Sub sea central axis turbine with rearwardly raked blades

Abstract

A central axis water turbine is described which comprises a turbine body having a central axis; a rotor mounted on the turbine body for rotation about the central axis, the rotor comprising a central hub supporting a plurality of blades, each blade extending from a blade root mounted on the hub to a blade tip; a generator driven by the rotor; and a housing surrounding the rotor and adapted to direct water flow towards the rotor, the housing converging from a front opening forward of the rotor to a narrower throat adjacent the turbine body; wherein the blades are splayed rearward from the blade root to the blade tip by a tilt angle of 1° to 20° from a plane perpendicular to the central axis.

What is claimed is: 
     
         1 . An apparatus for generating electricity from a natural water current in a body of water, the apparatus comprising:
 a turbine body having a central axis, the turbine body configured to be disposed in the body of water;   a rotor mounted on the turbine body for rotation about the central axis, the rotor including a central hub supporting a plurality of blades, each blade of the plurality of blades extending from a blade root mounted on the central hub to a blade tip, the rotor configured to be rotated by the natural water current within the body of water, the natural water current flowing parallel to a surface of the body of water;   a generator driven by the rotor, the generator configured to generate electricity;   a cowling defining a flow channel, an internal wall of the cowling surrounding the rotor, the cowling configured to direct the natural water current towards the plurality of blades;   at least one support strut for supporting the generator in a central position within the flow channel, the at least one support strut including a hollow duct for the passage of at least one of an electrical line or a hydraulic line;   wherein each blade tip of the plurality of blades is disposed adjacent to, but not contacting, the internal wall of the cowling and each blade of the plurality of blades is raked in a downstream direction from the blade root to the blade tip by a downstream rake angle of 1° to 20° from a vertical plane perpendicular to the central axis.   
     
     
         2 . The apparatus of  claim 1 , wherein the at least one support strut includes a plurality of support struts for supporting the generator in a central position within the flow channel. 
     
     
         3 . The apparatus of  claim 1 , wherein each one of the at least one support strut extends tangentially outward from the generator to the internal wall of the cowling. 
     
     
         4 . The apparatus of  claim 1 , wherein the housing extends upstream of the blades a selected distance to facilitate direction of water flow towards the blades. 
     
     
         5 . The apparatus of  claim 1 , wherein the flow channel includes a flow restriction comprising a convergent-divergent venturi, tapering from openings at either end of the flow channel towards an inner part of the flow channel. 
     
     
         6 . The apparatus of  claim 5 , wherein the convergent-divergent venture includes a housing comprising a converging section which converges from a front opening forward of the rotor to a narrower throat adjacent the turbine body. 
     
     
         7 . The apparatus of  claim 1 , wherein the rake or tilt angle is from 4° to 6°. 
     
     
         8 . The apparatus of  claim 7 , wherein the rake or tilt angle is about 5°. 
     
     
         9 . The apparatus of  claim 1 , wherein the generator is directly connected to a shaft. 
     
     
         10 . The apparatus of  claim 9 , wherein the generator is connected to the shaft by a splined connection. 
     
     
         11 . The apparatus of  claim 1 , wherein the plurality of blades includes 3 or 6 blades. 
     
     
         12 . The apparatus of  claim 1 , further comprising a plug disposed at the blade root, the plug configured to minimize interference to water flow. 
     
     
         13 . The apparatus of  claim 1 , further comprising a nose cone mounted on the rotor. 
     
     
         14 . The apparatus of  claim 1 , further comprising a variable speed drive. 
     
     
         15 . The apparatus of  claim 1 , wherein the housing includes portions which are fastened together when assembled into the turbine. 
     
     
         16 . A method for generating power from natural water currents in a body of water, the method comprising:
 providing a central axis water turbine according to  claim 1  to a body of water having natural water current flowing parallel to a surface of the body of water;   allowing natural water current flowing through the turbine to cause the blades to rotate; and   drawing power from the turbine.