US20120301283A1

US20120301283A1 - Turbine with unevenly loaded rotor blades

Info

Publication number: US20120301283A1
Application number: US13/481,444
Authority: US
Inventors: Walter M. Presz; Michael J. Werle; Robert H. Dold; Timothy Hickey
Original assignee: FloDesign Wind Turbine Corp
Current assignee: FloDesign Wind Turbine Corp
Priority date: 2011-05-27
Filing date: 2012-05-25
Publication date: 2012-11-29
Also published as: CN103597205A; WO2012166632A1; CA2832984A1; US20120315125A1; EP2715119A1; CA2834595A1; EP2715120A1; WO2012166625A1

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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

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

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 (Δp) during operation. Note that Δp/ρ=P/{dot over (m)}, wherein ρ 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.
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)}=ρνA, wherein ρ is fluid density, ν is flow velocity and A is the flow area (the “rotor swept area”). Flow area for each station may be calculated as A=2πrdr. 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.
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

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.
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.
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.
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.
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.
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.
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.
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:
$Δ P_{T} = \frac{1 / 2 \cdot ρ \cdot V_{w}^{3} \cdot C P}{V_{a}}$
Where ΔP_Tis the change in total pressure between the upstream and downstream sides of the rotor plane, ρ is the density of the fluid in the stream, V_w, is the free stream fluid speed V_ais the accelerated velocity through the rotor, and CP is the coefficient of power.
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.
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 ⅓ 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.
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.
These and other non-limiting features or characteristics of the present disclosure will be further described below.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

FIG. 1 is a front right perspective view of an example horizontal wind turbine of the prior art.

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.

FIG. 3 is an orthographic end view of the delineated cross sections that represent each station of the rotor blade of FIG. 2.

FIG. 4 illustrates even blade loading of a power-extracting region of the rotor blade of FIGS. 2 and 3.

FIG. 5 is a graphical representation of the pressure differential per station (blade loading) represented in FIG. 4.

FIG. 6 is a front perspective view of an exemplary turbine embodiment of the present disclosure.

FIG. 7 is a cross section of the turbine represented in FIG. 6.

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.

FIG. 9 is an orthographic end view of the delineated cross sections that represent each station of the rotor blade of FIG. 8.

FIG. 10 illustrates uneven blade loading of the rotor blade of FIGS. 8 and 9.

FIG. 11 is a graphical representation of the pressure differential per station (blade loading) represented in FIG. 10.

FIGS. 12-14 are views of further exemplary shrouded turbine embodiments of the present disclosure.

DETAILED DESCRIPTION

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).
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.
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.
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.
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.
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.
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.
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.
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.
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 (Δp) across different regions of the blade 112. Blade loading (Δp) 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.
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 (Δp) 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.
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.
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.
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.
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.
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.
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).
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.
FIG. 10, depicts blade loading (Δp) across different regions of the blade 240. Blade loading (Δp) 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.
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 (Δp) 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).
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.
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.
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.
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.
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.
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.

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.