U.S. patent application number 14/041895 was filed with the patent office on 2014-01-30 for fluid turbine with variable pitch shroud segments.
This patent application is currently assigned to FloDesign Wind Turbine Corp.. Invention is credited to Soren Dalsgaard, Soren Hjort, Bo Lovmand, Walter M. Presz, JR., Rune Rubak, Michael J. Werle.
Application Number | 20140030059 14/041895 |
Document ID | / |
Family ID | 45955128 |
Filed Date | 2014-01-30 |
United States Patent
Application |
20140030059 |
Kind Code |
A1 |
Presz, JR.; Walter M. ; et
al. |
January 30, 2014 |
FLUID TURBINE WITH VARIABLE PITCH SHROUD SEGMENTS
Abstract
One or more variable pitch airfoils in fluid communication with
a rotor of a fluid turbine can control the amount of energy
directed to the rotor, and further control the amount of energy
generated by the turbine. Varying the pitch of the airfoils may
provide a means of controlling the power output of a fluid turbine
without the need to control the pitch of the rotor blades, and may
further provide a means of mitigating the effects of wind shear on
the rotor. Variable pitch airfoils may also include a means of
controlling the active power, reactive power and SCADA, of a group
of fluid turbines.
Inventors: |
Presz, JR.; Walter M.;
(Wilbraham, MA) ; Werle; Michael J.; (West
Hartford, CT) ; Hjort; Soren; (Silkeborg, DK)
; Rubak; Rune; (Silkeborg, DK) ; Lovmand; Bo;
(Hadsten, DK) ; Dalsgaard; Soren; (Hadsten,
DK) |
Assignee: |
FloDesign Wind Turbine
Corp.
Waltham
MA
|
Family ID: |
45955128 |
Appl. No.: |
14/041895 |
Filed: |
September 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US2012/031490 |
Mar 30, 2012 |
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14041895 |
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61469133 |
Mar 30, 2011 |
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61493833 |
Jun 6, 2011 |
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Current U.S.
Class: |
415/1 ;
415/122.1; 415/155; 415/160 |
Current CPC
Class: |
F05B 2240/124 20130101;
F05B 2240/12 20130101; F03D 7/028 20130101; Y02E 10/72 20130101;
F03D 9/25 20160501; F01D 11/22 20130101; F05B 2240/122 20130101;
F05B 2250/41 20130101; F03D 1/0675 20130101; F03D 7/02 20130101;
F03D 1/04 20130101 |
Class at
Publication: |
415/1 ; 415/160;
415/155; 415/122.1 |
International
Class: |
F01D 11/22 20060101
F01D011/22 |
Claims
1. A shrouded fluid turbine comprising: a rotor; and a ringed
airfoil comprising a plurality of pivotable airfoil segments, each
pivotable airfoil segment having a low pressure surface in fluid
communication with the rotor.
2. The shrouded fluid turbine of claim 1, wherein each pivotable
airfoil segment is rotatable about an axis to change a pitch of the
pivotable airfoil segment.
3. The shrouded fluid turbine of claim 1, further comprising a
pitch control mechanism that alters the pitch of at least a portion
of the ringed airfoil.
4. The shrouded fluid turbine of claim 3, wherein the pitch control
mechanism is configured to continuously change a pitch of at least
a portion of the ringed airfoil while the shrouded fluid turbine is
in use.
5. The shrouded fluid turbine of claim 1, wherein a pitch of each
of the plurality of pivotable airfoil segments is individually
adjustable.
6. The shrouded fluid turbine of claim 1, wherein the plurality of
pivotable airfoil segments includes a plurality of outwardly
curving airfoil segments, and wherein the ringed airfoil further
comprises a plurality of inwardly curving airfoil segments.
7. The shrouded fluid turbine of claim 1, wherein the ringed
airfoil further comprises a frame, and each of the plurality of
pivotable airfoil segments is pivotably coupled to the frame.
8. The shrouded fluid turbine of claim 1, wherein the ringed
airfoil further comprises a plurality of arms, each arm coupled to,
and configured to adjust a pitch of, one or more of the plurality
of pivotable airfoil segments.
9. The shrouded fluid turbine of claim 1, wherein the ringed
airfoil comprises a plurality of mixing elements configured to
create a plurality of mixing vortices downstream of the rotor.
10. The shrouded fluid turbine of claim 9, further comprising a
second ringed airfoil downstream of the ringed airfoil having the
plurality of mixing elements.
11. The shrouded fluid turbine of claim 10, wherein the second
ringed airfoil comprises a second plurality of pivotable airfoil
segments.
12. The shrouded fluid turbine of claim 1, wherein the rotor is in
direct communication with a generator.
13. The shrouded fluid turbine of claim 1, wherein the rotor is in
communication with a generator via a gearbox assembly.
14. A shrouded fluid turbine comprising: a rotor defining a rotor
plane; and a ringed airfoil having a plurality of fluid contact
surfaces pivotable to change a unit mass flow rate through at least
a portion of the rotor plane.
15. A method of operating a shrouded fluid turbine, the method
comprising: providing a shrouded fluid turbine comprising: a rotor;
and a ringed airfoil including a low pressure surface in fluid
communication with the rotor; and altering a pitch of at least a
portion of the ringed airfoil.
16. The method of claim 15, wherein the ringed airfoil comprises a
plurality of pivotable airfoil segments, and wherein altering the
pitch of at least a portion of the ringed airfoil comprises
changing a pitch of at least one of the plurality of pivotable
airfoil segments.
17. The method of claim 15, wherein altering the pitch of at least
a portion of the ringed airfoil comprises altering the pitch to
reduce the unit mass fluid flow rate through the rotor plane.
18. The method of claim 15, wherein altering the pitch of at least
a portion of the ringed airfoil comprises altering a pitch of a
first portion of the ringed airfoil to be different than a pitch of
a second portion of the ringed airfoil.
19. The method of claim 18, wherein altering the pitch of the first
portion of the ringed airfoil to be different than the pitch of the
second portion of the ringed airfoil reduces fluid shear forces on
the shrouded fluid turbine.
20. The method of claim 15, wherein the pitch of at least a portion
of the ringed airfoil is altered at least once while the rotor is
rotating about a central axis of the shrouded fluid turbine.
21. The method of claim 15, wherein the pitch of at least a portion
of the ringed airfoil is continuously altered during operation of
the shrouded fluid turbine.
22. A method of operating a shrouded fluid turbine having a rotor
and a shroud with a low pressure surface in fluid communication
with the rotor, the method comprising: measuring at least one
variable associated with operation of the shrouded fluid turbine;
and altering a pitch of at least a portion of the shroud based on
the measured at least one variable.
23. The method of claim 22, wherein the shroud comprises a
plurality of pivotable shroud segments and altering a pitch of at
least a portion of the shroud comprises changing a pitch of at
least one of the plurality of pivotable shroud segments.
24. The method of claim 22, wherein altering a pitch of at least a
portion of the shroud based on the measured at least one variable
at least partially compensates for fluid shear forces on the
shrouded fluid turbine.
25. The method of claim 24, wherein the measured at least one
variable comprises a load variable selected from a group consisting
of: blade load, blade bending, blade tip acceleration, nacelle tilt
loading, and load as a function of azimuthal rotor position.
