FLUID FLOW INDUCED OSCILLATING ENERGY HARVESTER MAXIMIZING POWER OUTPUT THROUGH OFF-CENTER MOUNTED TOGGLING BLUFF BODY AND/OR SUSPENSION STIFFENING MECHANISM

Abstract

A fluid flow induced oscillating energy harvester includes a stand supporting the harvester in a fluid flow; a support member mounted for movement relative to the stand in a direction perpendicular to the flow direction; a bluff body positioned substantially perpendicular to the flow direction and pivotally mounted to the support member at a position off-center from the center of mass of the bluff body, wherein sufficient fluid flow causes an oscillating movement of the bluff body and the support member relative to the stand; and an electrical generator coupled to the support member and configured to convert oscillating movement of the support member to electrical power. The harvester may include a support member spring supporting the support member for oscillation about a support member rest position wherein the support member spring exhibits a higher stiffness at higher oscillation amplitudes of the bluff body and the support member.

Claims

1. A fluid flow induced oscillating energy harvester comprising: a stand supporting the energy harvester and configured to support the energy harvester in a fluid flow; a support member mounted for movement relative to the stand in a direction perpendicular to the direction of fluid flow; a bluff body configured to be positioned substantially perpendicular to the direction of fluid flow and pivotally mounted to the support member, wherein sufficient fluid flow causes an oscillating movement of the bluff body and the support member relative to the stand, and wherein the bluff body is pivotally mounted to the support member at a position off-center from the center of mass of the bluff body; an electrical generator coupled to the support member, wherein the electrical generator is configured to convert oscillating movement of the bluff body and the support member to electrical power.

2. The fluid flow induced oscillating energy harvester according to claim 1 wherein the bluff body is pivotally mounted to the support member at a position down-stream from the center of mass of the bluff body relative to the direction of fluid flow.

3. The fluid flow induced oscillating energy harvester according to claim 2 wherein the bluff body is pivotally mounted to the support member for rotation through about a 40 degree range of motion.

4. The fluid flow induced oscillating energy harvester according to claim 3 further including a torsional spring mounted between the support member and the bluff body and configured to bias the bluff body to a neutral bluff body rest position.

5. The fluid flow induced oscillating energy harvester according to claim 4 wherein the bluff body is pivotally mounted to the support member for rotation through about a +/−20 degree range of motion relative to the bluff body rest position.

6. The fluid flow induced oscillating energy harvester according to claim 5 further including a support member spring supporting the support member for oscillation about a support member rest position.

7. The fluid flow induced oscillating energy harvester according to claim 6 wherein the support member spring exhibits a higher stiffness at higher oscillation amplitudes of the bluff body and the support member.

8. The fluid flow induced oscillating energy harvester according to claim 7 wherein the support member spring exhibits no force on the support member for a range of motion about the support member rest position.

9. The fluid flow induced oscillating energy harvester according to claim 1 further including a support member spring supporting the support member for oscillation about a support member rest position.

10. The fluid flow induced oscillating energy harvester according to claim 9 wherein the support member spring exhibits a higher stiffness at higher oscillation amplitudes of the bluff body and the support member.

11. The fluid flow induced oscillating energy harvester according to claim 10 wherein the support member spring exhibits no force on the support member for a range of motion about the support member rest position.

12. A fluid flow induced oscillating energy harvester comprising: a stand supporting the energy harvester and configured to support the energy harvester in a fluid flow; a support member mounted for movement relative to the stand in a direction perpendicular to the direction of fluid flow; a bluff body configured to be positioned substantially perpendicular to the direction of fluid flow, wherein sufficient fluid flow causes an oscillating movement of the bluff body and the support member relative to the stand; an electrical generator coupled to the stand and coupled to the support member, wherein the electrical generator is configured to convert oscillating movement of the bluff body and the support member to electrical power; and a support member spring supporting the support member for oscillation about a support member rest position, wherein the support member spring exhibits a higher stiffness at higher oscillation amplitudes of the bluff body and the support member.

13. The fluid flow induced oscillating energy harvester according to claim 12 wherein the support member spring exhibits no force on the support member for a range of motion about the support member rest position.

14. The fluid flow induced oscillating energy harvester according to claim 12 wherein the bluff body is pivotally mounted to the support member.

