Patent Application
20160252074
The present invention relates generally to vane assemblies for fluid dynamic machines such as turbomachinery and particularly, but not exclusively, to wind and water-based turbines. The invention also relates to propulsion devices, such as for wind-driven apparatus like floating watercraft.
Much attention has been given to turbines for extracting useful energy from fluid flows, such as wind and tidal flows, and turbines for these application share many common features. A typical modern horizontal axis wind turbine (HAWT) has two or three slender blades oriented into the wind, which flows axially through the turbine. HAWTs characteristically rotate at velocities with tip speeds several times the wind speed, effectively presenting a disc to the wind. The blades are aerofoils with a high lift-to-drag ratio, and are driven through the air by aerodynamic lift. The aerofoil sections are specially designed to delay the onset of stall to further improve efficiency.
Turbines of another class use the aerodynamic drag forces pushing on flat or cupped vanes to turn a rotor and, advantageously, by orienting the axis of the rotor upright the flow is transverse, and a vertical axis wind turbine (VAWT) has no need of a device to orient the rotor to the wind direction. The theoretical maximum amount of useful energy that can be extracted from a given air flow is lower for drag based machines relative to lift based machines, but their advantages make them particularly suited to some niche applications. Their ability to operate in a wider range of wind speeds, constantly shifting wind direction and more turbulent wind conditions compared to horizontal axis rotors makes them well suited for use in urban environments, where VAWTs can be better integrated in building designs. Their relatively lower rotational speed can improve safety and reduce noise and vibration. Importantly, a VAWT may be well suited to coping with up-flows, such as commonly occur at the edge of buildings.
Inventors have come up with a number of ways for improving the efficiency of rotors that rely primarily upon drag. An example is the Savonius S-shaped cross-section rotor in which recirculating air flow between the two halves of the rotor provides a significant improvement. Another approach has been to use self-orienting vanes that orient themselves relative to the wind, without a separate control means, in a manner that improves performance. For example, U.S. Pat. No. 5,525,037 describes a VAWT where the vanes are mounted to the rotor by radially aligned hinges. The vanes are perpendicular to the airflow when moving downwind for maximum drag, and then the airflow causes them to rotate about the hinges through 90° to a low drag, flat shape when moving upwind. However, stops are required to limit the rotation of the vanes at their two ends, and the vanes oscillate back and forward between the stops, highly stressing the vanes and creating noise.
One of the major expenses for wind turbines in general is the ongoing maintenance costs, which occur after the turbine has been constructed and put into operation. Mundane causes include weathering and wear during normal operation. Wear can significantly increase for operating conditions outside the design envelope of the turbine. HAWTs require specific orientation of the turbine into the wind not only for optimization issues, but to minimize unsteady forces that are produced as the machine is yawed with respect to the wind. In some instances, active dynamic pitch control methods are used. However, the increasingly complex designs and subsequent maintenance costs can become high. This is another reason why passive dynamic pitch control systems are advantageous.
The power characteristics of the VAWT, providing features such as the ability to regulate the output or match the turbine output to a load, have also been addressed in a number of different ways in the past. WO2011044130 describes a self-regulating rotor like the Savonius S-shaped cross-section rotors, where the cups can pivot between open and closed positions for regulating power output. However, it is disadvantageous to have such a complicated and costly mechanism for vane control.
Furthermore, there is an ongoing need for improvements in efficiency, power characteristics and construction cost-effectiveness for fluid dynamic machines. Reference herein to “fluid dynamic machines” broadly refers to machines in which a working member such as a vane pushes on, or is pushed on, by a fluid. This term includes turbomachines, such as fans, blowers, compressors and pumps, as well as propulsion devices such as wind-driven propulsion devices for ships. It is an object of the present invention to address the above needs, to overcome or substantially ameliorate the above disadvantages or, more generally, to provide an improved turbomachine and propulsion device.
According to one aspect of the present invention, there is provided a vane assembly for a transverse flow turbine, or other fluid dynamic machine, the vane assembly comprising: a rotor having an axis of rotation; at least one vane with at least one concavo-convex part having a concave face and an opposing convex face; a pivot connecting the vane to the rotor, the pivot having a pivot axis inclined to the concave face such that, as the rotor turns, the vane is free to rotate about the pivot axis between a first position in which the vane defines a high-drag configuration for retreating with a transverse fluid flow, and a second position in which the vane defines a reduced-drag configuration for advancing against the transverse fluid flow.