26. The method of claim 24, wherein the measured at least one
variable comprises a first fluid velocity measured at first portion
of a rotor plane and a second fluid velocity measured at a second
portion of the rotor plane.
27. The method of claim 24, wherein altering a pitch of at least a
portion of the shroud based on the measured at least one variable
dampens oscillations in a support structure for the shrouded fluid
turbine.
28. The method of claim 24, wherein the measured at least one
variable comprises a tower base moment variable, and wherein
altering a pitch of at least a portion of the shroud based on the
measured at least one variable reduces movement of the tower
base.
29. The method of claim 28, wherein the tower base movement
variable is selected from a group consisting of: tower-top
acceleration, tower tilt and rotor-power output.
30. The method of claim 22, wherein the shrouded wind turbine
supplies power for a utility grid, and the measured at least one
variable comprises a control variable; and wherein a pitch of at
least a portion of the shroud is altered to augment or reduce a
power output of the shrouded wind turbine based on the measured at
least one variable.
31. The method of claim 30, wherein the control variable is
selected from a group consisting of: rotor speed, rotor-power
output, rotor-shaft torque, and ambient wind speed.
32. A method of controlling a power output of an array of shrouded
wind turbines, each shrouded wind turbine including a rotor and a
shroud having a low pressure surface in fluid communication with
the rotor, the method comprising: measuring a reactive power of the
array; and altering a pitch of at least a portion of the shroud of
at least one of the array of shrouded wind turbines based on the
measured reactive power to augment or reduce the reactive power of
the array.
33. The method of claim 32, wherein the shroud of each of the array
of shrouded wind turbines comprises a plurality of pivotable shroud
segments, and wherein altering a pitch of at least a portion of the
shroud of the at least one of the array of shrouded wind turbines
comprises changing a pitch of at least one of the plurality of
pivotable shroud segments.
34. The method of claim 32, wherein the power output is controlled
during a low-voltage ride-through.
35. The method of claim 32, wherein altering a pitch of at least a
portion of the shroud of the at least one of the array of shrouded
wind turbines causes a first turbine or a first set of turbines to
yaw.
36. The method of claim 32, wherein the yawing reduces the overall
power output of the first turbine or first set of turbines.
37. The method of claim 35, wherein the yawing deflects wind from
the first turbine or set of turbines toward a second turbine or set
of turbines to equalize power output from each turbine in the
array.
Description
RELATED APPLICATIONS
[0001] This present application is a continuation application of
International Application No. PCT/US2012/031490, filed Mar. 30,
2012, which claims priority to U.S. Provisional Patent Application
No. 61/469,133, filed Mar. 30, 2011, and U.S. Provisional Patent
Application No. 61/493,833, filed Jun. 6, 2011. The entire contents
of all the above identified applications are incorporated herein by
reference in their entirety.
BACKGROUND
[0002] Conventional horizontal axis wind turbines (HAWTs) used for
power generation typically have two to five open blades arranged
like a propeller, the blades being mounted to a horizontal shaft
attached to a gear box which drives a power generator. HAWTs often
comprise blades with pitch control for the purpose of furling the
blades into the wind to mitigate speed and torque on the generator.
Blade pitch control provides a means of regulating the power output
of an individual, or a group of turbines, and a means for
protecting the turbine and electrical generation equipment from
excessive wind speeds.
[0003] HAWT can experience asymmetrical loading resulting in
oscillations that cause stress on the tower and can effect
electrical generation equipment. Further, large HAWTs can
experience greater wind speeds in the upper regions of the rotor
plane than in the lower regions of the rotor plane, which is known
as wind shear. Other wind events can also cause various types of
asymmetrical loading on the rotor plane. By furling the blades of a
HAWT into the wind in the highly-loaded regions of the rotor plane,
and out of the wind in the lesser-loaded regions of the rotor
plane, oscillations can be mitigated.
[0004] In conventional large HAWTs, control of the pitch of blades
has been used to control power generated by the rotor, to mitigate
oscillations caused by wind shear, and to mitigate stress on the
tower caused by such oscillations or by excessive wind speed.
BRIEF DESCRIPTION
[0005] Embodiments include a shrouded fluid turbine in which a
pitch of at least a portion of the shroud is variable or
adjustable, and method of operating or using such a shrouded fluid
turbine. For example, in one embodiment, a shrouded fluid turbine
includes a rotor and turbine shroud with a ringed airfoil. The
ringed airfoil includes a plurality of pivotable airfoil segments,
each pivotable airfoil segment having a low pressure surface in
fluid communication with the rotor. Each pivotable airfoil segment
is rotatable about an axis to change a pitch of the pivotable
airfoil segment.
[0006] In some embodiments, the shrouded fluid turbine further
includes a pitch control mechanism that alters the pitch of at
least a portion of the ringed airfoil. The pitch control mechanism
may be configured to continuously change a pitch of at least a
portion of the ringed airfoil while the shrouded fluid turbine is
in use. A pitch of each of the plurality of pivotable airfoil
segments may be individually adjustable.
[0007] In some embodiments, the plurality of pivotable airfoil
segments includes a plurality of outwardly curving airfoil
segments, which may be referred to herein as outwardly directed
mixing elements. The ringed airfoil may also include a plurality of
inwardly curving airfoil segments, which may be referred to herein
as inwardly directed mixing elements.
[0008] In some embodiments each of the plurality of pivotable
airfoil segments may be pivotable coupled to a frame of the fluid
turbine. In some embodiments, the ringed airfoil further comprises
a plurality of arms, each arm coupled to, and configured to adjust
a pitch of, one or more of the plurality of pivotable airfoil
segments.
[0009] In some embodiments, the ringed airfoil comprises a
plurality of mixing elements configured to create a plurality of
mixing vortices downstream of the rotor. In some embodiments, the
shrouded fluid turbine also includes an ejector with a second
ringed airfoil downstream of the ringed airfoil having the
plurality of mixing elements. The second ringed airfoil may include
a second plurality of pivotable airfoil segments.
[0010] In some embodiments, the rotor is in direct communication
with a generator. In some embodiments, the rotor is in
communication with a generator via a gearbox assembly.
[0011] Another embodiment includes a shrouded fluid turbine
including a rotor defining a rotor plane and a ringed airfoil. The
ringed airfoil has a plurality of fluid contact surfaces pivotable
to change a unit mass flow rate through at least a portion of the
rotor plane.
[0012] One embodiment includes a method of operating a shrouded
fluid turbine. The method includes providing a shrouded fluid
turbine having a rotor, and a ringed airfoil including a low
pressure surface in fluid communication with the rotor. The method
also includes altering a pitch of at least a portion of the ringed
airfoil.
[0013] Another embodiment includes a method of operating a shrouded
fluid turbine having a rotor and a shroud with a low pressure
surface in fluid communication with the rotor. The method includes
measuring at least one variable associated with operation of the
shrouded fluid turbine, and altering a pitch of at least a portion
of the shroud based on the measured at least one variable.
[0014] In some methods, the ringed airfoil, or the shroud, may
comprise a plurality of pivotable airfoil segments, and altering a
pitch of at least a portion of the ringed airfoil, or of the
shroud, may include changing a pitch of at least one of the
plurality of pivotable airfoil segments.
