Note: Descriptions are shown in the official language in which they were submitted.
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A WIND TURBINE WITH A RING AIRFOIL SHROUD HAVING A FLAP
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application
Serial No. 61/620,792, filed on April 5, 2012 and U.S. Provisional Application
Serial
No. 61/763,805 filed on February 12, 2013, respectively, the disclosures of
which are
incorporated herein by reference in their entirety.
BACKGROUND
[0002] The present disclosure relates to the field of ring airfoils and
more
particularly to shrouded turbines comprising unique airfoil characteristics.
More
specifically, taught herein are embodiments directed to a modified ringed
airfoil that
provides a reduced cross sectional area for reduced side loads and reduced
material
use while maintaining performance. Airfoils with structural leading edges
engaged
with substantially curved planar surfaces are common in the fields of light
aircraft and
sailing vessels. Curved planar surfaces are defined as those that have an
upper
surface that is substantially parallel to a lower surface. Such an airfoil has
a reduced
cross sectional area from that of an airfoil with continuous varying distance
between
the upper and lower surface. Utility scale wind turbines used for power
generation
have one to five open blades comprising a rotor. Rotors transform wind energy
into a
rotational torque that drives at least one generator that is rotationally
coupled to the
rotor either directly or through a transmission to convert mechanical energy
to
electrical energy.
[0003] A shrouded wind turbine has been described in U.S. Patent
Application
Serial No. 12/054,050, the disclosure of which is incorporated herein by
reference in
its entirety.
SUMMARY
[0004] The embodiments taught herein relate to a ringed airfoil with a
cross
section that includes a leading edge portion with varying distance between the
upper
and lower surface, a symmetrical region having symmetry about the chord line
through said symmetrical region wherein in one embodiment the upper surface is
substantially parallel to a lower surface, and a trailing edge region
providing a flap on
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the trailing edge that is substantially perpendicular to the chord line of the
airfoil.
Providing a flap on the trailing edge of such an airfoil further reduces the
cross
sectional area of the airfoil compared to convention air foils.
[0005] Lack of support structure(s) in an intermediate symmetrical region
does
not allow for a flap to function when configured perpendicular to the chord
line of the
resulting airfoil. Such a flap on the trailing edge of a curved planar surface
would
flex until the flap failed to have any effect on the flow over the airfoil. In
embodiments, taught herein, an orientation of the flap can be fixedly with
respect to
the chord line of the ring airfoil. For example, in one embodiment, the ring
airfoil can
include a rigid trailing edge that provides sufficient structure for a flap
that is disposed
substantially perpendicular to the chord of the airfoil.
[0006] In one embodiment, an aerodynamically contoured ring airfoil is
disclosed.
A body extends circumferentially about a center axis having an aerodynamic
structure
formed by an outer surface and an inner surface. The outer and inner surfaces
extend
axially with respect to the center axis along a camber line. The body includes
a
leading edge region, a trailing edge region, and an intermediate region
extending
between the leading edge region and the trailing edge region. The leading edge
region having a non-uniform cross-sectional thickness extending along the
camber
line defined by the outer surface and the inner surface of the body. The
trailing edge
region includes a flap extending therefrom and orientated at an angle with
respect to
a chord line of the body to allow a fluid flow flowing along the inner surface
to
remain attached to the inner surface.
[0007] In one example, embodiment, an energy extracting shrouded fluid
turbine
is disclosed that includes an energy extracting assembly and an airfoil. The
energy
extracting assembly includes a rotor disposed radially about a center axis.
The airfoil
has a body extending circumferentially about the center axis. The body has an
aerodynamic structure formed by an outer surface and an inner surface. The
outer and
inner surfaces extend axially with respect to the center axis along a camber
line. The
body includes a leading edge region a trailing edge region, and an
intermediate region
that extends between the leading edge region and the trailing edge region. The
leading edge region has a non-uniform cross-sectional thickness extending
along the
camber line defined by the outer surface and the inner surface of the body.
The
trailing edge region includes a flap extending therefrom and orientated at an
angle
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with respect to a chord line of the body to allow a fluid flow flowing along
the inner
surface to remain attached to the inner surface.
[0008] In some embodiments, the flap extends from the trailing edge region
perpendicularly to the chord line, has a length of about one-tenth to about
one-third a
length of the chord line, and/or includes at least one perforation to permit
fluid flow
through the flap.
[0009] In some embodiments, the flap extends from a trailing edge of the
airfoil.
[0010] In some embodiments, the flap extends between a first ring structure
and a
second ring structure, the first and second ring structures providing a hoop
strength to
the flap.
[0011] In some embodiments, the first ring structure provides a hoop
strength to
the trailing edge region of the body.
[0012] In some embodiments, the intermediate region includes at least one
intermediate support portion extending between the leading edge region and the
trailing edge region. In some embodiments, the intermediate support portion is
composed of a rigid material and/or has a uniform cross-sectional thickness
extending
along the mean camber line defined by the outer surface and the inner surface
of the
body.
[0013] In some embodiments, the intermediate region includes at least one
intermediate membrane portion extending between the leading edge region and
the
trailing edge region. In some embodiments, the intermediate membrane portion
has a
uniform cross-sectional thickness extending along the mean camber line defined
by
the outer surface and the inner surface of the body and/or is composed of a
non-rigid
material.
[0014] In some embodiments, the intermediate support portions provide
structural
support to the intermediate membrane portion.
[0015] Any combination or permutation of embodiments is envisioned. Other
objects and features will become apparent from the following detailed
description
considered in conjunction with the accompanying drawings. It is to be
understood,
however, that the drawings are designed as an illustration only and not as a
definition
of the limits of the present disclosure.
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BRIEF DESCRIPTION
[0016] The present disclosure relates to a ringed airfoil having a unique
airfoil
cross sectional shape with rigid portions at the leading and trailing edges,
providing
hoop strength that supports a membrane intermediate portion and allows for a
trailing
edge flap. In example embodiments, a combination rigid structural portions and
non-
rigid membrane portions can be used to form an example ring airfoil that
provides for
controlling a boundary layer at the trailing edge of the airfoil and provides
for
increased suction through the center of the ring airfoil compared to
conventional ring
airfoils. Such an airfoil provides a means of utilizing lightweight materials
while
generating aerodynamic circulation resulting in a pressure differential on the
inside of
the ring airfoil as compared to the exterior of the airfoil.
