GB2417760A

GB2417760A - Transforming the energy of fluid flow, eg wind or river flow, into another form of energy

Info

Publication number: GB2417760A
Application number: GB0517808A
Authority: GB
Inventors: Vladimir Zubarev; Avaz Karimov; Alexandr Smirnov; Vladimir Shatko
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-09-01
Filing date: 2005-09-01
Publication date: 2006-03-08
Anticipated expiration: 2025-09-01
Also published as: GB0517808D0; GB2417760B

Abstract

The kinetic energy of fluid flow, eg wind or river flow, is transformed into another form of energy, eg electrical, heat or mechanical, by flowing the fluid medium through a duct 1 and over a working surface of a working element 2 of an energy converter 28 so that the flow induces oscillations of the working element 2. The working element 2 may form a moving rectangular vane hinged at its downstream end and forming a partition separating the flow into two channels. The duct may have an inlet 10 in the form of a nozzle and an outlet 12 in the form of a diffuser. The vane 2 may be connected mechanically, eg via crank (50, fig.6), to the energy converter, eg dynamo (28, fig.5) or a pump. One or more turbines 200 may be located downstream of the vane 2; oscillation of the vane causes pulsations which actuate the turbine(s) more effectively than would a steady flow.

Description

24 1 7760 - 1 -

A METHOD AND APPARATUS FOR TRANSFORMING ENERGY IN A FLUID

MEDIUM

The present invention relates to a method and apparatus for generating energy from renewable natural sources of energy, in particular to methods of transforming the kinetic energy of naturally occurring moving fluids, such as wind and river water, into movement of working bodies placed in the path of flow of fluid. The method is applicable to the generation of electricity, heating or mechanical energy in wind- and hydro-powered plants. The apparatus can work in any fluid medium including gas, liquid, powder, loose material, etc. The constantly rising cost and depletion of non-renewable energy resources such as oil, natural gas and coal, has made the use of sources of renewable energy such as moving air, for example wind power, and moving water, for example natural flow of rivers or tides, a desirable basis for the creation of devices for generating energy from the kinetic energy of fluids.

A problem with the use of such renewable sources of energy is the low efficiency of known devices for transforming the kinetic energy of the flow of fluid into other forms of energy. A shortcoming of the known devices is the difficulty in achieving efficient use of the energy of the fluid when the speed of flow is low, as is the case, for example, with rivers situated on plains and flatlands, and consequently the dynamic pressure on the blades of the turbine is low.

The aim of the present invention is to increase the efficiency of the extraction of the kinetic energy of the flow of fluid to provide useable energy. - 2 -

The invention in its various aspects is defined in the independent claims below, to which reference should now be made. Advantageous features are set forth in the appendant claims.

According to a first aspect of the present invention, a method for transforming energy in flow in a fluid medium into another form of energy comprises flowing a fluid medium through a duct and over a working surface of a working element of an energy converter so that the flow of fluid induces oscillations of the working element. The working element forms a moving partition in the duct. The transformation of energy is carried out by the inducement of oscillations of the working element placed in the flow of fluid. Oscillations or back and forth movements of the working element are induced automatically by turbulence in the fluid flow and maintained by the oscillating element.

The oscillation of the working element transforms the energy of the fluid flow inside of the duct into movement of the working element which in turn may be converted into another form of energy, for example electricity.

Preferably, the partition separates the path of the flow of fluid into two channels.

Preferably, the partition can alternately open and close the two channels such that at times there is no fluid flow through one or the other channel.

According to a second aspect of the present invention, an apparatus for converting the kinetic energy from the flow in a fluid medium into another form of energy comprises a duct and at least one movable partition which separates the duct into at least two channels, the or each partition being pivoted and including means for coupling the at least one partition to a converter for converting the movement of the at least one partition into another form - 3 - of energy, movement of the at least one partition alternately increases and decreases the flow of fluid medium through the respective channels, the arrangement being such that the at least one partition is caused to oscillate by flow of fluid medium in the duct.

