Power generating water turbine assembly

Abstract

An accelerator and water turbine assembly is provided for mounting in a tidal stream having a water turbine (12) and a water flow accelerator for providing a turbine driver current having a speed greater than that of the uninterrupted ambient tidal stream in which the accelerator has an accelerator body member (11) having a water flow facing front face (13) and side faces (14) depending therefrom around which the water flows adjacent each of the side faces as a turbine driver current and in which the water turbine (12) is mounted to be at least partially shrouded by the accelerator body member from the accelerated turbine driver current flowing adjacent and relatively close to a side face of the accelerator where the water flow achieves substantially maximum velocity and in which the accelerator is laterally spaced apart from the turbine driver current modifying effect of any other flow obstruction.

Claims

1. An accelerator and water turbine assembly for mounting in a tidal stream, said assembly comprising: a water flow accelerator for providing a turbine driver current, the water flow accelerator comprising an accelerator body member including side faces and a water-flowing facing front face; and at least one water turbine mounted to the accelerator body member rearward of the water-flowing facing front face surface and laterally spaced apart from one side face of the side faces respectively; the water-flowing facing front face including ends forward of the widest width of the accelerator body member, each end extending in a lateral direction beyond a respective side face so that the front face covers at least 10% but not more than 30% of an outermost cylinder width of the at least one water turbine, wherein the at least one water turbine projects a lateral distance from the respective side face that is 0.4 of the widest width of the accelerator body member.

2. The accelerator and water turbine assembly as claimed in claim 1 in which the water-flowing front face of the accelerator body member is of arcuate shape.

3. The accelerator and water turbine assembly according to claim 2 in which the arcuate shape is semi-circular.

4. The accelerator and water turbine assembly according to claim 2 in which the accelerator body member water-flowing front face is ellipsoidal in plan.

5. The accelerator and water turbine assembly as claimed in claim 1 in which the ends are at least one flap or deflector to increase velocity and deflect flow from the side faces and partially shield the at least one water turbine from the turbine driver current.

6. The accelerator and water turbine assembly according to claim 1 in which the accelerator body member is a pontoon.

7. The accelerator and water turbine assembly according to claim 1 in which the accelerator body member is tethered to a bottom of a waterway.

8. An accelerator and water turbine assembly for mounting in a tidal stream, said assembly comprising: a pair of water turbines, each water turbine comprising a set of blades that are circumferentially spaced apart from each other around an axis of rotation and define a turbine width of the respective water turbine, wherein the respective axes of rotation of the water turbines are parallel to each other to lie in a common plane, and wherein a spacing between the water turbines is greater than either of the respective turbine widths; and a water flow accelerator disposed in the spacing between the water turbines, the water flow accelerator comprising: a convex front face that extends laterally between the water turbines upstream of the respective axes of rotation of the water turbines to accelerate a respective turbine driver current flowing through each water turbine, wherein the front face is laterally narrower than a lateral distance between the respective axes of rotation of the water turbines; and side faces that extend longitudinally to intersect the common plane in which the axes of rotation of the water turbines lie, each side face extending adjacent to a respective one of the water turbines; wherein each side face of the water flow accelerator and the respective adjacent water turbine diverge in a downstream direction from the axis of rotation of the respective water turbine.

9. The accelerator and water turbine assembly according to claim 8, wherein the front face is shaped to direct at least a portion of each turbine driver current between the axis of rotation of the respective water turbine and the water flow accelerator.

10. The accelerator and water turbine assembly according to claim 8, wherein the front face extends laterally beyond each side face.

11. The accelerator and water turbine assembly according to claim 10, wherein the water flow accelerator comprises a pair of laterally-extending deflector flaps, each deflector flap being disposed at a respective lateral end of the front face and being configured to direct water towards the blades of a respective one of the water turbines.

Description

(1) The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which:

(2) FIG. 1 is a plan view of four cylindrical prototype flow accelerators used for laboratory testing,

(3) FIG. 2 illustrates the transects along which velocities were measured in the laboratory testing,

(4) FIG. 3 is a graph comparing flow of accelerations recorded along a 90 transect for the cylindrical prototype flow accelerators of the laboratory testing,

(5) FIG. 4 is a plan view of a barge used in field testing,

(6) FIG. 5 is a plan view of another barge configuration used in the field testing,

(7) FIG. 6 is a graphical comparison of the total available power from an uninterrupted ambient stream and the same stream flow accelerated by 80%,

(8) FIG. 7 is a stylised perspective view of a pontoon used for carrying out the invention, and

(9) FIG. 8 is a plan view of another construction of an accelerator body showing the flaps used to deflect accelerated water flow.

(10) FIGS. 9a and 9b show further examples of deflector flaps and their effect on the flow.