[0017] In one embodiment, the ring airfoil surrounds a rotor and electrical
generation equipment of a shrouded fluid turbine. The fluid turbine may have a
single
shroud, or may include multiple shrouds. The shrouds are comprised of
generally
ring airfoils that may include a turbine shroud and an ejector shroud.
[0018] In one embodiment, the turbine shroud houses a rotor and includes
mixing
elements at the trailing edge of the ring airfoil that are in fluid
communication with an
ejector shroud fluid stream providing a mixer-ejector pump. The shroud(s)
generate
aerodynamic circulation resulting in suction on the inside of the turbine
shroud and
are part of a tightly coupled system that, combined with the mixer-ejector
pump,
allow the acceleration of more air through the turbine rotor than that of un-
shrouded
designs, thus increasing the amount of power that may be extracted by the
rotor.
[0019] In the field of fluid dynamics, the term "stall" refers to the
condition in
which fluid flow separation occurs. In other words, the fluid flowing closely
around
the airfoil starts to detach from the surface and become turbulent. The
embodiments
taught herein are described be described in view of a mixer only embodiment
and a
mixer-ejector turbine embodiment. One skilled in the art will recognize that
the
example embodiments of the present disclosure may be readily applied to any
ringed
airfoil including any number of ducted or shrouded fluid turbine applications.
The
recitation of a mixer only embodiment and a mixer-ejector turbine embodiment
is
therefore not intended to be limiting in scope as is solely for convenience in
illustrating an example embodiment of the present disclosure. Separation of
airflow
from the aerodynamic surfaces through a mixer turbine and/or Mixer-Ejector
Turbine
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(MET) can be substantially prevented to advantageously maintain an efficiency
of the
turbine and to advantageously mitigate diffuser stall.
[0020] The Kutta-
Joukowski theorem describes the circulation around any closed
surface. It is this circulation that causes lift and increases the air flow
through the
shrouded turbine. The theorem determines the lift generated by one unit of
span in a
=
closed body and states that when the circulation is known,
the lift L per unit span
(or 1!) of a cylinder can be calculated using the following equation:
L=
Equation 1
where igN.= andt=is=N,..,. are the fluid density and the fluid velocity far
upstream of the
cylinder, respectively. The circulation is defined as a line integral in
the
following equation:
roc, = V cos 0 ds
cc
Equation 2
[0021] Improved
circulation through the use of an aerodynamic modified region
(AMR) on the trailing edge of the mixer and/or ejector shroud airfoil provides
for
increased performance of the shrouded turbine. The Kutta condition (as a
function of
the Kutta¨Joukowski theorem) controls circulation generated by the airfoil and
generally prevents flow separation from the aerodynamic surfaces until the
flow
reaches the trailing edge.
[0022] Fluid moves
through or across an airfoil shape and produces an
aerodynamic force. The component of the aerodynamic force that is
perpendicular to
the direction of fluid flow is called lift and the component parallel to the
direction of
fluid flow is called drag. Additionally, an airfoil has a suction surface and
a pressure
surface through which lift forces are generated. The airfoil suction side is
defined by
the airfoil surface turning away from the oncoming flow. Usually the top (or
outer)
and bottom (or inner) airfoil surface are joined by a curved leading edge and
a sharp
trailing edge. The camber line of the airfoil dissects this trailing edge at
one end and
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extends to the apex, or most upwind point, of the leading edge. Aerodynamic
circulation is a result of flow turning and is usually limited by flow
separation on the
airfoil suction side.
[0023] An example
embodiment of the present disclosure provides for obtaining
increased airfoil circulation, or effective flow turning, as compared to
conventional
airfoil structures by modifying the airflow across the pressure side of the
airfoil
aerodynamic surfaces, especially proximate to the trailing edge. In example
embodiments of the present disclosure, an increase in circulation can be
accomplished
by increasing surface turning on the pressure side of the airfoil. Increasing
the turning
on the pressure side is possible because the surface is turning into the flow
direction
and the flow is less apt to separate from the surface on the pressure side. In
one
embodiment, increasing the flow turning can be achieved using a trailing edge
flap on
the top (or outer) surface of the airfoil (i.e., the pressure side).
[0024] In example
embodiments, the flap can be a flat plate or other protrusion
from the trailing edge. In some embodiments, a length of the trailing edge
flap can be
on the order of 1-30% of a length of the airfoil chord extending between the
leading
edge and the trailing edge of the airfoil. The trailing edge flap can be
oriented
perpendicular to the chord line and disposed on the airfoil pressure side at
or
proximate to the trailing edge. In some
embodiments the trailing edge flap is
perforated. The perforations can allow the flap to provide an effective height
to cause
increased circulation while also providing reduced drag.
[0025] The use of
a flap effectively changes the flow-field in the region of the
trailing edge of the ring airfoil by introducing contra-rotating vortices aft
of the flap,
which alters the Kutta condition and circulation in the region.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a front, perspective view of an example ring airfoil of the
present
disclosure.
Figure 2 is a side, cross sectional view of the example airfoil of Figure 1.
Figure 3 is a side, cross sectional view of the example airfoil of Figure 1.
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Figure 4 is a side, detail, cross sectional view of the example airfoil of the
embodiment of Figure 1.
Figure 5 is a side, cross sectional view of the example airfoil of the
embodiment
of Figure 1 with flow lines.
Figure 6 is a front, perspective view of another example ring airfoil of the
present
disclosure.
Figure 7 is a side, cross sectional view of the example airfoil of Figure 6.
Figure 8 is a front, right, perspective view of an example shrouded turbine
for
which the turbine shroud corresponds to the example airfoil of Figure 1.
Figure 9 is a front, right, perspective view of an example shrouded turbine
for
which the turbine shroud corresponds to the example airfoil of Figure 6.
.Figure 10 is a front, right, perspective view of an example mixer-ejector
turbine
incorporating the example airfoils of Figures 1 and 6.
Figure 11 is a rear, right, perspective view of an example mixer-ejector
turbine of
Figure 10.
Figure 12 is a side, perspective, detail cross section of an example mixer-
ejector
turbine of Figure 10 and Figure 11, cut through the outward turning mixer
airfoil section.
Figure 13 is a side, perspective, detail cross section of the mixer-ejector
turbine of
Figure 10 and Figure 11, cut through the inward turning mixer airfoil
section.
Figure 14 is a detailed view of the flaps disposed on a trailing edge regions
of the
example mixer ejector turbine of Figure 10 and Figure 11.
Figure 15 is a front, right, perspective view of another example mixer-ejector
turbine for which the turbine shroud and the ejector shroud have a faceted
configuration.