15. The fluid flow induced oscillating energy harvester according to claim 14 wherein the bluff body is pivotally mounted to the support member at a position off-center from the center of mass of the bluff body.

16. The fluid flow induced oscillating energy harvester according to claim 14 wherein the bluff body pivotally mounted to the support member at a position down-stream from the center of mass of the bluff body relative to the direction of fluid flow.

17. The fluid flow induced oscillating energy harvester according to claim 16 wherein the bluff body is pivotally mounted to the support member for rotation through about a 40 degree range of motion.

18. The fluid flow induced oscillating energy harvester according to claim 17 further including a torsional spring mounted between the support member and the bluff body and configured to bias the bluff body to a neutral bluff body rest position.

19. The fluid flow induced oscillating energy harvester according to claim 18 wherein the bluff body is pivotally mounted to the support member for rotation through about a +/−20 degree range of motion relative to the bluff body rest position.

20. The fluid flow induced oscillating energy harvester according to claim 19 wherein the support member spring exhibits no force on the support member for a range of motion about the support member rest position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 is a schematic view of a fluid flow induced oscillating energy harvester according to the present invention;

[0038] FIGS. 2A and B are schematic views of a fluid flow induced oscillating energy harvester with off-center mounted toggling bluff body according to one embodiment of the present invention;

[0039] FIGS. 3A and B are schematic views of the fluid flow induced oscillating energy harvester of FIGS. 2A and B;

[0040] FIG. 4A is a schematic view of a fluid flow induced oscillating energy harvester with a suspension stiffening mechanism according to one embodiment of the present invention;

[0041] FIG. 4B is an enlarged schematic view of the fluid flow induced oscillating energy harvester of FIG. 4A;

[0042] FIG. 5 is a schematic view of a fluid flow induced oscillating energy harvester according to another embodiment of the present invention;

[0043] FIGS. 6A-C are schematic views of alternative linkage arrangements of the fluid flow induced oscillating energy harvester according to further embodiments of the present invention; and

[0044] FIG. 7 is a plot of experimental results of power outputs over a range of flows of a system of the present invention using low high and variable stiffness according to the present invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] This invention is directed to a cost effective, efficient, fluid flow induced oscillating energy harvester 10 that maximizes power output and overcomes at least some of the drawbacks of the existing proposed designs. The up and down orientations in the figures is arbitrary. The harvester 10 may be supported in a fluid flow 16 extending vertically upwards generally as viewed in the figures or may be supported downward in the flow 16, such as being suspended from a barge or deck structure on the surface of a river.

[0046] One embodiment of the energy harvester 10 of the present invention is shown in FIGS. 1 and 2A and B and 3A and B. The currently proposed oscillating energy harvester 10 includes a stand 12 supporting the oscillating energy harvester 10 in a fluid stream or current, such as on a river bed or suspended into the river. The stand 12 may also be called a base, housing, support and/or piling. The construction of the stand 12, such as the shape shown in FIG. 1, is generally known in the art and need not be described in detail herein.

[0047] The stand 12 supports at least one, and generally a plurality of spaced bluff bodies 14. A pair of cantilevered bluff bodies 14 is shown in FIG. 1 extending from the stand 12, but other number of bodies 14 could be utilized. Further FIG. 1 shows a pair of bodies 14 extending from the side of the stand 12, which may be more common arrangement while FIGS. 2A-B, 3A-B and 4A and B suggest a placement of the bodies 14 above the stand 12 mainly to simplify the schematic illustration of the components of the harvester 10. Both arrangements are possible, as is suspending the bodies 14 below the stand 12 where the stand 12 is mounted above the primary flow to a floating platform or deck, such as a barge (and which surface location may represent a simpler easier location for the electrical generator and associated elements).

[0048] Each bluff body 14 may also be referenced as a prism or a beam. In the preferred embodiment each bluff body 14 is extending from the stand 12 in a cantilevered fashion as shown in FIG. 1. Alternatively, each bluff body 14 may be supported between a pair of stands 12 at opposed ends thereof, however the cantilevered arrangement shown in FIG. 1 is believed to be more economical and more efficient. Each bluff body 14 is configured to be positioned substantially perpendicular to the direction of fluid flow (shown at 16). The particular construction of the bluff bodies 14 is believed to be known to those of ordinary skill in the art and the shape and surface of the bluff body 14 may be optimized for maximizing oscillation.

