GB2479380A

GB2479380A - Wind or water turbine rotor

Info

Publication number: GB2479380A
Application number: GB1005797A
Authority: GB
Inventors: Paul Trevor Hayden; David Anthony Whiley
Original assignee: Blade Dynamics Ltd
Current assignee: LM Wind Power UK Ltd
Priority date: 2010-04-07
Filing date: 2010-04-07
Publication date: 2011-10-12
Anticipated expiration: 2030-04-07
Also published as: GB2479380B; GB201005797D0

Abstract

A turbine rotor 100 for a wind or water turbine comprises a hub 20 with a plurality of stubs 22 for connection to a respective blade 21. Each blade 21 has a pair of spaced apart annular bearings 41, 42 located within a root end 23 of the blade. Each stub 22 protrudes into and is rotatably received within a respective spaced apart bearing 41,42 and the blades are supported on the hub. The bearings 41,42 may be supported by bulkheads 31,32 and may spaced by at least 1.5m. The rotor diameter may be at least 45m. The stubs 22 may be detachable from the hub core (19, fig.7B). The stub (22", fig.7C) may comprise male and female parts (50,51).

Description

A TURBINE ROTOR

The present invention relates to a turbine rotor. In particular the present invention relates to a wind turbine rotor and to a rotor suitable for use in water.

Current large-scale horizontal axis wind turbines have tower head weights (including the rotor, nacelle and drive train) of the order of 120 to 200 metric tonnes. There is an increasing trend for larger diameter turbines and the weight of the tower head is increasing approximately as the cube of the diameter of the turbine. The rotor itself (made up of the hub and blades) accounts for roughly 30% of the tower head weight. Approximately 60% of this is attributed to the blades while 40% is attributable to the hub.

US 4,029,434 discloses the blade mounting for a windmill. The root of the blade extends into the hub where it is supported by a journal bearing assembly and a combined journal and thrust bearing assembly which allow the blade to rotate about its axis. The combined journal and thrust bearing assembly must be built around the root once the root is in situ. Further, the blade root bears directly against the two bearings and therefore must have a circular cross section. The mounting is suitable for a windmill in the 1970s (which would have had a rotor diameter of less than 20m), but is not suitable for a modern day wind turbine blade, the blade length of which could be in order of magnitude greater than the blade contemplated by US 4,029,434.

US 4,668,109 discloses a bearing assembly for a wind turbine. The bearing is a sealed unit which has an outer cylinder which is bolted to the hub by an array of bolts.

Within the cylinder is a shaft which is supported on a pair of bearings. A wind turbine blade terminates in a flange which is bolted by an array of bolts to a flange which is integral with the shaft. The bearing has an expansive pressure ring which is arranged to apply equal compressive force to the bearings so that the pressure is maintained as the bearing wears. The bearing is designed to be suitable for a small scale wind turbine. The manner in which the bearing is connected makes it unsuitable for a modern day large wind turbine. In particular1 the requirement for two arrays of bolted joints, one at either end of the bearing would make the joint too heavy to be scaled up to the size required for a modern day turbine. Its use in a modern large scale wind turbine blade would only make the problems referred to below with regard to the plurality of bolts US 6,951,433 shows an unusual design of wind turbine.

Each blade is in two parts. An interior blade is fixed to the hub and an outer blade is fitted radially outwardly of the interior blade. A shaft extends a short distance into each outer blade and projects into a respective interior blade in which it is rotatably supported by bearings. The interior blades do not appear to be capable of rotation about their main axes. As a result of this, the efficiency of the turbine will be decreased as the interior blades cannot be rotated into the optimum aerodynamic position. In practice, this is likely to limit the size of the blade which can be constructed according to this design, such that the design is unlikely to be applicable to a modern day, large scale wind turbine.

GB 2 210 420 discloses a bearing arrangement for the hub of a wind turbine. The hub has a number of stub shafts, each of which is surrounded by an outer housing which is rotatably supported on the stub by bearings. Each blade is connected to this outer housing by a plurality of bolts and, as a result of this, this design will suffer from the problems referred to below in relation to Figs. 1 to 3. A similar design with a housing fitting over a stub shaft in the hub is shown in DE 1 270 411.

The current design of a conventional wind turbine rotor is shown in Figs. 1 to 3. The rotor comprises a hub 1 which is a large, heavy and typically cast metallic structure.

Three blades 2 are attached to the hub, one of which is shown in Fig. 1. The hub has a rotor axis 3 about which the rotor rotates and the blades are rOtatably mounted so as to be rotatable about a pitch axis 4 each driven by a pitch motor (not shown) . For each blade, the hub is provided with an annular pitch bearing 5 which supports the blade 2 so as to allow it to rotate about the pitch axis 4. The pitch bearing 5 typically has an outer race 6 and an inner race 7 with a pair of ball sets 8 inbetween.

