GB2551601A

GB2551601A - Tidal turbine with variable flow characteristics

Info

Publication number: GB2551601A
Application number: GB1701694.0A
Authority: GB
Inventors: Ayre Richard
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-02-04
Filing date: 2017-02-02
Publication date: 2017-12-27
Also published as: GB201701694D0; GB201602057D0

Abstract

A tidal turbine and generator assembly having a turbine with rotor blades 16 disposed around a rotor axis C and mounted on a tower 14, wherein a pair of aerofoils 22 is mounted upstream of the blades either side of the rotor 13, each aerofoil mounted on a rotatable support 26 and able to turn around a vertical axis Y while its chord line remains orthogonal thereto. Simultaneous and symmetrical swivel of the aerofoils can concentrate or diffuse the water flow incident on the turbine and thereby control rotor speed and power and also protect the turbine from overload in high tidal flows. The aerofoils effectively provide an inlet funnel and are preferably arc-shaped, curved around the rotor axis. They are preferably mounted in line with the yaw axis Z of the turbine, which is preferably weight balanced on axis Z and yaws with respect to the tower on a pintle 12. The turbine blades are preferably retractable, so that collision with large, heavy objects coming their way and detected by a sonar 34 may be avoided. Finally the rotor may have a buoyant part to counteract the weight of generator 15 and turbine blades 16.

Description

TIDAL TURBINE WITH VARIABLE FLOW CHARACTERISTICS

This invention relates to a tidal turbine. A freestanding tidal turbine harvests power from the kinetic energy entrained in moving water, by its nature tidal water movement varies significantly in its velocity

As the energy entrained is proportional to the cube of the velocity, a commercial tidal turbine should be able to capture significant power at low water speed, and yet stand the extreme loads of high speed flow. Sometimes excess loads, caused for example, by spring tides, can cause over rotation of tidal turbines and thus serious damage to the turbine. This risk of this can be reduced by using a tidal turbine having a variable coning angle, in which the area swept by turbine blades is reduced in high flow rates to reduce the load on the turbine, in extreme current the turbine blades may be retracted entirely in this instance rotation of the turbine would cease and power generation stop.

However, the control mechanism required to partially retract the blades to match the current flow can be quite complex and expensive. Further, the additional moving parts required for such a system inevitably will require increased maintenance and risk of breakdown.

According to the present invention a tidal turbine assembly, having a turbine with a plurality of blades which may extend laterally from a central rotor disposed around a horizontal rotor axis and mounted on a tower, additionally comprises at least one pair of aerofoils mounted either side of the rotor and upstream of the blades, the aerofoils being mounted on rotatable supports upstream from of the turbine blades, and each aerofoil having its chord line orthogonal to the vertical axes of the aerofoil mounting concerned.

Preferably the aerofoils are arcuate in vertical section, the centres of the arcs being on the rotor axis.

In normal flows the aerofoils have a zero angle of attack to the tidal stream.

In low flows the aerofoils are rotated about their mountings so that the chord lines of the aerofoils, when extended, converge down-stream of the turbine, thus creating a greater water flow velocity through the turbine blades. As the energy available to the turbine increases by the cube of the increase in water speed, more power is available to be harnessed In high flows above normal flows the aerofoils are rotated about their mountings in the opposite direction so that the chord lines of the aerofoils, when extended, converge up-stream of the turbine, creating a reduced water flow velocity through the turbine blades and the load is reduced.

The turbine blades may have two positions, fully extended or fully retracted; this avoids the need to control a coning angle. In emergency when there is the possibility of severe overload, the blades can be retracted. Alternatively the turbine blades may have a fixed swept area. A tidal turbine assembly normally has the turbine itself rotabably mounted atop a tower so that when the tide reverses, the turbine turns through 180° so that the turbine blades are in the right relationship to the tidal flow. In order to ensure that the aerofoils remain upstream of the blades when the turbine turns with the tide, the axis of rotation of the turbine about its tower is parallel to the axes of rotation of the aerofoils about the aerofoil mountings, and a horizontal line drawn between the pair of axes of rotation of the aerofoils passes orthogonally through the rotor axis and the axis of rotation of the turbine about its tower mid-way between the two axes of rotation of the aerofoils.

