WO2010051647A1

WO2010051647A1 - Turbine annular axial rotor

Info

Publication number: WO2010051647A1
Application number: PCT/CA2009/001640
Authority: WO
Inventors: Frédérick CHURCHILL; Ion Paraschivoiu; Octavian Trifu
Original assignee: Organoworld Inc.
Priority date: 2008-11-10
Filing date: 2009-11-09
Publication date: 2010-05-14
Also published as: EP2394052A4; CA2643587A1; EP2394052A1

Abstract

An annular axial rotor for a turbine. The rotor includes a hub structure having a hub diameter and attached to a rotating shaft of the turbine. The rotor also has a plurality of turbine blades extending radially from the hub structure, and at least one annular shroud surrounding the plurality of turbine blades. The annular shroud has a first annular shroud diameter. The turbine blades are held between the hub structure and the annular shroud and the hub diameter is at least 0.3 times the shroud diameter. This configuration greatly facilitates the use of a plurality of airfoils to adjust the solidity and the tip speed ratio of the rotor. This can be achieved while maintaining a high coefficient for the conversion of fluid energy into useful torque.

Description

TURBINE ANNULAR AXIAL ROTOR

FIELD OF THE INVENTION

The present invention generally relates to both wind and water turbine applications. More specifically, the present invention relates to an annular axial rotor for a turbine.

BACKGROUND OF THE INVENTION

The original standard for windmills to generate electrical power was the American Wind Turbine (AWT) that employs numerous full-length rotor blades and is designed to turn at the speed of the nominal wind or at a tip-speed ratio (TSR) of 1.0. The blades are supported by a series of two or more hoops that pass behind the blades and do not allow for pitch adjustments while in operation. The hoops are attached to arms that transmit the torque generated by the blades to the rotor shaft.

The AWT rotor develops much more torque than a Horizontal Axis Wind Turbine (HAWT) but is limited in diameter by its weight. It offers a lower efficiency, as it is essentially a drag-type rotor where the rotor blades generate little lift. On the contrary, the HAWT rotor turns much faster (normally between 6 and 9 times faster) and generates its torque from the lift generated by the blades passing through the air stream at high speeds.

There is global interest in the development of larger HAWTs as the cost of electricity normally decreases with the size of the turbine. The axial flow, three- blade, propeller turbine is presently the industry standard and almost all large recent commercial turbines are of the aforementioned configuration. The development of new synthetic materials now allows windmill fabricators to construct propeller blades of over 50 meters in length. These blades are only supported at one end by the hub of the rotor These synthetic HAWT blades are heavy and difficult to transport. The blades are twisted over their length to adjust for the fact that the TSR over the length of the blade will vary from the optimum 6 to 9 at the tip to often less than 1 at the rotor hub.

HAWT rotors are normally installed in relatively isolated sites given the fact that when the blades pass in front of the turbine tower the pressure wave created between the blade and the tower transforms into a large woof. The noise of the woof is an important disadvantage of an axial flow rotor. Decreasing the TSR of the rotor would greatly decrease the noise level. In the case of a standard three- blade turbine this requires adding additional full-length propeller blades and its corresponding weight to the rotor without any gain in turbine efficiency or electrical production. This is a difficult problem to solve and most residents living close to a wind power site are forced to accept the noise and a loss in their quality of environment.

Looking at Figure 1 , if one examines the torque produced by an axial rotor it is evident that the section of the rotor near the shaft 100 produces little useful torque and that the farther the distance from the shaft, such as in the area 110, the more torque is produced per unit of air mass passing through the swept area. This implies that a large part of the weight of the propeller is transmitting power to the shaft but contributing very little useful torque.

The fact that wind speeds vary all the time is a problem for windmill designers and windmill operators. Existing wind turbines designs offer little control over immediate wind speed variations. Most existing turbines are equipped with a hydraulic driven blade pitch adjustment. These systems adjust the blade pitch to average wind velocity as calculated over a time period and not to the instantaneous wind speed. At all wind speeds, and particularly at high wind speeds, wind gusts cause considerable operating problems. The energy in the gust will rapidly increase the rotor and generator rotational speed. This can cause voltage fluctuations in the power produced that must be removed electrically. In order to limit the rotational speed, the blade pitch can be adjusted but the blades are massive and the hydraulically driven pitch adjustment is not rapid. Consequently, the brake is often applied to limit the increase in rotor speed.

