VERTICAL AXIS WIND TURBINE

Abstract: A support structure for a vertical axis wind turbine in which the airfoil blades (1) are spaced radially from a spinning tower (3) by support arms (2) with the airfoil blades (1) being substantially straight and vertically oriented. The weight of the spinning tower (3) and the associated structure is supported by a load bearing (8) located on a fixed post (9) at approximately the mid point of the height of the airfoil blades (1). A lateral bearing arrangement (25) is associated with the lower end of the spinning tower (3) and locates the spinning tower (3) laterally in relation to the fixed post (9).

Description: VERTICAL AXIS WIND TURBINE This invention relates to a large scale wind turbine capable of providing power for a number of purposes including the generation of electricity. TECHNICAL FIELD Wind turbines can generally be classed into two categories, that is a vertical axis turbine or a horizontal axis turbine. Vertical axis turbines have particular advantages over horizontal axis turbines. Firstly a vertical axis turbine can accept the wind from any direction without requiring to be reoriented to that direction as is required by horizontal axis turbines. This means that complicated arrangements to maintain adequate orientation of the turbine into the wind are not required. A further and major advantage with a vertical axis wind turbine is that the larger the size of the turbine, the easier it is to construct because the greater the radius of the blades from the axis of the turbine, the slower will be the rotation of the turbine for any given wind speed. Consequently for large scale vertical axis wind turbines, the problem of centrifugal force generated by the rotation of the turbine is of a minor importance. This contrasts with a horizontal axis turbine where a small model can be constructed in which the centrifugal force is high and which holds the blades in a high tension force, thereby tending to offset the likelihood of buckling of the blade. However with large scale horizontal axis turbines, the lesser centrifugal force can cause severe mechanical constraints such as those brought about by blade bending stresses which become greatly magnified as the horizontal axis turbines are scaled up in size. Large scale vertical axis wind turbines generally use airfoil blades which are equally spaced around a supporting tower with the main axis of the blades being vertically orientated. It is also known to construct a vertical axis turbine in which the chord of the blades is shaped to have a Troposkein curve which results in the centrifugal force on the blade being a tension force rather than a bending force. However, the disadvantage in utilizing such a curve is that a large section of the blade is at an obscure angle to the wind and therefore only partial wind energy can be captured. It is therefore apparent that a more efficient airfoil blade will result in a considerable increase in efficiency. In designing a large scale vertical axis wind turbine it is possible to take advantage of a favourably high aspect ratio, that is the ratio of the span of the wing to the chord. This favourable aspect ratio can be obtained only when the blades are of a substantial length in relation to the swept diameter of the blades and this requires the utilisation of guy wires and the like to stabilize the structure. Because of the mechanical forces resulting when the turbine is operating, it is therefore necessary to take particular care in the design of the means to stabilise the structure and this is usually effected by guy wires and the like which stabilise the structure both below and above the spinning blades. A disadvantage with known vertical axis wind turbines lies in the difficulty experienced in adequately supporting the wind turbine structure. While it is possible to construct a static support tower that does not require guy wires and the like, the greater the aspect ratio, the more difficult this becomes because of the increase in physical size of the blades and the loads imposed on the turbine and consequently high aspect ratios are generally not catered for in the known forms of vertical axis turbines. Problems arise when constructing a large scale vertical wind turbine with a high aspect ratio and in particular the problem of adequately suppoπing the turbine which must withstand considerable forces resulting from the spinning of the turbine and of buffeting by the wind. Generally for this purpose guy wires and sometimes rigid braces are attached at various points to the structure so as to adequately support the turbine both above and below the spinning blades. To perform a satisfactory tack it is necessary to utilize an unrealistically high central system to provide adequate clearance between the tops of the airfoil blades and the guy wires. Apart from the spatial requirements resulting from the use of guy wires and the like, a further disadvantage arises in that it is possible for the guy wires to interfere with the airflow. A yet further disadvantage when using guy wires is that if the central support structure turns with the blades, then tension exerted on the structure by the guy wires will add extra loading to the bearings. The applicant considers that for maximum efficiency and power, the airfoil blades of a vertical axis turbine should be substantially straight and the longitudinal axis should be substantially vertical. For a large scale power generation the minimum size turbine should have at least two and preferably three, vertical airfoil blades equidistantly spaced from a supporting tower with the blades having a length which preferably equates to at least one and a half times the radial distance the blade is supported from the tower structure. KNOWN PRIOR ART United States patent specification 4,204,805 discloses a vertical