Patent Application
20120051914
1. Field of the Invention
The invention relates to a rotor system for a fluid-flow turbine comprising a hub mounted on a shaft, and a plurality of rotor blades.
2. Prior Art
In a typical horizontal-axis wind turbine, a nacelle is mounted on a tall vertical tower. The nacelle houses power-transmitting mechanisms, electrical equipment and supports a rotor system at one end. Rotor systems for horizontal-axis wind turbines ordinarily include one or more blades attached to a rotor hub on a shaft. Wind flow drives the rotor, which turns the shaft in the nacelle. The shaft turns gears that transmit torque to electric generator(s). The nacelle typically pivots about the vertical tower to take advantage of wind flowing from any direction. The pivoting about this vertical-axis in response to changes in wind direction is known as yawing or yaw response and the vertical-axis is referred to as the yaw-axis. As wind moves past the blades with enough speed the rotor system rotates and the wind turbine converts the wind energy into electrical energy through the generators. Electrical outputs of the generator(s) are transmitted to a power grid.
As the generating capacity of a wind turbine increases, the rotor blades must increase in length to expose a larger swept area to the wind for the added energy capture needed to drive the greater generating capacity. There are structural limitations to the length to which typical blades may be extended.
Typically, the end of a rotor blade (the root) is bolted to the hub which attaches to the main shaft. As wind turbines are scaled up, a point is reached where length and weight of the blade reaches the extreme of what can be reliably supported by the blade root attached to the hub. A key structural limitation on very large blades is with fatigue life at the root of the blade where the gravity effect on each rotation produces lead-lag loading, concentrated on the blade root. Larger blade size also is limited by a blade root diameter which meets width limits for road transportation. Thus, there are definite scaling limitations to increasing the size of conventional rotors. The invention provides a method to significantly increase rotor blade size.
Wind turbines are designed to yaw in response to changes in wind direction during operation by setting rotor alignment to face or hunt the new wind direction. Excessive hunting motion results in undesirable yaw-induced vibration and stress on the rotor system. Blade and rotor hub fatigue and ultimate failure of the blade and rotor hub where the blade and rotor hub meet is directly related to the number of hunting motions and the speed at which they occur. Rapid changes in yaw dramatically increase the forces acting against the rotational inertia of the entire rotor system, magnifying the bending moments at the blade root where it meets and is attached to the rotor hub. Vibration and stress cause fatigue in the rotor hub and blade root thereby decreasing the useful life of the equipment and reducing dependability. The invention provides added structural support to enable very large rotors to reduce yawing loads on the hub.
Publication No. WO/2006/097836 published Sep. 21, 2006 “Tension Wheel In A Rotor System For Wind And Water Turbines” describes a rotor system for a fluid-flow turbine comprising a hub mounted on a shaft, a plurality of rotor blades, and a tension wheel, the tension wheel comprising a rim structure mounted to the hub by a plurality of spokes. Each rotor blade is attached to the rim structure of the tension wheel. The lost energy in the area of the rotor circumscribed by the tension wheel rim structure is captured by applying airfoils, such as blades or sails, to the spokes of the tension wheel and/or an inner section of the rotor blades.
As wind turbine rotor size increases in the multi-megawatt size range, blade length imposes structural requirements on the blade root end, which adds weight, which in turn imposes even greater structural requirements, which in the end limits blade up-scaling possibilities.
It is therefore an object of the present invention to limit blade length to materials and designs, which provide sound structural margins but increase rotor diameter, to provide a greater rotor swept area resulting in greater wind energy capture.
It is also an object of the present invention to provide a rotor hub geometry that has a sound structure while increasing the rotor swept area.
The objects are solved by a rotor system for a fluid-flow turbine, comprising a hub assembly which is mounted on a shaft coupled with a power-transmitting device, a plurality of rotor blades, each of which comprises an inner blade section, a collar and an outer blade section. The inner blade section is rotatably supported by and extends outward from the hub assembly to its respective collar, wherein the outer blade section extends outward from a respective one of the collars. The inner blade section and the outer blade section are rotatable.
Further embodiments of the invention are described in the dependent claims.
Briefly, the invention is concerned with a rotor system for a fluid-flow turbine in which a number of rotor blades are attached to a hub and constrained in two dimensions by tension cables connected between collars on the rotor blades and the hub. The rotor blades are constrained in the plane of rotation (laterally) by blade-to-blade tension stays or cables connecting the blades or collars on the rotor blades together.
In accordance with an aspect of this invention, the rotor system includes a hub assembly mounted on a shaft, and a plurality of rotor blades mounted to and extending outward from the hub assembly. The hub assembly comprises a hub and a collar for each rotor blade or the blades can be mounted directly to the hub. Each rotor blade has an inner section extending outward from the hub to its respective collar or stay attachment and an outer section extending outward from this collar or stay attachment. Each rotor blade is attached to a collar in such a way that the rotor blade can be rotated for pitch control or the inner section and the outer section can be rotated independently for individual pitch control. The collars are connected to the hub by a plurality of tension stays that constrain the rotor blades in at least one dimension such that the inner blade section of each rotor blade is in compression.
The advantage of this structure is that the blade pitch motors can be located at the hub assembly (main hub), reducing strain on the rotor. The motor at the main hub can turn the inner and outer blade sections to capture wind across the entire structure.
