Segmented wind turbine airfoil/blade

Abstract

A wind foil blade/airfoil for a wind turbine wherein the airfoil includes a series of vertical segments having unique offset shapes to provide openings between segments enabling the segments to function as wind sails when moving downwind to thrust the blade forward and to act as an airfoil when the blade is moving into and upwind, wherein the wind foil blade has a high forward thrust.

Description

This application claims the priority filing date of provisional patent application USPTO application No. 61/337,665 having a filing date of Feb. 11, 2010, titled “Segmented Wind Turbine Airfoil/blade, the applicant being Troy W. Livingston, the same inventor hereof.

BACKGROUND OF INVENTION

Wind power turbines are largely divided into vertical axis wind power turbines and horizontal axis wind power turbines. The present invention is directed to a vertical axis wind power turbine and more particularly to the turbine foils/blades used in such vertical axis turbines. As is known, vertical axis wind turbines are often omni-directional, and are not influenced by the wind direction and have certain advantages over the horizontal axis turbines. However, in many prior art vertical axis turbines, the starting torque is low. Further the design of prior art wind/airfoils for vertical axis turbines need improvements in efficiency. This is the case because the vertical rotation of the air foils causes the blades to provide a substantial torque only during a portion of the rotational movement. To address this feature of vertical axis wind turbines, the present inventor has developed a vertical axis wind turbine using wind airfoils/blades which significantly improved the efficiency of the wind/air foil as well as providing a higher starting torque than provided by prior art wind foils.

SUMMARY OF INVENTION

This invention relates to wind turbines and more particularly to vertical axis wind turbines having wind foils of the airfoil type. It is an object of the present invention to provide a vertical axis wind turbine wind foil which airfoil is hollow and includes plurality of plate segments mounted in spaced contiguous relation to form openings there between. The foregoing feature provides airflow entry ports into the hollow airfoil and enable the wind to thrust against the segments and to enter into said airfoil and thrust against the interior thereof to push the airfoil forward. Also, the wind/airflow thrusts against the segments which more efficiently enables capture of wind energy than prior art blades regardless of the position of the foil in the rotating cycle or arc around the vertical axis. The invention provides an efficient high torque as well as a high starting torque.

The foregoing features and advantages of the present invention will be apparent from the following more particular description of the invention. The accompanying drawings, listed herein below, are useful in explaining the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a vertical axis wind turbine of the type utilizing the airfoils/blades of the invention;

FIG. 2 is a relatively enlarged isometric view showing the three airfoils used in the wind turbine of FIG. 1;

FIG. 3 is a top view depicting the three airfoils of FIG. 1 mounted on a central vertically oriented shaft;

FIG. 4 is an exploded isometric view showing the construction of a preferred embodiment of the inventive segmented airfoil/blade;

FIG. 4B is a depiction of a prior art;

FIGS. 5A and 5B comprise a composite view depicting a cross section view of the segmented blade, and the airflow moving around the blade to show the low turbulence effected by the segments;

FIG. 5C is an alternative embodiment of the foil depicted in FIG. 5A;

FIG. 6 is a graph showing the torque provided by the system comprising three airfoils;

FIG. 7 shows the airflow created on the inventive windfoil/blade at various positions of the blade relative to the wind direction as the airfoil rotates around a central axis; and

FIG. 8 is a graph showing a comparison of the torque provided by standard smooth airfoil and the torque provided by the inventive segmented foil.

DESCRIPTION OF INVENTION

FIG. 1 shows a vertical axis wind turbine assembly 21 having a rotatable shaft 23 that provides a central axis of rotation for the segmented airfoils/wind foils 25, 26 and 27 and is an example of a preferred structure. In the preferred embodiment described herein the airfoils are symmetrical in shape, although other standard shapes may be used. The wind turbine 21 is supported on a suitable base 28. In the embodiment shown an electrical generator 29 is mounted on a housing 31 that also encloses the shaft 23. As is well known, the generator 29 includes a suitable rotor rotated by shaft 23 which cooperates with a stator to generate electrical energy.

