GB2065787A - Rotor for Wind Power Plants - Google Patents

Abstract

The rotor has an approximately horizontal rotor axis and at least one rotor blade 6 which can be pivoted about its longitudinal axis and which can perform a deflection motion from the rotor plane about a shaft 3. The at least one rotor blade 6 has a base which is supported by a joint head disposed at one end of the rotor shaft 1. The rotor blade 6 has a pivoting shaft 2 for a pivoting motion of the blade within the rotor plane. Two rotor blades 6, 6' may be situated diametrically opposite to each other and their pivoting shafts 2 are jointed by a linkage 10. The pivoting shaft 2 in the joint head is connected to a rotating shaft 4 of the rotor blade 6 by a linkage 8, 9. The joint head has a shaft which is aligned at an angle to the plane of rotation that combines the pivoting shaft 2, 2' and a deflecting shaft 3, 3'. The construction reduces blade stress. The blades may be formed of connected half shells and may contain foamed plastics, or bulkheads. Various blade shapes are described. <IMAGE>

Description

SPECIFICATION Rotor for Wind Power Plants The invention relates to a rotor for wind power plants with an approximately horizontal rotor axis and with at least one rotor blade.

In wind power plants with a rotor axis which is horizontal or nearly horizontal and with a rotor which rotates in the vertical plane and having one or more rotor blades, it is convenient to reduce the forces which act at higher wind velocities on the rotor blades and on the entire plant. To this end, the prior art discloses adjusting mechanisms which move the rotor blades by rotation about the longitudinal blade axis into a so-called feathering position in which both the active surface area of the blades and the rotor speed are reduced.

Known systems designed to this end suffer from the disadvantage that a suitable regulating mechanism is complex and therefore troubleprone and moreover the rotational support of the blades causes these to be rigidly clamped in the sense of a bar, clamped on one side, so that the forces applied by the air stress the blade in bending. Appropriate design measures must therefore be taken to counter the bending forces and this results in a substantial weight of the construction which in turn stresses the support for the rotor shaft and the blade pivoting shafts as well as the pivoting support of the machine set as far as the mast or calls for a reinforced and therefore heavier building construction of the entire plant.

An improvement in these conditions can be achieved by the provision of a so-called deflecting joint at the base of the rotor blade or rotor blades so that during operation of the rotor, which is situated in the lee of the mast, the rotor blade is able to yield to heavy wind and on the other hand can be forced back into the rotor plane by centrifugal forces when the wind force is less powerful. Part of the bending forces is thus eliminated and a lighter construction is made possible thereby.

In another construction, setting the deflecting joint axis at an angle to the axis of rotation enables the rotor blade to perform a pivoting motion about its longitudinal axis together with its deflecting motion to obtain better adaptation to different operating conditions (German Offenlegungsschrift 25 46 884). This known system however suffers from the disadvantage that the mass centre of gravity and the point at which the resultant lift forces act on the blade of aerofoil construction are situated at a substantial distance from each other, so that the couple can produce bending forces within the rotor blade which in turn call for a construction which is reinforced and therefore heavier, than would be desirable. Moreover, there are certain operating conditions in which the plant is endangered, for example if the load suddenly ceases.

To construct rotor blades of lighter weight it is known (German Offenlegungsschrift 29 1 3 407) to construct the aerodynamic effective blade surface not over the entire radius as far as the rotor hub but to construct it as such only in the outer region of the rotor circle and to connect the blade portion to the hub by means of a strut. The deflecting joints of this known construction are situated at a substantial distance from the rotor axis and are supported by struts. This results in the disadvantage that the construction weights due to the design of the deflecting joints necessitate a larger radius and therefore increased centrifugal forces so that large forces act on the connecting strut. Moreover, the torque required to transmit power must be absorbed by the struts through bending stresses.The construction of the struts necessary to this end again calls for weight of construction.

Furthermore, synchronization of the blade movements with each other gives rise to difficulties if the deflecting joints are situated further to the outside and the means required to achieve such movements increase the weight and therefore the associated centrifugal forces and bending moments.

