NZ334681A - Annular diffuser, for a wind turbine, assembled from arcuate segments by lifting alternate ends and attaching segments - Google Patents

Abstract

A diffuser for a diffuser augmented turbine is assembled by lifting an end of segment, attaching another segment, and then lifting the resulting assembly, and attaching another segment. This procedure is repeated until the diffuser is assembled.

Description

Patents Form # 5 NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION AFTER PROVISIONAL # : 334681 DATED : 17 March 1999 TITLE : SEGMENTED DIFFUSER AUGMENTED TURBINE We, Vortec Energy Limited Address: 63 Albert Street, Auckland, New Zealand Nationality: A New Zealand company do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement. | INTELLECTUAL PROPERTY OFFICE 1.7 MAR 2000 ABSTRACT OF THE DISCLOSURE (Figure 23) A diffuser for a Diffuser Augmented Turbine, is constructed from arcuate space frame segments 115 by lifting one end of the first segment 115K and attaching the second segment 5 (not shown) thereto to form a main segment (larger than the first segment), lifting the other end of the main segment alternately (or at the same time) by jacking means 130, and attaching the third segment (not shown) thereto, and continuing in this way until the circular structure of the annular diffuser structure is completed. Each segment is hollow and covered with metallic cladding and approximates to an aerofoil shape. The centre body 140 of the 10 turbine can be lifted by slings 150 as the segments 115 are lifted into place.

T703UCA1 300/JP/ld FIELD OF THE INVENTION This invention relates to turbines extracting energy from a fluid flow such as wind turbines or sub-sea turbines and has particular application to the design and construction of a Diffuser Augmented Turbine (DAT) for the generation of electrical energy from wind or water.

BACKGROUND DAT's may be constructed in a range of sizes. We have designed a small DAT having a rotor blade of 3 metres diameter for both sub-sea or wind applications. We have also designed a number of larger diameter wind based DAT's for use in conjunction with a national grid. By way of example, a 54 metre diameter wind turbine of DAT design is 10 expected to produce 3 5 MW at rated power output. A DAT with a 66 metre diameter wind turbine should produce 5 MW at rated power output. In these sizes, the size and weight of the diffuser alone is significant, and requires heavy engineering techniques, and large cranes to erect such structures. However, wind farms on land are typically in remote locations, and DAT wind farms at sea are typically located on floating or fixed platforms, in both cases the 15 size and weight of the DAT is a significant detriment to the installation of such structures. Similar considerations apply to large sub-sea installations positioned in sub-sea currents or channels.

PRIOR ART Examples of prior art include: GB 1508752 A (BEN GURION UNIVERSITY) 26 April 1978 EP 016602 A1 (GILCHRIST) 1 October 1980 US 4388785 A (QUEFFELEC ET AL) 21 June 1983 US 4482290 A (FOREMAN ET AL) 13 November 1984 US 4545729 A (STORM) 8 October 1985 25 US 4606697 A (APPEL) 19 August 1986 EP 465997 (MERO-RAUMSTRUKTUR GmbH & Co ) 15 January 1992 T703UCA1 300/JP/ld OBJECT It is an object of this invention to provide an improved diffuser for a turbine, and/or an improved method of constructing such a diffuser, or one, which will at least provide the public with a useful choice.

STATEMENT OF INVENTION In one aspect, the invention provides a method of constructing a diffuser for a DAT, wherein an annular diffuser is assembled from arcuate segments by lifting one end of a first segment and attaching a second segment thereto to form a main segment (larger than the first segment), lifting the other end of the main segment and attaching a third segment thereto, and 10 continuing in this way until the annular diffuser structure is completed.

In some cases individual segments may be pre-assembled to form a series of segments which can be attached to an end of the main segment Although it is possible to lift the first (or main) segment totally (by a crane or the like) so that each end can be attached to the second and third segments at the same time, this is neither 15 necessary nor desirable Preferably the method involves lifting each end of the first segment one at a time, so that they are lifted alternately by jacking means. Suitable jacking means would involve a tank jack, tower crane sections, hydraulic lifters, or the like. It will be appreciated that the first segment will grow progressively larger as the other segments are attached to either end, until the first 20 segment becomes a complete circle.

Preferably each segment is constructed as a segment of a space frame, so that the entire diffuser structure comprises a completed space frame structure.

In another aspect the invention provides a diffuser for a DAT wherein the diffuser is formed from annular segments which have been connected together.

Preferably either the entire diffuser structure, or each diffuser segment, or both, are formed from space frame structures T703UCA1 300/JP/ld Preferably the diffuser is provided with an outer sheath or cladding.

In another aspect the invention provides a DAT wherein the diffuser is as described in the immediately preceding paragraphs.

These and other aspects of this invention, which should be considered in all its novel aspects, 5 will become apparent from the following description, which is given by way of example only with reference to the accompanying drawings.

DRAWINGS Figure 1 is a schematic perspective view of a preferred short diffuser assembly, showing the space frame structure.

Figure 2 is a top plan view of the diffuser of figure 1.