While three airfoils are shown in the wind turbine system disclosed herein, it will be appreciated that more airfoils may be used in the system. Vertical axis wind turbine systems having three or more airfoils are commonly used and the airfoils of this invention are applicable for use in a majority of such systems.

Refer now also to FIG. 2 that shows the airfoils/blades 25, 26 and 27 affixed between to two sets of three arms, generally labeled 32, 33, and 34, one set being mounted above the other. Airfoils 25, 26, and 27 are rigidly affixed to the end of the respective spaced arm pairs 32, 33 and 34. Airfoils 25, 26 and 27 are all identical and each has a leading edge or nose 35, two side surfaces 39 and 41 and a trailing edge 36, see also FIG. 3. The two sides of the airfoils comprise multiple segmented plates, to be more fully described herein below. The trailing edge of the airfoils 36 comprises two flat spaced vanes 61 and 62 and a tail fin 50, see also FIG. 5A. Top and bottom plates 43 and 45 cover the top and bottom of the airfoils, see FIG. 4.

In the embodiment shown, the airfoils 25, 26 and 27 are constructed of sheet aluminum. The leading edge or nose 35 is bullet nose in shape, i.e., rounded, and the body of the airfoil tapers down toward a thinner trailing edge 36. In one embodiment the nose of the of the airfoil is four inches in thickness, the chord or length of the foil (nose to trailing edge) is twelve inches, and the height of the airfoil indicated at 47 is two meters. The airfoils are hollow as indicated at 60. The width or spacing between the forward sides 39 and 41 at the nose end of the airfoils, normally stated as “thickness” is relatively large as compared to an airplane wing airfoil, for purposes that will become clear. Also in present wind turbines, an odd number of foils is commonly utilized, since an odd number of foils tend to be more easily balanced, while an even number of foils tend to impede the flow of the with respect to each other and also to cause vibration problems.

As also shown in FIGS. 4 and 5A-5C, the inventive airfoils 25, 26 and 27 are formed of plate segments or vanes 51, 52 and 53 which extend vertically from the top to the bottom of the foil 25 and form the major part of the surface panels or sides 39 and 41. Reference will be made to a single airfoil, but as stated above the airfoils 25, 26 and 27 are identical, and the description of one foil will applies to all three of the airfoils.

Each of the two sides of the airfoil 25 has segments 51, 52 and 53 mounted in symmetrical relation for forming the surfaces or panels 39 of the airfoil. In cross section the segments 51, 52 and 53 are in a zigzag shape and might be considered as a backward and modified broad “S” in shape, as clearly shown in the FIGS. 4 and 5A and 5B. The outer surface or panel of each segment 25, 26 and 27, provides a front-to-back offset configuration; that is, the outer arm 63 of the “S” is in line with the contoured side of the airfoil, see FIG. 5B. The inner arm 65 of the “S” extends toward the hollow center of the airfoil 25, and the middle arm 66 is angled (zigzags) to connect to the other two arms.

Importantly, segment 51 is mounted to establish an opening or gap (generally labeled) 57 that extends perpendicular to the chord of the airfoils between the vertical edge of segment 51 and the following adjacent segment 52. Likewise segment 52 is mounted to form an opening or gap 57 between it and segment 53. There are thus four vertical openings or gaps 57 formed on each side of the airfoils 25, 26 and 27. In an orientation looking from the leading edge or nose 35 to the trailing edge 36, the airfoils provide a smooth contour of a standard airfoil that reduces the wind force as the airfoil moves upwind and which also may provide lift or forward thrust to the turbine system. Moreover, and importantly, in the reverse orientation or looking from the trailing edge 36 toward the leading edge 35, the segmented foils 25, 26 and 27 provide or effect a series of openings or gaps 57 to provide entry or access ports for wind airflow into the hollow center 60 of the airfoil to push the airfoil and provide a positive torque to the airfoil. Further, as wind moves, past the segments 51, 52 and 53 the airflow also thrusts or pushes against the surfaces of all of the segments to provide propelling force for the turbine system.

