“CROSS CURRENT TIDAL TURBINE”
Provisional Patent US 63/206,027
Filed: January 25, 2021
Brief Summary of the Invention:
Described herein is a cross current tidal turbine that converts the motion of incoming and outgoing oceanic tides into electricity. The bi-directional flows can also be harvested from estuaries and rivers that empty into the ocean. The upstream water flow impinges upon multiple slanted vanes positioned about the rotor’s periphery. The flow then passes through the rotor’s hollow center and impinges upon the vanes at the downstream side of the rotor. This cross-flow action allows the drum-shaped rotor to efficiently spin in one direction. Torque values are further enhanced by using fixed guide vanes which are placed at an optimal angle within the turbine’s inlet and outlet.
Brief description of the Three Views of the Invention:
Fig. 1: A cross sectional view of the turbine assembly showing the casing, rotor and guide vanes. The Turbine’s inlet and outlet chambers are shown having inverse mirror-imaged contoured walls that, when combined with the fixed guide vanes, efficiently directs the incoming water flow to impinge upon the slanted rotor blades.
Fig. 2: A simplified isometric cross-sectional view of the turbine assembly showing how the base and rotor with blades are arranged. The drum-shaped rotor and blade assembly is supported by two bearings and retainer caps that can be removed for easy removal of the rotor. The fixed guide vane is shown.
Fig. 3: An isometric view showing the bell-mouth-shaped, rectangular inlet and outlet chambers that serve to increase the velocity of incoming tidal flows from either direction. The figure shows how the axle and rotor assembly can be raised from the casement. One of the two mirror-imaged fixed guide vanes is shown.
Background of the Invention:
The present disclosure was inspired by the Bánki-Michell Turbine. The B-M turbine was developed by Australian Anthony Michell, the Hungarian Donát Bánki and the German Fritz Ossberger. Michell obtained patents for his turbine design in 1903. The B-M design is commonly used in small hydropower plants that are generally fed by streams that flow in one direction only. The B-M design is a cross-flow type turbine which means that the one-way flow first enters the turbine, passing across the rotor blades transversely. Then, the flow passes across the rotor’s hollow center section where it then impinges upon the inside blades of the rotor’s opposite side. The flow then continues outward to rejoin the tidal stream.
The present iteration takes its design cues from the 100-year-old B-M invention. It now discloses a novel and unique application by altering the turbine’s function from being a one-way flow, stream-driven device by converting it into a cross-current, oceanic tidal driven design.
A diligent search for existing or former cross current designs yielded the following results. One of those, a tidal turbine that uses a rotor which is oriented transversely to the flow, is a design offered by Ocean Renewable Power Company of Portland, ME USA. Their patent (US 8,393,853 B2) claims a turbine using a plurality of airfoil-shaped blades that are joined to the central shaft by a plurality of radial spokes. The blades have a spiral wound trajectory being injection molded of a durable, light weight, high strength plastic material. The ORPC rotor is similar to designs seen in Vertical Axis Wind Turbines or the water-based Gorlov Helical Turbine. The GHT is another prior art design that came up in the search (US 5,451,137). the expired GHT patent describes airfoil-shaped blades with a helical trajectory and a plurality of radial spokes that connect its blades to the central shaft. Other designs are being offered by HydroQuest in France and the Canadian New Energy Corporation.
Detailed Description of the Invention:
The present invention is an impulse-type turbine where the water pressure remains constant at the rotor. The rotor is drum shaped, having a simple, welded “squirrel-cage” structure. The design allows the rotor to turn at 250 to 300 RPM’s in one continuous direction regardless of which way the bi-directional tidal flows impact the turbine’s rotor. The rotor has a central drive shaft that is supported by two bearings. Releasing the bearings from their mounts allows the entire rotor assembly to be easily raised for maintenance. Disk-shaped aluminum plates are at either end of the rotor to hold the blades in place. The blades are held in a slanted position and are made of a corrosion resistant aluminum alloy. The blades do not have an airfoil-shaped cross section; instead, they are flat or curved strips. The angle of incidence for the blades is 45° (+/- 5°).
Depending on the direction of the tidal streams, water enters the turbine through one of the two opposing intake ducts. Both intakes have a bell-mouth-shape to concentrate the incoming flow and to increase the flow’s velocity. Horizontal, fixed guide vanes span both inlets. In addition to the guide vanes, the walls of the inlets and casement openings are fared and contoured in such a way as to direct the incoming flows to efficiently drive the rotating blades with optimal force. The rotor’s cross flow design allows the passing water to impinge upon the vanes at both the upstream and the downstream side of the rotor.
The turbine casement is symmetrical. It can be placed on a river bottom or the sea floor. Alternatively, turbines can be attached to a frame structure or suspended from a floating platform or bridge. A full-sized casement can be made of modular concrete sections. Smaller turbines will have their nacelles made of sheet steel. The axle shaft extends from the casement and drives a simple transmission. There are several generator topologies to choose from. The generators are specifically designed for low and variable-speed wave and tidal energy converters.
Preferred Embodiment of the Invention:
The present invention is a novel and unique adaptation of the 100-year-old Bánki-Michell hydropower turbine that converts one-way flows into clean, renewable electricity. The new design captures bi-directional tidal flows. It is an improvement over existing and prior art cross-flow turbines.
The new rotor offers improved power capture due to its angled, axisymmetric blades. The blades are protected inside the structural casement and are manufactured with a more durable aluminum alloy. The competing design is expensive to produce with helical blades made of a plastic material, making them more vulnerable to damage from debris.
The preferred embodiment of the new design would have an array of turbines resting on the sea bed or river bottom. Lighter turbines can be stacked upon a structural framework or suspended from a floating, anchored platform or attached to the bottom of a swinging gate-like structure.
A second iteration of the new turbine is a departure from the cross-flow design. In this instance, the rotor has an inner lining that serves to capture the flows from passing through the rotor (as illustrated in Fig. 1). The rotor vanes are welded to the liner thus making the individual rows of radial vanes into separate, lengthwise buckets that fill up with the flowing water; much like a common water wheel does. This secondary iteration will have side-by-side units with dual, independently operated rotors, each having one-way, Sprague-type bearings attached to the common drive shaft. Each turbine unit would spin independently and each would have its own bell-mouth inlet pointing 180° from the other. In this way, each separate unit will turn the drive shaft in one direction only, while the other unit will be in a freewheeling mode. The water flows would simply exit the units unhindered, without restrictions to the expelled flows. This, combined with the new solid buckets in each rotor, provides optimal energy capture.
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