GB2454024A

GB2454024A - Wind powered reciprocating device with passive blade angle control

Info

Publication number: GB2454024A
Application number: GB0721212A
Authority: GB
Inventors: Peter John Dunn; Heath Henry Evdemon
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-10-23
Filing date: 2007-10-23
Publication date: 2009-04-29
Anticipated expiration: 2027-10-23
Also published as: GB2454024B; GB0721212D0

Abstract

A wind powered generating device 1 has a one piece symmetrical aerofoil 2, which is driven by the wind in a reciprocating motion. The foil 2 is pivoted at mid chord and has end stops 3 to limit the pitch angle (angle of attack). A piston and cylinder arrangement 7 is used to reverse the pitch at each end of the stroke, and also serves to damp the reversing movement. The end stops 3 can be adjusted by actuators 8 according to the operating conditions. The device may be pivotally mounted so that it automatically turns into the wind, and may be installed on a floating platform

Description

1 2454024

WIND POWERED GENERATOR DEVICE

This invention relates to a wind powered generator device for harnessing wind energy using.a-singlepiece symmetncaIaercfoi1pivotedat the mid-chord point moving up and down on parallel arms in a reciprocating motion to provide power to a flywheel (see attached Figures).

Renewable energy sources such as this are much more environmentally friendly than the traditional use of fossil fuels as they will not contribute to the climate change effects that the world is currently experiencing. It may also lead to cheaper power for everyone in the long run The advantages of this device are many. It is estimated that a higher efficiency can be achieved compared to wind turbine due to the lower relative speeds of the machine and the fact that the whole length of the aerofoil is at the optimum angle of attack at all times (i.e. just below stall angle). Wind turbine blades have to be twisted along their length and are designed to reach peak efficiency at one wind speed only.

The fact that the aerofoil is a one piece symmetrical wing, has no twist along its length and is supported at both ends means it would be extremely cheap to manufacture compared to the blades on a turbine which cost hundreds of thousands of pounds each.

Theoretically, Betz's law states that the maximum amount of energy that can be obtained from an airflow using a Darius device (i.e. a device that harnesses the wind's energy using lift as opposed to Savonius devices which use drag) is 59%. Wind turbines generally operate in the 25-30% region dependant on wind speed. It is envisioned that the proposed device will be more efficient over all wind speeds. The device would also not suffer the high speed flutter fatigue problems that affect turbines. No tower would be required either so the visual environmental impact would be much less.

A protoype working model was constructed and tested to prove the device concept and help the development of the idea as the project progressed, notably the pitch change mechanism and the need for an over-centre spring as later described.

The invention will now be described in more detail with the aid of drawings as follows:-Figure 1:-Schematic view from the side of the device Figure 2:-Simplified view from the side showing just the aerofoil pitch change mechanism Figure 3a:-Simpified view from the side showing just the over-centre spring Figure3b:-Diagram showing aerofoil centre of pressure pivoting action Figure 4:-Schematic view from the front of the device Figure 5:-Plan view from above The device, 1, works as follows: -The single piece symmetrical aerofoil,2, is pivoted at each end at mid-chord point, 10 (figure 3b). Its angular movement about the pivots is limited by variable stops called the angle of attack stops,3, (see Figure 1). The whole aerofoil is mounted on parallel arms,4,attached to a main frame,13, by use of upper arms,5, and lower arms,6, as shown in Figure 1 to allow a parallel action vertical motion. This reciprocating motion is then converted into rotary motion to provide the drive for a flywheel, II The aerofoil,2, reverses its angle of attack from positive to negative and vice versa at the end of each stroke by means of a pitch change mechanism,7, comprised of pistons and cylinders which have internal stops limiting their length as shown in Figure 2. The pistons and cylinders,7, also act as dampers to prevent the aerofoil reversing its angle of attack too quickly at the end of each stroke. These pitch change devices work as follows (please refer to Figure 2). Towards the end of the stroke upwards shock absorber,7a, would reach its internal stop at fill extension which would reverse the aerofoils angle of attack to negative for the downward stroke. Shock absorber,7b, at this point would be acting as a damper to prevent excessively fast pitch changes once the aerofoil has passed over the filly horizontal point. Due to the fact that the aerofoil is pivoted mid-chord,l0, once the angle of attack has passed the horizontal point the centre of pressure, I 2,(point at which the lift is said to act) would automatically keep the aerofoil changing its angle of attack in the same direction as the pitch change mechanism (see Figure 3b). The shock absorbers,7, at full extent would hit internal springs or bump stops to ease the movement.

