WO2015101761A1

WO2015101761A1 - A turbine with outer and inner rotor being contra-rotating

Info

Publication number: WO2015101761A1
Application number: PCT/GB2013/000567
Authority: WO
Inventors: Patrice J.M. CULOT; Mario D'andrea; Chris Williams; Rick CURD
Original assignee: Global Vtech Limited
Priority date: 2013-12-30
Filing date: 2013-12-30
Publication date: 2015-07-09

Abstract

A radial inflow rotor assembly for a turbine having an outer rotor and an inner rotor, the rotors being nested and arranged, when in use, to be contra-rotating; the outer rotor arranged to divert fluid onto and/or towards the inner rotor.

Description

A TURBINE WITH OUTER AND INNER ROTOR BEING CONTRA-ROTATING

The invention relates to an improved design of turbine. Although intended originally as a wind turbine, it is feasible that the design may be used for turbines driven by other fluids such as water. DE10322919 discloses a wind turbine having pairs of rotors with vertical rotation axes. The rotors are contra-rotating.

BE 1002480 relates to a wind turbine composed of coaxial rotors rotating in the reverse direction around a fixed central vertical axis.

According to a first aspect of the invention there is provided a radial inflow rotor assembly for a turbine having an outer rotor and an inner rotor, the rotors being nested and contra-rotating; the outer rotor arranged to divert fluid onto the inner rotor.

By directing the fluid from the outer blades to the inner blades a greater proportion of the energy in the fluid can be drawn thereby increasing the efficiency of the turbine.

In a preferred embodiment the rotors are connected to drive one or more electrical generators. It is preferred that the inner and outer rotors are co-axial as this simplifies the arrangement by which the rotors turn said electric generator(s).

The outer and inner rotors each have a number of blades, the rotor with the greater number of blades having a number of blades that is not wholly divisible by the number of blades of the rotor having fewer blades. This prevents all of the blades of both rotors from aligning at the same time. Such alignment is undesirable as it may prevent the rotors from starting to turn when stationary, and cause a reduction in efficiency if rotating. It is preferred that the outer rotor has the greater number of blades, and most preferred that the outer rotor has thirteen blades and the inner rotor has eleven blades. This ratio is thought to provide the greatest efficiency.

In a preferred embodiment the inner rotor comprises two sets of blades that are circumferentially and radially spaced apart. This arrangement is believed to present a greater surface area to fluid that has passed through the outer turbine and so increase the efficiency of the turbine. The radial offset reduces shading by the inner blade of the trailing radially outer blade.

Preferably the two sets of blades of the inner rotor overlap in the radial direction. Preferably the blades of the inner set are or have a cup shaped portion. One of the blade sets of the inner rotor, preferably the innermost set of blades, may be shaped to divert fluid from a radial direction towards an axial direction. This directs fluid out from the turbine and away from the blades of the rotors that are positioned on the side of the axis of turbine opposite the direction of inflow of fluid.

It is preferred that the blades of the first and second sets of the inner rotor have equal circumferential spacing, the second set of blades being offset by substantially an angle less than half the angle between the blades of the first set. Most preferred the separation is substantially equal to one third of the angular separation between the blades of the first set. This is thought to maximises the volume of air in the cupped blades at different relative positions between the two rotors. This is believed to increase efficiency.

In a preferred embodiment the rotor assembly has a cowling comprising a number of, favourably, static blades arranged to divert fluid towards the outer and/or inner rotors. This helps to ensure that fluid impacting the rotor blades at optimal angle irrespective of the direction of flow of fluid into the casing. It is preferred that the casing comprises a corner stator blade having a leading edge which is spaced radially further from the rotor than side stators adjacent the corner stator.

This feature is believed to have independent inventive merit and therefore according to a second aspect of the invention there is provided a radial inflow assembly for a turbine; the assembly comprising a rotor arranged to be turned by a flow of fluid to drive an electrical generator; and a casing arranged around the rotor, wherein the casing has a plurality of stator blades spaced around the rotor to direct fluid flow towards the rotor; and wherein the casing comprises a corner stator blade having a leading edge which is spaced radially further from the rotor than side stators adjacent the corner stator.

It is preferred that the cowling comprises at least three corner stators arranged that an angle of substantially 90 degrees is formed between lines taken from the leading edge of central of the three corner stators to the leading edge of the other two corner stators. This allows the cowling to provides a greater capture area as compared with a circular shaped cowling. It is most preferred that the lines taken between each corner stator to its two closest define substantially a square.

