AU653429B2 - Wind engine - Google Patents

Description

P/00/01i 2WfviJ Regulation 3.2

AUSTRALIA

Patents Act 1990 s4 2

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT -1- Invenion Ttle:WIND ENGINE.

following statement is a full description of this invention, including the best 0::.:method of performing it known to me:- This invention is a self-acting engine that converts energy from a moving air mass int- mechanical energy.

I .1 1 The mechanical energy output canl be used to pump water or generate electricity The low power output and high cost of engines presently used for wind energy conversion have encumbered the development of this energy source.

The term Wind Turbine is used to describe a commonly used engine which consists of a multiblade propellor with radially spaced blades mounted on a hub on a horizontal axle which drives a gear system connected to an electrical I. generator or a water pump.

The whole system is mounted on a tower by means of a vertical pivot so that it can rotate about the yaw axis V3 to ensure that the propellor faces the wind directly.

2 Larger wind turbines which drive alternating-current generators synchronised to an electrical system are designed to rotate at constant speed, or over a limited range about a particular speed. Most medium and small wind turbines function at rotational speeds ranging from standstill to maximum speed depending on wind velocity and mechanical loading. Direct-current electrical generators and water pumps are suitable loads for such a variable-speed output.

The pitch angle of the blades relative to the natural wind must vary over a range nearly five times larger than the commonly used aerodynamic range of unstalled angles of attack of plain aerofoils to avoid stalling over the speed range, and a variable-pitch control system is used.

Due to the rotor rotation only the outer parts of the blade S 15 are effectively used as the lower velocities of the inner parts result in less force being generated than at the outer parts. Increased angles of attack also occur at the inner parts resulting in local blade stall and a twist must be built into the blade to prevent this.

20 In summary, a wind turbine having twisted, high-aspect-ratio, variable-pitch blades has the following disadvantages:- 1) Over the whole rotational speed range only the outer parts of the blades are functioning effectively.

2) The generated force is centred at a long moment radius 25 from the hub resulting in heavy stresses in the blade roots and the variable-pitch bearings located at the hub.

3) Commonly used variable-pitch systems are complicated and.

are not economically viable with small and medium sized turbines. They also require an energy input for operation.

4) Both the hub assembly and the blades are expensive to manufacture.

These disadvantages are diminished by the present invention which provides a self-acting wind engine for the conversion of wind energy into mechanical energy comprising a balanced rotor assembly disposed on a horizontal axis of rotation and a plurality of fenced, low-aspect-ratio blades each fixed to a securing bracket for pivotal mounting to the outer end of a rotor arm to have a limited range of free pivotal rotation about an aerodynamic axis perpendicular to the horizontal axis, and characterised in having a stabilising tailplane trailing approximately two blade chord lengths from said aerodynamic axis and fixed to the end of a strut which is pivotably mounted on two axes at its other end to securing bracket on said blade for setting said blade into deliberate Sangles of attack to a relative wind.

The blades pivot freely under the control of their tailplanes S: 15 over a range limited by a buffer stop between selected coarse •t .and fine pitch angles relative to the natural wind direction.

Each blade is fitted with a counter weight to degravitate the blade assembly. Each blade has an aerofoil section.

S" The said tailplane and strut assembly of each blade has means to swing about otrL, if said axes in an arc approximately Sparallel to the plane of said blade for rotating the blade about said aerodynamic axis to angles of attack to relative winds within the bounds of unstalled aerodynamic angles so as to vary the generated force on each blade and hence 25 control the rotational speed of the rotor.

The means of controlling the swing of said tailplane and S. strut assembly includes a rod fitted at each end with a ball joint, or equivalent device, connecting a longitudinal moment arm on said strut to a crank which is pivotably mounted on the rotor hub and further connected by means of a pivoted link to a sliding sleeve mounted on the rotor axle the sleeve being spring loaded in compression towards one end of said aliding movement. A thrust bearing is fixed to the said sleeve providing a non-rotating facility for the application of a linear motion.

4 Added control is achieved by rotating said strut about its longitudinal axis about second said axis located on said strut for slanting said tailplane in response to the aforesaid swing of the tailplane arnd strut assembly in order to superimpose a furvther rotation of said blade about said aerodynamic axis to angles of attack to relative winds within the bounds of unstalled aerodynamic angles to vary the generated force on each blade and hence control the rotor rotatien speed. At the extreme end of the tailplane and strut swing the slant of the tailplane will be a maximum to rotate said blade about said aerodynamic axis into an angle of attack to the relative wind at which no force is generated on the blade to bring the rotor to a standstill., or a very slow rotation speed, as a protection against the effecta of excessive wind velocity.