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Figure 16 is a side, perspective, detail cross section of an example mixer-
ejector
turbine of Figure 15, cut through the outward turning mixer airfoil section.
Figure 17 is a front, right, perspective view of another example shrouded
turbine
for which the turbine shroud has a faceted configuration.
DETAILED DESCRIPTION
[0026] 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.
[0027] Although specific terms are used in the following description, these
terms
are intended to refer only 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.
[0028] The term "about" when used with a quantity includes the stated value
and
also has the meaning dictated by the context. For example, it includes at
least the
degree of error associated with the measurement of the particular quantity.
When
used in the context of a range, the term "about" should also be considered as
disclosing the range defined by the absolute values of the two endpoints. For
example, the range "from about 2 to about 4" also discloses the range "from 2
to 4."
[0029] A shrouded turbine can include a turbine shroud with or without
mixing
lobes on a trailing end of the turbine shroud. As set forth previously, a
shrouded
turbine that includes a mixer shroud is one suitable example of a ringed
airfoil in
which the example embodiments of the present disclosure may be utilized. The
turbine shroud includes a cambered shroud, wherein the shroud is a
substantially
ringed airfoil. The turbine shroud contains a rotor, which extracts power from
a
primary fluid stream. The turbine shroud provides for increased flow through
the
rotor allowing increased energy extraction due to higher flow rates compared
to
shroudless fluid turbines.
[0030] A Mixer-Ejector Turbine (MET) can provide an improved means of
generating power from fluid currents using a mixer/ejector pump. As set forth
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previously, a MET is one suitable example of a ringed airfoil in which the
example
embodiments of the present disclosure may be utilized. The Mixer-Ejector
Turbine
includes tandem cambered shrouds, wherein each shroud is a substantially
ringed
airfoil, and a mixer/ejector pump. The primary shroud contains a rotor, which
extracts
power from a primary fluid stream. The tandem cambered shrouds and ejector
provide
for increased flow through the rotor allowing increased energy extraction due
to
higher flow rates compared to shroudless fluid turbines. The mixer/ejector
pump
transfers energy from the bypass flow to the rotor wake flow allowing higher
energy
per unit mass flow rate through the rotor. These two effects enhance the
overall
power production of the turbine system.
[0031] The term "rotor" is used herein to refer to any assembly in which
one or
more blades are attached to a shaft and able to rotate, allowing for the
extraction of
power or energy from wind rotating the blades. Example rotors include a
propeller-
like rotor or a rotor/stator assembly. Any type of rotor may be enclosed
within the
turbine shroud in the fluid turbine of the present disclosure.
[0032] The leading edge of a shroud may be considered the front of an
airfoil,
and the trailing edge of an airfoil may be considered the rear of the airfoil.
A first
component of the airfoil located closer to the front of the airfoil may be
considered
"upstream" of a second component located closer to the rear of the
airfoil(i.e. the
second component is "downstream" of the first component). Furthermore, the
term
"inner surface" is used herein to define a surface of ring airfoil that is
inwardly facing
towards a center axis of the airfoil. The term "outer surface" is used herein
to define a
surface that is outwardly facing away from the center axis of the airfoil such
that the
inner surface is closer to the center axis than the outer surface. Likewise,
the term
"suction side" or "low pressure side" of the ring airfoil is used herein to
refer to the
interior of the airfoil (i.e. radially inward of the inner surface) and the
term "pressure
side" of the airfoil is used herein to refer to exterior of the airfoil (i.e.
radially outward
from the outer surface).
[0033] The term "hoop strength" is used herein to refer to an ability of a
structure
to resist radially deformational forces about a circumference of a generally
cylindrical
or ring shaped structure and provide dimensional stability. For example,
example
embodiments of an airfoil described herein can include a rigid trailing edge
region
having a hoop strength to resist deformational forces of a fluid flow.
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[0034] In one embodiment, the present disclosure relates to a ring airfoil
that
includes a generally rigid structural leading edge region, an intermediate
region
formed of structurally rigid and non-rigid portions, and a generally rigid
structural
trailing edge region. The ring airfoil further comprises a flap on the
trailing edge
portion that is substantially perpendicular to the chord of the airfoil. An
orientation of
the flap with respect to the chord line can be fixed. In one embodiment, an
exemplary
embodiment of the ring airfoil can be implemented as a turbine shroud or a
turbine
mixer shroud that includes inward and outward turning segments that surround a
rotor
and/or an example embodiment of the ring airfoil can be implemented as an
ejector
shroud that generally surrounds an exit of a turbine shroud or a turbine mixer
shroud.
[0035] Figure 1 is a front perspective view of an example ring airfoil 100.
The
airfoil 100 can have a body 102 extending circumferential about a center axis
105.
The body 102 includes a leading edge region 112, an intermediate region 115
having
one or more intermediate membrane portions 138 and one or more intermediate
support portions 139, and a trailing edge region 116 having a flap 136. The
leading
edge region 112 can include a leading edge 162 of the airfoil 100 and the
trailing edge
region 116 can include a trailing edge 166 of the airfoil 100. The one or more
intermediate portions 138 and 139 of the intermediate region 115 can extend
between
the leading edge region 112 and the trailing edge region 116 to mechanically
couple
the leading edge region 112 to the trailing edge portion 116. The one or more
intermediate membrane portions 138 can be formed of one or more semi-rigid
and/or
non-rigid materials, e.g., as discussed herein, and the one or more
intermediate
support portions 139 can be formed of one or more a semi-rigid and/or rigid
materials,
e.g., as discussed herein. In an example embodiment, the ringed structurally
rigid
leading edge region combined with the rigid trailing edge region and
intermediate
discrete support portions provide sufficient rigidity to support the flap 136
on the
trailing edge region 116 in a fixed relationship to a chord line and cambered
line
while implementing the intermediate membrane portion(s) to form surfaces of
the
intermediate region 115 of the airfoil 100. Thus, the structure of the airfoil
100
facilitates a fixed angular relationship between the flap 136 and the chord
line 140 as
well as between the flap 136 and the mean cambered line 170. Example
embodiments
of the airfoil 100 including a flap as described herein (e.g., flaps 136 and
236) can
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result in a ringed airfoil that exhibits similar performance characteristics
as a
conventional airfoils that have a greater chord length and no flap.