Figure 3 shows an expanded underside perspective view of the diffuser assembly of figure 1, showing one half of the completed annulus.

Figures 4 through 14 show progressive stages in the erection sequence of the diffuser of figure 1.

Figure 4 shows the placement of a first annular series of five segments on the ground at a construction site.

Figure 5 shows the first annular segment attached to a series of second and third segments respectively, with two segments added to each end resulting in a main segment containing nine individual segments.

Figure 6 shows the continued growth of the upper portion of the diffuser.

Figures 7 and 8 show the diffuser assembly reaching midway.

Figure 9 shows the diffuser assembly having passed the midway point, with provision for a possible tie between the now converging bottom edges of the annular segment.

T703UCAI 300/JP/ld Figure 10 shows how one of the bracing legs may be attached to one side of the almost completed diffuser assembly.

Figure 11 shows the diffuser assembly almost complete.

Figure 12 shows that the annular segment has now reached a full circle, with the bracing legs 5 partially erected Figure 13 shows the bracing between the legs pairs (which can be site fitted), with the diffuser assembly raised off the ground and supported on the legs.

Figure 14 shows a typical section through the primary diffuser structure, with only the diagonals in the plane of section shown in this drawing.

Figure 15 shows a typical section through the secondary diffuser structure, with only the diagonals in the plane of section shown.

Figure 16 shows a perspective of view of a primary diffuser segment showing of the steel work making up the space frame structure of this primary diffuser segment.

Figure 17 shows a typical panel used in forming part of the primary diffuser structure of 15 figure 16.

Figure 18 shows a detail from the panel of figure 17.

Figure 19 shows further details from the primary diffuser structure.

Figure 20 shows a view on the arrow C of figure 19.

Figure 21 shows the centre top diffuser segments assembled on site prior to lifting.

Figure 22 shows the segments supported by tower crane sections, prior to the lifting of the entire body.

T703UCA1 300/JP/ld Figure 23 shows the centre body being suspended from the upper segments and the movement of the tower crane sections to the outside of the segments (contrast with figure 22).

Figure 24 is a side elevation showing the lifting of the centre body, and the positioning of the 5 support legs.

Figure 25 is a front elevation of a Diffuser Augmented Turbine on a floating marine platform.

Figure 26 is a side elevation of a diffuser and floating platform of figure 25.

PREFERRED EMBODIMENTS Example 1 shows a diffuser ring having primary and secondary diffuser sections with a slot or slots between them. Example 2 shows a diffuser ring having only a primary diffuser section but with an entry slot at its leading edge and exit slots on its interior face.

Example 1 In the following description, dimensions are mentioned, in order to aid in the understanding 15 of the construction of the preferred diffusers of this invention. They are not intended to be limiting, as this invention can be applied to small or large DAT's. In addition this example relates to the erection of an above ground DAT, i.e. a wind turbine.

Figures 1-13 illustrate the erection of a 44-metre diameter short diffuser assembly 10 on a concrete base or ring 13. The diffuser is supported by legs 17 attached to the base 13 In 20 figure 1 the primary diffuser ring 11 is of the smaller diameter than the secondary diffuser ring, so that the primary diffuser ring is visible towards the right-hand side of figure 1, i.e. wind enters the DAT from the right, and flows from right to left through the diffuser of figure 1, as shown by arrow 14.

Figures 1-13, illustrates the general nature of the space frame structure for both the primary 25 and secondary diffuser rings, which when connected together in the final structure provide an internal structure of venturi-like shape. Each segment 15 is made up of a space frame T703UCA1 300/JP/ld structure substantially as shown in figures 14 - 16, although the primary and secondary diffuser structures will be connected together on site before being used as an annular segment in the assembly of the entire diffuser.

Looking at figure 4, the first annular segment 15 is shown end on, i.e. the drawing presents 5 the leading edge of the primary diffuser section, with the secondary diffuser section being shown without framework extending to a larger diameter than the diameter of the primary diffuser section. The first segment 15 is made up of 3 sub-segments, with sub-segment 15A being the central sub-segment. Counting to the right and left alphabetically from centre 15A shows the outer sub-segment of figure 5 to be sub-segment 15D, and sub-segment 151 by the 10 time of figure 7, and sub-segment 15S by the time of figure 11.

This first annular segment can be placed on the ground, and then a tank jack or the like can lift one end, and a second annular segment attached to the first annular segment. As it grows the first annular segment will be referred to as the main segment. The other end can be lifted by a tank jack or the like and a third annular segment attached to the main segment. Figures 15 4 to 13 show the sequence The main segment will grow in length alternatively first at one end and then at the other end. As the main segment grows beyond the mid-chord position shown in figure 8, the ends of the main segment converge towards one another. It is possible to add a tie rod or a cable 20 (figure 9) between the converging ends of the main segment in order to pull them together.

