CROSS-REFERENCE TO RELATED APPLICATIONS Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not Applicable
REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX Not Applicable
BACKGROUND OF THE INVENTION 1. Field of Invention
This invention pertains to the field of fluid dynamics and more particularly to the field of wind turbines and tidal current turbines.
2. Description of Related Art
Wind turbines translate kinetic energy from the wind into usable torque to drive an application such as an electrical generator. Inasmuch as a wind turbine can drive an electrical generator there are a number of challenges arising in the successful deployment of this type of application. Horizontal Axis Wind Turbines (HAWTs) have been the most efficient and popular type of windmill to be used to convert wind energy into electricity. However, they typically do not operate in winds less than 7 mph (3 m/s); do not reach peak efficiency until the wind reaches 12-15 mph (5-7 m/s); if the wind rises past 25 mph (11 m/s) to where the electrical generator is over cranked, a brake is deployed to slow the blades. If the wind becomes too great the machine is shut down to prevent damage. Because of these factors HAWTs typically operate in a band of wind between 10 to 25 mph (4.5 to 11 m/s), which limits their use in areas with average wind speeds below 10 mph (4.5 m/s). Because of the narrow band of usable wind speed, utility scale wind turbines have become extremely large, expensive and located far away from population centers so as to maximize areas with favorable wind. This type of machine needs to be large to be cost effective and its blades have become large in response and are subjected to heavy loads that require their manufacture from composites which can contribute 20 to 25% to the machines total cost. Another problem that arises from large scale turbines is that the blades are placing an enormous torsional load onto the bearings causing them to be highly engineered and expensive, or alternatively, fail spectacularly. Smaller scale, Intra-grid, distributed applications of this type of windmill have not been cost-effective due to problems such as turbulence, siting concerns and size restrictions. Other negative factors with regard to these types of turbines are noise and negative impact on the surrounding wildlife.
Tidal currents should prove to be a very reliable renewable energy resource in areas with favorable tidal currents because they occur at regular well-known intervals at well-known velocities, unlike the wind which can be either too little, too much or at the wrong time with respects to demand. However, many challenges need to be overcome for the successful deployment of such applications. And in efforts to overcome these challenges, many types of turbines have been created, but unlike wind turbines which have common dimensions and proportions, tidal current turbines have been deployed in as many shapes, sizes and configurations as there have been deployments. This variety, which makes for interesting research, may not be as useful for energy utilities that need to be able to deploy economically feasible assets with known costs.
SUMMARY OF THE INVENTION The present invention addresses the aforementioned problems by introducing volumetric blades which can make effective use of fluid flow below 10 mph (4.5 m/s) and from any direction. The blades of the present invention are capable of handling turbulent flow due to the inherent strength of shape. Furthermore, due to the inherent strength of blade shape, the blades will be capable of being manufactured in plastic by repetitive production techniques such as rotational molding, injection molding, or thermoforming, thus reducing the cost per blade to well below that of blades manufactured using composites. Rotational molding in particular could create a turbine of the present invention up to 50 feet, (15 m) in diameter. The strength of blade shape allows for the aerodynamic optimum for blade thickness over the entire length of blade to be attained. Due to the blades high efficiency at low wind speeds and gradual decrease in efficiency at higher wind speeds, the resulting wind turbine can have a useful operating range of wind speeds from 3 mph to 25 mph, (1.34 m/s to 11.18 m/s) with less braking than the HAWT type turbines. This capability will result in significant gains in overall energy capture over time for surface level winds (FIG. 1-3). The resulting turbine will be compact, will have a large lift/drag surface area, will have a small moment of inertia when compared to HAWTs and will be able to be deployed in niche wind opportunities where large turbines would either not work or not be desired. The resulting turbine will be able to be deployed in any orientation to the incoming flow. The turbine will be able to be manufactured in such a way as to make the whole machine capable of standing up to extreme conditions. Bearings for a turbine of the present invention can be separated by half the diameter resulting in significantly reduced torsional loading. The large blade surface area should be easily observed and avoided by birds, bats and other wildlife resulting in minimal effect on the surrounding environment. Testing of the prototype revealed that this type of turbine is virtually silent. The sound of the wind produced more audible noise from 10 feet (3 m) away.
Because the same blades manufactured for a wind turbine of the present invention can also be used for a tidal current turbine, installation costs of a tidal current turbine should be greatly reduced allowing for deployment in a number of tidal energy configurations, such as anchored, suspended, tethered or buoyant units, while using the same basic machine.
