The present invention relates to a vertical axis wind turbine.

There are various types of vertical axis wind turbines. Certain of them have no stator, such as a Savonius turbine, which has curved, scoop-like blades which catch wind and are driven down wind. Their return up wind exerts less torque due to the backs of the blades being convex. Darrieus turbines also have no stator, their blades are aerofoil shaped. The wind flow past the aerofoils creates lift which acts with a circumferential component driving the foils around the turbine axis. More unusual is another class of turbine having: a stator having a circular array of deflector blades being angularly arranged to impart a rotary component to wind airflow exiting the stator inwards and a rotor also having a circular array of impeller blades arranged to receive the wind air with its rotary component from the stator and drive the rotor around.

One such turbine is disclosed in US patent application publication No. US 2013/0115069. Its abstract is as follows:

"A vertical axis wind turbine formed from a concentric arrangement of fixed stator blades to provide fluid flow acceleration into an arrangement of rotatable blades secured to a generator for invoking electrical power generation. The stator blades are maintained in a fixed position by use of an upper and lower stator plate. The rotor blades include an upper and lower plate, the upper plate coupled to the upper stator plate, and the lower rotor plate coupled to the generator. The amount of stator and rotor blades may be scaled in number and size depending upon the type of generator to be driven and associated mechanical energy to be obtained. The stator blades are designed for air deflection in a direction for optimal rotor blade rotation by accelerating air flow into a pre-swirl before the flow contacts the rotor blades. Each stator blade is oriented at a sufficient stagger angle so that an angle of the relative velocity does not exceed the stall angle of said rotor blade." A difficulty with such a turbine can arise when the rotor blades are curved, as they preferably are to maximise power absorption from the rotary flow imparted to the air, due to the wind air striking the back of the rotor blades and exercising a braking torque on the turbine, as in a Darrieus turbine. The object of the present invention is to provide an improved vertical axis wind turbine.

According to the invention there is provided a vertical axis wind turbine comprising: a stator having a circular array of deflector stator blades angularly arranged to impart to wind-air-flow incident on the blades a rotary flow component on exit inwards of the stator and a rotor also having a circular array of impeller rotor blades arranged to receive the wind-air from the stator and drive the rotor around;

Wherein: the stator blades are arrayed at a pitch to obviate radial wind air flow from impinging on a back face of the rotor blades and tending to brake it.

Whilst the rotor blades could be planar, they preferably have curvature to enhance flow direction change and extraction of work in driving of the rotor. The concave front faces of the rotor blade are preferably curved to a lesser extent than the convex rear faces. Whilst this arrangement improves efficiency in terms of airflow pressure imparted to the front faces and suction imparted to the rear faces, it aggravates the braking effect of radial wind-air-flow in the absence of the stator pitch of the invention.

In the preferred embodiment, the angle of the back face of the rotor blades at the inlet to the rotor is matched to the angle of the outlet angle of the stator blades. Whilst it is conceivable that the stator blades could be set at a pitch whereby a radial line of sight is available to the rotor, with the pitch being such that the overall wind-air-flow inwards to the rotor has no locally radial element, as is the case with a wider pitch; it is preferred that the pitch of the stator blades should be such that each circumferentially overlaps its neighbour.

Preferably the stator blades and the rotor blades are mounted on respective rings. In the preferred embodiment, the stator blades and the rotor blades are all of the same height, with upper and lower stator and rotor blade rings being equally spaced. Preferably the rotor has an open central region to which wind-air-flow passes after acting on the impeller blades and an open upper end, inwards of upper ends of the impeller blades, through which open upper end the wind air exits from the open central region, the arrangement being such that at least a portion of the wind air entering the open central region swirls within the rotor and exits it upwards in a vortex.

Advantageously, the concave front face of the rotor blades is at an angle from 5° to 10° to the vertical such that the concave face 'leans' back.

The rotor can be journalled with rolling element bearings. However in the preferred embodiment the bearings arc magnetic bearings, conveniently incorporating Halbach arrays. To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a side view of a vertical axis turbine of the invention;

Figure 2 is a cross-section side view in the same direction as Figure 1 and on the line II-II in Figure 3;

Figure 3 is a diagrammatic plan view of the turbine of Figure 1 and

Figure 4 is a side view, similar to Figure 1, with the blades partially broken away to show a central flow diverter.

