Patent Application
20130309081
The present disclosure relates to fluid turbines of a particular structure, more specifically to a fluid turbine having a rotor in fluid communication with at least a portion of a ringed airfoil having a leading edge coplanar with, or downstream of, the rotor plane.
Horizontal axis wind turbines typically include two to five rotor blades joined at a central hub, providing a rotor for capturing energy from a fluid stream. Generally speaking, a fluid turbine structure with an open rotor unshrouded design captures energy from a fluid stream that is smaller in diameter than the rotor. In an open rotor unshrouded fluid turbine, as fluid flows from the upstream side of the rotor to the downstream side, the fluid velocity remains constant as the flow passes through the rotor plane. Energy is extracted at the rotor resulting in a pressure drop on the downstream side of the rotor. The fluid directly downstream of the rotor is at sub-atmospheric pressure due to the energy extraction and the fluid directly upstream of the rotor is at greater than atmospheric pressure. The high pressure upstream of the rotor deflects some of the upstream air around the rotor. In other words, a portion of the fluid stream is diverted around the open rotor as if by an impediment. As it is diverted around the open rotor, the fluid stream expands, which is referred to as flow expansion at the rotor. Due to the flow expansion, the upstream area of the fluid flow is smaller than the area of the rotor.
In contrast, in a ducted or shrouded turbine, the upstream area of the fluid stream is larger than the area of the rotor. The duct or shroud contracts the fluid stream at the rotor plane and the fluid stream expands later after leaving the duct or shroud. The energy that may be harvested from the fluid is proportional to the upstream area where the fluid stream starts in a non-contracted state. In a conventional diffuser augmented turbine the diffuser surrounds the rotor such that the diffuser guides incoming fluid prior to the fluid interaction with the rotor, providing the largest unit-mass flow rate substantially proximal to the rotor plane. Expansion of the flow is delayed to the area downstream of the rotor, at the trailing edge of the duct or shroud. The upstream area of the fluid stream is larger than the area of the rotor plane due to the flow contraction at the duct or shroud.
A properly designed ducted or shrouded fluid turbine, delivers greater mass flow rate through the interior of the duct or shroud and, accordingly, through the rotor plane as compared with the mass flow rate through the rotor plane of an open rotor unshrouded fluid turbine. Improved performance of a fluid turbine including a rotor in fluid communication with a properly designed duct or shroud, in comparison to performance of a similar open rotor unshrouded fluid turbine, may be achieved due to a reduction in the production of tip vortices and due to the increased unit mass flow through the duct or shroud. However, the increased surface area and mass of the duct or shroud may cause unnecessary drag and loading that results in excessive forces on a support structure of the fluid turbine in high wind conditions.
Embodiments include fluid turbine systems having a rotor defining a rotor plane and at least a portion of a ringed airfoil in fluid communication with a wake of the rotor. The portion of ringed airfoil has a leading edge that is co-planar with or downstream of the rotor. Some exemplary fluid turbines draw a higher energy secondary air flow that bypassed the rotor past a suction surface of the ringed airfoil to mix with a lower energy primary air flow that passed through the rotor. In some embodiments, positioning the rotor upstream of the leading edge of the ringed airfoil at least partially mitigates excessive load forces on support structures of the fluid turbine support structures in high fluid flow (e.g., high wind) conditions.
An embodiment includes a fluid turbine system with a rotor and one or more ringed airfoil segments. The rotor is configured to rotate about a central axis with the rotation of the rotor defining a rotor plane. The one or more ringed airfoil segments are disposed around the central axis and in fluid communication with a wake of the rotor. Each ringed airfoil segment has a leading edge that is co-planar with or downstream of the rotor plane as measured along the central axis.
In some embodiments, the one or more ringed airfoil segments form less than half a perimeter of a circle around the central axis. In some embodiments, the one or more ringed airfoil segments form more than half a perimeter of a circle around the central axis. In some embodiments, the one or more ringed airfoil segments fully encircle the central axis.
In some embodiments, the one or more ringed airfoil segments are configured to create a maximum in the unit mass flow rate downstream of the rotor plane.