According to a third aspect of the present invention, an apparatus for converting the kinetic energy from a fluid medium into another form of energy comprises a duct, at least one moving partition separating the space within the apparatus into at least two channels, the or each partition being pivoted and being coupled to a converter for converting the movement of the at least one partition into another form of energy, movement of the at least one partition alternately increasing and decreasing the flow through the respective channels, the arrangement being such that the at least one partition is caused to oscillate by fluid flow in the duct.

Preferably, the duct comprises an entrance in the form of a nozzle. Preferably, the duct has an exit in the form of a diffuser. Preferably, the nozzle has a constriction.

Preferably, the or each partition is hinged about an axis on the downstream end of the or each partition.

Preferably, the or each partition is an aerodynamic surface with a tapered edge facing upstream.

Preferably, the at least one partition is mechanically connected to an energy converter.

Preferably, the or each partition is a vane.

Preferably, the or each vane has a symmetrical cross- section along its longitudinal axis. - 4 -

Preferably, the or each vane is rectangular in profile.

Preferably, the duct is symmetrical in the region of the at least one partition.

In use, the partition oscillates back and forth in the flow of fluid and the oscillations are converted into another form of energy.

In a modification of the invention, one or more turbines are located downstream of the partition. The movement of the partition causes the fluid downstream of the partition to pulsate. The pulsating movement of the fluid is more effective in actuating turbines, particularly at low fluid flow rates. By this means it is possible to achieve energy generation at speeds which could not produce energy with a conventional device such as, for example, a windmill. For example a wind speed of 10 metres per second is required for a conventional device. With a device according to the present invention, it is possible to generate energy with speeds as low as 3.5 to 5.Om per second or even lower.

A preferred embodiment of the invention is described in more detail below and takes the form of a method for transforming energy in flow in a fluid medium into another form of energy, the method comprising: flowing a fluid medium through a duct and over a working surface of a working element of an energy converter so that the flow of fluid induces oscillations of the working element. Hence, kinetic energy of the flow of fluid is extracted to provide useable energy.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings of which: - 5 - Figure 1 shows a horizontal section through a device for converting fluid flow energy into another form of energy in accordance with the present invention; Figure 2 shows a view similar to Figure 1 with the vane in a second position; Figure 3 shows a view similar to Figures 1 and 2 with the vane in a third position; Figure 4 shows a vertical section through line A-A of the device of Figures 1, 2 and 3; Figure 5 shows a perspective view of the device of Figures 1, 2, 3 and 4; Figure 6 shows a plan view from above of a first modified form of a device in accordance with the present invention; Figure 7 shows a plan view from below of the device of Figure 6; Figure 8 shows a perspective view from one end of the device of Figures 6 and 7; Figure 9 shows a horizontal section through a second modified form of a device embodying the present invention; Figure 10 shows a vertical section through line C-C of the device of Figure 9; Figure 11 shows a vertical section through line B-B of Figure 9 of the device of Figures 9 and 10; 6 - Figure 12 shows a perspective view from one end of the device of Figures 9 to 11; Figure 13 shows a horizontal section through a third modified form of a device in accordance with the present invention; and Figure 14 shows a fourth modified form of a device in accordance with the present invention.

Referring to Figures 1 to 5, these show a device 100 for converting fluid flow energy into other forms of energy in accordance with the invention. The device 100 comprises a duct 1 of generally rectangular cross-section.

Alternatively the duct could have a circular or other cross-section with a symmetrical shape. The duct 1 has an inlet 10 and an outlet 12. A fricative nozzle portion 14 adjacent the inlet 10 is of uniform external cross-section throughout its length but has an interior wall portion 11 which tapers in cross-section from the inlet 10 at its upstream end towards an intermediate interior wall portion of constricted but uniform cross section, and an interior wall portion 19 which is flared internally towards the outlet 12 at its downstream end. At the downstream end, the interior wall 19 of the nozzle 13 merges into an expansion chamber or diffuser 7 which is flared outwardly, internally and externally towards the outlet 12. Fluid entering the device 100 at the inlet 10 passes through the constriction formed by the interior wall 11 of the nozzle and through the diffuser 7 and leaves the device 100 at the outlet 12 as indicated by the dashed lines 8. The fluid may be air such as in a wind powered device or liquid such as water in a river driven device.

