WO2012113400A2

WO2012113400A2 - A wind turbine blade

Info

Publication number: WO2012113400A2
Application number: PCT/DK2012/050037
Authority: WO
Inventors: Peter Grabau; Michael Friedrich
Original assignee: Envision Energy (Denmark) Aps
Priority date: 2011-02-23
Filing date: 2012-01-27
Publication date: 2012-08-30
Also published as: DK201170097A; DE212012000014U1; CN203230534U; WO2012113400A3; DK201300035Y4; DK201300035U1

Abstract

A partial pitch wind turbine blade is described wherein a stall fence is provided at the partial pitch junction of the blade. The stall fence provides for the separation of the airflow between the inner blade section and the outer blade section, and furthermore can be used to seal the gap at the pitch system junction between the two blade sections.

Description

A Wind Turbine Blade

Field of the Invention

The present invention relates to a wind turbine blade, in particular a partial pitch wind turbine blade.

Background of the Invention

A partial pitch blade is a particular design of rotor blade for a wind turbine. A partial pitch blade generally comprises an inner and an outer blade section, the blade further comprising a pitch system, which allows for the outer blade section to be pitched relative to the inner blade section. The pitch angle of the outer blade section can be varied, in order to control the wind turbine operation.

With reference to Fig. 1, an enlarged view of the pitch junction section of a partial pitch wind turbine blade is shown. The partial pitch blade 10 comprises an inner blade extender (also called a hub extender) and which herein is referred to as inner blade sec- tion 12, which can be coupled to the rotor hub of a wind turbine (not shown). A pitch system 14 is provided at the distal junction end 12a of the blade section 12. The partial pitch blade 10 further comprises an outer blade section 16, an inner junction end 16a of the outer blade section 16 mounted to the pitch system 14, such that the blade section 16 is pitchable relative to said blade section 12. A gap 18 is defined between the re- spective junction ends 12a, 16a of the inner blade section 12 and the outer blade section 16 to allow for the relative pitching of the blade sections. Fig. 2 shows, in cross- section, the aerodynamic profile seen at the junction of the pitch system 14. The aerodynamic profile comprises a leading edge 20 and a trailing edge 22, the pitch system 14 provided at said leading edge 20. The profile further comprises an upper suction side 24 and a lower pressure side 26. As air moves about the profile of the blade 10, the upper suction side 24 is maintained at a lower air pressure than the lower pressure side 26, consequently generating lift in the direction of the suction side 24. This lift is used to drive an electric generator to provide the power output of a wind turbine. One example is disclosed in US 2009 0148285, which discloses a wind turbine blade with an inner section and an outer section. The presence of the gap 18 at the pitch junction reduces the overall efficiency of the partial pitch blade 10, as it introduces tip losses due to the break in the body of the blade 10 at the gap 18, and also allows for the leakage of air from the pressure side 26 to the suction side 24, thereby reducing the lift generated by the blade 10.

Although it is known to apply barriers or stall fences to wind turbine blades in order to reduce the effect of airflow along the length of the blade itself, for example US 7,585, 157. However, such barriers are simply attached to a continuous surface of the blade, and are not suitable for use in the region of a pitch junction of a partial pitch blade, which comprises a gap in the blade surface. As such these stall fences do not provide optimal an aerodynamic flow over each blade section nor do they provide any indications as how to provide means to fill a gap. It is an object of the invention to provide a partial pitch wind turbine blade construction having improved efficiency of operation, both in connection with the pitch system joint and for the overall blade.

Summary of the Invention

Accordingly, there is provided a partial pitch wind turbine blade comprising:

an inner blade section having an inner hub end and an outer blade end;

an outer blade section having an inner end and an outer tip end, said outer blade section pitchable relative to said inner blade section, wherein said blade further comprises at least one stall fence provided at the pitch junction interface between the outer blade end of said inner blade section and the inner section end of said outer blade section.

The use of a stall fence at the pitch junction of a partial pitch rotor blade prevents lateral airflow on the partial pitch blade between the inner blade section and the outer blade section. As the inner blade section and the outer blade section are formed as separate blade sections and are separated aerodynamically, this allows for the different sections of the blade to be specifically configured for separate functions, without con- cern for the impact of lateral airflow between sections along the blade body. Accordingly, the efficiency of each separate section of the blade can be maximised.

Preferably, said inner blade section comprises a stall-controlled blade profile and said outer blade section comprises a pitch-controlled blade profile.

As the different sections of the rotor blade have different aerodynamic profiles, one being selected for pitch control, the other for stall control, the airflow about the different sections can be isolated from one another. This can be useful for example in pre- venting early stall of the pitch-controlled outer blade section.