Preferably, the concavo-convex part is developable, the pivot axis is inclined at a first angle to a straight line on the concave face; the pivot axis and the straight line lie in a pivot axis plane that makes a dihedral angle of 15° or less, with an axial-tangential plane of the rotor that rotates with the vane about the axis of rotation, and both the first angle and a second angle between the pivot axis and the axis of rotation are between 30° and 60°.
Preferably, the dihedral angle is substantially 0°; both the first angle and the second angle are substantially 45°; the straight line is substantially parallel and perpendicular to the axis of rotation in the first and second positions respectively; and the vane is free to rotate substantially 180° about the pivot axis between the first and second positions.
Preferably, the vane is free to rotate 360° about the pivot axis, and no stops are provided to limit vane rotation.
Preferably, the axis of rotation is substantially upright, a leading end of the pivot axis is above a trailing end of the pivot axis; and in the first position the vane hangs below the pivot axis.
A pivot generally may comprise a round part received to turn in a complementary locating part, and may be, for instance, of the hinge type. Preferably, the pivot comprises at least one bearing for supporting the vane to rotate with low friction and many different well-known types of bearing could of course be used for this purpose. For instance the pivot may comprise a plain bearing, rolling element bearing or magnetic bearing, et cetera, with the bearing receiving a pivot shaft that is generally coaxial with the pivot axis, allowing the vane to rotate freely.
Optionally, the rotor comprises a hub defining the axis of rotation; and the pivot is offset from the hub.
Preferably, the concavo-convex part comprises at least one right half-cylinder having a cylindrical portion axis disposed in the pivot axis plane; wherein the vane has a substantially reflective symmetry about the pivot axis plane.
Preferably, the pivot axis intersects or passes proximate an axial end of the concavo-convex part.
Preferably, the vane further comprises at least one substantially flat fin portion aligned generally parallel with the pivot axis plane; the at least one fin portion projecting from the concave and/or the convex face of the concavo-convex part of the vane.
Preferably, the at least one fin portion projecting from the convex surface of an outermost one of the cylindrical portions is pointed.
Preferably, the at least one fin portion forms a spine of the vane that extends parallel to the pivot axis.
Preferably, the vane further comprises a counterweight eccentric to the pivot axis to counterbalance the mass of the vane. For instance, the counterweight may have a centre of mass generally disposed in the pivot axis plane on an opposite side of the pivot axis to a centre of mass of the vane.
Preferably, the pivot axis is inclined to the axis of rotation such that, with the axis of rotation upright, the concavo-convex part is downwardly concave in the second position.
The vane may comprise a plurality of concavo-convex parts, wherein each of the concavo-convex parts are of like form and are arrayed symmetrically about the pivot axis plane in one or more parallel linear rows, wherein the straight lines on each concave face of each concavo-convex part are substantially parallel to each other.
Preferably, the spacing along the pivot axis between adjacent concavo-convex parts is regular, most preferably substantially equal.
The rotor may comprise two rotor rings of like diameter, coaxial with the axis of rotation and fixed to one another at axially spaced positions, and wherein the pivot comprises a pivot shaft that extends between the rotor rings.
According to another aspect of the present invention, there is provided a propulsion device for a fluid-driven apparatus, the propulsion device comprising: at least one vane with at least one concavo-convex part having a concave face and an opposing convex face;
a pivot having a pivot axis inclined to the concave face such that, the vane is free to rotate about the pivot axis;
a mount on the fluid-driven apparatus to which the vane is attached by the pivot such that the pivot axis is inclined at an acute angle to an upright, and the vane is free to rotate about the pivot axis between a first position, in which a straight line on the concave face is substantially upright, and a second position, in which the straight line is substantially horizontal.
Preferably, the concavo-convex part is developable, the pivot axis is fixed relative to the fluid-driven apparatus, a first angle exists between the pivot axis and a straight line on the concave face; the pivot axis and the straight line lie in a pivot axis plane that makes a dihedral angle of 15° or less, with an upright plane, and both the first angle and a second angle between the pivot axis and the upright are between 30° and 60°.
Preferably, the dihedral angle is substantially 0°; both the first angle and the second angle are substantially 45°; and the vane is free to rotate substantially 360° about the pivot axis.
Preferably, the fluid-driven apparatus comprises a wind-driven apparatus, such as a floating watercraft or a wheeled vehicle, and the pivot axis plane is aligned longitudinally, and the pivot axis rises toward the forward end.
Preferably, the pivot axis is inclined to the upright such that the concavo-convex part is downwardly concave in the second position.
According to yet another aspect of the present invention there is provided vane assembly or propulsion device substantially as hereinbefore described with reference to the accompanying drawings.