The means of rotating said strut about its longitudinal axis inci~des a rod with a ball joint at each end connecting a radial mnom~ent arm on said strut to a fixture on said blade at the securing bracket.

Each blade is fitted with fences at the tips to restrict the :formation of tip vortices in the air flow, and said fences are airflow guiding surfaces fitted normal to the said 4 aerodynamic axis and are straight or curved so as to speed up the airflow on the low pressure side of the blade, and to slow down the airflow on the high pressure side of the blade for enhancing the aerodynamic performance of said blade.

to In one form of the invention the rotor is placed at the downwind end of the horizontal axle which is supported in bearings mounted on a base frame. The lengths of the base frame and the axle are sufficient to accomodate, at the upwind end of the axle, any device which absorbs and transmits the power output of the wind engine and to ensure that the centre of gravity of the whole assembly, including any other equipment, occurs at approximately one third of the assembly length from the upwind end.

A vertical pivot is used to support the whole assembly just at the position of the said centre of gravity on top of a suitable tower in such a manner that the whole assembly can rotate to face the blades into the oncoming natural wind. Fins attached to the cowling straighten the air flow which is disturbed as it passes the tower.

Aluminium in sheet or extruded form is a suitable structural material for use in the engine. On smaller units the blades may be of pressure-moulded plastic. Maintenance-free ball bearings can be extensively used.

STo assist with understanding the invention, reference will now be made to the accompanying drawings which show one example of the invention.

In the drawings: FIGURE 1 shows the assembly of a rear-mounted, two-blade rotor according to this invention.

FIGURE 2 shows a general assembly of a wind engine according to this invention having a rear-mounted, four-blade rotor and a geared load, the whole being mounted on a tower.

20 FIGURES 3 and 4 are plan and side views of a linkage assembly to couple the tailplane and strut assembly swing to .ji" a rotation of the strut about its longitudinal axis.

FIGURE 5 shows a theoretical vector diagram of natural wind, blade circumferential velocities and resultant relative winds.

FIGURE 6 shows the difference between the relative wind to a blade and that of the associated tailplane, at rotation speeds.

FIGURE 7 shows the incidence angle between the chord lines of a blade and its tailplane in one example of a setting.

6 Referring to FIGURE 1, the rotor of this invention comprises a horiaontal axle 1 to w ich are fixed radially-spaced arms 3 by means of a hub 2. At the outer ends of each arm is a pivot 4 which permits a blade 5 to undergo pitch change about an aerodynamic axis parallel to the associated arm.

The range of pitch variation is limited by buffer stop 7.

The blade assembly consists of blade 5, fences 8 and blade securing bracket 6 on which is mounted tailplane 11 and strut 10 assembly by means of pivot 13. The strut has a longitudinal pivot 14 built in close to pivot 13. An extension of the blade securing bracket supports counterbalance weight 9, used to degravitate the whole blade assembly. All the blade assemblies are identical to each other.

The longitudinal moment arm 12 of strut 10 is connected by a i ball joint to rod 15 the other end of which is connected by a ball joint to crank 16 which is pivotably supported near hub 2 by bracket 17. Crank 16 is further connected by a .4 pivot to link 18 the other end of which is pivotably connected via fixture 19 to sleeve 20 which slides freely along axle 1. Fixed to sleeve 20 is a thrust bearing 21 which provides a non-rotating facility to absorb a linear control movement which via the aforesaid linkage will rotate the tailplane and strut assembly 10, 11 in an arc about pivot 13. Spring 22 bears against sleeve 20 in S. compression biasing the sleeve towards hub 2.

The tailplane and strut assemblies do not have counterbalancing weights so that when rotor rotation occurs they are s e. subject to centrifugally induced force which tends to increase the tailplane radii from the axle of the engine. These forces act through the control linkages to counter the compression of spring 22 thus minimising the amount of applied control force required for sensitive control applied to the non-rotating part of bearing 21. At excessive rotation speeds the centrifugal force on the tailplane and strut assemblies will increase their radii further to the extent of reducing the angles of attack of the blades which will restrict the rotational speed.

7 If a device which is responsive to the natural wind velocity was used to apply a linear control to the non-rotating part of bearing 21 against the pressure of spring 22 it will have the effectoof reducing the angles of attack of the blades and in the extreme will reduce them to a value at which no generated force occurs and rotation will cease, thus protecting against the effects of excessive natural wind velocity.