[0036] In an example embodiment, the one or more intermediate support
portions
139 can provide structural support to the body 102 between the leading edge
portion
112 and the trailing edge portion 116. The intermediate support portions 139
can be
spaced apart from each other and can be distributed discretely and
circumferentially
about the center axis 105. The intermediate support portions 139 can be
dimensioned
and/or configured to specify a spatial relationship between the leading edge
portion
112 and the trailing edge portion 116 and/or a shape of the one or more
intermediate
membrane portions 138. As one example, in one embodiment, the one or more
intermediate support portions 139 can set a distance between the leading edge
and the
trailing edge of the airfoil 100, which conesponds to a chord line of the
airfoil 100.
As another example, in one embodiment, the intermediate support portions 139
can be
contoured to taper away from the center axis 105 towards the trailing edge
region 116
such that a diameter of the trailing edge portion is larger than a diameter of
the
leading edge portion 112. In some embodiments, the one or more intermediate
membrane portions 138 can generally conform to the contours of the
intermediate
support portions 139. In some embodiments, the one or more intermediate
portions
138 can be contoured independently of the one or more intermediate support
portions.
[0037] In some embodiments, the leading edge region 112, the trailing edge
region 116, and the one or more intermediate support portions 139 can be
integrally
formed as a single integral unit, and the one or more intermediate membrane
portions
138 can be separately attached to form the body 102. In some embodiments, the
leading edge region 112, the trailing edge region 116, the one or more
intermediate
portions 138, and the one or more intermediate support portions 139 can be
separate
components that are mechanically coupled together to form the body 102.
[0038] Some examples of plastic materials that can be used to form the
leading
edge region 112, the trailing edge region 116, and/or the one or more
intermediate
support portions 139 of the airfoil 100, or portions thereof, can include, but
are not
limited to polymers, such as a polyolefin or a polyamide, carbon composites,
and/or
metals. Some examples of polyolefins include polypropylene and polyethylene,
such
as high density polyethylene (HDPE) and low density polyethylene (LDPE). Some
examples of polyamides include nylons. In some embodiments, polyvinyl chloride
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and plastisols can be used to form the leading edge region 112 and trailing
edge
region 116.
[0039] Some
examples of materials that can be used to form the intermediate
membrane portions 138 can include, but are not limited to fabrics, polymeric
films,
thin metal sheets, thin composites, marine shrink wrap, and the like. For
embodiments in which fabric used, the fabric can be impregnated with a polymer
resin (such as polyvinyl chloride) or a polymer film (such as modified
polytetrafluoroethylene). Some examples of polymeric films include, but are
not
limited to polyvinyl chloride (PVC), polyurethane, polyfluoropolymers, multi-
layer
films of similar composition, and the like. Polyurethane films can be durable
and can
have good weatherability. Aliphatic versions of polyurethane films can be
generally
resistant to ultraviolet radiation. Some examples of polyfluoropolymers
include
polyvinyldidene fluoride (PVDF) and polyvinyl fluoride (PVF). Commercial
versions
are available under the trade names KYNAR and TEDLAR . Polyfluoropolymers
generally have very low surface energy, which allow their surface to remain
somewhat free of dirt and debris, and can shed ice more readily as compared to
materials having a higher surface energy.
[0040] In example
embodiments, the material or materials used to form the airfoil
100 and/or portions thereof can be reinforced with a reinforcing material,
such as, for
example, highly crystalline polyethylene fibers, paramid fibers, and
polyaramides.
[0041] The leading
edge region 112, the trailing edge region 116, the one or more
intermediate support portions 138, and/or the one or more intermediate
membrane
portions 139 can be formed of multiple layers of material, for example,
comprising
two, three, or more layers. Multi-layer constructions may add strength, water
resistance, ultraviolet (UV) stability, and other functionality.
[0042] In some
embodiments, the leading edge region 112 of the airfoil can be a
sandwich composite material, such as an epoxy-impregnated e-glass matte, and
the
space inside the sandwich composite can be filled with foam. This
configuration
provides for high beam stiffness construction with overall low density.
[0043] Figure 2 is
a cross sectional view of an example embodiment of a ring
airfoil of the present disclosure along the line 2-2 of Figure 1 depicting one
of the
intermediate membrane portions 138 of the airfoil 100. The leading edge region
112
can extend from the leading edge 162 to the intermediate region 115. The
leading
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edge region 112 can have a volumetric form with varying thickness TL between
the
inner surface 132 (i.e. suction side surface 132) and the outer surface 134
(i.e.
pressure side surface 134), thus creating a volume of varying thickness TL.
The
leading edge 162 of the airfoil 100 can be generally rounded, bull-nosed, or
otherwise
shaped to form an aerodynamic surface for dividing a fluid into at least two
flows or
streams (e.g., a suction side along the inner surface 132 and a pressure side
along the
outer surface 134. The cross-sectional shape of the leading edge region 112
can taper
away from the leading edge 162 increasing in cross-sectional thickness TL and
then
can taper towards a center or mean camber line 170 decreasing in cross-
sectional
thickness TL to a joint 131 between the intermediate membrane portion 138
along the
mean camber line 170 such that the cross-sectional thickness TL of the leading
edge
region 112 generally varies from the leading edge 162 to joint 131
mechanically
coupling the leading edge region 112 to the intermediate membrane portions
138.
The center or mean camber line 170 is generally positioned midway between
outer
and inner surfaces 132 and 134 of the airfoil 100, respectively, along the
longitudinal
extent of the airfoil 100.
[0044] As depicted in Figure 2, a chord 140 defines a length of the airfoil
100
between the leading edge 162 and the trailing edge 166 of the airfoil 100,
which can
be determined based on the mean camber line 170. A cross-sectional thickness
of the
airfoil 100 can correspond to a distance from the outer surface 134 to the
inner surface
132 of the airfoil 100, measured perpendicular to the mean camber line 170,
and can
vary with distance along the mean camber line 170 such that the cross-
sectional
thickness of the airfoil 100 varies over a length of the airfoil 100 from the
leading
edge 162 to the trailing edge 166. An interior area (or volume) 113 formed by
the
surfaces 132, 134 in the leading edge region 112 can be hollow, or can be
filled with
support members for providing structural rigidity and shape. In accordance
with one
embodiment, a foam material 172 may be utilized in providing both shape and
structural rigidity to the assembly.
