SUMMARY OF THE INVENTION
According to a first embodiment, the present disclosure relates to a fluid turbine comprising a rotor, having an axis of rotation, comprising at least two rotor blades disposed at a radius from the axis of rotation, moving along a circumferential tangent path line (TPL), each rotor blade having a pitch axis and a variable pitch angle. The fluid turbine further comprises a mechanism operable to control the pitch angle of at least one rotor blade about its pitch axis and to vary the pitch angle of the rotor blade from a first pitch angle at a first circumferential location about the axis of rotation to a second pitch angle at a second circumferential location about the axis of rotation.
According to a second embodiment, the present disclosure relates to a fluid turbine comprising a rotor, having an axis of rotation, comprising at least two rotor blades disposed at a radius from the axis of rotation, moving along a circumferential tangent path line (TPL), each rotor blade having a pitch axis and a variable pitch angle. The fluid turbine further comprises a mechanism operable to control the pitch angle of at least one rotor blade about its pitch axis and to vary the pitch angle of the rotor blade from a first pitch angle at a first circumferential location about the axis of rotation to a second pitch angle at a second circumferential location about the axis of rotation to a third pitch angle at a third circumferential location about the axis of rotation.
According to a third embodiment, the present disclosure relates to a fluid turbine comprising a rotor, having an axis of rotation, comprising at least two rotor blades disposed at a radius from the axis of rotation, moving along a circumferential tangent path line (TPL), each rotor blade having a pitch axis and a variable pitch angle. The fluid turbine further comprises a mechanism operable to control the pitch angle of at least one rotor blade about its pitch axis and to vary the pitch angle of the rotor blade from a first pitch angle at a first circumferential location about the axis of rotation to a second pitch angle at a second circumferential location about the axis of rotation to a third pitch angle at a third circumferential location about the axis of rotation to a fourth pitch angle at a fourth circumferential location about the axis of rotation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a fluid turbine according to certain embodiments of the present disclosure;
FIG. 2 is an end view of a fluid turbine according to certain embodiments of the present disclosure;
FIG. 3 is a graph of five profiles of rotor blade pitch (Θ) vs. rotor blade position (Ψ) about the central axis of rotation of the turbine; and
FIG. 4 is a table showing, for each of the five profiles in FIG. 3, the rotor blade pitch (Θ) at ten distinct blade positions about the central axis of rotation of the turbine.
DETAILED DESCRIPTION OF THE DRAWINGS
A system and method of the present patent application will now be described with reference to various examples of how the embodiments can best be made and used. Like reference numerals are used throughout the description and several views of the drawings to indicate like or corresponding parts, wherein the various elements are not necessarily drawn to scale.
FIG. 1 is an isometric view of a fluid turbine 100 according to certain embodiments of the present disclosure. Structurally, turbine 100 consists of a rotor assembly comprising a torque tube 104 riding on bearings 106 mounted on a frame 102. Torque tube 104 is designed to prevent each rotor hub 108 from rotating independently of the other rotor hubs 108. Torque tube 104 is oriented along a central axis which is intended to be disposed generally perpendicular to the direction of fluid flow. The turbine 100 comprises arrays of radially-disposed struts 110 mounted to rotor hubs 108 at their proximal ends and to a set of rotor blades 112 at their distal ends. The rotor blades 112 shown in FIG. 1 are high aspect ratio airfoils/hydrofoils having a clearly defined leading and trailing edge. Turbine 100 shown in FIG. 1 comprises 10 blades, but alternate embodiments may have more or fewer blades, depending on the application. The rotor blades 112 are attached to the struts 110 in such a manner as to allow the rotor blades 112 to be individually pivoted with respect to the circumferential tangent path line of turbine 100, thus altering the pitch angle of each rotor blade 112 as turbine 100 rotates. The angle of the rotor blades may be controlled via mechanical linkages, hydraulics, pneumatics, linear or rotary electromechanical actuators, or any combination thereof. In certain embodiments, the rotor pitch angle profile may be controlled by a cam-and-follower mechanism operating in concert with one or more of the above systems of actuation. According to one such mechanism, a set of cam followers ride along a surface of a centrally-located cam. The profile of at least one surface of the cam defines the pitch profile or pitch schedule for the rotor blades.