In some embodiments, the rotor and each of the one or more ringed airfoil segments are configured to draw blade tip vortices from rotation of the rotor past a surface of the ringed airfoil segment facing toward the central axis. In some embodiments, the rotor and each of the ringed airfoil segments are configured to draw a secondary flow that bypassed the rotor past a surface of the ringed airfoil segment facing toward the central axis.
In some embodiments, at least some of the one or more ringed airfoil segments include at least one mixing element. The mixing element may include a mixing lobe. The mixing element may include a mixing slot.
In some embodiments, the fluid turbine also includes a second ringed airfoil downstream of the one or more ringed airfoil segments.
In some embodiments, a radius of the rotor plane is less than or equal to a distance from the central axis to an outer surface of the ringed airfoil segment for each ringed airfoil segment.
An embodiment includes a fluid turbine system with a rotor configured to rotate about a central axis defining a rotor plane and one or more ringed airfoil segments disposed around a central axis. The ringed airfoil segments are configured to create a maximum in the unit mass flow rate at a location downstream of the rotor plane. Each of the one or more ringed airfoil segments is configured to draw a flow that bypassed the rotor along a surface of the ringed airfoil segment facing toward the central axis.
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. 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 embodiments. Further, like reference numbers refer to like elements throughout.
The present disclosure relates to a fluid turbine including a rotor in combination with at least one substantially annular duct, or a portion of a substantially annular duct, with an airfoil cross section, (hereinafter, a “ringed airfoil”). The ringed airfoil, or portion of a ringed airfoil, is configured such that the leading edge of the ringed airfoil is co-planar with, or downstream of, the rotor plane as measured with respect to the central rotational axis. In some embodiments, load forces on the ringed airfoil or portion of a ringed airfoil are reduced when the turbine is configured with the rotor coplanar with, or upstream of, the inlet of the ringed airfoil.
In some embodiments, the ringed airfoil includes mixing elements to provide rapid mixing of wake vortices. In one embodiment, these mixing elements serve to assist combining a higher energy bypass flow that did not pass through the rotor plane with a lower energy primary fluid flow. In some embodiments, an ejector provides performance enhancements such as introducing additional high energy fluid flow and a low-pressure region, into the trailing edge vortices in the wake of a ringed airfoil, down-stream of the rotor. Various combinations of the ringed airfoil, or partial ringed airfoil, the mixing elements, and the ejector may provide increased power extraction and efficiency as compared with open rotor turbines without a ringed airfoil.
Some embodiments of fluid turbines including at least a portion of a ringed airfoil as described herein provide several advantages over a conventional open rotor unshrouded wind turbine. First, embodiments provide increased power extraction at the rotor from increased mass flow rate through the rotor plane and increased energy exchange in the turbine wake. In some embodiments, the ringed airfoil or partial ringed airfoil is configured to draw in a higher energy bypass fluid flow that does not pass through the rotor plane to mix with a lower energy primary fluid flow from which energy has been extracted by the rotor. The higher energy secondary flow energizes the primary flow resulting in an increased cumulative mass flow rate through the rotor plane, and increased power extraction. Additionally, by mixing the primary and secondary flows with the ringed airfoil or partial ringed airfoil the turbine wake is more efficiently mixed out allowing increased power extraction by those fluid turbines located downstream of the front fluid turbine (e.g., in a wind turbine farm environment with an array of wind turbines). Finally, mixing out the wake in accordance with the present invention aids in reducing the noise heard by an observer.
Some embodiments have multiple advantages over conventional shrouded fluid turbines. For example, in some embodiments, load forces on the ringed airfoil or portion of a ringed airfoil are reduced when the fluid turbine is configured with the rotor coplanar with, or upstream of, the inlet of the ringed airfoil as compared with conventional shrouded fluid turbines in which the rotor is positioned in the shroud. In many conventional shrouded fluid turbines, most of the weight of the rotor, the shroud, and the nacelle is positioned downstream of a central axis of a fluid turbine support tower resulting in a significant bending moment acting on the tower and the foundation supporting the tower due to the unbalanced weight. By locating the rotor and parts of the nacelle in upstream of the tower central axis, some of the weight of the ringed airfoil behind the tower central axis is at least partially offset by the weight of the rotor and the portion of the nacelle upstream of the tower central axis, thereby reducing the bending moment acting on the tower and the foundation.
