Omni-Directional Horizontal Wind Turbine TECHNICAL FIELD

[0001] This invention concerns a wind turbine designed to drive an external load such as an electrical generator or water pump via the output shaft of the wind turbine.

BACKGROUND

[0002] Wind generators are generally grouped into two basic classes. The first group consists of a propeller type turbine system with a horizontal shaft in which the wind driving the turbine is normal to the axis of rotation and was first perfected by Simon Stevin (1548-1620) in Holland. The second group normally has a vertical shaft around which are fastened scoops, sails or blades to catch the wind perpendicular to the shaft and cause rotation of the shaft much like the turbines of Savonius (1922) or Darrieus (1888-1979).

[0003] For best results the propeller type turbine must face into the wind. To meet this requirement the turret must be pivoted and a rudder device or similar fitted to constantly realign the turbine. To transmit electricity, slip rings may also be needed or use made of an off-axis generator. Unfortunately propellers generate undesirable noise and vibration due to cutting action of the blades and the working of necessary ancillary mechanisms, thus making them unsuitable for use in built up areas. They are also vulnerable to damage in high winds necessitating some form of braking or feathering device. This limitation further erodes the range of usable winds that should be exploited for greater efficiency. Despite these shortcomings, propeller designs are used extensively in modern wind farms and on marine craft to charge batteries. The efficiency of the propeller system is between 31% and 47% (Rreith and Kreider - Solar Energy 1974).

[0004] There are many different designs of so called vertical shaft wind generators which either trap the wind in some sort of scoop or utilize the Beraoulli-Coanda aerodynamic principle to effect torque at the shaft. These turbines don't need to be aligned as they operate in winds from all directions and are safe to use even at gale strength. Most are suitable for use in a domestic environment as they make little noise, but they do suffer from major flaws.

[0005] The worst problem is the negative force of the wind on the advancing side of the turbine blades which must be subtracted from the positive force created on the opposite side of the shaft. This results in less than 15% efficiency for the Savonius designs and less than 35% for the Darrieus designs (K and K-Solar Energy 1974). Some attempts have been made to use mechanical devices to negate this flaw, but with only marginal success. As the power to operate such mechanisms must come from the wind there is little or no net gain in their use. Noise and vibration from such mechanisms and eccentric imbalance are also insurmountable problems.

[0006] The second major concern is the initial slow speed of this type of turbine being inversely proportional both to the rotational mass and the diameter of the revolving device as well as having to overcome any mechanical and electrical loads. Most vertical shaft turbines must invariably support a heavy rotational structure as part of the design and have a large diameter to take advantage of greater torque and wind capture. Unfortunately, both the rotational dead mass and the large diameter are responsible for the initial slow start-up speed, being incapable of utilizing the short bursts of wind that are typical of wind patterns over land.

[0007] For any given wind speed the output of the turbine is governed by the speed and volume of air it can capture and the principles of conservation of angular momentum. Regrettably, both these limitations are in direct conflict. To increase the torque the rotational diameter must be increased and invariably this means increased rotational mass. To increase the rotor speed, the rotational diameter and mass must be reduced, but this means sacrificing the power needed to drive the generator.

[0008] To try and overcome this problem step-up gearing must be fitted to match the faster speeds required for an electrical generator system. In some cases this could be as high as 20 to 1 which can place a considerable strain on smaller low powered turbines making it impossible for them to function efficiently in the real world. Adding gears only makes the situation worse because there is very little capacity in the system to overcome the extra loading. Increasing the height of the blades can improve the power factor but stability now becomes an issue for vertical shaft turbines because of the raised centre of gravity. In general the vertical shaft turbine (or to be more appropriately termed "cylindrical turbine") has failed to meet commercial needs to generate sufficient speed at the electrical generator end of the system at reasonable wind speeds. Thus nearly all previous patent applications for these types of devices have fallen by the way side.

SUMMARY OF INVENTION

[0009] The apparatus aspect of the invention provides a turbine frame fixed to a support structure for mounting the frame in an operational position, the frame containing a wind responsive rotor and an axle, multiple elongated blades extending along the axle, each with a leading edge parallel to the axle, each blade having an aerodynamic section with a concave and convex face arranged so that when the leading edge of each blade rotates to face into the wind the convexed surface of the blades exerts lift which rotates the axle for part of its travel and the concave surface traps the wind which further assists rotation. A pair of baffle plates is mounted one on each side of the rotor frame, and so arranged to block all wind from striking the advancing convexed face of the blades in their circular path but shaped to redirect the undesirable wind into the drive sector of the turbine. Thus all wind impacting on the system is utilized to rotate the turbine unilaterally devoid of any counter rotational force.

[0010] In a preferred example, the rotor has four blades extending radially at 90 degree intervals from the axle. The blades span a pair of circular discs which are secured at their centre to the axle and designed to hold the blades in their fixed relationship to each other. The pair of baffle plates extends the full length of the rotor. Both baffles are inclined toward the frame diverting wind into the drive sector of the rotors circular path. The preferred embodiment support structure holds two or more turbines arranged to contribute torque to a common drive.

