blade tip shaped to operate under one of drag or lift
conditions causing said deflection of said blade tip in said
direction of rotation of said ring.
7. The horizontal axis airfoil turbine as claimed in claim 6, each
said airfoil blade tip having an airfoil tear shaped cross-section
for reducing turbulent airflow past said airfoil blade tip.
8. The horizontal axis airfoil turbine as claimed in claim 6, each
said airfoil blade tip having an angle of attack between 30.degree.
and 50.degree..
9. The horizontal axis airfoil turbine as claimed in claim 8, said
airfoil blade tip angle of attack being substantially
40.degree..
10. The horizontal axis airfoil turbine as claimed in claim 3, each
said airfoil blade tip extending radially inwardly from said ring
between 10 to 40 percent of a radius of said ring.
11. The horizontal axis airfoil turbine as claimed in claim 10,
each said airfoil blade tip extending radially inwardly from said
ring substantially 25 percent of said radius of said ring.
12. The horizontal axis airfoil turbine as claimed in claim 2, each
said full airfoil blade shaped to operate under one of drag or lift
conditions causing additional deflection of said full airfoil blade
in said direction of rotation of said ring.
13. The horizontal axis airfoil turbine as claimed in claim 12,
each said full airfoil blade having an airfoil tear shaped
cross-section for reducing turbulent airflow past said full airfoil
blade.
14. The horizontal axis airfoil turbine as claimed in claim 12,
each said full airfoil blade having an angle of attack between
30.degree. and 50.degree..
15. The horizontal axis airfoil turbine as claimed in claim 14,
said full airfoil blade angle of attack being substantially
40.degree..
16. The horizontal axis airfoil turbine as claimed in claim 2, each
said full airfoil blade extending radially inwardly from said ring
between 80 to 95 percent of a length of said corresponding
spoke.
17. The horizontal axis airfoil turbine as claimed in claim 16,
each said full airfoil blade extending radially inwardly from said
ring substantially 88 percent of said length of said corresponding
spoke.
18. The horizontal axis airfoil turbine as claimed in claim 2,
wherein each said airfoil blade tip and each said full airfoil
blade have a substantially equal angle of attack.
19. The horizontal axis airfoil turbine as claimed in claim 2, said
plurality of full airfoil blades comprising an odd number of said
full airfoil blades for reducing harmonic resonant vibration.
20. The horizontal axis airfoil turbine as claimed in claim 19,
said odd plurality of full airfoil blades comprising a prime number
of said full airfoil blades for minimizing harmonic resonant
vibration.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to Canadian
Application No. 2,732,543, filed Feb. 23, 2011, the entirety of
which is hereby incorporated by reference.
TECHNICAL FIELD
[0002] The horizontal axis airfoil turbine described herein relates
to the general field of wind turbines, and in particular to wind
turbines operating at higher torque and lower cut-in-speed.
BACKGROUND
[0003] In the field of wind power generation, harnessing wind power
has been sought for some time. Initial designs concentrated on
harnessing wind power for conversion into a mechanical motive force
to actuate various machinery, for example for cutting wood or
grinding seed. The simplest of these designs included a number of
sails attached to a number of spokes on a hub and are generally
referred to as wind mills emphasizing the early need for a motive
force in processing raw materials. Some prior art wind mill designs
include what can be generally referred as paddles instead of the
sails. Such windmill designs operate simply by converting wind
forces impinging over an area into a motive force employing general
principles of sailing a sail ship.
[0004] Relatively recent research in fixed wing powered flight has
brought an understanding of aerodynamic forces, such as lift and
drag, which lead to aircraft wings having general tear shape
cross-sections and to propellers having tear shape cross-section.
War efforts have furthered the understanding of fixed wing power
flight providing extensive empirical knowledge leading to
extensively cataloguing the properties of airfoil cross-sections
with an emphasis on tear shape derived airfoils. Recently
propellers have been used "in reverse", so to speak, to generate
wind power, typically to convert wind forces into electrical power
via an electrical power generator. These propeller inspired designs
will be referred to herein as wind propeller generators. Currently
wind power generation is dominated by wind propeller generators
with three blades used for both residential applications and large
wind farms. The cut-in-speed for this current technology is
typically between 3 to 4.5 meters per second ("m/s"), wherein
cut-in-speed is the speed at which the power production starts.
