Note: Descriptions are shown in the official language in which they were submitted.
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FLUID TURBINE SEMI-SHROUD AND ASSOCIATED ROTOR
BLADE DUAL-WINGLET DESIGN
BACKGROUND
1. Technical Field
[0001] The present disclosure relates to shrouded and ducted fluid turbines
and to fluid
turbine rotor blade design.
2. Background
[0002] In general, horizontal axis fluid turbine rotor blades comprise two
to five blades
arranged evenly about a central axis and coupled to an electrical generation
machine.
[0003] Generally speaking, a fluid turbine structure with, for example, an
open
unshrouded rotor design captures energy from a fluid stream that is smaller in
diameter than
the rotor. In an open unshrouded rotor fluid turbine, as fluid flows from the
upstream side of
the rotor to the downstream side, the average axial fluid velocity remains
constant as the flow
passes through the rotor plane. Energy is extracted at the rotor resulting in
a pressure drop on
the downstream side of the rotor. The fluid directly downstream of the rotor
consists of air
that exists at sub-atmospheric pressure due to the energy extraction. The
fluid directly
upstream of the rotor consists of air that exists at greater than atmospheric
pressure. The
high pressure upstream of the rotor deflects some of the upstream air around
the rotor. In
other words, a portion of the fluid stream is diverted around the open rotor
as if by an
impediment. As the fluid stream is diverted around the open rotor, it expands,
which is
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referred to as flow expansion at the rotor. Due to the flow expansion, the
upstream area of
the fluid flow is smaller than the area of the rotor.
[0004] The Betz limit calculates the maximum power that can be extracted
from a
volume of moving fluid by an open blade, horizontal axial flow turbine,
otherwise referred to
as an open-rotor turbine. The Betz limit is derived from fluid dynamic control-
volume
theory for flow passing through an open rotor. According to the Betz limit,
and independent
of the design of the fluid turbine, a maximum of 16/27 of the total kinetic
energy in a volume
of moving fluid can be captured by an open-rotor turbine. Conventional
turbines commonly
produce 75% to 80% of the Betz limit, or about 44% of the total kinetic energy
in a volume
of moving fluid.
[0005] A fluid turbine power coefficient (Cp) is the power generated over
the ideal
power available by extracting all the wind kinetic energy approaching the
rotor area. The
Betz power coefficient of 16/27 is the maximum power generation possible based
on the
kinetic energy of the flow approaching a rotor swept area. For an open-rotor
turbine, the
rotor swept area used in the Betz Cp derivation is the system maximum flow
area described
by the diameter of the rotor blades. The maximum power generation occurs when
the rotor
flow velocity is the average of the upstream and downstream velocity. This is
the only rotor
velocity that allows the flow-field to be reversible, and the power extraction
to be
maximized. At this operating point, the rotor velocity is 2/3 the wind
velocity, the wake
velocity is 1/3 the wind velocity, and the rotor flow has a non-dimensional
pressure
coefficient of -1/3 at the rotor exit. The -1/3 pressure coefficient is a
result of the rotor wake
flow expanding out to twice the rotor exit area downstream of the rotor
station.
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[0006] Induced drag is generated by a rotor blade due to the redirection of
fluid during
the generation of lift as a column of fluid flows through the rotor plane. The
redirection of
the fluid may include span-wise flow along the pressure side of the rotor
blade along a radial
direction toward the blade tip where the fluid then flows over to the opposite
side of the
blade. The fluid flow over the blade tips joins a chord-wise flow, otherwise
referred to as
bypass flow, forming rotor-tip vortices. The rotor-tip vortices mix with
vortices shed from
the trailing edge of the rotor blade to form the rotor wake.
[0007] It is commonly known that the rotor wake affects the rotor intake. A
column of
fluid encounters a rotor as an impediment, in part, because a portion of the
fluid flowing
around the rotor expands in the wake of the rotor in a form referred to as the
stream column.