Preferably, said at least one stall fence extends across at least a portion of said pitch junction interface. The pitch junction interface refers to the area between the inner blade section and the outer blade section wherein the pitch system is normally exposed, and wherein a gap may be defined between portions of the blade section and the outer blade. As the stall fence extends across at least a portion of the pitch junction section, this acts to reduce leakage of air between the suction side and the pressure side of the partial pitch blade through this pitch junction section.

Preferably, said at least one stall fence substantially covers said pitch junction section.

As the stall fence mostly covers the pitch junction, this would hopefully eliminate any tip losses or air leakage at the pitch junction interface.

Preferably, said at least one stall fence projects at an oblique angle from the surface of said partial pitch rotor blade. In order to ensure that the stall fence covers the pitch junction interface, the stall fence is angled relative to the surface of the blade, to extend out over the pitch junction. Preferably, said at least one stall fence projects at an angle of between 100° to 135° relative to the surface of the partial pitch rotor blade.

In one embodiment, said partial pitch rotor blade comprises a first stall fence extending from said inner blade section at said outer blade end and a second stall fence extending from said outer blade section at said inner end, said first and second stall fences abutting one another at said pitch junction interface to form a combined stall fence barrier at said pitch junction interface. In this embodiment, a projecting collar is provided at the pitch system end of both of the inner blade section and the outer blade section. The collars effectively join together at the pitch junction, and accordingly form a stall fence between the blade extender and the outer blade section. Preferably, said first stall fence abuts said second stall fence to form a substantially A- shaped stall fence barrier at said pitch junction interface.

Preferably, said partial pitch blade further comprises a resilient filler material provided between said first stall fence and said second stall fence.

As the second stall fence must be able to pitch relative to the first stall fence, the two fences might not be touching one another, e.g. to prevent frictional damage between the stall fences during pitching. In such a situation, a resilient filler material can be provided between the stall fences, to allow the stall fences to move relative to one another, and to absorb the impact of any possible bending or deflection of the stall fences during use.

Preferably said filler material is formed from at least one of the following: rubber, plastics, foam, an inflatable article.

Preferably, said at least one stall fence provides a seal about said pitch junction section. As the stall fence provides a seal about the pitch junction, this can help to prevent the ingress of dirt and/or moisture into the pitch system, where it may damage or impede the workings of the pitch system. In one embodiment, said at least one stall fence is provided on the upper suction side of said partial pitch rotor blade. Alternatively, said at least one stall fence is provided on the upper suction side and the lower pressure side of said partial pitch rotor blade.

The stall fence may be provided on one side of the blade, or on both sides of the blade, depending on requirements.

It will be understood that said at least one stall fence may be formed integrally with the body of either said inner blade section or said outer blade section. Alternatively, said at least one stall fence may be mounted to said outer blade end of said inner blade section and/or the inner end of said outer blade section. The stall fence may be mounted using any suitable mounting means, e.g. bolts, adhesives, etc.

In one embodiment, said partial pitch blade comprises at least one plate member extending from said pitch system, said plate member extending proud of the external sur- face of the adjacent blade sections.

In some systems, the stall fence may be formed by a plate member which can be coupled to the pitch system. Such an approach may result in relatively easier construction methods, as no alteration needs to be performed to the inner blade section or to the outer blade section. Consequently, existing blade sections (which benefit from existing extensive testing, modelling and simulation) may be used in the system of the invention, with the only adjustment to the system occurring at the pitch system.

Preferably, said at least one plate member projects from the surface of said pitch sys- tern. In this case, the pitch system can be manufactured to comprise a projecting plate member, or the pitch system can be arranged to receive a projecting plate member, in order to form the stall fence of the invention. Alternatively, said at least one plate member is mounted between said pitch system and at least one of said inner blade section and said outer blade section.

The advantage of this approach is that no alteration needs to be performed on existing partial pitch blade components, the stall fence being formed by introducing said plate member into the connection between the pitch system and one of the blade sections.

Preferably, said at least one stall fence comprises a conductive material.

Preferably, said at least one stall fence comprises a lightning receptor. Preferably, said lightning receptor is provided at the distal end of said stall fence.

As the stall fence projects away from the surface of the partial pitch rotor blade, it is a prime target for a lightning strike. The provision of a lightning receptor on the stall fence, preferably at the highest point of the stall fence, ensures that any lightning strike may be received by the blade at the most likely strike point. This is particularly advantageous in the case of two-bladed wind turbines, when the blades are in a substantially horizontal position.