A technological solution that addresses the difficulties of wind speed variation mentioned above would greatly improve turbine efficiency, improve the electrical stability of the production and decrease the production costs for electricity.

Thus, there is presently a need for an axial rotor that generates much less noise at the same power output.

There is also a need for an axial rotor using untwisted, uniform section, airfoil blades that are inexpensive to fabricate and easy to transport.

There is also a need for a rotor that is almost as efficient as a standard three- blade rotor at a TSR of between 1.5 and 6.

There is also a need for large diameter rotors using a structural configuration that is more stable and reduces the stress and vibration experienced by the blades.

There is also a need to decrease substantially the size and weight of the airfoils to simplify and increase the rapidity of response of the blade pitch adjustment.

There is also a need to increase the rotor solidity with a minimum loss in rotor efficiency when compared to an equivalent diameter HAWT. There is also a need to locate the bladed area as far as possible from the rotating shaft to increase the torque developed per volume of fluid passing through the airfoils.

There is also a need to install measurement and control devices that form a closed control loop with the airfoil pitch actuators to hold the speed of rotation more constant.

There is also a need to improve performance by installing a compressor fan over the low torque area of the rotor to increase the velocity pressure over the high torque area.

There is also a need for a rotor configuration that decreases its weight and offers boundary layer control.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an annular axial rotor that satisfies at least one of the above-mentioned needs.

According to the present invention, there is provided an annular axial rotor for a turbine comprising:

-a hub structure having a hub diameter and attached to a rotating shaft of the turbine; -a plurality of turbine blades extending radially from the hub structure; and

-at least one annular shroud surrounding the plurality of turbine blades, the at least one annular shroud having a first annular shroud diameter, wherein the turbine blades are held between the hub structure and the at least one annular shroud.

Preferably, the hub diameter is at least 0.3 times the first annular shroud diameter. In the case of a HAWT rotor, the application of the concept of an annular rotor aims at creating a swept area by the blades that is centered on the high torque zone and the low torque zone is used simply to transmit the torque from the high torque zone to the rotating shaft. The central zone of the rotor is named the low torque zone as in this area the blades have reduced tangential speed, thus poor aerodynamic efficiency. Although the velocity pressure over the high torque and low torque zones are equal, the power generated over the zones is not equal.

Our approach to the problem has been to place the rotor blades as far as possible from the shaft and to use aerodynamically shaped spokes to transmit the torque to the shaft. As the role of the blades is now strictly to generate power the form of the blades is quite different. The centrally supported twisted blades are replaced by airfoils that are shorter, untwisted and of uniform section. The airfoils are located as far as possible from the central shaft and they have a much smaller cross section as the torque from the blades is now transmitted to the turbine shaft by spokes and not by the blades. In comparison with HAWT blades these airfoils that are supported at both ends are lighter in weight and very inexpensive to fabricate and transport.

In order to adjust blade pitch angle large, standard, three-blade propeller rotors normally use a hydraulic pump and hydraulic motors to rotate the heavy blades around their axis. As the airfoils mounted in an annular shaped frame are much shorter and lighter a small and rapid actuator attached to the end of each shaft blade is sufficient to adjust its pitch angle.

An annular rotor makes it possible to increase the solidity of the rotor without adding the heavy weight of full-length blades designed to both generate lift and transmit torque. The frontal area of each individual rotor blade is now smaller in area and the TSR has also decreased. Consequently, the woof created as the blades pass in front of the mast will decrease. As the rotational speed of the rotor is lower, the visual impact of its rotation will also decrease. However, the efficiency of the rotor may decrease slightly as the TSR decreases.

The structural integrity of an annular rotor that supports the blades at both ends will be higher than for a standard three-blade rotor. Where noise and visual impact are not a problem, such as in offshore installations, the design of very large diameter rotors will still remain a design challenge. The annular design makes it easier and simpler to build very large diameter rotors, the principal advantage being the simplicity of fabrication of the blades and the optimum use of the weight of the materials over the swept area.

