US 20110115228 A1
A flow enhancement improvement for an underwater turbine generator (10) is disclosed wherein a longitudinal hole (240) is disposed in the central area (26), typically a hub (20) of the generator (10), and a second, augmentor duct (41), preferably rigid, is disposed about the outer duct (40) or housing of the unit to create a slot (200) area. The slot (200) and hollow hub (20) create areas of smooth, laminar fluid flow. The leading edges of the hub (20) or central ring and the augmentor (41) and outer ducts (40) are elliptical to enhance the fluid dynamics of the structure.
1. A hydro turbine generator apparatus for generating electrical power from water flow, said apparatus comprising at least one rotor disk, and at least one generator, characterized by:
a) a bi-directional augmentor duct disposed about said at least one rotor disk; and
b) a longitudinal hole through the center of said at least one rotor disk.
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The present application is a continuation of previously filed U.S. patent application Ser. No. 11/663,001, which has a filing date of Aug. 27, 2007 and is an United States national phase entry of previously filed PCT International Patent Application No. PCT/CA2005/00267, which was filed on Feb. 24, 2005 and claims priority to previously filed Canadian Patent Application No. 2,481,820, which was filed on Sep. 17, 2004. The contents of the above-named previously filed patent applications U.S. Ser. No. 11/663,001; PCT/CA2005/00276; and CA 2,481,820; are herein incorporated by reference into the present application in their entirety as though they formed part of the specification as originally filed.
The present invention relates generally to underwater ducted turbines for hydrokinetic electrical power generation. More specifically, underwater ducted turbines comprising a dual augmentor duct structure and a longitudinal hole through the hub of the turbine which enhances water flow are disclosed.
Bi-directional, rim generating, ducted underwater turbines for generating electrical power are known, such as the applicant's previously filed PCT application PCT/CA02/01413 to Davis et al. There is a desire to improve the flow characteristics, and therefore, the efficiency of such designs. Fixed augmentors are known to increase flow through the turbine.
U.S. Pat. No. 4,219,303 to Mouton et al. disclosed a rigid inner primary nozzle within a flexible outer nozzle which slightly overlaps the primary nozzle, creating a space between the nozzles for uni-directional flow.
U.S. Pat. No. 6,406,251B1 to Vauthier disclosed a system of pivoting flaps on the exterior surface of a hydroturbine accepting bi-directional flow. However, this system is mechanically complicated.
The theoretical advantage of a slot in the duct of a conventional, uni-directional flow turbine with a single duct was discussed in Kirke, B., Developments in Ducted Water Current Turbines, School of Engineering, Griffiths University.
It is also known to have a central space through a hydroturbine generator. U.S. Pat. No. 2,509,442 to Matheisel disclosed a ducted propeller turbine with no hub or root section to the blade which is prone to excessive deflection, vibration and high cycle fatigue, particularly as without an inner support ring the blades are cantilevered towards the centre of the unit from the housing.
U.S. Pat. RE38,336E (Reissue of U.S. Pat. No. 5,592,816) to Williams disclosed a hydroelectric turbine with a central open area of unrestricted flow surrounded by the blades which proposed reducing down current turbulence. U.S. Pat. No. 6,648,589B2, also to Williams, disclosed a hydroelectric turbine with a central open area of unrestricted flow surrounded by the blades to aid in increasing the velocity of the water flowing through the single blade and to eliminate the turbulence that occurs behind the hub in traditional hub generator hydroelectric turbines. The Williams patents employ complicated hydraulic and mechanically driven generators with a uni-directional turbine blade configuration without ducting nor hydrodynamic structures to direct water flow in an efficient manner. The Williams patents do not incorporate a set of bearings at the hub to improve the structural integrity of the unit and reduce blade deflection.
The present invention satisfies the need for a structurally and mechanically simple and inexpensive to manufacture flow enhancement design which increases water flow, provides a bypass for sea life and debris thereby reducing the environmental impact of the unit, reduces vibration and hydrodynamic drag and increases the operating efficiency of underwater ducted turbines.
A flow enhancement structure in a hydro turbine generator apparatus for generating electrical power from water flow is provided according to one embodiment of the present invention, the apparatus comprising a hub substantially parallel to a water flow, at least one rotor disk, an outer duct disposed about the rotor disk and at least one generator and characterized by a second, bidirectional augmentor duct disposed about the outer duct; and a longitudinal hole through the hub. The flow enhancement structure may include a plurality of struts projecting from the hub, thereby reinforcing the turbine against vibration caused by water flow through the hole. The at least one rotor disk may include at least one blade having a blade area, the ratio of the area of the longitudinal hole to the blade area being between 1:1 and 1:15. The hub may include two ends and an outer surface, the ends having a diameter equal to or lesser than the diameter of the hub at any other point, thereby creating a hydrodynamic shape and improving the efficiency of the apparatus. The apparatus may be bi-directional. The plurality of struts may be operable as guide vanes along their length within the annular area between the hub and the outer duct. The plurality of struts may be curved along their length within the annular area between the hub and the outer duct. The plurality of struts may be dimensioned for smooth annular flow within the slot area.
