GB2471349A

GB2471349A - Wind turbine with fans

Info

Publication number: GB2471349A
Application number: GB0919574A
Authority: GB
Inventors: Douglas Stuart Tedham
Original assignee: DAVID JOHN HICKS
Current assignee: DAVID JOHN HICKS
Priority date: 2009-11-09
Filing date: 2009-11-09
Publication date: 2010-12-29
Anticipated expiration: 2029-11-09
Also published as: GB2471349B; GB0919574D0

Abstract

An energy generation apparatus 100 comprises a casing 104 containing a least one duct 106 to have fluid channelled therethrough and a region of reduced cross-section compared with other duct regions. At least one rotor 108 is located within the duct to be rotated by fluid passing through the duct to generate power therefrom. At least one driven fan 110 is arranged to influence movement of the fluid through the duct such that the driven fan increases the velocity of the fluid at the rotor to allegedly increase overall output. There may be multiple entry fans 110 and/or multiple exit fans. There may be main 108 and auxiliary 109 turbine rotors supplied by internal ducting 117, angular momentum inducing inlet deflectors or box or grid wind straighteners 118. The assembly may be a roof mounted wind turbine.

Description

WIND TURBINE

Field of the invention

This invention relates to a wind-turbine apparatus and related methods. In particular, but not exclusively, the invention relates to a wind-turbine apparatus arranged to increase the rate of wind flow therethrough. This may be by forced air induction and or alternatively forced air extraction.

Moreover, but again not exclusively, the invention relates to a wind-turbine apparatus arranged to be mounted on an elevated structure, such as a building, a vehicle, a vehicle roof or the like.

Background of the invention

As concerns for the environment increase the search for alternative forms of energy also increases. One such form of alternative energy that is often considered is wind power typified by large wind turbines, tens of metres in diameter. Such turbines suffer from disadvantages in that they can take up large tracts of land, tend to be large structures which are expensive to manufacture, transport, install, operate and maintain. As such, they tend not to be sited near to dwellings due to both their size and the noise that they generate, or near airports where they can interfere with radar.

To be efficient such turbines are optimised to a narrow range of wind speeds, typically from 25 to 97 km/h, and are limited to only achieving performance approaching their design efficiency in a narrow subset range of wind speeds, typically within �5 km/h of the average wind speed designed for. Such turbines do not produce net energy at low winds or at very high wind speeds or in turbulent wind conditions.

Further such turbines require gearboxes to increase the drive shaft speed to a useful speed to drive a generator, or to accommodate variations in rotor speed depending upon the wind. Such gearboxes have mechanical losses and as such reduce the efficiency of the system.

There is a limit to the amount of energy that they can extract from the wind since power extracted is proportional to the diameter of the blades squared. However, there is a limit to the diameter of the blades associated with maximum safe blade tip speeds in order to avoid structural failure of the blades or rotor.

A further disadvantage is that energy generated from such prior art turbines must generally be fed into a grid system, such as a national distribution system.

US Patent Application No. US200910097964 provides one way of addressing this by providing a shroud around a wind-turbine in order to improve the aerodynamics and thereby increase the efficiency of the wind-turbine. However, such a solution still does not extract power as efficiently as may be desired.

Summary of the invention

According to a first aspect of the invention there is provided an energy generation apparatus comprising: a casing containing at least one duct arranged to have a fluid channelled therethrough and comprising a region of reduced cross-section when compared with other regions of the duct; at least one rotor located within the duct and arranged to be rotated by fluid passing through the duct and to generate power therefrom; and at least one driven fan arranged to influence movement of the fluid through the duct such that the at least one driven fan is arranged to increase the velocity of the fluid at the or each rotor.

Such an apparatus is believed to be advantageous as it may increase the amount of energy obtained from fluid, generally wind, passing through the apparatus by increasing the velocity of the fluid. The skilled person will appreciate that the power extracted, from a fluid, by a rotor is proportional to the cube of the velocity of the fluid. As such, increasing the velocity of the fluid can significantly increase the power that can be extracted.

The skilled person will appreciate that the region of reduced cross-section when compared with other regions of the duct acts as a venturi and may be synonymous with venturi. As such, fluid flow increases through the venturi as the pressure is reduced.

Such an increase in the velocity of fluid through the apparatus may generate sufficient extra power from the or each rotor to power the powered fans and provide a net gain in power generated. As such, sufficient power may be generated be fed back into a grid system, such as a national grid, and/or be used to power devices in the locality of the apparatus. Devices in the locality of the apparatus may include batteries and/or capacitors in order to provide a reservoir of power.

Generally the casing comprises an upstream end region into which fluid enters the casing and a downstream end region in which fluid exits the casing.

At least one, and generally a plurality of, powered fans may be provided in a region of the upstream end region. Such an arrangement may increase the rate at which fluid is pulled into the casing.

Further, at least one, and generally a plurality of, powered fans may be provided in a region of the downstream end region. Such an arrangement may increase the rate at which fluid is ejected from the casing, which in turn may increase the rate at which fluid is drawn through the casing.

Where one or more powered fans are provided in one or both of the upstream and downstream end stream regions, the powered fans may be arranged so that their combined effect is to provide a steady, substantially, laminar fluid flow through the casing. Additionally or alternatively powered fans so provided may be arranged so that their combined effect is to provide an area of reduced pressure within the casing, when compared to the pressure outside of the casing, or pressure gradient, such that a greater quantity of fluid is drawn through the casing.

The region of reduced cross-section when compared with other regions of the duct may be thought of as a constriction in the duct. Such a constriction may be advantageous as it can help to increase the rate of fluid flow through the apparatus. This in turn is advantageous as it can increase the amount of power that can be extracted from fluid passing through the apparatus.

The or each rotor may be provided in a region of the or each constriction.

Such an arrangement is convenient since it provides the or each rotor in a region of where the highest rate of flow of the fluid may be expected. The skilled person will appreciate that a constriction increases the rate of fluid flow and is often referred to as a Venturi.

In some embodiments, there is provided more than one rotor. In such embodiments, it may be convenient if each of the rotors may be provided in a region of the constriction. Such an arrangement is convenient as it places each rotor at, or close to, the region of highest fluid flow within the casing.