The invention sets out to provide a rotor for wind power plants, in which the bending forces stress the rotor blades to the least possible degree and the rotors can therefore be constructed to the lowest possible weight so that the loads applied to the entire plant are kept as low as possible while an optimum output is provided. The invention therefore provides that the base of the rotor blade is supported by a jointed head disposed at the end of the rotor shaft and said jointed head provides, in addition to the other axes, a pivoting axis for a pivoting motion of the rotor blade within the rotary plane.

According to the invention, a rotor for wind power plants with an approximately horizontal rotor axis and at least one rotor blade which can perform a deflection motion from the rotor plane, wherein the at least one blade has a base which is supported by a joint head disposed at one end of a rotor shaft and the rotor blade has a pivoting shaft for a pivoting motion of the rotor blade within the rotor plane, in addition to other axes.

The invention will now be described by way of example with reference to the accompanying drawings, in which Fig. 1 a shows a two-bladed rotor according to the invention as seen in the wind direction; Fig. 1 b shows the rotor of Fig. 1 a seen from the side; Fig. 1 c shows one of the rotor blades of Figs.

1 a and 1 b seen from the side; Fig. 2 shows a perspective embodiment of a blade strut; Fig. 3 shows an end view of a jointed head with movement axes and connection; Fig. 3a-3c show other embodiments of the jointed head; Fig. 4 shows a single-bladed rotor with a counterweight; Fig. 5 shows exemplified embodiments of a strut member associated with a rotor blade and having different spring characteristics; Fig. 6 shows a plan view of blade examples; Fig. 7 shows a plan view of an embodiment of a blade tip; Fig. 8 shows exemplified embodiments of air guiding means and air flow under the action of centrifugal force; Fig. 9 shows in cross-section examples of blade embodiments; and Fig. 10 shows examples of transverse rotor blade surfaces.

Irrespective of whether the rotor comprises one or more rotor blades, the lightest construction of a rotor blade 6 is obtained if all forces acting from the outside function as tensile forces along the blade axis. One possible arrangement of such a construction is shown by the three illustrations of Fig. 1.

The rotor blade 6 comprises a strut member and an aerodynamically shaped blade surface member and is pivotedly mounted on a short lever 7, the iength of which is defined by the torque to be transmitted depending on the design rating.

The acting forces, namely the centrifugal force F and the pivoting force S resulting from the torque, can be combined, according to Fig. 1 a, into a resultant which is oriented along the longitudinal axis of the blade and has a pivoting angle y with the perpendicular. The longitudinal axis of the rotor blade adjusts itself in the direction of this resultant.

The pivoting mechanism according to the invention also enables the longitudinal axis of the blade, as seen in the side view shown in Fig. 1 b, to adjust itself at the taper angle cp of the resultant obtained from the effect of the centrifugal force F and the wind pressure W.

It is known that a blade constructed in accordance with an optimum blade width distribution is usually narrower in the clip region than at the blade base. Even in its reduced length, which is desired in the interests of weight and building cost reduction in accordance with the invention, this results in a blade shape of the kind shown in simplified form in Fig. 6a. Here, it should be noted fundamentally, that the mass centre of gravity of the surface part is situated on a shorter radius of the swept rotor circle than the so-called lift centre or the point of action of the resultant of all lift forces acting on the surface part. This distance between the two points at which the force acts, as shown in the side view of the area part of the blade in Fig 1 c, results in a couple which leads to bending stresses being imposed on the rotor blade.In addition to the conversion of the other forces into tensile forces oriented exclusively along the longitudinal blade axis, the invention sets out to minimize the effective lever arm of the couple by suitable construction measures so that the load bearing structure is stressed as little as possible by forces and can thus be constructed with a particularly low weight.

it can be convenient, more particularly for plants of large dimensions, to subdivide the strut member of the blade into one or more individual struts or into a lattice structure and for this to be clad either individually, or in its entirety, as shown in Fig. 2, in streamlined form.

The joints in the region of the rotor hub, i.e. the deflecting and pivoting joints can be wholly or partially omitted if the strut member of the leaf is constructed as a spring element with a characteristic which satisfies the previouslydescribed limiting conditions governing the force interaction on the blades in all operating conditions thereof.