The present invention provides a wind turbine rotor configuration that greatly facilitates the use of a plurality of airfoils to adjust the solidity and the TSR of the rotor. This can be achieved while maintaining a high coefficient for the conversion of wind energy into useful torque.

Almost all existing large commercial windmills are of the HAWT category and use a three-blade twisted propeller with an optimum efficiency at a TSR of 6 to 9. At the other extreme of prior art, the American Wind Turbine (AWT) has a great number of straight blades and a TSR of 1.0. This low TSR makes the AWT particularly unsuitable for generating electricity. Its efficiency is considerably lower than a HAWT and at the lower rotational speed an AWT requires a larger increase in the gear ratios between the turbine and electrical generator shafts.

This new annular shaped rotor is designed to employ three or more airfoils that are lighter and shorter than the propeller blades of a HAWT of equal diameter. Computer simulation has shown that the use of the same blade profile and swept area in both an annular and a HAWT rotor will result in a modest loss of efficiency for the annular rotor.

The new annular rotor design will operate at an optimum TSR range of 1.5 to 6. The rotor swept area is located as far as possible from the rotating axis. This increases the torque produced per unit of air volume per unit of swept area at all wind speeds.

The annular rotor comprises an inner hub with sprockets that are attached to the inner ring of an annular shaped rotor blade section. The annular shaped turbine section consists of an inner and outer ring and a series of uniform untwisted airfoils that are held between the inner and outer rings. Installing between 3 and 50 blades between the rings makes it very easy to adjust the solidity of the rotor to a desired TSR.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects and advantages of the invention will become apparent upon reading the detailed description and upon referring to the drawings in which:

Figure 1 is a schematic view of the zones (sectors) of low and high torque on the swept area of an axial flow turbine.

Figure 2 is a graph of chord and twist angle distribution along the blade used for a simulation of operation of a standard twisted HAWT rotor.

Figure 3 is a side view of an annular axial turbine rotor according to a preferred embodiment of the present invention.

Figure 4 is a side view of an annular axial turbine rotor according to another preferred embodiment of the present invention.

Figures 5A and 5B are perspective and partial side views respectively of an annular axial turbine rotor according to another preferred embodiment of the present invention. Figure 6 is a perspective view of an annular axial turbine rotor according to another preferred embodiment of the present invention.

Figure 7 is a perspective view of an annular axial turbine rotor according to another preferred embodiment of the present invention.

Figure 8 is a side view of an annular axial turbine rotor according to another preferred embodiment of the present invention.

Figures 9A and 9B are a front view and a detailed view taken along section C-C respectively of an annular axial turbine rotor according to another preferred embodiment of the present invention.

Figures 10A and 10B are a front view and a detailed view taken along section D- D respectively of an annular axial turbine rotor according to another preferred embodiment of the present invention.

Figure 11 is a graph of Power vs. Wind Speed during simulated operation of a conventional HAWT rotor and a rotor according to another preferred embodiment of the present invention.

Figure 12 is a graph of Power vs. Sectoring Ratio at three nominal wind speeds for a sectored conventional HAWT rotor and a rotor according to a preferred embodiment of the present invention.

Figures 13A and 13B are graphic representations of the performance and operating ranges of existing wind turbine rotor designs. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Although the invention is described in terms of specific embodiments, it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

As shown in Figures 3 to 8, according to the present invention, there is provided an annular axial rotor 1000 for a turbine. As better shown in Figure 6, the rotor 1000 includes a hub structure 1002 having a hub diameter and attached to a rotating shaft 1004 of the turbine. The rotor also has a plurality of turbine blades 1006 extending radially from the hub structure 1002, and at least one annular shroud 1008 surrounding the plurality of turbine blades 1006. The annular shroud 1008 has a first annular shroud diameter. The turbine blades 1006 are held between the hub structure 1002 and the annular shroud 1008.

Preferably, the hub diameter is at least 0.3 times the shroud diameter.

Preferably, the turbine blades 1006 are of uniform chord length and are untwisted.

Preferably, the plurality of turbine blades 1006 comprises between 3 and 50 turbine blades.