DESCRIPTION OF DRAWINGS FIG. 1 is a power curve of the prototype of the present invention created during tests in natural conditions. And a power curve of a comparably sized HAWT power curve created by Experimental pour le Petit Eolien de Narbonne (SEPEN), for comparison.
FIG. 2 is a graph of the mean distribution of surface level winds for Corpus Christi, Tex. The graph was compiled using raw hourly data gathered by the Texas Commission on Environmental Quality (TCEQ). This Sample was taken for April, 2012 to April, 2013 from 14 collection sites.
FIG. 3 is a graph comparing the projected collected watt-hours to mean wind speed distribution for a typical HAWT and the projected collected watt-hours to mean wind speed distribution of the present invention using the data from the power curves described in FIG. 1 and the surface level wind data described in FIG. 2.
FIG. 4 is a perspective view of the present invention with its axis of rotation horizontally aligned.
FIG. 5 is a perspective view of the present invention with its axis vertically aligned.
FIG. 6 is a perspective view of the present invention showing several blade sections.
FIG. 6A is a detail view of blade cross sections and their relative angles for flow that is axially aligned.
FIG. 7 is a perspective view of the present invention showing axial compression.
FIG. 8 is a perspective view of the present invention showing axial elongation.
FIG. 9 is a perspective view of the present invention showing blades axially mounted to a hub.
FIG. 10 is a perspective view of a horizontally aligned preferred embodiment of the present invention.
FIG. 10A is a perspective view showing bearing and drive shaft locations.
FIG. 11 is a perspective view of a vertically aligned preferred embodiment of the present invention.
FIG. 12 is a perspective view of a tidal current turbine resting on the sea floor.
FIG. 12A is a detail of a tidal current turbine showing a high pressure area along the blade to hoop connection area.
DETAILED DESCRIPTION OF THE INVENTION The Volumetric power curve depicted in FIG. 1 was produced from data gathered during tests in natural conditions with over 1300 recorded data points of a 6 foot, (1.8m) diameter prototype rotor aligned axially to the flow. The HAWT power curve was produced from a test of a popular 3.7 m diameter wind turbine that was tested by Site Experimental pour le Petit Eolien de Narbonne (SEPEN). The results were adjusted to compensate for the differences in diameter. The blades of the prototype rotor are high lift, deep camber 14 type blades as shown in FIG. 6. High lift type blades are important for starting and delivering power at low wind speeds. These blades can also be described as low aspect ratio blades; this also is for delivering power at low wind speeds. Turbines of the present invention could be manufactured with similar proportions to that as described in FIG. 4, but without the deep camber for deployment at sites where the mean wind speeds are higher than 5 mph (2.2 m/s). The result would produce higher overall output over time than the deep camber for winds higher than 5 mph (2.2 m/s). FIG. 9 shows blades embodied without a deep camber 15 for illustration.
FIG. 2 is a graph of the mean wind distribution of surface level winds for Corpus Christi, Tex. This area was chosen because of the large number of stations to gather data from in this area. The graph of the hourly data gathered from these sites for an entire year produces a bell curve distribution. Similar data was gathered for 20 cities from the Texas Commission on Environmental Quality (TCEQ). All the data gathered regardless of city, illustrated the opportunity for wind power generation that could utilize the energy from surface level winds better than a conventional HAWT.
FIG. 3 is a graph comparing the projected watt-hours to mean wind speed distribution for a typical HAWT and the projected watt-hours to mean wind speed distribution of the present invention using the data from the power curves described in FIG. 1 and the surface level wind data described in FIG. 2. The graph illustrates the watt/hours that can be captured using both the present invention and an equally sized HAWT.
FIG. 4 illustrates a horizontal alignment and the overall hemispherical shape of the rotor and shows a set of blades 1, attached radially to a central hub 2, and a hoop 3 attached to the outer diameter of the blade set for alignment and stability. Some embodiments of this invention will not require a hoop element 3, but it is included here because it is a fundamental part of some embodiments of this invention. FIG. 5 shows the overall hemispherical shape with a vertical alignment.