axis wind turbine which has a rotatable assembly attached to a central hub which is supported on bearings located at the top of a fixed tower. A torque shaft is attached at the axis of the hub and passes axially downwardly through the tower. Guys such as cables are attached near the top of the tower below the level of the rotating assembly to steady the tower. British Patent specification 2,008,202 discloses a rotor which is rotatable about a vertical axis on a shaft which projects upwardly from a tower which is also steadied by guy ropes. United States patent specification 4,082,279 describes a wind turbine of the Darrieus variety which has a rotor made up of two blades, the end of which are joined adjacent either end of a tower which is a lattice work structure supported in bearings at either end. The upper bearing includes means to join guy wires with the top of the structure being maintained in position by guy wires. The lower bearing is mounted on a support structure. United States patent specification 4,037,989 discloses a vertical axis wind turbine which has a stationary frame member above which is mounted a wind rotor with the stationary frame being made of legs which extend from a base member to form a pyramid like configuration. The top of the frame member has a bearing to locate the wind turbine while a rotatable shaft is journalled in the stationary frame member and extends below the frame member to a power transfer means which sits on a platform joined to the legs of the tower. The wind rotor is attached to the upper end of the rotary shaft. British patent specification GB 2,286,637 discloses a support tower which has rotor arms mounted for rotation about a pylon. The blades are supported on two spaced apart sets of rotor arms which form part of the turbine module. The lower set of rotor arms are journalled to the pylon. Australian Patent specification 91/79418 discloses a wind turbine in which each vertically orientated blade is attached by a radial support arm, the inner ends of which are attached to a vertical axis. United States patent specification 5,419,683 discloses a wind turbine which can be mounted on an existing tower. The turbine module comprises rotor arms which extend outw∑irdly from the module and which are attached at about the mid point of vertically aligned blades. The turbine module can comprise a framework around which the rotor arms may rotate. The rotor arms rotate around the tower by way of a rotor ring which also rotates. British patent specification GB 2,249,143 also discloses a vertical axis wind turbine which has pairs of arms connected to a rotor with the upper arm being inclined downwardly from its point of connection to the rotor and the lower arm being inclined upwardly from its point of connection to the rotor. In combination with the blade and rotor, the arms form a truss-like structure. A drive shaft extends upwardly from the tower and is journalled in bearings adjacent the top of the tower and part way down the tower. The bearings for the drive shaft and the support for the rotor are therefore situate below the rotor mechanism. British patent specification 2,202,592 discloses a vertical axis wind turbine comprising upper and lower wheels from which the blades extend. The upper and lower wheels are joined by linkage members. United States patent specification 4,764,090 discloses a wind turbine which utilises four air foil blades connected between upper and lower sets of support spokes which are in turn supported on a rotating vertical column. The vertical column is rotatably mounted on a support base so the whole assembly will turn about and be supported by the base which is positioned below the airfoil blades. British patent specification no. GB 2,175,350 discloses a vertical axis wind turbine which utilises braced air foil blades which are mounted in an essentially V configuration. A fixed support tower is provided with a vertically extending rotatable shaft from which the blades with their various braces extend. United States patent specification 4,383,801 also discloses a vertical axis wind turbine in which the turbine apparatus is rotatably supported on a central power shaft which extends upwardly from a fixed mount so that the bearing for the turbine mechanism is again below the actual mechanism. United States patent specification 4,355,956 also relates to a vertical axis wind turbine which has a rotating frame which carries a number of resilient blades which are secured at their leading edges to the rotating frame. The frame is fixed to the upper end of a vertical shaft which is carried by thrust bearings mounted in a frame. It will be apparent from the teachings in the prior art that known large scale vertical axis turbines with a satisfactory aspect ratio generally require guy wires attached to the structure above the spinning blades. OB.JECT OF THE INVENTION It is therefore an object of this invention to provide an improved support structure and to provide improvements to the construction of a large vertical axis wind turbine, which will overcome the above disadvantages or at least tend to reduce the disadvantages of known vertical axis wind turbines. DISCLOSURE OF THE INVENTION Accordingly, one form of the invention may be said to comprise a support structure for a vertical axis wind turbine, said support structure comprising a spinning tower supported for rotation about a fixed post in a substantially vertical position, said spinning tower including a plurality of arms extending substantially radially from the tower and being connected to spaced apart vertically arrayed airfoil blades and wherein the said spinning tower has a load bearing located at a point approximately midway of the height of the airfoil blades to support the weight of the spinning tower, the said arms and the airfoil blades on the fixed post, and