The invention would work equally well with a conventional up-current mounting, however four aerofoil sections would be needed. Two upstream and two downstream of the turbine, to have the same effect.

In order that the invention may be more fully understood, and example is described below with reference to the accompanying drawings, in which: Figure 1 shows a front elevation of a turbine assembly according to the invention looking in the direction A of figure 2;

Figure 2 shows a side section of the assembly of figure 1 viewed in the direction B-B’ offigurel;

Figure 3 is a plan view of the turbine assembly with the aerofoils oriented as for low flows;

Figure 4 is a plan view of the turbine assembly with the aerofoils oriented as for high flows; and

Figure 5 shows a side section of a modified assembly of the kind shown in viewed in the direction B-B’ of figurel;

In figures 1 to 4, an underwater turbine assembly includes a turbine 10 with a plurality of retractable blades 16 which normally may extend laterally from a central rotor 13 and mounted on a rotatable pintle 12 on a vertical tower 14, itself mounted on a base 11. The turbine may thus, rotate on the tower 14 about a vertical axis Z-Z’. The rotor drives a generator 15. A pair of aerofoils 22 is mounted either side of rotor 13 and upstream of the blades 16. The aerofoils 22 are pivotally mounted to rotate on pair of vertical aerofoil mountings 26, which rotate in vertical supports 28. The vertical supports 28 are upstream of the turbine blades 16. Each of the aerofoil mountings 26 has a vertical axis Y-Y’ orthogonal to the rotor axis X-X’ but spaced apart from the rotor. Each aerofoil has its chord line 24 orthogonal to the vertical axes Y-Y’

As can be seen in figure 1, the aerofoils 22 are arcuate in vertical section, the centre C of the arcs being aligned with the rotor axis X-X’. The swept area of the turbines blades is marked by the dotted circle 17.

The turbine blades 16 have two positions, fully extended as seen in the figures, or fully retracted. Retraction is achieved by the spigot 20 being pushed forward further out of the body of the turbine 10 by opening ram 23, links 18 pull the turbine blades forward toward the axis X-X’ of the rotor about the pivot supports 21. Each links 18 is connected by pivots 19 to a blade 16 at one end and the spigot 20 at the other. This enables the blades to be retracted in emergency when there is the possibility of severe overload or the turbine is being taken off-line. In addition, the turbine is fitted with a sonar 34 directed upstream, damage to turbines has occurred in the past as a result of objects such as logs or large fish or mammals coming into contact with the turbine blades. If the sonar detects a large object in the flow upstream of the turbine, the blades 16 can be retracted as described to allow the object to pass safely by.

Figure 3 particularly shows the disposition of the aerofoils 22 in low flows. In this figure the aerofoils have been rotated to flare outwards with respect to each other to provide a funnelling effect for water 32 approaching the turbine blades 16, as a result the rate of flow of water through the swept area 17 of the turbine blades is increased substantially beyond what would otherwise have been the case, and as the energy available to the turbine increases by the cube of the increase in water speed, substantially more power can be more power is available to be harnessed. As can been seen in figure 3, in this configuration, extensions 25 of the chord lines 24 will intersect downstream of the turbine 10.

Figure 4 particularly shows the disposition of the aerofoils 22 in high flows. In this figure the aerofoils have been rotated to divert some water 32 approaching the turbine around the outside of the aerofoils, as a result the rate of flow of water through the swept area 17 of the turbine blades is reduced significantly compared to what would otherwise have been the case reducing power generation by the turbine without out the need partially to retract the blades 16 to protect the turbine from over-rotation.

As can been seen in figure 4, in this configuration, extensions 25 of the chord lines 24 will intersect upstream of the turbine 10.