[0015] One embodiment includes a method of controlling a power
output of an array of shrouded wind turbines, each shrouded wind
turbine including a rotor and a shroud having a low pressure
surface in fluid communication with the rotor. The method includes
measuring a reactive power of the array, and altering a pitch of at
least a portion of the shroud of at least one of the array of
shrouded wind turbines based on the measured reactive power to
augment or reduce the reactive power of the array.
[0016] Some embodiments described in the present disclosure relate
to a shrouded (e.g., ducted) fluid turbine including a rotor and a
ringed airfoil having a particular structure, and to mixing
elements engaged with such ducts. A ringed airfoil with mixing
elements surrounds a rotor and is known as a turbine shroud, a
second shroud is in fluid communication with the mixing elements of
the turbine shroud and is known as the ejector shroud. The turbine
shroud is a ringed airfoil that may include of inward and outward
curving elements that each have an airfoil cross section. The
ejector shroud is a ringed airfoil that includes of an annular ring
with an airfoil cross section. In some embodiments, the shrouds are
comprised of airfoil segments arranged in a polygon. The present
disclosure relates to a configuration that comprises articulated,
variable pitch controlled shroud segments. By varying the pitch of
airfoil segments that comprise the shrouds, the force of the fluid
stream on the rotor can be controlled. Controlling the force of
fluid flow over the rotor provides a means of controlling the
torque on the generator and electrical generation components, a
means of controlling the power output of individual turbines or of
a group of turbines and a means of mitigating the effects of
oscillations caused by wind shear. Controlling the fluid flow in
this manner is a means of controlling the speed of the rotor
without necessarily having to control the pitch of the rotor
blades.
[0017] Altering the pitch of at least one shroud segment can
provide a means of shading the rotor-swept area in such a manner as
to reduce the effect of sun shadowing, also known as shadow
flicker, on the ground.
[0018] Pitching of shroud segments may be employed to break up ice
on the surface of the shroud segments.
[0019] The power output of the rotor/generator system may be
controlled by changing the pitch of one or more shroud segments.
Sensors may measure rotor torque, generator current, or other
indicator of power output. In some embodiments, the power-output
indicator is compared with a fixed-reference range to determine if
the power output is within the acceptable range. If the power
output is without the acceptable range, a power-error signal is
generated and shroud segments are articulated to correct the power
error, adjusting the power output to a value within the acceptable
range. Controlling power output in this manner allows for the set
of shrouds to be configured in such a manner as to gradually
increase speed during start-up, reduce speed during shutdown,
during low-voltage-ride-through, or to generate a minimum, or a
reduced, amount of power in excessive wind conditions, thus
allowing for continued optimal power output during a wide range of
operating conditions.
[0020] In some embodiments, tower stress is prevented by measuring
tower base moment or indicators thereof including tower top
acceleration, tower tilt or rotor power output; and responding by
pitching shroud segments in such a manner as to maintain constant
or reduce the tower base moment. In a similar manner, tower
oscillations can be dampened.
[0021] Often it is desirable to curtail power production in a wind
park, producing less than 100% of the potential power output so as
to de-rate a wind turbine or group of wind turbines or to operate
with what is known as a spinning reserve. Shroud segments can be
pitched in such a manner as to provide a spinning reserve.
[0022] Individual shroud segments can be pitched in order to
mitigate asymmetric loading, including wind-driven asymmetric
loading, nacelle tilt or yaw loading, or blade loading caused by
tower shadow. Shroud segments are pitched in response to blade
load, blade bending, tip acceleration or nacelle tilt loading, or
by monitoring the load vs. rotor azimuth for each blade
continuously, to reduce speed in a specific area of the rotor
plane.
[0023] Individual shroud segments can also be utilized to apply a
yaw moment to yaw the turbine upwind or downwind accordingly, to
reduce the overall power output of the rotor/generator and/or to
deflect wind to other turbines in a wind park so as to provide
equal power output from each turbine in the park.
[0024] An example shrouded wind turbine with a ringed airfoil
turbine shroud and a ringed airfoil ejector shroud has been
described in U.S. patent application Ser. No. 12/054,050, which is
incorporated herein in its entirety. Some embodiments provide a
means of controlling the pitch of airfoil segments about the ringed
airfoil for the purpose of controlling the power generated by the
rotor, for mitigating oscillations caused by wind shear and for
mitigating stress on the tower caused by such oscillations or by
excessive wind speed.
[0025] These and other non-limiting features or characteristics of
the present disclosure will be further described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] 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.
[0027] FIG. 1 is a front right perspective view of an exemplary
embodiment of a shrouded fluid turbine.
[0028] FIG. 2 is a side cross-sectional partial exploded view of
the fluid turbine of FIG. 1.
[0029] FIG. 3 is a side cross-sectional view of the fluid turbine
of FIG. 1.
[0030] FIG. 4 is a side cross-sectional detail view of the fluid
turbine of FIG. 1 depicting a configuration with an outwardly
curving airfoil segment angularly positioned for maximized, or
increased, energy extraction at the rotor.
[0031] FIG. 5 is a side cross-sectional detail view of the fluid
turbine of FIG. 1 depicting a configuration with outwardly curving
airfoil segment angularly positioned for minimized, or decreased,
energy extraction at the rotor.
[0032] FIG. 6 is a front perspective view of another embodiment
including fluid turbine having a turbine shroud with a first
plurality of pivotable airfoil segments and an ejector shroud with
a second plurality of pivotable airfoil segments.
[0033] FIG. 7 is a rear perspective view of the fluid turbine of
FIG. 6.
[0034] FIG. 8 is a side cross-sectional detail view of the fluid
turbine of FIG. 6 depicting a configuration with the outwardly
curving airfoil segments and the ejector airfoil segments angularly
positioned for maximized, or increased, energy extraction at the
rotor.
[0035] FIG. 9 is a side cross-sectional detail view of the fluid
turbine of FIG. 6 depicting a configuration with the outwardly
curving airfoil segments and the ejector airfoil segments angularly
positioned for minimized, or reduced, energy extraction at the
rotor.
[0036] FIG. 10 is a simplified, schematic, side cross-sectional
detail view of an embodiment including a fluid turbine in depicting
a configuration with the outwardly curving airfoil segments
angularly positioned to maximize, or increase, the energy
extraction at the rotor.
[0037] FIG. 11 is a simplified, schematic, side cross-sectional
detail view of the fluid turbine of FIG. 10 depicting a
configuration with the outwardly curving airfoil segments angularly
positioned to minimize, or decrease, energy extraction at the
rotor.
[0038] FIG. 12 is a side cross-sectional detail view of another
embodiment including a fluid turbine with an ejector shroud in the
form of a ringed airfoil with a plurality of pivotable airfoil
segments in a configuration with the outwardly curving airfoil
segments angularly positioned for maximized, or increased, energy
extraction at the rotor.
[0039] FIG. 13 is a side cross-sectional detail view of the fluid
turbine of FIG. 12 in a configuration with the outwardly curving
airfoil segments angularly positioned for minimized, or decreased,
energy extraction at the rotor.