(11) Before discussing and describing how the invention is constructed and operated it is important to make certain general comments and specifically in relation to various investigations carried out by the applicant. It is probably important to pose the question why when everybody skilled in this particular technology understood that when a tidal stream or current impinges on an object in its path and has to circumvent the object that the tidal stream or current is speeded up. However, nobody appears to have examined this acceleration and applied it to the problem of maximising the turbine driver current.

(12) Having considered the various problems in relation to this technology it became apparent that the most important issue was to, in some way, examine how the maximum acceleration of the uninterrupted ambient tidal stream could be achieved and how this knowledge could be best applied to hydroelectric power generation. This was decided on after various field trials with the associated field test results having been carried out. For ease of understanding the laboratory tests are described first and then the field tests though indeed many of the field tests were carried out prior to the laboratory tests.

(13) It was decided to carry out laboratory tests on various prototypes of different sizes and shapes so as to examine and analyse the flow diversion around an obstacle in an open channel flow. In order to achieve flow acceleration by means of flow diversion around an obstacle, the upstream face of the obstacle must be curved to avoid the generation of turbulence. A review of literature found that very little work has been conducted on quantification of accelerated flows around obstacles, the vast majority of the work in which accelerated flows have been observed is based on flow around cylinders or ellipses for the purpose of determining the stresses imposed on structures such as bridge supports etc. Further, it was decided to include an aerofoil profile as such aerofoils are used extensively for accelerating air flows.

(14) The laboratory testing for this study was carried out using the tidal basin facility located in the College of Engineering & Informatics of The National University of Ireland Galway (NUIG).

(15) Referring now to FIG. 1 there is illustrated three cylinders of respective diameters (0.2 m), (0.3 m), (0.4 m) and all of 0.4 m high, each together with an aerofoil section. So, for a cylinder with, for example, the diameter of (0.3) there is an aerofoil length and a total length of (0.63 m). All tests were run for the same tidal conditions with a maximum tidal flow of the order of 0.003 m/s scaled to represent real tidal conditions. For the cylindrical prototypes current measurements were recorded along the five transects shown in FIG. 2 and then at distances of 8 cm, 12 cm, 16 cm, 20 cm and 24 cm from the cylinder sides. The shapes of the aerofoil allowed a full set of measurements along the 0, 45 and 90 transects and apart from some measurements along the 135 transects.

(16) Table 1 below shows the mid-flood acceleration expressed as a percentage above the undisturbed ambient flow.

(17) TABLE-US-00001 TABLE 1 Distance from Mid-flood Acceleration [% above Undisturbed] Cylinder Side [cm] 0.2 m Cylinder 0.3 m Cylinder 0.4 m Cylinder 8 98 109 110 12 81 82 91 16 57 65 82 20 15 46 69 24 6 12 44

(18) Certain observations can now be made. Firstly the flow acceleration achieved close to the cylinders, namely at the 8 cm stations were quite similar ranging from 98% to 110%. This suggests that the acceleration achieved immediately adjacent to a cylinder is relatively independent of the cylinder size and will be approximately 100%. Further, it should be noted that there is a clear relationship between cylinders diameter and the width of the region of accelerated flow, the region increasing in size as the size of the cylinder increases. The results are given in FIG. 3.

(19) Referring to FIG. 3 this shows clearly the comparison between the flow velocity recorded along with the 90 transect for the cylindrical prototypes.

(20) Firstly, the negative slopes (m) indicates that the magnitude of the accelerations decrease with distance from the cylinder. It further shows that as the cylinder diameter increases, the rate of decrease in accelerations with distance decreases proportionally. This indicates clearly that once the cylinder diameter is known, the width of the accelerations zone can then be estimated. Since this results in considerable linearity it is possible to calculate the distance from the side wall of the accelerator beyond which the accelerations will fall below a certain level. These can clearly be worked out to show that there is a zone of flow velocity of 80% and greater than the undisturbed flow velocity, extending from the accelerator surface to 40% of the cylinder width from the surface, i.e. its diameter. Putting it another way these experiments clearly demonstrate that within a distance of 0.4 D with a cylinder of diameter D the flow velocity will be 80% greater than the uninterrupted tidal stream.

(21) Referring to FIG. 4, as previously mentioned, field test had been carried out on a prototype, namely an accelerator and water turbine assembly, indicated generally by the reference numeral 1. There is provided a barge 2 with a width of 2.5 m. The edges of the flow accelerator 3 extend beyond the barge 2 and are in the form of shoulders 5 across some of the vertical water turbine 4 is to shield the portion of the turbine from the accelerated flow in a flow direction as seen in FIG. 4 where the direction of rotation was in opposition to flow direction and therefore reduce the drag forces induced on the turbine.

(22) The shoulders 5 can also be configured to be flaps or deflectors to further accelerate the flow near the widest part of the accelerator body and so partially shield the turbine without the complexity of preparing a recess into which the turbine can be placed.