Since simultaneous rotation about the longitudinal blade axis is required in addition to the blade movement in a plane obtained if the blade strut is constructed as a leaf spring, it follows that the strut must be formed in a corresponding manner, for example as shown in Fig. 5a and 5b. If the strut is constructed as a lattice in accordance with Fig. 2, this can be achieved by different dimensioning of the individual structs, conical shaping thereof or by similar steps giving a different material distribution.

Streamlined cladding can contribute to achieve the required spring characteristic on the one hand by complete or partial fixed connection to the actual strut material or it can be wholly or partially detached from the strut material to merely perform its function as cladding and therefore to reduce the blade drag in flow.

To follow the partial pivoting motion of the struts, the trailing edge 21 in Fig. 5b of the streamlined cladding is advantageously not closed, i.e. beginning and end edge of the surface material of perimetric cross-section are in physical contact but are not fixedly connected to each other by welding, adhesive bonding, riveting, screwfastening or other conventional steps. The cladding therefore represents a tube which is substantially not stiff against torsion.

The combined deflecting and pivoting motion of the rotor blade as shown in Fig. 1 a and 1 b in conjunction with the pivoting motions about the longitudinal axis of the blade in accordance with the requirements of given operating conditions, more particularly the aerodynamic characteristics of the blade area part indicate according to the invention the need for separating the movements from each other and for controlling them individually and by contrast to known embodiments control is based on the purely geometrical co-ordination of the individual control elements so that it is not necessary to employ any additional control and regulating device which must be supplied with data from the outside.

As shown in Fig. 3, the joints are arranged in the form of cross-joints at a distance from the rotor axis corresponding to the lever arm 7 of the support member, as described in the explanation of Fig. 1. Embodiments shown as examples always take the form of two-bladed rotors although arrangements in accordance with the idea of the invention can be correspondingly applied to rotors with one or more blades. For example, Fig. 4 shows a joint head with only one rotor blade, the other rotor blade being replaced by counterweights 2A.

In Fig. 3, the wind W is shown as blowing from the right of the drawing. Under its effect the blades undergo the deflecting motion (p as shown in Fig. 1 b about the correspondingly associated axis 3 or 3'.

The pivoting motion as shown in Fig. 3 resulting from the transmission of power is made possible by the pivoting shafts 2 and 2'. In addition, the rotor blades are supported so as to be pivotable about their longitudinal axis 4 and 4'.

In the illustrated example, the motions are coupled to each other by means of track rods 8, 9 and 8', 9' so that both the deflecting and the pivoting motion results in a forceable rotation of the rotor blades in the sense of an aerodynamic blade adjustment. To this end, the fixed points of radius arms 12, 13 or 12', 13' can be arranged on the axis 2 and 2' and axis 3 and 3', but in all other respects can be rigidly connected to the base member 7 which is fixedly connected to the rotor shaft. It should be noted that Fig. 3 contains two alternative solutions. In one case, the fixed points of the radius arms 12, 12' can be mounted on a component 5 which is arranged to rotate about the rotor axis 1, and the position of said component 5 relative to the rotor axis permits preselection of the blade adjustment in relation to the rotor plane or the wind direction.

In the other case, which is also illustrated in Fig. 3, the fixed points are disposed on rigid out riggers of the base member 7 in an extension of the alternately co-ordinated axes 2, 2', so that in one of each of the directions of motions there is no corresponding change of the adjustment of the blades.

The track rods 10 and 11 which interconnect the deflecting shafts 2 and 2' and the pivoting shafts 3 and 3' synchronize the blade motion relative to each other. This would not be necessary for a revolving rotor or means for uncoupling of the connections can be provided for the operating state and coupling is only restored when the system is stationary or operating very slowly. Under stationary conditions however, the coupling also functions as a weight compensation between the rotor blades or a counterweight in the case of a single bladed rotor.

By installing additional resilient elements, not shown, for example rubber elements, in the bearings of the shafts 2 and 3 or 2' and 3' or by attaching tension springs, torsion springs, or spiral springs in a corresponding arrangement, possibly with the simultaneous use of the track rod levers or by the arrangement of additional levers, rope or gearwheel connections, it is possible to exert a restoring force on the blades to return these into their starting position, preferably into the rotor plane or close thereto under stationary conditions.