Further, it may be advantageous in embodiments, with more than one rotor, to partition the fluid entering the apparatus, by means of a combination of one or more ducts and/or sub-ducts, between the rotors so as to provide a more equal fluid flow to each rotor.

The plurality of rotors may or may not be mounted upon a common shaft.

Mounting the rotors on a common shaft may be advantageous in that it allows each rotor to provide torque to the same power generation means.

Sequential rotors may be arranged to operate in opposite senses such one of the rotors may be arranged to blow whereas a neighbouring rotor may be arranged to suck (or vice versa).

The apparatus may further comprise at least one inner duct, which may be provided in the upstream end region of the casing. Such an arrangement is advantageous because the casing of the inner duct may further constrict the flow of fluid to the or each rotor and therefore increase the fluid speed at the or each rotor, and may further provide a more even distribution of fluid incident upon the or each rotor Alternatively or additionally such an inner duct may be provided in the downstream region of the casing, arranged instead to dilate the flow of fluid from the or each rotor, and therefore increase the fluid speed at the or each rotor.

In some embodiments, the casing comprises an external guide arranged to direct fluid into the casing. Generally, the guide may be provided around a portion of the casing. For example, the guide may be provided around an upper region of the casing. However, the guide may be provided in order to intercept a prevailing motion of fluid, such as an up-draught, a down-draught, a crosswind, or the like. Such an arrangement may increase the rate of fluid flow through the casing and as such may increase the amount of power extracted from the fluid.

Conveniently, the casing may be swivel, or otherwise rotatably, mounted.

Such an arrangement enables the casing to rotate to help ensure that the maximum amount of fluid enters the or each duct. Such embodiments may conveniently be provided with one or more vanes. Such vanes are advantageous in helping the casing to rotate, particularly to rotate such that the upstream end region of the casing is facing the oncoming fluid.

In some embodiments, the downstream end region of the casing may be provided with an outer casing arranged to draw fluid into the downstream end region. The outer casing may comprise an enlarged portion of the casing arranged to direct fluid into the downstream end region.

The casing of the apparatus, such as the inner surface of the casing or the casing of the inner duct, may comprise one or more deflectors arranged to deflect the flow of fluid adjacent to their active surfaces. Further the deflectors may be planar, arcuate, spiral or helically shaped. Generally, the deflectors are equi-spaced around the circumference. Such deflectors are advantageous as they help to give fluid flowing through the duct angular momentum in the direction of the rotation of the or each rotor.

The apparatus may comprise one or more box wind straighteners arranged to make fluid flow through the casing in a manner generally perpendicular to the or each rotor. Such an arrangement may increase the consistency of the flow vector of the fluid incident on the rotor or rotors which may increase the efficiency of the or each rotor in extracting energy from the fluid flowing therethrough. Such a box wind straightener may generally comprise a grid, generally perpendicular to the direction of fluid flow, having a length in the direction of fluid flow.

Conveniently, the apparatus may comprise a generating means such as a generator, or other means to generate power from the or each rotor. The generating means may comprise driven drive shafts. The generating means may further comprise a cog free, multi-phase, multi-fielded or varying magnetic flux alternator. Such an altenator may be electronically controlled, and/or selectively voltage wired to maximise electrical collection from a wide range of wind power speeds.

The or each rotor may also comprise the rotor of the generating means. A stator may be provided around a circumference of the or each rotor so as to generate power from rotation of the or each rotor.

Embodiments of the invention may be sized appropriately, to be mounted on elevated structures. For example on roof of a house, which may be a domestic dwelling or the like.

Embodiments of the invention may be roughly 5 metres in diameter.

Other embodiments may be roughly in the range of 500 millimetres to 3 metres in diameter. A greater power demand may be met by the grouping together of a plurality of wind-turbines according to embodiments of the invention.

The rotor blades and/or powered fan blades may be arranged to provide low pressure points at at least one of: at the surface of the blades; between the blades, or in an area adjacent to and downstream of the blades of the or each rotor. Such an arrangement may be advantageous by increasing fluid suction through the rotor or powered fan and by increasing the volume of fluid flowing through the rotor or powered fan.

The downstream end region of the casing may comprise a flared region.

Such a flared region may cause a high pressure region in fluid flowing over the downstream end region which in turn causes a low pressure region within an opening of the downstream end region. Such an arrangement may help to draw fluid through the duct.

The powered fans may initially be driven by a battery or capacitor (such as a super capacitor), and the battery or capacitor recharged by energy subsequently generated by the apparatus. Such an arrangement may be advantageous in increasing the fluid speed at the or each rotor sufficiently that the or each rotor generates, by the efficiency of running the apparatus at that increased fluid speed, a net power gain.

Power produced by apparatus may be used to power any conventional device attached thereto, and/or may be supplied to a power network, for example a local power grid or the national grid.

The powered fan or fans may be at least one of: small diameter(lOOmm to 900mm), low wattage (5w to 1000w), low friction (for example with rotational friction coefficient less than 0.25).

Generally, the fans are axial flow fans. Suitable fans may be provided by the Seabreeze Electric Corporation, 40 Fima Crescent, Toronto who use the trade mark Turbo-Aire.

Each rotor or powered fan may have one or more blades. The blades may be made from a light high strength material, for example, carbon fibre, high strength polypropolene plastic or aluminium. The blades may be made at least partially hollow, and may filled with helium, hydrogen, or any other suitable gas, or any combination thereof. Alternatively, the or each blade may be evacuated, or at least partially evacuated. Such arrangements may be advantageous by reducing the moment of inertia of the rotor or powered fan. The blades of each rotor or fan may be made from different materials.

The blades of each rotor or powered fan may be any of: a conventional propeller design, curved, voided, arcuate, hollow comma shaped, twisted, "5" shaped, straight or tapered, concave or convex faced or any combination thereof, or otherwise shaped blades.

The blades may be connected to a hub by conventional feathering techniques The blades may be arranged around the hub to provide one or more rotors (or fans), for example a double rotor wherein the rotors (or fans) may differ in diameter, and/or rotating in opposite sense whilst connected to the same hub.