It will be understood that the blade may further comprise conducting means coupled to said at least one stall fence, said conducting means operable to conduct a lightning strike from said stall fence to the inner hub end of said inner blade section.

The conductor can act to direct the lightning strike through the partial pitch blade to the hub end of the blade, wherein the conductor may be coupled to further conduction means in the wind turbine tower for adequately dealing with a lightning strike.

Preferably, said at least one stall fence forms a Faraday cage about said pitch system. As the stall fence may form a Faraday cage at the pitch junction interface, it can act to prevent damage to the contained pitch system due to lightning strikes. In the case where the partial pitch blade comprises a pair of stall fences abutting one another to form a combined stall fence barrier at the pitch junction interface, said stall fences may be conductively coupled together to form said Faraday cage. For example, said coupling may be in the form of a split ring connection.

There is further provided a partial pitch wind turbine comprising at least two of said partial pitch blades. Description of the Invention

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a pitch junction section of a partial pitch rotor blade;

Fig. 2 is a cross-sectional view of the aerodynamic profile of the blade of Fig. i ;

Fig. 3 is a perspective view of a pitch junction section of a first embodiment of partial pitch rotor blade according to the invention;

Fig. 4 is a plan view of the pitch junction section of Fig. 3;

Fig. 5(a)-(c) shows cross-sectional views of different embodiments of the rotor blade with a stall fence according to the invention;

Fig. 6 is a plan view of a pitch junction section of a further embodiment of partial pitch rotor blade according to the invention;

Fig. 7 is a plan view of a pitch junction section of a further embodiment of partial pitch rotor blade according to the invention; and

Fig. 8 is a perspective view of the partial pitch rotor blade of Fig. 7.

With reference to Figs. 3 and 4, a partial pitch wind turbine blade according to the in- vention is indicated generally at 50. The partial pitch blade 50 comprises an inner blade section (also called a hub extender) 52, which can be coupled to the rotor hub of a wind turbine (not shown). A pitch system (not shown) is provided at the distal junction end 52a of the inner blade section 52. The partial pitch blade 50 further comprises an outer blade section 54, an inner junction end 54a of the outer blade section 54 mounted to the pitch system, such that the blade section 54 is pitchable relative to said inner blade section52.

The partial pitch blade 50 further comprises a stall fence 56 provided at the pitch system junction between the distal junction end 52a of the inner blade section 52 and the inner junction end 54a of the outer blade section 54. The stall fence 56 projects about the surface of the inner blade section 52 and the outer blade section 54, providing a barrier between the two sections of the partial pitch blade 52,54.

As the stall fence is provided at the pitch system junction, the aerodynamic flow over the inner blade section 52 is prevented from laterally flowing over the outer blade section 54, and vice versa. Accordingly, the aerodynamic flow over either blade section is separately maintained. As the airflows are separated, this means that the different blade sections 52,54 may be optimised for different operating conditions, wherein the airflow over one section does not affect or impact the airflow over the adjacent section. Preferably, the inner blade section 52 is designed to have a stall-controlled aerodynamic profile (e.g. the aerodynamic profile having a relatively high lift coefficient), and the outer blade section 54 is designed to have a pitch-controlled aerodynamic profile (e.g. the aerodynamic profile having a relatively low lift coefficient) - the inner blade section 52, being rigidly coupled to the rotor hub, is configured as a stall-controlled blade, while the outer blade section 54 can be pitched using the pitch system to control blade operation, and can be designed accordingly.

As can be seen from Fig. 4, the stall fence 56 projects around and covers the pitch system junction between the two blade sections 52,54. This provides a number of further advantages. Firstly, as any void between the blade sections 52,54 which would normally be present at the junction is covered by the stall fence 56, this prevents the leakage of any air from the lower pressure side of the blade 50 to the upper suction side of the blade 50. Secondly, tip losses as a result of the exposed ends of the trailing edges of the blade sections 52,54 are eliminated. This results in improved efficiency of the wind turbine blade 50, as well as a reduction in the noise pollution due to the pitch system junction.

As the outer blade section 54 is pitchable relative to the inner blade section 52, the stall fence 56 is configured to allow the section to pitch relative to one another. In the embodiment of Fig. 4, the stall fence 56 is a barrier formed by two separate stall fence elements 56a,56b. The first stall fence element 56a projects from the distal junction end 52a of the inner blade section 52, while the second stall fence element 56b projects from the inner junction end 54a of the outer blade section 54. The stall fence elements 56a,56b form a collar about the junction ends 52a,54a of the respective blade sections 52,54, and as the inner blade section 52 and the outer blade section 54 are coupled together via the pitch system, the stall fence elements 56a,56b meet to form the stall fence 56 at the pitch system junction.

