U.S. patent application number 13/481444 was filed with the patent office on 2012-11-29 for turbine with unevenly loaded rotor blades.
This patent application is currently assigned to FloDesign Wind Turbine Corp.. Invention is credited to Robert H. Dold, Timothy Hickey, Walter M. Presz, Michael J. Werle.
Application Number | 20120301283 13/481444 |
Document ID | / |
Family ID | 46246217 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120301283 |
Kind Code |
A1 |
Presz; Walter M. ; et
al. |
November 29, 2012 |
TURBINE WITH UNEVENLY LOADED ROTOR BLADES
Abstract
An unevenly loaded turbine rotor blade is disclosed herein, the
blade including a power-extracting region adapted for
radially-varied (relative to the axis of rotation) power extraction
per mass flow rate. The pitch and/or shape of the airfoil at a
first radial position may be configured, so that power extraction
per mass flow rate at the first radial position is different than
power extraction per mass flow rate at a second radial position.
Thus, the power-extracting region may be advantageously configured
to take advantage of a non-uniform flow profile across a rotor
plane such as may be induced using a shrouded turbine.
Inventors: |
Presz; Walter M.;
(Wilbraham, MA) ; Werle; Michael J.; (West
Hartford, CT) ; Dold; Robert H.; (Monson, MA)
; Hickey; Timothy; (East Longmeadow, MA) |
Assignee: |
FloDesign Wind Turbine
Corp.
Waltham
MA
|
Family ID: |
46246217 |
Appl. No.: |
13/481444 |
Filed: |
May 25, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61490841 |
May 27, 2011 |
|
|
|
Current U.S.
Class: |
415/182.1 |
Current CPC
Class: |
F03D 1/04 20130101; F05B
2240/13 20130101; F03D 1/0608 20130101; Y02E 10/72 20130101; F05B
2240/133 20130101; Y02E 10/20 20130101; Y02E 10/721 20130101; Y02E
10/223 20130101; Y02E 10/726 20130101; F05B 2210/16 20130101; F03B
3/126 20130101 |
Class at
Publication: |
415/182.1 |
International
Class: |
F04D 29/40 20060101
F04D029/40 |
Claims
1. A shrouded axial flow fluid turbine comprising: an
aerodynamically contoured turbine shroud having an inlet and
configured to produce a non-uniform fluid velocity profile across a
rotor plane when exposed to a fluid flow; and a rotor disposed
downstream of the inlet and configured to extract energy from fluid
passing through the rotor plane, the rotor comprising: a central
hub; and a plurality of blades, each blade including: a root region
having a blade root; a tip region having a blade tip; a mid-region
disposed between the root region and the tip region; and a blade
axis extending radially from the blade root to the blade tip; each
blade configured to have a value of power extraction per mass flow
rate at a radial position along the blade axis that is greater at a
first radius in the tip region of the blade than at second radius
in the mid-region of the blade when exposed to the non-uniform
fluid velocity profile.
2. The shrouded axial flow fluid turbine of claim 1, wherein an
average value of power extraction per mass flow rate for radial
positions along the blade axis in the tip region is larger than an
average value of power extraction per mass flow rate for radial
positions along the blade axis in the mid-region when exposed to
the non-uniform fluid velocity profile.
3. The shrouded axial flow fluid turbine of claim 1, wherein an
average value of power extraction per mass flow rate for radial
positions along the blade axis in the mid-region is larger than an
average value of power extraction per mass flow rate for radial
positions along the blade axis in the root region when exposed to
the non-uniform fluid velocity profile.
4. The shrouded axial flow fluid turbine of claim 1, wherein each
blade is configured to have a value of power extraction per mass
flow rate at a radial position along the blade axis that varies as
a function of distance of the radial position from a central axis
of rotation of the rotor when exposed to the non-uniform fluid
velocity profile.
5. The shrouded axial flow fluid turbine of claim 1, wherein a
pitch, a chord length and a camber of each blade at each radial
position along the blade axis are configured to produce a
non-uniform power extraction per mass flow rate profile along the
blade axis.
6. The shrouded axial flow fluid turbine of claim 1, wherein, for
each blade, an average value of power extraction per mass flow rate
for radial positions along the blade axis in the tip region is
between 20% and 45% greater than an average value of power
extraction per mass flow rate for radial positions along the blade
axis from the blade root to the blade tip.
7. The shrouded axial flow fluid turbine of claim 1, wherein, for
each blade, an average value of power extraction per mass flow rate
for radial positions along the blade axis in the root region is
between 20% and 45% less than an average value of power extraction
per mass flow rate for radial positions along the blade axis from
the blade root to the blade tip.
8. The shrouded axial flow fluid turbine of claim 1, wherein the
turbine shroud further comprises one or more mixing devices
disposed downstream of the rotor and extending downstream.
9. The axial flow fluid turbine of claim 10, wherein the one or
more mixing devices comprise mixer lobes.
10. The axial flow fluid turbine of claim 10, further comprising an
ejector shroud downstream of the turbine shroud.
11. The axial flow fluid turbine of claim 12, wherein turbine
shroud with one or more mixing devices and the ejector shroud form
a mixer-ejector pump, and the wherein the non-uniform flow velocity
profile at the rotor plane is created, in part, by the
mixer-ejector pump.
12. The axial flow fluid turbine of claim 10, wherein the mixing
devices function as flow straighteners to straighten a fluid flow
downstream of the rotor.