A partition or working element is formed by a vane 2 which is pivoted at or towards its downstream end about an axis - 7 - 6 transverse to the direction of flow of fluid through the device 100 on the centre line 16 of the device 100. The pivot axis 6 is located in the expansion chamber or diffuser 7 towards its narrower upstream end. The vane 2 extends into the nozzle 13 so that its upstream edge lies in the intermediate portion that forms the constriction.

The vane 2 is rectangular and has an aerofoil section 17 with a rounded downstream edge 18 and tapering towards the upstream edge 20. The vane 2 can pivot so that its upstream edge 20 moves between abutments formed by one side and the other of the device 100. When the vane 2 is in the median position, it forms two channels 22 and 24, one on each side of the vane 2 through the device 100.

Fluid entering the device 100 flows in a non-turbulent manner into the device 100. The constriction formed by the intermediate interior wall portion 15 acts on the fluid entering the device 100 to give a Venturi effect that produces a difference in fluid pressure in the two channels 22,24 on either side of the vane 2 when the vane is offset to one side or the other from the median position. This effect causes the vane 2 to swing towards the channel of lower fluid pressure. The vane 2 passes through its neutral position, in which the vane 2 is aligned with the centre axis 25 of the duct 1, by momentum and the force of the flow of fluid on the side of the vane 2 that the vane 2 is moving away from. When the force caused by the pressure difference between the two channels 22,24, now acting in the opposite direction, exceeds the force provided by momentum and the force from the flowing fluid, the direction of travel of the vane 2 is reversed.

This process is repeated causing the vane 2 to swing to- and-fro. In this embodiment, as the vane 2 swings to-and- fro it alternately closes the channels 22 and 24 on either side of the vane 2. - 8

In other words, if we start with the vane 2 in the position shown in Figure 3, the channel 24 on the open side of the vane 2 creates a Venturi effect with lower static pressure than in the closed channel 22 on the opposite side of the vane 2. This static pressure difference causes the vane 2 to move away from the adjacent wall 23 as shown in Figure 2 towards a neutral position in which the vane 2 is aligned with the centre axis 25 of the duct 1. The angular momentum of the vane 2 causes the vane 2 to move past the neutral position towards the opposite wall 27 of the duct 1. As the channel 24 starts to close, the static pressure in this channel 24 will start to fall below the static pressure in the other channel 22. The dynamic force of the incoming fluid on the vane 2 together with the angular momentum of the moving assembly will overcome the static pressure differential until the tip of the vane 2 abuts the wall 27 of the duct 1. Thereupon, the static pressure difference caused by the Venturi effect in the channel 22 will cause the vane 2 to move away from the adjacent wall 27 and channel 24 will start to open, as shown in Figure 1. The cycle repeats so that the vane 2 moves continuously from side to side in the duct 1.

The vane 2 will swing towards the channel which has the lower fluid pressure. As illustrated in Figure 1, when the fluid pressure in the channel 22 is less than the fluid pressure in the channel 24 the vane 2 swings towards the channel 22. Figure 2 illustrates the situation when the fluid pressure in the channel 22 is greater than the fluid pressure in the channel 24. In this situation, the vane 2 swings towards the channel 24. As the vane 2 swings towards one channel, for example channel 22, the pressure of the fluid in both channels is affected. This can cause the pressure in the other channel 24 to decrease and the pressure in the channel 22 to increase and the vane 2 will swing back from the direction it came from. 9 -

This produces the oscillating behaviour in the vane 2. As the vane 2 oscillates, the end of the vane 2 touches the wall portion 11 on opposite sides of the intermediate portion 15, alternately stopping the flow down the channels 22 and 24.