Correspondingly, all jointed connections or couplings, shown as track rods in the illustrated example of Fig. 3, can be constructed as rope pulls, gearwheels or gear segments, hydraulic or magnetic power transmissions or other structural components of conventional kind.

Modifications of the above-described construction of the joints are illustrated as exemplified embodiments in Figs. 3a, 3b and 3c.

In Fig. 3a, the previously-described cross-joints comprising the shafts 2 and 3 or 2' and 3', are combined into a joint head with an axis that is orientated at 45 to the rotor axis. The controlling motion of the rotor blades is obtained automatically by their motion relative to the rotor axis without the need for any linkage. In this case, a dependence, defined by the motion of the crossjoint components relative to the rotor axis, is imposed on the rotor blade motion and corresponds approximately to the aerodynamic and output characteristic requirements, that in the previously-described embodiment shown in Fig. 3 it is possible to obtain very precise matching by appropriate adjustment of the track rods and of the associated lever lengths.

Synchronization of the blade movement is achieved in the embodiment shown in Fig. 3a by a pair of bevel gears which replaces the linkage 10, 11 of the embodiment of Fig. 3. Another modification of the embodiment of Fig. 3a is shown by the example of Fig. 3b and 3c and these two drawings illustrate two different states of movements of the same embodiment. The position in Fig. 3c is assumed by the rotor blades under the effect of wind pressure and a load in running operation (deflection angle (p) while Fig.

3a shows the stationary position.

The axes 2 and 3 correspond to the half crossjoint shafts 2 and 3 in Fig. 3a. Synchronization of the blade movements in Fig. 3b and 3c is provided by two track rods whose levers are connected to an intermediate bearing which is arranged to rotate about the rotor axis. The lever arm which transmits the torque resulting from the load is not shown in this drawing. The lever arm is produced by the eccentricity of the blade axis position in relation to the point of intersection of the cross-joint half shafts.

The operation of all modifications of the abovedescribed system is as follows.

It is assumed that in its starting position in or close to the rotor plane, the rotor blade, when stationary, has a large angle of attack or action in relation to the wind direction which impinges perpendicularly upon the rotor plane. This encourages the starting characteristic and at high speed ensures that the rotor speed assumes the position for the low high speed under the given flow direction -- i.e., the ratio between blade tip velocity and wind velocity - and the rotor cannot overspeed even at hurricane wind velocities.In this position the pivoting angle y, resulting from the load, is very small because on the one hand the power obtained from the system in relation to the energy contained in the wind can be regarded as negligibly small and on the other hand the centrifugal force predominates substantially so that the rotor blade in fact assumes the position which is practically perpendicular or in the rotor plane. After starting at the lower wind velocity, the rotor speed initially increases without any power load to a speed close the design speed or nominal speed which is associated to a predefined wind velocity.

A pivoting angle y as well a deflection angle P is obtained when there is a load on the system.

Both angles result in twisting of the blade, in the sense that it acquires a favourable angle zone in relation to the flow and is therefore able to convert more energy by higher lift forces and lower drag acting on the aerodynamic blade profile. A speed increase is a simultaneous consequence which in turn gives rise to blade adjustment in the reversing sense so that a condition of equilibrium is obtained. The specific operating points thus found for each operating state can be precalculated for association and optimization with a specific geometry of the joint and lever system.

Since the wind pressure is relatively low in relation to the centrifugal forces resulting from the blade weights, this construction can be embodied only on the assumption that the blade weights are kept very low. This will in any case be complementary to the efforts for a reduction in building costs. Exceptionally low component weights can be achieved only if the forces to be absorbed permit corresponding dimensioning.

It is known that the contribution made by the blade in the inner swept circle of the rotor to the production of energy represents a fraction of the contribution in the outer region so that optimization in terms of construction and weight led to a blade shape in which only the outer swept rotor circle region is constructed as an aerodynamically effective surface area, even with slight losses of efficiency.