13. A rotor blade coupleable to a rotor of a shrouded fluid turbine
having a turbine shroud that produces a non-uniform fluid velocity
profile across a rotor plane when exposed to a fluid flow, the
rotor including a central hub configured to receive one or more
rotor blades, the rotor blade comprising: a root region having a
blade root; a tip region having a blade tip; a mid-region disposed
between the root region and the tip region; and a blade axis
extending from the blade root to the blade tip; wherein the blade
is configured to, when connected with the central hub, have a value
of power extraction per mass flow rate at a radial position along
the blade axis that is greater at a first radius in the tip region
of the blade than at a second radius in the mid-region of the blade
when exposed to the non-uniform fluid velocity profile.
14. The rotor blade of claim 13, wherein a pitch of the blade as a
function of radial position along the blade axis is configured to,
when connected with the central hub, produces an average value of
power extraction per mass flow rate for radial positions along the
blade axis in the tip region greater than an average value of power
extraction per mass flow rate for radial positions along the blade
axis in the mid-region when exposed to the non-uniform fluid
velocity profile.
15. The rotor blade of claim 13, wherein a pitch of the blade as a
function of radial position along the blade axis is configured to,
when connected with the central hub, produce a negative average
value of power extraction per mass flow rate or radial positions
along the blade axis in the root region when exposed to the
non-uniform fluid velocity profile.
16. A rotor configured for use with a shrouded fluid turbine having
a turbine shroud that creates a non-uniform fluid velocity profile
across a rotor plane when exposed to a fluid flow, the rotor
comprising: a central hub with a central axis of rotation; one or
more rotor blades, each of the one or more rotor blades comprising:
a root region having a blade root that couples with the central
hub; a tip region having a blade tip; a mid-region disposed between
the root region and the tip region; and a blade axis extending from
the blade root to the blade tip; wherein, for each of the one or
more rotor blades, a pitch of the blade as a function of radial
position along the blade axis is configured to, when connected with
the central hub, produce a power extraction per mass flow rate that
is greater at a first radius in the tip region of the blade than at
second radius in the mid-region of the blade when exposed to the
non-uniform fluid velocity profile.
17. A method of operating a shrouded axial flow fluid turbine
including an aerodynamically contoured turbine shroud having an
inlet, and a rotor disposed downstream of the turbine shroud inlet,
the rotor including a plurality of blades, each blade having a root
region including a blade root, a tip region including a blade tip,
and a mid-region disposed between the root region and the tip
region, the method comprising: establishing a non-uniform fluid
flow through a rotor plane in which an average velocity of fluid
flowing through an area of the rotor plane associated with the tip
region of each blade is greater than an average velocity of fluid
flowing through an area of the rotor plane associated with the
mid-region of each blade; and extracting power from the non-uniform
fluid flow using the plurality of blades by extracting a greater
average power per mass flow rate over the tip region of each blade
than an average power per mass flow rate extracted over the a
mid-region of each blade.
18. The method of claim 17, wherein the rotor has an axis of
rotation, and wherein each blade has a value of power extraction
per unit mass flow rate at a radial position along a blade axis
that varies as a function of the distance of the radial position
from the rotor axis of rotation when exposed to the non-uniform
fluid velocity profile.
19. The method of claim 17, wherein, for each blade, an average
value of power extraction per mass flow rate for radial positions
along the blade axis in the tip region is between 20% and 45%
greater than an average value of power extraction per mass flow
rate for radial positions along the blade axis from the blade root
to the blade tip.
20. The method of claim 17, wherein the turbine shroud further
includes one or more mixing devices disposed downstream of the
rotor and extending downstream.
21. The method of claim 20, wherein the one or more mixing devices
comprise mixer lobes.
22. The method of claims 20, wherein the axial flow fluid turbine
further includes an ejector shroud downstream of the turbine
shroud.
23. The method of claim 21, wherein turbine shroud with mixing
devices and the ejector shroud form a mixer-ejector pump, and the
wherein the non-uniform flow velocity profile at the rotor plane is
created, in part, by the mixer-ejector pump.
24. The method of claim 20, wherein the mixing devices function as
flow straighteners to straighten a fluid flow downstream of the
rotor.
25. The method of claim 17, wherein the shrouded axial flow turbine
generates electricity from the power extracted from the non-uniform
fluid flow by the rotor.
26. A turbine comprising a rotor that (i) is configured to extract
energy from a fluid flow characterized by a turbine-induced
non-uniform fluid velocity profile across a rotor plane and (ii)
includes at least one unevenly-loaded rotor blade having a
power-extracting region in which power extraction per mass flow
rate at a first radial position relative to an axis of rotation is
different than power extraction per mass flow rate at a second
radial position relative to the axis of rotation.
27. The turbine of claim 26, wherein an airfoil of the blade at
each of the first and second radial positions is configured based
on a pitch or a shape of the airfoil to affect the difference
between power extraction per mass flow rate at the first radial
position and power extraction per mass flow rate at the second
radial position.
28. The turbine of claim 26, wherein the turbine-induced
non-uniform velocity profile is characterized by a greater flow
velocity at the first radial position than at the second radial
position and wherein power extraction per mass flow rate at the
first radial position is greater than power extraction per mass
flow rate at the second radial position.