The vane 2 is coupled to a device which converts the movement into other forms of energy. As shown in Figure 5, an axle 26 extends from the vane 2 into a dynamo 28 which produces electricity from the oscillations of the vane 2.

The transducer which converts the kinetic energy of the oscillating vane 2 into other forms of energy may vary according to the application. Rather than using a dynamo as described in the present example, the transducer may be a mechanical device that converts the movement of the vane 2 into mechanical energy, for example reciprocating or rotary movement, or it may be a pump which converts the movement into hydraulic energy.

We have found that a device 100 can be constructed as described above which converts fluid energy into other forms of energy efficiently and at low flow rates.

In one embodiment, the device 100 will start to operate when the fluid moves at speeds of 3.5 to 5.0 metres per second and will produce mechanical energy with 80% efficiency. Increasing the speed will increase efficiency. At speeds of 7 to 8 metres per second, efficiency will reach a maximum value. Further increase of speed will reduce efficiency.

The operation of the device 100 is governed by an aerodynamic coefficient called the Strouhal number, - 10 Sh= - w where: L is the length of the oscillating vane 2, f is the oscillation frequency of the vane 2 in Hz and w is the rate of movement of the incoming flow in m/s.

Changing the ratio 5 (Figure 5) of the length of the oscillating vane 2 to the width 4 of the duct 1 will change the vane oscillating frequency. The device 100 operates at She 0.25.

Increasing the Strouhal number leads to an increase in efficiency of the apparatus. Therefore, for high efficiency the device 100 should have high Strouhal numbers, such as Sh > 25.

As it can be seen from the formula, it is possible to increase Sh by: a) Decreasing speed of flow at the entrance to the inlet 10, i.e. regulating the flow. This kind of regulation of speed of flow is not expedient with wind-powered plants, in view of the complexity, inconvenience and expense of having a regulator.

or b) Increasing the width 4 of the vane 2 or increasing its length 5. Which is more suitable depends on how the change alters the speed of the flow.

Increasing the rate of movement of the fluid towards the mouth or the opening will lead to a decrease in the Strouhal number. i

In a preferred embodiment for w = 10 m/s and f = 8 Hz, the thickness 3 of the vane 2 at the axis 6 is between 25 and 30mm. The width 4 of the vane 2 is lOOmm. The length 5 of the vane 2 is between 350 and 500mm. If the device is intended to function in an air stream, its overall dimension will be about an order of magnitude greater than if it is intended to function in a river.

Figures 6, 7 and 8 show a modification of the device 100 of Figures 1 to 5. It is similar to the device of Figures 1 to 5 and like components have been given the same reference numerals.

The vane 2 of the device 100' is mounted on a shaft 57 to oscillate about an axis 6. The vane is mechanically connected to a dynamo 28 by a crank mechanism 50. In the embodiment of Figures 6, 7 and 8, the crank 50 is configured such that as the vane 2 oscillates in a fluid flow it causes the dynamo 28 to rotate about an axis 51 extending through the centre of the dynamo 28 continuously in the direction indicated by the arrow 52.

Alternatively, the crank 50 can be configured such that as the vane 2 oscillates in a fluid flow it causes the dynamo 28 to oscillate to-and-fro about the axis 51, in the direction indicated by the arrow 54.

The crank 50 comprises three linkages. A first linkage 55 is fixed to the vane 2 and shaft assembly 57 to oscillate as the vane 2 oscillates. The vane 2 extends outwardly from the pivot axis 6, to a pivotal connection 61 to one end 62 of a longer connecting linkage 58. The other end 64 of the connecting linkage 58 is pivotally connected to one end 66 of the shortest, third linkage 60. The other end 68 of the third linkage 60 is fixed to one end of the drive shaft 56 of dynamo 28. The drive shaft 56 of the dynamo 28 is directly downstream of the pivot axle 57 of the vane 2. 12

The fricative nozzle portion 14, expansion chamber or diffuser 7, vane 2 and crank 50 are located on one side of a planar substrate 69. The dynamo 28 is located on the other side of the planar substrate 69.