It has been found convenient and represents an example of an exceptionally weight-saving construction of the surface area part of the rotor blade according to the idea of the invention to bend such surface parts from a single sheet-metal web by corresponding bending of precut sheet metal into the shape of the profile radius and by connecting the trailing edge of the profile by welding, riveting, plunging, adhesive bonding or a similar connecting network or combination of the above-mentioned methods. A slight offset, required merely for the outer region of the blade, can be obtained within the elastic deformation of the sheet metal or optionally by press forming.

The profiled sheet metal tube thus obtained is filled with self-expanding foam section blanks 23 (as shown in Fig. 9) to withstand local indenting forces which result from aerodynamic torsion and momentary loadings applied during the assembly phase. This method permits a further reduction of the sheet metal thickness and therefore of the weight.

The strut member of the blade can be represented by a simple tube, where appropriate of streamline cross-section (Fig. 5a), or with a conical transition member (Fig. 6a, 6b) which is non-positively attached to the blade surface part and is combined into a single unit by the connecting means described previously.

A sheet metal shell of this kind can also be produced by joining two half-shells 22 which, as shown in Fig. 9b, form a sectioned tube by the interaction of bent or flanged edges of blanks of different width and by virtue of the internal stress of the material within the tube (as shown in Fig.

9), and can be made to acquire a predefined flow dynamic profiled shape by the application of slight external forces. The half-shells 22 can be produced by press-forming of the sheet metal in the plastic region and can be connected to each other in a conventional manner while advantage can be obtained by filling the cavity with foam or adhesive bonding foam webs.

In this case, the conical transition member and the strut member together with the blade surface area member can each be prefabricated integrally from a top and bottom half shell. The half shells can be made of fibre-reinforced plastics, more particularly from fibres with a high modulus of elasticity to increase the stiffness of the component if this as a shell of thin wall thickness and can have a high modulus of elasticity in the manner described above to increase the stiffness of the component if the thickness of the shell wall is thin and can be combined in the manner described above or the blade can be produced in its entirety by known methods of cooling, by inflation or similar methods in the form of an imperforate shell which can subsequently be filled with foam substance.

Blades with contours of the kind shown in Figs.

6b, 6c and 6d can be produced by the last three of the production methods described above.

These shapes ensure more particularly that the distance between the mass centre of gravity and the lift centre in each blade is as close as possible to zero, while in addition the highest possible aerodynamic efficiency is obtained by exceptionally careful forming.

In this connection, the construction of the blade tip has a special significance in the case of the high blade speed velocities which can be achieved. The blade tip should be constructed so that pressure equalization between the bottom and top of the blade, and therefore the induced drag, is as low as possible. This is achieved in accordance with the invention shown in Fig. 7 and Fig. 6d. The back-pressure along the inclined leading edge prevents pressure equalization and the almost pointed edge curve draws only a slight vortex, thus achieving very low drag values.

Figure 8 shows particular examples of air guiding means and air flow 18 and 19 over the blade under the action of centrifugal force. A cavity is provided in the interior of the blade surface area part and communicates with the ambient air through a perforation 1 6 in the blade skin. The cavity is subdivided by at least one bulkhead 17.

If a cavity remains within the blade and communicates with the external air at the blade base as well as at the tip, an air flow will be produced in the interior of the blade due to centrifugal force. By subdividing the cavity into closed chambers and simultaneously perforating the blade shell, it is possible to direct the air flow so that the boundary layer is drawn off in the desired regions of the blade, resulting in an increase of the lift forces. This again permits displacement of the lift centre. Conversely, air discharge on the underside of the profile can assist this effect and lift peaks on the top of the profile can be reduced and both steps perform the same purpose. Altogether, drawn-off the boundary layer permits an increase in the overall efficiency of the blade surface area part and the size of the latter and the weight thereof can thus be further reduced.

Displacing the mass centre of gravity close to the lift centre can be achieved by appropriate shaping, as illustrated in Fig. 6b and 6c. However, broadening of the blade to the tip region is subject to certain limits defined by high speed operation of the rotor. These limits can be extended by the above-described drawing-off of the boundary layer.