Thus conventional wind propeller generators generally require high
start speeds, which limits deployment to geographic regions
benefiting from high winds. Additionally, despite requiring high
wind speeds wind propeller generators generally produce low motive
forces available for power conversion.
[0005] Much of the knowledge regarding the general field of
aerodynamics is best supported by experimentation. In numerous
cases theoretical models only approximate experimental reality due
to air drag and air turbulence effects, which are not fully
understood presently despite enormous prior research and
development efforts. Theoretical analysis can explain linearly
varying real world phenomena, a phrase reserved to characterize
phenomena well approximated by some simple well behaved
mathematical function(s). It is generally accepted and understood
that actual real world phenomena do not fit perfectly such
theoretical mathematical analysis. The phrases "well approximated"
and "well behaved" have varying definitions: "well approximated"
implies due consideration being given to measurement error, whereas
"well behaved" implies smoothly varying with respect to some
parameter. Measurement error is minimized in respect of laminar air
flows; however, turbulent airflow defies functional mathematical
modeling. Largely, turbulent airflow is modeled statistically. Real
airflow phenomena are anything but well behaved and smoothly
varying. A number of parameters such as air compressibility, air
density, air pressure, etc. are not smoothly varying. For example,
air compressibility and air density vary with temperature having
abrupt discontinuities with temperature and air pressure (dew
point); air pressure varies with airflow speed and airflow
direction, having discontinuities at the sound barrier; etc. Much
work has been done and much work remains to be done in aerodynamics
in general and therefore in the field of wind power generation.
[0006] There is a need in the wind power generation industry to
address the above-mentioned issues in order to more efficiently
produce wind power.
SUMMARY
[0007] It was found that one of the prior art problems may best be
described in terms of an acceptance by the scientific community
that the energy in the wind is proportional to the cube of the wind
velocity. In view of this relationship, some sources claim that the
cut-in-speed does not matter because there is little energy in the
wind at low speed levels. The present solution is contrary to this
position:
[0008] It is pointed out that, assuming all other parameters
remaining constant, employing the Weibull distribution for the wind
in a chosen geographic location, each cut-in-speed decrease of 0.5
m/s results in an annual increase in the available energy by about
6 to 7%. The corresponding energy extraction percentage increase
depends in a synergistic way on location, energy conversion
apparatus and cut-in-speed reduction. Thus, it has been found that
the cut-in-speed is actually very important, not only from the
point view of energy production by also when considering areas apt
for deployment. Geographic areas with lower wind speed particularly
benefit from a lower cut-in-speed due to the fact that harnessing
wind energy can be economically viable in these additional
areas.
[0009] The proposed solution provides increased wind power
production employing a Horizontal Axis Airfoil Turbine (HAAT)
having an airfoil design configured for low cut-in-speed and
operational speeds, and for high torque operation. HAAT
implementations overcome the disadvantages of current technology by
providing higher torque at all wind speeds. The main advantage of
the proposed solution over conventional designs is that the
increased torque at lower wind speed means that the cut-in-speed is
reduced and therefore additional wind energy can be harnessed.
While an increase in torque is associated with an increase of power
and whereas a decrease in rotational speed is associated with a
decrease in output power, field testing indicates that the overall
effect is an increase in power out compared to conventional
technologies.
[0010] In accordance with the proposed solution, the HAAT apparatus
utilizes short radial airfoils that are primarily mounted on a
periphery of the turbine, but include some full radius airfoils.
The airfoil arrangement maximizes torque, yet captures wind energy
across the cross-sectional area of the turbine.
[0011] In accordance with a broad aspect, there is provided a
horizontal axis airfoil turbine for harnessing wind energy to
provide a motive force for use in a power generator, the horizontal
axis airfoil turbine comprising: a ring configured to provide
structural support for an airfoil blade arrangement; a plurality of
airfoil blade tips mechanically connected to, and depending
radially from the ring, the blade tips being configured to interact
with an airflow incident thereon, the airflow causing a deflection
of the blade tips in a direction of rotation of the ring; a
plurality of spokes mechanically connected to, and depending
radially inwardly from, the ring, each spoke extending from the
ring to a central hub, the spokes providing structural support for
the ring and the airfoil blade arrangement; a plurality of full
airfoil blades, each full blade being configured to provide airfoil
characteristics to a corresponding spoke for reducing turbulent
airflow past the spoke, mechanical engagement between the spokes
and the hub providing torsional force transfer to the hub, the hub
transforming the torsional force into the motive force for use in
the power generator.