It is preferred that the corner stator blade has a greater maximum thickness than the side stator blades. This allows a support structure of the rotor assembly to pass through the centre without disrupting airflow.

It is preferred that the corner blade has a trailing edge and a thickness profile that decreases along a chord line of the blade towards the trailing edge, and then increases. It is further preferred that the thickness profile along the chord line of the blade from the leading edge first increases from the leading edge in order to be sized to house the support structure.. It is preferred that the corner stator has a front and back surface, and wherein said surfaces diverge to provide two trailing edges. This allows either side of the corner stator to direct air in different directions. This is important as it is likely much of the time that air striking the front and back surfaces will have quite different, and possibility opposing angles of attack. By providing two trailing edges it is possible to increase laminar flow of the fluid over the corner stator irrespective of the angle of attack of the fluid.

It is also preferred that the stators are arranged so that their leading edge have a greater separation than their trailing edge. This acts to increase the velocity of fluid before it reaches the rotors.

It is also preferred that the distance between adjacent side stators increases sequentially in a direction away from the rear surface of the corner stator. And further preferred that a spacing between the corner stator and adjacent side stator is less than smallest distance between the side stators. This assists to reduce the high pressure fluid zone caused by the increased angle of attack when fluid direction moves away from leading edge of the corner stator towards an angle which is perpendicular to the rear surface. The increased spacing between the stators distal to the corner reduces impedance to fluid which passes through the cowling away from the rear side of the rear surface of the corner stator. The arrangement of the previously mentioned inner rotor is also considered to be inventive in its own right and therefore according to a third aspect of the invention there is provided a radial inflow rotor for a turbine comprising two sets of blades that are circumferentially and radially spaced apart. Preferably the radially inner set of blades is arranged to re-direct radially inflowing fluid towards an axial direction. A preferred embodiment relates to a turbine having a rotor assembly with one or more features described above arranged to drive at a least one electrical generator. The two rotors may be connected to separate electrical generators According to a further aspect of the invention there is provided a turbine having a rotor assembly having a first rotor and second rotor; the rotors being counter rotating; an electric generator comprising a magnet and a coil arranged to rotate relative to one another to generate electricity, wherein the magnet is arranged to be rotated in a first direction by one of the first or second rotors, and the coil is arranged to be rotated in an opposite direction by the other of said rotors. It is thought that such an arrangement may provide increased power output without the need for a second alternator.

According to yet a further aspect of the invention there is provided a plurality of turbines comprising a stack (preferably vertical) of radial inflow turbine assemblies; each having a rotor arranged to be rotated by fluid flow to drive one or more electrical generators; wherein each turbine is configured to extract the maximum power from the fluid flow at its rotor's respective height within the stack.

The invention will now be described by example with reference to the following figures in which:

Figure 1 is a perspective view of a radial inflow rotor assembly for a turbine;

Figure 2 is a perspective view of the radial inflow turbine of Figure 1 shown without the outer cowling;

Figure 3 is a perspective view of the inner rotor; Figure 4 is a plan view of the rotor assembly cut away to show the arrangement of the blades;

Figure 5 is side sectional view of a turbine comprising the rotor assembly of the previous Figures with an electric generator; Figure 6 is a side section magnified view showing the elements of the electrical generator of Figure 5;

Figure 7 is a side section view of an electrical generator of an alternative embodiment; Figure 8 is a schematic of a control system for controlling the speed of the rotors of the rotor assembly; and

Figure 9 is a perspective view of a stack of wind turbines using the rotor assembly of the previous Figures.

Figures 1 - 5 illustrate a radial inflow rotor assembly 1, commonly referred to as a vertical axis rotor assembly, arranged to be connected to an electrical generator 2 (best seen in Fig 5). The rotor assembly 1 may be powered by the wind, but may also/instead be positioned near the exhaust of a large ventilation system, e.g. of a factory unit, to be driven by said exhaust.

The rotor assembly 1 comprises an outer rotor 3, and inner rotor 4 and a cowling 5, each having blades 3 A, 4 A, 5 A. The outer rotor 3 and inner rotor 4 are co-axial with the inner rotor 4 nested within the outer rotor 3. Both the outer rotor 3 and inner rotor 4 are arranged such that a moving fluid acting on the blades 3A 4A of the rotors 3 4 cause them to rotate.