The turbine 10 turns through 180° on its pintle 12 when the tide reverses. To ensure that the aerofoils 22 remain upstream of the blades 16 when the turbine turns with the tide, the axis of rotation of the turbine Z-Z’ about its tower is parallel to the axes of rotation Y-Y’ of the aerofoils on the aerofoil mountings 26 , and a horizontal line 30 drawn between the pair of axes of rotation Y-Y’ of the aerofoils 22 passes orthogonally through the rotor axis X-X’ and the axis of rotation Y-Y’ of the turbine about its tower mid-way 31 between the two axes of rotation Y-Y’ of the aerofoils 22.

If the geometric relationship between the aerofoils and the axis of rotation Z-Z’ of the turbine 10 about the tower 14 described in the previous paragraph was not adopted, the invention would work equally well with two pairs of aerofoils, so that one pair was up stream of the turbine for either direction of tidal flow.

Referring to figure 5, advantageously, the centre of gravity of the turbine assembly passes axially along axis Z-Z’ through the pintle 12. To achieve this, the rotor 13 comprises a doughnut shaped cylindrical pressure float having an outward face 13A and an inward face 13B. The turbine blades 16 are pivotally mounted on the outward face 13A of the rotor 13, and the inward face 13B connected to and driving the generator 15. The doughnut shape is necessary to allow the spigot 20 to move along the axis X-X’.

The buoyancy of the doughnut shaped pressurised rotor 13 gives equalises the downward force of weight of the generator 15 and turbine blades 16. The pressure in the rotor 13 can be varied to ensure equalisation of the upward force of the buoyancy of the rotor and the downward forces of the weights of the blades and generators, which will vary as the depth of the tidal turbines. Further trimming of the rotor may be necessary to ensure downward forces either side of the pintle 12 are balanced.

The whole assembly spins together. A smaller trimming arrangement 27 can be fitted behind the mounting for the turbine opening ram 23.

Claims

1. A tidal turbine assembly, having a turbine with a plurality of blades which may extend laterally from a central rotor disposed around a rotor axis and mounted on a tower, additionally comprising at least one pair of aerofoils mounted either side of the rotor and upstream of the blades, the aerofoils being mounted on rotatable supports upstream from of the turbine blades, and each aerofoil having its chord line orthogonal to the vertical axes of the aerofoil mounting concerned and in which the rotor drives a generator.

2. A tidal turbine assembly according to claim 1 in which the aerofoils are arcuate in vertical section and the centres of the arcs are on the rotor axis.

3. A tidal turbine assembly according to claim 1 or 2 in which in low tidal lows the aerofoils are rotated about their mountings so that the chord lines of the aerofoils, when extended, converge down-stream of the turbine.

4. A tidal turbine assembly according to any preceding claim in which in high tidal flows the aerofoils are rotated about their mountings so that the chord lines of the aerofoils, when extended, converge up-stream of the turbine.

5. A tidal turbine assembly according to any preceding claim in which the turbine is fitted with a sonar to scan water up-stream of the turbine and in which the turbine blades are retracted if a significant object.

6. A tidal turbine assembly according to any preceding claim, the turbine being mounted atop a tower to rotate about a vertical axis, in which the vertical axis of rotation of the turbine about its tower is parallel to the axes of rotation of the aerofoils about the aerofoil mountings, and a horizontal line drawn between the pair of axes of rotation of the aerofoils intersects both the rotor axis and the axis of rotation of the turbine about its tower orthogonally at the mid-point of the horizontal line.

7. A tidal turbine assembly according to any one of claims 1 to 5 comprising two pairs of aerofoil sections, one pair placed in the flow either side of the turbine.

8. A tidal turbine according to any preceding claim in which the rotor comprises a buoyant assemble the buoyancy of the rotor counteracting the weight of the turbine blades and generator.

9. A tidal turbine according to claim 8 in which the assembly rotates on a pintle about a tower and in which the centre of gravity of the turbine is on the axis of the pintle.

10. A tidal turbine according to claim 8 or 9 additionally comprising trimming means associated with the mechanism for retracting the turbine blades.