[0040] FIG. 14 is a side cross-sectional view of a fluid turbine
having a rotor in direct communication with a generator, in
accordance with some embodiments.
[0041] FIG. 15 is a side cross-sectional view of a fluid turbine
having a rotor in communication with a generator via a gearbox
assembly, in accordance with some embodiments.
[0042] FIG. 16 schematically depicts a wind park including an array
of wind turbines, in accordance with some embodiments.
[0043] FIG. 17 is a flow diagram schematically depicting a method
of operating a shrouded fluid turbine, in accordance with some
embodiments.
[0044] FIG. 18 is a flow diagram schematically depicting a method
of operating a shrouded fluid turbine that includes measuring one
or more variable associated with operation of the wind turbine, in
accordance with some embodiments.
[0045] FIG. 19 is a flow diagram schematically depicting a method
of controlling a power output of an array of shrouded wind
turbines, in accordance with some embodiments.
DETAILED DESCRIPTION
[0046] 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 exemplary
embodiments.
[0047] 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.
[0048] 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."
[0049] A Mixer-Ejector Wind/Water Turbine (MEWT) provides an
improved means of generating power from fluid currents. A primary
shroud contains a rotor which extracts power from a primary fluid
stream. A mixer-ejector pump is included that ingests flow from the
primary fluid stream and secondary flow, and promotes turbulent
mixing of the two fluid streams. This enhances the power system by
increasing the amount of fluid flow through the system, increasing
the unit mass airflow at the rotor for more power availability, and
reducing back pressure on turbine blades. The fluid dynamic
principles of a Mixer-Ejector Turbine are not restricted to air and
apply to any fluid, defined as any liquid (e.g., water) or gas
(e.g., air) In other words, the aerodynamic principles of a mixer
ejector wind turbine apply to hydrodynamic principles in a mixer
ejector water turbine.
[0050] The term "airfoil" is used in the description and the claims
as a generic term to refer to a foil used with a moving fluid and
includes both airfoils used with flowing gas (e.g. air) and
hydrofoils used with flowing liquid (e.g., water). Generally
speaking, a cambered airfoil has a low pressure/high fluid flow
velocity surface, which may be called the suction surface (e.g.,
the upper surface of a subsonic aircraft wing), and a high
pressure/low fluid flow velocity surface, which may be called the
pressure surface (e.g., the lower surface of a subsonic aircraft
wing).
[0051] The term "rotor" 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 wind rotating the
blades. Exemplary rotors include a propeller-like rotor or a
rotor/stator assembly. Any type of rotor may be used with turbine
shroud in the wind turbine of the present disclosure.
[0052] The leading edge of a turbine shroud may be considered the
front of the wind turbine, and the trailing edge of an ejector
shroud may be considered the rear of the wind turbine. A first
component of the wind turbine located closer to the front of the
turbine may be considered "upstream" of a second component located
closer to the rear of the turbine. Put another way, the second
component is "downstream" of the first component.
[0053] Some embodiments of the present disclosure relate to a wind
turbine including a rotor and a turbine shroud in the form of a
ringed airfoil with a plurality of pivotable airfoil segments, in
which each pivotable airfoil segment has a low pressure surface in
fluid communication with the rotor. Each pivotable airfoil segment
may be rotated about an axis that changes a pitch of the pivotable
airfoil segment. The turbine shroud may include mixing elements,
some or all of which may be incorporated into the pivotable airfoil
segments. In some embodiments, the fluid turbine may include an
ejector shroud in fluid communication with the exit of the turbine
shroud. The ejector shroud may include a second ringed airfoil with
a second plurality of pivotable airfoil segments.
[0054] Generally speaking, the pivotable airfoil segments, which
may be described as articulated shroud segments or variable pitch
airfoil segments, provide a means of controlling the rotational
speed of the rotor and therefore the torque on the generator and
electrical generation components. The pivotable airfoil segments
may provide a means of mitigating tower stress caused by excessive
fluid speeds (e.g., wind speeds or current speeds) and oscillations
resulting from fluid shear (e.g., wind shear or hydroshear). The
pivotable airfoil segments may be used in, and may serve these
functions in, fluid turbines incorporating a fixed-blade rotor as
well as fluid turbines incorporating a variable pitch rotor.
[0055] Although some exemplary embodiments are described below as
wind turbines including ringed airfoils and pivotable airfoil
segments, the description also applies to fluid turbines generally,
(e.g., ringed hydrofoils and pivotable hydrofoil segments). The
term "airfoil" as used in the specification and the claims,
includes, but is not limited to, airfoils for use with air and
other gases, and hydrofoils for use with water or other liquids.
Further, the description below referring to wind-related phenomena
(e.g., wind shear) also applies to fluid-related phenomena
generally (e.g. hydroshear).
[0056] FIG. 1 is a perspective view of an exemplary embodiment of a
shrouded fluid turbine of the present disclosure. FIG. 2 is a
perspective, exploded view of the shrouded fluid turbine of FIG. 1.
Referring to FIG. 1, the shrouded fluid turbine 100 comprises a
first ringed airfoil, which may be referred to herein as a turbine
shroud 110, a nacelle body 150, and a rotor 140. In some
embodiments, the fluid turbine 100 further includes a second ringed
airfoil, which may be referred to herein as an ejector shroud 120.
The turbine shroud 110 includes a front end 112, also known as an
inlet end or a leading edge. The turbine shroud 110 also includes a
rear end, also known as an exhaust end or trailing portion 116. The
ejector shroud 120, which may also be referred to herein as the
ejector, includes a front end, inlet end or leading edge 122, and a
rear end, exhaust end, or trailing edge 124.
[0057] The rotor 140 surrounds the nacelle body 150. The rotor 140
comprises a central hub 141 at the proximal end of the rotor
blades. The central hub 141 is rotationally engaged with the
nacelle body 150. The nacelle body 150 and the turbine shroud 110
are supported by a tower 102. The rotor 140, turbine shroud 110,
and ejector shroud 120 are coaxial with each other, (i.e., they
share a common central axis 105).
[0058] The turbine shroud 110 has the cross-sectional shape of an
airfoil with a suction side 111 (i.e., low-pressure side or low
pressure surface) on the interior of the turbine shroud and a
high-pressure side or high pressure surface on the exterior of the
turbine shroud 113. In some embodiments, the trailing portion 116
of the turbine shroud has mixing elements that extend downstream
beyond the rotor blades. The mixing elements include inwardly
directed mixing elements 117 extending inward toward the central
axis 105 of the turbine shroud and outwardly directed mixing
elements 115 extending outward away from the central axis 105. In
some embodiments the trailing portion 116 of the turbine shroud is
shaped to form the mixing elements.
[0059] In some embodiments, a mixer-ejector pump is formed by the
ejector shroud 120 in fluid communication with the ring of inwardly
directed mixing elements 117 and outwardly directed mixing elements
115 of the turbine shroud 110. The mixing elements extend
downstream of the rotor 140 and, in some embodiments, may extend
into the inlet end 122 of the ejector shroud 120. One skilled in
the art will recognize that the mixer may not extend into the inlet
end 122 of the ejector shroud 120 in all embodiments.