The stall fence elements 56a,56b abut each other, to form a substantially closed stall fence structure at the pitch system junction. As the stall fence elements 56a,56b are not directly connected to one another, the second element 56b may be pitched relative to the first element 56a as the outer blade section 54 is pitched. The elements 56a,56b may touch each other, or a filler material (not shown) may be provided between the elements 56a,56b, to provide a seal about the pitch system junction. The filler material may comprise any suitable resilient material, e.g. rubber, foam, plastics, or an inflatable article. As the stall fence elements 56a,56b meet over the pitch system junction, the elements 56a,56b project from the respective junction ends 52a,54a at an oblique angle to the surfaces of the adjacent blade sections 52,54. The angle of projection may be selected based on any number of factors, e.g. the distance between the junction ends 52a,54a, the desired height of the stall fence 56, etc. Preferably, the stall fence elements 56a,56b project at an angle of between 100° to 135° relative to the external surface of the inner blade section 52 and the outer blade section 54 respectively. Such an arrangement provides a stall fence 56 having a substantially A-shaped profile, as can be seen from the plan view of Fig. 4. While in the embodiment shown in Figs. 3 and 4 the entire stall fence elements 56a,56b project at an angle, it will be understood that any suitable shape may be chosen for the elements 56a,56b, wherein only a portion of the elements 56a,56b is angled. It will further be understood that the stall fence 56 may be formed from any suitable arrangement of elements, for example instead of two separate stall fence elements 56a,56b, the stall fence 56 may be formed by a single shaped collar having an A-shaped profile provided at the junction end of either the inner blade section 52 or the outer blade section 54, said single collar forming the entire stall fence 56 and projecting from only one of the blade sections 52,54. Such a setup would provide for a relatively easier construction, as the partial pitch blade 50 only has to be reconfigured at one of said junction ends 52a, 54a, with the remainder of the blade apparatus taken from existing blade components. It will be understood that said stall fence 56 may be provided on said blade sections 52,54 using any suitable means. For example, the stall fence 56 (and/or stall fence elements 56a,56b) may be formed integrally with the body of the blade sections 52,54, or the stall fence 56 may be attached to the junction ends 52a,54a of the blade 50, for example using adhesives, bolting means, etc.

The stall fence 56 may also comprise a conductive element (not shown), wherein the stall fence 56 is conductively coupled to conducting means (not shown) provided in the blade 50. In the event of a lightning strike at the stall fence 56, such a conductive element is operable to conduct the lightning away from the body of the blade sections 52,54 and away from the blade 50 to the main wind turbine construction, which may comprise systems for safely dealing with a lightning strike. Furthermore, the stall fence may comprise at least one lightning receptor provided on the stall fence 56, e.g. at the upper end of the stall fence 56. Such a configuration is particularly advantageous in a two-bladed partial pitch wind turbine, as the stall fence on the blades of a two-bladed turbine will most likely be among the highest points of the turbine when the blades are in a substantially horizontal position. It will be understood that the stall fence 56 may comprise any suitable shape or profile. With reference to Figs. 5(a)-(c), a selection of sample stall fences 56 are shown for a variety of different aerodynamic blade profiles. Fig. 5(a) illustrates a standard airfoil profile having symmetrical camber, with the circular cross-section of the pitch system 58 provided at the leading edge of the blade profile 50, wherein the stall fence extends from the surface of the blade 50 in an equal distance about the blade surface. It can be seen that the stall fence 56 does not extend around the trailing edge of the blade 50, as the airflow at this point does not need to be separated. Fig. 5(b) shows an airfoil profile having increased camber, wherein the stall fence 56 again projects an equal distance above the surface of the blade 50, about the blade profile, but not at the extreme trailing edge of the profile.

Fig. 5(c) shows an airfoil profile having further increased camber, with the pitch system 58 provided towards the centre of the blade profile. In this embodiment, it can be seen that the stall fence 56 has a greater height above the surface of the profile on the pressure side and the suction side of the profile, with the stall fence 56 having a relatively shallow height at the leading edge of the profile. With reference to Fig. 6, a second embodiment of a partial pitch blade is indicated at 60. As before, the partial pitch blade 60 comprises an inner blade section 62 and an outer blade section 64, coupled together via pitch system 66 provided at the distal junction end 62a and the inner junction end 64a of the respective blade sections 62,64. The blade 60 further comprises a stall fence 68 which is provided on the pitch system 66, and which projects beyond the external surface of the adjacent blade sections 62,64.

