WO2018215037A1

WO2018215037A1 - Blade with pre-deflection for downwind type wind turbine

Info

Publication number: WO2018215037A1
Application number: PCT/DK2018/050111
Authority: WO
Inventors: Søren HJORT
Original assignee: Envision Energy Denmark ApS
Current assignee: Envision Energy Denmark ApS
Priority date: 2017-05-22
Filing date: 2018-05-18
Publication date: 2018-11-29
Anticipated expiration: 2019-11-22
Also published as: DK179472B1; DK201770364A1

Abstract

Blade with pre-deflection for downwind type wind turbine, where the blade has a radial proximal end portion, a radial distal end portion, and an intermediate portion which extends between the radial proximal end portion and the radial distal end portion, and where at least part of the intermediate portion of the blade is pre-deflected such that in an unloaded state, at least part of the blade is curved away from an imaginary pitch axis, connecting the radial proximal end portion and the radial distal end portion, where the pre-deflection shift curvature sign, from a first curvature to a second curvature, at an inflection point at the intermediate portion, whereby it is achieved that the pre-deflection radial distribution on a downwind turbine blade ensures sufficient tip-tower clearance and that the deflected blade is perpendicular to the wind passing through the rotor under loaded, power-producing conditions.

Description

Blade with pre-deflection for downwind type wind turbine Field of the Invention

The present invention relates to a blade with pre-deflection for downwind type wind turbine, where the blade has a radial proximal end portion being the root of the blade configured to be fixed to a hub, a radial distal end portion being the tip of the blade, and an intermediate portion which extends between the radial proximal end portion and the radial distal end portion, and where at least part of the intermediate portion of the blade is pre-deflected such that in an unloaded state, at least part of the blade is curved away from an imaginary pitch axis, connecting the radial proximal end portion and the radial distal end portion.

The invention further relates to the use of a blade with pre-deflection. Background of the Invention

During the last 5 decades, wind turbines have experienced a tremendous continuous growth, both in size and product volume. For reasons of aesthetics and low noise emission, the all dominating rotor configuration type has been upwind - not downwind, meaning that the rotor is upwind of the wind turbine tower during normal operation. The upscale of wind turbines have enabled a steady reduction of Cost-of-Energy (CoE), and the largest wind turbine blades are now approaching lengths of 100m. This poses many practical challenges. One of these challenges is the problem of the blades becoming so long and flexible that the dynamic blade deflections during wind turbine operation jeopardize the clearance between the blade tip and the turbine tower.

For many years, preventive design steps have been quite successful:

Increasing the overhang between the nacelle hub and the tower.

Increasing the cone angle between the rotor plane and the pitch axis.

Increasing the blade upstream pre-deflection.

Increasing blade stiffness by using thicker aerodynamic profiles.

Increasing blade stiffness by adding extra structural material with the sole purpose of reducing tip deflection. 6. Change to a stiffer Fibre-Reinforced-Plastic (FRP) material, e.g. from glass- fibre to carbon-fibre.

Common for the above preventive steps are that they either induce higher mechanical loads (1., 2., 4. and 5.), higher material cost (4., 5.), or impose manufacturing and transport related challenges (3.).

During the last decade, and due to the continued upscaling, the use of these preventive steps to secure sufficient tip-tower clearance is not always enough, especially if the use of carbon-fibre (6.) is not favoured for reasons of cost and/or manufacturing complexity. Consequently, some wind turbine manufacturers have been forced to use the tip- tower preventive steps 1.-5. excessively to the point where the aerodynamic efficiency is clearly compromised and the blade cost of material is clearly increased, both having an unfavourable impact on CoE.

From EP 2447523 Al a wind power generator is known where the blade geometry only works in combination with coning, since the applied pre-deflection is uniform with same side curvature from root to tip.

Object of the Invention

With the continuing upscale wind turbine size, there is a need for a technology change that somehow alleviates the need for excessive use of the preventive steps 1.-6. and associated adverse impact on CoE. One example of such a technology change is the use of downwind configured wind turbines, i.e. with the rotor being downwind of the wind turbine tower during normal operation. An object of the invention is the ad- vantage of a downwind turbine, which is the significantly reduced design constraint of securing sufficient tip-tower clearance, since the aerodynamic forces tend to push the rotating blade away from the tower - not towards it.