The blades 2 A and 3 A of the outer rotor 3 and inner rotor 4 are arranged in opposing orientations so the moving fluid causes the rotors 3, 4 to rotate in opposing directions relative to one another. From the vantage of Fig 4 the outer rotor 3 is arranged to rotate anti-clockwise and the inner rotor 4 clockwise.

The inner rotor 4 is positioned to receive and be acted upon by moving fluid that has been expelled or otherwise passed through the outer rotor 3. The inner rotor 4 comprises a further set of blades 4B. As can be seen most clearly in Fig 4, the further set of blades 4B are circumferentially spaced with respect the first set of blades 4A and are set radially inwards of the first set of blades 4A. The further set of blades 4B have a concave or cup like surface upon which fluid flow impinges to cause the rotor 4 to rotate. The second set of blades 4B are shaped to divert fluid flow from a radial direction towards an axial direction as shown by arrow X such that it exits out of the top of the rotor assembly 1.

Alignment of the blades 3A of the outer rotor 3 and radially outer set of blades 4A of the inner rotor 4 could prevent the rotors 3 4 from starting to rotate and/or reduce efficiency of power extraction from the fluid during rotation. To prevent this, the outer rotor 3 has a different number of blades from the inner rotor 4. It is preferred that the outer rotor has thirteen blades 3A and the inner rotor has eleven blades in it outer set 4A. It is, however, possible that a different ratio be used so long as the respective numbers of blades are not wholly divisible by one another. The blades 3 A of the outer rotor 3 are arranged to rotate as close as possible to the first set of blades 4A of the inner rotor 4 to reduce losses of fluid flow transferred between rotors 3, 4. The closeness of spacing can cause a stalling action as the blades approach one another. To mitigate this, the trailing edge of the blades 3A and the leading edges of blades 4A, which face one other when they pass, are convexly curved. It may be possible to provide this effect with a curve in only one set of the blades.

A supporting frame 6 (see Fig 3) supports the cowling 5. The cowling 5 comprises an upper section 5C and lower section 5D between which are supported stator blades 5A, 5B, The upper section 5C defines an opening 5E to allow exhaust fluid from the rotors 3, 4 to be expelled.

The cowling 5 is generally cuboidal with foar sides. The upper and lower sections 5C, 5D of each side have side walls 5F that slope radially inwardly and towards the other section so that the inlet narrows towards the rotors 3,4. This increases the velocity of the fluid before it reaches the rotors 3,4.

At each corner of the cowl 5 is a corner stator blade 5B. The corner stator 5B has a wider profile than the side stator blades 5A in order that the supporting frame 6 can pass through its interior. The comer stator blade 5B is shaped as an aerofoil having a generally convex front surface 7 and concave rear surface 8. The stator blade 5B increases in thickness from its leading edge before narrowing part way along its chord length. The front surface 7 and rear surface 8 then diverge to provide two trailing edges 7A. Between each comer stator blade 5B are a series of side stator blades 5 A which have leading edges that are radially inward of the comer blades 5B. The spacing between the side stator blades 5 A is not equi-distant. Rather, the distance D between adjacent side stator blades 5A increases sequentially in a direction away from the rear surface 8 of comer stator blade 5B. A spacing E between the comer stator blade 5B and adjacent side stator blade 5A is less than smallest distance D.

Figures 5 and 6 illustrate the rotor assembly 1 connected to an electrical generator 2 in order to generate electric power from the moving rotors 3, 4.

The electrical generator comprises two alternators 20, 30 that are stacked one above the other. Each alternator 20, 30 comprises a set of coils 21, 31, and a pair of magnetic plates 22, 32 between which the coils 21, 31 are interposed. The magnetic plates 22, 32 of each alternator 20, 30 are connected to a central boss 23, 33. The boss 23 of the first alternator 20 is connected to be rotated by a shaft 40 which is driven by the inner rotor 4. The boss 33 of the second alternator 30 is connected to a flange plate 50 driven by outer rotor 3. The flange plate 50 comprises an aperture 51 through which shaft 40 passes allowing the plate 50 and shaft 40 to rotate independently. Figure 7 illustrates an alternative embodiment of electrical generator 2 comprising a single alternator 60. The pair of magnetic plates 61 are connected to a boss 62 which in turn is connected to a central shaft 63 that is rotated by the inner rotor 4. The coils 64 are connected to a housing 65 that is in turn connected to a flange plate 66 which is turned by the outer rotor 3. Bearing configuration 67 allows relative motion between the housing 65 and shaft 63. Electrical power is taken from the coil 64 via a slip ring 68. The contra-rotation of the rotors 3 4 causes a corresponding contra- rotation of coil 64 and magnetic plates 61.