The last two or rear segments 61 and 62 of the airfoils are spaced flat plates with one of the segments having a tail fin 50 affixed thereto, as will be described herein below.

FIG. 4 depicts in pictorial view shows the construction of the inventive segmented wind airfoil/blade 25. A prior art air foil 25PR is shown in FIG. 4B to clearly show the difference in construction between the prior art and the inventive segmented foil 25; note particularly the closed external surface of the prior art foil 25PR. It has been found from test analysis (see FIG. 8 to be described below) that the inventive segmented air foil provides a much higher efficiency for a wind turbine operation than the prior art airfoil.

Refer now also to FIGS. 5A and 5B. It was necessary to establish that the inventive segmented foils developed minimal air turbulence which would reduce the efficiency of the airfoil. Test results showed that when the wind direction is against the nose of the airfoil 25 (see FIG. 5A), the airflow will be as shown in FIG. 5B. The airflow lines 56 show minimal turbulence at the segmented or gap opening 57. For present purposes, there is essentially no turbulence created by the inventive segments.

Refer now to FIG. 6 which depicts the function of the three airfoil 25, 26 and 27 as one operating assembly. In the graph of FIG. 6, the horizontal axis denotes degrees of the circular path about the shaft on which the foils rotate, the ordinate or vertical axis denotes the torque in ounce inches indicated as being developed by the foils. Note for example that as airfoils 25 and 27 are providing an increasing or more positive torque as airfoil 26 goes down toward a negative torque. Thus two of the three foils are continuously moving to provide a more positive torque. In composite or total, the three foils provide a high average positive torque throughout each circular path about the central axis; this is indicated by the horizontally line labeled “A”. The high positive torque developed by the three foils overcomes or minimizes the negative torque developed by the system wherein a stall condition of each of the airfoil that exists between approximately 270° and 290°, indicated by the horizontal line labeled B. The airflow effects of the wind on the segmented airfoils will be further explained with reference to FIG. 7.

As alluded to above, another improvement provided by the inventive airfoil 25 is the construction at the trailing edge 36 and of a tail fin 50. As mentioned above, the last two or trailing edge segments of the airfoil 25 are formed of flat rectangular shaped plates 61 and 62. The segments 61 and 62 are mounted in spaced relation to each other to provide a longitudinal air gap 64 at the trailing edge of the airfoil 25 and along the length of the foil. The tail fin 50 is affixed to rear segment 62. In the embodiment shown the fin 50 is affixed at an angle of five to ten degrees with relative to the plane of the surface of segment 62. Fin 50 provides an extended surface for creating positive torque when the turbine blade assembly is in the cross wind portion of its rotation. When the wind turbine blade is traversing 90% to the wind, or is going slightly downwind, the fin extension provides additional surface area for creating positive torque. The fin extension also creates negligible drag when going up wind or down wind therefore the net result is a positive torque added to the fin over the turbine blades complete 360% rotation.

The individual blade segments that combined make up the aerodynamic share of the turbine blade are arranged to create the greatest force when being pushed down-wind by the airflow. For up-wind rotation the combined segments create an airfoil effect similar to an airplane wing. This wing profile shape provides a low drag airfoil thus minimizing the negative torque created when the turbine blade is moving into the wind (up-wind). Thus, overall efficiency of the turbine blade may be measured as the net positive torque created by the turbine blade assembly as it rotates through 360%. Maximizing the positive torque when being pushed down-wind and minimizing the negative torque when moving into the wind (up-wind) is the desired function. Also a positive overall torque should be attained during the cross wind portion of the cycle without negatively affecting the other portions of the rotating cycle.