The angle of attack stops,3, mounted at the other end of the aerofoil,2, to the pitch change mechamsm,7, control the angle of attack in positive and negative directions by means of actuators,8. These would work of' electrical signals provided by microprocessors which would receive signals from strain or force gauges mounted on the upper arms,5, measuring the lift created. These would keep the angle of attack at an optimium (i.e. just below the stall angle) for all combinations of wind speeds and device operating speeds.

In addition to the centre of pressure, 12, helping rotate the aerofoil,2, after it has passed the horizontal position and holding it against the angle of attack stops,3,, there would also be an over-centre spring,9, helping to hold the aerofoil against the angle of attack stops,3, (see Figure 3a). This was found to be necessary on the prototype model in blustery or turbulent conditions.

In a fI.ill scale production of the device another aerofoil identically controlled would provide force to the flywheel 90 degrees out of phase. This would provide a smoother operation at the end of each aerofoil stroke as the accompanying aerofoil powers it over top and bottom dead centre and vice versa.

The whole device would be mounted on a rotating platform if constructed on land and held into wind by use of a rudder. Alternatively, the platform pivotal point could be put in front of the aerofoil, thus the drag on the machine would keep it pointed into wind.

If the device was on a floating platform at sea it would merely have to be anchored at the front on a pivot, again, the drag of the device would keep it pointed into wind.

This is probably the biggest possibility for the invention,as out at sea the device could be made as large as possible on a floating platform with no need for a tower anchored to the sea floor. It could in effect be placed m deep ocean water!

Claims

Claims I. A wind powered generating device comprising of one piece aerofoil (with no moving flaps or devices) pivoted and balanced at the mid chord point generating lift in an vertical direction attached by means of parallel linkages and arms to a rotating drive for power production.
2. A device according to Claim I with a linkage system at one end of the aerofoil consisting of 2 pistons and cylinders to reverse the angle of attack of the aerofoil at the end of each vertical stroke and also to provide a damping effect to the rate of change of the aerofoils pitch angle.
3. A device according to either one of Claims I and 2 having two movable angle of attack stops (or limiters) controlled by actuators to optimise the angle of attack of the aerofoil for different wind and device speeds
4. A device according to any one of the preceeding claims having a computer or microprocessor control of the angle of attack stop actuators using information obtained from strain or force gauges mounted on the device to keep the aerofoil at the optimium angle of attack.
5. A device according to any one of the preceeding claims having an over-centre spring to help hold the aerofoil against the angle of attack stops during each vertical stroke.
6. A device according to any one of the preceeding claims having a one piece symmetrical aerofoil pivoted at the mid-chord position, thus allowing the aerodynamic centre of pressure of the aerofoil to assist in helping the pitch change mechanism move the aerofoils incidence once it has past the horizontal position and also hold the aerofoil against the angle of attack stops during each vertical stroke along with the over-centre spring.
7. A device according to any one of the preceeding claims working in conjunction with an identical device attached to the same flywheel 90 degrees out of phase to assist in the smooth operation over the top and bottom dead centre of each devices strokes.
8. A device according to any one of the preceeding claims mounted on a rotating base such that a fin or drag of the device keeps it pointing into wind.
9. A device according to any one of the preceeding claims mounted on a floating platform on water such that the platform is anchored at the front allowing the drag on the device to keep it pointing into wind.
10. A device substantially described with reference to the accompanying drawings.