Fluid flowing around the rotor plane is referred to as the bypass flow. Bypass
flow passes
over the outer surface of the stream column. Increasing lift over the rotor,
and hence
increasing the amount of energy extracted from the stream column, creates
slower moving
flow in the rotor wake, therefore, impeding flow through the rotor. This
impediment
increases the volume of the rotor wake. In other words, as more power is
extracted at the
rotor, the rotor stream column will expand and more fluid flow will bypass the
rotor. If a
significant amount of energy is extracted, a majority of the fluid flow will
bypass the rotor
and the rotor can effectively stop extracting energy. This is referred to as
rotor stall. As a
result, maximum power is achieved from the two opposing effects of: increased
power
extraction resulting in relatively lower flow rates; and reduced power
extraction resulting in
relatively higher flow rates.
[0008] When a shrouded turbine is used for increased power extraction, in
general, it
extracts more power from the fluid stream than an open rotor by increasing the
mass flow
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through the rotor plane, employing specially designed rotor blades to extract
more power
than their open-rotor turbine counterpart, and then by dissipating the wake to
avoid diffuser
stall. Diffuser stall occurs when the increased mass flow through the rotor
encounters the
ambient fluid stream down-stream of the rotor plane and causes a back-pressure
at the rotor
plane. Proposed solutions to diffuser stall include: increasing the size of
the wake area to
allow for increased wake expansion; and injecting high-energy fluid into the
rotor wake.
Both solutions have been proven to allow for increased energy extraction at
the rotor.
[0009] Aside from the aerodynamic challenge of eliminating the causes of
diffuser stall,
shrouded turbines have some significant drawbacks. Shrouded turbines are
heavier than their
open rotor counterparts, they are more expensive to produce and construct, and
they create a
bluff body when hit by commonly occurring side winds and gusts. Side winds
produce a
large amount of drag force that places considerable strain on structural
components.
[0010] Wind shear is the difference in wind speed by height. The higher the
wind shear,
the higher the wind velocity at the upper region of a rotor plane compared
with the wind
'velocity at the lower regions of the rotor plane. As turbines increase in
scale, they take
advantage of higher wind velocities at higher altitudes while also
experiencing greater wind
shear. Extreme wind shear is also responsible for worst case noise emissions
that are likely
to be out of compliance with existing noise pollution regulations,
[0011] Stress and strain on rotor blades is a considerable concern in the
wind turbine
industry. A rotor blade rotating in a high wind shear environment will
experience more
down-wind flexing while passing through the upper regions of the rotor plane
than while
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passing through the lower regions of the rotor plane due to the variation in
wind velocities.
As turbines increase in size, the likelihood of greater wind shear also
increases.
[0012] Noise caused by wind turbines is also a product of the wind velocity
and the rotor
blade trailing-edge and tip vortices. Trailing-edge and tip vortices create a
random noise of
similar decibel level, otherwise referred to as white-noise. Tower signature
is a term often
used to describe the sound created as rotor tip vortices encounter the turbine
tower. The
tower interrupts the flow of the trailing-edge and tip vortices, occurring as
each blade passes
the tower introducing a pattern, interrupting the random sound, and creating
white noise. As
the tower interrupts the vortices, it creates a low-frequency tonal signal of
sharply rising and
falling pulses. The greatest complaints of turbine noise are with regard to
the reoccurring
pattern of the tonal signal more so than the white noise generated by wind
turbines. Some
studies have shown that this tonal signal also occurs in the infrasound range,
typically about
0.75 Hz, 1.5 Hz, 2.25 Hz, 3.0 Hz, and so on. At this frequency these pulses
may be "felt or
sensed" more than "heard" by the ears.
[0013] The tip-speed ratio is the ratio between the tangential speed of the
rotor blade tip
and the actual wind velocity. This is expressed by the following formula:
[0014] 2 = Rotor tip¨speed
Wind velocity
[0015] The tip-speed can also be calculated as co times R, where co is the
rotor rotational
speed in radians/second, and R is the rotor radius in meters. This is
expressed in the
following formula:
[0016] A = ¨
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[0017] The tip-speed ratio is an indicator of the efficiency of the
turbine. The power
coefficient, Cp is a quantity that expresses the fraction of the power in the
wind that is being
extracted by the turbine.
PE
[0018]
Pw
[0019] Where PE is the total energy extracted by a rotor and Pwis the total
power in the
column of wind that is the velocity of the wind and the diameter of the rotor.