The tailplane and strut assemblies do hot have counterbalance weights but any gravitational tendency to rotate said assembly about its pivot 13 is neutralised by the same tendency in a diametrically opposite tailplane and strut ID assembly because of the interlocking effect where all control linkages are pivotally Joined to the common sleeve 20 on axle 1.

FIGURE 2 shows a practical form of the wind engine according to this invention in which the rear-mounted rotor turns on :axle I which is supported in bearings fitted to base plate 26. The axle drives gear train 27 which in turn drives an electrical generator 28. A speed comtrol device 29 having a linear movement is connected to the non-rotating part of ~:.bearing 21.

FIGURE 3 is a plan view and FIGURE 4 is a side view of a simple control linkage by means of which the rotation of the strut about its longitudinal axis in pivot 14 will slant the tailplane in response to the swing of the tailplane and strut assembly about pivot 13. A radial moment arm 24 is 9....,fixed to the strut a short distance from pivot 14, the other end being Joined to a rod 23 by means of a ball joint.

The other end of the rod is connected by a ball joint to a fixture 25 on the blade bracket 6, so that any swing of the strut will result in a strut xotation about its longitudinal axis.

The aerodynamic force generated by the air fl.ow over the tailplane acts over the strut length with sufi~icient turning moment to overcome any pitching moment arising from any displacement between the blade pivot line and the aerodynamnic axis on which occurs the centre of pressure of the forces generated on the blade. The tailplane tends to align itself with its relative wind at close to zero angle of attack so the set angle between the chord lines of the tailplane and the blade would be the aihgle of attack of the blade, in the same relative wind.

The blade and the tailplane seldom encounter the same relative wli' 4d but the weathercocking action of the tailplane is used to, maintain the blade at unstalled angles of attack over rotor rotation speeds from standstill to rnaximum,thus S providing automatic pitch control of the blade.

At rotation speeds the blade is subject to the natural. wind and another wind component due to the circumferential WO. 0 15 movement of t1he blade. By interchanging the variable and the parameter of the latter one can draw a vector diagram of :these two winds, normal to each other, acting on the blade.

At any instant a vector represents a wind velocity, proportional to its length, and the direction by means of the too. 20 arrowhead. In FIGURE 5 let W represent the natural wind of constant velocity,ana B 0 the wind equivalent to the circumferential velocity of~ the blade outer tip. Their resultanxt is R 0 which represents the relative wind encountered by the Ott blade tip in magnitude and direction. It is assumed that the 'bo 6 25 centre of pressure of the tail~plane has the same radius as that of the outer blade tip, both measured from the axlet, and both experience the same relative wind.

By swinging the tailplane and strut assembly towards the axle the rotational radius of the centre of pressure of the tailplane is reduced and its circumferential velocity is lowered, as represented by vector B 1 so that the restiltant R, represents a new relative velocity of wind past the tailplane. The tailplane will now align itself with R, and in doing so will reduce the angle of attack oX the blade by =agle 0 while the blade still has relative wind Rot Hence swinging the tailplane and strut assembly in an arc of about 459varies the radius of the centre of pressure of the tailplane in providing a means of control of the angles of attack of the blade to its relative wind, at any of the pitch angles of the blade to the natural wind. Reducing said radius will reduce the angles of attack, and vice versa.

During rotation the movements of both blade and tailplane relative to the air mass are approximately circular but having radii in excess of that of the outer blade tip.

Referring to FIGURE 6, at any instant the blade encounters its relative wind head on, vector 30, but because the S tailplane physically lags behind its blade by about 450 of itotation the relative wind encountered by the tailplane is approximately tangential to its circumferential movement 15 which can be an inclination to the longitudinal axis of the 6 0 strut of as much as 50", vector 31, depending on the :position of the tailplanie' Hence a rotation of the strut about its longituditnal axis slants the tailplane into its relative wind. In tending to 20 align itself to a near zero angle of attack to the relative wind the tailplane will rotate the blade about its aerodynamic axis thus changing the angle of attack of the blade to its relative wind. The rotation of the strut to GO, slant the tailplane in the aforesaid manner provides a further control over the angles of attack of the blade to its relative wind.

in one form of control the set angle between the chord lines of tailplanes and associated blades is fixed at 13 0, as in FIG~URE 7s which aligns each blade at an angle of attack of approximately this positive value over the whole length of the blade to generate a good starting force at standstill.

