Patent Application
20150211482
The present invention relates to apparatus and operational method for an impeller having a specific blade structure and attachment means, more particularly, to an impulse-effected wind turbine having a circumferentially extended blade.
Sail rotor windmills are one of the oldest documented types of wind mill, which used flat pieces of cloth to deflect the wind for pumping water by absorbing kinetic energy from the wind. Savonious type windmills such as water wheels operate on flow drag and also harness working fluid kinetic energy. Savonious type wind turbines are regarded as less practical than today's most popular wind turbines which have a horizontal propeller axis and utilize blades based on airfoil lift. Following the oil embargo of the 1970's NASA invested capital into the development of alternative energy. NASA research results deemed the horizontal axis type wind turbine to be the most effective design configuration for investment. A vertical axis wind turbine system called the “Cyclogyro” (see
Referring particularly to
It is an objective of our invention to introduce a less complex and more dependable turbine system with greater return on investment, i.e., a power generating wind turbine that is more cost effective because it is more efficient in converting flow field energy into available power.
The present application discloses one or more inventions concerning a turbine configuration with unique blade design that is simpler to construct and more cost effective in converting flow field kinetic energy into available power by dynamics that differ from that of the prior art, including, for example: horizontal axis turbine airfoil lift or Savonious turbine type airfoil drag.
In brief, the invention(s) disclosed herein concerns a novel turbine and turbine blade that has greater simplicity in its construction and can be used to improve the return on investment and improve performance of wind turbines. This is especially true for so-called vertical axis wind turbines. The new improved blade implements a new concept for driving a turbine. In other words the present invention concerns a new method and means of operation for a turbine, and thus a novel type of wind turbine.
In a preferred embodiment the present invention involves turbine blades that extend as curved cantilever beams fixed (attached) at one end to the periphery of a supporting structure. Without any applied flow field forces, the curvature of the blade is concentric to the turbine center axis. As flow field forces interact with the turbine, resilience within the turbine system allows the blades to deflect away from their concentric neutral positions resulting in applied torque and angular velocity to the turbine which can be harnessed for the generation of energy such as electricity. Whether the cantilevered blades deflect radially inward toward center or outward, the resulting direction of torque and angular velocity of the turbine system is consistent with the fixed end of the cantilevered blade leading as the blades rotate about the turbine center axis. As the blades resiliently deflect from their relaxed (neutral) concentric positions, energies can be stored internally within the blade or within the interface between the blade and turbine structure, or within the turbine structure itself. All three components have the potential of acting as springs to store potential energy derived from the kinetic energy of blade deflection. Any blade deviation from the relaxed neutral position will produce torque and resulting rotation in a single consistent rotational direction.
The best turbine structure for use with the inventive blade is a cylindrical or annular turbine structure such as a “vertical axis” type of wind turbine wherein one, or preferably a plurality of blades circumferentially extend from attachment nodes spaced apart on the periphery of the cylindrical turbine carrier structure.
The inventive blade translates kinetic energy from impacting air molecules of a fluid flow field into torque and rotational speed about the turbine center (axis of rotation). The kinetic energy of the impacting flow field molecules cause resilient deflection of the cantilevered blade in a generally radial direction (either radially inward or outward) resulting in a moment couple about turbine center. The blade rotates about the turbine center consistent with the blade attachment node being the leading edge. The plurality of the impacting flow field molecules may also be referred to as flow field pressure or also as a pressure differential between the external and internal effective blade surface. The system acts as a spring when deflected from the neutral position, translating the kinetic energies of the impacting flow field molecules into turbine torque and rotational speed.
As the turbine rotates submersed within a flow field each blade oscillates radially about a neutral blade position at a frequency equal to the rotational frequency of the turbine. Two opposing blade neutral positions exist perpendicular to two maximum effective area positions within the rotational cycle. The flow field deflects the blade farthest inward when the turbine is rotated to place the blade center at the middle of the windward half of the swept area, and deflects the blade farthest outward when it is rotated to place the blade center at the middle of the downwind half of the swept area. Blade resilience also continues to produce torque as opposing wind forces are decreasing to zero as the internal blade stresses perpetually try and return the blade back to its neutral position once at the left, and once at the right end of the swept area where the blade becomes somewhat parallel to the flow field and cannot be deflected by the wind. Thus one cycle of 360 degree turbine rotation correlates with one cycle of blade deflection from radial maximum to radial minimum, then returning to maximum. The neutral position being passed through at both radial extents of the turbine sweep area.