The interior wall portion 11 of the fricative nozzle portion 14 of the embodiment of Figures 6, 7 and 8 curves inwardly in cross section from the inlet towards an interior wall portion 19 which is flared internally towards the outlet which forms the expansion chamber or diffuser 7. The expansion chamber or diffuser 7 terminates upstream of the axle 57. The fricative nozzle portion 14 terminates adjacent the upstream end of the vane 2. Hence, the vane 2 lies in the expansion chamber or diffuser 7.

Figures 9 to 12 show a further embodiment of a device 100'' for converting fluid flow energy into other forms of energy. It is similar to the devices of Figures 1 to 5 and 6 to 8 and like components have been given the same reference numerals.

The device 100'' has two vanes 2 located on either side of a fixed partition or divider 70. The vanes 2 can both pivot about their respective pivot axes 6. The vanes 2 are each mechanically connected to a common axle or shaft 72 by a respective crank 50. The common axle 72 is connected to a dynamo or other suitable device (not shown) in order to convert the rotary motion of the common axle 72 to electrical energy or other forms of energy.

The mechanical connections 74 of the cranks 50 to the common axle 72 are offset so that as the vanes 2 oscillate in a fluid flow they cause the common axle 72 to rotate continuously in the same direction about its axis 76.

Furthermore, this arrangement allows rotation of the - 13 common axle 72 to be started, whatever the previous stop position of the cranks 50. The vanes 2 and cranks 50 are configured such that the vanes 2 both move at the same time between their extreme position at one side to their extreme position at the other side.

The vanes 2 are both mechanically connected to an axle or shaft 78 at their downstream end. Each of the axles 78 extends along a pivot axis 6 through bearings 80 in opposing sidewalls 82 of the diffuser 7. The vanes 2 each extend away from their respective axle 78, towards the upstream end of the device 100''. The vanes 2 have sides which are parallel at the downstream end and which taper at the upstream end at their tips only. The tapered ends of the vanes 2 terminate adjacent the interface between the fricative nozzle portion 14 and the diffuser 7. The vanes 2 lie entirely within the diffuser 7.

In this embodiment, the interior wall portion 11 of the fricative nozzle portion 14 tapers in cross section from the inlet 10 at its upstream end towards the expansion chamber or diffuser 7 at the downstream end. The walls of the fricative nozzle portion 14 are of uniform thickness throughout. The diffuser 7 is flared outwardly, internally and externally towards the outlet 12. The sides 82 of the fricative nozzle portion 14 are open as shown in Figure 12.

The fixed partition 70 has parallel sides at the downstream end. The sides of the fixed partition 70 taper at the upstream end. The common axle 72 is located at the downstream end of the fixed partition 70 and extends through it to project through bearings 84 in opposing sidewalls 82 of the diffuser 7.

Similar cranks 50 to those described above for the second embodiment are used to make mechanical connections between one end of the axle 72 of one vane 2 and one end of the common axle 78, and the other end of the axle 72 of the other vane 2 and the other end of the common axle 78.

In this embodiment, the connecting linkages 58 are both divided into two portions, which are joined together by fasteners 86, for example screw bolts. The third linkages of these cranks 50, which connect to the common axle 72 are disc shape.

Figure 13 shows another modification of the device 100 of Figures 1 to 5. Downstream of the vane 2 is a turbine 200 which is coupled to another device for generating another form of energy. The turbine 200 rotates in the fluid flowing through the device 202.

In Figure 13, the upstream arrangement is similar to that of Figures 1 to 5. The upstream arrangement leads to a middle portion 204. The middle portion 204 has a fixed divider 206, with a rectangular cross section, which is spaced from and downstream of the vane 2. The fixed divider 206 is located between two side walls 208 and 210 such that two channels 212 and 214 are formed. The channel 212 is longer than the channel 214. This is achieved by inclining the middle portion 204 relative to the centre line 16 of the device 202 and offsetting the turbine 200 from the centre line 16.