It has been found that a tail fin affixed to the airfoil also functions in similar fashion as a fin on an airplane wing. That is, the fin flap creates additional lift to a wing at low negative wind positions. This additional lift is utilized in the turbine blade assembly to add positive rotation torque to the turbine blade as it passes through the cross wind position depicted in FIG. 7 at the 0% and 180% positions relative to the wind direction.

FIG. 7 is a schematic view showing the position of the foils at various degrees with relation to the indicated wind 70 direction. It is known in the art that the subject type wind turbine is an omni-directional system; it is independent of the wind direction and will operate for all wind directions. For convenience in explanation, the illustrative airfoil in FIG. 7, is depicted as rotating in a counter clockwise direction with the wind direction being from 0° toward 180°. The forces on the segmented wind foil and the resulting torque will also be described at the positions where the foil is at 0°, 45°, 90° etc. It will of course be appreciated that FIG. 7 shows stationary positions, but that the foil is attached to a respective arm and is actually rotating around a central axis. Every airfoil goes through all of these positions, as well as all intervening positions during each revolution around the central axis. Also, it should be understood that FIG. 7 depicts a single airfoil while in actuality, the three airfoils 25, 26 and 27 are rotating simultaneously and developing rotating torques which are additive.

Since the disclosed wind turbine is an omni-directional turbine, the same operating parameter exist when the air stream flows from any; direction around the “clock”. For convenience, in FIG. 7, the wind stream 70 is shown flowing into or impinging on the rotating air foils from the North or 0°. This is of course an arbitrary selection. Accordingly as viewed from above, the rotation of the central axle will be in a counter clockwise direction. As depicted in FIG. 7, the leading edge 35 of airfoil 25 at the position shown at 0° will progress downwardly to 90° and continue around the circular path. It will be understood that between 0° and 180°, the leading edge of the air foil moves into the wind/air stream or upwind, and between 180° and 0° the air foil moves with the wind/air stream or downwind.

The segmented airfoil 25 reacts differently with the wind stream at its various orientation around the rotating path. It is an objective of the segmented foils that the net sum of the force of the wind stream against the airfoil around the circular path is a strong positive torque. As mentioned above, the wind foils are not only driven by the wind stream, but since the three airfoils are mounted on the same shaft each air foil is also driven by the other airfoils.

To obtain some comparison data, a standard prototype smooth airfoil model was compared with a similar size and construction of the inventive segmented wind foil model. Tests were performed in a steady state mode with the airfoils placed in set positions, data taken and the models were then placed in a next position and data taken, etc. The results of the data are shown in FIG. 8. In the graph of FIG. 8, the abscissa, or horizontal axis, denotes degrees of the circular path about the shaft on which the foils rotate, the ordinate or vertical axis denotes the torque in ounce inches indicated as being developed by the foils. The line labeled “P” indicates the torque being developed by the prior art smooth airfoil at the various positions around the circular path starting at 0° and ending at 360/0°. The line labeled “S” indicates the torque developed by the segmented foil at the same positions as the smooth foil. The shaded area in the graph depicts the improved torque provided by the segmented inventive foil. The segmented blade provides a much higher positive torque than the smooth foil. Note that at about 200° to about 280°, the segmented blade provides a slightly more negative torque than the smooth blade, but overall from 0° through the complete circular path, the segmented foil provides a much higher net torque.

Refer now back to FIG. 7 and the various positions of an airfoil 25 depicted in the figure. The results or data of FIGS. 6 and 8 can be more fully understood. Starting at the position of the inventive the segmented airfoil at the 0° position.

At 0° The wind impacts the blade/wind foil 25 at its side and only the shape of the backward offset of the segments provides a forward thrust.

At 45° The wind impacts the outside surface of the side of the blade at a 45 degree inclined angle. The segments act as a series of sails to catch the wind and improve the thrust on the blade over a single airfoil shape blade.

At 90° The wind airfoil shape created by the segments and leading edge round shape provide a greater thrust than a smooth airfoil shape when being pushed by the wind directly from the rear.