In use, the rotor assembly 1 is orientated with a corner of the cowling 5 towards the prevailing wind direction. This provides the largest capture area towards the prevailing wind to maximise power in general conditions.

Fluid passes through cowling 5, accelerated by the narrowed opening provided by tapered surfaces 5F, and directed by stator blades 5A, 5B towards the blades 3A of rotor 3 so as to cause it to revolve. Fluid leaving the blades 3A(or otherwise past rotor 3) is directed onto blades 4A and 4B of rotor 4 causing rotation of rotor 4 in a direction opposing rotor 3. The rotation of the rotors 3, 4 turns the generator 2 to generate electricity. The fluid is directed by blades 4B towards an axial direction X and out of outlet 5E.

When the wind direction changes away from the prevailing, the configuration of stator blades 5A, 5B reduce the high pressure zone in front of surface 8 caused by the greater angle of attack, and thus optimises laminar flow towards the rotors 3, 4.

The ratio of the rotational speed of the outer rotor 3 and inner rotor 4 varies for a given wind speed. At relatively low winds speeds, e.g. up to 5 ms^"1, the ratio has been observed to be around 3: 1, i.e. the outer rotor rotates 3 times faster than the inner rotor 4. As the wind speed increases this ratio can increase which may result in stalling of the inner rotor 3. To ameliorate this problem a mechanism can be used to control one or both of the speeds of the rotors. An example mechanism, illustrated schematically in Fig 8, comprises means 81 for providing an indication of the speed of both rotors (though it may only be the outer rotor 3). A processing means 80 to monitor the indication of speed and to operate an braking mechanism 82 to slow down the outer rotor 3 when the rotational speed is outside optimal limits.

By controlling the speed of the outer rotor, in particularly slowing down the outer rotor when its rotation speed gets too high, the speed of the inner rotor 4 can be controlled and stalling prevented. The means 81 for providing an indication of the speed of both rotors may comprises a detector(s), such as a tacho, to measure the speed of revolution; alternatively, the speed may be inferred from the characteristics of the power output, such as the frequency of the a c voltage from the alternator to which the rotor 3, 4 is connected.

The processor 80 is arranged to receive the indicated speeds and to process them using a optimisation algorithm to identify whether the speeds fall within preferred limit. A simpler design may use pre-set ranges. The processor 80 may only be arranged to operate the brake when the outer rotor 3 is determined to be rotating above a certain speed and the inner rotor below a different, slower speed.

The braking mechanism 82 may be mechanical, such as comprising a magnetic brake arranged to slow down the rotor(s) (in this example of Fig 5& 6 the magnetic plates) of the electrical generator. Alternatively braking may be effected by electrical means, for example by routing some of the power from the generator 2 through a load, such as a power resistor.

Figure 9 illustrates a series of turbines such as shown in Figures 5 or 7 supported by a frame 100 in a stacked configuration. In order to derive as much power as possible from a striated wind profile in which the frame sits, each turbine of the stack is optimised for the prevailing wind velocity for the strata in which it sits. This can be achieved for each turbine by, for example, doing any one or more of: increasing/ decreasing the number of turns on the generator coil; increasing the magnetic field strength; or adjusting the algorithm of the control circuit. In a typical situation, wind velocities tend to increase with altitude. Therefore the upper turbines may be arranged to take advantage of this by using generators 2 which generate more power but require more force to be turned, and using lower powered generators with the turbines positioned lower in the stack where the prevalent wind speed is slower.

Claims

1 A radial inflow rotor assembly for a turbine having an outer rotor and an inner rotor, the rotors being nested and arranged, when in use, to be contra-rotating; the outer rotor arranged to divert fluid onto and/or towards the inner rotor.

2 A radial inflow rotor assembly for a turbine according to claim 1 wherein the outer and inner rotors each have a number of blades, the rotor having the greater number of blades having a number of blades that is not wholly divisible by the number of blades of the rotor having fewer blades.

3 A radial inflow rotor assembly for a turbine according to claim 2 wherein the outer rotor has a greater number of blades than the inner rotor.

4 A radial inflow rotor assembly for a turbine according to claim 3 wherein the outer rotor has thirteen blades and the inner rotor has eleven blades.

5 A radial inflow rotor assembly for a turbine according to any previous claim wherein the inner rotor comprises two sets of blades that are circumferentially and radially spaced apart.