A hydro turbine generator apparatus for generating electrical power from water flow is provided according to another embodiment of the present invention. The hydro turbine generator apparatus comprises at least one rotor disk, and at least one generator, characterized by a bi-directional augmentor duct disposed about said at least one rotor disk; and a longitudinal hole through the center of said at least one rotor disk.
A flow enhancement structure in a hydro turbine having a hub and at least one blade projecting from a longitudinal axis therethrough is provided according to yet a further embodiment, the hub comprising a longitudinal hole substantially along the longitudinal axis and defined by an interior surface of the hub, the hub also comprising two ends and an outer surface, the ends having a diameter equal to or lesser than the diameter of the hub at any other point, thereby creating a hydrodynamic shape and improving the efficiency of the turbine, whereby a flow enhancement structure further comprises a plurality of struts projecting radially from the hub to a housing disposed about the turbine, thereby reinforcing the turbine against vibration caused by water flow through the hole. The ratio of the area of the longitudinal hole to a blade area of the at least one blade may be between 1:1 and 1:15. The turbine may be bi-directional. The plurality of struts may be operable as guide vanes between the hub and the outer duct. The plurality of struts may be curved between the hub and the outer duct.
The apparatus and method of the present invention will now be described with reference to the accompanying drawing figures, in which:
The dual duct structure 43 is secured to the hub 20 by a plurality of struts 24 which also act as guide vanes within the area of the annulus 51. The struts 24 are shaped merely as structural support struts in the area of optional slot 200 and not as curved guide vanes. In the preferred embodiment there are five guide vanes 24 at each of the two ends of the turbine generator 10. The vanes 24 are preferably evenly spaced radially about the hub 20 axis. In a preferred embodiment, two counter-rotating rotor disks 50 are rotatably attached to the hub 20 and a plurality of blades 30, optimally symmetric hydrofoil blades, extend radially from said hub 20 to a rotor rim 54 which seats in a groove (not shown) in the interior surface of the outer duct 40 and is rotatable in a bearing race, or in a variation, a magnet bearing race. In other variations, single or multiple rotor disks 50 may be employed. The flow enhancement slot 200 and hole 240 structures may be employed not only for tidal applications, but also for other turbine generation applications, as one skilled in the art can appreciate.
In the preferred embodiment the dual augmentor duct 43 is a rigid structure manufactured from composite material. The dual augmentor duct 43 may be made from any composite material such as fiberglass, Kevlar™, carbon fiber, fiber-reinforced concrete or any other combination known in the art. Advantages of the rigid, symmetrical dual duct 43 arrangement include simplicity of manufacture, installation and maintenance and low capital cost. In a variation, a stainless steel rigid frame covered by a flexible composite material is used.
The interior wall of the augmentor duct 41 diverges towards the augmentor duct rim 62, thereby producing a venturi effect as the water 100 flows through the duct 20. Both ends of the dual augmentor duct 43 are effectively water inlets as the turbine generator 10 is bidirectional. The central portion of the augmentor duct 41, is cylindrical. In operation, water flow 100 converges as it passes the inlet rim 62 and follows the profile of the augmentor duct 41 and outer duct 40. The gap or slot 200 between the outer duct 40 and augmentor ducts 41 is a smooth annular flow area. The blade tips 30 and rotor rim 54 (not shown here) are contained in annulus 51 and are not disposed in the slot 200. After the water flow 100 passes the rotor disks 50, the outer duct 40 and augmentor duct 41 diverge again, to allow for the smooth diffusion of the water flow 100 back to free stream conditions. The symmetry of the dual augmentor duct 43 achieves high hydraulic efficiencies in a bi-directional tidal environment. In a preferred embodiment, the duct entry 45 and exit 46 are axi-symmetric. Alternate configurations such as square, rectangular or any other arbitrary shape may be employed as dictated by the parameters of specific sites or applications such as tidal regime and local bathymetry. The optimal shape for each site is determined by performing a computational fluid dynamic analysis of the site. A preferred embodiment, however, is axi-symmetric.
The optimal design is further characterized by an inlet area 45 (augmentor duct rim 62) equal to the exit area 46 (opposite augmentor duct rim 62) and a throat area, turbine blade area, or annulus 51 (cylindrical section) that ranges from about nine-tenths (0.9) to one quarter (0.25), and preferably between about one half (0.5) to one quarter (0.25) of the exit area 46 depending on the site-specific tidal conditions. The annulus 51 is the area between the inner surface of the outer duct 40 and the outer surface of the hub 20 through which the turbine blades 30 pass. In a preferred embodiment, for general applications, the ratio of the central throat or inner surface of the outer duct 40 central portion to the augmentor duct rim 62 diameter is 0.5. In variations the ratio may be between about 0.1 and 0.9, and more particularly between about 0.1 and 0.8.
The leading and trailing edges or rims of both ducts 43 (including outer duct 40 rim 64) optimally have a hydrodynamic profile with a cross section that is similar in shape to an airplane wing. This profile increases the flow 100 into the turbine annulus as well as creates a smooth transition of the flow 100 into the adjacent slot 200 and around the entire tidal turbine generator 10.