Preferably, the hub structure 1002 comprises a hub ring 1010 and a plurality of sprockets 1012 connecting the hub ring 1010 to the rotating shaft 1004 of the turbine.

Preferably, the rotor 1000 further comprises a turbine blade pitch angle adjustment system for selectively adjusting a pitch angle of the plurality of turbine blades. Preferably, the rotor 1000 further comprises a fluid velocity measurement system located upstream of the rotor and producing a signal indicative of fluid velocity entering the turbine. The turbine blade pitch angle adjustment system adjusts the pitch angle of the plurality of turbine blades based on the signal indicative of fluid velocity entering the turbine.

Preferably, a tip-speed ratio of the turbine is between 1.5 and 6.

Preferably, as better shown in Figures 5A and 5B, the rotor 1000 further comprises a convergent nozzle 13 for directing fluid entering the rotor and a divergent nozzle 14 for directing fluid exiting the rotor.

Preferably, as better shown in Figure 4, the rotor 1000 further comprises a directing system 16 mounted over the hub structure for directing fluid entering the turbine towards the plurality of turbine blades.

Preferably, as better shown in the embodiment illustrated in Figure 7, the rotor further comprises at least one additional annular shroud 1020 concentrically surrounding the first annular shroud 1008 and at least one additional plurality of turbine blades 1022 held between the first annular shroud 1008 and the at least one additional annular shroud 1020.

Preferably, the rotor further comprises at least one additional turbine blade pitch angle adjustment system for independently selectively adjusting a pitch angle of the at least one additional plurality of turbine blades.

Preferably, as better shown in Figure 4, the rotor 1000 further comprises a compressor fan 18 positioned upstream of the hub structure and increasing velocity of the fluid entering the turbine.

Preferably, the turbine blades are hollow, perforated and connected to a vacuum system for controlling boundary layers in proximity of the turbine blades. Preferably, the turbine blades are hollow, perforated and connected to a pressurized fluid supply system for controlling boundary layers in proximity of the turbine blades.

Preferably, the hub structure is integrated to a generator and is composed of two circular inner and outer hub sections. The outer circumference of the inner hub section supports the poles 26 of the turbine generator. The outer hub section includes a plurality of radial support arms 24 attached to one or both sides of the inner hub section that supports the turbine blades and an inner hub shroud, the diameter of the inner hub shroud corresponding to the hub diameter.

As shown in Figure 9A (radial support arms and blades on one side only), the generator stator winding 30 is supported using tension from a centrally mounted stator base and the integrated turbine-generator rotor is single bladed. In Figure 10A, the integrated turbine-generator rotor is double-bladed and the stator winding is supported by compression from an exterior-mounted stator base. The stator winding support using an exterior-mounted stator base may be used for single or double bladed integrated turbine-generator rotors.

According to the present invention, there is also provided an annular shaped rotor that easily permits changes in rotor solidity and TSR for use with at least one wind turbine to decrease the noise levels of the turbine. The annular shaped rotor includes: -inner and outer rings that support the turbine blades at both ends by a shaft that passes through the thicker cross section of the turbine blades; -a rotor radius as defined by the radius of the outer ring; - turbine blades being of a regular and untwisted form that is simple and inexpensive to produce; -a rotor hub and sprockets that connect the rings and blades to the turbine rotating shaft; -an entrance and exit adapter designed to minimize the velocity pressure losses of the air stream reaching the turbine blades; -a high torque area as defined by the blade swept area created by the turbine blades; -a low torque area defined as the area between the rotor shaft and the inner ring;

-three or more turbine blades held between the inner and outer rings; -a measurement device for upstream wind velocity of the turbine blades and a programmable controller to continuously adjust the pitch angle of the turbine blades to the measured upstream wind velocity,

-an aerodynamic deflector mounted over the swept area of the spokes of the rotor to increase the wind total pressure at the blades;

Preferably, the ratio of blade length to rotor radius is comprised between 0.70 and 0.10.

Preferably, the TSR is comprised between 1.5 and 6.

Preferably, the number of blades is comprised of between 3 and 50 and most preferably between 3 and 25.

Preferably, the rotor provides a rapid and continual adjustment of the airfoil pitch angle through rotary actuation provided to all turbine airfoil blades.