29. A method for manufacturing an unevenly-loaded rotor blade, the
method comprising: identifying along a power extracting region of
the blade a first radial position relative to an axis of rotation
of the blade having an expected exposure to a greater flow velocity
than a second radial position relative to the axis of rotation
along the power extracting region of the blade; and configuring the
power-extracting region to affect greater power extraction per mass
flow rate at the first axial position than at the second axial
position.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Application Ser. No. 61/490,841, filed May 27, 2011, the entirety
of which is incorporated by reference herein.
TECHNICAL FIELD
[0002] The present disclosure relates to turbine rotor blades of a
particular structure, and to shrouded turbines incorporating such
blades. More specifically, the present rotor blade design comprises
uneven loading (also known as "asymmetrical loading" or "unbalanced
loading").
BACKGROUND
[0003] Horizontal axis turbines (HAWTs) typically include two to
five bladed rotors joined at a central hub. A conventional HAWT
blade is commonly designed to provide substantially even blade
loading across a power-extracting region of the blade. One common
mathematical tool for predicting and evaluating blade performance
is blade element theory (BET). BET treats a blade as a set of
component elements (also known as "stations"). Each component
element may be defined by a radial cross section of the blade
(known as an airfoil) at a radial position (r) relative to the axis
of rotation and width of the element (dr). Applying BET analysis,
even blade loading may be characterized as each component element
of the blade along the power-extracting region having a same
pressure differential (.DELTA.p) during operation. Note that
.DELTA.p/.rho.=P/{dot over (m)}, wherein .rho. is fluid density, P
is power and in is mass flow rate. Given that fluid density is
typically constant, pressure differential may be assumed
proportional to power over mass flow rate. Thus, even blade loading
may also typically be characterized as each component element of
the blade along the power-extracting region exhibiting a same power
extracted per mass flow rate. Note that a conventional HAWT blade
may also include one or more non-power-extracting regions. For
example, conventional HAWT blades are often tapered at the tip
and/or root of the blade, for example, to reduce vortices. Such
tapered regions or otherwise minimally loaded regions proximal to
the tip and/or root of the blade are considered
non-power-extracting regions for the purposes of the present
disclosure.
[0004] Stations are typically designed/configured so as to maximize
power extraction across the blade while maintaining a constant
power extracted per mass flow rate. Mass flow rate is defined as
{dot over (m)}=.rho..nu.A, wherein .rho. is fluid density, .nu. is
flow velocity and A is the flow area (the "rotor swept area"). Flow
area for each station may be calculated as A=2.pi.rdr. Note that
station flow area increases as a function of radial position
impacting mass flow rate. Thus, the airfoil for each station is
typically designed to maintain even loading while accounting for
different mass flow rates. Parameters which may be adjusted to
ensure even loading for different mass flow rates include pitch
(also known as the "angle of attack") and/or airfoil shape, for
example, characterized by chord length, maximum thickness
(sometimes expressed as a percentage of cord length), mean camber
line, and/or the like. Airfoils for a conventional evenly loaded
HAWT blade typically exhibit longer chord lengths and greater pitch
toward the root than toward the tip to account for a higher mass
flow rate toward the tip (note that for conventional unshrouded
HAWTs, there is little difference between fluid velocity at the
center of the rotor plane and fluid velocity at the perimeter of
the rotor plane.
[0005] Recent development efforts have seen the implementation of
shrouded turbines, for example, to reduce the affect of fringe
vortices and/or to increase fluid flow velocity. One example of a
shrouded mixer-ejector wind turbine has been described in U.S.
patent application Ser. No. 12/054,050, which issued as U.S. Pat.
No. 8,021,100 and is incorporated herein in its entirety.
Development of shrouded turbines for power extraction is still in
its infancy. Thus, there is a need for new and improved blades
designed and optimized to work within a shrouded turbine
environment. These and other needs are addressed by way of the
present disclosure.
BRIEF DESCRIPTION
[0006] The present disclosure relates to novel turbine blade
designs characterized by uneven blade loading. The present
disclosure further relates to systems and methods for utilizing and
methods for manufacturing unevenly loaded turbine blades. Uneven
blade loading teaches away from the norm of the industry and is
particularly useful for taking advantage of non-uniform flow
profiles, e.g. such as may be created by a shroud. Indeed, as
recognized herein unevenly loaded blades may provide particular
advantages, for example, greater power extraction and/or greater
efficiency relative to conventional evenly loaded blades
particularly in a shrouded turbine environment or in other turbine
environments where fluid flow velocity is non uniform across the
rotor plane.
[0007] An embodiment includes a shrouded axial flow fluid turbine
including an aerodynamically contoured turbine shroud having an
inlet and configured to produce a non-uniform fluid velocity
profile across a rotor plane when exposed to a fluid flow. The
fluid turbine also includes a rotor disposed downstream of the
inlet and configured to extract energy from fluid passing through
the rotor plane. The rotor includes a central hub and a plurality
of blades, with each blade including a root region having a blade
root, a tip region having a blade tip, a mid-region disposed
between the root region and the tip region, and a blade axis
extending radially from the blade root to the blade tip. Each blade
is configured to have a value of power extraction per mass flow
rate at a radial position along the blade axis that is greater at a
first radius in the tip region of the blade than at second radius
in the mid-region of the blade when exposed to the non-uniform
fluid velocity profile.