[0045] In some embodiments, the one or more intermediate membrane portions
138 of the intermediate region 115 can extend linearly from the leading edge
region
112 to the trailing edge region 116. In some embodiments, the intermediate
membrane portions 138 can have a curvature between the leading edge region 112
and the trailing edge region 116. The intermediate membrane portions 138 can
have a
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substantially uniform and constant cross-sectional thickness Tim along its
length. In
the example embodiment, the surfaces 132, 134 can be positioned adjacent to
each
other and can be in contact to form the intermediate membrane portions 138
such that
the cross-sectional thickness Tim of the intermediate membrane portions 138
can be
approximately equal the thickness of the material or materials between the
surfaces
132, 134. In some embodiments, the intermediate membrane portions 138 can be
formed of a sheet of material with a thickness such that no space or void
exists in the
intermediate membrane portions 138. For example, the intermediate membrane
portions 138 can be a curved planar form with relatively constant thickness.
[0046] In one example embodiment, the intermediate membrane portions 138
can
be tacked, adhered, friction fit, or otherwise attached or fixed to the
leading edge
region 112 to secure the intermediate membrane portions 138 to the leading
edge
region 112. In one example embodiment, the joint 131 between the leading edge
region 112 and the intermediate membrane portions 138 can be formed by a
groove or
channel 117 configured to receive and hold an upstream end 143 of the
intermediate
membrane portions 138. For example, the upstream end 143 can have a circular
cross
section corresponding to a circular cross section of the channel 117 such that
the
upstream end 143 of the intermediate membrane region 138 can slide into,
engage,
and be retained by the channel 117 of the leading edge region 112.
[0047] In example embodiments, the trailing edge region 116 can be formed
as a
ringed structure extending circumferentially about the center axis 105 and the
trailing
edge 116 can have a diameter or width that is greater than a diameter or width
of the
leading edge 162. An end of the trailing edge region 116 opposite of the
trailing edge
166 can include a recessed portion, such as a notch or channel 182 configured
to
receive and mechanically couple to the intermediate membrane portions 138. In
an
example embodiment, the trailing edge region can provide rigidity to the
trailing edge
166 of the airfoil 100 such that the trailing edge 166.
[0048] The trailing edge region 116 can include the flap 136 extending
therefrom.
In one example embodiment, the flap 136 can extend radially outward from or
proximate to the trailing edge 166. The flap 136 can have a length L that
extends at
an angle 0 with respect to the chord line 140. In an example embodiment, the
angle 0
between the chord line 140 and the flap 136 can be fixed. The length L of the
flap
136 can be about ten to about thirty percent less than a length of the chord
line 140.
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In an example embodiment, the length L of the flap 136 can extend
perpendicularly to
the chord line 140 and can be implemented to turn the airflow along the outer
surface
134. In example embodiments, the flap 136 can include perforations 184 to
allow
some air to flow through the flap 136 to reduce the force exerted on the flap
by the
airflow. In exemplary embodiments, the flap 136 can be formed of the same or a
similar material as the intermediate membrane portions 138.
[0049] Figure 3 is a cross sectional view of the airfoil of Figure 1 along
the line
3-3 of Figure 1 depicting one of the intermediate support portions 139 of the
intermediate region 115, which can be disposed between and between the leading
edge region 112 and the trailing edge region 116. In one example embodiment,
as
depicted in Figure 3, the intermediate support portions 139 can be integrally
formed
with the leading edge region 112 such that the intermediate support portions
139
forms a unitary structure with the leading edge region 112 and the
intermediate
support portions 139 can be mechanically coupled to the trailing edge region
116. In
another example embodiment, the intermediate support portions 139 can be
mechanically coupled to the leading edge region 112 and/or the trailing edge
region
116. In yet another example embodiment, the intermediate support portions 139
can
be integrally formed with the leading edge region 112 and/or the trailing edge
region
116.
[0050] The intermediate support portions 139 can provide structural
support for
the air foil 100 to define a distance between the leading edge region 112 and
the
trailing edge region 116 and/or can provide a support structure for the
intermediate
membrane portions 139, e.g., to define a contour of the intermediate membrane
portions 138. The intermediate rigid portions 139 can be elongate members have
a
generally rod-like or bar-like configuration. The intermediate support
portions 139
can be configured to engage the channel 182 formed in the trailing edge region
116 to
mechanically couple the intermediate support portions 139 to the trailing edge
region
116. In some embodiments the intermediate support portions can be integrally
formed with the leading edge region 112 and/or the trailing edge region 116.
[0051] In some embodiments, the intermediate support portions 139 can
extend
linearly from the leading edge region 112 to the trailing edge region 116. In
some
embodiments, the intermediate support portions 139 can have a curvature
between the
leading edge region 112 and the trailing edge region 116. The intermediate
support
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portions 139 can have a substantially uniform and constant cross-sectional
thickness
TN along the length. In the example embodiment, the surfaces 132, 134 of the
intermediate support portions 139 can be positioned adjacent to each other and
can be
in contact to form the intermediate support portions 139 such that the cross-
sectional
thickness TB of the intermediate support portions 139 can be approximately
equal the
thickness of the material or materials between the surfaces 132, 134. In some
embodiments, the intermediate support portions 139 can be formed of a sheet of
material with a thickness such that no space or void exists in the
intermediate support
portions 139. For example, the intermediate support portions 139 can be a
curved
planar form with relatively constant thickness.
[0052] In one embodiment, the intermediate membrane portions 138 can
encompass or encircle the intermediate support portions 139. In some
embodiments,
the intermediate membrane portions 138 can be tacked, adhered, friction fit,
or
otherwise attached or fixed to the intermediate support portions 139 to secure
the
intermediate membrane portions 138 to the intermediate support portions 139.
For
example, in one embodiment, a polyethylene shrink wrap can be used as the
intermediate membrane portion(s) 138, and the polyethylene shrink wrap can
encircle
the intermediate support portions 139 and heat can be applied to the
polyethylene
shrink wrap to shrink the polyethylene shrink wrap onto the intermediate
support
portions 139 forming a tight friction fit. In some embodiments, the
intermediate
membrane portions 138 can each extend between a pair of intermediate support
portions 139 from the leading edge region 112 to the trailing edge region 116.
[0053] Referring to Figure 4, an orthographic detail section view of
trailing edge
region 116 of the airfoil 100 of Figure 2 is depicted. The example embodiment
includes the flap 136 on the trailing edge 116. The flap 136 is generally
perpendicular, or in other words, is at the angle 0 between approximately 85
and
120 relative to the chord line 140 of the airfoil cross section. In some
embodiments
the trailing edge region 116 can include a rigid member 148 that engages the
membrane intermediate portion 138 (e.g., via channel 182). The rigid member
148 is
engaged with a ring 146 that is in turn engaged with a flap 136. The ring 146
provides hoop strength to the rigid member 148. The flap 136 contains at least
one
ring 144 that provides hoop strength to the outer edge of the flap 136. As
discussed
above, rigid structural support members in the form of the intermediate
support
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portions 139 are spaced radially about the ringed airfoil proximal to
intermediate
membrane portions 138 (Figures 1 and 3). The intermediate support portions 139
provide structure to support the location and configuration of the trailing
edge 116.