[0012] In other aspects, the ring further comprises an
aerodynamically shaped leading edge for reducing resistance to
incident wind. The ring may also have a structural shroud
preventing radial airflow spill over distal ends of blades in the
airfoil blade arrangement, each airfoil blade tip depending
radially inwardly from the ring. The structural shroud may have an
airfoil tear shaped cross-section for reducing turbulent airflow
around the turbine. Each airfoil blade tip may be shaped to operate
under one of drag or lift conditions causing the deflection of the
blade tip in the direction of rotation of the ring and each airfoil
blade tip may have an airfoil tear shaped cross-section for
reducing turbulent airflow past the airfoil blade tip. Moreover,
each airfoil blade tip may have an angle of attack between
30.degree. and 50.degree. and in particular substantially
40.degree.. Each airfoil blade tip may extend radially inwardly
from the ring between 10 to 40 percent of a radius of the ring and
in particular substantially 25 percent of the radius of the
ring.
[0013] In still other aspects, each full airfoil blade may be
shaped to operate under one of drag or lift conditions causing
additional deflection of the full airfoil blade in the direction of
rotation of the ring. Each full airfoil blade having an airfoil
tear shaped cross-section for reducing turbulent airflow past the
full airfoil blade. Moreover, each full airfoil blade may have an
angle of attack between 30.degree. and 50.degree. and in particular
substantially 40.degree.. Each full airfoil blade may extend
radially inwardly from the ring between 80 to 95 percent of a
length of the corresponding spoke and in particular substantially
88 percent of the length of the corresponding spoke.
[0014] In other aspects, each airfoil blade tip and each full
airfoil blade may have a substantially equal angle of attack. The
full airfoil blades may comprise an odd number of full airfoil
blades for reducing harmonic resonant vibration and the odd number
of full airfoil blades may be a prime number of full airfoil
blades.
[0015] Advantages over conventional designs are derived from a
lower wind speed required to start up the horizontal axis airfoil
turbine and from higher torque operation in general.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The features and advantages of the HAAT will become more
apparent from the following detailed description of several aspects
of the proposed solution illustrated by way of example, and not by
way of limitation, in detail in the figures, wherein:
[0017] FIG. 1 is a schematic diagram illustrating, in accordance
with one embodiment of the proposed solution, a front view of a
horizontal axis airfoil turbine;
[0018] FIG. 2 is a schematic diagram illustrating, in accordance
with one embodiment of the proposed solution, a rear view of the
horizontal axis airfoil turbine;
[0019] FIG. 3 is a schematic diagram illustrating, in accordance
with one embodiment of the proposed solution, a perspective view of
the horizontal axis airfoil turbine;
[0020] FIG. 4 is a schematic diagram illustrating a perspective
view of the horizontal axis airfoil turbine hub;
[0021] FIGS. 5a, 5b and 5c illustrate examples of shroud
cross-sections in accordance with the proposed solution: FIG. 5a
illustrates a low profile shroud having an aerodynamic shape; FIG.
5b illustrates a tear shaped shroud in cross-section, and FIG. 5c
illustrates a composite shroud having an overall aerodynamic
shape;
[0022] FIG. 6 is a schematic diagram illustrating a cross-sectional
view of a prototype airfoil blade employed in a horizontal axis
airfoil turbine implemented in accordance with the proposed
solution;
[0023] FIG. 7 is a plot of actual comparative rotational speed
versus wind speed measurements for a conventional wind propeller
generator and horizontal axis airfoil turbines implemented in
accordance with the proposed solution; and
[0024] FIG. 8 is a plot of actual comparative torque versus wind
speed measurements for conventional wind propeller generators and
horizontal axis airfoil turbines implemented in accordance with the
proposed solution.
[0025] In the attached figures like reference numerals indicate
similar parts throughout the several views. As will be realized,
the HAAT is capable for other and different embodiments and its
several details are capable of modification in various other
respects, all without departing from the spirit and scope of the
present description.