Preferably, the rotor can adjust airfoil pitch angle to the instantaneous upstream wind velocity.

Preferably, the rotor, to increase performance, can include several concentric independently controlled swept areas in the high torque zone of the same rotor.

Preferably, the rotor, to increase performance, can include two or more stages of blades mounted on the same rotor. Preferably, the rotor uses a deflector over the swept area of the spokes to increase the total wind pressure at the blades and the power output.

Preferably, the rotor can apply either vacuum or compressed air for boundary layer control on the surface of the blades to increase performance.

Preferably, the rotor can be used for air turbine and water turbine applications.

The aforesaid and other objectives of the present invention are realized by generally providing an annular rotor for use with a wind turbine and to increase the rotor solidity and establish the TSR in the range of 1.5 to 6, the annular rotor compromising a rotor shaft and hub, a series of aerodynamically shaped spokes that connect the hub to the inner ring, an inner and outer ring that holds the blades in place, the difference in the radius of the rings equal to the length of the blades establishing a length ratio (B/R) between the length of the blades on the radius of the rotor, a set of straight, untwisted, airfoil sections held in place at their extremities by the rings, the number of airfoils establishing a TSR for the rotor in the range of 1.5 to 6, a set of actuators located at one or both ends of the blades that adjust the pitch angle of the blades, an air speed measuring device located on an upstream extension of the rotor shaft, a programmable controller capable of controlling rotor speed by adjusting instantaneously the airfoil pitch angle to the wind speed.

The shape, width and length of the blade will vary with each application, as such the number of blades required to obtain a set TSR will also vary. It has been determined that the number of blades per swept area will vary between 3 and 50 and most preferably between 3 and 30.

The material of the annular rotor should be resistant enough to retain its structural integrity in all operating conditions. The material or combination of materials may be, for example, be made of aluminum and compromises structural reinforcement made of steel. The blades can be constructed in aluminum, steel, plastic or composite materials such as fiberglass etc.

Depending on the desired capacity of the turbine the overall dimensions of the rotor can be considerable. All the weight and forces generated by the wind are transferred to the shaft by the rotor hub and spokes. Their design stresses strength, lightweight and aerodynamic shape to minimize both rolling friction and parasitic drag.

In a further embodiment and in order to decrease further the length of the blades the swept area of the rotor may be divided into a series of concentric swept areas by adding an additional inner ring(s) and additional blades. Each swept area has its own operating TSR. The concentric swept areas may have different sizes and blade lengths. The programmable controller controls independently the pitch angle of the blades in each swept area.

In a further embodiment, the inner and outer rings will take the shape of shrouds. In order to reduce the velocity pressure losses as the air stream enters and exits the shrouded rotor, inlet and outlet adapters are attached to the extremities of the shrouds. These adapters are designed using best practices for minimizing velocity pressure losses and as such may take on a variety of shapes including conical, bell shaped, etc. Depending on the system configuration they may or may not increase the velocity pressure at the blades. If there is an increase in velocity pressure for air, it will be of the order of 0 to 25.4 mm of water.

In a further embodiment, as shown in Figure 8, two stages of blades are mounted, one in front of the other, on a common shroud. They may or may not be of equal area and their pitch angles are controlled independently.

In a further embodiment the inner and outer rings may take on other structural shapes than circular such as multisided (example octagon or hexagon, oval, etc). In a further embodiment a wind deflector covers the area swept by the spokes. The wind deflector directs the entire air stream striking the area occupied by the spokes to the annular shaped blade section. This deflector may take several aerodynamic shapes. Figure 3 illustrates a conically shaped deflector 1050 while Figure 4 is a semi-circular shaped deflector 16. While other shapes whether bell- shaped or parabolic may be used, the main criterion is to direct the entire air stream with the least pressure loss.

In a further embodiment as shown in Figure 4, anemometer(s) 19 are placed upstream of the rotor mounted on the ends of a vertical rod 20. The rod 20 serves to position the devices outside of the influence of the compressor fans and the deflector that covers the face of the rotors. A bearing assembly 22 that allows the rod to remain stationary connects the rod to the rotor shaft. A counterweight 21 is installed on one of the ends of the vertical rod.