[0008] Another embodiment includes a rotor configured for use with
a shrouded fluid turbine having a turbine shroud that creates a
non-uniform fluid velocity profile across a rotor plane when
exposed to a fluid flow. The rotor includes a central hub with a
central axis of rotation and one or more rotor blades. Each each of
the one or more rotor blades includes a root region having a blade
root that couples with the central hub, a tip region having a blade
tip, a mid-region disposed between the root region and the tip
region, and a blade axis extending from the blade root to the blade
tip. For each of the one or more rotor blades, a pitch of the blade
as a function of radial position along the blade axis is configured
to, when connected with the central hub, produce a power extraction
per mass flow rate that is greater at a first radius in the tip
region of the blade than at second radius in the mid-region of the
blade when exposed to the non-uniform fluid velocity profile.
[0009] An embodiment includes a method of operating a shrouded
axial flow fluid turbine including an aerodynamically contoured
turbine shroud having an inlet, and a rotor disposed downstream of
the turbine shroud inlet. The rotor includes a plurality of blades
with each blade having a root region including a blade root, a tip
region including a blade tip, and a mid-region disposed between the
root region and the tip region. The method includes establishing a
non-uniform fluid flow through a rotor plane in which an average
velocity of fluid flowing through an area of the rotor plane
associated with the tip region of each blade is greater than an
average velocity of fluid flowing through an area of the rotor
plane associated with the mid-region of each blade. The method also
includes extracting power from the non-uniform fluid flow using the
plurality of blades by extracting a greater average power per mass
flow rate over the tip region of each blade than an average power
per mass flow rate extracted over the a mid-region of each
blade.
[0010] In an example embodiment, an unevenly loaded turbine blade
is disclosed, the blade including a power-extracting region adapted
for radially-varied (relative to the axis of rotation) power
extraction per mass flow rate. More particularly, the pitch and/or
shape of the airfoil at a first radial position may be configured,
so that the power extraction per mass flow rate of the blade at the
first radial position is different than the power extraction per
mass flow rate of the blade at a second radial position. In one
example embodiment, the power-extracting region may be configured
to take advantage of a non-uniform flow profile, for example, a
flow profile where flow velocity is expected to be greater at a
first radial position than at a second radial position. Thus, the
power-extracting region may be configured such that power
extraction per mass flow rate at the first radial position is
greater than power extraction per mass flow rate at the second
radial position. In one embodiment, the power-extracting region may
optimized for an expected relative flow velocity between fluid flow
at a first radial position and fluid flow at a second radial
position. For example, the power-extracting region may optimized
based on optimal lift/drag ratios for each radial position such as
a maximal lift/drag ratio prior to stall or prior to a selected
safety threshold. Thus, the greater the flow velocity at a radial
position, the greater the optimal lift/drag ratio at that position
and the greater the power extraction per mass flow rate at that
position. In an example embodiment, relative flow velocity between
two radial positions may be related, for example, proportional to
relative power extraction per mass flow rate between the two radial
positions.
[0011] Another example embodiment relates in general to turbine
environments wherein fluid flow velocity is non-uniform across the
rotor plane. For example, a turbine may include at least one shroud
that is in close proximity to or surrounds at least a portion of a
rotor and affects a non-uniform flow profile. One skilled in the
art will readily recognize that the unevenly loaded rotor blades as
taught herein may be employed in conjunction with numerous turbines
that are, at least in part, shrouded.
[0012] One suitable example of a shrouded turbine is a
mixer-ejector turbine in which an ejector shroud may be in close
proximity to or surround an exit of a turbine shroud. It will be
appreciated that embodiments of unevenly loaded blades as described
herein may be incorporated into to the design of the rotor of the
mixer-ejector turbine. In one example embodiment, the turbine
shroud may include a set of mixing lobes along the trailing edge
that are in fluid communication with the inlet of the ejector
shroud. Together, the mixer lobes and the ejector shroud may form a
mixer-ejector pump that provides a means of energizing the wake
behind the rotor plane. The mixer-ejector pump may further provides
increased fluid velocity near the inlet of the turbine shroud, at
the cross sectional area of the perimeter of the rotor plane.
[0013] The power coefficient of the mixer-ejector wind turbine may
be between approximately 1.2 and 2.0. The power output is derived
from the rated fluid velocity and rotor area and results in a given
average total pressure drop across the rotor plane. The total
pressure is represented by:
.DELTA. P T = 1 / 2 .rho. V w 3 C P V a ##EQU00001##
[0014] Where .DELTA.P.sub.T is the change in total pressure between
the upstream and downstream sides of the rotor plane, .rho. is the
density of the fluid in the stream, V.sub.w, is the free stream
fluid speed V.sub.a is the accelerated velocity through the rotor,
and CP is the coefficient of power.
[0015] A mixer ejector turbine (MET), as described herein, uses a
mixer/ejector pump in combination with highly cambered ringed
airfoils to improve turbine efficiency. Two factors which may be
important for optimal blade design for the MET system include the
speed up of the flow at the rotor station and/or the energy
addition to the rotor wake flow in the mixer/ejector. The
one-dimensional control volume power predictions (above) account
for and utilize both of these effects. The cambered shrouds and
ejector bring more flow through the rotor allowing more energy
extraction just due to higher flow rates. The mixer/ejector
transfers energy from the bypass flow to the rotor wake flow
allowing higher energy per unit mass flow rate through the
rotor.
[0016] The higher velocities at the different radial positions
along the blade (at different stations) can be taken advantage of
through induction factor analyses in wind turbine blade design.