DETAILED DESCRIPTION
[0026] The instant disclosure is provided to further explain in an
enabling fashion the best modes of making and using various
embodiments in accordance with the proposed solution. The detailed
description set forth below in connection with the appended
drawings is intended as a description of various embodiments of the
HAAT and is not intended to represent the only embodiments
contemplated by the inventor. The detailed description includes
specific details for the purpose of providing a comprehensive
understanding of the HAAT. However, it will be apparent to those
skilled in the art that the HAAT may be practiced without some of
these specific details. For certainty, while the following
description of the proposed solution concentrates on describing
aspects of the horizontal axis airfoil turbine, some consideration
will be been given, where appropriate, to aspects of an electrical
generator needed to convert wind power to electrical power, and
with respect to an overall necessary support structure of a typical
installation.
[0027] In accordance with a preferred embodiment of the proposed
solution, a frontal view of a Horizontal Axis Airfoil Turbine
(HAAT) is illustrated in FIGS. 1 to 3. HAAT 10 includes a central
hub 20 configured to connect the HAAT 10 to a generator (not
shown), for example an electrical power generator, via a shaft (not
shown), for example in the form of a support rod. The shaft
provides motive force transfer from the HAAT 10 to the electrical
power generator for conversion. The hub 20 is configured to provide
mechanical support for the HAAT 10 while aggregating motive forces
in providing torque. Hub 20 includes a faired design best shown in
FIG. 3, for example having an aerodynamic shape, in order to reduce
air drag and/or to reduce turbulence. The HAAT is not limited to
hub 20 including a spherical section nose cone. It is envisioned
that the hub 20 can be configured to actively minimize air drag
and/or to minimize turbulence.
[0028] With reference to FIG. 4, illustrating a hub 20 without the
nose cone, hub 20 includes a bore 22 providing mechanical
engagement with the shaft. Hub 20 also includes a number of spoke
bores 24 configured to provide mechanical engagement and support
for a number of spokes 30.
[0029] Returning to FIGS. 1 to 3, the overall mechanical support
structure of the HAAT 10 includes spokes 30 which extend from the
hub 20 to an outer ring 40. The number of spokes 30 can be varied
to optimize various structural aspects of the HAAT 10, for example
an odd number of spokes 30 reduces vibration. Preferably a prime
number of spokes 30 is employed to minimize resonant harmonics.
[0030] Ring 40 can include a substantially cylindrical structure.
Preferably ring 40 is a cylindrical structural shroud having an
aerodynamic cross-section to reduce drag. The HAAT is not limited
to shroud 40 having a tear shaped cross-section as shown in FIG.
5B. A variety of airfoil profiles can be employed. An airfoil
profile providing superior structural support and turbulent flow
reduction is preferred. FIGS. 5A, 5B and 5C illustrate examples of
cross-sections through shrouds 40. FIG. 5A illustrates a low
profile shroud 40 having an aerodynamic shape. FIG. 5B illustrates
a tear shaped shroud 40 in cross-section. FIG. 5C illustrates a
composite shroud 40 having an overall aerodynamic shape.
[0031] With the spokes 30 providing mechanical connectivity between
hub 20 and structural shroud 40, shroud 40 rotates with the hub 20.
Such a rotating structural shroud 40 has the potential to store a
large angular momentum (inertia). The angular momentum contribution
of the shroud 40 is proportional to mass of the shroud 40
multiplied by the corresponding square of the radius of the shroud
40, and is proportional to the angular velocity of rotation. The
angular momentum and inertia of the HAAT 10 have an impact on the
implementation and operation thereof. The disadvantage of high
angular momentum implementations is that yaw control can be more
difficult. In some implementations a larger rudder may be required.
In other implementations, a separate motor driven yaw control
system may be required for larger units. In yet other
implementations, the center of mass of the HAAT may have to be
displaced further from the yaw axis to provide adequate drag
induced yaw control. In order to minimize the angular momentum,
HAAT implementations would benefit from utilizing the lightest
economically viable and suitable (e.g. water resistant, corrosion
resistant) materials available which provide sufficient strength.