In a further embodiment boundary level control action serves to reduce the component of drag on the rotating airfoils. The inner shroud, the shaft of the blade and the blade itself all have a hollow center and are interconnected. Piping run from the inner shroud along the spokes, along the outside circumference of the rotor shaft and along a rotary joint situated on the shaft deliver either compressed air or vacuum into this continuous system. The hollow airfoils are equipped with distribution plates along its length that serve to provide a boundary layer control action. This action has the purpose of energizing the blades boundary layer.

The annular rotor of the present invention may be used in a plurality of environments including very high wind speeds incurred in augmented wind turbines where the blades of a standard HAWT rotor would become trans-sonic. It may also be applied to applications that use a wind turbine apparatus to augment the velocity pressure to the blades and/or with a rotor-sectoring apparatus. The proposed annular rotor may be used to replace existing standard three-blade HAWT rotors with the intent of decreasing the noise level created by the rotating blades. Given its lower noise and visual impact it is suited to be installed in urban areas. The increase in solidity and lower rotational speeds decrease the risks for injury or death to birds and bats.

A novel wind turbine rotor will be described hereinafter. Although the invention is described in terms of specific illustrative embodiment(s), it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

The embodiments of the present invention are described in the non limitative following examples that were derived from recognized computer simulation software applied by recognized experts in the field of wind turbines.

To assess quantitatively the effects of using the rotor on augmented HAWT, a computer program, which has the capability to calculate the performance (power output) of such wind turbines, has been used. For HAWT analysis, the code used was WT Pert.

The WT Pert code

WT Perf uses blade-element momentum (BEM) theory to predict the performance of HAWT2. It was developed at the National Renewable Energy Laboratory (NREL) from the code PROP, originally set up by Oregon State University decades ago. The staff at the National Wind Technology Center from the NREL has recently modernized PROP by adding new functionalities developed it into the current WT Perf.

Figure 6 shows the principal sections of the annular rotor including the outer ring or shroud 1008, the uniform section, airfoil turbine blades 1006, the inner ring or shroud 1010, the aerodynamically shaped spokes 1012, the rotor hub 1002 and the rotor shaft 1004. Also shown are two non-dimensional references, the radius of the inner ring (R1 ) and the radius of the outer ring (R2)

Figure 4 shows an annular rotor equipped with an entrance adapter 8A and an exit adapter 8B. These adapters 8A, 8B are designed to minimize the loss of velocity pressure as the wind stream approaches and exits the blades. If an augmented turbine apparatus is used, the convergent nozzle 13 attaches to the entrance adapter 8A and the diffuser 14 attaches to the exit adapter 8B.

The adapters may also be used to adjust from straight-walled convergent- divergent sections to a curved turbine rotor section.

If a rotor-sectoring device is used, the dimensions R1 and R2 become equal to the dimensions of the retracted and fully deployed segments of the sectoring cone. The turbine shaft 1004 is lengthened to support the sectoring apparatus for non-augmented turbines.

For augmented wind turbines, the sectoring device is supported from the floor structure supporting the turbine shaft.

The airfoils themselves turn around a central shaft that can be located in the section of the airfoil where the airfoil thickness is largest. Rotary actuators (not shown) are mounted on the outside faces of the rims to be located outside the air stream. The actuators rotate the blades around their axis to adjust the pitch angle. The power for rotary actuation may be mechanical, electrical, pneumatic or hydraulic. The power source for the rotary actuation of the blades may be centralized (pump) or decentralized (electric coils).

The cross sectional area of spokes is minimized and their shape is aerodynamic to reduce parasitic drag. They are designed to transmit the torque from the blades in the blade swept area to the rotor shaft. The spokes may attach directly to the inner ring or the spokes may attach to an intermediate ring that fits inside the inner ring. Both rings may be of the same metals or of different metals such as steel and aluminum.

In a further embodiment a solid disk replaces the above-mentioned spokes.

