WO2010031545A2

WO2010031545A2 - A wind turbine component

Info

Publication number: WO2010031545A2
Application number: PCT/EP2009/006698
Authority: WO
Inventors: Yoshiki Haraguchi; Erwin Merijn Wouterson; Chee-Kang Lim; Feng Shen
Original assignee: Vestas Wind Systems A/S
Priority date: 2008-09-19
Filing date: 2009-09-16
Publication date: 2010-03-25
Also published as: GB0817214D0; WO2010031545A3; GB2463675A

Abstract

A wind turbine component surface, and in particular, a wind turbine blade surface (10) comprising neighbouring areas (12,14) of different ice forming propensity in predetermined positions and a method of applying such a surface (10) to a wind turbine component. In use, the difference in ice forming propensity between neighbouring areas (12,14) readily causes ice to fall from the surface (10), and such a surface (10) is simple to apply.

Description

A WIND TURBINE COMPONENT

Background of the invention

The invention relates to a wind turbine component surface, and a method of applying a surface to a wind turbine component. The invention relates, in particular, to a wind turbine blade surface.

Wind turbines are located in windy, exposed locations. Such locations are often cold and as a result wind turbines become covered in ice. The formation of ice is particularly a problem on wind turbine blades. The ice increases the weight and detrimentally affects the aerodynamic performance of the blade. Furthermore, inhomogeneous ice formation across a blade surface can lead to blade imbalance. All of these effects lead to a significant reduction in the efficiency of the wind turbine. As such it is desirable to reduce the amount of ice on wind turbine components and, in particular, wind turbine blades.

Many techniques are known for reducing the formation of ice on wind turbine components, and wind turbine blades, in particular. There are passive systems, which do not require energy to be applied to the wind turbine blades, and active systems, which require energy, and typically electrical energy, to be applied to the wind turbine blades.

A known passive system is to coat the surface of a wind turbine component, such as a blade, all over with ice resistant paint, such as an epoxy or polyurethane paint. These paints are not very effective because as well as ice adhering poorly to them they also adhere poorly to the surface of the wind turbine blade they cover. As such, the ice-resistant paint is soon shed by the turbine blade itself and the ice resistance of the blade is significantly reduced.

International patent application No. WO-A-2006/066593 discloses a passive system in which areas of a wind turbine blade of different levels of ice repellence are coated differently to provide a blade surface that has homogeneous ice repellence across its surface. There are many active systems for reducing ice formation on wind turbine blades. For example, US patent No. US-A-6145787, US patent application No. US-A-2006/0018752, International patent application No. WO-A-00/79128, and International patent application No. WO-A-2006/093480 all disclose systems for heating wind turbine blades to reduce the formation of ice on them. These are discussed in more detail below.

US patent No. US-A-6145787 discloses a wind turbine blade having a number of heated zones spaced apart along it. The heated zones are separated by heated parting strips. This system provides an even distribution of heat along the turbine blade.

International patent application No. WO-A-0079128 also discloses a wind turbine blade with heating elements. The heating elements are made of metal foil and they giving a uniform heating surface of the wind turbine blade. The heating elements are arranged at the front rim of the blade because icing often starts forming there.

An ice management system for a tiltrotor aircraft is disclosed in International patent application No. WO-A-2006/093480, in which each blade of a prop rotor is divided into heating zones each having a separate set of heating elements that can be controlled independently. The same zone is operated on all three blades of the rotor at the same time to avoid imbalance caused by different amounts of ice accumulating on each of the three blades.

US patent application No. US-A-2006/0018752 describes a system for de- icing the leading edge of a wind turbine rotor blade. Heated air is circulated through an outflow channel from the blade root to the blade tip and then recirculated via a return channel from the blade tip to the blade root.

Another active system is the apparatus for de-icing the leading edge of an aircraft airfoil disclosed in US patent No. US-A-5584450. The apparatus comprises electro-expulsive elements spaced apart by filler sections along the leading edge of the airfoil. Electro-expulsive elements are mechanical devices that use interacting magnetic fields to force conductors of the devices apart to deform ice collecting walls of the airfoil to shed ice formed on them. This force is caused by high surface accelerations and displacements developed by the electro-expulsive elements in the element areas adjacent the filler areas.

We are the first to appreciate that a wind turbine component with predetermined neighbouring areas of different ice forming propensity between them effectively causes ice to fall from the surface of the wind turbine component. We are the first to appreciate that a surface of varying ice forming propensity can beneficially produce a turbine blade surface that is particularly able to shed ice formed on it.

Summary of the Invention

The invention in its various aspects is defined in the independent claims below. Advantageous features are defined in the dependent claims below.

According to the invention in a first aspect, there is provided a wind turbine component surface, the surface comprising neighbouring areas of different ice forming propensity in predetermined positions, wherein the difference in ice forming propensity between neighbouring areas causes ice to fall from the surface.

