GB2292191A

GB2292191A - Vertical axis wind-powered generator

Info

Publication number: GB2292191A
Application number: GB9516233A
Authority: GB
Inventors: Ronald George Munday
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-08-08
Filing date: 1995-08-08
Publication date: 1996-02-14
Also published as: GB9516233D0

Abstract

A vertical axis wind-powered generator comprises a vertically disposed output shaft 3 and at least two wind engaging surfaces 21, 22, 23 rotatably mounted on support arms 11, 13 which are radially attached to the output shaft 3. Means for varying the relative angular relationship of the wind engaging surfaces 21, 22, 23 to each other and to the direction of the prevailing wind are provided. A drive arrangement involving bevel gears or chains and sprockets, may be connected to a wind vane 30 to determine the positions of the surfaces 21, 22, 23 with respect to the prevailing wind. The output shaft 3 powers an electrical converter housed in an easily accessible supporting base structure 5. <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO VERTICAL AXTS WIND-POWERED GENERATORS The invention relates to vertical axis wind-powered generators.

Vertical axis wind powered generators are known but are not as effective as horizontal axis wind-powered generators There are, however, disadvantages associated with horizontal axis wind-powered generators and particularly generators which utilize standard low-a laminar flow aerofoils to derive rotational energy from the prevailing wind. One of these disadvantages is a runaway condition when the generator is unloaded, occasionally leading to self-destruction. Aerofoil generators may also have difficulties in starting.

The present invention provides a vertical axis wind-powered generator comprising a vertically disposed output shaft, at least two wind engaging surfaces rotatably mounted on support arms which are radially attached to the output shaft and means for varying the relative angular relationship of the wind engaging surfaces to each other and to the direction of the prevailing wind.

The angular relationship of the wind engaging surfaces to the direction of the prevailing wind ensures reliable self-starting of the rotation of the output shaft Power extracted from the wind impinging on the surfaces rotates the support arms which transfer rotational energy via the output shaft to an electrical converter.

The rotation of the output shaft drives a turbine housed in an easily accessible supporting base structure.

The means for varying the angular relationship of the surfaces includes pairs of radial support arms, one at the upper end and one at the lower end of the output shaft, for rotatably supporting each wind engaging surface. The means for varying the angular relationship of the surfaces further includes a mounting shaft for each surface pivotally held between each of the pairs of support arms.

Each mounting shaft is provided at one end with a driven member which is linked to a centrally disposed wind vane and associated drive member which determines the positions of the wind engaging surfaces with respect to the prevailing wind.

The invention will now be described more particularly with reference to the accompanying drawings which show, by way of example only, two embodiments of vertical axis wind-powered generator according to the invention. In the drawings: Figure 1 is a front elevation of a first embodiment of wind powered generator; Figure 2 is a phasing diagram for the generator of Figure 1; Figure 3 is a phasing diagram for a second embodiment of wind powered generator; Figure 4 is a detailed perspective view of a chain and sprocket drive arrangement for the generator represented by the phasing diagram of Figure 3; Figure 5 is a detailed perspective view of a geared drive arrangement for the generator represented by the phasing diagram of Figure 3; Figure 6 is a schematical plan view of a geared drive arrangement for the generator shown in Figure 1; and Figure 7 is a graph, of total torque output (normalised) against arm position, for the generator of Figure 1.

Referring to the drawings and initially to Figures 1 and 2, the wind-powered generator has a vertical output shaft 3 rotatably mounted on a base 5. The output shaft 3 has at its upper and lower ends three radial arms 11,12,13 disposed at 1200 from each other and supporting three blades 21,22,23 fixed to the axles 25. Each blade axle 25 is provided with a drive member such as a sprocket or a bevel gear which when rotated alters the angle of the blade so that for one revolution of an arm about the output shaft 3 the blade turns through 1800. A wind vane 30 is provided at the upper end of the output shaft 3 and is used to determine the position of a primary drive member, described in more detail hereinafter, which engages the drive members of each blade. An approximate scale of the wind-powered generator is illustrated by the person P standing adjacent the base 5.As illustrated in the blade phase diagram in Figure 2, the blades 21a,22a,23a are positioned so that a first blade 21a is presented perpendicularly to the direction of the prevailing wind W. The second and third blades 22a,23a are angled to provide minimum resistance to motion by presenting a lower total surface area to the wind than the first blade 21a.