The first sidewall 212 is arcuate and extends outwardly before curving around an apex and then extending straight towards the turbine 200 which is offset towards the second sidewall 214. The first sidewall 212 extends into a substantially straight sidewall along the centre line 16 of the device 202, forming an outlet 216. The second sidewall 210 has an internal side which is straight and extends outwardly. The external side of the second sidewall 210 also extends straight outwardly at a greater angle to the internal side. A semi-circular sidewall extends around the turbine 200 from the second sidewall 210 to a straight sidewall of an outlet 216 that extends parallel to the centre line 16 of the device.

The turbine 200 has arcuate blades 218 which extend outwardly from an axle 220. The blades 218 are spaced equally around the circumference of the axle 220. The outer side 222 of the blades 218 faces the direction of rotation of the turbine 200.

In operation, the vane 2 oscillates and the movement of the vane 2 is converted into other forms of energy as in the first embodiment. As the vane 2 swings from side to side, it causes a pulsating stream of fluid downstream of the vane 2 as the channels 212 and 214 on either side of the vane 2 are opened and closed. As the vane 2 swings it decelerates the flow in some areas of the stream, giving these areas a lower kinetic energy, while accelerating the flow in other areas of the stream, giving these areas a higher kinetic energy. The higher kinetic energy flow bears on the blades of the turbine 200 to produce sufficient torque on the turbine 200 to overcome the inherent friction in the turbine 200 using a lower overall flow rate.

The arrangement of Figure 13 provides the advantage that the pulsating flow rotates the turbine 200 in one direction only and the arrangements is also more effective at rotating the turbine, particularly at low fluid flow speeds.

Figure 14 shows a further modification similar to that of Figure 13 but in which two turbines 300 and 302 are located in the fluid flow stream. The two turbines 300 and 302 and the vane 2 are each coupled to another device for generating other forms of energy.

The upstream arrangement is similar to that of Figures 1 to 5 and 13. The upstream arrangement leads to a middle portion 304. The middle portion 304 has a fixed divider 306, which has a uniform cross section along its length and, which is spaced from and downstream of the vane 2.

The vane 2 extends along the centre line 16 of the device 308. The fixed divider 306 is located between two side walls 310 and 312 such that two channels 313 and 320 are formed. The sidewalls 310 and 312 are straight and extend outwardly to two semi-circular walls which accommodate the two turbines 300 and 302. The downstream ends of the semi- circular walls extend into an outlet 314 which has straight sidewalls 316 which extend parallel to the central axis 16. The turbines 300 and 302 are of the same design as that described above and shown in Figure 13.

They are equidistant from the central axis 16 of the device 308.

Again, in operation, as the vane 2 swings from side to side it causes a pulsating stream of fluid downstream of the vane 2 as the channels 318 and 320 on either side of the vane 2 are opened and closed. As the vane 2 swings it decelerates the flow in some areas of the stream, giving these areas a lower kinetic energy, while accelerating the flow in other areas of the stream, giving these areas a higher kinetic energy. The higher kinetic energy flow bears the blades of the turbines 300 and 302 to produce sufficient torque on the turbines 300 and 302 to overcome the inherent friction in the turbines 300 and 302 using a lower overall flow rate.

Embodiments of the present invention have been described with particular reference to the examples illustrated.

However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention. In particular, the - 17 position of the turbine or turbines can be varied from those illustrated in order to use the energy from the pulsating flow particularly efficiently and the number of the turbines used can be more than the illustrated number.

The form of the duct and the length of the vane may be adjustable to tune the device and improve its effectiveness. Abutments can be provided which limit the pivoting movement of the partition about the pivot axis.

The abutments can be formed by the walls of the duct. The lo abutments can be arranged such that when the partition engages one or other of the abutments, it stops the flow in the fluid medium through one or the other of the channels.