For example, durable non-corrosive carbon fiber reinforced plastic,
fiberglass and other composites can be used. As well, angular
momentum can be reduced by minimizing the amount of material used,
for example by employing spin molding techniques to produce hollow
shroud 40. As another example illustrated in FIG. 5C, structural
support can be provided by a support structure 44 within the shroud
40 made of a first dense high strength material, while the
aerodynamic surface of the shroud 40 can be provided by a shell 46
made of a second low density material. The leading edge 42 (i.e.
edge facing the wind) of the shroud 40 is aerodynamically shaped to
reduce resistance to the wind.
[0032] A balance needs to be struck between the need to minimize
angular momentum to reduce stress on the anchoring structure of the
HAAT 10 in operation, and operability of the HAAT 10 in gusty
conditions. Higher inertia provides a more stable HAAT 10 for
operation in gusty conditions, the advantage being less variation
in power output easing operational requirements of the electrical
power generator. Field tests have shown that the HAAT 10 sped up
slower with increased angular momentum implementations; however,
advantageously a HAAT 10, having a large angular momentum, slowed
down more slowly in response to decreasing wind speed.
[0033] In accordance with the proposed solution, a number of
airfoil blade tips 50 cooperate together in harnessing wind power
(at slow speed) along the periphery of the shroud 40, such that in
operation the structural shroud 40 rotates with the blade tips 50
it supports. As shown in FIGS. 1 to 3, a large number of short
length airfoil blade tips 50 are disposed along the circumference
of the shroud 40 depending inwardly from the shroud 40 providing
high torque. For example, the airfoil blade tips 50 can extend
between 10 to 40 percent of the radius of the shroud 40, preferably
25 percent. From an angular momentum perspective, the airfoil blade
tips 50 add angular momentum to the HAAT 10 while the airfoil blade
tips 50 are subjected to wind forces over a large peripheral wind
swept area exerting a greater torsional force due to a greater
mechanical advantage at reduced bulk per blade compared to
conventional wind propeller generator designs.
[0034] FIG. 6 illustrates an airfoil blade tip 50 in cross-section.
Blade tip 50 illustrates an example of angular momentum reduction
wherein blade tip 50 can be produced by extrusion techniques. Blade
tip 50 has an overall airfoil shape with a rounded leading edge 52
and a tipped trailing edge 54. A longitudinal bore 56 provides
anchoring, for example by receiving a short spoke, a support rod or
a bolt. While FIGS. 1 to 3 show short spokes depending inwards from
the shroud 40 and extending the length of the corresponding airfoil
blade tip 50, the HATT is not limited thereto. For example, each
airfoil blade tip 50 can be made of structurally rigid materials,
such as but not limited to: aluminum, high density plastic, etc.
employing a shot bolt and countersunk nut to hold the airfoil blade
tip 50 in place. If the angle of attack of the blade tips does not
require adjustment, it is envisioned that the blade tips 50 can be
welded or bonded to the shroud 40 by employing suitable attachment
techniques. Airfoil blade tips 50, can also be mounted to depend
outwardly from the shroud 40. In accordance with the proposed
solution, airfoil blade tips 50 preferably depend inwardly from the
shroud 40 in order to prevent radial air spill. As the wind
impinges on the airfoil blade tips 50 the airfoil blade tips 50
rotate, which in turn imparts a centrifugal component to the air as
the air transfers linear momentum into HAAT 10 angular momentum.
Unimpeded, the centrifugal component tends to push the air radially
outwards and past the distal end of each airfoil blade tip 50.
Employing the shroud shaped ring 40 stops radial motion of the wind
air providing an increased momentum transfer. Advantageously, the
HAAT 10 provides increased torque.
[0035] Referring back to FIGS. 1 to 3, in accordance with the
proposed solution, a number of full airfoil blades 60 cooperate
together with the airfoil blade tips 50 to capture wind power in
the centre of the HAAT 10 closer to the hub 20. Full airfoil blades
60 depend inwardly from shroud 40 and benefit from reduced air
spill.