The initial positions of the blades are denoted by the subscript "a". As the supporting arms iia,12a,13a and the output shaft 3 are urged to rotate, the first blade 21b moves angularly and pivots about the blade shaft 25 to present an angled face to the prevailing wind. The angled face separates the impelling force into its normal and quadrature components increasing the overall angular velocity. The third blade 23b also adopts a position in which the impelling force of the wind acts to sustain the rotation R of the central shaft 3. This position of the blades is denoted by the subscript "b".The next position illustrated, denoted by subscript "c", shows the first blade arm lic angularly disposed by 800 from its first position ila and the blade 21c angled to provide a rotational component force. The second blade 22c is positioned to provide a minimal surface area as before but has now adopted an angle relative to the wind in preparation for wind pick-up. The third blade 23c is now almost perpendicular to the prevailing wind for maximum torque. Thus, the apparatus is arranged to ensure that the blades 21,22,23 are always held at the optimum angle to maximise the torque generated regardless of the relative direction of the wind W.

A similar phasing diagram is shown in Figure 3 for a two arm wind-powered generator. As before the sequential relative positions of the arms 11, 12' and blades 21',22' are denoted by the subscripts "a", "b", "c" and "d".

Initially, the first blade 21'a is perpendicular to the prevailing wind w and the second blade 22'a is at 900 to the first blade 21'a. It will be seen that through the whole rotation R of the arms 171,12' the blades 21, 22 are maintained at 900 from each other.

The apparatus acts essentially as an impulse turbine but is configured, by the blade arrangement, to utilise a vortex-induced depression (low pressure area) on the lee side of the blades. Calculations indicate that the apparatus functions most efficiently when the circumferential or angular velocity is 35% of the wind speed.

In both embodiments, an electrical converter (not shown) for converting rotational motion R to electrical energy is housed with the base 5 and is connected via gearing to the output shaft.

Figure 4 shows a chain and sprocket drive arrangement for a two arm generator. The wind vane 30 is attached at one end to a shaft 32 mounted concentrically with the output shaft 3 and to a pair of sprockets 35,36. A chain 37 couples each sprocket 35,36 to a corresponding sprocket 36,39 on a blade axle 25. The sprocket 38,39 is fixed to the blade axle 25 which is rotatably mounted to its cross-arm 11',12' by appropriate selection of the sprockets 35,36,38,39 a 2:1 ratio is established between the rotation R of the output shaft 3 and the blade axles 25.

Alternatively, bevel gears 40,42 are provided on each of the shafts or axles 25,32 as illustrated in Figure 5. The cross-arms 11",12" are modified to rotatably retain a drive shaft 45 for orienting the blades with respect to the prevailing wind.

Figure 6 shows a geared drive arrangement for a three arm generator. As in the two arm generator, the wind vane 30 is mounted on a shaft disposed concentrically with the output shaft 3 and has a bevelled gear 50 which drives blade drive shafts 55 to orient the wing engaging blades 21,22,23. The blades 21,22,23 are mounted on vertical axles 25 which carry a bevel gear 57 which engage gears on the blade drive shafts 55. The support arms 11,12,13 are modified to rotatably carry the blade drive shafts 55.

The gearing ratio between the wind vane bevel gear 50 and the blade drive shafts is 1:1. However, the ratio between the drive shafts 55 and the blade axle bevel gears 57 is 1:2 to ensure that the blades 21,22,23 rotate through 1800 for each 3600 rotation of the output shaft 3.

These gearing arrangements require little torque as the blades are centrally pivoted. It will be seen that the gearing arrangements may be disposed at either the upper or lower ends of the output shaft and other suitable gearing techniques are applicable.

Although maximum torque is generated when the horizontal cross-arm is perpendicular to the prevailing wind direction, torque is approximately 70% of this value when the cross-arm is aligned with the wind direction. Thus, low torque modulation over the effective arc of each blade ensures reliable self-starting of the apparatus.