FIG. 2 is an end view of a fluid turbine 100 according to certain embodiments of the present disclosure. The fluid turbine 100 shown in FIG. 2 incorporates ten rotor blades 112. The pitch angle of the ten rotor blades 112 are designated angles A-J with the blade pitch angle of the rotor blade at angular position 0 being designated angle “A”. The blade pitch angles of the other rotor blades 112 are designated angles “B” through “J”, at multiples of 36 degrees from angle “A”, counter-clockwise. Thus, angle “B” is the pitch angle of a rotor blade 112 disposed at an angular position 36 degrees counter-clockwise from 0, angle “C” is the pitch angle of a rotor blade 112 disposed at an angular position 72 degrees from 0, and so forth.
Because of the fact that the angle between a rotor blade 112 and the fluid flow will vary as the rotor blade 112 moves around the axis of rotation of the turbine 100, the optimal pitch angle for torque generation will vary accordingly as that rotor blade 112 moves around the axis of rotation. In order to optimize the angle between the blade pitch and the fluid flow, turbine 100 disclosed herein incorporates at least one mechanism to vary the blade pitch according to angular position as a rotor blade 112 moves around the rotational axis of the turbine 100. The pattern or profile of blade pitch vs. angular position may vary depending on a number of factors, including but not limited to rotor velocity and free stream fluid velocity. Thus, it may be desirable to modify the blade pitch profile as conditions change.
As described above, those of skill in the art will recognize that a blade pitch value of zero in FIG. 4 represents the condition wherein chord line is aligned with the circumferential tangent path line of the blade, while a positive value represents the condition wherein the nose of the blade is disposed in toward the axis of rotation of the turbine and a negative value represents the condition wherein the nose of the blade is disposed out away from the axis of rotation of the turbine.
FIG. 3 is a graph of five profiles of rotor blade pitch (theta) vs. rotor blade position (psi) about the central axis of rotation of the rotor. The profiles are designated “Profile 1,” “Profile 2,” “Profile 3,” “Profile 4” and “Profile 5.” Profiles 1 through 5 are non-sinusoidal profiles, although each incorporates certain sinusoidal attributes. Angular positions A-J about the axis of rotation of the rotor are designated by the appropriate letters and correspond to the positions shown in FIG. 2. Those of skill in the art will recognize that a blade pitch value of zero represents the condition wherein the blade chord is aligned tangent to the circumferential path line along which the blade moves. This alignment may also be described as one lying normal to a vector from the axis of rotation of the rotor to the pitch axis of the rotor blade. As above, a positive value represents the condition wherein the nose of the blade is disposed in toward the axis of rotation of the turbine, while a negative value represents the condition wherein the nose of the blade is disposed out away from the axis of rotation of the turbine.
FIG. 4 is a table showing, for each of the five profiles shown in FIG. 3, the rotor blade pitch (theta) at the ten distinct blade positions A-J about the central axis of rotation of the turbine. Angular positions A-J set forth in FIG. 4 correspond to the angular positions shown in FIG. 2 about the axis of rotation of the rotor. Those of skill in the art will appreciate that the angles depicted in FIG. 4 are certain specific angles which have been shown to be useful within the context of the present disclosure. Those of skill in the art will also appreciate that similar profiles to those shown and described will be useful within the context of the present disclosure.
It is believed that the operation and construction of the embodiments of the present patent application will be apparent from the Detailed Description set forth above. While the exemplary embodiments shown and described may have been characterized as being preferred, it should be readily understood that various changes and modifications could be made therein without departing from the scope of the present invention as set forth herein.
Patent Application
20120134820