Principles of both BET and momentum conservation analysis may be
applied to facilitate turbine blade design. Iterative empirical
testing may be utilized as well. Results of tests conducted by the
Inventors have shown that the energy transfer from the bypass flow
occurs primarily in the lobe region of the wake flow with virtually
no energy addition near the centerbody. Thus, by varying the blade
power extraction (total pressure extraction profile) with high
power extraction per mass flow rate for the flow that passes
through the lobes and mixes quickly with the bypass flow (e.g., at
the top 1/3 of the blade) and lower power extraction per flow rate
for the unmixed flow (e.g., toward the blade root) a greater amount
of power may be extracted. Further, without reducing the power
extraction per unit flow rate at the blade root section, the center
region of the ejector flowfield would not be able to pass through
the wake diffusion without stalling. In tests conducted, screens
were used to optimize radial power extraction profiles for the MET
system.
[0017] A MET in accordance with one embodiment provides increased
fluid flow velocity at the perimeter region of the rotor plane
relative to the fluid flow velocity at a center region of the rotor
plane. An unevenly loaded blade, as described herein, may be
designed to accommodate more energy extraction per unit mass flow
rate at the perimeter region and less energy extraction per unit
mass flow rate at the center region of the rotor plane. Thus, an
unevenly loaded blade, as described herein is better suited than a
conventional symmetrically loaded blade to maximize power
extraction from fluid with a non-uniform flow velocity.
[0018] These and other non-limiting features or characteristics of
the present disclosure will be further described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] 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.
[0020] FIG. 1 is a front right perspective view of an example
horizontal wind turbine of the prior art.
[0021] FIG. 2 is a perspective view depicting delineated cross
sections that represent stations of one of the rotor blades of the
turbine of FIG. 1.
[0022] FIG. 3 is an orthographic end view of the delineated cross
sections that represent each station of the rotor blade of FIG.
2.
[0023] FIG. 4 illustrates even blade loading of a power-extracting
region of the rotor blade of FIGS. 2 and 3.
[0024] FIG. 5 is a graphical representation of the pressure
differential per station (blade loading) represented in FIG. 4.
[0025] FIG. 6 is a front perspective view of an exemplary turbine
embodiment of the present disclosure.
[0026] FIG. 7 is a cross section of the turbine represented in FIG.
6.
[0027] FIG. 8 is a perspective view depicting delineated cross
sections that represent the stations of one of the rotor blades of
the turbine of FIGS. 6 and 7.
[0028] FIG. 9 is an orthographic end view of the delineated cross
sections that represent each station of the rotor blade of FIG.
8.
[0029] FIG. 10 illustrates uneven blade loading of the rotor blade
of FIGS. 8 and 9.
[0030] FIG. 11 is a graphical representation of the pressure
differential per station (blade loading) represented in FIG.
10.
[0031] FIGS. 12-14 are views of further exemplary shrouded turbine
embodiments of the present disclosure.
DETAILED DESCRIPTION
[0032] 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 disclosed
embodiment(s).
[0033] 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.
[0034] A value modified by the term "about" or the term
"substantially" should be interpreted as disclosing both the stated
value as well as a range of values proximal to the stated value
within the meaning dictated by the context and as would readily be
understood by one of ordinary skill in the art. For example, a
value modified by the term "about" or the term "substantially"
should be interpreted as disclosing a range of values proximal to
the value accounting for at least the degree of error related to
the value, for example, based on design/manufacture tolerances
and/or measurement errors affected the value.
[0035] Turbines may be used to extract energy from a variety of
suitable fluids such as air (e.g., wind turbines) and water (e.g.,
hydro turbines), e.g., to generate electricity. In general,
principles relating to turbine design and operation, such as
described herein, remain consistent regardless of fluid type. For
example, the aerodynamic principles of a wind turbine also apply to
hydrodynamic principles of a water turbine. Thus, while portions of
the present disclosure may be directed towards one or more example
embodiments of turbines it will be appreciated by one of ordinary
skill in the art that such teachings may be universally applicable,
for example, regardless of fluid type.
[0036] A Mixer-Ejector Turbine (MET) provides an improved means of
extracting power from flowing fluid. A primary shroud contains a
rotor which extracts power from a primary fluid stream. A
mixer-ejector pump is included that ingests bypass for use in
energizing the primary fluid flow. This mixer-ejector pump may
promote turbulent mixing of the aforementioned two fluid streams.
This mixing enhances the power extraction from the MET system by
increasing the amount of fluid flow through the system, increasing
the velocity at the rotor plane for more power availability, and
reducing the pressure on down-wind side of the rotor plane and
energizing the rotor wake. As understood by one skilled in the art,
the aerodynamic principles of a MET are not restricted to a
specific fluid, and may apply to any fluid, defined as any liquid,
gas or combination thereof and therefore includes water as well as
air. In other words, the aerodynamic principles of a mixer ejector
wind turbine apply to hydrodynamic principles in a mixer ejector
water turbine.
[0037] Exemplary rotors, according to the present disclosure, may
include a conventional propeller-like rotor, a rotor/stator
assembly, a multi-segment propeller-like rotor, or any type of
rotor understood by one skilled in the art. In an example
embodiment, a rotor may be associated with a turbine shroud, such
as described herein, and may include one or more rotor blades, for
example, one or more unevenly loaded rotor blades, such as
described herein, attached to a rotational shaft or hub. As used
herein, the term "blade" is not intended to be limiting in scope
and shall be deemed to include all aspects of suitable blades,
including those having multiple associated blade segments.