The present invention provides a vane assembly for a fluid dynamic machine, particularly a turbine for wind or water applications which is effective and efficient in operational use, which may be economically constructed and has an overall simple design which minimizes manufacturing costs and maximizes performance. Pivoting the vane in the manner of the invention varies the effective area of the vane projected into an axial-radial plane, between a maximum when the cylindrical portion axis is substantially parallel to the axis of rotation and a minimum when the cylindrical portion axis is substantially perpendicular to the axis of rotation, and has been found to provide advantageous self-regulating properties, as well as other improvements.
Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein:
Referring to
Features of the vane assembly of the invention are described with reference to the axis of rotation 11, and unless the context implicitly or explicitly requires reference to a different axis, then as used herein, the term “axial” refers to a direction substantially parallel to the axis of rotation 11. Likewise, the term “radial” refers to a direction substantially orthogonal to the axis of rotation 11. The term “circumferential” refers to the direction of a circular arc having a radius substantially orthogonal to the axis of rotation 11. The term “tangential” refers to the direction tangential to a circular arc having a radius substantially orthogonal to the axis of rotation 11. As is conventional, the angle between two given lines is referred to as the angle between two intersecting lines which are parallel respectively to the two given lines, and the angle between two intersecting lines as the smallest angle between them. Consistent with these terms, and with reference only to the axis of rotation 11, the rotor 10 may define two mutually orthogonal rotating reference planes shown in
As presented in
As shown in
The pivot axis 19 is inclined at a first angle α1 of 45° to the straight line 160 and at a second acute angle α2 of 45° to the axis of rotation 11. The vane 15 is rotated by an angle □=180° about the pivot axis 19 between the first and second positions, while it is simultaneously turned 180° about the axis of rotation 11. The pivot axis 19 may be inclined relative to the axis of rotation 11 such that with the axis of rotation 11 upright, the vane 15′ is downwardly concave in the second position i.e. the concave surface 26 faces downward. A leading end 162 of the pivot axis 19 is above a trailing end 164 of the pivot axis 19, and in the first position the vane 15 hangs below the pivot axis 19. The pivot axis 19 may intersect proximate an axial end of each vane 15 which is uppermost when the vane 15 is at rest. The geometry illustrated in the drawings thus comprises two important fixed angles, the first angle α1 between the straight line 160 and the pivot axis 19, and the second angle α2 between the pivot axis 19 and the axis of rotation 11, which are both preferably 45°.
The first and second positions shown in
In addition to the concavo-convex part 22, 24, 25, at least one fin portion 28 (shown in
In operation, the vane 15 may be oriented in first and second positions when on diametrically opposite sides of the rotor 10 as described above, where the tangential directions are aligned parallel with the wind direction 75. The vane 15 rotates freely under the applied forces between these positions without the need for any mechanism acting on the vanes 15, thus achieving passive dynamic pitch control. Without wishing to be limited by theory, when in the first position and instantaneously heading directly downwind the drag force pressing on the vane 15 applies a torque that has no component tending to rotate the vane 15 about the pivot axis 19, while as it retreats toward its most downstream position the torque does tend to rotate the vane about the pivot axis 19. The further the vane 15 rotates about the pivot axis 19 the greater the extent to which air is able to flow from the high to the low pressure side of the vane 15, providing a self-regulating property, that assists, for instance, in avoiding the generation of excessive torque in high winds. As the vane 15 passes its most downstream position, the fins portions 28, 29 may assist in feathering or further turning the vane about the pivot axis 19 as it starts to advance into the wind, and becoming fully feathered in the second position, before it then reverses rotation about the pivot axis 19, as the vane rotates again to the position (15′) where it is instantaneously heading directly downwind. Like a mainsail on a sailing boat properly trimmed for the direction of travel, the vanes 15 are oriented for maximum drag when going directly downwind, and are fully feathered for minimum drag when going directly upwind, and at all intermediate positions drag and lift forces combine to produce torque on the rotor 10. In this manner the rotor 10 is able to extract energy from a transverse wind, or horizontal wind when the axis 11 is upright, but advantageously it may also extract energy from an axial flow, such as when integrated into a building it can take advantages of up-flows and down-flows.
To mathematically model the rotation of the vane 15 a cylindrical and Cartesian coordinate system may be defined. The z-axis points up vertically and corresponds with the axis of rotation 11. A plane is defined by the x and y coordinates in such a way as to be consistent with a right hand coordinate system. A cylindrical coordinate system is convenient to best describe the local flow to the vane 15. The radial direction, r, is positive outward and the circumferential direction, θ, is positive to maintain a right-handed coordinate system.