further wherein the lower end of the said spinning tower includes a lateral bearing arrangement associated with said fixed post and which locates the said spinning tower laterally in relation to said fixed post. Preferably a drive shaft for connection to machinery to be driven by the turbine is attached to the spinning tower at the location of the said load bearing and extends down through the spinning tower and through the lateral bearing arrangement. Preferably the airfoil blades are equidistantly supported from the spinning tower and the height of the airfoil blades is at least one and a half times the radial distance between the spinning tower and the said blade. Preferably each airfoil blade is substantially planar. Preferably each blade is supported from the spinning tower by at least two support arms equidistantly spaced from each other. Preferably the lateral bearing arrangement comprises a series of bearing wheels journalled in a fixed spatial relationship to each other about said fixed post and wherein the perimeter of each said bearing wheel bears against a race associated with the spinning tower. BRIEF DESCRIPTION OF THE DRAWINGS Preferred forms of the invention will now be described with the aid of the accompanying drawings wherein: Figure 1 is a partly diagrammatic three dimensional view of a large scale vertical axis wind turbine according to the present invention; Figure 2 is a view of a detail; Figure 3 is a diagrammatic side elevation of the vertical axis turbine of Fig. 1; and Figure 4 is an enlarged sectional view of a portion of the turbine shown in Fig. 3. Figure 5 is a view of the turbine shown in Figure 1 but indicating alternative forms of bracing for the blades. BEST MODE OF CARRYING OUT THE INVENTION Referring to the drawings, the turbine includes three straight blades 1 which are held in a vertical orientation by being connected by support .arms 2 to a spinning tower 3. The length of the blades is preferably approximately equal to at least one and a half times the radius of the blades from the spinning tower but this can be varied as required. As indicated, the blades 1 are of an airfoil section as is known in the art. The spinning tower 3 which may be of a known lattice type construction or otherwise, is suitably constructed as is known in the art, and is supported on a pylon 4. While the pylon 4 is preferably triangulated as shown in the drawings it can also be of a lattice construction .and can have a variety of shapes to provide the necessary structural rigidity while presenting as small a profile as possible to provide a minimum of wind resistance. The spinning tower 3 is constructed with a multiple of beams 6 joined by triangulated braces 7 to form a rigid structure with the tower being supported in a substantially vertical position by a main load bearing 8 which is positioned approximately midway of the height of the spinning tower 3. The bearing 8 is journalled to the top of a fixed post 9 which is supported by the pylon 4 in a manner that it will extend vertically above the pylon 4. The fixed post can be a solid or hollow structure or can be of a lattice or semi- open structure as required. As shown more particularly in Fig. 4 the load bearing 8 comprises a boss 12 to which the support arms 2 and the spinning tower 3 is attached in a manner that the weight of the support arms 2. the spinning tower 3. and the blades 1. will be imposed on the boss 12 and transmitted to the thrust bearings 13 which are caged in a manner that the boss 12 can rotate on and be located by a bearing support member 15 which is fixed to the upper portion of the fixed post 9. A drive shaft 20 is suitably attached to the boss 12 such as by means of an extension 20a which is steadied by the bearings 13. The drive shaft can be connected to the boss 12 by any suitable means, one such means being for instance the nut 21 which is engaged on a screw threaded stub of the extension 20a. The drive shaft may extend through the base of the fixed post 9 for connection to the machinery to be driven. The drive shaft 20 may have suitable bearings within the fixed post 9 (not shown in the drawings) to maintain correct alignment of the drive shaft. The main load bearing 8 supports the weight of the spinning tower 3. the support arms 2 and the airfoil blades 1 , and is located at a point of approximate balance in terms of aerodynamic forces. The lower portion of the spinning tower 3 is located in a fixed spatial position but has free rotation. One preferred means of obtaining this is by utilising a plurality of bearing wheels 25 (see in particular Fig. 2) and in a highly preferred form, the bearing wheels are journalled by arms 26 to the frame of the spinning tower 3. The bearing wheels 25 are so located and positioned that the periphery of the bearing wheels will bear against a circumferential surface 28 which is in the form of an annular land on the base of the fixed post 9. Consequently, as the spinning tower 3 rotates, the bottom of the tower is maintained in a specific spatial relationship with the fixed post by reason of the bearing wheels 25 rolling around the periphery of the annular land 28 of the fixed post, thereby reducing any out of balance movement that may occur in the spinning tower. Preferably. the bearing wheels 25 are located at approximately 120° in relation to each other to take advantage of the maximum leverage at the base of the spinning tower which will minimize the loading on the three wheels. In a modification to the method of supporting the lower end of the spinning tower, the bearing wheels can be journalled to a framework which surrounds the fixed post 9 and the peripheries of the wheels can bear on the inside of a circular track located and supported on the spinning tower. In yet another modification, instead of utilizing bearing wheels, a large diameter