[0038] The leading edge of a turbine blade and/or the leading edge
of a turbine shroud may be considered the front of the turbine. The
trailing edge of a turbine blade and/or the trailing edge of an
ejector shroud may be considered the rear of the turbine. A first
component of the 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.
[0039] In an example embodiment, the present disclosure relates to
a turbine for extracting power from a non-uniform flow velocity. In
one example embodiment, the turbine may be configured for affecting
the non-uniform flow velocity in the fluid (for example, the
turbine may be a MET including a turbine shroud that is in close
proximity to or surrounds a rotor and an ejector shroud that is in
close proximity to or surrounds the exit of the turbine shroud).
More particularly, the present disclosure relates to the design and
implementation (for example, in a shrouded turbine) of unevenly
loaded rotor blade(s). In one example embodiment, the tip to hub
variation in power extracted per mass flow rate is between 40% and
90%, or in other words, the area toward the tip region of the rotor
extracts between 40% and 90% more power per mass flow rate than the
area toward the root region at the hub of the rotor blade.
Advantageously, the mass-average total pressure drop from the
upstream area to the downstream area may remain the same.
[0040] FIG. 1 is a perspective view of an embodiment of a
conventional HAWT 100 of the prior art. The HAWT 100 includes rotor
blades 112 that are joined at a central hub 141 and rotate about a
central axis 105. The hub is joined to a shaft that is co-axial
with the hub and with the nacelle 150. The nacelle 150 houses
electrical generation equipment (not shown). The rotor plane is
represented by the dotted line 115.
[0041] Referring to FIGS. 2-4, an exemplary rotor blade 112, (e.g.,
for the HAWT 100 of FIG. 1) is shown. Cross sections 160, 162, 164
. . . 180 are delineated at different radial positions relative to
the axis of rotation (e.g., relative to the central axis of FIG. 1)
along a central blade axis 107. Each cross section 160, 162, 164 .
. . 180 represents a station along the blade 112 and defines an
airfoil. According to the illustrated embodiment, each airfoil may
be characterized based on the length and pitch of a cord between
the leading and trailing edges of the airfoil (note this is merely
an illustrative embodiment, however, and any number of parameters
relating to the shape and/or pitch of the airfoil may be identified
and used to characterize the airfoil). Cross section 160 defines
chord 161. Similarly, cross section 180 defines chord 181.
Referring to FIG. 3, each chord has a length and a pitch as seen in
the length and relative pitch angle between chords 161 and 181. The
chord length and pitch of each cross section affects the loading on
the blade at the corresponding station. FIG. 4, depicts blade
loading (.DELTA.p) across different regions of the blade 112. Blade
loading (.DELTA.p) is illustrated using horizontal hash markings
wherein the spacing between the hash markings is inversely
proportional to blade loading. As depicted in FIG. 4, conventional
HAWT blades are designed to have even blade loading at each station
across a power-extracting region of the blade 112 when operating in
a fluid stream. Note that the blade 112 includes two
non-power-extracting regions proximal to the root and tip of the
blade (see cross sections 160 and 180, respectively). The non-power
extracting regions are identifiable by the sudden minimal blade
loading represented in FIG. 4 by sparse horizontal hash marking at
the root and tip of the blade 112.
[0042] FIG. 5 depicts a graphical representation of blade loading
per station as represented in FIG. 4 for blade 112. As noted with
respect to FIG. 5 even blade loading is evident for stations in a
power-extracting region of the blade 112 (see, e.g., cross sections
162, 164, 166 and 178). Minimal blade loading is evident for
stations in non-energy extracting regions of the blade 112 near the
root and tip (see, e.g., cross-sections 160 and 180, respectively).
The position of the cross sections 160, 162, 164 . . . 180 along
the axis 107 is represented along the vertical axis of the graph.
Blade loading, characterized by a pressure differential (.DELTA.p)
in pounds per square foot (psf) is represented along the horizontal
axis of the graph. The vertical alignment cross sections from the
power-extracting region of the blade 112 represents substantially
identical, or even, blade loading.
[0043] FIG. 6 is a perspective view of an exemplary embodiment of a
shrouded turbine 200 of the present disclosure. FIG. 7 is a
cross-sectional view of the shrouded turbine of FIG. 6. Referring
to FIG. 6, the shrouded turbine 200 includes a turbine shroud 210,
a nacelle body 250, a rotor 239, and an ejector shroud 220. The
turbine shroud 210 includes a front end 212, also known as an inlet
end or a leading edge. The turbine shroud 210 also includes a rear
end 216, also known as an exhaust end or trailing edge. The ejector
shroud 220 includes a front end, inlet end or leading edge 222, and
a rear end, exhaust end, or trailing edge 224. Support members 206
are shown connecting the turbine shroud 210 to the ejector shroud
220.
[0044] The rotor 239 is operatively coupled to the nacelle body
250. The rotor 239 includes a central hub 241 at the proximal end
of one or more rotor blades 240 and defines a rotor plane where the
fluid flow intersects the blades 240. The central hub 241 is
rotationally engaged with the nacelle body 250. The nacelle body
250 and the turbine shroud 210 are supported by a tower 202. In the
present embodiment, the rotor 239, turbine shroud 210, and ejector
shroud 220 are coaxial with each other, i.e. they share a common
central axis 205.