[0020] A fluid power coefficient (Cp) is a function of the power generated
by the turbine
and the total power available in the column of fluid that is the diameter of
the rotor plane and
the velocity of the fluid. The efficiency of a mechanical generator is less
than 100%;
therefore, measurements studied are appropriate relative measurements only and
do not
predict the absolute power coefficient of any of the rotors tested and
mentioned herein.
[0021] A need exits for a fluid turbine rotor blade that provides increased
rotor tip speed,
reduced noise due to tip and trailing-edge vortices and tower signature, and
reduced blade
loading.
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SUMMARY
[0022] Disclosed herein is an apparatus providing an annular formation of
varying
relative pressures, creating a rotor blade tip that interacts with the high
speed flow over a
diffuser, also referred to as a semi-annular airfoil or semi-diffuser, which
occupies between
10% and 50% of the rotor swept area of a fluid turbine. A rotor blade tip is
designed to both
improve rotor tip speed and also to increase the beneficial interaction
between a diffuser and
a rotor blade.
[0023] A dual tip on each rotor blade is designed to take advantage of a
high rotor thrust
coefficient, providing reduced coefficient of pressure in the rotor-wake and a
high flow
stream for increased mixing of rotor-wake flow with bypass flow at the exit
plane of the
rotor.
[0024] The fluid power coefficient (Cp) as a function of wake velocity
ratio and thrust
coefficient (Ct) may be increased because of the low exit-plane pressure
coefficient that
allows for a relatively higher rotor-thrust coefficient. The rotor design may
take advantage
of a highly cambered rotor shaft, designed for a greater Cp without stalling
as it would
without the dual winglet in combination with a semi-shroud.
[0025] A ringed airfoil surrounding a rotor swept area increases the mass
flow through
the rotor plane. This increased mass flow must be returned to ambient fluid
stream flow rates
in order to prevent diffuser stall. A diffuser segment that occupies less than
the whole rotor
swept area creates two wake flow conditions. One portion of the rotor wake is
similar to an
open rotor turbine, the remaining portion flows over the diffuser and has a
lower energy flow
downstream of the rotor than that of the open rotor fluid stream. As the two
wake streams
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mix, the rotor wake will return to ambient flow conditions with sufficient
rapidity to avoid
diffuser stall. Diffuser airfoil cross sections that occupy only a portion of
a rotor plane may
be designed with considerably higher camber and, therefore, higher lift
coefficients than
those designed to occupy the entire rotor swept area. The relatively higher
lift coefficient
over the semi-shroud increases tip-speed ratio for any rotor. A rotor without
a winglet
experiences an increase in tip-speed ratio between 12% and 18% whereas a rotor
with a
winglet designed to interact with the region of increased mass flow over a
semi-shroud airfoil
experiences an increase in tip-speed ratio that is between 15% and 25% over
that of the same
rotor without a semi-shroud.
[0026] One skilled in the art understands the importance of tip clearance
in regards to
shrouded turbines. The gap between the rotor blade tip and the turbine shroud
is referred to
as tip clearance. Smaller tip clearance is associated with increased effect of
the shroud on the
rotor. Excessively small tip clearance can result in rotor-shroud interference
that can damage
both rotor blades and electrical generation equipment. Applying significantly
high camber
airfoil cross sections and relatively higher lift coefficients in the tip
regions of a semi-shroud
results in an area of greatest mass flow at the tip regions of the semi-
shroud. Therefore, it is
possible to have a larger tip clearance at the ends of the semi-shroud than at
the center of the
semi-shroud. The area of greatest mass flow at the tip region of the semi-
shroud guides the
rotor tip into alignment with the semi-shroud.
[0027] Disclosed herein is an apparatus having a blade tip design that both
increases
performance in open fluid flow and also increases the performance of a rotor-
blade/diffuser
interaction. As a rotor blade rotates within a diffuser, the blade tip
interacts with an area of
increased mass flow. Increased rotor-blade surface area in the region of
increased mass flow
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increases rotor-blade tip speed. That same rotor-blade surface area is also
designed to
improve the performance of the rotor blade in open-rotor turbine conditions.
Therefore, the
same rotor blade performs with significantly increased rotor tip speed and
significantly
increased coefficient of power in both a diffuser augmented environment and an
open-rotor
environment.