The turbine rotates with a rotational velocity, n (Hz), and angular frequency, ω(rad/sec). For a coordinate system that moves with the leading edge center of a single vane, the resultant velocity due to the rotational motion of the turbine may be described as:
V
r=0,Vθ=−2πnRNT=−ωRNT (1)
where the subscripts r refers to the radial direction and θ refers to the circumferential direction. The θ velocity component is in a direction opposite the rotation as this is the velocity relative to the vane.
The total velocity at the vane leading edge center can then be described as:
V
r
=V
x cos(θ)+Vy sin(θ),Vθ=−ωRNT−Vx sin(θ)+Vy cos(θ) (2)
The circumferential velocity variation is plotted in
The radial velocity variation is plotted in
The circumferential and radial velocity components can be defined by a velocity magnitude (Vmag) acting on the vane surface at an effective flow angle (β). In this geometry, the effective flow angle due to wind and rotational velocities is defined as:
V
mag=√{square root over (Vr2+Vθ2)},β=atan(Vr/(Vθ) (3)
The velocity components of the wind may be characterized by x and y components. For a reference frame located at the leading edge center of a given vane 15, the corresponding velocity components are:
V
r
=V
x cos(θ)+Vy sin(θ),Vθ=−Vx sin(θ)+Vy cos(θ) (4)
wherein subscripts x and y refer to the wind velocity components and θ refers to the circumferential angular position.
The proposed machine in the present embodiment contains an additional degree of freedom. As stated, the vane assembly rotates about the central axis 11, and the individual vanes can rotate about a pivot axis 19. By design, this allows the vane to adjust to the varying wind direction as it rotates through the cycle. The angle which the vane rotates about axis 19 can be seen in
V
θlocal
=V
θ
−ωR
vane(sin(φ+γ)−sin(γ)),φmax≦φ≦φmax (5)
Note that both γ and φ follow the right hand rule and are positive counter-clockwise.
Due to the non-zero pivot angle, α2, and the angle of the vane relative to the pivot axis, α1, a vane tilt angle may be defined as η, and is dependent on the rotation of vane by the angle γ:
η=α2−α1 cos(γ) (6)
For cases where α2=α1, this expression can be simplified as:
η=α2(1−cos(γ)) (7)
The velocity field at any point on the front surface of the vane may now be described as:
V
n
=[V
θlocal cos(γ+φ)+Vr sin(γ+φ)] cos(η)
V
s
=−V
θlocal sin(γ+φ)+Vr cos(γ+φ)
V
t
=[V
θlocal cos(γ+φ)+Vr sin(γ+φ)] sin(η) (8)
Based on these flow velocities, local pitch, roll and yaw angles of the vane relative to the flow may be defined as follows:
pitch=atan(Vn/Vt),roll=atan(Vs/Vt),yaw=atan(Vt/Vs) (9)
The circumferential variation in γ is the same as the β angle and was plotted in
A second embodiment of the machine of the present invention is illustrated in
As per a third embodiment of the machine shown in
The vane 215 may comprise like half-cylinder parts 122 arrayed symmetrically about the pivot axis plane in a linear row parallel to, and equally spaced from one another along the pivot axis 19, optionally overlapping one another, such that the effective area of the vane 15 projected into an axial-radial plane 21 is rectangular, with a width W and height somewhat less than 3×H according to the amount of axial overlap. The fin portions of the vanes 215 project from the convex side 27 are connected to form a spine 44 of the vane 215 that is elongated parallel to the pivot axis 19, and serves the same function as the fin 28. A fin portion projecting from the convex surface of the outermost half-cylinder 122 may have tapered edges 45. A single counterweight 31 may be provided, having its centre of mass generally disposed in the bisecting plane 32 on an opposite side of the pivot axis 19 to a centre of mass of the half-cylinders 122. The counterweight 31 may be fixed to the pivot shaft 217 or the fin by a bar 233.
A brake (not shown) may be provided to lock the pivot, to prevent rotation of the vane 215 about the pivot axis 19.
The rotor is hubless, and comprises two rotor rings 46, 47. The pivot comprises a pivot shaft 217 coaxial with the pivot axis 19 and connected at opposing ends to the rotor rings 46, 47, and permits free 360° rotation of the vane 215 about the pivot axis 19. The rotor rings 46, 47 are of like diameter, coaxial with axis of rotation 11 and fixed to one another at axially spaced positions. In the position illustrated in
In a fifth embodiment of the machine of the present invention as illustrated in
A vane 15, 115, 315 or, a vane 215 as shown in
Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13111823.5 | Oct 2013 | HK | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2014/089137 | 10/22/2014 | WO | 00 |