Conveniently, the hub comprises a substantially conical portion, similar to a Boss Cap of a propeller. Such a conical portion aims to modify fluid flow thereover in order to increase the flow rate through a reduction in pressure and consequent increase in flow rate over the surface.

The blades, rotors, powered fans, hubs, or any combination thereof may be movably adjustable to performance balance the apparatus for variations in the operational fluid speed range or incident fluid speed range. Such moveable adjustments may be self-regulating, or may be driven by electromechanical mechanisms, such as servos, and controlled by electronic or computerised instrumentation, or by feedback from one or more sensors. Moveable adjustments may include at least one of: adjustments to one or more blade angles or orientations, adjustments made sequentially or simultaneously to multiple blades, trimming any rotor or powered fan, blinding one or more rotors (or fans) together with trimming the rotor blades by feathering techniques.

Alternatively, the blades of the or each rotor may be helical or spiral (or both) shaped such that the rotor rotates about an axis of rotation lying in a vertical plane, or a plane transverse, perhaps perpendicular, to the principal axis of the apparatus.

The blade arrangement of the or each rotor or the or each fan may be chosen to complement the characteristics of a fluid flow arriving thereat from a rotor or fan or open duct located upstream, or from the interaction of such components located upstream or downstream. Such arrangements may increase the rate of flow of fluid through the or each rotor and/or the or each fan and increase the pressure gradient and suction force forcing fluid through the apparatus. Such arrangements may also allow more energy to be extracted from or imparted to the fluid as it flows through the or each rotor.

The skilled person will appreciate that not only is the power that can be extracted from a turbine proportional to the cube of fluid velocity but it is proportional to the diameter of the rotor squared. As such, the diameter of the constriction should be large enough to optimise the diameter of the or each rotor.

In some embodiments the apparatus may be arranged increase the fluid velocity at the rotor or rotors to a target speed range, such as substantially 20-40 m/s, or to a target speed, such as substantially 30 m/s.

Alternatively a target power output of the apparatus may be used. For example the apparatus may be arranged to adjust the output of the powered fans in response to feedback determined by the rotor speed or apparatus power output.

From the above description, it will be appreciated that many of the parts of the apparatus may be adjusted. For example there are discussed adjustable rotors, powered fans, blades, inner hubs may be adjusted in response to feedback. Such parts that may be adjusted may be thought of

as adjustable means.

Feedback used to control the adjustable means may be provided directly by mechanical feedback, or from more or more sensors through an electronic control system, or any suitable means. Such arrangements may be advantageous in reducing the range of, or holding substantially constant, the rate of rotation of the rotor or rotors. This may increase the efficiency of the apparatus by reducing or eliminating the need for gearing of the rotors or a drive shaft to accommodate variations in rotor speed.

According to a second aspect of the invention there is provided a method of generating energy comprising increasing the velocity of fluid incident upon at least one rotor of a wind turbine by placing the rotor within a duct in a casing at a constriction within the duct and using at least one powered fan to increase the velocity of fluid passing through the duct.

Features of the first aspect of the invention may be applicable to the second aspect of the invention.

Brief description of the drawings

There now follows by way of example only a detailed description of embodiments of the present invention with reference to the accompanying drawings of which: Figure 1 schematically shows a cross section through an embodiment of the invention; Figure 2 schematically shows an embodiment of an apparatus of the invention in which powered fans are provided in sub-ducts; Figure 3 schematically shows an embodiment of an apparatus of the invention comprising a downstream end region outer duct; and Figure 4 schematically shows an approximate model of the fluid flow through different embodiments of an apparatus of the invention; Figure 5 schematically shows two embodiments of an apparatus of the invention and a roof structure; and Figure 6 shows a graph of power against wind speed;

Detailed description of the drawings

It is convenient to describe the embodiments in relation to a system in which the fluid flowing through the apparatus is air.

A wind-turbine apparatus 100, as shown in Figure 1, is provided with a casing 104 containing a duct 106 arranged to have a fluid 102 channelled therethrough and a rotor 108 that is rotated by the fluid 102 passing through the duct. In motion the rotor 108 sweeps out a surface area substantially corresponding to the surface area of a cross section of the duct adjacent the rotor 108. The duct is arranged such that the flow of the fluid 102 through the duct is substantially parallel to the principal axis 112 of the duct and the rotor 108 is arranged such that the flow of the fluid 102 through the rotor 108 is substantially parallel to the axis of rotation of the rotor 108.

In some embodiments, the rotor comprises a number of blades mounted upon a hub in a conventional design. The blades may be rotably moveable relative to the hub in order that the rotational force generated by the rotor can be varied. To this end the hub of the rotor comprises a servo mechanism arranged to rotate the blades in response to a demand signal generated as described below. Because the rotor and hub may be adjusted relative to one another they may be thought of as an adjustable means.

A control circuit 150 is provided and takes an input from sensors and generates a control signal in order to move the blades of the rotor relative to the hub in order to provide the desired output from the apparatus. One sensor is arranged to measure the air speed flowing into the duct 106.

The duct 106 comprises an upstream end region 113 before the rotor 108 and a downstream end region 115 after the rotor 108. The casing 104 adjacent the upstream end region 113 is frusto conical, and the casing 104 adjacent the downstream end region 115 is frusto conical, arranged such that the regions 113,115 taper from their largest diameter at their openings to their narrowest diameter adjacent the rotor 108.

The upstream end region 113 is provided with an inner casing 117 running from an outer end region toward the rotor 108 and providing an inner duct 119b and an outer duct 119a within the upstream end region 113 of the duct 106 such that the outer duct 119a surrounds and is concentric with the inner duct 119b. The inner casing 117 is frusto conical and tapers inwards to its narrowest diameter at an end region adjacent the rotor 108. The inner casing 117 is provided concentrically about the principle axis 112 of the apparatus, and the tapering of the inner casing 117 complements the tapering of the casing 104 at the upstream end region 113 such that the outer duct 119a and inner duct 119b have a substantially uniform and covariant cross sectional area. The inner casing 117 and the casing 104 at the upstream end region 113 together provide constrictions through which fluid 102 passing through the ducts 106, 119a, b travels.