Some embodiments also have benefits in manufacturing, assembly and design as compared with conventional shrouded turbines in which the rotor is located within the shroud. In some embodiments, because the rotor is not rotating within the ringed airfoil, the concentricity of the ringed airfoil is less critical than for conventional shrouded fluid turbines. A relatively small distance separates the rotor blade tips from the shroud surface in a conventional shrouded turbine, which means that that shroud cannot significantly change shape during use without risk of damage from blade tips hitting the shroud surface. In some embodiments, the ringed airfoil may be more free to deform (e.g., oval in shape) during maximum power extraction without increased risk of damage due to blade tip-ringed airfoil contact, which means freedom to use different designs, different materials and/or less structural material in manufacturing the ringed airfoil than would be required for a conventional shroud. Some embodiments may also provide benefits during assembly and erection (e.g., more rapid assembly) due to not having to position the rotor within the shroud and not having to finely adjust blade tip-shroud gaps. Finally, maintenance, such as blade replacement, is more easily accomplished when the rotor need not be carefully withdrawn from within the shroud before lowering the blades/generator to the ground.
Fluid turbines in accordance with the present disclosure may be used to extract energy from a variety of suitable fluids such as air (i.e., wind) or water. The aerodynamic principles of a wind turbine of the present invention also apply to hydrodynamic principles of a comparable water turbine and may be employed in conjunction with numerous fluid turbines that are at least in part shrouded.
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.
The term “about” when used with a quantity includes the stated value and also has the meaning dictated by the context. For example, it includes at least the degree of error associated with the measurement of the particular quantity. When used in the context of a range, the term “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the range “from about 2 to about 4” also discloses the range “from 2 to 4.”
A turbine of the present disclosure provides an improved means of extracting power from a fluid stream. A substantially ringed airfoil is in fluid communication with a rotor having at least one mixing element combines bypass flow with flow that has passed through the rotor. A rotor is configured to extract more power in the region of the rotor plane that is in fluid communication with the mixing elements. This enhances the power extraction from the system by energizing the rotor wake where the most power is extracted.
Mixing elements include but are not limited to mixing lobes, mixing slots, vortex generators or ringed airfoil aerodynamic modifications that promote mixing and may be disposed at a variety of regions such as, but not limited to, the trailing edge of the ringed airfoil.
The term “rotor” is used herein to refer to any assembly in which one or more blades or blade segments are attached to a shaft and able to rotate, allowing for the generation or extraction of power or energy from fluid flow rotating the blade(s) or blade segments. Exemplary rotors may include any of 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 that may be associated with the ringed airfoil of the present disclosure. 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.
In one embodiment, the present disclosure relates to a fluid turbine comprising a rotor in combination with at least one substantially ringed airfoil (or a portion of a substantially ringed airfoil) in fluid communication with the circumference of the rotor plane, configured such that the leading edge of the ringed airfoil is coplanar with, or downstream of, the rotor plane. In some embodiments, of the ringed airfoil (or portion of the ringed airfoil) includes associated mixing elements that surround the exit of the ringed airfoil (or portion of the ringed airfoil). Other embodiments comprise associated mixing elements in fluid communication with a second ringed airfoil known as an ejector. In some embodiments, the mixing elements have the greatest effect on the perimeter of the exit region of the ringed airfoil.
A ringed airfoil 110 is in fluid communication with the rotor plane 115 and is co-axial with the central axis 105. The ringed airfoil 110 includes a leading edge 112, which may also be identified as an inlet end or a front end, and a trailing edge 116, which may also be identified as a rear end, an exit or trailing edge. In some embodiments, support structures 106 are used to connect the nacelle 150 and the ringed airfoil 110. In some embodiments, each support structure 106 includes a proximal end engaged with the nacelle 150 and a distal end engaged with the ringed airfoil 110. The nacelle 150 and ringed airfoil 110 are supported by a tower structure 102.