Claims

1. A method for transforming energy in flow in a fluid medium into another form of energy, the method comprising: flowing a fluid medium through a duct and over a working surface of a working element of an energy converter so that the flow of fluid induces oscillations of the working element, the working element forming a moving partition in the duct, the partition separating the path of the flow of fluid medium into two channels.

2. A method according to claim 1, wherein the partition alternately opens and closes the channels such that at times there is no flow of fluid medium through one or the other channel.

3. A method according to claim 1 or 2 in which the duct includes a constriction and the movable partition is pivoted about an axis transverse to the duct downstream of the constriction with its free end pointing upstream and located in the region of the constriction.

4. A method according to any of claims 1 to 3, wherein the method operates at a Strouhal number, Sh > 25, where Sh = L.f w where L is the length of the working element, f is the oscillation frequency of the working element and w is the rate of movement of the flow of fluid medium.

5. An apparatus for converting the kinetic energy from the flow in a fluid medium into another form of energy, comprising a duct and at least one movable partition which separates the duct into at least two channels, the or each partition being pivoted and including means for coupling - 19 the at least one partition to a converter for converting the movement of the at least one partition into another form of energy, movement of the at least one partition alternately increases and decreases the flow of fluid medium through the respective channels, the arrangement being such that the at least one partition is caused to oscillate by flow of fluid medium in the duct, wherein the duct comprises an entrance in the form of a nozzle, and wherein the nozzle has a constriction.

6. An apparatus according to claim 5, wherein the duct has an exit in the form of a diffuser.

7. An apparatus according to claim 6, wherein the at least one partition lies in the diffuser.

8. An apparatus according to any of claims 5 to 7, wherein the or each partition is hinged about an axis on the downstream end of the or each partition.

9. An apparatus according to any of claims 5 to 8, wherein the or each partition is an aerodynamic surface with a tapered edge facing upstream.

10. An apparatus according to claim 9, wherein the or each aerodynamic surface tapers along its entire length.

11. An apparatus according to claim 9, wherein the or each aerodynamic surface tapers at its tip only.

12. An apparatus according to any of claims 5 to 11, wherein the at least one partition is mechanically connected to an energy converter.

13. An apparatus according to claim 12, wherein the at least one partition is mechanically connected to an energy converter by at least one crank. 20

14. An apparatus according to any of claims 5 to 13, wherein the or each partition is a vane.

15. An apparatus according to claim 14, wherein the or each vane has a symmetrical cross-section along its longitudinal axis.

16. An apparatus according to claim 14 or 15, wherein the or each vane is rectangular in profile.

17. An apparatus according to any of claims 5 to 16, wherein the duct is symmetrical in the region of the at least one partition.

18. An apparatus according to any of claims 5 to 17, further comprising one or more turbines located downstream of the at least one partition.

19. An apparatus according to any of claims 5 to 18, comprising a single movable partition.

20. An apparatus according to any of claims 5 to 18, comprising at least two movable partitions.

21. An apparatus according to claim 20, wherein the at least two movable partitions are mechanically connected to a common shaft.

22. An apparatus according to claim 21, wherein the movable partitions are each mechanically connected to the common shaft by a crank.

23. An apparatus according to claim 22, wherein the mechanical connections between the cranks and the common shaft are offset at the common shaft. 21

24. An apparatus according to any of claims 20 to 23, comprising two movable partitions.

25. An apparatus according to claim 24 further comprising a fixed partition located between the two movable partitions.

26. A method for transforming energy in flow in a fluid medium into another form of energy, the method comprising: placing a working surface of a working element of an energy converter continuously in a flow of fluid medium through a duct, fluid enters at an inlet and passes through a constriction formed by the interior wall of a nozzle and through a diffuser and leaves at an outlet, the working element extends into the nozzle so that its upstream edge lies in the intermediate portion forming the constriction, the working element pivots so that its upstream edge moves between one side and the other of the energy converter and so that the flow of fluid induces oscillations of the working element.