A variation of the inventive concept involves altering the component of most resilient flexure from the blade itself to an interface component between the blade and turbine central hub. For example, the blade may be rigid but one or a combination of several of the interface components between blade and turbine hub may instead provide resilient flexure. For example, instead of beam-type flexure, a spring biased hinge may be provided between the blade and turbine axis. For example, spring-like resilience may be advantageously distributed among two or more components of the turbine such as the blade and carrier (interface) components. Using different materials and shapes to provide resilience in different ways in different components gives the turbine designer great latitude for determining a design in which none of the components is likely to be stressed beyond its elastic limits.
As common to all turbine systems, the efficiency in energy extraction (e.g., electric power generation) from the surrounding flow field is important, yet of lesser significance as compared to the entire system cost per unit of energy produced. With both factors considered critical to overall turbine system economics, the present invention offers reduced cost per unit of energy produced with comparable efficiencies to that of prior art turbine systems.
A turbine system using our inventive spring blade turbine concept is expected to be useful as a wind or water flow field energy conversion system. The system may also be reversible for the purpose of imparting energy to a surrounding medium for such purposes as for providing lift, or thrust as a fan or propeller.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.
Reference will be made in detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying drawing figures. The figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these preferred embodiments, it should be understood that it is not intended to limit the spirit and scope of the invention to these particular embodiments.
Certain elements in selected ones of the drawings may be illustrated not-to-scale, for illustrative clarity. The cross-sectional views, if any, presented herein may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines which would otherwise be visible in a true cross-sectional view, for illustrative clarity.
Elements of the figures can be numbered such that similar (including identical) elements may be referred to with similar numbers in a single drawing. For example, each of a plurality of elements collectively referred to as 199 may be referred to individually as 199a, 199b, 199c, etc. Or, related but modified elements may have the same number but are distinguished by primes. For example, 109, 109′, and 109″ are three different versions of an element 109 which are similar or related in some way but are separately referenced for the purpose of describing modifications to the parent element (109). Such relationships, if any, between similar elements in the same or different figures will become apparent throughout the specification, including, if applicable, in the claims and abstract.
The structure, operation, and advantages of the present preferred embodiment of the invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying drawings, wherein:
FIGS. 11A-11D—are schematic top views of a single blade portion of the disclosed turbine, each view illustrating details about the dynamic reactive blade deflection in progression at a windward most key point in the rotational cycle, all according to the present invention.
Elements of the present disclosure will be described in text with element names and terms having the following reference numbers (and symbols) used in the accompanying drawings.
Turbine Dynamics
In accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention is a turbine described herein to have spring like characteristics with working blade surfaces somewhat concentric to turbine center and mounted as a cantilever beam to a periphery of a supporting turbine structure. Referring to
A general description of the deflection cycle for a single blade 102 on the periphery of a vertical axis turbine is illustrated in
Determining the magnitude of torque for any blade position of cycle can be considered complex when dealing with a blade of curvature and somewhat parabolic deflection along its length. Therefore, for the purpose of simplification, a construction line 132 will be used to represent the equivalent effective area Aeff equal to that of the resilient curved blade as shown in
The fastened portion of the cantilevered blade 124 always leads the freely suspended blade end while the system is rotating. The resulting turbine central shaft torque and rotational speed equates to the extractable output power.
Each air molecule moving with the flow field of an approaching wind possesses a quantum of kinetic energy proportional to its momentum, i.e., mass times velocity. When these air molecules come into contact with a working surface of the turbine blade, an impulse of momentum and kinetic energy transfer to the blade. The turbine of the present invention operates on a principal of resilient blade action and reaction to impacting air molecules. The accumulation of impacting air molecules is commonly referred to in fluid dynamics as “dynamic pressure” acting as seen in
The reasoning for the blade's production of greater torques in the downwind hemicylinder can be seen in
Resilience for storing internal elastic energy is not limited to the blade.