The structural support provided by the intermediate support portions 139
maintains
the angle 0 of the flap 136 with respect to the chord 140 and provides a
structure to
support the membrane intermediate portions 138.
[0054] Referring to Figure 5, an orthographic cross section of a ring
airfoil of an
example embodiment 100 is depicted. The direction and path of fluid flow
around the
airfoil 100, from the leading edge 112 to the trailing edge 116 is represented
by arrow
152 on the suction side 132 (i.e. the inner surface 132), and arrow 154 on the
pressure
side 134 (i.e. the outer surface).
[0055] Referring again to Figure 5, the flap 136 causes an area of
stagnation 141
in the flow on the pressure side of the airfoil 134. The addition of the flap
136 on or
proximate to the trailing edge 166 of the airfoil 100 also generates vortices
118
downwind of the trailing edge 116 of the airfoil 100. The addition of the flap
136
causes the air stream 154 on the pressure side 134 of the airfoil 100 to be
pushed
upward thus allowing the fluid stream 152 on the suction side 132 of the
airfoil 100 to
stay attached to the surface and generate improved circulation of the fluid
streams.
[0056] Figure 6 depicts a perspective view of another example airfoil 200.
A
body 202 of the airfoil 200 can include a leading edge region 212, an
intermediate
region 215, and a trailing edge region 216. The airfoil 200 can include mixing
elements 226, 228 that may be formed by the intermediate region 215 and the
trailing
edge region 216. As depicted, the mixing lobes may include low energy mixing
lobes
228 that extend inward toward the central axis 205, and high energy mixing
lobes 226
that extend outward away from the central axis 105. In other words, the
trailing edge
124 of the turbine shroud 104 is shaped to form two different sets of mixing
lobes.
The mixing lobes 126, 128 can form a general circular crenellated or
circumferential
undulating in-and-out shape about the center axis 205.
[0057] The trailing edge region 216 of the airfoil 200 can be formed of a
rigid
material and can have a general circular crenellated or circumferential
undulating in-
and-out shape about the center axis 205, which can import the structural
configuration
of the mixing lobes 126, 128 to intermediate membrane portions 238 of the
intermediate region 215. The trailing edge region can include one or more
flaps 236.
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In an example embodiment, as depicted in Figure 6, each low energy mixing lobe
228
can include one of the flaps 236 and high energy mixing lobes 226 can be
devoid of
the flap 236. In another example embodiment, the high energy and low energy
mixing lobes 226, 228 can include a flap 236. In yet another example
embodiment,
the flap 236 can extend continuously along the trailing edge region 216 to
form a
single flap continuously disposed about the center axis 205. In an example
embodiment, the ringed structural leading edge region 212 combined with the
rigid
trailing edge region 216 and intermediate discrete support portions of the
intermediate
region 215 provide sufficient rigidity to support the flap 136 on the trailing
edge
region 116 in a fixed relationship to the chord line while implementing the
intermediate membrane portion(s) as to form the surfaces of the intermediate
region
of the airfoil. Thus, the structure of the airfoil 100 facilitates provide a
fixed angular
relationship between the flap 136 and the chord line 140 as well as between
the flap
136 and the mean cambered line 170. Example embodiments of the airfoil 200
including the flap 236 can result in a ringed airfoil that exhibits similar
performance
characteristics as a conventional airfoils that have a greater chord length
and no flap.
[0058] In an
example embodiment, the one or more intermediate support portions
239 can provide structural support to the body 202 between the leading edge
portion
212 and the trailing edge portion 216. The intermediate support portions 239
can be
spaced apart from each other and can be distributed discretely and
circumferentially
about the center axis 205. The intermediate support portions 239 can be
dimensioned
and/or configured to specify a spatial relationship between the leading edge
portion
212 and the trailing edge portion 216. As one example, in one embodiment, the
one
or more intermediate support portions 239 can set a distance between the
leading edge
and the trailing edge of the airfoil 200, which corresponds to a chord line of
the airfoil
200.
[0059] Figure 7 is
a cross sectional view of the airfoil 200 of Figure 6 along
the line 7-7. As depicted in Figure 7, the cross section of the airfoil 200
generally
corresponds to the cross-section of the airfoil 100 in that that the leading
edge region
includes a varying volume and the intermediate membrane portion(s) 238
includes a
generally uniform volume. The leading edge 262 of the airfoil 100 can be
generally
rounded, bull-nosed, or otherwise shaped to form an aerodynamic surface for
dividing
a fluid into at least two flows or streams (e.g., a suction side along the
inner surface
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232 and a pressure side along the outer surface 234. The cross-sectional shape
of the
leading edge region 212 can taper away from the leading edge 262 increasing in
cross-sectional thickness and then can taper towards a center or mean camber
line 270
decreasing in cross-sectional thickness to the intermediate region along the
mean
camber line 270. The center or mean camber line 270 is generally positioned
midway
between outer and inner surfaces 232 and 234 of the airfoil 200, respectively,
along
the longitudinal extent of the airfoil 200.
[0060] As depicted in Figure 7, a chord 240 defines a length of the airfoil
200
between the leading edge 262 and the trailing edge 266 of the airfoil 200,
which can
be determined based on the mean camber line 270. The intermediate membrane
portion 238 can have a substantially uniform and constant cross-sectional
thickness
along its length. In the example embodiment, the surfaces 232, 234 can be
positioned
adjacent to each other and can be in contact to form the intermediate membrane
portion 238.
[0061] Similar to the intermediate region 115 of the example airfoil 100
described
herein, the intermediate region 215 can include intermediate membrane portions
238
and intermediate support portions 239. The intermediate membrane portions 238
can
be formed of semi-rigid and/or non-rigid materials and the intermediate
support
portions 239 can be formed of semi-rigid and/or rigid materials. The
intermediate
region 215 provides the transitional area between the inward turning mixing
elements
226 and the outward turning mixing elements 228. The rigid trailing edge
region 216
provides the structure to support the membrane surfaces that make up the
mixing
elements 226 and 228. In example embodiments, the trailing edge region 216 can
be
formed as a rigid structure extending about the center axis 205 in the
circumferential
undulating manner. In an example embodiment, the trailing edge region 216 can
provide rigidity to the trailing edge 266 of the airfoil 200 such that the
trailing edge
266.
