Cross Flow Twist Turbine

Abstract

A cross flow turbine having one or more aerofoil blades rotatably mounted about a central axis and connected to said axis at or near each end of the one or more blades. The blades have a degree of torsional flexibility that make them twistable about the longitudinal blade axis to reduce the aerodynamic efficiency of the blades to control the rotational speed of the turbine. The twist of the blades can be actively controlled by means of a spring, other mechanical actuator or motor.

1 . A cross flow turbine comprising: 
 one or more aerofoil blades rotatably mounted about a central axis and connected to said axis at or near each end of the one or more blades    wherein said one or more blades are provided with a degree of torsional flexibility such that they are twistable about a longitudinal blade axis to reduce the aerodynamic efficiency of the one or more blades to control the rotational speed of the turbine.    
   
   
       2 . A turbine as claimed in  claim 1  wherein, the one or more blades are provided with a rotatable connector to allow the one or more aerofoil blades to twist about the longitudinal blade axis.  
   
   
       3 . A turbine as claimed in  claim 2  wherein, the rotatable connector couples the one or more aerofoil blades to the central axis at one end of the one or more blades.  
   
   
       4 . A turbine as claimed in  claim 2  wherein, the rotatable connector couples the one or more aerofoil blades to the central axis at both ends of the one or more blades.  
   
   
       5 . A turbine as claimed in  claim 2  wherein, the rotatable connector is positioned a distance along the longitudinal axis of the one or more aerofoil blades to couple two sections of the one or more aerofoil blades.  
   
   
       6 . A turbine as claimed in  claim 1  wherein, rotation of the one or more aerofoil blades is driven by tension in the one or more blades caused by centripetal force.  
   
   
       7 . A turbine as claimed in any of  claim 2  wherein, rotation of the rotatable connector is driven by tension in the one or more blades caused by centripetal force.  
   
   
       8 . A turbine as claimed in any of  claim 2  wherein the rotatable connector is provided with a rotation inhibiting means that prevents rotation below a predetermined centripetal force threshold.  
   
   
       9 . A turbine as claimed in  claim 8  wherein, the rotation inhibiting means comprises a torsion spring wound against a rotation stop which holds the one or more blades in place.  
   
   
       10 . A turbine as claimed in  claim 8  wherein, the rotation inhibiting means comprises one or more springs fixed at a helical angle to the central axis of rotation and to the one or more blades at the other end.  
   
   
       11 . A turbine as claimed in  claim 8  wherein, the rotation inhibiting means comprises two triangular sections of stiff material with flexible links therebetween, said links forming a Z shape.  
   
   
       12 . A turbine as claimed in  claim 1  wherein, the one or more aerofoil blades are configured to twist in a predetermined direction when a tension threshold is reached.  
   
   
       13 . A turbine as claimed in  claim 1  wherein, the one or more aerofoil blades are configured to twist in a first direction to feather turbine rotation.  
   
   
       14 . A turbine as claimed in  claim 1  wherein, the one or more aerofoil blades are configured to twist in a second direction to stall turbine rotation.  
   
   
       15 . A turbine as claimed in  claim 2  wherein, rotation of the rotatable connector is driven by an actuator.  
   
   
       16 . A turbine as claimed in  claim 15  wherein, the actuator operates at a predetermined threshold of central axis rotational velocity.  
   
   
       17 . A turbine as claimed in  claim 15  wherein, the actuator is powered.  
   
   
       18 . A turbine as claimed in  claim 15  wherein, the actuator is manually controllable.  
   
   
       19 . A turbine as claimed in  claim 15  wherein, the actuator is automatically controllable.  
   
   
       20 . A turbine as claimed in  claim 1  wherein, the torsional flexibility of the one or more aerofoil blades are set at a predetermined level.  
   
   
       21 . A turbine as claimed in  claim 1  wherein, the one or more aerofoil blades are capable of adopting a troposkien shape during rotation about the central axis.  
   
   
       22 . A turbine as claimed in  claim 1  wherein the one or more aerofoil blades comprise one or more flexible ropes enclosed by an aerofoil shaped profile.  
   
   
       23 . A turbine as claimed in  claim 22  wherein, the aerofoil shaped profile contains a packing material to mechanically fix the aerofoil shaped profile to the one or more ropes.  
   
   
       24 . A turbine as claimed in  claim 1  further comprising 
 connection means provided at an end of the one or more blades which are releasably connectable to the central axis such that when speed of rotation of the turbine about the central axis increases to or over a predetermined threshold level the one or more blades are released.    
   
   
       25 . A turbine as claimed in  claim 24  wherein, the connection means is releasably connectable by means of a clamp.  
   
   
       26 . A cross flow turbine comprising: 
 one or more aerofoil blades rotatably mounted about a central axis and connected to the central axis at or near each end of the one or more blades by connection means wherein the connection means provided at one end of the one or more blades is releasably connectable and is released when speed of rotation of the turbine about the central axis increases to or over a predetermined threshold level.    
   
   
       27 . A turbine as claimed in  claim 26  wherein releasing one end of the one or more aerofoil blades causes the forward driving force of the one or more blades to be reduced.  
   
   
       28 . A turbine as claimed in  claim 26  wherein excess tension in the one or more blades due to centripetal forces caused by excess rotational speed causes the one or more blade ends to be released.  
   
   
       29 . A turbine as claimed in  claim 26  wherein the one or more aerofoil blades are flexible.  
   
   
       30 . A turbine as claimed in  claim 26  wherein the connection means is releasably connectable by means of a clamp.  
   
   
       31 . A turbine as claimed in  claim 26  wherein each of the one or more aerofoil blades are releasably connectable and wherein release of the one or more blades occurs upon reaching said predetermined speed of rotation threshold.  
   
   
       32 . A turbine as claimed in  claim 26  wherein the one or more blades are released substantially simultaneously.  
   
   
       33 . A turbine as claimed in  claim 26  wherein a single mechanism is used to release all of the one or more blades.  
   
   
       34 . A turbine as claimed in  claim 26  wherein when the one or more blades are released they swing out under centripetal forces.  
   
   
       35 . A turbine as claimed in  claim 34  wherein release of the one or more blades immediately slows the turbine.  
   
   
       36 . A turbine as claimed in  claim 35  wherein further slowing then occurs due to the adverse aerodynamic geometry of the one or more blades when held at one end only.