The blade on the right side of
Blade stiffness is critical to the speed of blade response. The resulting operating frequency of the turbine will be greater for resilient blades of greater stiffness (i.e., greater spring bias).
For flexible blades, the amount of blade deflection progressively increases starting from near zero deflection at the fixed end of the blade to maximum deflection at the blade tail. As the magnitude of flow field force decreases, elastic energies stored within the blade act as a spring opposed the impacting air molecules or pressure differential until the blade returns to its non-stressed (neutral) position. As the blade rotates about the turbine center submersed within a flow field, cyclic blade deflections toward and away from turbine center continue. The blade deflection is always inward toward turbine center when the blade position lies in the upwind hemicylinder of the turbine and the blade deflection is always outward away from turbine center when the blade position lies within the downwind hemicylinder of the turbine. In other words, the blade deflects to a position inside the turbine periphery when the blade is upwind as in
As blade deflection increases, the center of effective blade area moves and affects the location and direction of the sum equivalent force vector creating the torque. The optimal position for the center of blade area is dependent upon flow conditions and individual turbine design performance criteria and requires involved analysis.
Looking at the blade deflection more closely, the amount of blade deflection can be divided into infinitesimal vertical segments from leading to trailing edge. Each section of which will articulate to a different angular displacement relative to the neutral position. If the blade has equal height and thickness from leading edge to tail, blade deflection will appear somewhat parabolic in shape as viewed from above, with least deflection at the fixed end. By tapering down the blade thickness as on the right side of
For simplifying any mathematical analysis, the net force applied to the entire blade can be represented by a single force vector. This force being equal to the resulting wind pressure times the effective area perpendicular to the flow field direction and passing through the effective area centroid 130. The direction of the resultant force vector will be perpendicular to 132. By mathematical analysis of a single blade throughout the peripheral cycle, the prediction of resulting static forces for a plurality of the blades can be determined by replications of the blade out of phase. The results can then be compared to experimentally recorded data.
Blade reaction to changes in direction of the approaching wind are instantaneous and result in adjustment of the reference X axis which maintains the theoretical intersection of opposing neutral positions between the windward and downwind hemicylinders.
Comparison of Static Torque
A mathematical comparison of produced static torque was made between a four-cup anemometer type of Savonious turbine shown in
For the Savonious turbine, cup geometry was a hollow straight sided wedge 602 (see
The new inventive turbine example 700 (embodiment of resilient blade turbine 100) used for comparison is shown in
For the new concept turbine, within this static analysis, the angular displacement of blade from the defined neutral position was assumed to vary linearly in oscillating fashion such that blade deflection from neutral position is zero at 0 and 180 degrees of spoke displacement, +45 degrees from neutral position at 90 and 270 degrees of spoke rotation within the cycle of turbine rotation.
For both types of turbine, static torque was calculated for a single cup or blade starting at the positive X axis=0° (degrees), and then recalculated at every 5 degree increment in the counterclockwise (positive angular displacement) direction about the turbine center. The results for each of the remaining three cups or blades was generated by shifting the complete series of torque values for one blade to be 90 degrees out of phase for the next blade. Three graphs were then generated for both turbine types. One graph showing static torque versus angular displacement from starting position for a single blade, another showing the four phase-shifted plots of torque superimposed, and finally a graph of the sum torque for all four cups or blades. The average static torques for the entire cycle was then determined.