6 A radial inflow rotor assembly for a turbine according to claim 5 wherein the two sets of blades of the inner rotor overlap in the radial direction.

7 A radial inflow rotor assembly for a turbine according to claim 6 wherein the radially inmost set of blades of the inner rotor are shaped to divert fluid from a radial direction towards an axial direction.

8. A radial inflow rotor assembly for a turbine according to any claim 5, 6 or 7 wherein the blades of the first and second sets each have equal circumferential spacing, each of blades of the second set being offset from the rear surfaces of first set of blades by substantially an angle less than half of the angular separation between each of the first set of blades, and more preferably equal to one third of the angular separation between each of the first set of blades.

9 A radial inflow rotor assembly for a turbine according to any previous claim having a cowling comprising a number of blades arranged to divert fluid towards the outer and/or inner rotors.

10. A turbine having an electrical generator, and a rotor assembly according to any previous claim.

11. A turbine having a rotor assembly having a first rotor and second rotor; the rotors arranged to be counter rotating; an electrical generator comprising a magnet and a coil arranged to rotate relative to one another to generate electricity, wherein the magnet is arranged to be rotated in a first direction by one of the first or second rotors, and the coil is arranged to be rotated in an opposite direction by the other of said rotors.

12. A plurality of radial inflow turbine assemblies arranged on a support at different height; each having a rotor arranged to be rotated by fluid flow to drive one or more electrical generators; wherein each turbine is configured for the prevailing wind velocity at its rotor's respective height within the stack.

13. A plurality of turbines according to claim 12 comprising a vertical stack of radial inflow turbine assemblies.

14. A radial inflow assembly for a turbine; the assembly comprising a rotor arranged to be turned by a flow of fluid to drive an electrical generator; and a casing arranged around the rotor, wherein the casing has a plurality of blades spaced around the rotor to direct fluid flow towards the rotor; and wherein the casing comprises a corner stator blade having a leading edge which is spaced radially further from the rotor than side stators adjacent the corner stator.

15. A radial inflow assembly for a turbine according to claim 14 comprising at least three corner stators that are arranged such that an angle of substantially ninety degrees is formed between lines taken from the leading edge of a central of the three stators to the leading edge of the two adjacent corner stators.

16. A radial inflow assembly according to claim 14 or 15 having four corner stators.

17. A radial inflow assembly according to claim 16 wherein lines taken between each of the four corner stators define a square.

18. A radial inflow assembly according to any claim 14-17 wherein the corner stator blade has a greater maximum thickness than the side stator blades.

19. A radial inflow assembly according to claim 18 wherein the corner blade has a trailing edge; and a thickness profile that decreases along a chord line of the corner blade towards the trailing edge, and then increases.

20. A radial inflow assembly according to claim 19 wherein the thickness profile along the chord line of the blade from the leading edge first increases before decreasing.

21. A radial inflow turbine according to claim 14 - 20 wherein the corner blade has a front and rear surface, and wherein said surfaces diverge to provide two trailing edges.

22. A radial inflow turbine according to any claim 14 - 21 wherein adjacent blades are arranged so that their leading edge has a greater separation than their trailing edge.

23. A radial inflow turbine according to any claim 14 -21 wherein the corner blade has a front convex surface and rear concave surface; and where a distance D between adjacent blades increases sequentially in a direction away from the rear surface of corner blade.

24 A radial inflow rotor for a turbine comprising two sets of blades that are circumferentially and radially spaced apart.

25. A radial inflow rotor for a turbine according to claim 24 wherein at least one of the sets of blades are arranged to re-direct radially inflowing fluid towards an axial direction.

26. A radial inflow rotor according to claim 25 wherein the radially inner set of blades is arranged to re-direct radially inflowing fluid towards an axial direction.

27. A radial inflow rotor assembly for a turbine having an outer rotor and an inner rotor, the rotors being nested and arranged, when in use, to be contra-rotating; the outer rotor arranged to divert fluid onto and/or towards the inner rotor; and further comprising means to control the rate of rotation of the outer rotor and/or inner rotor;

28. A radial inflow rotor assembly according to claim 27 comprising means to provide an indication of the rate of rotation one or both of the inner rotor and outer rotor; a control to receive said indication of the rate of rotation and in response to actuate a brake to slow down the outer rotor to inhibit reduction in the rate of rotation of the inner rotor.

29. A radial inflow rotor assembly according to claim 28 wherein the braking mechanism comprises diverting electrical power from the generator through a high impedance load.