As shown in the side cross-sectional schematic view of
In some embodiments, the rotor has a diameter less than or equal to that of the ringed airfoil. For example, in
Generally speaking, a conventional open rotor unducted fluid turbine in a fluid stream is an impediment to the flow of the fluid stream. When the fluid stream encounters the open rotor, a portion of the stream enters the rotor plane and a portion of the stream is diverted around the impediment (e.g., beyond the tips of the rotor blades). For comparison, the fluid flow around a conventional open rotor unshrouded fluid turbine, (i.e., the flow that would occur if ringed airfoil 110 was not present) is schematically depicted by dotted line arrow(s) 230 in
As depicted in
A primary fluid stream 31 is drawn through the rotor plane 15 by the low pressure associated with the increased velocities 35 in the ringed airfoil 10. Specifically, the lower pressure created within the ringed airfoil 10 draws flows from a larger cross-sectional area upstream, which is referred to as contraction. The rotor 40 extracts energy from the primary fluid stream 31 as is passes through the rotor 40 resulting in a lowered energy primary fluid stream 31 downstream of the rotor 40. The lower pressure created within the ringed airfoil 10 also draws in a secondary fluid stream 39 that bypasses the rotor 40 and the rotor plane 15. Because no energy is extracted from the secondary fluid stream 39 by the rotor 40, the secondary fluid stream 39 generally has a higher energy than the primary fluid stream 31 downstream of the rotor 40.
The configuration of the ringed airfoil 10 and the rotor 40 in the simulation shown in
For comparison,
The energy differential between the higher energy secondary stream including propagating tip vortices 160 and the lower energy flow 163 is represented by the length of difference arrow 165. Another turbine located downstream from fluid turbine 100 would experience a fluid flow field having a portion with reduced energy content 163 and a portion with relatively higher energy content and propagating tip vortices 160. However, due the injection of energy by the secondary fluid stream 132 and due to mixing of the two fluid streams 132, 131 through the aerodynamic effect of the ringed airfoil 110, the resulting downstream energy differential as represented by 165, is smaller than the energy differential downstream of a similar open rotor fluid turbine without a ringed airfoil (see
As shown in
The ringed airfoil 110 of
The ringed airfoil 510 includes a leading edge 512 and a trailing portion 516. The ringed airfoil 510 has the cross-sectional shape of an airfoil with a suction side (i.e., low pressure side, high velocity side) facing the central axis 105 and a pressure side (i.e., high pressure side, low velocity side) facing away from the central axis 105. The trailing portion 516 of the ringed airfoil 110 has mixing elements including outwardly turning mixing elements 515 that direct flow away from the central axis 105 and inwardly turning mixing elements 517 that direct flow toward the central axis 105. In some embodiments, the trailing portion 516 of the ringed airfoil 510 is shaped to form two different sets of mixing elements. The increased mixing due to the mixing elements 515, 517 may provide an increase in the unit mass flow rate within the ringed airfoil 510.
For comparison, the flow of a fluid stream around the open rotor in the absence of the ringed airfoil is depicted by dotted line arrow 530 in
A mixer-ejector pump is formed by the ejector shroud 620 in fluid communication with the ring of inwardly turning mixing elements 617 and outwardly turning mixing elements 615 on the turbine shroud 610. The mixing elements 615, 617 extend downstream toward or into an inlet 622 of the ejector shroud 620.
For comparison, the fluid stream flow over a conventional open rotor unshrouded fluid turbine is schematically depicted by dotted line arrow 630. The flow around the rotor 140 and through the ringed airfoil 610 is depicted by the solid line arrow 632 showing flow along a surface of an outwardly turning mixing element 615 and by the solid line arrow 634 showing flow along a surface of an inwardly turning mixing elements 617. The interaction of flows 632 and 634 creates mixing vortices including clockwise vortices 636 and counter-clockwise vortices 638. Additional high energy bypass flow is introduced to the turbine wake through the ejector 620, as shown depicted by arrow 639.
In some embodiments, the rotor plane of the fluid turbine is coplanar with the leading edge of the ringed airfoil. For example,
One of ordinary skill in the art in view of the present disclosure would recognize that features in various embodiments may be combined or modified in various ways. For example, in some embodiments some or all of the ringed airfoil segments may include mixing elements. In some embodiments, the ringed airfoil may include multiple ringed airfoil segments with gaps between the segments. In some embodiments, the mixing elements take the form of mixing slots.
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.
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/648,362, entitled “FLUID TURBINE WITH A ROTOR UPWIND OF A RINGED AIRFOIL” and filed on May 17, 2012, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61648362 | May 2012 | US |