[0028] As understood by one skilled in the art, the aerodynamic principles
the present
disclosure are not restricted to a specific fluid, and may apply to any fluid,
defined as any
liquid, gas or combination thereof and, therefore, includes water as well as
air. In other
words, the aerodynamic principles of a dual-tip wind rotor blade apply to
hydrodynamic
principles in a dual-tip water rotor blade.
[0029] These and other non-limiting features or characteristics of the
present disclosure
will be further described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The following is a brief description of the drawings, which are
presented for the
purposes of illustrating the disclosure set forth herein and not for the
purposes of limiting the
same. Example embodiments of the present disclosure are further described with
reference
to the appended figures. It is to be noted that the various features and
combinations of
features described below and illustrated in the figures can be arranged and
organized
differently to result in embodiments which are still within the spirit and
scope of the present
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disclosure. To assist those of ordinary skill in the art in making and using
the disclosed
systems, assemblies and methods, reference is made to the appended figures,
wherein:
[0031] FIG. 1 is front, perspective view of the present embodiment;
[0032] FIG. 2 is a detail, section view of a dual-tip rotor of the present
embodiment in
combination with a semi-shroud;
[0033] FIG. 3 is front, perspective view of an iteration of the present
embodiment;
[0034] FIG. 4 depicts a rotor blade of the embodiment of FIG 3;
[0035] FIG. 5 is a detail, section view of a dual-tip rotor of the
embodiment of FIG 3 in
combination with a semi-shroud;
[0036] FIG. 6 is front, perspective view of an iteration of the present
embodiment;
[0037] FIG. 7 depicts a rotor blade of the embodiment of FIG 6;
[0038] FIG 8 is a detail, section view of a dual-tip rotor of the
embodiment of FIG 6 in
combination with a semi-shroud;
[0039] FIG. 9 is front, perspective view of an iteration of the present
embodiment;
[0040] FIG. 10 depicts a rotor blade of the embodiment;
[0041] FIG. 11 is a detail, section view of a dual-tip rotor of the
embodiment on a turbine
without a semi-shroud;
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[0042] FIG. 12 is a detail, section view of a dual-tip rotor of the
embodiment of FIG 10
in combination with a semi-shroud.
DETAILED DESCRIPTION
[0043] The example embodiments disclosed herein are illustrative of
advantageous fluid
rotor systems, and assemblies of the present disclosure and methods or
techniques thereof. It
should be understood, however, that the disclosed embodiments are merely
examples of the
present disclosure, which may be embodied in various forms. Therefore, details
disclosed
herein with reference to example fluid rotor systems or fabrication methods
and associated
processes or techniques of assembly and or use are not to be interpreted as
limiting, but
merely as the basis for teaching one skilled in the art how to make and use
the advantageous
fluid rotor systems of the present disclosure.
[0044] A more complete understanding of the components, processes, and
apparatuses
disclosed herein can be obtained by reference to the accompanying figures.
These figures are
intended to demonstrate the present disclosure and are not intended to show
relative sizes and
dimensions or to limit the scope of the example embodiments.
[0045] Although specific terms are used in the following description, these
terms are
intended to refer to particular structures in the drawings and are not
intended to limit the
scope of the present disclosure. It is to be understood that like numeric
designations refer to
components of like function.
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[0046] The term "rotor" or "rotor assembly" is used herein to refer to any
assembly in
which blades are attached to a shaft and able to rotate, allowing for the
generation of power
or energy from fluid rotating the blades. Example embodiments of the present
disclosure
disclose a fixed-blade rotor or a rotor assembly having blades that do not
change
configuration so as to alter their angle or attack, or pitch.
[0047] In certain embodiments, the leading edge of a rotor assembly may be
considered
the front of the fluid rotor system, and the trailing edge of a rotor assembly
may be
considered the rear of the fluid rotor system.
[0048] FIG. 1 presents a front perspective view of a rotor/semi-shroud
combination of
the present disclosure in situ on a wind turbine. A wind turbine has a tower
114 that is
rotationally engaged about a vertical axis 144 with a nacelle 116 that houses
electrical
generation equipment. A rotor comprised of at least one rotor blade 112 is
rotationally
engaged about a horizontal axis 146 with the nacelle 116 and electrical
generation
equipment. A semi-shroud 110 is in fluid communication with the rotor blades
112 and is
rotationally engaged with the tower 114 about a rotational alignment means
126. Torsion
bars 118 are engaged with both the nacelle 116 and with the semi-shroud 110
and ensure that
the semi-shroud rotates about a vertical axis at the same rate as the nacelle
116 to avoid
collision between the rotor blades 112 and the semi-shroud 110.