Results indicate that the new inventive turbine produces on average 2.4 times the static torque of the Savonious cup anemometer turbine for equal blade/cup area and equal turbine sweep area. A prototype of the new turbine concept shown in
The cantilevered blade is attached to the turbine structure near the leading edge. A plurality of blades would normally be equally spaced on the turbine periphery resulting in a concert of blades deflecting independently throughout the rotational cycle. The fact that the blades are allowed to react with a flexure reaction independent of other blades on the same turbine is of critical value. While the overall turbine system including turbine structure and plurality of blades react to the applied wind forces as a single component with spring like properties, each blade instantaneously reacts to both flow field forces and accelerations caused by other blades of the same turbine. It can be said that mechanical communication exists between blades as each blade independently reacts in balancing all applied forces. The flow-field forces acting upon the curved blade surfaces will accelerate the turbine tangential speed until balance between rotational drag and the accumulated blade torque is reached, total rotational drag being the sum of resistance drag and generator resistance. The entire plurality of blades of the new turbine concept will have varying amounts of cantilevered deflection while in operation as the plurality of blades are forced to rotate at the same single turbine rotational speed. The action and reaction of each blade imposing relatively instantaneous effect on all other blades through and of the same system.
Hemispherical Torque Imbalance
As illustrated in
HAWT Tip Speed Ratio Vs. VAWT Blade Speed Ratio
With horizontal axis turbines, the tip speed ratio is defined as the ratio of blade tip speed to that of the working fluid speed. Tip speed ratios correlate directly to power coefficient. Today's best performing horizontal axis wind turbines operate at tip-speed ratios near 6.0. In comparison, a Savonious type turbine operating off working fluid drag cannot exceed a cup speed ratio of 1.0. Because of differences in blade position and orientation about the turbine, and because the entire blade effective surfaces lie on turbine periphery, the tip speed ratio is not applicable to the new turbine, and a practical substitute can be called the “Blade Speed Ratio”. The blade speed ratio being defined as the turbine tangential speed divided by the approaching flow field velocity. A working prototype of the inventive turbine 100 was designed and tested in order to determine the blade tangential speed ratio.
Turbine Tilt
As illustrated in
Blade Design
The resilient blade 102 of the present invention has resemblance to a single leaf of a common automobile leaf spring in that both are relatively flat and curved with design intent to reflect loads in the radial direction with longevity in cyclic loading being of major design concern. The blade of the present invention differs by having the tail end free and representative of the free end of a cantilevered beam with progressive deflection toward the tail. As the turbine diameter becomes large enough, the blade of the present invention can be generally flat with minimal frontal drag and can be constructed with lesser mass of materials per unit of power output as compared with conventional airfoil blades based on airfoil lift which are considerably more complex to construct with complex airfoil geometry. The present inventive blades 102 may have shape resembling an airfoil by having a taper in thickness from leading edge to trailing edge and a rounded forward edge however the principal of turbine thrust development is considered dynamically different. Where the conventional airfoil varying thickness and profile are determined based on desired airfoil lift, the varying thickness and profile for the blade of the present invention is based on the desired proper internal stress distribution and desired spring characteristics or elastic energy storage capacity. With optimization, the present invention has potential to be more efficient than conventional designs as based on the power output per unit area of frontal sweep.
The cantilevered blade of the present invention has advantage in being tailorable in design such that the blade will naturally deflect to a lesser effective frontal area as wind forces become excessive. As blade deflection progresses, resulting torque climbs simultaneously as the effective blade surface area perpendicular to the approaching wind decreases. This can be seen for blade positions at the upwind hemicylinder in
The blade geometry is best starting with greater thickness at the leading edge where stresses are greatest while tapering to a relatively lesser thickness at the trailing edge or tail of the blade where induced stresses are minimal. The objective of taper is to minimize and balance externally applied energies along the blade length so that the induced stresses are distributed as even as possible to promote longevity. Excessive blade mass correlates to excessive blade momentum during oscillation and can be detrimental by reducing oscillation frequency and unnecessarily adding to the internal stresses generated. Blade area near the tail end supports significantly less load thus requiring less blade mass. The blade material properties of resilience, strength and elasticity are critical to blade performance. Perfectly rigid blades and turbine system would not suffice for the concept to work. If the materials used to construct the blade and turbine system were perfectly rigid, impacting air molecules would not impose deflection from the concentric neutral position and no torque would be produced. At the other extreme, perfectly elastic blades would not suffice. Perfectly elastic blades would have no resistance to deflection at all, and again no torque would be produced. The blade's resistance to deflection is critical to function of the blade invention and thus engineered to deflect by such an amount as to optimize performance and longevity. The engineering details of which can be exhaustive in the documentation necessary to properly define.
