GB2296048A - Vertical axis wind turbine - Google Patents

Abstract

In a vertical axis wind turbine a pivotally mounted frame 10 coaxially supports a rotor 13 on which is mounted aerofoils 14 which feather in high winds but normally orientate with respect to the wind through an eccentric pivot 18 to extract maximum power. Venturi shielding 15 deflects the wind towards the aerofoils which are mainly orientated substantially normal to the air flow direction. <IMAGE>

Description

VERTICAL AXIS WIND TURBINE This invention relates to wind turbines.

Wind turbines are of two types - horizontal axis (H.A.W.T.) and vertical axis (V.A.W.T.). Numerous H.A.W.T.'s have been built chiefly at wind farms in Holland, Denmark and California. The H.A.W.T. has several drawbacks: (a) Wind farms are unsightly and may be unacceptable environmentally as a serious source of wind power.

(b) The diameter of the rotor is limited because, as the rotor blade tips may travel at 4 to 10 times the speed of the wind, then in high winds the tips may reach supersonic speed causing unacceptable noise and danger of disintegration through centrifugal forces. For this reason expensive blade-feathering devices and braking arrangements must be used.

(c) As only a small blade area can be presented to the wind (2 to 6 blades per rotor are common) the output is small and thus the conversion of wind power to useful energy is low. Manufacturers of this type of H.A.W.T. measure output as a function of the swept area, but this cannot be true because the wind can only act on the portion of blade orientated towards the wind. The rest of the wind passes between the blades uselessly. H.A.W.T.'s can be grossly overrated.

(d) Blade configuration can only be designed to operate at one wind speed for optimum results, losing efficiency at lower or higher speeds. The speed of rotation must be controlled at approximately 150 r.p.m.

(e) As the gearbox and generator must be placed close to the axis at the top of a high tower, able to bear the heavy machinery, the costs are high compared to a V.A.W.T. where the machinery is at ground level and thus easily installed and maintained.

(f) H.A.W.T.'s cannot reasonably be used for pumping water (because of the height), to higher levels, but V.A.W.T.'s can. Certainly those of the following design can, because the rotor shaft is close to the ground.

Put simply H.A.W.T.'s are too costly to build and maintain to ever be ever able to compete successfully with fossil fuel generators or hydropower, although of necessity they may be required.

V.A.W.T.'s of previous design have suffered from being too simplistic usually having fixed aerofoils which rely on their profile for rotation, after being started to revolve by other means. Some have vanes to direct the wind into the rotor irrespective of the wind direction. The torque created is largely cancelled out by the negative side of the rotor and so the power conversion is extremely poor. Speed control has been very difficult and in high winds they can disintegrate.

According to the present invention there is provided a rectangular framework pivoting on a single pivot and directed into the wind by a vane on top of a strong structure firmly attached to the ground. This structure is stationary and contains all necessary machinery for converting the power from the rotor into useful electricity or pumps for transferring water from low level to high for generating electricity in the future.

The framework supports a rotor advantageously in free air several metres above surrounding buildings or land. This rotor has vertical aerofoils equally spaced on the periphery and is pivotally mounted top and bottom within the rectangular frame. The aerofoils are pivotally mounted on the lightly built rotor frame so that they are free to reciprocate within predetermined limits by means of linkages to an eccentric point within the framework. This eccentricity effectively orientates the aerofoils so that their surface is presented to the wind as advantageously as possible on one side of the rotor, i.e. the positive side, and feathered as advantageously as possible on the negative side. The centre of eccentricity can be varied mechanically, electrically or hydraulically towards or away from the rotor axis and thus the rate of rotation can be controlled, either automatically or manually.

It will be apparent from the drawings that the arm supporting the eccentric pivot is most advantageous when angled at 300 -450 towards the wind.

As the aerofoils and vane can be constructed from several identical sections, bolted together and mounted in many different configurations it is possible to use this modular construction to advantage to construct very small turbines for supplying an isolated farm or very large using many thousand sections to supply moderately sized towns.