Current art large wind turbines use two types of general blade design, those with a structural spar bonded inside an aerodynamic shell and those with the stiffening structure within the aerodynamic shell. In both cases the main structural elements of each blade are terminated at the hub end in what is known as a root structure. This is the last piece of blade structure (typically 3 -Bm in length) at the proximal end of the blade. This root structure takes all of the bending loads out of the blade and into a cylindrical shape ready for transfer to the hub via the pitch bearing.

The root end of the blade has a number of bolt attachment points 9 (typically 60 to 80) around the circumference of the root. These take the form of holes 10 into which threaded steel inserts 11 are bonded. A plurality of bolts 12 are inserted through the inner race 7 and into the inserts 11 to hold the blade 2 in place.

The current design has a number of shortcomings.

The rotor mass is significant both in terms of the load on the drive train and also the tower head mass. This has a significant effect, particularly for large turbines, on the dynamic interaction between the rotor and the tower. For off-shore installations, a large tower head mass is one of the significant problems with cost-effective deployment of the technology in this environment.

The inserts 11 are very difficult to produce with a high degree of repeatability. These are one of the most highly loaded points on the blade structure yet this relies on a number of secondary bonds where very high performance adhesive is used to bond the metallic studs to the composite root component.

In addition, the inserts are typically metallic and can cause problems due to differences in thermal expansion coefficient relative to the composite root structure, as well as difficulties in bond adhesion to the steel insert.

Additionally, thicker sections of composite are needed at the root end of the blade to reduce flexural mismatch with the metallic inserts. This leads to the root end of the blade being heavy.

The pitch bearing also has to take the full flapwise (Miap in Fig. 3) and edgewise (MEdge) bending moments of the blade. It also has to take the axial load (FAxIa1) caused by centrifugal and gravitational loading as well as radial flap-wise (FFlap) and edgewise (FEdge) loads. This means that the bearings are large diameter, expensive and heavy components in order to be able to cope with the large and varied forces. A number of pitch bearings have failed in use under these loads.

The large diameter required for the pitch bearing for the reasons set out above means that the root end of the blade needs to be made thicker (larger diameter) than is desirable for aerodynamic performance, thereby decreasing the efficiency of the blade.

The assembly of the blade onto the hub requires accurate torquing of a large number of bolts in order to achieve adequate fatigue resistance at the bolts and to avoid distortion of the pitch bearing. This is a time-consuming process which must be carried out with great care if problems are to be avoided.

The present invention provides an interface between the hub and the wind turbine blades which addresses at least some of the shortcomings set out above. In a first aspect, the present invention provides a turbine rotor comprising a hub and a plurality of blades, the hub comprising a plurality of stubs for connection to a respective blade, each blade having a pair of spaced apart annular bearings located within a root end of the blade, each stub protruding into and being rotatably received within the respective spaced apart bearings when the blades are supported on the hub.

Rather than terminating the blade with a bulky root end, the present invention takes the approach of providing the hub with stubs which extend into the root end of the blade and which support the blade via a pair of spaced apart bearings located in the root end.

This means that instead of one large bearing taking the full bending moment of the blade perpendicular to the plane of rotation, there are now two smaller bearings taking the bending moment out of the blade within the plane of rotation of each bearing. Not only does this provide a load situation which is more suitable for a bearing (in plane of bearing rotation as opposed to perpendicular to plane of bearing rotation) but also allows the loads on each bearing to be further reduced by increasing the separation of the bearings. Therefore the load on each bearing is reduced and is in a direction that the bearing is more able to support, leading to a smaller and more reliable bearing arrangement.

Ultimately this leads to reduced bearing cost and increased reliability when compared to the prior art. It also allows the means by which the blade is fixed to the hub to be simplified reducing or eliminating the need for a thick root end to accommodate the array of bolts.

The turbine rotor of the present invention may be a wind turbine rotor. Alternatively the turbine rotor of the present invention may suitable foruse in water.

Preferably, the spacing between bearings is at least lm and more preferably at least l.5m. Preferably, the rotor has a rotor diameter (i.e. the diameter of the circle swept by the blades) of at least 45m.

The hub may preferably comprise a hub core to which the stubs are detachably mounted to make assembly of the rotor easier.

Each bearing preferably comprise an inner race and a complementary outer race, each stub fitting into the inner race of its two respective bearings so as to rotate together with the inner race.