In accordance with an aspect of the invention, blade-to-blade tension stays connect the collars or blades one to another to constrain the blades laterally.
The invention has the advantage that cable stays allow for many narrow, high aspect ratio blades to be used on a fluid-flow turbine rotor. This results in greater performance and smaller, less costly and easy to transport blades.
The invention has the advantage that fore and/or aft stays provide resistance to the rotor's thrust forces and can assist in transmitting the rotor torque to the hub, the blade-to-blade stays resist the “lead-lag” loads.
The invention has the advantage that it provides a structural means to support blades efficiently on very large rotors which would otherwise exceed the structural capacity of typical rotors where blades are simply attached to the hub with no other means of structural support.
The invention has the advantage of reduced cost and increased efficiency of large-scale wind and water turbines.
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The rotor system further includes outer blade sections 50, 52, 54, 56, 58. Each outer blade section 50, 52, 54, 56, 58 may be attached to a collar 9, 11, 13, 15, 17, respectively or may be integral with the inner blade sections 8, 10, 12, 14, 16, i.e. one blade. Alternatively, the outer blade sections 50, 52, 54, 56, 58 may telescope into the inner blade sections 8, 10, 12, 14, 16 to provide variable length blades.
According to the present invention, each of the outer blade sections 50, 52, 54, 56, 58 is rotatable dependently in relation to a respective one of the inner blade sections 8, 10, 12, 14, 16. Alternatively, each of the outer blade sections 50, 52, 54, 56, 58 is rotatable independently in relation to a respective one of the inner blade sections 8, 10, 12, 14, 16. Accordingly, pitch motors located at the hub assembly may pitch dependently or independently the inner blade sections 8, 10, 12, 14, 16 and outer blade sections 50, 52, 54, 56, 58.
The collars 9, 11, 13, 15, 17 may be either compression rings or wheels. If the collars 9, 11, 13, 15, 17 are compression rings, the inner blade sections 8, 10, 12, 14, 16 may have a fixed compression beam with a pitchable aerodynamic shell that pitches with the outer blade section 50, 52, 54, 56, 58. If the collars 9, 11, 13, 15, 17 are wheels, the inner blade sections 8, 10, 12, 14, 16 are free to rotate within a collar 9, 11, 13, 15, 17 and the pitch motors are located at the hub and pitch the inner and outer blade sections as one.
Each of the blades may have a blade extension section that is variable in length to provide a variable diameter rotor and may be geared to change pitch.
The nacelle 1 houses power-transmitting mechanisms, electrical equipment and a shaft that supports the rotor. The rotor system shown in
The rotor diameter may be controlled to fully extend the rotor at low flow velocity and to retract the rotor as flow velocity increases such that the loads delivered by or exerted upon the rotor do not exceed set limits. The turbine is held by the tower structure in the path of the wind current such that the turbine is held in place horizontally in alignment with the wind current. The electric generator(s) is driven by the turbine to produce electricity and is connected to power carrying cables inter-connecting to other units and/or to a power grid.
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The thrust bearing 65 prevents the tension of the stays from forcing the collar 9 down.
The collar 9 also functions as an anchoring plate with four holes 64, 66, 68,70, through which the individual cables or stays 24, 33, 40, 48 are passed. Each hole has initially a cylindrical and subsequently a conical area in which the stays or cables are anchored by means of a ring wedge (not shown). Two or three of the stays or cables 24, 33 are fore and aft stays, respectively. The remaining two stays or cables 40, 48 are lateral stays that connect to the respective collars on the adjacent blades.
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The fore flange 20 functions as an anchoring plate with five holes 76, through which the five individual fore stays 24, 26, 28, 30, 32 are passed. The aft flange 21 functions as an anchoring plate with five or ten holes 74, through which the individual aft stays 25, 27, 29, 31, 33 are passed. Each hole 74, 76 can have initially a cylindrical and subsequently a conical area in which the stays or cables are anchored by means of a ring wedge (not shown).
The stays used in the apparatus of the present invention may comprise a bundle of individual wires, solid or airfoil shaped rod or other tension carrying devices. The stays, which are to be tensioned, are pre-stressed by use of a conventional tensioning press. For individual wires, this tensioning press works in conjunction with a wedge push-in apparatus. The tensioned (pre-stressed) wires are anchored conventionally by means of wedges in the anchoring plate of the collar 9 and the fore and aft anchoring flanges 20 and 21. The cable-retaining wedges must be pushed in the holes 74, 76 before or during reduction of the tensioning force on the cable wires, to maintain tension. This is accomplished by a wedge push-in plate, which is displaced by a hydraulic press.
The hub assembly may be assembled at ground level, the cables tensioned and the hub assembly raised by a crane for attachment to the turbine shaft. Alternatively, the hub assembly may be assembled piece-by piece at the turbine: the hub attached to the turbine shaft, the inner blades attached to the hub, the collars and cables installed and the cables the cables tensioned.
In assembling the components of the invention it may be necessary to employ falsework, i.e. a temporary structure to hold the components in place until the rotor assembly and cable tensioning is sufficient to support itself.
The invention has been shown and described with reference to a wind turbine mounted atop a land-based tower, those skilled in the art will realize that the invention is also applicable to underwater turbines wherein the turbine is tethered underwater and the blades are turned by the force of water current.
While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the scope of the invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2009/007189 | 10/11/2009 | WO | 00 | 11/18/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61197247 | Oct 2008 | US |