(23) Referring to FIG. 5 there is illustrated the same barge 2, all reference numerals being the same as that in the previous FIG. 4 as they illustrate the same parts. In this embodiment there are two vertical water turbines 4. There is a device area A.sub.D and a turbine area AT which is partially shielded by the shoulder 5. The efficiency of the vertical water turbine 4 was checked and it was found to be operating at approximately 20% that is 34% of the theoretical maximum, being the 59.3% betz theoretical maximum already referred to, for such water turbines. It is very important to appreciate that clearly the turbine being used was not very efficient and could clearly be improved. However, even with that the device efficiency was of the order of 45.9% and this compares very favorably with that reported by Marine Current Turbines Ltd a leader in this industry. They have reported average peak efficiencies of 48% and indeed an instantaneous maximum efficiency of 52% for their 1.2 MW SeaGen device horizontal-axes, twin rotor system operating in Strangford Lough, Northern Ireland since 2008. This clearly demonstrates the advantage of the proposed device over existing technology.

(24) Certain conclusions can be drawn from the laboratory and field tests, namely: The greatest accelerations are achieved at the widest part of the flow accelerator that is to say along the 90 transect. The accelerations are highest close to the walls of the accelerator and then decrease linearly with distance from the walls. Proportionally larger areas of acceleration of more than 80% are achieved with wider accelerators and occur up to approximately 40% of the width.

(25) Referring now to Table 2 there is illustrated the effect of flow accelerator and on the total available power in the flow stream. This Table 2 and the corresponding graph (FIG. 6) compare the power available from free stream flows of different velocities typical of coastal waters with the power available from the same flow following an 80% acceleration. This demonstrates that an 80% acceleration of ambient flow rates increases the power available for extraction by a factor of 5.8.

(26) TABLE-US-00002 TABLE 2 Free-stream Available Accelerated Available Velocity [m/s] Power [kw/m.sup.2] Velocity [m/s] Power [kW] 0.50 0.04 0.90 0.22 1.00 0.30 1.80 1.77 1.50 1.03 2.70 5.99 2.00 2.43 3.60 14.19 2.50 4.75 4.50 27.72 3.00 8.21 5.40 47.90 3.50 13.04 6.30 76.06 4.00 19.47 7.20 113.54

(27) To provide a more accurate comparison with the operation of the SeaGen operation which employs two 16 m diameter rotors with a combined swept area of 402.18 m.sup.2 and achieves its rated power output of 1.2 MW at 2.5 m/s. All our testing and investigations to date suggest that the device of the design used in the present testing, using two vertical axis turbines mounted at the sides of the water flow accelerator, as described herein, and having a total area similar to that of the Strangford device would generate 1.44 MW. The total swept area of the turbines used with the arrangement described in this specification would be 176 m.sup.2 compared to the 402 m.sup.2 of the SeaGen installation in Strangford. The forward facing area of the water flow accelerator would be of the order of 222 m.sup.2. It should be appreciated that this figure is based on field test results that used a water turbine with an indicative efficiency of the order of 15-20%. Since there are already existing vertical axis turbines with efficiencies of 35% it would not be unreasonable to suggest that an output of 2.88 MW compared to that of the SeaGen installation, namely, 1.2 MW is achievable. Without going into the matter in any great depth it is reasonable to suggest that the size of the turbine used is of the order of 40-50% SeaGen turbine size. Since this is clearly the very expensive part of the total installation cost the capital outlay will also be considerably cheaper.

(28) The present proposal is smaller turbines operating in the laminar flow zone of highest velocity as this seems to be the most logical advance.

(29) These comparisons clearly show that the present invention has considerable advantages over what is known in the industry. Further, because of the acceleration process it becomes viable to deploy existing turbines in locations were maximum speeds do not exceed 1.5 m/s as existing turbines are not viable in flow velocities below 2.5 m/s.

(30) There were some other interesting results from the field trials which showed that shrouding too much of the water turbine was not that successful.

(31) FIG. 7 shows an arrangement in which the accelerator body has a more aerofoil shape and in which a portion of the water turbine would be mounted within a recess of the accelerator body adjacent its widest portion.

(32) In this embodiment the accelerator and water turbine assembly, indicated generally by the reference numeral 10, comprises an accelerator in the form of a pontoon 11 mounting two water turbines 12. The pontoon 11 has a front face 13 and side faces 14, each side face 14 having a recess 16 for receiving one of the water turbines 12.

(33) The accelerator body could additionally be provided with shoulders just at the edge of the body, as can be seen in FIGS. 4 and 5.

(34) There are clear advantages in using a pontoon, not least one of which is being able to position the water turbines where the uninterrupted ambient tidal stream is greatest, but also for ease of operation and maintenance.