[0060] The mixer-ejector pump provides the means for turbulent
mixing of fluid (e.g., air) that passes through the rotor 140 with
fluid that bypasses the rotor 140. The fluid stream is divided into
a low pressure--high velocity stream on the side of the turbine
shroud 110, or first ring airfoil, that is proximal to the rotor
plane, which may be referred to as a primary flow or primary
stream, and a high pressure--lower velocity stream on the exterior
of the turbine shroud, or second ring airfoil 100, which may be
referred to as a bypass flow or bypass stream. Mixing elements,
such as inwardly directed mixing elements 117 and outwardly
directed mixing elements 115, cause the primary fluid stream and
the bypass fluid stream to intersect downstream of the rotor plane.
Mixing elements include but are not limited to: mixing lobes,
mixing slots, vortex generators or other ringed airfoil aerodynamic
modifications that promote mixing. The mixing elements may be
disposed at a variety of regions such as, but not limited to, the
trailing portion 116 of the ringed airfoil.
[0061] Power extraction at the rotor 140 is coupled to, or defined
by, energy exchange at the wake, which is downstream of the rotor
plane. A pressure drop occurs in the wake of the rotor as a result
of the energy taken out by the rotor 140. Mixing elements, such as
inwardly directed mixing elements 117 and outwardly directed mixing
elements 115, in combination with the ejector shroud 120 provide
turbulent mixing of the primary and bypass streams such that the
air pressure in the wake of the turbine rapidly returns to ambient
pressure. With energized wake from mixing elements, it is possible
to extract more energy from a shrouded rotor than from an open
rotor of similar size. Although fluid turbine 100 of FIGS. 1
through 5 incorporates an ejector shroud, some embodiments obtain
enhanced mixing and a resulting increase in energy extraction using
a turbine including a turbine shroud having mixing elements without
an ejector shroud.
[0062] FIGS. 2 and 3 are partially-exploded, partial section views
illustrating various structural elements of the fluid turbine 100.
In some embodiments, the turbine shroud 110 includes a polygonal or
circular frame 130 that encircles the central axis 105. As
illustrated in FIGS. 2 and 3, the outwardly directed mixing
elements 115, which may also be referred to herein as outwardly
curving airfoil segments, may be pivotally engaged with straight
portions of the frame 130. Rotation of a pivotable airfoil segment,
such as an outwardly directed mixing element 115, relative to an
axis defined by a corresponding straight portion of the frame 130
changes the pitch of the pivotable airfoil segment relative to the
central axis 105. In turbine shroud 110 of FIGS. 1 to 5, inwardly
directed mixing elements 117, which may also be referred to herein
as inwardly curving airfoil segments, maintain a fixed orientation
with respect to the frame 130. However, in some embodiments,
inwardly directed mixing elements may pivot with respect to the
frame. In some embodiments, only some of the outwardly directed
mixing elements may be pivotally engaged with the frame.
[0063] Some embodiments include active or passive pitch control
mechanisms that alter the pitch of one or more of the pivotable
airfoil segments with respect to the central axis. For example, in
fluid turbine 100, outwardly directed mixing elements 115 are
pivotally engaged with arms 132 that are, in turn, laterally
engaged with the nacelle body 150 as shown by FIGS. 2 through 5.
Movements of the arms 134 provide actuation of the outwardly
directed mixing elements 115 in a manner that changes the pitch of
the airfoil segment with reference to the central axis 105. FIG. 2
shows the turbine shroud 110 with the outward directed mixing
elements configured with the leading edge 112 pitched toward the
central axis and the trailing portion 116 pitched away from the
central axis 105. In contrast, FIG. 3 shows the outward directed
mixing elements 115 configured with the leading edge 112 pitched
away from the central axis 105 and the trailing portion 116 pitched
toward the central axis 105.
[0064] In some embodiments, the pitch of each airfoil segment may
be individually adjustable. In other embodiments, the pitch of the
plurality of pivotable airfoil segments is adjusted as a group. For
example, the pitch of the outwardly directed mixing elements 115
may be adjusted simultaneously or individually.
[0065] The pitch control mechanism may incorporate one or more
actuators for providing force to adjust the pitch of the pivotable
airfoil segments. The one or more actuators may include, but are
not limited to: mechanical actuators, hydraulic actuators,
pneumatic actuators, electrical actuators, piezoelectric actuators,
magnetic actuators and any combination of the aforementioned. One
skilled in the art will readily recognize that the illustrated
pivot and arm actuation mechanism is only one suitable embodiment
and is not intended to be limiting in scope.
[0066] The cross-sectional views in FIGS. 4 and 5 illustrate the
fluid flow (e.g., airflow) over the mixer shroud 110. In FIG. 4,
the outwardly directed mixing elements 115 are in a configuration
that generates a maximum, or a relatively increased, amount of
energy at the rotor 140. In FIG. 5, the outwardly directed mixing
elements 115 are in a configuration that generates a minimum, or a
relatively reduced, amount of energy at the rotor 140. An incoming
fluid stream (e.g., free stream air) is indicated generally by
arrows 166. A primary fluid stream 164 enters the turbine shroud
164 and passes through the rotor plane at the rotor 140, where
energy is extracted and a pressure drop occurs in the portion of
the primary fluid stream 164 that continues along the interior 111
of the turbine shroud 110 and along the interior surface of
outwardly directed mixing elements 115. Fluid flowing over the
exterior 113 of the turbine shroud, indicated by arrows 162,
bypasses the turbine shroud 110 and the rotor 140 and therefore
does not experience the pressure drop after the rotor plane. As
shown, the inwardly directed mixing elements 117 direct a portion
of the relatively higher pressure bypass fluid stream 162 inward
toward the central axis 105 and the relatively lower pressure
primary fluid stream. Similarly, outwardly directed mixing elements
115 direct a portion 164 of the relatively lower pressure primary
fluid stream exiting downstream from the rotor 140 to be directed
away from the central axis 105 and toward the relatively higher
pressure bypass fluid stream. The interaction of bypass fluid
stream portions 162 from the inwardly directed mixing elements 117
and the primary stream portions 164 from the outwardly directed
mixing elements 115 creates a plurality of mixing vortices that mix
the relatively higher pressure bypass fluid stream with the
relatively lower pressure primary fluid stream. This mixing may be
referred to as turbulent mixing.
[0067] For the bypass stream that enters the ejector shroud 120,
the camber of the ejector shroud creates a relatively lower
pressure on the inner surface 121 of the ejector shroud near the
leading edge of the ejector, in comparison to the relatively higher
pressure on the exterior surface 123 of the ejector shroud. The
lower pressure stream 160 on the interior of the ejector serves to
draw in additional fluid flow that is further mixed with the
inwardly directed bypass stream 162 and outwardly directed primary
stream 164. An increase in pressure occurs on the interior of the
ejector shroud as the flow moves from the upstream end of the
ejector to the downstream end of the ejector 120. Airflow returns
to ambient pressure upon exiting the ejector 120.