A convenient size of aerofoils would be 2 1/2M wide x 4M high (10 sq metres). Size is dictated to some extent by available machinery, i.e. C.N.C. punching presses. The smallest machine would have 4 aerofoils of say 6 sections each and a similar vane (30 identical sections). The rotor diameter would be around 6 metres, and revolutions per minute at average wind speed of 7M/sec would be around 30.

Increasing the number of aerofoils to twelve positioned 300 to each other would increase the diameter to 18M and reduce the speed to 10 r.p.m. For larger machines it is preferable to build upwards in tiers to avoid reducing rotational speed too much thus lessening gearing-up problems to drive a generator (usually 1,500 r.p.m.), i.e. 150:1.

The efficiency of this arrangement is fairly low when the rotor is unguarded but if the negative side is screened off and the wind funnelled in via a venturi forcing the wind towards the positive side the velocity of the wind is considerably increased and the efficiency of extraction of wind power will be greatly enhanced because the power is proportional to the cube of wind velocity.

The modular construction is the fundamental method of reducing costs. A moderately sized machine would have 12 columns of aerofoils, 10 tiers high, i.e. 12 x 10 x 6 = 720 sections (1200 sq metres) + vane. The effective blade area of a H.A.W.T. is 60 sq metre approximately. With screening the venturi effect must be balanced as shown in the accompanying drawings, Fig.l, so that the screening causes no turning moment on the rotor frame, its orientation being controlled by the vane. Turbulence will be produced on the negative side.

At wind speeds above 35/40 m.p.h. the stress and strain on the structure becomes very considerable and the whole would disintegrate in hurricane winds unless some method of feathering the aerofoils was incorporated in the design.

Feathering reduces the necessary strength to a small fraction of what would be necessary to produce a machine capable of standing up to hurricane conditions. As winds over 35/40 m.p.h. only occur about 4% of the time in G.B. it is economically best to feather the aerofoils and brake the rotor completely and simultaneously. This can be achieved by a hydraulically extracted key on the linkage responding to a switch linked to a pitot tube or anemometer. The key can be extracted by several means. This frees the aerofoils from the central linkage and as the aerofoils axis is nearest the leading edge, they all turn into the prevailing wind. Gusts of wind are accommodated instantly by this means irrespective of their direction.This is in direct contrast to H.A.W.T.'s where gusts veering as much as 10 are not quickly accommodated because of the static inertia inherent in the machinery at the top of the tower. Thus H.A.W.T.'s are much more liable to wind damage or destruction.

0 The aerofoils do not need to turn more, than 180 when released and are urged by a relatively light spring to return to their operative position once the wind speed drops and the brake is released. The compression spring is arranged circumferentially so that it urges the aerofoil towards its operative position clockwise or anticlockwise, i.e. the mechanism is self-centring.

The framework is built of light steel or aluminium tube appropriately braced and can be designed in a modular form, so that the power extracted from the wind can be varied according to local requirements. The aerofoils are pivoted on extensions so that the frame cannot foul them in any position.

In multistorey machines aerofoils are connected in columns by flexible couplings and mounted on plummer blocks. In very large machines the linkage to the eccentric pivot is repeated at top and bottom and interconnected to prevent distortion.

A specific embodiment of the invention will now be described by way of example with references to the accompanying drawings in which: Figure 1 shows in diagrammatic plan a twelve aerofoil version of a vertical axis turbine, with shielding and venturi effect to concentrate the wind.

Figure 2 shows in elevation a three tier rotor with four columns of aerofoils, without shielding for clarity.

Figure 3 shows in more detail the aerofoil feathering mechanism (diagrammatic).

Figure 4 shows in more detail the linkage between the eccentric fulcrum and the frame which must move together (diagrammatic).

Referring to the drawings the windmill comprises a frame 10 supporting directional vane 11 which turns the assembly into the wind to take optimum advantage of the wind available. The frame 10, would be constructed of angle-iron or tube and cross-braced for lightness and strength. It is pivotally mounted on the machinery house 12 which is securely anchored to the ground and contains gearbox and generator or water pumps or a combination of these (not shown). The rotor 13 turns within the frame 10 on pivots top and bottom, so that the rotor carrying the aerofoils 14 has clearance from the screening 15 and 16 to allow the aerofoils to turn in any direction. The bottom of the rotor must be sufficiently high to be in free air, i.e. several metres above surrounding buildings and land.