In a preferred embodiment each blade may further comprise a collar rotatably received within the spaced apart bearings, each respective stub being received within and connected to the collar. This allows for the use of metal and composite components.

The stubs and bearings are preferably configured to allow each blade to be slid onto and off of the hub along the respective axis of rotation of the blade. This provides a simple way of assembling the blades to the hub.

The present invention also extends to a method of assembling a turbine rotor according to the first aspect of the invention, the method comprising assembling each blade with the pair of annular bearings in each respective root end; inserting each stub into its respective pair of annular bearings; and supporting each blade on the hub.

The method is an improvement on the prior art as it allows for a much simpler way of supporting the blades on the hub.

The inserting of each stub into its respective pair of annular bearings preferably comprises inserting the stub in the direction of the axis of rotation of the blade to allow for a simple method of assembly.

The supporting of each blade on the hub may comprise fixing a plurality of detachable stubs to a hub core to make assembly of the rotor easier.

In one example, the inserting of each stub into its respective pair of annular bearings may comprise inserting the stub into a collar.

The method also offers the possibility of fixing a hub to a wind turbine tower and subsequently assembling the wind turbine according to the above method. At present, the fully assembled rotor is lifted onto the tower. This is a complex process using very expensive cranes to move a heavy, physically large and reasonably delicate component into place. If the hub can be put in place before the blades are attached, it is a much simpler task to lift the individual blades into place either using a more basic crane, or a winch at the top of the tower.

The present invention also provides a blade for a turbine rotor comprising a pair of inwardly facing spaced apart annular bearings located within a root end of the blade.

Examples of a rotor for a wind turbine blade will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a schematic cross-section of a prior art

rotor; Fig. 2 is a cross-section through the part labelled as II in Fig. 1; Fig. 3 is a schematic perspective of a rotor showing the various loads on the rotor; Fig 4 is a schematic view of the rotor of the present invention; Fig 5 is a schematic view showing a comparison between a prior art rotor and the rotor of the present invention; Fig 6 is a schematic view of part of the rotor shown in Fig 4; Figs 6A to 6D are schematic cross-sectional views of the rotor shown in Fig 6; and Figs 7A to 7C are schematic views of alternative rotor arrangements according to the present invention.

Throughout this specification, the term distal refers to a part towards the radially outermost edge of the rotor (i.e., towards the tips of the blades), while the term proximal refers to the radially innermost part of the rotor (i.e., towards the centre of the hub).

Figure 4 shows the general layout of a turbine rotor 100. The rotor comprises a hub 20 to which three blades 21 are attached. The rotor is rotatable about a main axis 25 and each of the blades is rotatable about a pitch axis 26 by a respective pitch motor (not shown) in order to optimise the angle of the blade for the prevailing wind conditions.

-10 -Each blade comprises an outer shell 27 which extends to the tip of the blade in order to form the outer profile of the blade.

The blades 21 terminate as with most current art in a substantially cylindrical root end 23 which carries all of the structural loads of the blade. The root end 23 comprises at least two bulkheads 31, 32 which are permanently attached to the root end of the blade. These bulkheads are typically made from fibre reinforced plastic and each support a respective bearing 41, 42.

In the assembled rotor 100 each stub 22 extends into the root end 23 of a respective blade 21. The stubs 22 are received within the respective pairs of bearings 41, 42 in each blade so that the blades 21 are supported on the hub 20. The blades 21 are attached to the stubs 22 via collars (not shown) which connect the inner race of the bearings 41, 42 to the stubs 22. The stubs 22 can be made from metal or fibre reinforced plastic.

The bulkheads 31, 32 and bearings 41, 42 are assembled into the root end 23 of the blade 21 during assembly of the blade. A dummy stub is preferably used to ensure correct alignment.

Figure 5 shows a comparison of a rotor according to the prior art versus the rotor 100 described above. The significant differences are the simplification of the connection by removing a number of the threaded inserts, a reduction in the size of the bearings, a reduction in the thickness of the blade (xl < x) and a reduction in the mass of the blade in this area.

-11 -Figure 6 shows more detail of the turbine rotor 100.

Figure 6A shows the cross-section of the blade 21 at line A-A in Figure 6. As shown in Figure 6A the blade 21 has a conventional wind turbine blade shape which may or may not have a spar and can be of any technology of wind turbine blade construction and design.