A blade designed for downwind configuration - i.e. a downwind blade - should be differently shaped than a traditional upwind blade. The difference concerns the so- called pre-deflection shape of the blade. The pre-deflection is the radial distribution of the non-pitched blade's out-of-plane distance to the pitch axis. Pre-deflection was not necessary on old small wind turbine blades. On modern conventional upwind turbines, the pre-deflection radial distribution is always upstream away from the tower. Modern downwind turbines are not common, so no preferred method for applying pre- deflection has been established. Another object of the invention is the pre-deflection radial distribution on a modern downwind turbine blade that should be designed with the following requirements in mind: a. The pre-deflection must help ensure sufficient tip-tower clearance.

b. The pre-deflection must be such that the deflected blade is perpendicular to the wind passing through the rotor under loaded, power-producing condi- tions.

These requirements are the same as for a conventional upwind turbine, but will for a downwind turbine lead to a different, unique optimal shape of the pre-deflection radial distribution.

On a traditional upwind turbine, requirements a. and b. are both satisfied by applying the blade pre-deflection such that the radial distribution span from root to tip of said pre-deflection curves uniformly upstream, i.e. away from the tower. If this type of pre-deflection, with uniform upstream curvature, is used on a downwind turbine, then requirement b. is satisfied, but certainly not requirement a. If the opposite type of pre-deflection, with uniform downstream curvature, was used on a downwind turbine, then requirement a. would be satisfied, but not requirement b. Therefore, pre-deflection curvature on a downwind turbine should not be monotone, i.e. with same sign curvature from root to tip, but should change curvature direction, i.e. sign of curvature, at a certain radial location between root and tip. Geometrically, according to definition, a point on a curve, where the curvature shifts sign, is an inflection point.

A wind turbine blade pre-deflection curve, seen from root to tip, which curves downstream, i.e. away from the tower, on the inner part of the blade, and then flips sign of curvature at a radial position, say at the 50% between root and tip, and then curves upstream towards the tower on the remaining outer section of the blade, will be able to satisfy both requirement a. and requirement b.

The key to obtaining both requirement a. and b. on a downwind turbine is to abstain from the uniform curvature pre-deflection, and introduce an inflectional point where the pre-deflection curvature shifts sign from downwind curvature to upwind curvature.

Description of the Invention

According to a first aspect of the invention, the above object is achieved with a blade with pre-deflection for downwind type wind turbine of the type mentioned in the in- troduction, where the blade has a radial proximal end portion being the root of the blade configured to be fixed to a hub, a radial distal end portion being the tip of the blade, and an intermediate portion which extends between the radial proximal end portion and the radial distal end portion, and where at least part of the intermediate portion of the blade is pre-deflected such that in an unloaded state, at least part of the blade is curved away from an imaginary pitch axis, connecting the radial proximal end portion and the radial distal end portion, and where the pre-deflection shift curvature sign, from a first curvature closest to the proximal end to a second curvature closest to the distal end, at an inflection point at the intermediate portion between the proximal end portion and the radial distal end portion.

This makes it possible to fulfil the overall objects of the invention, where the advantage is the significantly reduced design constraint of securing sufficient tip- tower clearance, since the aerodynamic forces tend to push the rotating blade away from the tower - not towards it.

A curvature in this aspect means any geometrical shape, from a straight line/shape via a curvature with a constant radius to a curvature with change- able radii. The cylindrical section span adjacent to the root is normally straight, i.e. with zero curvature. In that case the monitoring of curvature, inflection point, and opposite-signed curvature starts at the radial point where the straight section adjacent to the root ends. In a second aspect, the present invention also relates to a blade with pre-deflection, where the inflection point is positioned between the proximal end portion and the radial distal end portion, where the first curvature makes up 20-70 %, preferably 35-60 % and even further preferably 50 % of the intermediate portion.

This makes it possible to vary the percentage depending on the requirements for the specific blade for a specific wind turbine setup, i.e.:

Tip-tower clearance constraint.

Blade flexibility.