Another means of connection is obtained by the attachment of transverse surfaces as shown in Fig. 1 Oa and 1 Ob. As the deflection angle (p of the blades increases, the transversely positioned surfaces assume a position which is perpendicular to the inflow direction and thus additionally improve the rotor efficiency at a high load. These surfaces can be arranged perpendicularly to the blade surface or at some other angle, at different lengths or merely as bent surfaces in the tip and base region of the blade and in this wide variety provide excellent means for force equalization accompanied by simultaneous improvement of efficiency of the blade surface in the sense of the invention.

Claims (26)

Claims

1. A rotor for wind power plants with an approximately horizontal rotor axis and at least one rotor blade which can be pivoted about its longitudinal axis which can perform a deflection motion from the rotor plane, wherein the at least one rotor blade has a base which is supported by a joint head disposed at one end of a rotor shaft and the rotor blade has a pivoting shaft for a pivoting motion of the rotor blade within the rotor plane, in addition to other axes.

2. A rotor according to claim 1, wherein two rotor blades are situated diametrically opposite to each other and their pivoting shafts are joined by a linkage.

3. A rotor according to claim 1 or 2, wherein the pivoting shaft in the joint head is connected to a rotating shaft of the rotor blade by a linkage.

4. A rotor according to any one of the preceding claims, wherein the joint head has a shaft which is aligned at an angle to the plane of rotation and combines the pivoting shaft and a deflecting shaft.

5. A rotor according to claim 3 or 4, wherein the linkage for the rotating shaft of the rotor blade is rotatably supported at fixed points which are situated on axial extensions of the deflecting shaft and the pivoting shaft.

6. A rotor according to claim 1, wherein there is a fixed point of a radius arm on a rotary member, which is rotatably supported on the rotor shaft.

7. A rotor according to any one of the preceding claims, wherein the joints are constructed as cross-joints.

8. A rotor according to claim 1 or 6, wherein intermediate levers which are rotatable about the rotor shaft are provided for synchronizing the blade position for axes which are aligned at an angle.

9. A rotor according to claim 8, wherein a differential gear transmission is provided for synchronizing the blade position.

10. A rotor according to claim 1, wherein the rotor blade has a resiliently flexible strap which supports a blade surface area part.

11. A rotor according to claim 1, wherein a strut comprises a lattice structure.

1 2. A rotor according to claim 11, wherein the strut has a streamlined covering.

13. A rotor according to claim 12, wherein the covering has a trailing edge which is open.

14. A rotor according to any one of claims 11 to 12, wherein the strut comprises a sectioned sheet metal plate.

1 5. A rotor according to any one of claims 10 to 14, wherein the strut and the blade surface area part are integrally constructed.

16. A rotor according to claim 10 or 15, wherein the blade surface area part is constructed so that its width expands radially in an outward direction.

17. A rotor according to claim 10, 15 or 16, wherein the blade surface area part has surfaces which are aligned at an angle or perpendicularly to the blade surface area.

1 8. A rotor according to claim 1, 2, 3, 5 or 10, wherein the rotor blade is filled with foamed plastics.

19. A rotor according to claim 10, 15, 1 6 or 17, wherein the blade surface area part is bent from a sheet metal web.

20. A rotor according to claim 10, 1 5, 16, 17 or 19, wherein the blade surface area part comprises two whells which are joined to each other by interlinking flanges.

21. A rotor according to any one of the preceding claims, wherein the blade tips are constructed approximately in triangular form and their trailing edge extends approximately radially and the leading edge is aligned at an acute angle thereto.

22. A rotor according to claim 10, 15, 16, 17, 1 9 or 20, wherein a cavity is provided in the interior of the blade surface area part and communicates with the ambient air through a perforation in the blade skin.

23. A rotor according to claim 22, wherein the cavity is subdivided by at least one bulkhead.

24. A rotor according to claim 21, wherein the blade tip is open.

25. A rotor according to claim 1, wherein the base of the rotor blade has an air inlet port.

26. A rotor as claimed in claim 1 and substantially as herein described with reference to and as illustrated in the accompanying drawings.