Referring to the drawings, a vertical axis wind turbine has a stator 1, which has upper and lower stator rings 2,3, between which extend thirty six stator blades 4. These stator blades 4 are curved on both sides with a thick mid-section 5 and thin inlet and outlet ends 6,7. They have concave and convex sides 8,9. The surface of the concave sides are set generally radial with respect to the central axis 10 of the turbine at their inlet ends. At their outlet ends, the convex sides are set at 33° to radial. The included angles between the surfaces at the inlets are 26° and 18° at the outlets. These angles have the following results: wind air flow into the stator leaves inwards at approximately 33° to the radial direction at the exit from the stator; nearly 90% of wind air flow incident on the stator, that is to say wind incident on its blades within 60° of either side of a central direction truly radial to the stator, is directed into the blades as a result of their inlet angles; wind air flow truly radial to the stator cannot pass rectilinearly through the stator; wind air flow that can pass rectilinearly, or approximately so, through the stator leaves it internally, locally angled to the radial direction.

Concentrically within the stator, a rotor 11 is rotationally mounted. This has upper and lower rotor rings 12,13, between which extend twelve rotor blades 14. These are curved on both sides with a thick mid-section 15 and thin inlet and outlet ends 16,17. They have concave and convex sides 18, 19. The surface of the convex sides are set generally parallel with the concave exits of the stator blades, when tip to tip, i.e. at 32° to the radial. At their outlet ends, the convex sides are set at 82° to radial. The included angles between the surfaces at the inlets are 29° and 31 ° at the outlets. These angles have the following results: wind air flow out of the stator flows parallel to the convex side to the rotor blades when the blades are tip to tip and is drawn around the blades exerting suction on them to draw the rotor around; wind air flow out of the stator does not impinge on the convex side of the rotor blades in a manner to brake rotation of the rotor; as soon as tip to tip alignment has been passed, the wind air flow out of the stator impinges on the concave side of the rotor blades to drive the rotor around; the wind air flow would be turned by the rotor blades to leave inwards in the opposite rotational direction to that in which it enters the rotor if the rotor were not rotating. In practice, the rotor rotates at a speed determined by the load on it - and the wind speed. The resultant air speed tangentially of the rotor at the rotor's exit will be slower than at the inlet, and may in fact be in the opposite direction.

Accordingly the exit air is likely to be turning as a body of air. The rotor rotates around it with the shape of the rotor blade exits discouraging the exit air from entering the rotor, even on the downwind side, for the time being, of the turbine. The rotor blades 4 advantageously 'lean' back such that the concave side 18 faces upwards, preferably at an angle of from 5° to 10° to the vertical.

Before describing exit of the air from the turbine as a whole, certain other features should be described. To maximise the power extraction from the wind, stator blades and the rotor blades are all the same height, with the upper and lower stator rings 2,3 set at the same height as the upper and lower rotor rings 12, 13. A typical height for a rotor blade is from around l-5m with a width of from 0.4-3.0m. The lower values will be utilised for smaller turbines generating around 100W. Both sets of rings have sets of spokes 21,22, with the stator spokes being spaced further apart to allow the rotor spokes to pass inside them. Either of the lower spokes can be replaced by a closure plate 23 locally closing a central region 25 within the rotor.

The rotor spokes 22 arc fast with a central shaft 26. This is journaled at the centre of the stator spokes 21 and closure plate 23 via Halbach-array magnetic bearings 27 typically around 27 inches (68cm) in size, although different sizes can be used, depending on the use of the turbine. For example, an industrial unit may require a magnet of large dimensions. The shaft will normally extend to an electromagnetic alternator - not shown. The central region is open upwardly. As described above the rotor discourages the central body of exit air from exiting through the rotor and it exits upwards in a vortex, normally spinning in the same sense as the rotation of the rotor.

The invention is not intended to be restricted to the details of the above described embodiment. For instance, as shown in Figure 4, a central, upwardly tapering, substantially conoidal deflector 51 is provided to deflect upwards flow out of the rotor. Additionally a covering, roof structure can be included to protect the working elements of the turbine and optionally to aid wind flow, and also to improve the aesthetic appearance of the turbine. Further additionally, rotor blades 14 can also be mounted on the central shaft 26 to provide improved energy capture. The turbine as herein described extends the power band of the turbine providing more kilowatts per hour over a wider rpm range.