[0062] The trailing edge region 216 can include the flap 236 extending
therefrom.
In one example embodiment, the flap 236 can extend radially outward from or
proximate to the trailing edge 266. The flap 236 can have a length L that
extends at
an angle 0' with respect to the chord line 240. In an example embodiment, the
angle
0' between the chord line 140 and the flap 236 can be fixed and/or the length
L of the
flap 236 can be about ten to about thirty percent less than a length of the
chord line
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240. In an example embodiment, the length L of the flap 236 can extend
perpendicularly to the chord line 240 and can be implemented to turn the
airflow
along the outer surface 234. In the
present example embodiment, the flap 236 is
engaged with the trailing edge 266 of the outward turning mixing elements 228.
The
trailing edge 266 is comprised of similar components as depicted and described
in
Figures 3-4 . In example embodiments, the flap 236 can include perforations
284 to
allow some air to flow through the flap 236 to reduce the force exerted on the
flap 236
by the airflow. The flap 236 is dimensioned and configured to allow a fluid
flow
flowing along the inner surface to remain attached to the inner surface.
[0063] Figure 8
depicts a front perspective view of an example shrouded fluid
turbine 300 in the form of a wind turbine having a support structure 302, an
energy
extracting assembly 345 and a turbine shroud formed by the example airfoil 100
having the leading edge region 112, the intermediate region 115, and the
trailing edge
region 116. The energy extracting assembly 345 can include a nacelle body 350
and a
rotor 340. The rotor 340 is engaged with the nacelle body 350 at the proximal
end of
the rotor blades. The airfoil 100 can encircle the rotor 340. In one example,
embodiment the leading edge 166 of the airfoil 100 can be positioned up stream
of the
rotor 340 and/or the trailing edge 166 of the airfoil 100 can be positioned
downstream
of the rotor 340. The leading edge 162 can form an inlet of the shrouded fluid
turbine
300 and the trailing edge 166 can form the exhaust of the shrouded fluid
turbine 300.
The flap 136 can allow a fluid flow (e.g., airflow) flowing along the inner
surface of
the air foil to remain attached to the inner surface. In an example
embodiment, the
airfoil 100 can be positioned relative to the nacelle body 350 and rotor 340
using
elongate support structures 307 such that the nacelle body 350, the rotor 340,
and the
airfoil 100 are position coaxially with respect to each other about the center
axis 105.
[0064] Figure 9
depicts a front perspective view of an example shrouded fluid
turbine 400 in the form of a wind turbine having the support structure 302,
the energy
extracting assembly 345, and a turbine mixer shroud formed by the example
airfoil
200 having the leading edge region 212, the intermediate region 215, and the
trailing
edge region 216. The airfoil 200 can encircle the rotor 340. In one example,
embodiment the leading edge 266 of the airfoil 200 can be positioned up stream
of the
rotor 340 and/or the trailing edge 266 of the airfoil 200 can be positioned
downstream
of the rotor 340. The leading
edge 262 can form an inlet of the shrouded fluid
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turbine 400 and the trailing edge 266 can form the exhaust of the shrouded
fluid
turbine 400. As described above, the trailing edge 266 includes inward turning
mixing elements 226 and outward turning mixing elements 228. The inward
turning
mixing elements 226 curve inward toward the central axis 205 and the outward
turning mixing elements 228 curve outward from the central axis 205. The flap
236
can allow a fluid flow (e.g., airflow) flowing along the inner surface of the
air foil to
remain attached to the inner surface. In an example embodiment, the airfoil
200 can
be positioned relative to the nacelle body 350 and rotor 340 using elongate
support
structures 307 such that the nacelle body 350, the rotor 340, and the airfoil
200 are
position coaxially with respect to each other about the center axis 205.
[0065] Figure 10 is a front, perspective view of an example embodiment of a
shrouded fluid turbine 500 incorporating example embodiments of the ring
airfoils
100 and 200 of the present disclosure. Figure 11 is a rear, perspective view
of the
shrouded fluid turbine of Figure 10. Figure 12 is a side perspective, detail,
section
view of the shrouded fluid turbine 500 of Figures 10 and 11 cut through the
outward
turning mixing elements 228. Figure 13 is a side perspective, detail, section
view of
the shrouded fluid turbine 500 of Figures 10 and 11 cut through the inward
turning
mixing elements 226. The detail cross sections of Figure 12 and 13 depict the
ring
airfoils 100 and 200 of the present disclosure incorporated into the mixer-
ejector
turbine shrouds. The ring airfoil 100 includes the leading edge region 112,
the
intermediate region 115, and the trailing edge region 116. The ring airfoil
200
includes the leading edge region 212, the intermediate region 215, and the
trailing
edge region 216.
[0066] In an example, embodiment, the shrouded fluid turbine 500 may be
refened to as a mixer/ejector fluid turbine, where the airfoils 200 and
airfoil 100 form
an mixer/ejector pump. Referring to Figures 10-13, the shrouded fluid turbine
500 is
supported by the support structure 302 and comprises a turbine mixer shroud
formed
by an example embodiment of the airfoil 200, the energy extract assembly
formed by
the nacelle body 350 and the rotor 340, and an ejector shroud formed by the
airfoil
200. The rotor 340, airfoil 200 (i.e. turbine mixer shroud), and the airfoil
100 (i.e. the
ejector shroud) are coaxial with each other, i.e. they share a common central
axis 505.
In an example embodiment, the airfoil 200 can be positioned relative to the
nacelle
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body 350 and rotor 340 using elongate support structures 307 and the airfoil
100 can
be positioned relative to the airfoil 200 using elongate support structures
506.
[0067] In one example, embodiment the leading edge 266 of the airfoil 200
can be
positioned up stream of the rotor 340, the trailing edge 266 of the airfoil
200 can be
positioned downstream of the rotor 340, the leading edge 162 of the airfoil
100 can be
disposed downstream of the rotor 340, and/or the trailing edge 166 of the air
foil 166
can be positioned downstream of the trailing edge 266. The leading edge 262
can
form an inlet of the airfoil 200 in the shrouded fluid turbine 400 and the
trailing edge
266 can form the exhaust of the airfoil 200 in the shrouded fluid turbine 400.
[0068] The ejector shroud formed by the airfoil 100 includes a front end or
inlet
end defined by the leading edge 162, and a rear end or exhaust end defined by
the
trailing edge 166.