[0049] In some embodiments, a semi-shroud 110 has varying airfoil cross
sections,
particularly at the semi-shroud tip 111. One skilled in the art understands
that as a rotor
approaches a semi-shroud it is important to avoid interference between the
rotor blade tip and
the semi-shroud. Varying airfoil cross sections at the semi-shroud tip 111 may
have
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relatively higher camber and relatively higher angle of attack providing a
relatively higher
lift coefficient than the airfoil cross sections along the majority of the
semi-shroud 110. One
skilled in the art understands that a high lift coefficient will create an
area of increased wind
velocity for a relatively greater distance from the surface area of the
airfoil. The increased
lift coefficient and increased wind velocity at a greater distance from the
airfoil begins the
fluid interaction between the rotor blade and the semi-shroud prior to the
rotor blade tip
coming into close proximity with the semi-shroud. In other words, the varying
airfoil cross
sections may be designed to create a means of aligning the rotor blade with
the semi-shroud
using airflow.
[0050] FIG 2 is a detailed cross section view, depicting the fluid
interaction between the
rotor blade 112 and the semi-shroud 110 in the vicinity of the center of the
semi-shroud 110.
Wind approaching a turbine 140 encounters an airfoil cross section of a semi-
shroud 120 and
divides into a higher velocity stream over the lift surface of the airfoil and
a lower velocity,
higher pressure flow 141 over the pressure surface of the airfoil. The region
depicted by
dashed line 128 is a region of increased lift that generates the region of
relatively greater
mass flow through the rotor plane. The increased mass flow provides increased
energy that
may be extracted by the rotor as it surrounds the tip of the rotor blade 112
thus increasing the
blade tip-speed and the coefficient of power.
[0051] FIG 3 is an illustration that depicts an iteration of the embodiment
having a dual
winglet on the tip of each rotor blade 212. Each dual winglet comprises a
forward winglet
222 and a rearward winglet 224. The illustration depicts a rotor/semi-shroud
combination of
the present disclosure in situ on a wind turbine. A wind turbine has a tower
214 that is
rotationally engaged about a vertical axis 244 with a nacelle 216 that houses
electrical
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generation equipment. A rotor comprised of at least one rotor blade 212 is
rotationally
engaged about a horizontal axis 246 with the nacelle 216 and electrical
generation
equipment. A semi-shroud 210 is in fluid communication with the rotor blades
212 and is
rotationally engaged with the tower 214 about a rotational alignment means
226. Torsion
bars 218 are engaged with both the nacelle 216 and with the semi-shroud 210
and ensure that
the semi-shroud rotates about a vertical axis at the same rate as the nacelle
216 to avoid
collision between the rotor blades 212 and the semi-shroud 210.
[0052] In some embodiments, a semi-shroud 210 has varying airfoil cross
sections,
particularly at the semi-shroud tip 211. One skilled in the art understands
that as a rotor
approaches a semi-shroud it is important to avoid interference between the
rotor blade tip and
the semi-shroud. Varying airfoil cross sections at the semi-shroud tip 211 may
have
relatively higher camber and relatively higher angle of attack providing a
relatively higher
lift coefficient than the airfoil cross sections along the majority of the
semi-shroud 210.
[0053] FIG 4 depicts a rotor of the present disclosure having a dual
winglet. The rotor
has a primary structure, otherwise referred to as the rotor shaft 240 that
extends from the root
238 to the dual tip along a centerline 242. The shaft 240 has a pressure-
surface 236 and a lift
surface 234 according to the shape of the airfoil cross section. The rotor
blade 200 further
comprises a pressure-surface winglet 222 and a lift-surface winglet 224. The
pressure-
surface winglet 222 turns from the pressure-surface 236 to angle 230 that is
between 15 and
35 with respect to a centerline 242. The lift-surface winglet 232 turns from
the lift-surface
234 at angle 232 that is between 70 and 120 with respect to the centerline
242.