In this way, in use, a large bond variation/instability is created between the two different surfaces or neighbouring areas, which readily causes ice formed on the wind turbine component to be shed. This is particularly the case in heavy icing conditions. Furthermore, such a surface is simple to apply.

Preferably, the surface alternates between an ice-resistant area and an ice- prone area of greater ice forming propensity. Preferably, the ice forming propensity is affected passively and, typically, the ice forming propensity is affected by the surface finish or coating. This results in a very convenient system to implement that has a simple construction and, in use, no power source is required.

Preferably, the surface finish comprises a film or paint. Such an arrangement is quick and low cost to apply.

Preferably, ice-resistant areas are on top of ice-prone areas, and preferably, an ice-prone layer is over substantially the entire surface and ice-resistant layers are over portions of the ice-prone layer. Thus, if the ice-resistant layers partly wear or fall away, the wind turbine component surface remains protected by the ice-prone areas below.

According to the invention in a second aspect, there is provided a method of applying a surface to a wind turbine component, the method comprising applying predetermined areas to a wind turbine component surface such that predetermined neighbouring areas have a different ice forming propensity and the difference in ice forming propensity between neighbouring areas causes ice to fall from the surface.

Preferably, the predetermined areas are defined by a mask. This allows the predetermined pattern to be applied quickly and at low cost. The pattern may be produced by laying a film of ice-resistant material only where there are through holes in the mask. Alternatively, ice-resistant material may be applied over the surface and then chemically etched away where there are through holes in the mask in predetermined locations to produce the desired pattern.

Brief Description of the Drawings

Preferred embodiments of the invention will now be described, by way of example, and with reference to the drawings in which:

Fig. 1 is a side view of a known wind turbine; Fig. 2 is a side view of a wind turbine component illustrating an example implementation of the invention;

Fig. 3 is a cross-section of the wind turbine component of Fig. 2;

Fig. 4 is a side view of a wind turbine component illustrating another example implementation of the invention; and

Fig. 5 is a schematic view illustrating a method of applying a surface to the wind turbine component of Fig. 2 illustrating another example implementation of the invention.

Detailed Description of Preferred Embodiments

Figure 1 illustrates a wind turbine 1 , comprising a wind turbine tower 2 on which a wind turbine nacelle 3 is mounted. A wind turbine rotor 4 comprising at least one wind turbine blade 5 is mounted on a hub 6. The hub 6 is connected to the nacelle 3 through a low speed shaft (not shown) extending from the nacelle front. The wind turbine illustrated in Figure 1 may be a small model intended for domestic or light utility usage, or may be a large model used, such as those that are suitable for use in large scale electricity generation on a wind farm for example. In the latter case, the diameter of the blades could be as large as 100 metres or more.

Figure 2 shows an example of the invention in the form of a wind turbine component surface or blade surface 10 having neighbouring areas 12,14 of different ice forming propensity in predetermined positions. As illustrated in the cross-sectional view of Figure 3, the surface 10 (greatly exaggerated in size in Figure 3) is the outermost portion of the blade 5. It is the portion of the blade directly in contact with the surrounding environment, including the air, wind and ice. It covers the load-bearing element of the blade. The different ice forming propensity or ice forming propensity gradient between neighbouring areas is achieved by selectively coating some areas 12 in an ice resistant material, such as polysilicone or polysiloxane, while leaving other areas 14 without a further coat. In the example of Figure 2, the blade surface alternates between an uncoated area or patch of low ice forming propensity (an ice-resistant surface) 14 and an area or patch of high ice forming propensity (an ice-prone surface) 12 across the entire surface of the blade, to form a checkerboard-like pattern. There are two different surface finishes in small patches one after another, side-by-side both longitudinally and transversally over the surface of the blade.

In use, the ice-prone surface 12 "attracts" and builds-up ice faster than the ice-resistant surface 14. Eventually, the ice growing out from its originated ice-prone surface grows into the ice-resistant surface and this creates an unstable bond to the surface. The instability of the surface bond leads to the ice becoming detached or shed from the surface of the blade 5, for example, due to its gravitational weight, due to the centripetal force as the blade rotates, due to the shear forces as the blade rotates and/or due to the aerodynamic forces as the blade rotates. That is to say, the difference in ice forming propensity between neighbouring areas causes ice to fall from the surface.

The ice resistant surface or surface finish 12,14 is passive; it does not require the input of energy, such as electricity, to the blade 5, to, for example, heat the blade or cause movement of the surface of the blade 10. The passive surface may be made using a film or paint. The ice-resistant surface 14 may include plastics and, in particular, a synthetic plastics, for example, at least one of the following materials: polysilicone; polysiloxane, such as polydimethylsiloxane (PDMS); fluorinated polymer, such as Teflon (registered trade mark) or polytetrafluoroethylene (PTFE); epoxy; and polyurethane. The material types for the surface are selected so that their ice adhesion properties (how quickly ice forms) are at a predetermined level. They are also selected such that the level of shear before ice is shed is at a predetermined level.

