Fluid turbine with variable pitch shroud segments

Abstract

One or more variable pitch airfoils in fluid communication with a rotor of a fluid turbine can control the amount of energy directed to the rotor, and further control the amount of energy generated by the turbine. Varying the pitch of the airfoils may provide a means of controlling the power output of a fluid turbine without the need to control the pitch of the rotor blades, and may further provide a means of mitigating the effects of wind shear on the rotor. Variable pitch airfoils may also include a means of controlling the active power, reactive power and SCADA, of a group of fluid turbines.

1 . A shrouded fluid turbine comprising:
 a rotor; and   a ringed airfoil comprising a plurality of pivotable airfoil segments, each pivotable airfoil segment having a low pressure surface in fluid communication with the rotor.   
     
     
         2 . The shrouded fluid turbine of  claim 1 , wherein each pivotable airfoil segment is rotatable about an axis to change a pitch of the pivotable airfoil segment. 
     
     
         3 . The shrouded fluid turbine of  claim 1 , further comprising a pitch control mechanism that alters the pitch of at least a portion of the ringed airfoil. 
     
     
         4 . The shrouded fluid turbine of  claim 3 , wherein the pitch control mechanism is configured to continuously change a pitch of at least a portion of the ringed airfoil while the shrouded fluid turbine is in use. 
     
     
         5 . The shrouded fluid turbine of  claim 1 , wherein a pitch of each of the plurality of pivotable airfoil segments is individually adjustable. 
     
     
         6 . The shrouded fluid turbine of  claim 1 , wherein the plurality of pivotable airfoil segments includes a plurality of outwardly curving airfoil segments, and wherein the ringed airfoil further comprises a plurality of inwardly curving airfoil segments. 
     
     
         7 . The shrouded fluid turbine of  claim 1 , wherein the ringed airfoil further comprises a frame, and each of the plurality of pivotable airfoil segments is pivotably coupled to the frame. 
     
     
         8 . The shrouded fluid turbine of  claim 1 , wherein the ringed airfoil further comprises a plurality of arms, each arm coupled to, and configured to adjust a pitch of, one or more of the plurality of pivotable airfoil segments. 
     
     
         9 . The shrouded fluid turbine of  claim 1 , wherein the ringed airfoil comprises a plurality of mixing elements configured to create a plurality of mixing vortices downstream of the rotor. 
     
     
         10 . The shrouded fluid turbine of  claim 9 , further comprising a second ringed airfoil downstream of the ringed airfoil having the plurality of mixing elements. 
     
     
         11 . The shrouded fluid turbine of  claim 10 , wherein the second ringed airfoil comprises a second plurality of pivotable airfoil segments. 
     
     
         12 . The shrouded fluid turbine of  claim 1 , wherein the rotor is in direct communication with a generator. 
     
     
         13 . The shrouded fluid turbine of  claim 1 , wherein the rotor is in communication with a generator via a gearbox assembly. 
     
     
         14 . A shrouded fluid turbine comprising:
 a rotor defining a rotor plane; and   a ringed airfoil having a plurality of fluid contact surfaces pivotable to change a unit mass flow rate through at least a portion of the rotor plane.   
     
     
         15 . A method of operating a shrouded fluid turbine, the method comprising:
 providing a shrouded fluid turbine comprising:
 a rotor; and 
 a ringed airfoil including a low pressure surface in fluid communication with the rotor; and 
   altering a pitch of at least a portion of the ringed airfoil.   
     
     
         16 . The method of  claim 15 , wherein the ringed airfoil comprises a plurality of pivotable airfoil segments, and wherein altering the pitch of at least a portion of the ringed airfoil comprises changing a pitch of at least one of the plurality of pivotable airfoil segments. 
     
     
         17 . The method of  claim 15 , wherein altering the pitch of at least a portion of the ringed airfoil comprises altering the pitch to reduce the unit mass fluid flow rate through the rotor plane. 
     
     
         18 . The method of  claim 15 , wherein altering the pitch of at least a portion of the ringed airfoil comprises altering a pitch of a first portion of the ringed airfoil to be different than a pitch of a second portion of the ringed airfoil. 
     