30. An apparatus for converting the kinetic energy from the flow in a fluid medium onto another form of energy comprising a duct, at least one moving partition separating the space within the duct into at least two channels, the or each partition being pivoted and being coupled to a converter for converting the movement of the at least one partition into another form of energy, the partition extends into a nozzle so that its upstream edge lies in the intermediate portion that forms a constriction, the partition pivots so that its upstream edge moves between one side and the other of the duct and movement of the at least one partition alternately increases and decreases the flow through the respective channels, the arrangement being such that the at least one - 22 partition is caused to oscillate by fluid flow in the duct.

31. A method for transforming energy in flow in a fluid medium into another form of energy, the method comprising: flowing a fluid medium through a duct which has a constriction, a movable partition mounted in the duct for pivoting movement about an axis transverse to the duct, the free end of the partition pointing upstream and being located in the region of the constriction, whereby the partition divides the fluid flowing through the duct into two channels in the region of the constriction and being caused by the flow of fluid to oscillate to-andfro about the pivot axis alternately increasing and decreasing the flow of the fluid medium through the respective channels, and using the movement of the movable partition to drive another device.

32. A method according to claim 31, wherein the vane is pivoted at or towards its downstream end.

33. A method according to claim 31 or 32, wherein the duct comprises a rectangular cross section.

34. A method according to any of claims 31 to 33, wherein the partition is rectangular in profile.

35. A method according to any of claims 31 to 34, further comprising abutments which limit the pivoting movement of the partition about the pivot axis.

36. A method according to claim 35, wherein the abutments are formed by the walls of the duct.

37. A method according to claim 35 or 36, wherein the abutments are arranged such that when the partition - 23 engages one or other of the abutments it stops the flow in the fluid medium through one or other of the channels.

38. A method according to any of claims 31 to 37, wherein the duct has an exit in the form of a diffuser.

39. A method according to claim 38, wherein the pivot axis of the partition lies in the diffuser.

40. A method according to any of claim 31 to 39, wherein the arrangement of the duct and the partition is symmetrical along a centre line.

41. A method according to any of claims 31 to 40, wherein the to-and-fro oscillation about the pivot axis is due to the varying pressure differential between the channels as the partition moves.

42. An apparatus for converting the kinetic energy from the flow in a fluid medium into another form of energy, comprising a duct which has a constriction, a movable partition mounted in the duct for pivoting movement about an axis transverse to the duct, the free end of the partition pointing upstream and being located in the region of the constriction, whereby the partition divides the duct into two channels in the region of the constriction and is caused by a flow of a fluid medium in the duct to oscillate to-and-fro about the pivot axis alternately increasing and decreasing the flow of the fluid medium through the respective channels.

43. An apparatus according to claim 42, wherein the vane is pivoted at or towards its downstream end.

44. An apparatus according to claim 42 or 43, wherein the duct comprises a rectangular cross-section. - 24

45. An apparatus according to any of claims 42 to 44, wherein the partition is rectangular in profile.

46. An apparatus according any of claims 42 to 45, further comprising abutments which limit the pivoting movement of the partition about the pivot axis.

47. An apparatus according to claim 46, wherein the abutments are formed by the walls of the duct.

48. An apparatus according to claim 46 or 47, wherein the abutments are arranged such that when the partition engages one or other of the abutments it stops the flow of the fluid medium through one or other of the channels.

49. An apparatus according to any of claims 42 to 48, wherein the duct has an exit in the form of a diffuser.

50. An apparatus according to any of claims 42 to 49, wherein the pivot axis of the partition lies in the region of the diffuser.

51. An apparatus according to any of claims 42 to 50, wherein the apparatus is symmetrical along a centre line.

52. A method for transforming energy in a flow of fluid medium into another form of energy substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

53. An apparatus for converting kinetic energy from a flow of fluid medium into kinetic energy in a moving partition substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.