In a preferred embodiment, an anti-fouling coating, such as Si-Coat 560™, is applied to the ducts 43. In a variation, specific areas susceptible to the buildup of aquatic organisms are coated. The anti-foul coating has the additional benefit of providing a high lubricity surface which facilitates laminar flow, thereby improving the efficiency of the turbine generator 10.
Buoyancy material may be incorporated into the internal structure of the dual augmentor duct 43 and the generator housing 92 in order to increase the overall buoyancy of the tidal turbine generator 10. Neutral buoyancy is a key optional characteristic of the unit as it may facilitate the process of unit removal and maintenance. In a preferred embodiment, the ducts 43 are comprised of a composite shell structure filled with poly vinyl chloride closed cell marine foam (not shown) in order to achieve neutral buoyancy for the entire tidal turbine generator 10. Other closed cell foams, as known in the art, may also be employed. In addition to the buoyancy function, the closed cell foam acts as a noise suppression device by attenuating the hydrodynamic and electrical noise produced by the tidal generator 10, thus mitigating any possible acoustic impacts of the tidal turbine generator 10 on cetaceans and other marine mammals.
The second unique flow characteristic is a longitudinal hole 240 through the hub 20. The inner surface of the hub 20 is optimally cylindrical. The outer surface of the hub is optimally elliptical, or barrel shaped, rising from the hub rim 27 to an apex in the flat central portion of the hub 20. The inner surface of the hub 20 defines the longitudinal hole 240 along the hub 20 axis. In other variations, the profiles are varied as determined by a computational fluid dynamic analysis of the specific tidal site.
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In variations, depending on the results from specific computational fluid dynamics (“CFD”) analyses, the contours of the slot surface 200 may be varied. The leading 34 and trailing 35 edges have a hydrodynamic profile with a cross section that is similar in shape to an airplane wing. This edge profile increases the flow 100 into the annulus area 51 as well as creates a smooth transition of the flow 100 into the central opening 240.
The central hole 240 is a region where the conservation of fluid momentum is maintained. This feature both eliminates the region of separation that previously existed behind the hub 20, and in addition, draws additional flow 100 through the surrounding turbine rotor disk area 51. Elimination of the region of separation also reduces the vibratory loading on the structure 10 resulting in improved reliability and therefore reduced maintenance cost.
This central hole 240 increases both the output torque, and therefore the overall efficiency of the tidal turbine 10.
The central hole 240 concept also has a positive environmental benefit in addition to its performance enhancing effects. This central region 240 provides a fish and marine mammal bypass in the event that this sea life enters the tidal turbine generator 10. The hole 240 through the centre is large enough to accommodate all types of fish, and the majority of other marine mammals (with the exclusion of large whales).
The area occupied by the central hole 240 is less than or equal to the area occupied by the turbine rotor disk 51. The exact ratio of these areas is determined by CFD analysis performed using site-specific parameters. The optimal hole 240 to turbine rotor disk area 51 ratio is between 1:15 and 1:1, but in variations other ratios may be employed to some advantage.
The hub 20 that defines the central hole 240 is an integral structural member of the tidal turbine generator 10. The radial load or force on the turbine 10 is transferred from the hub 20 to the guide vanes or struts 24 and then through to the primary structural member, the outer duct 40. This produces a very stiff and robust structure. The hub 20 houses a series of bearings 58 that provide the principal radial alignment and thrust support for the turbine rotor 50. Water lubricated, low friction bearings 58 are mounted at the turbine rotor hub 20. A central journal bearing 58 (or bearings) provides radial support for the rotor 50 and two thrust bearings 58 are located on either side of the rotor 50 to accommodate axial excursions resulting from the bi-directional hydrodynamic load on the turbine 10. An additional set of water lubricated bearings 58 is also employed at the blade (rotor) rim 54 location to counteract the axial thrust load of the rotor 50. This complete bearing arrangement 58 reduces the susceptibility of the turbine rotor 50 to racking. Optionally, a magnetic bearing system or any other bearing system that is well known in the art can be employed.
In a preferred embodiment, the hub 20 consists of marine grade stainless steel. An alternate embodiment includes a hub 20 manufactured from a composite material such as fiberglass, Kevlar™, Carbon fiber or any combination known in the art.
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The fluid that enters the slot 200 maintains its momentum through the slot 200 and then imparts this momentum into the boundary layer of the diverging section of the dual augmentor duct 43. This injection of fluid has the effect of both delaying the region of separation on the divergent portion of the duct 43 as well as drawing additional flow through the enclosed annulus 51 area. The net result of these effects is a significant increase in performance in blade 30 torque, and therefore an overall efficiency improvement of the tidal turbine generator 10.
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In operation, the reduced vibrational loading on the tidal turbine generator 10, smoother laminar flow, increased water flow 100 through the rotor disks 50 due to the slot 200 and hole 240 features increase the output torque of the rotor disk 50 by above 50% in comparison to a similar turbine generator without the above-described flow enhancement structure, depending on the unit 10 type and site parameters, which in turn translates into an overall efficiency improvement of greater than 10%.
As will be apparent to those skilled in the art in light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.