Referring to exemplary illustrations in
It should be noted that as the size of the turbine diameter increases, the cyclic loading frequency will decrease resulting in greater blade longevity for the same resilience. The internally stored energy inside a blade can be perceived as an array of material atoms separated by springs that lie between holding the atoms together. Point being that the inventive blade works the same whether resilience lies within the blade material itself, or if the blade is physically constructed of segments separated by springs.
Blade Material
Some applicable materials (but not limited to) for blade material include spring steels, silicon carbide, carbon Fiber-Epoxy composites, elastomers, rubber and polyurethanes which demonstrate high resistance to cyclic flex, fatigue and creep. Some urethane resins are demonstrating excellent results as well finding use as automotive leaf springs. By designing the blade such that stress limits remain below the material elastic limit, the cycles to blade failure are deemed economically practical. The critical material property being resilience and resistance to fatigue and creep.
Techniques applied to design and construction of parts made of composite materials can result in the blade having sufficient longevity and cost effectiveness.
For example:
Orient composite filaments into a wave pattern traversing from leading to trailing edge for greater flexibility.
Minimize composite filament end count.
Tailor composite fiber path continuously around fixed nodes at the leading edge.
Tailoring blade thickness from leading edge to tail according to variations in imposed stress.
Application of unidirectional fibers in a direction parallel with the turbine periphery.
Proper selection of fiber
Proper selection of matrix or resin
Application of vacuum resin infusion techniques that minimize voids where crack propagation can initiate.
The blade material is not limited to composites. The blade material can be any material with elastic properties, or a somewhat rigid material for designs incorporating a rigid blade with spring like node. Materials such as spring steel, wood or polymers may be practical choices for some applications.
Two Stage Turbine Potential
Whereas conventional horizontal axis wind turbine systems have a single stage and single frontal sweep area, a vertical axis system has the potential of two times the frontal sweep area of a horizontal axis system. This is due to the fact that if the vertical axis turbine is large enough, the upwind half or semi cylinder of blades may be considered an independent stage while the same holds true for the downwind half or semi cylinder of blades. If large enough, the flow which has been slowed by the upstream blades has time to intermix with the surrounding kinetic energies of the flow field passing directly above and below the turbine to regain kinetic energy to a level substantially comparable to the original flow field velocity before passing the downstream blades. In theory, each of the two stages has the potential of approaching near the Betz limit thereby doubling the potential output based on the same value of frontal sweep area. Fluid dynamic effects involved with the flow field passing into the central area of the turbine may also contribute to output.
Potential for Increased Wind Farm Power Density
Public regulations require conventional horizontal axis wind turbines to be spaced a minimum of seven diameters in between turbines to reduce the potential destructive effects that turbulence can have on the blade of an adjacent turbine. For the inventive turbine, spacing may require significantly less space between turbines based on structural integrity of the turbine as a whole being extended to the periphery of the turbine, and the ability to also space turbines in an overlapping grid like fashion in the vertical direction. An example of stacking a vertical axis wind turbines upon a common axis can be seen in same inventor's patent on turbine structure.
Control of Start Up Speed
Blade design variables of the present invention can be tailored to meet practically any desired start up speed. Turbine diameter, blade elastic properties, blade thickness and distance from the center of effective blade area to the fixed end of blade are all design factors that control turbine start up speed. An increase in distance from the center of effective blade area to the fixed end of blade yields greater mechanical advantage for the flow field forces, allowing the blade to deflect and begin producing power at lesser approaching wind speeds. Increasing blade length implies moving the center of effective blade area to a greater distance from the fixed leading edge. The result is less required wind pressure for the same amount of blade deflection from the neutral position resulting in a lesser start up speed. Increasing turbine diameter also increases mechanical advantage by increasing the resulting value of d for the same amount of angular blade deflection. By decreasing blade thickness and or incorporating blade material with lesser resistance to flex, the amount of blade deflection can be increased for the same amount of flow field force applied to the blade. The start up speed for any new design can be tailored to start power production at significantly lesser flow field velocities than conventional designs such as horizontal axis propeller type turbines. The benefit of the present invention being the allowing for renewable energy to be available in areas previously thought of as impractical because of their lesser average wind speed. Again, it should be noted however that it becomes improper for the blade length to exceed ninety degrees of turbine periphery. In doing so, the resultant force vector may not pass on the correct side of turbine center, thus creating torque in the negative direction.