The apparatus 100 is provided with a second rotor 109 located within the inner casing 117 in a region of an exit thereof adjacent the rotor 108 and within the inner duct 119b. The second rotor 109 sweeps out a surface area substantially corresponding to the surface area of a cross section of the inner casing 117 adjacent the rotor 109. The inner casing 117 and second rotor 109 are arranged such that the flow of fluid 102 through the inner duct 119b and through the second rotor 109 is substantially parallel to the principal axis 112 of the apparatus. The first and second rotors 108, 109 share a common axis of rotation and are linked together by a shaft 111. Shaft 111 is substantially parallel to the principal axis 112 of the apparatus.

The upstream end region 113 of the casing is provided with eight powered fans 110 (only two of which are shown in Figure 1) in the outer duct 119a, the fans 110 equi-spaced around the circumference and adjacent to an entrance of the outer duct 119a, two of which can be seen in Figure 1.

The inner duct 119b is also provided with four powered fans 116, two of which can be seen in Figure 1. The powered fans 116 are equi-spaced around the circumference and are provided adjacent an entrance to the inner duct 119b.

In some embodiments, the blades of the powered fans may also be adjustable relative to a hub thereof in the same manner as blades of the rotor as described above. As such, the blades and hub of a powered fan may also be thought of as an adjustable means.

In many embodiments, the powered fans will be electrically powered and may be arranged to be powered from electricity generated by the rotors 208, 209.

The downstream end region 115 of the duct 106 is provided with eight powered fans 114, two of which can be seen in Figure 1, in a region of the exit of the duct 106. The fans 114 are equi-spaced around the circumference of the duct 106.

The powered fans 110, 114, 116 are arranged such that each powered fan has an axis of rotation substantially parallel to the flow of fluid 102 adjacent each fan.

Each of the rotors 108, 109 is provided, at an upstream side thereof, with a box wind straightener 118. Each boxed wind straightener 118 is arranged to substantially aid the flow of fluid 102 in the region of the corresponding rotor 108, 109 to be parallel to the axis of rotation of that rotor. The box wind straightener comprises a grid of plates arranged such that the straightener provides a grid of rectangular ducts arranged generally parallel to the direction of flow of fluid through the duct 106.

In other embodiments, a similar effect may be achieved by providing a plurality of tubes or other shaped ducts. Should be the ducts be hexagonal in shape then the structure would be similar to that of a honeycomb.

The apparatus 100 is provided with a vertical stand 124 attached to the casing 104 about which the apparatus 100 may freely rotate. The apparatus 100 may be provided with two vanes 122 attached to the casing 104 at the downstream end region 115, and the vanes 122 are located on opposite sides of the downstream end region 115 and arranged to lie in a vertical plane through the principal axis 112 of the apparatus. In one embodiment the centre of mass of the apparatus 100 is arranged to be as close as possible to the axis of the vertical stand 124 about which the apparatus 100 may freely rotate.

In other embodiments, the stand 124 may itself rotate thereby achieving the same result as the casing 104 rotating relative to stand 104 through a swivel system. The centre of gravity of the entire apparatus will generally be behind the centre line of the stand to ensure that the apparatus always heads into the prevailing wind.

The casing of the upstream end region 113 is provided with an upstream guide 120, arranged to have a profile corresponding to a portion of a cylinder of radius equal to that of the upstream end region 113 of the casing 104. The guide 120 extends from the casing 104 to its greatest extent from a top region of the casing as viewed in Figure 1 (ie on an opposite side thereof to the stand 124).

Kinetic energy is imparted to the rotor 108 by fluid 102 passing from the upstream end region 113 to the downstream end region 115. Kinetic energy is imparted to the rotor 109 by fluid 102 passing through the inner duct 119b provided by the inner casing 117. The apparatus 100 therefore extracts energy from flow of fluid 102 through the casing 104 with the energy being transferred into the rotational movement of the rotors 108, 109 and the shaft 111. Energy is extracted from the fluid through the pressure differential across the blades of the rotor 109 resulting in rotational forces acting on the rotor 109 and causing it to spin. Energy is extracted from rotational movement of the rotors 108, 109 and the shaft 111 by any means (not shown in Figure 1) such as a generator, an alternator or the like. The skilled person will appreciate that generators and alternators are examples of generating means.

In this embodiment, a sensor may be provided and arranged measure the power output from the generating means and feed this information into the control circuit 150.

Power generated by the generator or alternator may then be used to power the powered fans 110, 114, 116.

The tapering of the upstream end region 113 and downstream end region 115 of the duct 106 to their narrowest diameter adjacent the rotor 108 creates a constriction through which fluid 102 passing through the duct 106 travels with the maximum constriction occurring adjacent the rotor 108. The constriction may also be thought of as a region of reduced cross-section when compared with other regions of the duct.

The tapering of the inner casing 117 complements the tapering of the casing 104 adjacent the outer duct 119a such that a further constriction in created in the inner duct 119b with the maximum constriction occurring adjacent the rotor 109. According to the equation of continuity of the fluid flow and in order to conserve the energy of the system, the flow of fluid 102 increases as the cross section of the duct in which it is flowing decreases. As such, and as shown in Figure 1, the flow of fluid 102 has its highest velocity adjacent the rotors 108, 109.

The skilled person will appreciate that the energy that can be extracted from a fluid flow is proportional to the cube of the velocity of the flow (which may be thought of as the rate of fluid flow). As such, as the speed of the fluid flow increases then the amount of energy that may be extracted increases exponentially.

The powered fans 110, 116 impart kinetic energy to the fluid passing therethrough thereby increasing the velocity of the fluid 102. This faster fluid mixes with fluid otherwise passing through the upstream end region 113, outer duct 119a or inner duct 119b such that the fluid speed at the rotors 108, 109 is further increased beyond the velocity increase due to the constriction alone. From Bernoulli's principle the increase in the speed of the fluid caused by the powered fans 110, 116 occurs simultaneously with a decrease in pressure in the region of the powered fans 110, 116. The resultant drop in pressure causes a negative pressure gradient that acts to suck additional fluid into the upstream end region 113, outer duct 119a or inner duct 119b. Such an effect increases the flow of fluid 102 through the casing 104 and increases the fluid speed at the rotors 108, 109. The apparatus 100 therefore extracts more energy from a fluid flow 102 in which it is positioned when compared to an apparatus without the powered fans 110, 116 and/or the constriction provided by the casing 104.