[0045] Referring to FIG. 7. The turbine shroud 210 has the
cross-sectional shape of an airfoil with a leading edge 212 and the
suction side (i.e. low pressure side) on the interior of the
shroud. The rear end 216 of the turbine shroud also has mixing
lobes including rotor flow (low energy) mixing lobes 215 and bypass
flow (high energy) mixing lobes 217. The mixing lobes extend
downstream beyond the rotor blades 240. Put another way, the
trailing edge 216 of the turbine shroud is shaped to form two
different sets of mixing lobes. High energy mixing lobes 217 extend
inwardly towards the central axis 205 of the mixer shroud. Low
energy mixing lobes 215 extend outwardly away from the central axis
205. An opening in the sidewall 219 between the low energy lobe 215
and the high energy mixing lobe 217 increases mixing between high
and low energy streams.
[0046] A mixer-ejector pump is formed by the ejector shroud 220 in
fluid communication with the ring of high energy mixing lobes 217
and low energy mixing lobes 215 on the turbine shroud 210. The
mixing lobes 217 extend downstream toward the inlet end 222 of the
ejector shroud 220. This mixer-ejector pump provides the means for
increased operational efficiency. The area of higher velocity fluid
flow is generally depicted by the shaded area 245 (FIG. 7). In
accordance with the present disclosure, rotor blades in a
mixer-ejector turbine may be designed appropriately to take
advantage of the energy transfer as a result of the mixing between
the bypass flow and the rotor wake flow. This mixing is strongly
determined by the height and shape of the lobes 217.
[0047] Referring to FIG. 8-10, an example rotor blade 240 (e.g.,
for the mixer-ejector turbine 200 of FIGS. 6-7), is shown. The
blade 240, advantageously includes a power-extracting region
adapted for radially-varied (relative to the axis of rotation)
power extraction per mass flow rate. Cross sections 260, 262, 264 .
. . 284 are delineated at different radial positions relative to
the axis of rotation (e.g., relative to axis 205 of FIGS. 6-7)
along the central axis 207 of the blade. Each cross section 260,
262, 264, . . . , 284 represents a station along the blade 240 and
defines an airfoil. According to the illustrated embodiment, each
airfoil may be characterized based on the length and pitch of a
cord between the leading and trailing edges of the airfoil (note
this is merely an illustrative embodiment, however, and any number
of parameters relating to the shape and/or pitch of the airfoil may
be identified and used to characterize the airfoil). Cross section
260 defines chord 261. Similarly, cross section 284 defines chord
283.
[0048] In one example embodiment, the rotor blade 240 may be
constructed and/or modeled using multiple blade segments, e.g.,
such as defined between cross sections, wherein each blade segment
actually has or is assumed to have a constant airfoil shape and
pitch (e.g., a constant chord length and chord pitch). In this
embodiment, the airfoil shape and/or pitch of one segment need not
be contiguous with the airfoil shape and/or pitch of an adjacent
segment. In another example embodiment, the rotor blade 240 may be
constructed and/or modeled as a contiguous structure, e.g., wherein
the shape and pitch of the airfoil changes contiguously with
respect to radial-position. Thus, for example, the rotor blade 240
may be modeled as an infinite number of blade segments of a width
(dr) approaching zero. Analysis of forces and/or structural
parameters can be achieved by integrating over a length of the
blade 240 (0 to R).
[0049] Referring to FIG. 9, each chord has a length and a pitch as
seen in the length and relative pitch angle between chords 261 and
283. Airfoil characteristics, such as the chord length and pitch of
each cross section affect the loading on the blade at the
corresponding station. Thus, for blade 240, the pitch and/or shape
of the airfoil at a first cross section, e.g., cross section 284,
is configured, so that the power extraction per mass flow rate of
the blade 240 at that first cross section is different than the
power extraction per mass flow rate of the blade 240 at a second
cross section, e.g., cross section 260. Blade 240 is advantageously
configured to take advantage of the non-uniform flow profile
resulting from the mixer-ejector pump of the turbine 200 of FIGS.
6-7 with greater loading toward the tip to take advantage of the
region of greater fluid flow velocity (shaded area 245 of FIG. 7).
Blade 240 illustrates how a power-extracting region of an unevenly
loaded blade may optimized for an expected relative flow velocity
between fluid flow at a first radial position and fluid flow at a
second radial position. In example embodiments, the
power-extracting region of an unevenly loaded blade may optimized
based on optimal lift/drag ratios for each radial position such as
a maximal lift/drag ratio prior to stall or prior to a selected
safety threshold. As illustrated by blade 240, the greater the
relative flow velocity at a radial position, the greater the
optimal lift/drag ratio at that position and the greater the power
extraction per mass flow rate at that position. In an example
embodiment, relative flow velocity between two radial positions may
be related, for example, proportional to relative power extraction
per mass flow rate between the two radial positions.
[0050] FIG. 10, depicts blade loading (.DELTA.p) across different
regions of the blade 240. Blade loading (.DELTA.p) is illustrated
using horizontal hash markings wherein the spacing between the hash
markings is inversely proportional to blade loading. As depicted in
FIG. 10, blade 240 is designed to have uneven blade loading at each
station across a power-extracting region of the blade 240 when
operating in the fluid stream of turbine 200 of FIGS. 6-7. More
particularly, blade 240 is configured to exhibit greater loading
toward the tip to take advantage of the region of greater fluid
flow velocity. Note that for the embodiment depicted in FIG. 4 the
power-extracting region includes portions of the blade from cross
section 260 to cross section 284, e.g., there are no non-power
extracting regions toward the tip or root.