The number of uniform airfoil sections will vary to produce a TSR of between 1.5 and 6. This is achieved by installing between 3 and 50 airfoils on the rotor. Figures 4 to 6 show only one swept area. It is possible to add additional rings and airfoil sections to create several layers of sectored area of different diameters, as shown in Figure 7. This will shorten the length of the blades and create operating zones in which the pitch angle of the blades is adjusted independently from one layer of swept area to another.

The width of the rings is established based on the structural solidity required. Their width will normally exceed the length of the airfoils and is more a function of the overall system design. If there is an increase in the velocity pressure of the air stream upwind of the airfoils, the rings also serve the important function of preventing the loss of wind pressure over the tips of the airfoils and the leakage of velocity pressure into the low torque zone.

The simulation was performed using as the reference a standard 22-meter diameter HAWT blade. The simulations were carried out on shrouded rotors at wind speeds of 4, 7 and 12 m/s. The sectoring ratio was varied between 1.0 and 0.25. The sectoring ratio may be defined as the ratio of the free area of the blades over the total area of the rotor. The same S-809 profile was used for both the HAWT propeller blades and the annular rotor airfoils.

The examples described here below were evaluated using computer simulation as described earlier. The specifics of the rotor and blade are documented in Table 1 : Table 1

Rotor & Blade Characteristics

standard HAWT rotor annular rotor

airfoil type S-809 S-809 rotor radius (m) 11.0 11.0 blade length (m) 10.93 7.64 number of blades 3 25 optimum TSR 5.8 2.3

B/R ratio (Blade/Rotor radius) (10.93/11.0) = 1.0 7.64/11.0 = .69 chord of blade variable constant at 0.80 m twisted blade yes no rotor-sectoring example 2 only example 2 only power output (%) 100 85-88 rotor soliditv (%) 11 45

Example 1

Computer simulations were performed to evaluate a three-blade propeller HAWT rotor and a multiple airfoil annular rotor. Wind speeds were varied between 0 and 24 m/s and the power produced in kW was calculated using non sectored rotors. The results are shown in Figure 11. The power produced by the lower TSR, 25- blade annular rotor is approximately 12-15 % lower than the standard three-blade propeller rotor.

Much can be done to improve the performance of the annular rotor by selecting a better airfoil configuration for the lower TSR. The purpose of this simulation was to confirm the relationship between solidity, TSR and high torque zone performance. Further simulation will be undertaken to demonstrate whether the performance of an annular rotor of equivalent swept area and equivalent high torque zone can exceed the performance of a three-blade propeller rotor. However it would be very simple to compensate for the lower blade performance of the annular rotor simply by increasing the swept area by 10-15%. This requires lengthening the blades by only a couple of percent as the area increases with the square of the radius. Another simple alternative includes decreasing the B/R ratio by increasing the rotor radius while keeping the blade length constant. Neither of the aforementioned changes will greatly raise the noise of the annular rotor and the power output will remain constant.

Example 1 shows that an annular airfoil rotor of slightly larger radius can easily exceed the performance of a three-blade propeller HAWT at a lower TSR and consequently at a lower noise level.

Example 2

The same HAWT, three-blade, propeller rotor and the 25 blade, annular rotor were evaluated with a rotor-sectoring apparatus installed. The rotors were evaluated at wind speeds of 4.0, 7.0 and 12.0 m/s and with sectoring ratios varying between 1.0 and 0.25. The results are tabulated in table 2 and illustrated graphically in Figure 12. As the results for both rotors were essentially the same at 4.0 m/s, these results are only shown graphically.

Table 2

Performance of Sectored Rotors Sectoring ratio versus Power (kW)

Sectoring ratio ssttaannddaarrdd HHAAWWTT rroottoorr annular rotor

7.0 (m/s) 12.0 (m/s) 7.0 (m/s) 12.0 (m/s)

1.0 5500 220000 50 200 .9 5500 225500 50 250 .8 5500 227755 50 275 .7 60 300 60 400 .6 70 400 70 550 .5 100 525 125 775 .4 200 750 250 1200 .3 250 1200 400 1900 .25 300 1500 500 2700

The example 2 illustrates that a sectored annular rotor of equivalent swept area will largely outperform a three-bladed propeller HAWT. Over a sectoring ratio of 1.0 to 0.25 the improvement in performance is 4 fold.