The powered fans 114, positioned at an exit region of the downstream end region 215 impart kinetic energy to the fluid passing therethrough; ie on exit from the casing 104. This faster fluid mixes with fluid otherwise passing through the downstream end region 115 such that the velocity of the flow of fluid 102 from out of the casing 104 is increased. From Bernoulli's principle, described above, the increase in the speed of the fluid caused by the powered fans 114 occurs simultaneously with a decrease in pressure in the region of the powered fans 114. The resultant drop in pressure causes a negative pressure gradient that acts to suck additional fluid into the downstream end region 115 from the upstream end region 113. Again, such an effect increases the flow of fluid 102 through the duct and increases the fluid speed at the rotors 108, 109.

This again enables the apparatus 100 to increase the energy extracted from the flow of fluid 102 compared to an apparatus without the fans 114.

The following discussion of Figure 1 assumes that the fluid 102 is air/wind of Earth's atmosphere, as used to power conventional wind turbines, although the discussion may apply equally or to a lesser or greater extent to other fluids and in other environments. The skilled person will appreciate that from the Standard Wind Power Equation (equation 1) the power output of an ideal wind turbine is proportional to the cube of the wind speed in a direction parallel to the principal axis of the turbine. The power output of an ideal wind turbine is also proportional to the diameter of the rotors squared.

Windpower = c x p x d2 x equation (1) Where c = pi/8; p = density of medium; d = rotor diameter; v = velocity of fluid.

Figure 6 shows a graph of wind power (axis 602, units: Watts) against wind speed (axis 600, units: metres per second) and curve 604 shows the Standard Wind Power Equation in the case where the fluid density (p)kg/m3 and the rotor of the ideal turbine sweeps out an area of 1 m2.

Curve 608 shows the Betz Limit (coefficient of performance C = 16/27) applied to the power output of an ideal wind turbine governed by equation 1. Curve 609 shows the actual power output achieved by a wind turbine reflecting Betz's Law and mechanical and electrical losses (coefficient of performance C = 0.35).

In view of equation 1, it is believed that the increase in velocity caused by the powered fans 110, 114, 116 causes a sufficient increase in the power generated by the apparatus such that there is a net power output from the apparatus. That is an alternator powered by rotors 108, 109 produces more power than is required to power the powered fans 110, 114, 116.

In the present arrangement, when the fluid 102 is air, the arrangement of powered fans 110, 114, 116 imparts kinetic energy to the fluid 102 entering the casing 104 of the apparatus 100, thereby increasing the fluid 102 speed at the rotors 108, 109 that extract power from the fluid 102. The skilled person will appreciate that although the powered fans consume energy, according to equation 1 the apparatus 100 allows the extraction of power by the rotors 108, 109 at a higher velocity of fluid 102 which results in a greater net power gain from the apparatus 100.

The skilled person will appreciate that conventional wind turbines are arranged to extract energy from the wind at a particular speed or over a limited range of ground, or near ground wind speeds, for example in the ground wind speed range 7-2? mIs. The skilled person will appreciate that conventional wind turbines are unsuitable for extracting power from low (less than roughly 10 mIs) or very low (less than roughly S m/s) ground wind speeds, and that large areas of the Earth have ground wind speeds in such a range and typically of the order of 1 mIs. In contrast the apparatus 100 may increase the speed of low or very low ground wind speeds incident upon the apparatus to reach a higher airflow speed range at the rotors 108, 109 that increases the efficiency of power extraction from the wind. Such a higher airflow speed range, shown in Figure 6 by hatched area 606 and crosshatchecl area 60? combined, of airflow speeds for apparatus 100 may be in the range 10-40 mIs when measured at the rotors 108, 109. Further, the apparatus 100 may be arranged to increase the airflow speed at the rotors to within a narrower range, 20-40 mIs, as shown in Figure 6 by crosshatched area 60?, or to a particular speed such as 30m/s. The skilled person will appreciate that these arguments apply, either equally or to a lesser or greater extent, to the apparatus 100 located in wind or fluid 102 flow at any other altitude.

Some embodiments of the invention may achieve the adjustment of the windspeed as discussed in the preceding paragraph by the control circuit 150 controlling at least one of the following: the speed of the or each powered fan; the position of rotor; and fan blades relative to the respective hubs. As described above, some embodiments, provide at least one sensor that can provide an input to the control circuit 150.

At higher incident wind speeds (for example greater than roughly 10 ms') conventional rotors may fail under the stress placed on the rotor, or may be required to shutdown in order to prevent damage to the power generation means attached to the rotor.

At wind speeds above a threshold determined by the Reynolds number (above approximately 30 ms') laminar wind flow becomes substantially turbulent wind flow. At a range of ground wind speeds in the range of roughly 20-40 ms' the provision of the first rotor 108 and second rotor 109 provides a method of extracting the power from wind speeds in this range that reduces stress on the rotors 108, 109 compared to a single rotor design. The two rotors 108, 109 may have smaller diameters than a single rotor capable of extracting the same amount of power. A smaller diameter rotor endures less stress at the blade tips of the rotor.

The concentric and equi-spaced around the circumference arrangement of the powered fans 110, 114, 116 provides a more symmetrical and uniform transfer of kinetic energy to the fluid 102 from the powered fans 110, 114, 116. The uniform or symmetrical flow of fluid 102 incident on the rotors 108,109 should reduce stresses on these rotors and the likelihood of turbulent fluid flow through these rotors. The apparatus 100 should therefore be more efficient and durable than conventional designs.

The linking of the rotors 108, 109 by shaft 111 aims to provide a more uniform rate of rotation of the linked rotors 108, 109, 111 by averaging out variations between the fluid velocity at each of the rotors 108, 109.

The apparatus 100 should therefore extract energy from the fluid flow 102 at a more uniform rate than single rotor designs.

The box wind straighteners 118 adjacent to each rotor 108, 109 aims to maximise the component of the flow of fluid 102 parallel to the axis of the rotors 108, 109 such that an increased amount of energy is imparted to the rotors 108,109. As such, the box wind straighteners 118 may be thought of as reducing turbulent flow in the fluid 102.