(35) However, it will be appreciated that there are other means of mounting and securing the accelerator body in a flow. It can advantageously be tethered to the bottom of the waterway or seabed and be fully or nearly fully submerged. An alternative is that the accelerator body could be formed around a support or column for a bridge and the turbines could be attached to the accelerator body or bridge support in an appropriate manner.

(36) FIG. 8 shows an alternative arrangement for the accelerator body. The accelerator body 3 is shown with the arrows indicating the direction of water flow. Mounted on and depending from the sides of the body 3 are a pair of turbines 4. These are spaced slightly away from the accelerator body and are also located slightly downstream of the widest part of the accelerator body 3. The body 3 is provided with flaps or deflectors 5. The flaps 5 are used to modify the surface of the body and the flow across it near the widest point. They accelerate the flow and also provide some shielding for the turbine so that the portion of the turbine closest to the body is shielded from the accelerated flow. It is envisaged that the turbines will rotate in opposite directions and so shielding the portion of the turbine closest to the body will reduce the drag on that part of the turbine rotating against the flow. Various designs of flap or deflector can be envisaged. It has been found to be more convenient to use flaps to deflect the flow than to construct recesses into which the turbines can be partially inserted.

(37) It will also be noted that when of the order of 50% of the width of the water turbine was buried/shrouded within the water flow accelerator the efficiency dropped. This would appear to be related to the design of turbine used. This particular design of turbine which is not being disclosed at the present moment is of a particularly innovative design and does not form a part of the present invention.

(38) FIGS. 9a and 9b show an alternative design of deflector flap. The figures show an accelerator body 3 in a flow stream. The representation of the flow pattern is conventional flow lines, with lines closer together representing a faster flow rate. The turbine body 4 is shown as mounted at the widest part of the accelerator body or just downstream from it. Any disturbance or perturbation of the flow by the turbine is not shown. Arrows on the turbine body indicate the preferred direction of rotation of the turbine. Deflector flaps 5a are shown just upstream of the widest part of the accelerator body. In this example, the deflector flaps are relatively small but provide sufficient deflection of the flow to further accelerate the flow and also to shield the portion of the turbine closest to the accelerator body (where the flow is fastest). The advantage of the shielding effect is that it enables the portion of the turbine moving in an upstream direction to do so shielded from the accelerated flow, so reducing drag and inefficiency.

(39) It is essential when placing an accelerator and water turbine assembly in a tidal stream whether in the form of a permanent, semi-permanent or floating, submerged or semi-submerged structure such as a pontoon that the entire assembly is far enough removed from any other flow obstruction that would have a relatively significant influence on the turbine driver current. It is probably ideal in many instances that laterally spaced apart from any turbine forming part of the assembly there is an effectively uninterrupted ambient tidal stream. The important factor here is that any such flow obstruction should not have a relatively significant negative influence on the turbine driver current. For these reasons, accelerator and water turbines of the present invention are well suited for use in expansive (relatively wide and deep) open flows where fluids could find an easier path of less resistance. Therefore if two accelerators are too close together their combination becomes a single obstruction and the area between them restricts the flow and causes turbulence.

(40) It is envisaged on the basis of various tests carried out that the placement of what are affected a series of cascading accelerator and water turbine assemblies according to the invention may be arranged in a tidal stream whereby the local tidal stream impinging on the next succeeding accelerator and water turbine assembly being such as to provide what is effectively an accelerated tidal stream over and above that of the uninterrupted ambient tidal stream, upstream of the array of accelerator and water turbine assemblies. It would appear that having an array in the form of rows and columns of accelerator and water turbine assemblies according to the invention could be advantageous where the rows of accelerator and water turbine assemblies are substantially transverse across the direction of the ambient tidal stream, namely at 90 thereto and the columns are at 45 with respect to the ambient tidal stream. Effectively, the following accelerator and water turbine assemblies are staggered with respect to those on the preceding row. The purpose of the arrangement being such as to provide for the succeeding accelerator and water turbine assemblies an arrangement whereby the tidal stream being experienced by these succeeding accelerator and water turbine assemblies has a speed greater than that of the uninterrupted ambient tidal stream.

(41) Another interesting result, not originally expected, was that because of using a turbine driver current considerably greater than that of the uninterrupted ambient current, the debris that in many instances appears with existing inventions to have been delivered to their respective turbines, was not a problem with the present invention. It appears that because the direction of flow of the driver current is somewhat outwards and away from the accelerator body and side portions before it meets the water turbine which is clearly an obstruction and changes in hydraulic pressures adjacent to the accelerator faces, that it tends to divert the debris away from the accelerator body or pontoon and water turbine.

(42) In this specification the terms include and comprise and any necessary grammatical variations thereof are to be considered interchangeable and to be accorded the widest possible interpretation.

(43) The invention is not limited to the embodiments described above but may be varied in both construction and detail within the scope of the claims.