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[0054] FIG. 5 is a detailed cross section view, depicting the fluid
interaction between the
rotor blade 212 and the semi-shroud 210 in the vicinity of the center of the
semi-shroud 210.
The rotor blade 212 has a dual winglet tip that has a relatively greater
surface area that
interacts with the region of high speed flow, otherwise referred to as the
area of greater mass
flow 228 over the airfoil of the semi-shroud 220. Wind approaching a turbine
240
encounters an airfoil cross section of a semi-shroud 220 and divides into a
higher velocity
stream over the lift surface of the airfoil and a lower velocity, higher
pressure flow 241 over
the pressure surface of the airfoil. The region depicted by dashed line 228 is
a region of
increased lift that generates the relatively greater mass flow through the
rotor plane. The
increased mass flow provides increased energy that may be extracted by the
rotor as it
surrounds the dual tip of the rotor blade 212 thus increasing the blade tip-
speed and the
coefficient of power. Both the pressure surface winglet 222 and the lift
surface winglet 224
are substantially inside the area of greater mass flow 228, providing more
rotor-blade
surface-area in contact with the area of greater mass flow 228, than that of a
rotor blade
without a winglet such as 112 (FIG. 2).
[0055] FIG. 6 is an illustration that depicts an iteration of the
embodiment having a dual
winglet on the tip of each rotor blade 312. Each dual winglet comprises a
forward winglet
322 and a rearward winglet 324. The illustration depicts a rotor/semi-shroud
combination of
the present disclosure in situ on a wind turbine. A wind turbine has a tower
314 that is
rotationally engaged about a vertical axis 344 with a nacelle 316 that houses
electrical
generation equipment. A rotor comprised of at least one rotor blade 312 is
rotationally
engaged about a horizontal axis 346 with the nacelle 316 and electrical
generation
equipment. A semi-shroud 310 is in fluid communication with the rotor blades
312 and is
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rotationally engaged with the tower 314 about a rotational alignment means
326. Torsion
bars 318 are engaged with both the nacelle 316 and with the semi-shroud 310
and ensure that
the semi-shroud rotates about a vertical axis at the same rate as the nacelle
316 to avoid
collision between the rotor blades 312 and the semi-shroud 310.
[0056] F IG. 7 is an illustration that depicts an iteration of a rotor
blade design the
embodiment having a dual winglet on the tip of each rotor blade 300. The rotor
has a
primary structure, otherwise referred to as the rotor shaft 340 that extends
from the root 338
to the dual tip along a centerline 342. The shaft 340 has a pressure-surface
336 and a lift
surface 334 according to the shape of the airfoil cross sections. The rotor
blade 300 further
comprises a winglet that transitions arcuately from a pressure-surface portion
322 to a lift-
surface portion 324. The pressure-surface portion 322 resides between the
centerline 342 and
the upwind end of the winglet 322, at an angle 330 that is between 15 and 35
with respect
to a centerline 342. The lift-surface portion 332 resides between the
centerline 342 and the
downwind end of the winglet 324 that is between 70 and 120 with respect to
the centerline
342. A point along the arcuate curve of the winglet is tangent with a plane
that is
perpendicular to the centerline 342. One skilled in the art understands that
the winglet exists
in the upwind area and the downwind area with respect to the centerline and
that the airfoil
cross sections at either end of the arcuate winglet may be similar to those
that transition from
the lift surface 334 and pressure surface 336 as illustrated in the
aforementioned embodiment
(FIG. 4) without the separation otherwise referred to as a crease that exists
in the
embodiment of FIG. 4.
[0057] FIG. 8 is a detailed cross section view, depicting the fluid
interaction between the
rotor blade 312 and the semi-shroud 310 in the vicinity of the center of the
semi-shroud 310.
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Wind approaching a turbine 340 encounters an airfoil cross section of a semi-
shroud 320 and
divides into a higher velocity stream over the lift surface of the airfoil and
a lower velocity,
higher pressure flow 341 over the pressure surface of the airfoil. The region
depicted by
dashed line 328 is a region of increased lift that generates the relatively
greater mass flow
through the rotor plane. The increased mass flow provides increased energy
that may be
extracted by the rotor as it surrounds the tip of the rotor blade 312 thus
increasing the blade
tip-speed and the coefficient of power. The tip clearance is the distance
between the furthest
point of a rotor blade from the rotor center and the surface of the semi-
shroud. The tip
clearance when a rotor blade is proximal to the center of the semi-shroud is
between 0.5%
and 3% of the rotor blade length and is illustrated by measurement lines 350.