At 135° At this angle, the inside surface segments are acting as a series of sails to provide the maximum forward thrust to the blade assembly creating the maximum torque through the 180° rotation

At 180° At this angle, the blade is in transition from being pushed downwind to moving into and up wind direction. Lift created by the airfoil shape of the assembly provides forward thrust to the system until the angle of attack of the blade is increased to the stall point at approximately 200° and no forward thrust is generated by the wind motion.

At 225° At this angle, the blade is rotating into the wind and any lift created by the airfoil is lost as the airfoil shape is in a stall or no lift condition, and its wind resistance is creating a negative torque on the system through approximately 300° rotation.

At 270° At this angle, the airfoil shape is in a stall condition creating no forward thrush and the airfoil shape is heading into the wind causing it drag to create a negative thrust on the blade. This condition continues to exist until the blade reaches approximately 290° and lift created by the airfoil shape of the blade creates more lift thrust than the drag resistance of the blade creating a net positive thrust for the system.

At 360/0° Returning to this angle, the net positive thrust of the wind on the blade creates the torque on the central shaft supporting the multiple blades. The torque is then used to generate output energy from the system and kinetic energy for the blade assembly to continue rotating through the zero and negative thrust angle areas while the blade assembly rotates through the full 360°.

It should of course be understood, that the three airfoils 25, 26 and 27 shown in FIGS. 1, 2 and 3 operate or function together as a single unit wherein each foil is identical to the other two foils and each foil cooperates and adds to the other foils to create a desired torque. For this purpose, the results of one segmented airfoil were interpolated or combined with the torque of the other two segmented airfoils 26 and 27 which followed the first airfoil by 120° and 240° respectively. FIG. 6 is the result that shows that the three airfoils aid or assist each other as a single unit to provide a net positive torque.

Note for example that as output of airfoils 25 and 27, indicated by the graph lines labeled 25 and 27, are providing an increasing or more positive torque as airfoil 26, indicated by line 26, goes down toward a negative torque. Thus two of the three airfoils are continuously moving to provide a more positive torque. In composite or total, the three airfoils provide a high positive torque throughout each circular path of central shaft 23; this is indicated by the line labeled “A” in FIG. 6. The high positive torque developed by the three airfoils overcomes or minimizes the negative torque indicated by the liner labeled “B” in FIG. 6 developed by the system. As described with reference to FIG. 7 a stall condition exists for each of the airfoil between approximately 270° and 290°.

FIG. 5C depicts an alternative embodiment of the airfoil labeled 25A also including segmented vanes 51A, 52A, and 53A. The difference of the segments shown in FIG. 5A to that shown in FIG. 5C is clear. In cross section the alternative embodiment of the vanes, for example vane 53A, forms an inverted arc of a circle. However, the vane 53A of FIG. 5C is mounted to function similarly as the corresponding vane 53 of FIG. 5A.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. An airfoil/wind foil for a wind turbine formed of a thin housing with the airfoil being is hollow and having a leading edge, two contoured sides and a trailing edge, said airfoils length being longer than the dimensions of its chord, and said airfoil being mountable to rotate about a central vertical axis of a wind turbine when said turbine is subject to wind airflow, said airfoil comprising

a) a series of vane segments forming a section of the sides of said airfoil housing and extending normal to the chord of the airfoil;

b) said segments being mounted in spaced contiguous relation to one another to form openings between said to provide airflow paths into the interior of said airfoil to enable said airfoil to function as a wind sail when moving downwind to thrust the blade forward; and

d) said segments being positioned to conform to the external configuration of an airfoil to provide an airfoil effect when the blade is moving upwind.