The tailplane is positioned at a rotational radius about the same as that of the inner blade tip, say 65Y6 of the outer blade tip radius, and during the run up of rotation the angof attack of inner blade tip increases by about 100, but this is countered with the tailplane in said position which reduces the angle of attack of the whole blade thus avoiding blade stall over the rotation speed range. The average angle of attack over the blade length ranges from about +13 0 at standstill down to about +8 0 at maximum rotational speed.

For speed control at any rotational speed, and .axly working load, the tailplane and strut assembly is swung so as to increase the radius of the tailplane. This will tend to make the blade angle of atrack more positive while the slant of the tailplane is changed by this tailplane and strut assembly swing to provide a counter rotation of the blade in a negative direction to override the increase to a lesser angle of attack which will reduce the generated force with a subsequent drop in rotation speed.

Swinging the tailplane and strut assembly further will increase the radius and slant of the tailplcme, and aided by the attitude of the strut at the end of the swing will rotate the blade about its aerodynamic axis to a sufficien- 5:20 tly large negative angle of attack to its relative wind to reduce the generated force to zero so that the rotor comes to stnsil~i a very slow rotating speed, as a protection against the effects of excessive wind velocity.

The Wind engine of this invention will respond to a single 25 applied control, in tche form of a linear movement over a short distance, to cover the rotation speed range from standstill to maximum and a range of sustainable mechanical loads. The wind engine is applicable to constant-speed operation, as driving a synchronous, alternating-current generator, as well as loads such as direct-current genera'tors which can absorb a varying speed output.

Claims (5)

1. A wind engine for conversion of wind energy into mechanical energy comprising a rotor with a horizontal axle and a plurality of radially disposed arms for rotation about a horizontal axis, and characterised in having a wind vane consisting of a bracket, a strut and a tailplane, said bracket being pivotally mounted at the outer end of each of said arms for rotation about an axis perpendicular to said horizontal axis, said strut is supported at one end by means of a dual pivot on said bracket and said tailplane is fastened to the remote end of said strut, said tailplane being movable in attitude and position, with respect to said bracket, for encountering various relative wind directions occurring at different radii about said horizontal axis for orienting said wind vane so that a blade, fastened to said bracket, is directed into unstalled angles of attack, with respect to the centres of pressure of said blade, to a 15 relative wind passing over said blade.

2. A wind engine for conversion of wind energy into mechanical energy of claim 1 wherein said tailplant is fastened to one end of said strut the other end of which is mounted by means of said dual pivot to said bracket, with one of said dual pivot permitting a swing of said tailplane 20 in an arc approximately parallel to the plane of said blade, the other one of said dual pivot permits the rotation of said strut about its longitudinal axis, both actions controlling the angles of attack of said blade to a relative wind passing over said blade.

3. A wind engine for conversion of wind energy into mechanical energy of claim 1 wherein said blade, being fastened to said bracket, rotates freely about said axis perpendicular to said horizontal axis between the limits of coarse and fine pitch relative to the natural wind as determined by a buffer stop.

4. A wind engine for conversion of wind energy into mechanical energy of claim 1 wherein said blade is of low aspect ratio with an aerofoil section and fitted at both inner and outer tips with aerodynamic fences to reduce tip vortices and enhance the performance of said blade. A wind engine for conversion of wind energy into mechanical energy of claim 2 wherein means of rotating s"id tailplane and strut about an arc parallel to the plane of said blade includes a rod fitted at each end with a ball joint, or equivalent,connecting a longitudinal moment arm on said strut to a crank pivotally mounted at the rotor hub of said horizontal axle and further connected by means of a link to a sliding sleeve mounted on said horizontal axle, said sliding sleeve being spring loaded one end thereof, and a thrust bearing is fixed to said sliding sleeve to provide a non-rotating facility for the application of a linear movement. A wind engine for conversion of wind energy into mechanical energy of claim 2 wherein means of rotating said strut about its longitudinal axis includes a rod with a ball joint, or equivalent, at each end connecting a radial moment arm on said strut to a fixture on said bracket.

7. A wind engine for conversion of wind energy into mechanical energy as herein described with reference to the accompanying drawings. Name of applicant) (Date) BLOCK LETiERS *ii '•o o *oo, *oo O*I I I i I I I Q ll l 0 t t 1 t l Nam ofapiat)(Dt BLC *~F