[0058] FIG.9 is a front view of the embodiment, illustrating the tip
clearance when rotor
blades are proximal to the ends of the semi-shroud. Tip clearance at the ends
of the semi-
shroud is between 1% and 6% of the rotor blade length.
[0059] FIG. 10 is an illustration that depicts an iteration of a rotor
blade design the
embodiment having a dual winglet on the tip of a rotor blade 400. The rotor
has a primary
structure, otherwise referred to as the rotor shaft 440 that extends from the
root 438 to the
dual tip 430/422 along a centerline 442. The shaft 440 has a pressure-surface
436 and a lift
surface 434 according to the shape of the airfoil cross sections. The rotor
blade 400 further
comprises a first winglet 430 that transitions arcuately from the pressure-
surface 436. The
pressure-surface winglet 430 resides at an angle 430 that is between 75 and
85 with respect
to a centerline 442. A second winglet 422 transitions arcuately from the lift
surface 434. The
lift-surface winglet 422 resides at an angle that is between 80 and 120 with
respect to the
centerline 442.
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[0060] FIG. 11 presents a detailed view of a double winglet. The rotor
shaft 440 is
rotationally engaged at the root 438 with a nacelle 416 shown in section view
against a
center-line 446. The lift-surface winglet 422 has a lift surface 421 and a
pressure surface
423. The pressure surface 423 transitions from the lift surface 434 of the
primary shaft 440.
The pressure-surface winglet 430 is an airfoil that has a lift side 431 and a
pressure side 433.
One skilled in the art will understand that the lift surfaces will create
increase velocity when
compared to the pressure surface. Two streams are created as the fluid stream
encounters
each of the winglets.
[0061] FIG. 12 is a detailed cross section view, depicting the fluid
interaction between
the rotor blade 412 and the semi-shroud 410 in the vicinity of the center of
the semi-shroud
410. Wind approaching a turbine 440 encounters an airfoil cross section of a
semi-shroud
420 and divides into a higher velocity stream 440 over the lift surface of the
airfoil and a
lower velocity, higher pressure flow 441 over the pressure surface of the
airfoil. The region
depicted by dashed line 428 is a region of increased lift that generates the
relatively greater
mass flow through the rotor plane. The increased mass flow provides increased
energy that
may be extracted by the rotor as it surrounds the tip of the rotor blade 412
thus increasing the
blade tip-speed ratio and the coefficient of power. The tip clearance is the
distance between
the furthest point of a rotor blade from the rotor center and the surface of
the semi-shroud.
Both winglets 430 and 422 interact with the area of increased mass flow 428
and each
contributes to the increased tip-speed ratio. The tip clearance when a rotor
blade is proximal
to the center of the semi-shroud is between 0.5% and 3% of the rotor blade
length and is
illustrated by measurement lines 350.
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[0062] The present disclosure has been described with reference to example
embodiments. Modifications and alterations will occur to others upon reading
and
understanding the preceding detailed description. It is intended that the
present disclosure be
construed as including all such modifications and alterations insofar as they
come within the
scope of the appended claims or the equivalents thereof
Although the systems and methods of the present disclosure have been described
with
reference to example embodiments thereof, the present disclosure is not
limited to such
example embodiments and or implementations. Rather, the systems and methods of
the
present disclosure are susceptible to many implementations and applications,
as will be
readily apparent to persons skilled in the art from the disclosure hereof. The
present
disclosure expressly encompasses such modifications, enhancements and or
variations of the
disclosed embodiments. Since many changes could be made in the above
construction and
many widely different embodiments of this disclosure could be made without
departing from
the scope thereof, it is intended that all matter contained in the drawings
and specification
shall be interpreted as illustrative and not in a limiting sense. Additional
modifications,
changes, and substitutions are intended in the foregoing disclosure.
Accordingly, it is
appropriate that the appended claims be construed broadly and in a manner
consistent with
the scope of the disclosure.
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