WO1995014169A1

WO1995014169A1 - Blade profile for wind turbine

Info

Publication number: WO1995014169A1
Application number: PCT/GB1994/002555
Authority: WO
Inventors: Stanley Le Baigue
Original assignee: Le Baigue Research Ltd.
Priority date: 1993-11-19
Filing date: 1994-11-21
Publication date: 1995-05-26
Also published as: AU1071795A; GB9323828D0

Abstract

A rotor device powered by a moving fluid, has an elongate rotor blade mounted in the path of the moving fluid for rotation about a fixed axis. The blade has a generally rectangular planar front face (10) and a curved rear face (11) joining the longitudinal edges of the front face. The rear face is uniform along the length of the blade, and symmetrical about the longitudinal axis of the blade.

Description

BLADE PROFILE FOR WIND TURBINE

The present invention relates to machines in which the energy associated with a moving fluid is converted to mechεinical energy by positioning a rotor blade in the path of the moving fluid. The invention has particular application to wind-powered machines.

In a typical horizontal axis windmill, the rotor blades are driven by lift forces generated when 'propeller' or airscrew like blades are set at such an angle that at their optimum speed of rotation they make a small angle with the wind and generate lift forces in a tangential direction. Because the rotor tips travel faster than the roots, they 'feel' the wind at a shallower angle. Accordingly, in a high speed horizontal axis rotor, the blades are preferably twisted so that the angle at which they meet the wind is constant from root to tip. However, accurately shaped airfoils are generally difficult and expensive to manufacture.

Flat plate windmills are also known but the plates are set at a predetermined pitch angle so that once the blades have been accelerated to a maximum speed and the wind drops, although the blades are initially rotating at a higher speed than the wind, they lose kinetic energy by drawing air through the rotating blades and therefore rapidly slow down. This is a limiting factor in the speed of any such mill with the blades at a pitch angle. It is also necessary that the mill should be constructed with opposed pairs of blades.

Windmills have also been constructed using symmetrical aerofoil blades without any pitch angle but such blades are not only expensive to manufacture but are also retarded by the relative wind striking the blunt nose of the aerofoil at a shallow angle when the blade is rotating at high speeds. The use of an aerofoil section also requires an opposed pair of blades.

According to the present invention, these problems are alleviated by providing a rotor blade which has a planar front face and a curved rear face joining the longitudinal edges of the front face, the rear face being uniform along the length of the blade and symmetrical about the longitudinal axis of the blade. The blade preferably has a plano¬ convex cross-section.

Accordingly, a single length of material can be used to form a pair of blades by using the centre point of the length as the turning axis. This has the advantage of a single length replacing two conventional opposed blades. The one piece construction not only provides added strength, but also has the advantage of simple design and low cost manufacture.

In use, the planar front face is preferably presented at about 90° to the moving fluid over the entire length of the blade, i.e. with zero pitch angle. With such an arrangement, the wind is no longer drawn through the rotating blade if the wind drops, and this is no longer a factor limiting the speed of the blade.

Although such a rotor will not rotate of its own accord when the blade is first presented to the moving fluid (because no turning moment is created), the blade will continue to rotate without external assistance once a rotary movement has been imparted to it. The blade might comprise, for example, a single length of extruded metal or plastic material, or it might be formed from a piece of timber by feeding the timber through an appropriate timber shaping machine.

The blade may be hollow with internal reinforcing ribs, or it may be solid.

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

Figure 1 is a schematic elevation view of a wind pump embodying the invention.

Figure 2 is a side view of the rotor blade. Figure 3 is a cross-section of the rotor blade, and

Figure 4 is a front view of the rotor blade.

Referring to these drawings, a conventional water pump 2 is supported above the ground on a vertical pole 3 which rests on the ground and is stabilised by three or more guy lines 8 and 9 (only two shown). The guy lines 8 and 9 are attached to a pivot 7 so that the pole can be rotated about its vertical axis.

The pump 2 has a projecting horizontal shaft 4 driven by a rotor blade 1 secured at the free end of the shaft. The centre point of the blade has an opening 6 for receiving the shaft 4 so that the blade rotates the shaft about its horizontal axis. As illustrated in Figures 2-4, the blade is solid and has a plano-convex cross-section with an outwardly facing rectangular planar front face 10 and a convex rear face 11. Alternatively, the blade could be hollow with internal reinforcing ribs.

In operation, the front face 10 of rotor blade 1 is orientated to face the oncoming wind with zero pitch by rotating support pole 3 about its pivot 7. The rotor blade 1 is then rotated either manually or with mechanical assistance until it reaches a speed at which the oncoming wind continues to rotate and accelerate the blade without assistance.

It has been found that once started the blade is self-orientating and will always tend to face the oncoming wind.

Using a 8' (2.44 m) blade having a width of 4" (10.16 cm) and a maximum thickness of 0.75" (19 mm), the pump 2 was able to pump an 11.5'

(3.5 m) head of water at a pumping rate varying from 2.0 tonnes/hour (0.565 Kg/s) with a wind speed of about 8 mph (12.9 Km/h) to 6.0 tonnes/hour (1.69 Kg/s) with a wind speed of about 22 mph (35.4 Km/h).

The blade was made from a plank of timber, the convex rear face being formed by feeding the plank on a flat bed beneath a rotary planing tool having the required profile.

The wind pump is therefore simple and inexpensive to manufacture, and is portable. It has a variety of possible applications but is particularly suitable for irrigation schemes.

Claims

1. A rotor device powered by a moving fluid, the device comprising an elongate rotor blade mounted in the path of the moving fluid for rotation about a fixed axis, the blade having a generally rectangular planar front face and a curved rear face joining the longitudinal edges of the front face, the rear face being uniform along the length of the blade and symmetrical about the longitudinal axis of the blade.

2. A rotor device according to claim 1 in which the blade is orientated such that the planar front face is presented at substantially 90° to the moving fluid over the entire length of the blade.

3. A rotor device according to claim 1 or claim 2 in which the rotational axis is substantially horizontal.

4. A rotor device according to claim 1, 2, or 3 in which the rotational axis passes through the centre of the blade.

5. A rotor device according to any one of the preceding claims in which the rear surface of the blade is convex.

6. A windmill comprising a rotor device according to any one of the preceding claims and a mechanical device driven by the rotor device.

7. A windmill according to claim 6 in which the mechanical device is driven by an output shaft of the rotor.