[0068] Referring to FIG. 5, a cross-section depicts an exemplary
outwardly directed mixing element 115 of the turbine shroud 110
rotated resulting in a different pitch of the pivotable airfoil
segment. When the pitch of the pivotable airfoil segment (e.g.,
outwardly directed mixing element 115) is changed in this manner,
turbulent mixing is reduced or eliminated. Without the substantial
turbulent mixing of the primary 164 and bypass 160, 162 fluid
streams, the pressure of the combined fluid stream does not
approach ambient pressure as it exits the ejector shroud 120, which
restricts the flow over the rotor 140 in a phenomenon known as
diffuser stall.
[0069] In excessive fluid flow conditions (e.g., under high wind
conditions) it is often desirable to slow the speed of the rotor to
prevent damage to the electrical generation equipment. By
controlling the pitch of some or all of the airfoils, the speed of
the rotor 140, and thus the amount of energy transferred to the
electrical generation equipment, is controlled without the
alteration of the pitch of the rotor blades.
[0070] FIGS. 6 and 7 depict another embodiment including a fluid
turbine in which both the turbine shroud and the ejector shroud
have pivotable airfoil segments for pitch control. FIGS. 6 and 7
are perspective views of a fluid turbine 200 with multiple
pivotable airfoil segments omitted to show a frame. The turbine
shroud, in the form of a first ringed airfoil, includes a first
plurality of pivotable airfoil members, outwardly directed mixing
elements 215. The ejector shroud, in the form of a second ringed
airfoil, includes a second plurality of pivotable airfoil members,
pivotable ejector segments 220. The frame includes turbine shroud
frame members 230 and ejector frame members 232. Outwardly directed
turbine mixing elements 215 are pivotally engaged with the turbine
shroud frame members 230. Frame members 230 comprise a polygon or a
faceted ring that encircles a central axis 105 of the fluid
turbine. The outwardly directed mixing elements 215 are also
pivotally engaged with arms 234 that are in turn engaged with the
nacelle body 250. Movements of the arms 234 provide actuation of
the outwardly directed mixing elements 215 in a manner that changes
the pitch of the airfoil segment with reference to the central axis
205. The outwardly directed mixing elements 215 may be actuated
simultaneously or individually.
[0071] The pivotable ejector segments 220 are pivotally engaged
with the ejector frame members 232. The pivotable ejector segments
220 are also pivotally engaged with arms 236 that are, in turn,
laterally engaged with the nacelle body 250. Movement of the arms
236 provides actuation of the pivotable ejector segments 220 in a
manner that changes the pitch of the pivotable ejector segments 220
with reference to the central axis 205. The pivotable ejector
segments 220 may be actuated simultaneously or individually.
[0072] In some embodiments, all of the pivotable turbine shroud
segments and/or all of the pivotable ejector shroud segments may
adjust together to change an overall pitch of the turbine shroud
and/or of the ejector shroud. In some embodiments, the pivotable
turbine shroud segments and the pivotable ejector shroud segments
may be adjustable such that a portion of the turbine shroud, or of
the ejector shroud, has a different pitch than another portion of
the turbine shroud, or of the ejector shroud.
[0073] FIGS. 8 and 9 illustrate the airflow over and through the
fluid turbine with the outwardly directed mixing elements 215 and
pivotable ejector segments 220 in different configurations. In FIG.
8, the outwardly directed mixing elements 215 and pivotable ejector
segments 220 are configured for generating the maximum, or a
relatively increased, amount of energy at the rotor 240, which in
turn is transferred to electrical generation equipment (not shown).
In FIG. 9, the outwardly directed mixing elements 215 and pivotable
ejector segments 220 are configured for generating a minimum, or a
relatively decreased, amount of energy at the rotor 240.
[0074] In FIGS. 8 and 9, an incoming fluid flow (e.g., free stream
air) is indicated generally by arrows 266. Fluid entering the
turbine shroud 264 passes through the rotor plane at rotor 240
where energy is extracted and a pressure drop occurs in the
following stream that continues along an interior surface 211 of
the turbine shroud and a portion continues along the interior
surface of outwardly directed mixing element 215. Fluid flowing
over the exterior of the turbine shroud, indicated by arrow 262,
bypasses the turbine shroud 210 and is directed inward by the
inwardly directed mixing element 217. The outwardly directed mixing
elements 215 cause the relatively lower pressure air exiting
downstream from the rotor 240 to be mixed with the relatively
higher pressure air 262.
[0075] The ejector shroud camber creates a relatively lower
pressure on the inner surface of the ejector 221, near the leading
edge, in comparison to the relatively higher pressure on the
exterior surface 223 of the ejector. The relatively lower pressure
stream 260 on the interior of the ejector 220 serves to draw in
additional airflow that is further mixed with the inwardly directed
fluid stream 262 and outwardly directed fluid stream 264. An
increase in pressure occurs on the interior of the ejector 220 as
the flow moves from the upstream end of the ejector 220 to the
downstream end of the ejector 200. Upon exiting the ejector 220,
the fluid flow returns to ambient pressure.
[0076] Referring to FIG. 9, a cross section depicts the outwardly
directed mixing element 215 of the turbine shroud rotated, with its
pitch changed relative to a central axis 205. The pivotable ejector
segment 220 is also rotated, changing its pitch relative to the
central axis 205. When the pitch of the outwardly directed mixing
elements 215 and the pivotable ejector segments 220 are changed in
this manner, turbulent mixing of the primary fluid stream 264 and
the secondary fluid stream 262 is reduced, and the additional fluid
stream 260 through the ejector is not sufficient to provide
turbulent mixing. Without the mixing of the primary fluid stream
264 and the bypass fluid stream 262, and without the injection of
the fluid stream 260 at the ejector, the pressure of the combined
fluid stream does not approach ambient pressure as it exits the
ejector shroud, which restricts the flow of high speed, low
pressure air over the rotor 240 causing diffuser stall. By
controlling the pitch of some or all of the turbine shroud and
ejector shroud airfoil segments, the speed of the rotor 240, and
thus the amount of energy transferred to the electrical generation
equipment may be controlled even without the alteration of the
pitch of the rotor blades.
[0077] Turbine shroud interior surface 211, turbine shroud exterior
surface 213, ejector shroud interior surface 221 and turbine shroud
exterior surface 223 may be described as fluid contact surfaces.
Pivoting the fluid contact surfaces changes a unit mass flow rate
through at least a portion of the rotor plane associated with the
pivoted fluid contact surfaces. The change in the unit mass flow
rate changes the amount of energy extracted from the rotor, and the
amount of energy transferred to associated electrical generation
equipment (e.g., a generator).
[0078] FIGS. 10 and 11 illustrate the basic principle of variable
pitch ringed airfoils in fluid communication with a rotor blade,
for the purpose of controlling the amount of energy directed to the
rotor. The variable pitch turbine shroud airfoil and variable pitch
ejector shroud airfoil may reduce or eliminate the need to pitch
the rotor blades for control of energy extracted by the rotor from
the fluid stream. A free stream fluid (e.g., free-stream air or
wind) represented by arrows 366 enters the fluid turbine as a
primary fluid stream 364, and bypass fluid streams 362 and 360. In
the configuration depicted in FIG. 10, the outwardly directed
mixing elements 315 and ejector airfoil segments 320 have
relatively little pitch, .alpha..sub.1, and .alpha..sub.2
respectively, for maximum, or relatively increased, power
extraction at the rotor 340. In the configuration depicted in FIG.