[0011] Where the turbine location is subjected to changeable winds the preferred embodiment utilizes the ornni-directional configuration in which three turbines are arranged radially at 120 degree intervals in a common horizontal plane. If more power is desired, additional radial arrays may be stacked one array above the other and geared to the vertical output shaft.

[0012] Subject to existing conditions it may be desirable to design the system with the output shaft in a horizontal plane and the radial array in a vertical plan so that all three turbines are subjected to a common wind force. With such an arrangement all turbines would contribute equally to the output, achieving a much higher power output, provided the system was arranged to face into the prevailing wind.

[0013] Where there is predominately a prevailing wind direction as is common along the coast, a pair of turbines arranged perpendicular to the wind along a common horizontal axis may be used. Alternatively they may be arranged one above the other or stacked singularly one above the other utilizing a common output shaft.

[0014] In the omni-directional configuration the three rotor axles terminate at the centre of the array in a gear box with each turbine axle fitted with a bevel gear for transmitting rotation to a common drive shaft. The bevel gears supply torque to the common drive through an automatic clutch device that permits each rotor assembly to contribute independently to the output without rotational detrimental drag.

[0015] The turbine assembly is suited to the generation of electric current without step up gearing and in our co-pending application for Patent Application No. 2012900528 we describe an alternator for this purpose. In practice the turbine may be configured to drive any other device that may be able to utilize its output such as a pump for irrigation or extracting water from a bore. In some applications the installation of step up gearing may be necessary. This is made possible by the way in which the turbine utilises wind force. When wind strikes the input surfaces of the rotor of this assembly, five events follow:

[0016] 1. On striking the concaved side of the blade it drives the rotor with maximum force relative to conservation of angular momentum and inertial forces.

[0017] 2. On striking the baffle it is unable to exert a detrimental effect on the approaching convexed side of the turbine blade and therefore does not oppose the positive force.

[0018] 3. The wind is deflected upward against the baffle on one side of the turbine at 45 degrees and downward on the other side of the turbine depending on the direction of the wind.

[0019] 4. The combination of the deflected wind and the laminar wind move over the convexed surface of the blade as the leading edge of the blade approach the end of the baffle sector thus forming a temporary vacuum as the wind accelerates momentarily over the curvature to assist in the upward (or downward) rotation of the blades.

[0020] 5. Once the blade has fractionally passed the baffle this deflected wind is also captured by the concaved side of the blade to add to the force already driving the concaved side of the preceding blade now approaching the vertical position.

[0021] Other than the mechanical friction and initial mass of the turbine rotors, there are no negative forces acting on the turbine blade system. By putting all the heavy components on the static frame, minimising the mass of the rotors and reducing the centre of gravity to its lowest point the system is stable, robust and extremely efficient.

Advantageous Effects of Invention

[0022] The rotor design in this invention has been geometrically designed to utilize wind dynamics through every angle of rotation and maximize the laminar nature of wind gusts at all wind speeds. There is no necessity for any braking device, feathering device, mechanical realignment of blades, nor any other ancillary system to sap the energy of the wind away from its primary function. The fixed diametrically balanced geometry of the blades ensures that they will function efficiently at all reasonable wind speeds. [0023] The horizontal radial layout of the omni-directional rotor system is so designed as to take full advantage of prevailing winds. No matter which direction the wind approaches the turbine system, two of the three rotor units will capture the wind's full force without loss.

Should wind strike a rotor cage perpendicular to the rotation of the turbine then this may be regarded as a full deflection of the interacting blades and can be considered as unity deflection. Should wind strike a turbine at an angle of say 45 degrees then by Pythagoras theorem the vector force on the blade is now approximately 0.7 that of a perpendicular force. However the wind interacts with the blade over a greater area than when striking it at 90 degrees to the rotation which is given for a 45 degree angle of impact as or 1.4 times the surface impact of a perpendicular force. But as the blade is rotating in unison with the wind, its prolonged impact along the blade is somewhat greater than therefore the net effect is approximately the same no matter what angle the wind strikes the blade. The end result is that no matter which direction the wind is blowing, two of the three turbines will always feel the full effect of the wind over the full length of the rotor blade system. Thus the impact is approximately equal to twice the length of one blade of the turbine or using the standard formula for wind force at sea level:

Available Wind power in Watts = 2(0.6AV ³ ),

where "A" m ² (Area of impact) = Radius of rotor x length of rotor

and "V" = Velocity of wind in ms ^"1

[0024] In a conventional vertical shaft turbine half of the vertical shaft system has a positive wind component with the other half negative. In this invention all negative impact has been removed resulting in a far more efficient drive than any previous design of cylindrical turbine. In this design the operation is completely silent as all wind is utilized without any diametric reaction to generate noise.

[0025] In the omni-direction configuration, the multi-shaft mitre box is the only real load on the system other than the electrical generator itself. With two rotors driving the single output mitre gear at any one time and assuming a one to one ratio, the loading is almost negligible. However, the third rotor in most situations would not contribute to the driving force and may be considered a parasite on the system if it were not for the automatic freewheeling clutch fitted to each rotor. This feature therefore allows each rotor to contribute independently to the final output without any detrimental effect on the system.