The radial arm 17 is pivotally mounted in the axis of the rotor 13 and is preferably angled towards the wind at about 0 30 . The radial arm 17 is connected through gearing (see Fig.

4) with the frame 10 so that they move together with change of wind direction. The arm 17 bears a pivotally mounted plate 18 at its outer end and this plate interconnects all the linkages 19a and 19b with the corresponding aerofoils 14. The effect of the linkages is to rotate the aerofoils 14. The effect of the linkages is to rotate the aerofoil 14 through approximately 90 land back again with every revolution. This has the effect of presenting the minimum profile to the wind on the negative side and the maximum on the positive side.

The fulcrum of the plate 18 can be moved towards the central axis hydraulically or by other means if the rotor speed becomes excessive (not shown). This movement reduces the presentation to the wind and so can keep the power output constant. An alternative is to use surplus power to charge batteries, pump water to higher levels, or heat water in insulated tanks.

The linkage 19b controls the orientation of each aerofoil through a self-centring clutch 20 mounted on shaft 20a (the aerofoil shaft) with hydraulically operated bolt 21 which can be automatically withdrawn by cylinder 22 in the event of wind speed rising above a predetermined limit as measured by pitot tube or anemometer (not shown). Pneumatic electrical or mechanical means could alternatively be used. The withdrawal of the bolts 21 releases aerofoils 14 to turn into the wind and present their narrowest profile. the fulcrum 20a is nearer the leading edge than the tail. The bolt 21 is shown withdrawn at 21a. As the area presented to the wind is reduced to about a tenth, the material strength required and cost are greatly reduced.Fig. 3 shows in plan and section the link 19b and bolt 21 with aerofoil presentation to the wind in dotted outline 14a after the bolt 21a has been withdrawn from tapered notch 21c. The compression spring 23 is compressed (in either direction) by the tongue 22a as shown at 23a. This tongue 22a passes between a forked tongue 22b attached to link 19b. Thus the mechanism is self-centring and relocks when the wind drops and the disc brake (not shown) releases the rotor.

Preferably the hydraulic or pneumatic pump would be situated in the machine house 12 and pressure conveyed to cylinders via a swivelling connection in the centre of the rotor shaft 20a and the eccentric arm shaft 17 to a pitot-operated switch adjusted to bring into operation all clutch-bolt cylinders 22 and disc brake simultaneously at predetermined wind speed.

The disc brake is mounted on the frame 10 and moves with this frame to orientate into the wind, thus the rotor is stalled relative to the frame 10 in high winds, and turns with it.

In Fig. 2 the assemblies 24 consists of plummer blocks for upper and lower aerofoils 14 with their shafts connected by flexible couplings. The gear train 25 and 28 connect with similar toothed gear 25a and gear ring 28a which is mounted on an annular ring 10a bolted to frame 10, and thus any rotation of the rotor 13 does not affect the relative positions of radial arm 17 and frame 10.

In Fig. 3 the plummer block 29 and flexible coupling 30 are shown individually.

As this design of V.A.W.T. is completely novel, and can be built to very large dimensions with many times the capacity of the largest H.A.W.T. to convert windpower into electricity, thus even if the principle may not be as efficient as the H.A.W.T. the capital cost per unit of electricity promises to be lower than even fossil fuels, perhaps less than half. The design has economy of scale and is to the H.A.W.T. as the Jumbo Jet is to the Tiger Moth.

Claims (5)

1. A vertical axis wind turbine mounted on a robust machine room the rotor being in free air turning within a pivotal frame which supports a directional vane. The rotor supports vertical aerofoils which orientate sequentially to the wind.

2. A vertical axis wind turbine as claimed in Claim 1 wherein speed control means and rotor braking is provided.

3. A vertical axis wind turbine as claimed in Claims 1 and 2 wherein the negative side of the rotor is shielded from the wind and the wind directed towards the positive side by venturi shielding.

4. A vertical axis machine as previously claimed wherein the rotor is braked and the aerofoils released to feather automatically at a predetermined wind speed, and resume normal function when the wind drops.

5. A vertical axis wind turbine substantially as described herein with reference to Figures 1 to 4.