Horizontal axis turbines with propeller type blades require increasing the blade size, mass and structural strength to increase sweep area and potential power. The size, mass and structural strength for blades of the present invention can be independent of the applied turbine structure size.
The present invention does not require blade mechanics and is a turbine that can be characterized as a single component with flexible spring like components. The present blade is not based on airfoil lift but is based on the conventional physics of providing leverage to “molecule collisions” or “molecule deflection” and the resulting pressures of accumulated molecule deflection. The blades of the present invention are generally flat with the highest concentration of stresses at the leading edge of the blade, differing from conventional airfoil blades which have highest concentration of stresses at the location of aerodynamic center. Also, instead of camber, the blades of the present invention possess curvature that is ideally concentric to the turbine or system center when not deflected from the relaxed neutral position or in other words co-radial with the turbine periphery. The blades of the present invention possess deliberate flexibility that is critical to operation. The present invention achieves the objective of minimizing drag while optimally transferring imparted flow field kinetic energies to torque and rotation of the turbine. The blade of the present invention is essentially a cantilevered spring.
Society needs a turbine design that provides the means of which the wind turbine industry can survive and become self-sustaining. Today's wind turbines (or water turbines) are considered complex and require significant maintenance increasing the risk factors that can affect the return on investment.
The term “bigger is better” is well known in the wind turbine industry. Today's wind turbine designs are reaching engineering limitations decelerating the expanse to larger than eight megawatt systems for wind and lesser for underwater. The present invention proposes a system of lesser moving parts that is robust and has the potential of greater efficiencies than today's documented designs. Systems without complex blade actuation mechanics and with greater structural integrity have greater potential for achieving larger turbine capacity. Today's composite materials have significantly greater potential in combating material failure due to cyclic loading, fatigue or creep. While staying within a materials elastic range, the blade of the present invention has the potential to survive for many years or possibly near indefinite with minimum need for service. Also, as turbine size increases the frequency of blade cyclic loading decreases resulting in less cycles per unit of time thereby increasing system longevity. As society continues to pursue increasing the ratio of clean renewable energy use to that of fossil fuels, the present invention claims significant improvements to today's technology.
Used in conjunction with the inventor's previous turbine structure patent, the structural integrity of the system as a whole evenly distributes potential stresses and minimizes the potential wind loads imposed by the approaching wind resulting in the potential for significantly larger capacity systems with possible greater return on investment. The system as a whole requires less mass of construction materials per kilowatt hour of system capacity.
The present invention can be used as an underwater turbine for extracting energy from underwater currents. The present invention has advantage in not requiring any external mechanism or algorithms or electronics to optimize blade orientation.
Comparison with Cyclogyro
Referring to Prior Art
Comparison with Other Vertical Axis Turbine Systems
Many different vertical axis wind turbine systems exist with similarities in general configuration by possessing a plurality of blades equally spaced about the turbine central axis.
These other systems do not incorporate a blade of concentric curvature.
Although the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character—it being understood that the embodiments shown and described have been selected as representative examples including presently preferred embodiments plus others indicative of the nature of changes and modifications that come within the spirit of the invention(s) being disclosed and within the scope of invention(s) as claimed in this and any other applications that incorporate relevant portions of the present disclosure for support of those claims. Undoubtedly, other “variations” based on the teachings set forth herein will occur to one having ordinary skill in the art to which the present invention most nearly pertains, and such variations are intended to be within the scope of the present disclosure and of any claims to invention supported by said disclosure.
This application claims the benefit of U.S. Provisional Patent Application No. 61/924,876, filed Jan. 8, 2014 by Radisek, said application hereby incorporated in its entirety by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61924876 | Jan 2014 | US |