[0049] In the harvester 10, each bluff body 14 is mounted for movement relative to the stand 12 at least in a direction perpendicular to the direction of fluid flow 16. As shown each bluff body 14 is coupled to a support member 18 which extends into the stand 12 to an electrical generator coupled to the stand. The electrical generator may be generally within the stand 12, or in a configuration in which the harvester 10 is suspended from a platform above the flow 16 it may be easier and more efficient to locate the electrical generator on the platform above the stand 12.

[0050] The support member 18 may take a number of forms and can include several elements, but can be generally described as the coupling between the moveable elements of the electrical generator and the oscillating bluff bodies 14. The schematic FIGS. 2A and B, 3A and B and 4A and B form a representational image of the function of the support member 18. The electrical generator may be moving a magnet coupled to the support member 18 through coils or a rotational generator as known in the art.

[0051] The electrical generator may be mounted within the stand 12, particularly for sub-fluid positioning, but may be located anywhere where it can obtain the necessary mechanical movement of the support member 18 and convert this to electrical energy. The construction of the electrical generator, per se, is known to those of ordinary skill in the art.

[0052] Conventional bearing, packing and sealing structures 22 can maintain and restrict the movement of the support member 18 and associated bluff body 14 to a constrained oscillation motion. The details of constructing the support member 18 and the bearing, packing and sealing structures 22 are generally known in the art. The form of the sealing structures 22 is dictated by the particulars of the support member 18.

[0053] Oscillation of the bluff body 14 is driven by fluid flow 16 past the bluff body 14, wherein sufficient fluid flow 16 causes an oscillating movement of the bluff body 14 and support member 18 relative to the stand 12 and provides mechanical movement to the electrical generator thus providing a fluid flow induced oscillating energy harvester 10.

[0054] A key feature of the present invention is that the bluff body 14 is pivotally mounted to the support member 18 via pivot member 20. Specifically, the fluid flow induced oscillating energy harvester 10 according to the invention provides that the bluff body 14 is pivotally mounted via pivot 20 to the support member 18 at a position off-center from the center of mass of the bluff body 14 as shown. The bluff body 14 is pivotally mounted to the support member 18 at a position down-stream from the center of mass of the bluff body 18 relative to the direction of fluid flow 16 as shown.

[0055] The fluid flow induced oscillating energy harvester 10 will have in one embodiment of the invention each bluff body 14 pivotally mounted to the support member for rotation through about a 40 degree range of motion. A torsional spring (not shown) may be mounted between the support member 18 and the bluff body 14 about the pivot 20 and configured to bias the bluff body 14 to a neutral bluff body rest position (i.e. the torsion spring provides a restoring force). Thus the bluff body 14 may be pivotally mounted to the support member 18 for rotation through about a +/−20 degree range of motion relative to the bluff body 14's rest position. Other restoring force members may be utilized such as elastic members coupled to the bluff body 14 or around the pivot 20.

[0056] The toggling bluff body 14 concept provides the mounting the bluff body 14 so that it can oscillate about the point of pivot member 20 downstream of the center of mass of the bluff body 14. Testing has shown that the torsion spring is helpful to provide a restoring force to the bluff body rotation and improvements to oscillation robustness have been observed with toggle ranges of about ±20°. This toggling body 14 design provides higher harvesting (higher energy yields).

[0057] One way to understand the effect is illustrated in FIGS. 3A and B which illustrate that the fluid loading is a function of the net flow direction 17 of fluid over the surface of the bluff body 14. The net flow direction 17 depends on the flow velocity 16 and the velocity of the bluff body 14 perpendicular to the flow 16. The attack angle of the flow oscillates as the bluff body 14 oscillates. If, for example, the peak driving force of the shape illustrated in the figures for the body 14 was maximum when the net flow 17 was parallel to the top surface of the trapezoidal bluff body 14, then the peak driving force would occur when the oscillator reaches a higher velocity in the case of the toggling bluff body 14.