11, the outwardly-directed mixing elements 315 and ejector airfoil
segments 320 have relatively more pitch, .alpha..sub.3, and
.alpha..sub.4 respectively, for decreased mixing, and less pressure
differential across the ejector shroud 320, and consequently
minimum, or relatively decreased, power extraction at the rotor
340.
[0079] FIGS. 12 and 13 schematically depict fluid flow in another
embodiment of a fluid turbine including a turbine shroud with mixer
elements, but no ejector shroud. As shown, the turbine shroud
includes outwardly curving airfoil segments 415 that are pivotable.
In FIG. 12, the outwardly curving airfoil segments 415 have a
relatively small pitch .alpha..sub.5 relative to a central axis 405
of the fluid turbine, resulting in increased mixing of a primary
fluid stream 464 that flows along the outwardly curving airfoil
segment 415 and a bypass fluid stream 462 that flows along an
inwardly curving airfoil segment 417. Even without an ejector,
mixing elements of the turbine shroud (e.g., outwardly curving
airfoil segment 415 and inwardly curving airfoil segment 417)
produce a plurality of mixing vortices downstream of the rotor 440.
In comparison, in FIG. 13, outwardly curving airfoil segments 415
have a relatively larger pitch .alpha..sub.6, similar to that of
the inwardly curving airfoil segments 417, which greatly reduces
mixing between the primary fluid stream 464 and the bypass fluid
stream 462, and, consequently, decreases power extraction from the
rotor 440.
[0080] In some embodiments, a nacelle body of a fluid turbine
includes a generator. For example, FIGS. 14 and 15 depict
embodiments of a fluid turbine 510 including a turbine shroud with
a plurality of pivotable airfoil segments, outwardly curving mixing
elements 515, and a plurality of fixed airfoil segments, inwardly
curving mixing elements 517. The pivotable airfoil segments are
actuated using arms 532. Fluid turbine 510 also includes an ejector
with ejector airfoil segments 520 that are actuated using arms 536.
In the embodiment of FIG. 14, a nacelle body 550 includes a
generator 543 that is in direct communication with a rotor 540, or
more specifically, in direct communication with a central body 541
of the rotor. In the embodiment of FIG. 15, a nacelle body 551
includes a generator 544 that is in communication with the rotor
540, or more specifically, in communication with a central body 541
of the rotor through via a gearbox assembly 545. One of ordinary
skill in the art will recognize that, in various embodiments, a
generator may communicate with a rotor via many different
structures or mechanisms.
[0081] FIG. 15 depicts a wind park or wind farm including an array
600 of individual wind turbines 602 . . . 620 that supply power for
a utility grid 630, in accordance with some embodiments. The
individual wind turbines 602 . . . 620 each include one or more
ringed airfoils (e.g., turbine shroud, or turbine shroud and
ejector shroud) that have pivotable airfoil segments for varying a
pitch of at least a portion of the ringed airfoil as described
above.
[0082] Some embodiments include methods for operating a shrouded
fluid turbine. For example, in method 700 of FIG. 17, a shrouded
fluid turbine is provided that includes a rotor 140 and a ringed
airfoil (e.g., turbine shroud 110) including a low pressure surface
111 in fluid communication with the rotor 140 (step 710). A pitch
of at least a portion of the ringed airfoil (e.g., turbine shroud
110) is altered (step 720).
[0083] In some embodiments, the ringed airfoil includes a plurality
of pivotable airfoil segments (e.g., outwardly curving segments
115) and altering a pitch of at least a portion of the ringed
airfoil including changing a pitch of at least one of the plurality
of pivotable airfoil segments. In some embodiments, the pitch is
altered to reduce a unit mass flow rate through the rotor
plane.
[0084] In some embodiments, a pitch of a first portion of the
ringed airfoil is altered to be different than a pitch of a second
portion of the ringed airfoil. In some embodiments, altering a
pitch of the first portion of the ringed airfoil to be different
than a pitch of a second portion of the ringed airfoil reduces
fluid shear forces (e.g., wind shear forces) on the shrouded fluid
turbine.
[0085] In some embodiments, the pitch of at least a portion of the
ringed airfoil is altered at least once while the rotor is rotating
about a central axis of the shrouded fluid turbine (e.g., while in
use). For example, during use under excessively windy conditions,
the pitch may change to reduce the unit mass fluid flow through the
wind turbine. In some embodiments, the pitch of at least a portion
of the ringed airfoil is continuously altered over a period of time
during operation of the shrouded fluid turbine (e.g., to
continuously respond to wind shear or support structure
oscillations).
[0086] In method 800 of FIG. 18 at least one variable associated
operation of a shrouded fluid turbine is measured (step 810). A
pitch of at least a portion of a shroud of the shrouded fluid
turbine is altered based on the measured at least one variable
(step 820).
[0087] In some embodiments, altering a pitch of at least a portion
of the shroud based on the measured at least one variable at least
partially compensates for fluid shear (e.g., wind shear) forces on
the shrouded fluid turbine. In some embodiments, the measured at
least one variable includes a load variable. Examples of load
variables include, but are not limited to: blade load, blade
bending, blade tip acceleration, nacelle tilt loading, and load as
a function of azimuthal rotor position. In some embodiments, the
measured at least one variable includes a first fluid velocity
measured at a first portion of a rotor plane and a second fluid
velocity measured at a second portion of the rotor plane.
[0088] In some embodiments, altering a pitch of at least a portion
of the shroud based on the measured at least one variable dampens
oscillations in a support structure for the shrouded fluid turbine.
In some embodiments, the measured at least one variable includes a
tower base movement variable and altering the pitch of at least a
portion of the shroud based on the measured at least one variable
reduces movement of the tower base. In some embodiments, the tower
base movement variable is any of tower-top acceleration, tower tilt
and rotor-power output.
[0089] When the fluid velocity at a given area (e.g., the lower
portion) of the turbine rotor plane is of a different velocity than
that a different area (e.g., the upper portion) of the turbine
rotor plane, fluid shear (e.g., wind shear) and resultant
oscillations can occur adversely affecting the rotor blades, tower
and electrical generating equipment. By controlling the pitch of
individual shroud segments, the effects of fluid shear can be
mitigated.
[0090] In some embodiments, the shrouded wind turbine supplies
power for a utility grid, such as one of shrouded fluid turbines
602 . . . 620 that supplies power to utility grid 630. The measured
at least one variable may include a control variable and the pitch
may be altered to augment or reduce a power output of the shrouded
wind turbine. The control variable may be any of, but is not
restricted to: a rotor speed, a rotor-power output, a rotor-shaft
torque, and an ambient wind speed.
[0091] FIG. 19, schematically illustrates a method 900 of
controlling a power output of an array 600 of shrouded wind
turbines 602 . . . 620. One or more of the shrouded wind turbines
may include a ringed airfoil with pivotable shroud segments for
changing a pitch of the pivotable shroud segments. An active power
of the array 600 is measured (step 910). A pitch of at least a
portion of the shroud of at least one of the array 600 is altered
based on the measured reactive power to augment or reduce the
active power of the array 600 (step 920). In some embodiments, the
method 800 controls power during a low-voltage ride-through.