As discussed above, the casing 104 rotates, perhaps freely, in a horizontal plane about the vertical stand 124 and tracks a substantially horizontal flow of fluid 102 such that the flow is parallel to the principle axis 112 of the apparatus. Tracking of changes in the direction of the horizontal fluid flow is assisted by vanes 122 which impart a corrective rotational movement to the casing 104 when the principal vane surfaces are not parallel to the fluid flow 102. Such tracking is made more responsive by the close location of the centre of mass of the apparatus 100 to the axis of the stand 124, as discussed above, so as to minimise the moment of inertia of the apparatus 100 about its axis of rotation. Such tracking aims to increase the flow of fluid 102 through the apparatus and therefore the power that may be extracted from the flow of fluid 102 by the apparatus 100. The upstream guide 120 deflects fluid 103 flowing with a substantially upward flow vector into the inner and outer ducts 119a,119b to increase fluid flow through the apparatus 100. The substantially upward component of the flow vector 103 may be imparted to the fluid by obstacles located in the vicinity of the apparatus 100. In the case where the fluid is air, such an obstacle may be a sloping roof (eg the roof of a house or other building), to which the apparatus 100 may be attached by a vertical stand 124 or to which the apparatus 100 may be adjacent.

In a second embodiment as shown in Figures 2a to 2c, the apparatus 200 is a wind turbine with features in common with the first embodiment and like parts have been referred to prefixed with a 2 rather than a 1 as in Figure 1. For example, rotor 108 of Figure 1 becomes rotor 208 of Figure 2.

Figure 2b shows a partial view 250 of the front of the apparatus; ie viewed from the right of Figure 2a. Figure 2c shows a partial view 260 of the rear of the apparatus; i.e. viewed from the left of Figure 2a.

The upstream end region 213 of the casing 204 is provided with eight concentrically arranged powered fans 210, arranged around a square to fit around four powered fans 216 provided in inner duct 219b. The downstream end region 215 is provided with eight concentrically arranged powered fans 214. The powered fans 214 are arranged so as to not protrude into the airspace directly downwind of the rotor 208.

The second rotor 209 located in the inner duct 219b is substantially exposed to airflow 202, with air flowing both directly to the rotor 209 and indirectly by first flowing through the powered fans 216. The first rotor 208 located in the upstream end region 215 is exposed to airflow 202, with air flowing both directly into the rotor 208 through outer duct 219a between the powered fans 210 in the upstream end region 215 and indirectly by first flowing through the powered fans 210.

It will be appreciated that the cross shaded region of Figure 2b represents an absence of material, i.e. an open entrance to outer duct 219a, and as such it is possible for fluid 202 to flow therethrough.

The inner casing 21? provides four sub-ducts 252 within the inner duct 219b spaced equally around the sides of the inner duct 219b and arranged to protrude partially into the outer duct 219a of the casing 204.

The sub-ducts 252 are substantially half-conical or half-frusto conical and taper inwards in the direction of rotor 208 (i.e. in the downstream direction). The sub-ducts 252 terminate in a region adjacent the rotor 209.

Each sub-duct 252 corresponds to a powered fan 216 and is arranged to at least partially circumscribe the area swept out by the powered fan 216, such that flow of fluid 202 incident on the area swept out by the powered fans 216 is directed, as shown by arrows 256, via the sub-ducts 252 onto the rotor 209.

Such an arrangement of sub-ducts 252 helps to increase flow into and through the apparatus 200 in order to increase the rate of flow of fluid 202 (i.e. speed) at the rotors 208, 209 and so increase the amount of power that may be extracted by the apparatus 200 according to equation 1 above. A skilled person will appreciate that a sub-duct 252 built into the wall of the inner casing 21? may reduce any turbulence caused by the powered fan 216 blades or blade tips during their rotational cycle and enhance fluid flow rates through the sub-duct 252.

The downstream end region 215 is provided with eight sub-ducts 262 spaced equally around the sides of the downstream end region 215. The sub-ducts 262 are substantially conical or frusto conical and taper inwards in the direction of rotor 208 (i.e. in the upstream direction) such that the wider end region is adjacent an exit of the apparatus 200.

Each sub-duct 262 corresponds to a powered fan 214 and is arranged to circumscribe the area swept out by the powered fan 214. A portion of the fluid 202 exiting the rotor 208 is channelled, as shown by arrows 266, by the downstream suction force generated by the powered fans 214, via the sub-ducts 262 out of the downstream end region 215 and so out of the apparatus 200.

Such an arrangement of sub-ducts 262 helps to increase flow of fluid out of the apparatus 200 in order to increase the speed of fluid 202 at the rotors 208, 209. As with the sub-ducts 252, a skilled person will appreciate that a sub-duct 262 built into the wall of the downstream end region 215 adjacent to the powered fan 214 blades during their rotational cycle may reduce any turbulence caused by the powered fan 214 blade tips. Such an arrangement may more forcefully suck fluid 202 through the sub-duct 262, and so increase the negative pressure in the downstream end region 215 and urge a greater flow of fluid 202 through the apparatus 200. Such an arrangement advantageously does not protrude into and therefore does not constrain or restrict airflow in the airspace directly downwind of the rotor 208.

In a third embodiment as shown in Figures 3a, 3b and 3c, the apparatus 300 is a wind turbine with features in common with the first and second embodiments and like parts have been referred to prefixed with a 3 rather than a 1 as in Figure 1. For example, rotor 108 of Figure 1 becomes rotor 308 of Figure 3. Figure 3b shows a partial view 350 of the front of the apparatus, Figure 3c shows a partial view 360 of the rear of the apparatus.

The apparatus 300 is provided with three powered fans in the outer duct 319a, three powered fans in the inner duct 319b, and six powered fans in the downstream end region 315. arranged substantially as previously described. The powered fans in the inner duct 319b and downstream end region 315 are provided substantially within ducts. Flowing fluid 303 enters the inner duct 319b through the powered fans there provided and through the gap therebetween. Flowing fluid 303 enters outer duct 319a directly through either the powered fans there provided or through the gaps therebetween, the gaps being depicted by the cross hatched area in Figure 4b.