In a third aspect, the present invention also relates to a blade with pre-deflection, where the first curvature pre-deflection shape and the second oppositely signed curvature pre-deflection shape are different. This makes it possible to further vary the form and shape of the blade, where the blade does not have similar curves or monotone curves, but curves with different shape/form/radii, etc.

In a fourth aspect, the present invention also relates to a blade with pre-deflection, where the first curvature is configured to curve upstream towards a tower when fixed to a hub at a wind turbine, and the second curvature is configured to curve downstream away from a tower when fixed to a hub at a wind turbine.

In a fifth aspect, the present invention also relates to a blade with pre-deflection, where the first curvature is configured to curve downstream away from a tower when fixed to a hub at a wind turbine, and the second curvature is configured to curve upstream towards a tower when fixed to a hub at a wind turbine.

With the fourth and fifth aspect it becomes possible to construct, produce and conduct a blade with an S-shape or mirror image S-shape, when looking at the blade from the leading edge or the trailing edge along the chord line. Thus, it becomes possible to define a first curvature which is in one direction, and hence a second curvature which is then in the opposite direction. In a sixth aspect, the present invention also relates to a blade with pre-deflection, where the radial distal end portion being the tip of the blade is positioned upstream in relation to the imaginary pitch axis, when the radial proximal end portion, being the root of the blade, is fixed to a hub.

In a seventh aspect, the present invention also relates to a blade with pre-deflection, where the radial distal end portion, being the tip of the blade, is positioned at the imaginary pitch axis, when the radial proximal end portion being the root of the blade is fixed to a hub.

In an eight aspect, the present invention also relates to a blade with pre-deflection, where the radial distal end portion, being the tip of the blade, is positioned downstream in relation to the imaginary pitch axis, when the radial proximal end portion, being the root of the blade, is fixed to a hub.

With the sixth, seventh and eighth aspects it is possible to construct, produce and conduct a blade with pre-deflection suitable for any purpose, need and situation, where the impact, according to the influence of aerodynamics, is taken into account.

In a ninth aspect, the present invention also relates to a use of a blade with pre- deflection, for downwind type wind turbine.

Description of the Drawing

The invention will be described in further detail below by means of non-limiting embodiments with reference to the drawing, in which:

Fig. 1 shows an upwind type wind turbine.

Fig. 2 shows a downwind type wind turbine.

Fig. 3 shows a schematic view of a blade with pre-deflection for a downwind type wind turbine according to the invention.

Fig. 4 shows a schematic view of a blade with an S-shape pre-deflection for a downwind type wind turbine according to the invention.

Fig. 5 shows a schematic view of a blade with a mirror image S-shape pre- deflection for a downwind type wind turbine according to the invention. Fig. 6-9 shows examples of downwind type wind turbines with blades with pre- deflections according to the invention.

In the drawings, the following reference numerals have been used for the designations used in the detailed part of the description:

1. Wind turbine

2. Tower

3. Foundation

4. Nacelle

5. Hub

6. Wind turbine blade

7. Radial proximal end portion/the root of the blade

8. Radial distal end portion / the tip of the blade

9. Blade with pre-deflection

10. Intermediate portion

11. Pre-deflection

12. Imaginary pitch axis

13. First curvature

14. Second curvature

15. Inflection point

16. Wind direction

17. Third curvature

Detailed Description of the Invention

In figure 1 a typical upwind type wind turbine 1 is seen comprising a tower 2 installed at a foundation 3. At the top of the tower 2, a nacelle 4 comprising e.g. a gearbox, a generator and other components is seen, where the mentioned components are covered by a nacelle cover. At the nacelle 4, there is also installed a shaft for carrying a rotor comprising a hub 5 and two wind turbine rotor blades 6. The rotor blades 6 are ar- ranged at the hub 5 at a radial proximal end portion 7 called the root of the blade 6. The second end 8 of the rotor blades 6 constitutes a tip end. The wind direction 16 is shown and indicated at the figure with a number of arrows. In figure 2 a downwind type wind turbine 1 is seen comprising a tower 2 installed at a foundation 3. At the top of the tower 2, a nacelle 4 comprising e.g. a gearbox, a generator and other components is seen, where the mentioned components are covered by a nacelle cover. At the nacelle 4, there is also installed a shaft for carrying a rotor com- prising a hub 5 and two wind turbine rotor blades 6. The rotor blades 6 are arranged at the hub 5 at a radial proximal end portion 7 called the root of the blade 6. The second end 8 of the rotor blades 6 constitutes a tip end. The wind direction 16 is shown and indicated at the figure with a number of arrows. In figure 3 a blade with pre-deflection 9 for a downwind type wind turbine is seen, where the blade 6 has a radial proximal end portion 7 being the root of the blade configured to be fixed to a hub 5, a radial distal end portion 8 being the tip of the blade 6, and an intermediate portion 10 which extends between the radial proximal end portion 7 and the radial distal end portion 8, and where at least part of the intermediate portion 10 of the blade 6 is pre-deflected such that in an unloaded state, at least part of the blade 6 is curved away from an imaginary pitch axis 12, connecting the radial proximal end portion 7 and the radial distal end portion 8 where the pre-deflection 11 shift curvature sign, from a first curvature 13 closest to the radial proximal end 7, to a second curvature 14 closest to the radial distal end 8, at an inflection point 15 at the in- termediate portion 10 between the radial proximal end portion 7 and the radial distal end portion 8.

The figure also shows that the radial distal end portion 8, being the tip of the blade 6, are positioned: upstream (dotted line) in relation to the imaginary pitch axis 12; at the imaginary pitch axis 12 and downstream (dotted line) in relation to the imaginary pitch axis 12, when the radial proximal end portion 7, being the root of the blade 6, is fixed to a hub 5.

Figure 3 also shows that the inflection point 15 is positioned between the proximal end portion 7 and the radial distal end portion 8, where the first curvature 13 makes up a smaller part of the blade 6 than the second curvature 14.

Figure 4 and figure 5 shows that the inflection point 15 is positioned right between the proximal end portion 7 and the radial distal end portion 8, where the first curvature 13 makes up approximately the same part of the blade 6 as the second curvature 14. However, the figures are examples and the first curvature 13 could in fact make up 20- 70 %, preferably 35-60 % and even further preferably 50 % of the intermediate portion 10.

In fig. 4 a blade with a S-shape pre-deflection for a downwind type wind turbine according to the invention and in fig. 5 a blade with a mirror image S-shape pre- deflection for a downwind type wind turbine according to the invention. The figures thus shows, that the first curvature 13 pre-deflection shape and the second oppositely signed curvature 14 pre-deflection shape are different.

Where figure 4 shows that the first curvature 13 is configured to curve upstream towards a tower 2 when fixed to a hub 5 at a wind turbine 1 and the second curvature 14 is configured to curve downstream away from a tower 2 when fixed to a hub 5 at a wind turbine 1, figure 5 shows that the first curvature 13 is configured to curve downstream away from a tower when fixed to a hub at a wind turbine, and the second curvature is configured to curve upstream towards a tower when fixed to a hub at a wind turbine.

Figures 6 to 9 shows different examples of downwind type wind turbines 1 with blades 6 with pre-deflections 11 according to the invention. All figures basically show a downwind type wind turbine 1 as shown in figure 2 with blade with pre-deflection 9 as shown in figure 3.

Hence, the figures show a downwind type wind turbine 1 comprising a tower 2 installed at a foundation 3. At the top of the tower 2, a nacelle 4 comprising e.g. a gearbox, a generator and other components is seen, where the mentioned components are covered by a nacelle cover. At the nacelle 4, there is also installed a shaft for carrying a rotor comprising a hub 5 and two wind turbine rotor blades 6. The rotor blades 6 are arranged at the hub 5 at a radial proximal end portion 7 called the root of the blade 6. The second end 8 of the rotor blades 6 constitutes a tip end. The wind direction 16 is shown and indicated at the figure with a number of arrows. The figures likewise shows rotor blades 6 with pre-deflection 9, where the blades 6 has a radial proximal end portion 7 being the root of the blade configured to be fixed to a hub 5, a radial distal end portion 8 being the tip of the blade 6, and an intermediate portion 10 which extends between the radial proximal end portion 7 and the radial distal end portion 8, and where at least part of the intermediate portion 10 of the blade 6 is pre-deflected such that in an unloaded state, at least part of the blade 6 is curved away from an imaginary pitch axis 12, connecting the radial proximal end portion 7 and the radial distal end portion 8 where the pre-deflection 11 shift curvature sign, from a first curvature 13 closest to the radial proximal end 7, to a second curvature 14 closest to the radial distal end 8, at an inflection point 15 at the intermediate portion 10 between the radial proximal end portion 7 and the radial distal end portion 8.