     
         19 . The method of  claim 18 , wherein altering the pitch of the first portion of the ringed airfoil to be different than the pitch of the second portion of the ringed airfoil reduces fluid shear forces on the shrouded fluid turbine. 
     
     
         20 . The method of  claim 15 , wherein the pitch of at least a portion of the ringed airfoil is altered at least once while the rotor is rotating about a central axis of the shrouded fluid turbine. 
     
     
         21 . The method of  claim 15 , wherein the pitch of at least a portion of the ringed airfoil is continuously altered during operation of the shrouded fluid turbine. 
     
     
         22 . A method of operating a shrouded fluid turbine having a rotor and a shroud with a low pressure surface in fluid communication with the rotor, the method comprising:
 measuring at least one variable associated with operation of the shrouded fluid turbine; and   altering a pitch of at least a portion of the shroud based on the measured at least one variable.   
     
     
         23 . The method of  claim 22 , wherein the shroud comprises a plurality of pivotable shroud segments and altering a pitch of at least a portion of the shroud comprises changing a pitch of at least one of the plurality of pivotable shroud segments. 
     
     
         24 . The method of  claim 22 , wherein altering a pitch of at least a portion of the shroud based on the measured at least one variable at least partially compensates for fluid shear forces on the shrouded fluid turbine. 
     
     
         25 . The method of  claim 24 , wherein the measured at least one variable comprises a load variable selected from a group consisting of: blade load, blade bending, blade tip acceleration, nacelle tilt loading, and load as a function of azimuthal rotor position. 
     
     
         26 . The method of  claim 24 , wherein the measured at least one variable comprises a first fluid velocity measured at first portion of a rotor plane and a second fluid velocity measured at a second portion of the rotor plane. 
     
     
         27 . The method of  claim 24 , wherein altering a pitch of at least a portion of the shroud based on the measured at least one variable dampens oscillations in a support structure for the shrouded fluid turbine. 
     
     
         28 . The method of  claim 24 , wherein the measured at least one variable comprises a tower base moment variable, and wherein altering a pitch of at least a portion of the shroud based on the measured at least one variable reduces movement of the tower base. 
     
     
         29 . The method of  claim 28 , wherein the tower base movement variable is selected from a group consisting of: tower-top acceleration, tower tilt and rotor-power output. 
     
     
         30 . The method of  claim 22 , wherein the shrouded wind turbine supplies power for a utility grid, and the measured at least one variable comprises a control variable; and wherein a pitch of at least a portion of the shroud is altered to augment or reduce a power output of the shrouded wind turbine based on the measured at least one variable. 
     
     
         31 . The method of  claim 30 , wherein the control variable is selected from a group consisting of: rotor speed, rotor-power output, rotor-shaft torque, and ambient wind speed. 
     
     
         32 . A method of controlling a power output of an array of shrouded wind turbines, each shrouded wind turbine including a rotor and a shroud having a low pressure surface in fluid communication with the rotor, the method comprising:
 measuring a reactive power of the array; and   altering a pitch of at least a portion of the shroud of at least one of the array of shrouded wind turbines based on the measured reactive power to augment or reduce the reactive power of the array.   
     
     
         33 . The method of  claim 32 , wherein the shroud of each of the array of shrouded wind turbines comprises a plurality of pivotable shroud segments, and wherein altering a pitch of at least a portion of the shroud of the at least one of the array of shrouded wind turbines comprises changing a pitch of at least one of the plurality of pivotable shroud segments. 
     
     
         34 . The method of  claim 32 , wherein the power output is controlled during a low-voltage ride-through. 
     
     
         35 . The method of  claim 32 , wherein altering a pitch of at least a portion of the shroud of the at least one of the array of shrouded wind turbines causes a first turbine or a first set of turbines to yaw. 
     
     
         36 . The method of  claim 32 , wherein the yawing reduces the overall power output of the first turbine or first set of turbines. 
     
     
         37 . The method of  claim 35 , wherein the yawing deflects wind from the first turbine or set of turbines toward a second turbine or set of turbines to equalize power output from each turbine in the array.