[0092] In fluid turbine arrays, such as wind farms, generally
speaking, upwind or leading turbines (e.g., shrouded fluid turbines
602, 604, 606) encounter faster incoming wind than downwind
turbines (e.g., shrouded fluid turbines 610, 612, 616, 618), and
accordingly are able to extract more energy than downwind turbines.
In some circumstances, it may be desirable to reduce the amount
energy extracted by the upwind or leading turbines by changing the
fluid flow through the turbine. As explained above, increasing a
pitch of outwardly extending mixing elements in a turbine shroud
and increasing a pitch of ejector segments reduces an overall fluid
flow through the fluid turbine. In some embodiments, a pitch may be
changed on only a portion of a ringed airfoil of one or more
selected fluid turbine(s) (e.g., fluid turbines 604, 605, 606) in
the array causing the selected fluid turbines 604, 605, 606 to yaw
out of the wind. The selected fluid turbines 604, 605, 606, which
are rotated out of the wind, do not extract as much power from the
incoming wind creating a lower wind reduction for trailing fluid
turbines (e.g., fluid turbines 610, 612). Further, if the selected
fluid turbines 604, 605, 606 yaw far out of the wind, profiles of
the selected fluid turbines 604, 605, 606 may be reduced, which
results in less wind reduction for trailing fluid turbines 610,
612. In some embodiments the yawing deflects wind from the selected
fluid turbines 604, 605, 606 to a second set of turbines 610, 612
to equalized power output from each turbine in the array.
[0093] The active power production of a group of mixer-ejector
turbines can be controlled based on grid frequency or deviation
from a grid frequency target, or may be controlled based on maximum
KWh supplied to the grid. Further, articulated or pivotable shroud
segments can be configured to deliver less than the maximum power
output so that a reserve of available power is available as
required.
[0094] By controlling the power output of each turbine individually
the reactive power of the group of mixer-ejector turbines is
controlled. Fluid turbines controlled in this manner can respond
appropriately based on grid voltage or an external target power
production.
[0095] Embodiments may be utilized in conjunction a variety of
forms of decentralized energy resources. One skilled in the art
will recognize that the fluid turbine arrangements in embodiments
may be utilized in the generation of power in conjunction with
overall power production in large-scale power grids. To ensure
stable and controllable power production, some embodiments may be
interfaced with the power grid in a variety of suitable ways. One
suitable approach for controlling and monitoring the output of some
embodiments is a Supervisory Control And Data Acquisition (SCADA)
system. A SCADA system for use with embodiments typically includes
inpuVoutput signal hardware and controllers at the various
location(s) to be monitored and/or controlled; a SCADA hub for
monitoring and controlling the location(s); a communication link(s)
from the location(s) to the SCADA hub; and one or more supervisory
stations at location(s) remote from the SCADA hub and in
communication with the SCADA hub.
[0096] The SCADA system for use may be configured to collect a
large amount of data from one or more shrouded fluid turbines to
which it is connected, either directly or indirectly. Additionally,
in accordance with some embodiments, the SCADA system may be
configured to control one or more shrouded fluid turbines to which
it is connected by means of control routines feeding control
parameters and settings to fluid turbine assembly, so that a stable
and controlled power supply can be ensured. As appreciated by one
of skill in the art, ensuring a stable and controllable power
generation from one or more shrouded fluid turbines may include the
use of meteorological modeling to predict changes in power
production from fluid turbine generators. In accordance with one
embodiment, a SCADA system may use data derived from monitoring the
power output from the fluid turbine generators of a turbine farm
(e.g., wind farm or wind park), and the power-transmission line. In
accordance with this embodiment, the power output may be predicted
using system-modeling algorithms understood in the art, and the
power generation may be stabilized by storing or releasing
generated power in unstable periods. Such system-modeling
algorithms may be based on meteorological predictions as well as a
variety of suitable alternative modeling and prediction data.
[0097] In accordance with other aspects, the pitch of at least one
shroud segment can be altered such that at least a portion of the
rotor-swept area may be shaded while the fluid turbine is in
operation. When employed in a wind turbine application, for
example, such shading of at least a portion of the rotor-swept area
may reduce the effect of sun shadowing, also known as shadow
flicker, on the ground.
[0098] In accordance with some embodiments, one or more shroud
segments may be actively or passively controlled to break up any
negative coatings that may attach to the shroud segments. For
example, one or more shroud segments may be actuated to break up
ice accumulation.
[0099] Furthermore, the power output of the fluid turbine system
may be controlled by changing the pitch of one or more shroud
segments. In one embodiment, a control parameter representative of
power output may be measured for use in the control of one or more
shroud segments. Suitable control parameters, as understood in the
art, may include rotor torque, generator current, or other suitable
indicators of power output. In an embodiment, the control parameter
may be compared with a fixed reference range to determine if the
power output is within an acceptable range. If the power output is
outside the acceptable range, one or more shroud segments may be
articulated to adjust the power-output to a value within the
acceptable range. Controlling power output in this manner allows
for the set of shrouds to be configured in such a manner as to
gradually increase speed during start-up, reduce speed during
shutdown, during low-voltage-ride-through or to generate the
minimum amount of power in excessive wind conditions, thus allowing
for continued optimal power output during excessive wind
conditions.
[0100] Some embodiments may be used to minimize or control stress
from asymmetric loading to within an acceptable range. In one
embodiment, a measurement of the tower base moment or indicators
thereof including tower top acceleration, tower tilt or rotor power
output may be obtained and the pitching shroud segment(s) of the
current invention may be utilized in a manner such that tower
stress is maintain constant and/or reduced.
[0101] Individual shroud segments can be pitched in order to
mitigate asymmetric loading including wind-driven asymmetric
loading, nacelle tilt or yaw loading, or blade loading caused by
reverberation between the tower and the blade, known as tower
shadow. Shroud segments are pitched in response to blade load,
blade bending, tip acceleration or nacelle tilt loading; or by
monitoring the load vs. rotor azimuth for each blade continuously,
to reduce increased speed in a specific area of the rotor
sweep.
[0102] Individual shroud segments can also be utilized to apply a
yaw moment to yaw the turbine upwind or downwind accordingly to
reduce the overall power output of the rotor/generator and/or to
deflect wind to other turbines in a wind park so as to provide
equal power output from each turbine in the park.
[0103] In view of the embodiments described in detail above, those
skilled in the art will readily appreciate that many modifications
are possible in the example embodiments without materially
departing from this invention. Accordingly, all such modifications
are intended to be included within the scope of this disclosure as
defined in the following claims. In the claims, means-plus-function
clauses are intended to cover the structures described herein as
performing the recited function and not only structural
equivalents, but also equivalent structures. Thus, although a nail
and a screw may not be structural equivalents in that a nail
employs a cylindrical surface to secure wooden parts together,
whereas a screw employs a helical surface, in the environment of
fastening wooden parts, a nail and a screw may be equivalent
structures. It is the express intention of the applicant not to
invoke 35 U.S.C. .sctn.112, paragraph 6 for any limitations of any
of the claims herein, except for those in which the claim expressly
uses the words `means for` together with an associated
function.
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