[0036] Without limiting the scope, each full airfoil blade 60 can
have the same cross-section as the airfoil blade tips 50
illustrated in FIG. 6. The bore 56 receives each spoke 30 and
therefore the number of full airfoil blades 60 corresponds to the
number of spokes 30 employed. In view of the vibration and harmonic
resonance considerations presented hereinabove, an odd/prime number
of full airfoil blades 60 are employed. Balance considerations lead
to employing an equal number of airfoil blade tips 50 between full
airfoil blades 60 and therefore to an odd total number of airfoil
blades 50, 60. While six full airfoil blades 60 are illustrated in
FIGS. 1 to 3 and employed in tested prototypes, three or five full
airfoil blades 60 are preferred, however, seven or more are not
excluded. While larger numbers of airfoil blade tips 50 would
increase the swept area, the closer the airfoil blades 50, 60 are
to each other, the more slipstreams from each airfoil blade 50, 60
interfere with each other creating turbulent air flow behind the
HAAT 10 which creates to drag against the HAAT 10 depleting
available power. The number of airfoil blades 50, 60 can be
increased compared to conventional wind propeller generator designs
because fewer full airfoil blades 60 extend in the center of the
HAAT 10 providing ample spacing therebetween, and along the shroud
40 larger spacing is available between all airfoil blades (50,
60).
[0037] While each full airfoil blade 60 provides a corresponding
spoke 30 with an aerodynamic shaped shell to reduce turbulence
while harnessing additional wind power, the full airfoil blades 60
need not extend from the shroud 40 all the way to the hub 20. For
example full airfoil blades 60 extend radially inwardly from the
shroud 40 between 80 to 95 percent of the length of the
corresponding spokes 30, typically 88 percent. Spokes 30 rotate
slower at the hub 20 and therefore contribute less turbulence. It
has been discovered that a crossover point exists along the radius
of the HAAT 10 for spokes 30 of constant angle of attack and
constant chord length where the aerodynamic cross-section of each
full airfoil blade 60 no longer provides a power extraction
advantage, on the contrary the full airfoil blade 60 simply stirs
air. The full airfoil blades 60 can extend inwardly only to the
crossover point for the intended rotational speed range of the HAAT
10. Such limited extension can also reduce bulk and angular
momentum. In accordance with the proposed solution all surfaces of
the HAAT 10 are aerodynamically shaped. However this is not an
absolute requirement, for example the spokes 30 near the hub 20 can
be sufficiently aerodynamic.
[0038] While FIGS. 1 to 3 illustrate airfoil blade tips 50 and full
airfoil blades 60 of constant cross-section, the scope of the HAAT
is not limited thereto. Constant cross-section construction
benefits from simplified manufacturing. For example, if variable
cross-section construction is employed, the cross-section can be
made to taper from the shroud 40 to the crossover point.
[0039] It is envisioned that the airfoil blade tips 50 and full
airfoil blades 60 can have either different cross-sections or
different angles of attack. For example, the cross-section and/or
angle of attack of the airfoil blade tips 50 can be configured to
provide low cut-in-speed operation, while the cross-section and/or
angle of attack of the full airfoil blades 60 can be configured to
control rotational speed and therefore angular momentum.
[0040] Various airfoil cross-sectional shapes permit the airfoil
blades to operate either under lift conditions or under drag
conditions. Under drag conditions the airfoil blades 50/60 act as
sails being deflected by the wind to cause HAAT 10 rotation, while
under lift conditions the airfoil blades 50/60 minimize drag being
deflected by an experienced lift which causes HAAT 10 rotation.
Depending on the angle of attack, an airfoil blade having a
cross-sectional shape capable of operation under lift conditions
can be configured to operate under drag conditions. The available
wind speed factors into which operating conditions are
appropriate.
[0041] For certainty, the proposed solution includes a variation in
the number, shape, dimensions and angle of attack for the airfoil
blades 50/60 depending on the wind speed and diameter of the HAAT
10.
[0042] It is noted that current thinking in the art is that, in
view of economic considerations, increasing rotor blade length of a
wind propeller generator is cheaper and easier to sustain high wind
speed operation than to utilize a shroud around a propeller.
However, increasing rotor blade length without a shroud is limited
by: material strength, angular momentum considerations, blade
vibration, drag which increases nonlinearly with blade length, and
at an extreme by tips rotating at very high speeds incompatible
with the wind speed. In contrast, the shroud 40 proposed not only
provides a support structure for the airfoil blade tips 50 but also
restricts radial air spill.