Figures 6B and 60 show the cross-sections at lines B-B and 0-0 in Figure 6. As shown in Figure 6B the distal bearing 41 is connected to the distal bulkhead 31 and the distal end of the stub 22 is received within the distal bearing 41. Similarly, the proximal bearing 42 is connected to the proximal bulkhead 32 and the proximal end of the stub 22 is received within the proximal bearing 42. Each bearing 41, 42 comprises an inner race and an outer race. The outer races of the bearings 41, 42 are connected to the respective bulkheads 31, 32 and the inner races of the bearings 41, 42 are connected to the stub 22 via collars (not shown) . The stub 22 is shown in these Figures as solid and cylindrical in cross-section. However, in another example (not shown) the stub may be hollow and any other sectional shape as may be dictated by manufacturing processes and/or structural requirements.

Figure 6C shows the cross-section at line C-C in Figure 6. Figure 6C shows the area between the two bulkheads 31, 32. As shown this section comprises the outer shell 27 of the blade 21 and the stub 22.

Figures 7A to 7C show alternative ways of assembling the rotor 100. The method selected will depend, among other things, on how the blade 21 is constructed and what -12 -materials the blade 21 and hub 20 are made from. Figure 7A shows the general design and layout as described above.

Figure 7B shows an alternative arrangement whereby stubs 22' of hub 20' are detachable from a hub core 19. In this example, the stubs 22' are made from metal and are detachably mounted to the hub core 19 by a number of bolts (not shown) at flanges 17 on the hub core 19 and flange 18 on the stubs 22'. In this example, the stub 22',. bearings 41, 42 and bulkheads 31, 32 are assembled within the blades 21 when they are fabricated to ensure a good connection and tight tolerances. The blades 21 containing the stubs 22' are then connected to the hub by a metallic flange connection 17, 18 which is well known in the art and highly

repeatable.

Figure 70 shows a further alternative arrangement which facilitates the use of metal and composite materials. In this arrangement the stub 22' comprises a male part 50 and a female part 51. The female part 51 is received within the bearings 41, 42 and built into the blade 21 with the bearings 41, 42 and bulkheads 31, 32 when the blade 21 is fabricated. This ensures a good fitting and tolerance in the factory. The female part 51 of the stub 22' is then slid over the male part 50 of the stub during assembly at the wind turbine site and mechanically joined to the male part 50 by a circular ring flange connection between the stub 22' and the female part 51 at the proximal end, or by directly bolting through the female part 50 into the stub 22''.

Although the invention has been described above with reference to wind turbine blades, the turbine rotor design -13 -is also suitable for use in water. For example, in river flow or tidal environments.

Claims

-14 -Claims: 1. A turbine rotor comprising a hub and a plurality of blades, the hub comprising a plurality of stubs for connection to a respective blade, -each blade having a pair of spaced apart annular bearings located within a root end of the blade, each stub protruding into and being rotatably received within the respective spaced apart bearings when the blades are supported on the hub.
2. A wind turbine rotor according to claim 1.
3. A turbine rotor according to claim 1 or 2, wherein the spacing between bearings is at least lm.
4. A turbine rotor according to claim 3, wherein the spacing between bearings is at least l.5m.
5. A turbine rotor according to any one of the preceding claims having a rotor diameter of at least 45m.
6. A turbine rotor according to any one of the preceding claims wherein the hub comprises a hub core to which the stubs are detachably mounted.
7. A turbine rotor as claimed in any one of the preceding claims, wherein each bearing comprises an inner race and a complementary outer race, each stub fitting into the inner race of its two respective bearings so as to rotate together with the inner race.
8. A turbine rotor according to any one of claims 1 to 6, wherein each blade further comprises a collar rotatably -15 -received within the spaced apart bearings, each respective stub being received within and connected to the collar.
9. A turbine rotor as claimed in any one of the preceding claims, wherein the stubs and bearings are configured to allow each blade to be slid onto and off of the hub along the respective axis of rotation of the blade.
10. A method of assembling a turbine rotor as claimed in any one of the preceding claims, the method comprising assembling each blade with the pair of annular bearings in each respective root end; inserting each stub into its respective pair of annular bearings; and supporting each blade on the hub.
11. A method as claimed in claim 10, wherein the inserting of each stub into its respective pair of annular bearings comprises inserting the stub in the direction of the axis of rotation of the blade.
12. A method as claimed in claim 10 or 11, wherein the supporting of each blade on the hub comprises fixing a plurality of detachable stubs to a hub core.
13. A method as claimed in any one of claims 10 to 12, wherein the inserting of each stub into its respective pair of annular bearings comprises inserting the stub into a collar.
14. A method of assembling a wind turbine comprising fixing a hub to a wind turbine tower and subsequently assembling the wind turbine according to the method of any one of claims 10 to 13.

-16 -
15. A turbine rotor according to claim 1 suitable for use in water.
16. A blade for a turbine rotor comprising a pair of inwardly facing spaced apart annular bearings located within a root end of the blade.