IE20120347U1 - Aerofoil blades - Google Patents

Abstract

ABSTRACT An aerofoil blade such as a wind turbine blade 10 has a plurality of dimples 18 distributed over an area of the upper surface of the blade which extends from immediately adjacent to the leading edge 12 of the blade at least partially towards the rear edge 14 of the blade.

Description

Field oftheinvention The present invention is concerned with aerofoil blades (i.e. blades having an aerofoil cross-section), for example as used in wind turbines or the like, and in particular blades having improved flow characteristics, for example reduced boundary layer separation, reduced turbuience, etc.

Background of the invention Aerofoil blades are used in a large number of applications, and in many of those applications it is desirable to improve the efficiency and/or performance of the blade through various means. In one application aerofoil blades are utilised in augmented wind turbine systems, for example comprising a shroud surrounding a set of aerofoil blades such as to take advantage of the higher velocity profile.

By improving the performance and/or efficiency of such blades a greater power output can be achieved and/or the turbines can be located in a more diverse range of locations. it will also be appreciated that the invention can also be used in conventional wind turbine systems or other rotational blade applications.

Summary of the invention According to the invention there is provided an aerofoil blade having a plurality of dimples distributed over an area of the upper surface of the blade which extends from immediately adjacent to the leading edge of the blade at least partially towards the rear edge of the blade.

Preferably, the area of dimples extends along at least a major part of the length of the leading edge ‘ of the blade.

Preferably, the dimples are generally teardrop-shaped with their wider ends facing towards the leading edge of the blade.

Preferably, the dimples vary in distribution density.

Preferably, the dimples vary in depth.

Preferably, the trailing edge of the blade has a localised rearward extension. sl lE12o347ie Preferably, the localised rearward extension is at the free end of the blade.

Preferably, the blade is a wind turbine blade.

Preferably, dimples are also provided on the lower surface of the blade.

Brief description of the drawings Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an embodiment of wind turbine blade according to the invention.

Figure 2 is a schematic partial cross section through the blade of Figure 1.

Figure 3 is a partial top view of the blade of Figure 1.

Figure 4 is a perspective view of a modification of the wind turbine blade of Figure 1.

Detailed description of the drawings Referring to Figures 1 to 3, a wind turbine blade with an aerofoil cross-section comprises an outwardly tapered blade 10 with a leading edge 12, a trailing edge 14 and an outer free end 16. A large number of dimples 18 are distributed over the upper surface 20 of the blade. in this I embodiment the dimples 18 extend fully from the leading edge 12 of the blade to the trailing edge 14, i.e. they cover substantially the entire upper surface 20. in general, however, the dimpled area of the upper surface 12 may extend rean/vardly from immediately adjacent to the leading edge 12 of the blade only partially to the trailing edge 14, preferably at least one quarter the way to the trailing edge.

Also, the dimpled area does not necessarily need to extend along the full length of the leading edge 12 of the blade, although it preferably extends along at least a major part of the length of the leading edge.

In this embodiment the dimples 18-are generally concave teardrop-shaped depressions aligned with their wider ends facing towards the leading edge 12 of the blade, as shown in Figure 3. The dimples 18 are preferably closely spaced, but their distribution density may vary over the dim pied area. The dimples may also vary in depth.

\E1203t7 The dimples 18 can be created directly in the upper surface 20 of the blade, or by using blade protection tape 22 (Figure 2) which is embossed with the teardrop shaped dimples and applied to the upper surface.20. , In the embodiment shown in Figures 1 to 3 the length of the blade 10 was 2.45m with an average chord of 300mrn. The dimples are 15mm long by 9mm wide at their widest part, with a maximum depth of 033mm.

The above turbine blade design serves to accelerate airflow, increase lift and reduce the wake created by the blade. The dimples serve to create a micro-turbulent layer across the blade which in turn causes the wind-force acting on the blade to be greater. The dimples delay boundary layer separation thereby reducing the wake of the blade. The dimples, when in an inverted teardrop shape, may also act as mini—augmenters and give the air direction. The depth, size, shape and distribution density of the dimples may vary with blade characteristics. in a modification of the above embodiment, Figure 4, the trailing edge 14 of the blade 10 has a localised rearward paddle—like extension 24, preferably at its free end 16. The extended paddle-like "tip 24 of the blade serves to increase the surface area. However the dimples can still work effectively on a conventional aerofoil blade which does not have the projection, i.e. as shown in Figure 1.

If desired, similar dimples may be provided on the lower surface of the blade (not shown), again extending rearwardly from the leading edge.

The invention is not limited to the embodiments described herein which may be modified or varied without departing from the scope of the invention.

Claims (5)

1. An aerofoil biade having a plurality of dimples distributed over an area of the upper surface . of the blade which extends from immediately adjacent to the leading edge of the blade at least partially towards the rear edge of the blade.

2. An aerofoil blade as claimed in claim 1, wherein the area of dimples extends along at least a major part of the length of the leading edge of the blade. 1 O

3. An aerofoil blade as claimed in claim 1 or 2, wherein the dimples are generally teardrop- shaped with their wider ends facing towards the leading edge of the blade.

4. An aerofoil blade as claimed in claim 1, 2 or 3, wherein the dimples vary in distribution density. 1 5

5. An aerofoil blade as claimed in claim 1, 2 or 3, wherein the dimples vary in depth. V