Experiments and Results:
[0043] With reference to FIG. 7, field testing outdoors has
confirmed that the rotational speed for HAAT wind turbines JA306
and JA246621 implemented in accordance with the proposed solution,
was less than that for a commercially available wind propeller
generator Prop51. Because, both centrifugal forces and vibration
increase with the square of the speed, the wind turbines
implemented in accordance with the proposed solution operating at
lower speeds benefit from improved structural stability. Further
benefits are derived from lower rotational speeds due to the
rotational speed dependence of angular momentum which minimizes
stresses on the HAAT support structure (not shown). Overall, the
radial distribution of the wind swept area was closer to the outer
ring (shroud 40) of the HAAT wind turbines than for the wind
propeller generator(s). Comparatively, the angular momentum of the
HAAT prototypes was estimated to be eight or nine times greater
than the angular momentum of the wind propeller generator(s)
tested.
[0044] A variety of angles of attack were tried with airfoil blades
50, 60 having the cross-sectional profile shown in FIG. 6. An angle
of attack of approximately 40.degree. produced the best results.
For certainty, the HAAT is not limited to the airfoil blade
cross-sectional profile illustrated in FIG. 6 or to the 40.degree.
angle of attack.
[0045] Advantageously, the total wind swept area of the prototype
illustrated in FIGS. 1 to 3 is more than half of the inner area of
the shroud 40, which is about five times the normalized swept area
of a wind propeller generator, thereby a significantly increased
wind power was expected.
[0046] FIG. 8 illustrates comparative torque measurements at
different wind speeds for both conventional design wind propeller
generators Prop51 and Prop69, and HAAT wind turbines JA306 and
JA246621 implemented in accordance with the proposed solution.
Advantageously, in the low wind speed operational range of the HAAT
prototypes, the HAAT prototypes have been measured to have
developed substantially larger torque. The increased torque
developed in accordance with the proposed solution, confirmed the
expectation.
[0047] As would be apparent to a person skilled in the art, the
rotational speed vs. wind speed plots (FIG. 7) and the torque vs.
wind speed plots (FIG. 8) show real outdoors gusty conditions. The
data confirms the expected benefits of increased torque and
decreased cut-in-speed. Employing HAAT derived wind turbines opens
access to large geographic areas for deployments harnessing wind
power, even under gusty wind conditions.
[0048] Surprisingly, the gusty wind conditions have shown that the
low cut-in-speed overcome static friction on start up better and
the additional angular momentum prevented, through inertial forces,
the HAAT prototypes from falling back into the static friction
regime between gusts.
[0049] Although various aspects of the proposed solution have been
described herein including for example multiple airfoil blade tips,
a full airfoil blades, and a shroud having an aerodynamic
cross-section, it is to be understood that each of these features
may be used independently or in various combinations, as desired,
in a horizontal axis airfoil turbine.
[0050] While the above description of the proposed solution
concentrates on the horizontal axis airfoil turbine, some
consideration has been given in the above with respect to aspects
of an electrical generator needed to convert wind power to
electrical power, and with respect to an overall necessary support
structure of a typical installation. For example, odd number
airfoil implementations are preferred in order to reduce harmonic
resonant vibration, low inertial mass designs are preferred in
order to reduce toppling, shear, angular momentum restorative
forces, etc.
[0051] The previous description of the disclosed embodiments has
been provided to enable any person skilled in the art to make or
use the present horizontal axis airfoil turbine described. Various
modifications to those embodiments will be readily apparent to
those skilled in the art, and the generic principles defined herein
may be applied to other embodiments without departing from the
spirit or scope of the horizontal axis airfoil turbine. Thus, the
present horizontal axis airfoil turbine is not intended to be
limited to the embodiments shown herein, but is to be accorded the
full scope consistent with the claims, wherein reference to an
element in the singular, such as by use of the article "a" or "an"
is not intended to mean "one and only one" unless specifically so
stated, but rather "one or more". All structural and functional
equivalents to the elements of the various embodiments described
throughout the disclosure that are known or later come to be known
to those of ordinary skill in the art are intended to be
encompassed by the elements of the claims. Moreover, nothing
disclosed herein is intended to be dedicated to the public
regardless of whether such disclosure is explicitly recited in the
claims. No claim element is to be construed under the provisions of
35 USC 112, sixth paragraph, unless the element is expressly
recited using the phrase "means for" or "step for". The horizontal
axis airfoil turbine is defined solely by the appended claims
including any amendments made during the pendency of this
application and all equivalents of those claims as issued.
* * * * *