An outer casing 341 is provided concentrically about and at least partially downwind of the downstream end region 315, arranged such that airflow enters the outer casing 341 from the downstream end region 315 and from the aperture 342 and exits the outer casing 341 through aperture 346.

The outer casing 341 is substantially frusto conical and tapers inwards in a downwind direction as shown in Figure 3a.

Such an embodiment aims to capture fluid 346 from the wind otherwise flowing externally past the apparatus 300 in the principal direction of the fluid (generally wind). Flow of fluid 346 entering the outer casing 341 encounters a constriction caused by the inward downwind taper of the outer casing 341 which according to the equation of state of the fluid increases the fluid velocity through, and decreases the air pressure at, the constriction in the outer casing 341. The faster fluid flow in the outer casing 341 mixes with slower fluid exiting the downstream end region 315 into the outer casing 341 and helps to force this fluid out of the apparatus 300 faster. As such, the rate of flow of fluid through the rotor 308 may be increased further.

Figures 4a-4f show side elevation cross-sections through five embodiments of features of the invention that may be present individually 2? or may be combined in further embodiments, for example as discussed in the first to third embodiments above.

The simplified and approximate flow of fluid 402 through each apparatus is represented by the fluid vector arrows shown, with longer fluid vectors denoting the faster flow of fluid 402. The apparatuses 400,430,440,450,460 are wind turbines and like parts have been referred to prefixed with a 4 rather than a 1 as in Figure 1. For example, rotor 108 of Figure 1 becomes rotor 408 of Figures 4a-e.

Figure 4a shows an embodiment of the apparatus in which a plurality of powered fans 410 (of which only two are shown) are arranged around and adjacent to an entrance to the upstream end region 413. The powered fans 410 impart kinetic energy in a downstream direction to the fluid flowing therethrough which subsequently may mix with fluid otherwise flowing into the upstream end region 413, increasing the velocity of the fluid in a direction substantially parallel to the axis 412 of the apparatus 400 and incident upon the rotor 408. The increase in fluid velocity results in a corresponding decrease in pressure in the upstream end region 413 and adjacent to the rotor 408 and adjacent to the powered fans 410.

This pressure decrease provides a pressure gradient through and around the apparatus 400 which may suck fluid at an increased rate, and so a greater amount of fluid, into the entrance of the upstream end region 413.

The skilled person will appreciate that such an arrangement may allow the extraction of more power by the rotor 408 from the fluid flowing into the apparatus 400 compared to an arrangement without powered fans 410.

A deflector 405 is provided, protruding from an inner surface of the casing 404. The deflector 405 is arranged to impart rotational momentum to fluid passing through the duct 406. The deflector may be a portion of a helix or the like.

Moreover, Figure 4a exemplifies that the downstream end region 415 of the casing 404 may comprise a flared region 40?; one in which the casing undergoes an increase in diameter along an axial length. Such a flaring causes a high pressure at region 460 which consequentially causes a low pressure region 462. This can help to increase the rate at which fluid is drawn through the duct.

Figure 4b shows an embodiment of the apparatus 430 in which a plurality of powered fans 414 (of which only two are shown) are arranged around and adjacent to an exit of the downstream end region 415. In a similar manner to that discussed above for Figure 4a such an arrangement may increase the velocity or rate of flow of fluid through the downstream end region 415, forcing fluid out of the apparatus 430 at a greater rate and so increasing the pressure gradient through the duct 406 defined by casing 404, thus allowing more or more efficient power extraction by rotor 408.

Figure 4c shows an embodiment of the apparatus 440 in which a plurality of powered fans 416 (of which only two are shown) are arranged around and adjacent to an entrance of an inner duct 419b, defined by an inner casing 41?, the inner duct 419b being provided in the upstream end region 415. An alternative arrangement (not shown) to powered fans 416 is to provide a single powered fan that may sweep out all or a portion only of the cross-section through the inner duct, the inner duct and powered fan being concentrically arranged about the axis 412 of the apparatus. The powered fans of such arrangements operate in a similar manner to the powered fans 410 as discussed for Figure 4a, acting to provide a pressure gradient in the inner duct 419b that may increase the rate of flow of fluid 402 through the duct 406, thus allowing more or more efficient power extraction by rotor 408.

Figure 4d shows an embodiment of the apparatus 450 which combines complementary features from Figures 4a-c, and further provides a second rotor 409 located in the inner duct 419b downstream of the powered fans 416, the second rotor being connected by shaft 411 to the first rotor 408.

The operation of the apparatus may be explained in a similar manner to the explanation given above in connection with apparatus 100 of Figure 1.

The combination of complementary features from Figures 4a-c may provide a greater pressure gradient through the apparatus which may increase the power extracted by or overall efficiency of the apparatus 450.

Figure 4e shows an embodiment of the apparatus 460 that provides an outer casing 441, the operation of which may be explained in a similar manner to the explanation given above in connection with apparatus 300 of Figure 3. Eight powered fans 414a (only two of which are shown) are provided in the outer casing 441 and operate in a similar manner to the explanation given above in connection with powered fans 414 of apparatus 430 of Figure 4b. The apparatus 460 further provides a collector duct 419c, (which may be thought of as an external guide) defined by frusto conical casing 465 and casing 404 that may capture fluid flowing past the exterior of the casing 404 and deflect and this fluid into an entrance 466 of the outer casing 441, to further enhance the rate of fluid flow through the apparatus 460 which may increase the power extracted by or overall efficiency of the apparatus 460.

Figure 4f shows an embodiment in which a plurality of casings 404a-c are arranged in series such that the downstream end regions 415a, 415b of the first two form an input to the upstream end regions 413b, 413c of the adjacent casing. This can allow further fluid to be drawn into the gaps between the casings as shown by the arrow 464. In order to assist such fluid being drawn into the gaps between the casings then one or more fans 468 can be used to increase such fluid flow.

The apparatuses 400,430,440,450,460 also provide a constriction in a manner discussed above in previous embodiments and which the skilled person will appreciate also increases the fluid velocity as previously discussed. The collector duct 419c of Figure 4c in other embodiments may be provided with powered fans in a manner similar to the previously mentioned inner and outer ducts 419a,b and/or be arranged to provide a further constriction as discussed previously.