ball or roller bearing with the bore of the inner race being engaged on the spinning tower and the periphery of the outer race located within a cage fixed to pylon 4. It will be apparent the function of the bearing system 25 is to absorb any sideways thrust that will be generated when the tower 3 is rotating. In the construction depicted in the drawings, the spinning tower is shown as being constructed of a number of sections of a lattice work. It is to be understood that as the length of the blades increases, it may be necessary to utilise additional support arms 2 and in that case the construction of the spinning tower can be varied by adding additional sections of lattice work to provide a tower of the desired height and rigidity. By reason of the present invention it is possible to build a support structure for a vertical axis turbine that does not require guy wires or other forms of support. Consequently the airfoil blades will not be subject to any shrouding effect as a result of the guy wires and other support members which were previously required to support the structure for the vertical axis turbine. The present invention also enables the construction of a vertical axis turbine which has straight or substantially straight vertical airfoil blades. Ideally the length of the blades and the distance they are supported from the spinning tower should be arranged to limit the centrifugal force to provide the optimum stress criteria. It has been found, for instance, that within reasonable limits, the further the radial distance at which the blades 2 are spaced from the spinning tower the less the centrifugal stress. A further advantage of the vertical axis turbine of the present invention is that sufficient support can be provided to minimise the bending stresses on the blades due to the centrifugal force at the tip speeds of the blades which can be up to eight times the wind speed. If necessary additional bracing such as the stays indicated at 30 and 31 in Figure 3 can be utilised to further support the blades. While it is preferred that the pylon and spinning tower be of a triangular shape as indicated in the drawings it will be understood that these items can be formed from a variety of shapes. For instance, the pylon can be an extension of the fixed post of either the same or different general construction. While the form of the pylon illustrated in the drawings is self supporting, it will be understood that other shapes of pylons might require the use of guy wires or other types of supports and stabilising means, but because of the general construction, all of these supports can be maintained below the level of the spinning blades and consequently will not interfere with or shroud the wind flow to the airfoil blades. Having described a preferred form of the invention it is to be understood that various modifications and changes can be made to the vertical axis turbine as will be apparent to those skilled in the art and all such modifications and amendments are intended to be included within the scope of the present invention.

Claims: CLAIMS 1. A support structure for a vertical axis wind turbine, said support structure comprising a spinning tower supported for rotation about a fixed post in a substantially vertical position, said spinning tower including a plurality of arms extending substantially radially from the tower and being connected to spaced apart vertically arrayed airfoil blades and wherein the said spinning tower has a load bearing located at a point approximately midway of the height of the airfoil blades to support the weight of the spinning tower, the said arms and the airfoil blades on the fixed post, and further wherein the lower end of the said spinning tower includes a lateral bearing arrangement associated with said fixed post and which locates the lower part of said spinning tower laterally in relation to said fixed post. 2. The support structure as claimed in claim 1, wherein a drive shaft for connection to machinery to be driven by the turbine is attached to the spinning tower at the location of the said load bearing and extends down through the spinning tower and through the lateral bearing arrangement. 3. The support structure as claimed in claim 1, wherein the airfoil blades are equidistantly supported from the spinning tower and wherein the height of the airfoil blades is at least one and a half times the radial distance between the spinning tower and the said blade. 4. The support structure as claimed in claim 1, wherein each airfoil blade is substantially planar. 5. The support structure as claimed in any one of the preceding claims, wherein each blade is supported from the spinning tower by at least two support arms equidistantly spaced from each other. 6. The support structure as claimed in claim 1 , wherein the lateral bearing arrangement comprises a series of bearing wheels journalled in a fixed spatial relationship to each other within a cage associated with the lower end of the spinning tower and wherein the perimeter of each said bearing wheel bears against a hub associated with the fixed post. 7. The support structure as claimed in claim 1 , wherein the lateral bearing arrangement comprises a series of bearing wheels journalled in a fixed spatial relationship to each other about said fixed post and wherein the perimeter of each said bearing wheel bears against an internal track associated with the spinning tower. 8. The support structure as claimed in claim 1 , wherein the lateral bearing arrangement comprises a ball or roller bearing race acting between a hub on the fixed tower and an annular housing associated with said spinning tower.

Inventors: WILLIAMSON OWEN GARTH, WILLIAMSON, OWEN, GARTH
Applicants: WILLIAMSON OWEN GARTH, WILLIAMSON, OWEN, GARTH
Application year: 1996
Main classification: F03D3
IPC codes: F03D3, F03D11