In this embodiment, the stall fence 68 can be formed integrally with the surface of the pitch system 66, or alternatively may be mounted to the surface of the pitch system 66 using any suitable method, e.g. bolting, adhesives, etc. The stall fence 68 may be formed from a single plate member, or may be formed from two separate plate members abutting one another at the pitch junction, the separate plate members operable to pitch relative to one another via the pitch system 66. With reference to Figs. 7 and 8, a third embodiment of a partial pitch blade is indicated at 70. As with the other embodiments, the partial pitch blade 70 comprises an inner blade section 72 and an outer blade section 74, coupled together via pitch system (76, indicated by outline) provided at the distal junction end 72a and the inner junction end 74a of the respective blade sections 72,74.

The blade 70 further comprises a plate member 78 which is provided at or adjacent the pitch system 76, and which projects beyond the external surface of the adjacent blade sections 72,74. The plate member 78 acts as a stall fence at the pitch junction, between the blade sections 72,74. The plate member 78 may be provided as a single plate, or may be provided as two closely adjacent plates, a first plate coupled to the inner blade section 72 and a second plate coupled to the outer blade section 74. The plate member 78 can be provided on the blade 70 in the coupling between the pitch system 76 and either the inner blade section section 72 or the outer blade section 74, or a pair of plate members may be provided on either side of the pitch system 76. Accordingly, the plate member 78 is arranged to receive the coupling between the pitch system 76 and one or both of the blade sections 72,74. An advantage of the embodiments of Figs. 6-8 is that the blade sections 62,64,72,74 are unaltered, through use of the stall fence 68,78 at the pitch system 66,76. Accordingly, the blade sections do not have to be newly-designed to accommodate the stall fence 68,78, and may be selected from existing blade components, which may benefit from pre-existing extensive testing, modelling and simulation of performance. A further advantage of the embodiment of Figs. 7-8 is that a standard pitch system 76 may be used, with the plate member 78 located at either or both sides of the pitch system 76, and secured via the coupling between the pitch system 76 and the blade sections 72,74.

In the embodiments shown in Figs. 6-8, it can be seen that a space is defined between the stall fence 68,78 and the respective junction ends 62a,64a,72a,74a of the blade sections 62,64,72,74. It will be understood that the stall fence 68,78 may be shaped to substantially fill or cover the area between the junction ends 62a, 64a, 72a, 74a. Additionally or alternatively, a filler material may be provided to substantially fill or cover the spaces between the stall fence 68,78 and the junction ends 62a, 64a, 72a, 74a, the filler material comprising any suitable filler substance, e.g. rubber, foam, plastics, etc.

The partial pitch rotor blade of the invention is suitable for use in any wind turbine comprising a plurality of rotor blades.

The partial pitch rotor blade of the invention provides a partial pitch blade having improved efficiency and performance, for minimal additional design and construction cost.

The invention is not limited to the embodiment described herein, and may be modified or adapted without departing from the scope of the present invention.

Claims

1. A partial pitch wind turbine blade comprising:

an inner blade section having an inner hub end, an outer blade end and having a stall-controlled blade profile;

an outer blade section having an inner blade end, an outer tip end and having a pitch-controlled blade profile,

said outer blade section pitchable relative to said inner blade section, wherein said blade further comprises at least one stall fence provided at the pitch junction interface between the outer blade end of said inner blade section and the inner blade end of said outer blade section

for maintaining a aerodynamic flow over either blade section or for separating the aerodynamic flows on the blade sections.

2. The partial pitch blade of claim 1, wherein said at least one stall fence extends across at least a portion of said pitch junction interface.

3. The partial pitch blade of claim 1 or claim 2, wherein said at least one stall fence substantially covers said pitch junction section.

4. The partial pitch blade of any preceding claim, wherein said at least one stall fence projects at an oblique angle from the surface of said partial pitch rotor blade.

5. The partial pitch blade of any preceding claim, wherein the partial pitch rotor blade comprises a first stall fence extending from said inner blade section at said outer blade end and a second stall fence extending from said outer blade section at said inner section end, said first and second stall fences abutting one another at said pitch junction interface to form a combined stall fence barrier at said pitch junction interface.

6. The partial pitch blade of any preceding claim, wherein said at least one stall fence provides a seal about said pitch junction section.

7. The partial pitch blade of any preceding claim, wherein said at least one stall fence comprises a lightning receptor.

8. The partial pitch blade of any preceding claim, wherein said at least one stall fence forms a Faraday cage about said pitch system.

9. A partial pitch wind turbine comprising at least two partial pitch blades as claimed in any preceding claim.