Figure 5 shows two embodiments of the apparatus 510, 512, similar to the first embodiment, in use and in conjunction with the roof 507 of a building 504, which may for example be a typical two storey dwelling.

The roof comprises sloping sides 505 that terminate at a roof ridge 506.

Apparatus 510 is provided with a mast 514 about which it may rotate to track the direction of the wind 502, the mast 514 being attached to the base of the roof of the building. Apparatus 512 is provided with a mast 516 about which it may rotate to track the direction of the wind 502, the mast 516 being located adjacent the building 504 and attached to the ground, and in this example reinforced by guy ropes 518.

The walls of building 504 and the sloping sides 505 of the roof provide an obstacle to the flow of wind 502, which may impart a substantially upward flow vector to the wind 503. The upstream guide 520, as discussed above in relation to Figure 1, deflects fluid 503 flowing with a substantially upward flow vector into the apparatus 510,512 to increase fluid flow through the apparatus 510,512.

Claims

CLAIMS1. An energy generation apparatus comprising: a casing containing a least one duct arranged to have a fluid channelled therethrough and comprising a region of reduced cross-section when compared with other regions of the duct; at least one rotor located within the duct and arranged to be rotated by fluid passing through the duct and to generate power therefrom; and at least one driven fan arranged to influence movement of the fluid through the duct such that the at least one driven fan is arranged to increase the velocity of the fluid at the or each rotor.
2. An apparatus according to claim 1 in which at least one, and generally a plurality of, powered fans are provided in at least one of in an upstream end region of the duct and in a downstream end region of the duct.
3. An apparatus according to claim 1 or 2 in which the or each rotor is provided in a region of the or each region of reduced cross-section.
4. An apparatus according to any preceding claim which comprise more than one rotor and which partition the fluid entering the apparatus, by means of a combination of one or more ducts and/or sub-ducts, between the rotors.
5. An apparatus according to any preceding claim in which the apparatus further comprises at least one inner duct, provided in at least one of an upstream end region of the duct and a downstream end region of the duct and arranged to further constrict the flow of fluid to or from the or each rotor.
6. An apparatus according to any preceding claim in which the casing comprises an external guide arranged to direct fluid into the casing.
7. An apparatus according to any preceding claim which further comprises one or more deflectors arranged to impart an angular momentum onto fluid passing through the duct.
8. An apparatus according to any preceding claim which comprises one or more box wind straighteners arranged to make fluid flow through the casing in a manner generally perpendicular to the or each rotor.
9. An apparatus according to any preceding claim which comprises a generating means to generate power from the rotor.
10. An apparatus according to any preceding claim in which the outer region of the downstream end region of the casing comprises a flared region.
11. An apparatus according to any preceding claim in which the hub of the or each rotor comprises a substantially conical portion.
12. An apparatus according to any preceding claim in which a plurality of casings are arranged in series such that fluid exiting a downstream end region of one casing is input to the upstream end region of a further casing.
13. An apparatus substantially as describer herein with reference to the accompanying drawings.
14. A method of generating energy comprising increasing the velocity of fluid incident upon at least one rotor of a wind turbine by placing the rotor within a duct in a casing at a constriction within the duct and using a powered fan to increase the velocity of fluid passing through the duct.
15. A method of generating energy substantially as described herein with reference to the accompanying drawings.Amendments to the claims have been filed as followsCLAIMS1. A wind-turbine apparatus arranged to generate power from low incident wind and to increase the velocity of the incident wind to a target velocity at, at least one rotor, the apparatus comprising: a casing containing at least one duct and at least one outer duct provided in, at least one of, an upstream end region of the casing at which wind enters the casing, and a downstream end region of the casing, opposite the upstream region, the outer duct(s) and the duct being arranged to have wind channelled therethrough and the duct comprising a constriction provided by a region of reduced cross-section when compared with other regions of the duct and the constriction arranged to have wind flowing therethrough at the target velocity; the, at least one rotor, located within a region of the constriction and arranged to be rotated by the wind at the target velocity passing through the constriction to generate power therefrom, wherein the outer duct(s) and the duct direct wind to and/or from the at least one rotor, and a plurality of driven fans provided around the circumference of the casing in at least one of the downstream end-region, and upstream end-region, of the casing, and arranged to influence movement of the wind through the ducts such that each driven fan is arranged to increase the velocity of the wind at the rotors to the target velocity.2. An apparatus according to claim 1 in which a plurality of driven fans is provided at both the downstream and upstream end-regions.3. An apparatus according to claim 1 or 2 in which the duct and outer duct constitute ducting and the apparatus is arranged such that the constriction occurs within both of the duct and outer duct.4. An apparatus according to claim which comprise more than one rotor and which partition the fluid entering the apparatus, by means of a combination of one or more ducts and/or sub-ducts, between the rotors.5. An apparatus according to any preceding claim in which the apparatus further comprises at least one inner duct, provided in at least one of an upstream end region of the duct and a downstream end region of the duct and arranged to further constrict the flow of fluid to or from the or each rotor.6. An apparatus according to any preceding claim in which the casing comprises an external guide arranged to direct fluid into the casing.7. An apparatus according to any preceding claim which fbrther comprises one or more deflectors arranged to impart an angular momentum onto fluid passing through the duct.8. An apparatus according to any preceding claim which comprises one or more box wind straighteners arranged to make fluid flow through the casing in a manner generally perpendicular to the or each rotor.9. An apparatus according to any preceding claim which comprises a generating means to generate power from the or each rotor.10. An apparatus according to any preceding claim in which the outer region of the downstream and/or upstream end region of the casing comprises a flared region.11. An apparatus according to any preceding claim in which the hub of the or each rotor comprises a substantially conical portion.12. An apparatus according to any preceding claim in which a plurality of casings are arranged in series such that fluid exiting a downstream end region of one casing is input to the upstream end region of a fbrther casing.13. An apparatus substantially as describer herein with reference to the accompanying drawings.14. A method of generating energy substantially as described herein with reference to the accompanying drawings.