[0058] The oscillating support member 18 and bluff body 14 is suspended or supported by a support member spring 24 shown in FIGS. 4A and 4B. The support member spring 24 establishes a zero-displacement or rest position for the support member 18. If there is no flow, the structure formed of support member 18 portion of the electrical generator coupled thereto and body 14 will rest at this position and when there is sufficient flow, the structure will oscillate about this rest position. FIG. 4A and B do not illustrate the toggling prism or body 14 of FIGS. 2A-3B merely to illustrate that the features of the suspension stiffening mechanism of FIGS. 4A and 4B may be used independent of the toggling bodies 14 and vice versa. An important feature of this embodiment shown in FIGS. 4A and B is that the support member spring 24 exhibits a higher stiffness at higher oscillation amplitudes of the bluff body 14 and the support member 18. Further the support member spring 24 may be configured, as shown, to exhibits no force on the support member 18 for a range of motion about the support member rest position. Specifically the spring 24 is coupled to the support member 18 through a pin 26 within a slider 28 such that spring 24 effectively disengages near the neutral or zero displacement point. An alternative to this design is to have a single spring engaged at lower amplitudes and added springs become engaged at higher amplitudes. In a further alternative, a single spring design could also be implemented that exhibits higher stiffness at higher amplitudes

[0059] It is apparent that many variations to the present invention may be made without departing from the spirit and scope of the invention. For example, FIG. 5 is a schematic view of a oscillating energy harvester 10 according to another embodiment of the present invention in which a rack 36 is mounted to a linkage 42 coupled to the support 18 and meshes with a pinion 32 driving a rotary generator (the electrical generator) with the pinion 32 mounted on a separate linkage 44 coupled to the stand 12. The compound motion of the support 18 and the linkages 42 and 44 provides for an improved harvesting rate. Specifically as the amplitude of the motion of the body 14, increases the motion of the rack 36 relative to the pinion 32 increases thereby increasing the rotation rate of the pinion 32. Similarly, FIGS. 6A and B are schematic views of a proposed linkage assemblies for the fluid flow induced oscillating energy harvester 10 according to further embodiments of the present invention. In FIG. 6A the support 18 is replaced with a four bar linkage 46 and the electrical generator, here in the form of a rotary generator, is moved outside of the stand 12 to a position between the four bar linkage 46 as shown using the linkages 42 and 44 similar to FIG. 5. Analogous to FIG. 5 the compound motion of the four bar linkage 46 and the linkages 42 and 44 provides for increased harvesting yield. Specifically, as the amplitude of the motion of the body 14 increases the motion of the rack 36 relative to the pinion 32 increases thus increasing the rotation rate of the pinion 32. The spring 24 can be replaced with torsional springs to maintain the rest position of the body 14. FIG. 6B is analogous to the embodiment of FIG. 6A except the four bar linkage 46 is replaced with a Peaucellier-Lipkin linkage 48, wherein the compound motion of the Peaucellier-Lipkin linkage 48 provides for an increased harvesting rate. Specifically as the amplitude of the motion of the body 14 increases the motion of the rack 36 relative to the pinion 32 increases thus increasing the rotation of the pinion 32. FIG. 6C shows an alternative harvester 10 linkage arrangements (with the generator removed for clarity) that may be more applicable for a suspended harvester 10 described herein and is merely illustrating further linkage possibilities.

[0060] Further there can be many other methods and spring designs for providing a nonlinear suspension of the support member 18 with higher stiffness at higher oscillations. The tuning of the system dynamics of the harvester 10 is important to efficiency. Variation in the flow rate is one of the factors that impacts energy harvester 10 tuning. FIG. 7 illustrates a plot of experimental results of power outputs over a range of flows of a system of the present invention using low high and variable stiffness according to the present invention. As can be seen in the figures the variable stiffness design can result in a higher yield over the expected flow ranges, as in this example it meets or exceeds the low K system yields at all reasonable flows and will exceed the high K values at flow rates below a kick in threshold. Maintaining tuning of the energy harvester 10 over a broad range of flow rates may be easier if the oscillation frequency would increase as the flow rate increases and this can be achieved to some degree if the suspension is stiffer at higher displacements as shown in FIGS. 4A and B.

[0061] It should be apparent that other alternatives are possible within the spirit and scope of the present invention. The present invention is defined by the appended claims and equivalents thereto.