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[0026] With this invention most of the mass of the system is built into the fixed support structure and therefore the turbine is much lighter than in earlier turbines. In addition the diameter of each turbine need not be as great as a conventional vertical shaft system because its length can be extended without increasing its centre of gravity and its horizontal disposition to the wind is able to operate much more efficiently. The lightweight smaller diameter of these rotors is therefore able to more easily capture the short bursts of wind energy that are typical over uneven terrain.

[0027] To sum up the (Hilton) turbine according to the invention, it is robust, highly efficient and silent and admirably suited as a domestic power plant. The wind generator may be fixed to its own support structure to improve its exposure to the prevailing wind but it works

satisfactorily when fixed to a flat roof of a building or a level platform provided on a sloping roof.

BRIEF DESCRIPTION OF DRAWINGS

[0028] One embodiment of the invention is now described with reference to the accompanying drawings, in which:

[0029] Figure 1 is an isometric view.

[0030] Figure 2 is a plan of the view of Figure 1.

[0031] Figure 3 is a side elevation.

[0032] Figure 4 is an isometric view of the dynamic components of the embodiment without end discs and turbine cages. [0033] Figure 5 is a side view of Figure 4.

[0034] Figure 6 is a plan of Figure 4.

[0035] Figure 7 is a section of the aero-dynamic blade.

[0036] Figure 8 is a plan of one of the three turbine rotor assemblies.

[0037] Figure 9 is an end elevation of Figure 8.

[0038] Figure 10 is a plan of the central part of the gearbox.

[0039] Figure 11 is a side elevation of Figure 10.

DESCRIPTION OF EMBODIMENTS

[0040] Referring now to the drawings, roof derrick 2 is fixed to the roof 4 and access to the roof space beneath is arranged so that the electric current produced by the wind generator can reach the interior of the building via cable 6. The alternator housing 8 is screwed to the structure 9 below the gear box 10. A prism-shaped gearbox 10 has three sides 12, 14, 16 which are supported by the top of the alternator housing 8 and the frame structure 66.

[0041] A turbine cage 18, 20, 22 is secured to each face of the gearbox so that the cages extend horizontally and radially at 120 degree spacing and form a unitary component 9. Each cage consists of parallel frame members 24 which define a turbine box. Cross rails 26 act as turbine supports.

[0042] Mounted within each of the three cages 18, 20, 22 is a single horizontally arranged cylindrical turbine rotor 28 consisting of four horizontally aligned elongated aerodynamically shaped turbine blades 30 fixed parallel to and disposed radially around a central horizontally oriented rotational input axle 32. The blades are evenly spaced and dynamically balanced around the input axle and fixed between two end discs 34, the end discs being fixed at their centre point to the input axle of each cylindrical turbine rotor so that the whole turbine may rotate as a unit. Each input axle 32 extends through an aperture into the gearbox 10 structure to terminate in a mitre gear 36, at the centre of the array. The mitre gears 36, 38, 40 of all three cylindrical turbine structures are so arranged to mesh with a matching output mitre boss gear 42 fixed to the vertically disposed output axle 62. The output axle 62 is in turn coupled to the alternator inside housing 8. Other systems can effectively utilize the power output of the turbine.

[0043] A fixed elongated baffle board 46, 48 extends along each side of each fixed cage 18, 20, 22 covering approximately 35% of the vertically exposed face of each cage. Each baffle board is so arranged as to block the undesirable wind force on the advancing leading side of each cylindrical turbine 52. These baffles are inclined or streamlined vertically so as to redirect the negative component of the wind force directly into the positive or desirable windward face of each turbine rotor (see Figure 9).

[0044] In Figure 7 blade 30 has a concaved windward face -50 and a convex rearward face 52. Although blade 30 is the ideal shape, it is not essential that the blade conforms to this identical profile. A blade made from flat material and shaped to conform to the upper curvature would also be satisfactory.

[0045] In Figures 10 and 11 each of the three sides 12, 14, 16 have a central thrust bearing 54, 56, 58 for the rotor axles 32 which each supporting a mitre gear 36, 28, 40. Between the end of axle 32 and the gears 36, 38, 40 is a coaxial, 3-part slip drive 60, the purpose of which is to allow each axle to contribute torque to alternator shaft 62 through boss mitre gear 42. Output mitre gear 42 is secured to the output shaft 62 in a fixed relationship.

[0046] For a typical wind exposure one rotor will experience high wind force, the second rotor at 120 degrees will experience lesser force and the third rotor will experience hardly any force because it is shielded partially by the other two turbines. Although the gear is meshed for common rotation, the slip drives allows the rotor axles to turn at lesser speeds than the one experiencing the main wind thrust with each turbine operating independently from each other without drag.

[0047] It is to be understood that the word "comprising" as used throughout the specification is to be interpreted in its inclusive form, ie. use of the word "comprising" does not exclude the addition of other elements.

[0048] It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention, these modifications and/or additions are therefore considered to fall within the scope of the invention.