In the example of Figure 2, the separate ice-prone 12 and ice-resistant areas 14 are tessellated together. All the areas have the same rectangular shape, and in particular square shape 16, alternating in ice-forming propensity, edge- by-edge, both longitudinally and transversely across the entire blade 5. However, other shapes are possible, such as triangles 18, as illustrated Figure 4. The triangles are equilateral triangles tessellated together.

The illustrated square and triangular areas have a side length of 10cm. However, the sides could have other lengths, such as between 5cm and 20cm.

The shape of the areas of different ice-forming propensity may change across the surface of the blade (not shown). For example, the areas may be one shape at the leading edge of the blade and another shape at the trailing edge of the blade, such as tessellated triangles at the leading edge and tessellated squares at the trailing edge. The different areas may be of shapes other than squares and triangles, particularly between the leading and trailing edges of the blades.

The matrix or tessellated surface 10 is applied by using a mask 20 to select the area to be covered by the ice-resistant coating. The mask 20 is sheet-like and comprises gaps or through holes 22 through it where the ice-resistant coating is desired in predetermined locations. The ice-resistant coating is then applied over the mask, for example, by spraying using sprayer 24 or by brush (not shown). The mask 22 is then removed. The uncoated portion of the blade forms the ice-prone areas.

Ice-resistant areas may be located on top of ice-prone areas; ice-prone areas which also protect the wind turbine component itself. Thus, if the ice-resistant layers partly wear or fall away, the wind turbine component surface remains protected by the ice-prone areas below.

An ice-prone surface finish could also be made by roughening the surface, such as by rubbing with an abrasive material or by chemical etching or other chemical treatment. Alternatively, a particularly ice-resistant surface finish could be made by smoothing the outermost, exposed surface of the blade in predetermined areas. Although the examples are described with particular reference to wind turbine blades, the surface described herein could be applied to any wind turbine component, such as the wind turbine tower 2, hub 6, or wind turbine nacelle 3.

The invention has been described with reference to example implementations, purely for the sake of illustration. The invention is not to be limited by these, as many modifications and variations would occur to the skilled person. The invention is to be understood from the claims that follow.

Claims

1. A wind turbine component surface, the surface comprising neighbouring areas of different ice forming propensity in predetermined positions, wherein the difference in ice forming propensity between neighbouring areas causes ice to fall from the surface.

2. A surface according to claim 1 , wherein the surface alternates between an ice-resistant area and an ice-prone area of greater ice forming propensity.

3. A surface according to claim 1 or claim 2, wherein the ice forming propensity is affected passively.

4. A surface according to claim 1 , 2, or 3, wherein the ice forming propensity is affected by the surface finish or coating.

5. A surface according to claim 4, wherein the surface finish comprises a film or paint.

6. A surface according to claim 4 or 5, wherein ice resistant areas are on top of ice-prone areas.

7. A surface according to any preceding claim, comprising an ice-prone layer over substantially the entire surface and ice-resistant layers over portions of the ice-prone layer.

8. A surface according to claim 7, wherein the ice-resistant layers comprise at least one of the following: polysilicone; polysiloxane, such as polydimethylsiloxane; fluorinated polymer, such as Teflon or polytetrafluoroethylene; epoxy; and polyurethane.

9. A surface according to any preceding claim, wherein the areas comprise sides of length between substantially 5cm and substantially 20cm.

10. A surface according to claim 9, wherein the areas comprise sides of length of substantially 10cm.

11. A surface according to any preceding claim, wherein the neighbouring areas are substantially the same shape.

12. A surface according to any of claims 1 to 10, wherein the neighbouring areas are different shapes.

13. A surface according to any preceding claim, wherein the neighbouring areas are substantially rectangular.

14. A surface according to claim 13, wherein the neighbouring areas are substantially square.

15. A surface according to any preceding claim, wherein the neighbouring areas are substantially triangular.

16. A wind turbine component comprising the surface of any preceding claim.

17. A wind turbine blade comprising the surface of any of claims 1 to 15.

18. A wind turbine blade comprising the surface of any of claims 1 to 10, comprising a leading edge and a trailing edge, wherein the shape of the areas of the leading edge is different to the shape of the areas of the trailing edge.

19. A wind turbine blade according to claim 18, wherein the areas of the leading edge are substantially triangular and the areas of the trailing edge are substantially rectangular, such as substantially square.

20. A method of applying a surface to a wind turbine component, the method comprising applying predetermined areas to a wind turbine component surface such that predetermined neighbouring areas have a different ice forming propensity and the difference in ice forming propensity between neighbouring areas causes ice to fall from the surface.

21. A method according to claim 20, wherein predetermined areas are defined by a mask.

22. A wind turbine component surface made using the method of claim 20 or 21.