Figures 13A and 13B are graphic illustrations of the performance of almost all common windmill types. As demonstrated, the optimum operating zone for the annular rotor that is situated over the range of TSR range of 1.5 to 6 and a rotor power coefficient slightly less than a three-bladed propeller has no existing equivalent.

As a person skilled in the art would understand a plurality of types of axial flow or horizontal axis turbines may be used with the device of the present invention. Also for each wind turbine different combinations may be used for example a different number and/or configuration of blades, the space between the wind section and the wind turbine, etc.

As a person skilled in the art would understand the parameters of the annular rotor may differ from the examples shown in this document. Similarly the mechanism for adjusting the opening of the blades or flow channel may differ based on the fluids, operating conditions and turbine apparatus.

While illustrative and presently preferred embodiment(s) of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.

Claims

1. An annular axial rotor for a turbine comprising:

-a hub structure having a hub diameter and attached to a rotating shaft of the turbine;

-a plurality of turbine blades extending radially from the hub structure; and -at least one annular shroud surrounding the plurality of turbine blades, said at least one annular shroud having a first annular shroud diameter, wherein the turbine blades are held between the hub structure and the at least one annular shroud.

2. The annular axial rotor as claimed in claim 1 , wherein the hub diameter is at least 0.3 times the first annular shroud diameter.

3. The annular axial rotor as claimed in any of claims 1 or 2, wherein the turbine blades are of uniform chord length and are untwisted.

4. The annular axial rotor as claimed in any of claims 1 to 3, wherein the plurality of turbine blades comprises between 3 and 50 turbine blades.

5. The annular axial rotor as claimed in any of claims 1 to 4, wherein the hub structure comprises a hub ring and a plurality of sprockets connecting the hub ring to the rotating shaft of the turbine.

6. The annular axial rotor as claimed in any of claims 1 to 5, further comprising a turbine blade pitch angle adjustment system for selectively adjusting a pitch angle of the plurality of turbine blades.

7. The annular axial rotor as claimed in claim 6, further comprising a fluid velocity measurement system located upstream of the rotor and producing a signal indicative of fluid velocity entering the turbine, and wherein turbine blade pitch angle adjustment system adjusts the pitch angle of the plurality of turbine blades based on the signal indicative of fluid velocity entering the turbine.

8. The annular axial rotor as claimed in any one of claims 1 to 7, wherein a tip-speed ratio of the turbine is between 1.5 and 6.

9. The annular axial rotor as claimed in any one of claims 1 to 8, further comprising a convergent nozzle for directing fluid entering the rotor and a divergent nozzle for directing fluid exiting the rotor.

10. The annular axial rotor as claimed in any one of claims 1 to 9, further comprising a directing system mounted over the hub structure for directing fluid entering the turbine towards the plurality of turbine blades.

11. The annular axial rotor as claimed in any one of claims 1 to 9, further comprising at least one additional annular shroud concentrically surrounding the first annular shroud and at least one additional plurality of turbine blades held between the first annular shroud and the at least one additional annular shroud.

12. The annular axial rotor as claimed in claim 11 , further comprising at least one additional turbine blade pitch angle adjustment system for independently selectively adjusting a pitch angle of the at least one additional plurality of turbine blades.

13. The annular axial rotor as claimed in any one of claims 1 to 12, further comprising a compressor fan positioned upstream of the hub structure and increasing velocity of the fluid entering the turbine.

14. The annular axial rotor as claimed in any one of claims 1 to 13, wherein the turbine blades are hollow, perforated and connected to a vacuum system for controlling boundary layers in proximity of said turbine blades.

15. The annular axial rotor as claimed in any one of claims 1 to 13, wherein the turbine blades are hollow, perforated and connected to a pressurized fluid supply system for controlling boundary layers in proximity of said turbine blades.

16. The annular axial rotor as claimed in any one of claims 1 to 15, wherein hub structure is integrated to a generator and comprises two circular inner and outer hub sections, an outer circumference of the inner hub section supporting poles of the generator, the outer hub section including a plurality of radial support arms attached to at least one side of the inner hub section supporting the turbine blades and to an inner hub shroud, a diameter of the inner hub shroud corresponding to the hub diameter.