FIG. 6 shows blade cross sections and how the chord length becomes longer towards the outer diameter. FIG. 6 also shows the high lift, deep camber 14 properties of that exhibited in the prototype. Blade cross sections 4-10 were taken in evenly spaced planes perpendicular to the axis of rotation at approximate 15% intervals starting with 4, at 15%, 5 at 30%, 6 at 45%, 7 at 60%, 8 at 75% and 9 at 90%. FIG. 6A shows 5 evenly spaced cross sections 24-28 and their relative pitch angles. Cross sections for 6A were taken in evenly spaced axially aligned planes. For flow that is axially aligned proportional changes in chord length makes the pitch angle change. Lengthening chord at the apex decreases pitch angle, shortening the chord at apex increases the pitch angle. The blade thickness of in this depiction is uniform over the length of the blade, however, varying blade thickness can also have the effect of varying pitch angle over the length of the blade.
The shape of the rotor does not need to be substantially hemispherical, but the hemispherical shape does allow the rotor the ability to run efficiently in many different orientations to the incoming flow. To illustrate how a change in shape changes the capabilities of the rotor consider the following. If the rotor was proportionally compressed axially as in FIG. 7, then the implementation would present a wider surface area for an axial flow type application. On the other hand if the rotor was elongated proportionally axially as in FIG. 8, the implementation would present a longer profile for a cross-flow type application. But for a general application that can realize flow from any direction a hemispherical shape allows for a sufficient surface area for both of these orientations and the angles in between.
FIG. 9 shows a turbine of the present invention with the blades 1 attached axially to a central hub 11. This arrangement presents more surface area to the fluid flow when oriented axially to the flow than a radially attached arrangement. The manufacture of the blades 1 for axial attachment can be the same as those for radial attachment. However, the blades 1 will need to be skewed so that the median line of the blades 1 follows a circular path similar to an offset-rotated semicircle, offset-rotated parabola, or offset-rotated arch. This axially attached embodiment also indicates the need for a spar to be inserted into the blade 1 to reinforce the hub attachment area.
FIG. 10 shows a turbine of the present invention with blades 1 mounted radially and the rotor horizontally aligned. In this embodiment a turbine could be placed on top of, or on the side of, an existing structure. A turbine of this configuration could be used in both axial flow and cross flow type applications. In the cross flow application the turbine would be placed on a surface with its axis rotated 90° to the flow. FIG. 10A illustrates that bearings 16 on this embodiment are separated by the distance of the radius of the rotor, this separation results in a significantly reduced torsional load. FIG. 10A also shows a drive shaft 17 at the apex on the convex side of the rotor. A load could be applied to this shaft in the form of a direct drive alternator (not shown), or, a pulley or sprocket (not shown), could be attached to this shaft to drive an application indirectly. The siting of the application on this side or the opposite side of the rotor will have as much to do with cosmetic value as efficiency. A brake (not shown) could be applied to this shaft or electronic braking could also be employed. Alternatively, a bicycle style caliper brake (not shown) could be electronically deployed on the hoop 3, which would have a much greater mechanical advantage over a brake deployed on the drive shaft 17. In siting a large wind turbine in an area that has significant wind above 25 mph (11 m/s), it may be cost effective to use an energy recovery braking system (not shown) onto the hoop area like those employed on some cars and other vehicles. In that way very little energy will be lost because the wind is too high for the primary electrical generator.
FIG. 11 shows a roof mounted turbine of the present invention vertically oriented on a roof that is pitched perpendicular to the prevailing wind direction. An airfoil 12 is utilized in this embodiment that diverts the wind from the upwind side of the rotor into the center of the rotor. Tests reveal that when an airfoil of this nature is deployed a significant increase in efficiency is obtained. During the test, telltales on the opposite side of the airfoil from the flow indicated that air was moving toward the rotor at the angle of the airfoil. The inventor is not sure if a synergistic vortex was created, or a venturi ducting effect or the diversion of air from the upwind side alone is responsible for the increase in efficiency. Further tests are planned.
FIG. 12 shows a possible implementation of a tidal current turbine resting on the sea floor. This depiction features a buoyant blade rotor and flexible support 20. In this depiction the blades 1 are filled with foam to make the blade rotor buoyant. A nacelle 19 houses the generator. A support 20 is made from materials that ties the rotor securely to the base 21, and yet be pliant enough to flex back and forth with the ebb and flow of the current. The rotor is turned with the convex side towards the incoming current to minimize impact on the surrounding wildlife. The area where the blade is attached to the hoop 3 creates a high pressure region 18 when positioned this way in the flow. This region 18 increases the overall torque of the unit when flow is directed at the rotor in this way. FIG. 12A, is a more detailed look at this area. Although this high pressure area 18 in this depiction is minimal in size, this area could be increased to create more torque, which would make the overall shape look more like a bell.