Figure 6 shows that the radial distal end portion 8, being the tip of the blade 6, is positioned upstream in relation to the imaginary pitch axis 12; figure 7 shows that the ra- dial distal end portion 8, being the tip of the blade 6, is positioned at the imaginary pitch axis 12 and figure 8 shows that the radial distal end portion 8, being the tip of the blade 6, are positioned downstream in relation to the imaginary pitch axis 12, where the radial proximal end portion 7, being the root of the blade 6, is fixed to a hub 5. The figures also shows that the inflection point 15 is positioned between the proxi- mal end portion 7 and the radial distal end portion 8, where the first curvature 13 makes up a smaller part of the blade 6 than the second curvature 14.

Figure 9 shows an example of a downwind type wind turbine 1 with blades 6 with pre- deflections 11 according to the invention. The figure basically shows a downwind type wind turbine 1 as shown at figure 2 with blades with pre-deflection 9 as shown in figure 3, but where the figure shows one inflection point 15 positioned between the proximal end portion 7 and the radial distal end portion 8, where the first curvature 13 makes up a smaller part of the blade 6 than the second curvature 14 and an inflection point 15 also positioned between the proximal end portion 7 and the radial distal end portion 8, but at a point where a third curvature 17 makes up a smaller part of the blade 6 than the second curvature 14.

Claims

1. Blade with pre-deflection for downwind type wind turbine, where the blade has a radial proximal end portion being the root of the blade configured to be fixed to a hub, a radial distal end portion being the tip of the blade, and an intermediate portion which extends between the radial proximal end portion and the radial distal end portion, and where at least part of the intermediate portion of the blade is pre-deflected such that in an unloaded state, at least part of the blade is curved away from an imaginary pitch axis connecting the radial proximal end portion and the radial distal end portion characterized in that the pre-deflection shift curvature sign, from a first curvature closest to the proximal end to a second curvature closest to the distal end, at an inflection point at the intermediate portion between the proximal end portion and the radial distal end portion.

2. Blade with pre-deflection according to claim 1, characterized in that the inflection point is positioned between the proximal end portion and the radial distal end portion, where the first curvature makes up 20-70 %, preferably 35-60 % and even further preferably 50 % of the intermediate portion.

3. Blade with pre-deflection according to any of claims 1 and 2, characterized in that the first curvature pre-deflection shape and the second oppositely signed curvature pre-deflection shape are different.

4. Blade with pre-deflection according to any of the claims 1 to 3 characterized in that the first curvature is configured to curve upstream towards a tower when fixed to a hub at a wind turbine, and the second curvature is configured to curve down- stream away from a tower when fixed to a hub at a wind turbine.

5. Blade with pre-deflection according to any of the claims 1 to 3, characterized in that the first curvature is configured to curve downstream away from a tower when fixed to a hub at a wind turbine and the second curvature is configured to curve upstream towards a tower when fixed to a hub at a wind turbine.

6. Blade with pre-deflection according to any of the claims 1 to 5, characterized in that the radial distal end portion, being the tip of the blade, is positioned upstream in relation to the imaginary pitch axis, when the radial proximal end portion, being the root of the blade, is fixed to a hub.

7. Blade with pre-deflection according to any of the claims 1 to 5, characterized in that the radial distal end portion, being the tip of the blade, is positioned at the imaginary pitch axis, when the radial proximal end portion, being the root of the blade, is fixed to a hub.

8. Blade with pre-deflection according to any of the claims 1 to 5, characterized in that the radial distal end portion, being the tip of the blade, is positioned down- stream in relation to the imaginary pitch axis, when the radial proximal end portion, being the root of the blade, is fixed to a hub.

9. Use of blade with pre-deflection according to any of the claims 1 to 8, for downwind type wind turbine.