An advantage of using substantially flat blades is that the effects of a vortex-induced depression on the lee side of each blade assists rotation of the cross-arms.

Avoiding the use of standard lower laminar flow aerofoils ensures that no runaway condition occurs if the generator is operated in an unloaded condition. In the embodiment of the present invention, the circumferential velocity of the blades or arms will always be less than the wind speed.

The power output from the generator may be written as a function of wind speed and total blade area. The following is a suggested formula for calculating power output Pout: PoUt = 1.39 x 0.613 x (0.65 Vs)2 x A x 0.35 Vs x 1.2 Watts.

Where 1.39 is a correction factor for the vortex effect; 0.613 is a first factor of wind pressure on one blade; 0.65 is a second factor of wind pressure on one blade; Vs is the incident wind speed; A is the area of one blade; and 1.2 is a correction factor for a three blade machine.

This formula is valid only for three blades. The power output is 50% greater with three blades than with two.

Figure 7 graphically represents the normalised output torque of a three arm generator as a function of arm position for each arm 11, 12, 13 and for the total output torque for the three arms. The positions "a", "b" and "c" refer to those subscripts used with reference to Figure 2.

The angular position in degrees is made with reference to the first arm 11 where Do is the initial position of said arm Ila.

The table below is to be read together with the graph shown in Figure 7.

Blade angle Projected Relative Force Angle to prevailing Blade Force Applied (degrees) Wind W Area** (circumferential: to (6 degrees) radial) Blade4 0** 90 1.0 1.0 1.0 45 67.5 0.924 0.75 0.693 90 45 0.707 0.5 0.354 135 22.5 0.383 0.25 0.096 180 0 0 0 0 * Normalised Projected Blade Area = w.h. sin e wherein w=blade width blade height # = blade angle Initial position normal to prevailing wind W as exemplified by arm 77a of Figure 2.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alternations are possible within the scope of the appended claims.

Claims

CLAIMS:

1. A vertical axis wind-powered generator comprising a vertically disposed output shaft, at least two wind engaging surfaces rotatably mounted on support arms which are radially attached to the output shaft and means for varying the relative angular relationship of the wind engaging surfaces to each other and to the direction of the prevailing wind.

2. A vertical axis wind-powered generator as claimed in claim 1, in which the means for varying the angular relationship of the surfaces includes pairs of radial support arms, one at the upper end and one at the lower end of the output shaft, for rotatably supporting each wind engaging surface.

3. A vertical axis wind-powered generator as claimed in claim 2, in which the means for varying the angular relationship of the surfaces includes a mounting shaft for each surface pivotally held between the respective pairs of support arms.

4. A vertical axis wind-powered generator as claimed in claim 3, in which each mounting shaft is provided at one end with a driven member which is linked to a centrally disposed wind vane and associated drive member which determines the position of the wind engaging surfaces with respect to the prevailing wind.

5. A vertical axis wind-powered generator as claimed in any one of the preceding claims, in which each wind engaging surface rotates 1800 within the support arms for each full revolution (3600) of the output shaft.

6. A vertical axis wind-powered generator as claimed in either claim 4 or claim 5, in which the rotation of the wind engaging surfaces with respect to the output shaft is controlled by a chain and sprocket drive arrangement.

7. A vertical axis wind-powered generator as claimed in either claim 4 or claim 5, in which the rotation of the wind engaging surfaces with respect to the output shaft is controlled by a bevel gear arrangement.

8. A vertical axis wind-powered generator as claimed in any one of the preceding claims in which each of the wind engaging surfaces comprises a flat blade which creates a vortex-induced depression on the lee side of the blade to assist starting and to prevent runaway conditions in an unloaded generator.

9. A vertical axis wind-powered generator as claimed in any one of the preceding claims, which includes an electrical converter mounted in a base support for the output shaft.

10. A vertical axis wind-powered generator substantially as herein described with reference to and as shown in Figures 1,2,6 and 7.

11. A vertical axis wind-powered generator substantially as herein described with reference to and as shown in Figures 3,4, and 5.