Note: Descriptions are shown in the official language in which they were submitted.
CA 02732543 2011-02-23
HORIZONTAL AXIS AIRFOIL TURBINE
TECHNICAL FIELD
[01] 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
[02] 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.
[03] 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 benefitting
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from high winds. Additionally, despite requiring high wind speeds wind
propeller generators
generally produce low motive forces available for power conversion.
1041 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.
[05] 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
1061 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
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matter because there is little energy in the wind at low speed levels. The
present solution is
contrary to this position:
[07] 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.
[08] 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.
[09] 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.
[10] 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
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inwardly 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.
[11] 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 and 50 and in
particular substantially
400. 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.
[12] 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 300 and 50 and in particular substantially 40 . 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.
[13] 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
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for reducing harmonic resonant vibration and the odd number of full airfoil
blades may be a
prime number of full airfoil blades.
1141 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
[15] 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:
[16] 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;
[17] 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;
[18] 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;
[19] Fig. 4 is a schematic diagram illustrating a perspective view of the
horizontal axis airfoil
turbine hub;
[20] 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;
[21] 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;
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[22] 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
[23] 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.
[24] 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
[25] 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.
[26] In accordance with a preferred embodiment of the proposed solution, a
frontal view of a
Horizontal Axis Airfoil Turbine (HAAT) is illustrated in Figures 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
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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
Figure 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.
[27] With reference to Figure 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.
[28] Returning to Figures 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.
[29] 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 Figure
5B. A variety of
airfoil profiles can be employed. An airfoil profile providing superior
structural support and
turbulent flow reduction is preferred. Figures 5A, 5B and 5C illustrate
examples of cross-
sections through shrouds 40. Figure 5A illustrates a low profile shroud 40
having an
aerodynamic shape. Figure 5B illustrates a tear shaped shroud 40 in cross-
section. Figure 5C
illustrates a composite shroud 40 having an overall aerodynamic shape.
[30] 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
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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
Figure 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.
[31] 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.
[32] 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
Figures 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
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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.
[33] Figure 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 Figures 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.
[34] Referring back to Figures 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.
[35] Without limiting the scope, each full airfoil blade 60 can have the
same cross-section as
the airfoil blade tips 50 illustrated in Figure 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
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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 Figures 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).
[36] 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.
[37] While Figures 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
CA 02732543 2011-02-23
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.
[38] 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.
[39] 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.
[40] 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.
[41] 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:
[42] With reference to Figure 7, field testing outdoors has confirmed that
the rotational speed
for HAAT wind turbines JA306 and JA246621 implemented in accordance with the
proposed
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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.
[43] A variety of angles of attack were tried with airfoil blades 50, 60
having the cross-
sectional profile shown in Figure 6. An angle of attack of approximately 40
produced the best
results. For certainty, the HAAT is not limited to the airfoil blade cross-
sectional profile
illustrated in Figure 6 or to the 40 angle of attack.
[44] Advantageously, the total wind swept area of the prototype illustrated in
Figures 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.
Figure 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.
[45] As would be apparent to a person skilled in the art, the rotational
speed vs. wind speed
plots (Figure 7) and the torque vs. wind speed plots (Figure 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.
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[46] 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.
[47] 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.
[48] 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.
[49] 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
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. 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.
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