[0051] FIG. 11 depicts a graphical representation of blade loading
per station as represented in FIG. 10 for blade 240. As noted with
respect to FIG. 10 uneven blade loading is evident for stations of
the blade 240 (see, e.g., the gradual decrease in blade loading
from station 284 to station 260). The position of cross-sections
260, 262, 264 . . . 284 along the central blade axis 207 is
represented along the vertical axis of the graph. Blade loading,
characterized by a pressure differential (.DELTA.p) in pounds per
square foot (psf) is represented along the horizontal axis of the
graph. In some embodiments, the load at a station that represents
the blade tip (cross section 284) is between 20% and 45% greater
than the load at a mean section (cross section 270), similarly, the
load at a station that represents the blade root (cross section
260) is 20% to 45% lower than that of the mean section (cross
section 270).
[0052] It is noted that mixer/ejector turbine 200 of FIGS. 6-7 is
only one example of a shrouded turbine which may be used in
accordance with the apparatus, systems and methods of the present
disclosure to produce a non-uniform flow profile across a rotor
plane. Indeed, other implementations of shrouded turbines, e.g.,
with or without an ejector shroud and/or with or without mixing
lobes may also be used instead to produce non-uniform flow profile
across a rotor plane. See, for example, FIGS. 12-14, depicting
further exemplary shrouded turbine embodiments capable of producing
a non-uniform flow profile across a rotor plane.
[0053] FIG. 12 is a perspective view of a further example
embodiment of a shrouded turbine 300 including a turbine shroud 310
characterized by a ringed airfoil. Unlike the turbine 200 of FIGS.
6-7, turbine 300 does not include an ejector shroud. Turbine 300
also includes a nacelle body 350 and a rotor 339 including a
plurality of rotor blades 340. Unlike the turbine 200 of FIGS. 6-7,
turbine 300 in the embodiment of FIG. 12 does not include an
ejector shroud. The turbine shroud 310 advantageously induces a
non-uniform flow profile across a rotor plane. Turbine shroud 310
further includes mixing elements 315 and 317. Mixing elements 315
and 317 include inward turning mixing elements 317 which turn
inward toward a central axis 305 and outward turning mixing
elements 315 which turn outward from the central axis 305. The
turbine shroud 310 includes a front end 312 also known as an inlet
end or a leading edge. Mixing elements 315 and 317 include a rear
end 316, also known as an exhaust end or trailing edge. Support
structures 306 are engaged at the proximal end, with the nacelle
body 350 and at the distal end with the turbine shroud 310. The
rotor, nacelle body 350, and turbine shroud 310 are concentric
about a common axis 305 (which is the axis of rotation for the
rotor 339) and are supported by a tower structure 302.
[0054] FIG. 13 depicts a cross-sectional view of a further example
embodiment of a shrouded turbine 400. Turbine 400 includes a
shrouded turbine 410 characterized by a ringed airfoil. Turbine 400
also includes a nacelle body 450 and a rotor 439 including a
plurality of rotor blades 440. Similar to the turbine 300 of FIG.
12, the turbine 400 depicted in FIG. 13 does not include an ejector
shroud. The turbine shroud 410 advantageously induces a non-uniform
flow profile across a rotor plane 409. Unlike the turbine shroud
310 in FIG. 12, the turbine shroud 410 in the embodiment of FIG.
13, does not include mixing elements. The turbine shroud 410
includes a front end 412 also known as an inlet end or a leading
edge and a rear end 416, also known as an exhaust end or trailing
edge. Support structures 406 are engaged at a proximal end with the
nacelle body 450 and at the distal end with the turbine shroud 410.
The rotor 439, nacelle body 450, and turbine shroud 410 are
concentric about a common axis 405 (which is the axis of rotation
for the rotor 439) and are supported by a tower structure 402.
[0055] FIG. 14 depicts a cross section view of a further example
embodiment of a shrouded turbine 500. Turbine 500 includes a
shrouded turbine 510 characterized by a ringed airfoil. Turbine 500
also includes a nacelle body 550 and a rotor 539 including a
plurality of rotor blades 540. Similar to the turbines 300 and 400
of FIGS. 12-13, the turbine 500 depicted in FIG. 14 does not
include an ejector shroud. The turbine shroud 510 advantageously
induces a non-uniform flow profile across a rotor plane 509.
Instead of including mixing lobes, turbine shroud 510
advantageously defines a plurality of passages 519 extending from
the outer surface to the inner surface of the turbine shroud 510.
Passages 519 act as bypass ducts that providing mixing between a
bypass flow 503 and the fluid flow through the turbine 500
down-stream from the rotor plane 509 thus introducing a volume of
high energy flow to the exit flow. The turbine shroud 510 includes
a front end 512 also known as an inlet end or a leading edge and a
rear end 516, also known as an exhaust end or trailing edge.
Support structures 506 are engaged at a proximal end with the
nacelle body 550 and at the distal end with the turbine shroud 510.
The rotor 539, nacelle body 550, and turbine shroud 510 are
concentric about a common axis 505 (which is the axis of rotation
for the rotor) and are supported by a tower structure 502.
[0056] It is contemplated that a turbine shroud may not be the only
mechanism in a turbine for inducing a non-uniform flow profile
across a rotor plane of a turbine. Indeed, any appropriate
mechanism may be used to manipulate fluid flow instead of or in
addition to a turbine shroud.
[0057] The present disclosure has been described with reference to
exemplary 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.
* * * * *