2. An airfoil/wind foil for a wind turbine wherein the airfoil is hollow and has a rounded leading edge, two contoured sides and a trailing edge, said airfoils length being longer than the dimensions of its chord, an said airfoil being mountable to rotate about a central vertical axis of a wind turbine, said airfoil comprising

a) a series of vane segments extending normal to the chord of the airfoil;

b) said segments being formed to be of a zigzag shape in cross section in the general form of a broad backward “S”;

c) said segments being mounted in spaced contiguous relation to one another to provide openings between segments to provide airflow paths through said openings into the interior of said blade to enable said airfoil to function as a wind sail to when moving downwind to thrust the blade forward; and

d) said segments being positioned to conform to the external configuration of an airfoil to provide an airfoil effect when the blade is moving upwind.

3. An airfoil as in claim 1 further including

a) a pair of flat vertically extending segments mounted in relative spaced relation on the trailing edge of said air foil; and

b) a fin extending back from and along the vertical edge one of said flat segments;

c) said fin providing an extended surface for creating positive torque when the turbine blade is in the cross wind portion of its rotation.

4. An airfoils as in claim 1 further including

a) a pair of flat vertically extending segments mounted in relative spaced relation on the trailing edge of said air foil; and

b) a fin extending back from and along the vertical edge one of said flat segments;

c) said fin providing an extended surface for creating positive torque when the turbine blade is in the cross wind portion of its rotation.

5. An airfoil as in claim 1 further including

a) a pair of flat vertically extending segments mounted in relative spaced relation on the trailing edge of said air foil; and

b) a fin extending back from and along the vertical edge one of said flat segments; said fin comprising a first section mounted in parallel to the plane of said flat segments and an end section formed at an angle to said first section, said angle being in the range of five to ten degrees angled inwardly toward the axis of said wind turbine;

c) said fin providing an extended surface for creating positive torque when the turbine blade is in the cross wind portion of its rotation.

6. An airfoil as in claim 1 wherein

a) said segments are mounted in spaced contiguous relation to one another to form said openings there between whereby airflow paths are provided extending from openings on one side of said airfoil into the interior of said airfoil and to openings on said other side of said airfoils to enable said airfoil to function as a wind sail when moving downwind to thrust said blade forward; and

d) said segments being positioned to conform to the external configuration of an airfoil to provide an airfoil effect when the blade is moving upwind.

7. An airfoil/wind foil for a wind turbine wherein the airfoil is hollow and has a rounded leading edge, two contoured sides and a trailing edge, said blade's length being longer than the dimensions of its chord, and said airfoil being mountable to rotate about a central vertical axis, said blade comprising

a) a series of plate segments extending normal to the chord of the airfoil;

b) said segments being formed with an offset shape of first, second and third plate surfaces joined in series, said second surface having one side joined to said first surface at an angle, and said second surface having a side opposite to said first side joined to said third surface at an angle wherein said first and third surface are in parallel spaced relation;

c) said segments being mounted spaced contiguous relation to one another to provide openings between segments to provide an air paths through said openings into the interior of said blade to enable said airfoil to function as a wind sail to when moving downwind to thrust the blade forward; and

d) said segments being positioned to accommodate the external configuration of an airfoil to provide an airfoil lift effect when the blade is moving upwind.

8. A airfoil as in claim 2 wherein

a) said first and third surfaces of said segments are in parallel spaced relation;

b) said trailing edge of said inverted “S” of a segment being positioned adjacent, but spaced from, the leading edge of an adjacent segment;

c) said positioning of said segments forming a gap or spacing between said to adjacent segments in an orientation essentially perpendicular to the chord of said airfoil;

9. A airfoil as in claim 1 wherein said airfoil includes

a) an elongated slit constructed between the sides of the trailing edge of said airfoil;

b) said slit forming an inlet port entry for air when the airfoil is moving downwind; and

c) said slit forming an outlet port for air when the airfoil is moving upwind.

10. An airfoil as in claim 1 which is symmetrical and of relatively wide thickness in relation to its chord dimension to provide maximum volume for wind input into said hollow airfoil.

11. An airfoil as in claim 1 wherein top and bottom cover plates are mounted on said segmented vanes.

12. An airfoil as in claim 1 wherein said individual vane segments are in the form of an arc of a circle.