[0069] Figure 14 depicts the trailing edge regions 116 and 216 in more
detail to
illustrate example perforation 184 and 284, respectively. The perforations 184
and
284 can be formed in the flaps 136 and 236, respectively to allow some air to
flow
through the flaps 136, 236 to reduce the force exerted on the flap 236 by the
airflow.
[0070] Figure 15 is a front, perspective view of another exemplary
embodiment of
a shrouded fluid turbine 600 incorporating example ring airfoils 700 and 800
of the
present disclosure. Figure 16 is a side, orthographic, detail, section view of
the fluid
turbine of Figure 15. Referring to Figures 15-16, the shrouded fluid turbine
600 is
supported by the support structure 302 and includes the energy extracting
assembly
345 having the rotor 340 and the nacelle body 350. The ring airfoil 700 forms
a
turbine shroud and the ring airfoil 800 forms an ejector shroud of the
shrouded fluid
turbine 600. The rotor 340, turbine shroud (i.e. the airfoil 700), and ejector
shroud
(i.e. the airfoil 800) are coaxial with each other, i.e. they share a common
central axis
605.
[0071] The airfoils 700 and 800 can be formed in a similar manner to the
example
airfoils 100 and 200, as described herein. The airfoil 700 can include a
leading edge
region 712 having a leading edge 762 that forms a front end or inlet end of
the airfoil
700. The leading edge region 712 can have a substantially similar or identical
cross-
sectional structure (depicted in Figure 16) to that of the leading edge
regions 112 and
212, as described herein.
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[0072] The airfoil 700 also includes a trailing edge regions 716 having a
trailing
edge 766 that form a rear end or outlet (exhaust) end of the airfoil 700. The
trailing
edge region 716 can have a substantially similar or identical cross-sectional
structure
(depicted in Figure 16) to that of the trailing edge region 112, as described
herein. In
the present example, the trailing edge region 716 can have multi-sided polygon
shape
having a faceted structure. For example, the trailing edge regions 716 can
include
facets 775 that are enjoined at nodes 777.
[0073] The airfoil 800 includes a leading edge region 812 having a leading
edge
862 that forms a front end or inlet end of the airfoil 800 and a rear end. The
airfoil
800 also includes a trailing edge region 816 having a trailing edge 866 that
forms an
exhaust end or outlet end of the airfoil 800. The airfoil 800 includes a
faceted annular
airfoil for which the leading edge region 812 can have a substantially similar
or
identical cross section as the leading edge regions 112, 212, and 712
described herein.
In the present example, the trailing edge region 816 can have multi-sided
polygon
shape having a faceted structure. For example, the trailing edge regions 816
can
include facets 875 that are enjoined at nodes 877.
[0074] The airfoils 700 and 800 can include intermediate regions 715 and
815,
respectively, that extend between the leading edge regions 712 and 812,
respectively,
to the trailing edge regions 716 and 816, respectively. The intermediate
regions 715
and 815 can be formed of intermediate support portions and intermediate
membrane
portions.
[0075] A detail cross section of the shrouded turbine of Figure 15 is
depicted in
Figure 16 and illustrates the faceted annular airfoils 700 and 800
incorporated into the
mixer-ejector turbine shrouds. The airfoils 700 and 800 have the voluminous
leading
edge regions 712 and 812, respectively, that is engaged with the intermediate
regions
715 and 815, respectively, which form a transitional area between the leading
edge
regions 7 12/8 12 and the trailing edge regions 716/816, respectively. A rigid
trailing
edge region 716 is comprised of similar components as shown and described
herein
and provides the structure to support the intermediate membrane portions of
the
intermediate region 715.
[0076] In some embodiments, intermediate support portions may be
incorporated
into either or both, nodes 777 or facets 775, which are generally formed the
intimidate
membrane portions. A flap 736 is engaged with the trailing edge region 716 of
the
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airfoil 700 to extend from the trailing edge at a fixed angle (e.g.,
perpendicular) with
respect to the chord line of the air foil 700. Likewise, the airfoil 800 is
comprised of
the voluminous leading edge region 812, the intermediate region 815, and the
trailing
edge region 816. A flap 836 is engaged with the trailing edge region 816 of
the airfoil
800 to extend from the trailing edge at a fixed angle (e.g., perpendicular)
with respect
to the chord line of the air foil 800. The intermediate region 815 can include
intermediate membrane portions depicted as the facets 875 and nodes 877.
Intermediate support portions 839 of the intermediate region 815 can be
dispersed
radially about the central axis 705 and also engage with the airfoil 700 to
connect the
airfoil 700 to the airfoil 800.
[0077] Figures 17 depicts a front perspective view of an example shrouded
fluid
turbine 900 in the form of a wind turbine having the support structure 302,
the energy
extracting assembly 345 and a turbine shroud formed by the example airfoil 700
having the leading edge region 712, the intermediate region 715, and the
trailing edge
region 716. The energy extracting assembly 345 can include a nacelle body 350
and a
rotor 340. The rotor 340 is engaged with the nacelle body 350 at the proximal
end of
the rotor blades. The airfoil 700 can encircle the rotor 340. In one example,
embodiment the leading edge 766 of the airfoil 700 can be positioned up stream
of the
rotor 340 and/or the trailing edge 766 of the airfoil 700 can be positioned
downstream
of the rotor 340. The leading edge 762 can form an inlet of the shrouded fluid
turbine
900 and the trailing edge 766 can form the exhaust of the shrouded fluid
turbine 900.
The flap 736 can allow a fluid flow (e.g., airflow) flowing along the inner
surface of
the air foil to remain attached to the inner surface. In an example
embodiment, the
airfoil 700 can be positioned relative to the nacelle body 350 and rotor 340
using
elongate support structures 307 such that the nacelle body 350, the rotor 340,
and the
airfoil 100 are position coaxially with respect to each other about the center
axis 605.
[0078] Example embodiments of the present disclosure advantageously provide
a
ringed airfoil having a generally lightweight structure relative to
conventional ringed
airfoils. Example embodiments of the airfoil including the flap can result in
a ringed
airfoil that exhibits similar performance characteristics as a conventional
airfoil with
a greater chord length and no flap. Furthermore, example embodiments of the
present
disclosure provide for generally easier and less time consuming maintenance
and
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repair of the airfoils as compared to conventional airfoils, particularly with
respect to
the maintenance and repair of the intermediate membrane portions and the flap.
[0079] As set forth previously, the present embodiment is not specific to
an
ejector of a MET and may be applied to those ducted or shrouded fluid turbines
as
understood in the art. The present disclosure has been described with
reference to
example embodiments. Obviously, 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.