As the diffuser ring nears completion as shown m figure 10, a portion of the ground 19A can be removed to enable the insertion of a first leg for attachment to the required portion of the main segment. The original ground level is shown as 19B to the left of figure 10. A channel can also be dug in the ground on the other side, to enable the second leg to be attached to the main segment as shown in figure 11. When both legs 17 have been attached to the main 25 segment as shown in figure 12, the main segment can be raised off the ground by the jacking means, and the two legs can be pulled towards one another, to enable the erection of the diffuser ring to the position shown in figure 13. As these drawings illustrated front views they do not show the erection of the other legs (see figure 1 for example) Figure 12 also shows the insertion of the final sub-segment 15Y T703UCA1 300/JP/ld Turning now to the primary and secondary diffuser sections (i.e. a section cut through the ring of figure 1) shown in figures 14 and 15, they show the aerofoil shape of these two sections. In this example they will be connected together to allow an air-flow slot between the primary and secondary diffuser sections, as described in our co-pending PCT application 5 number PCT/NZ00/00020 (or its equivalent New Zealand patent application number 334382), the contents of which are incorporated herein by way of reference. (Note that Example 2 has only a modified primary section, i.e. no secondary section as the primary section has an air inlet slot at its leading edge).

Each of the primary and secondary diffuser sections can be made up of a number of 10 substantially rectangular frames 30 (see Figure 17) which have curved outer ends making up the shape shown in figure 16 (which applies to the primary diffuser segment). The secondary diffuser segment, will have a similar structure to that of the primary diffuser segment, although it will be spaced radially outwardly from the primary diffuser segment so that the completed assembly approximates to that shown in figure 1, i.e. the secondary diffuser 15 segments create an annulus of greater diameter than the primary diffuser annulus, allowing for an air inlet slot between the primary and secondary diffuser sections.

Figure 16 shows the diagonal bracing 31 between the various rectangular frames, and the diagonal bracing within each frame, so that the entire assembly is a space frame structure, which in the completed diffuser can be covered by appropriate cladding (not shown).

Figures 17-20 shows the main plates of the space frame structure in more detail. Each plate as shown in figure 17 is substantially rectangular, for the most part, although its precise shape would depend on where it fits within the diffuser structure as shown in figure 16. In this example they are 2-3 metres wide. For example the plate shown in figure 17 has two approximately equal straight side bars 34, a pair of diagonal bars 35, and curved end bars 36. 25 The dimensions of the side bars, and the radius of the end bars is shown in figure 17 The plates are bolted together preferably by bolting them together to form the flat section shown in figure 17 A similar second flat section is placed above the first flat section and can be connected together by the struts shown in black in figure 16, and the rest of the components are fitted together by additional diagonal bracing. The shaped nose and tail of the primary 30 diffuser section is formed by specially shaped, non-rectangular plates, for example triangular T703UCA I 300/IP/ld or trapezoidal plates. The corner connections are shown in detail in figure 18, and the connection between the respective bracing components is shown figures 19 and 20.

In more detail, the construction is described as follows.

Fabrications Stage 2.3m wide frames (30A, 30B, 30C, etc) Primary diffuser internal radius 50 is 15 metres from the interior of the primary diffuser to the centre line Secondary diffuser internal radius 51 is 20.5 metres measured from the tail of the secondary diffuser to the centre line as shown in figure 15.

Utilising light sections steel components: - RHS sections to provide frame vertical members 10 of 4 sided rectangular frame comprise the subframe to carry the cladding.

This subframe can be constructed from right-angle steel sections rolled to the required radius dictated by diffuser design share or can also be fabricated from standard roofing purling for use in generally (unrolled) straight sections.

The means of connecting the rectangular frame together at the point of vertical RHS section 15 and top and bottom cladding subframe as follows: At or near the four corners of the rectangular frame are plates welded in place to accept pipe flange connections. The plates are pre-drilled to accommodate connection of diagonal braces (angle irons) as well as thru-bolted comprising the pipe flange connections.

The pipe connection and diagonal plates are welded to the RHS vertical as shown in figure 20 18. The same drawing shows cladding 20 attached top and bottom.

The rectangular frame sections are packed into containers ex fabricating factory for onward shipment.

Pre-Assemblv Stage Refer figure 14.

T703UCAI 300/JP/ld Rectangular frames are bolted to one another side by side to comprise a flat one dimensional primary and secondary diffusers figure 15. The Pre-assembly can be conducted on site in specially designed portable sheds.

Site Installation The aforementioned flat primary and secondary diffuser sections are delivered to wind turbine site.

The next process is connecting (flat) frames together to form a 1/36 or 1/48 section in three dimensions.

The flat section connections are achieved by pipe lengths - flanged and cut (refer to figure 10 16).

Figure 16 shows a fully assembled 1/36 or 1/48 section of primary diffuser example.

Cladding 20 can be fixed after this operation. In the drawing are also shown transverse diagonal braces which run diagonally in the same plane as the pipe connections.

Each full assembled 1/48 or 1/36 section of primary diffuser is then connected to a 1/48 or 15 1/36 section of pre-assembled secondary diffuser (assembled in the same manner as a primary diffuser) to form one of the segments.

The primary/secondary segment is then shifted into position for connection to similar 1/48 or 1/36 segment and positioned for jacking as shown in figures 4-13 in sequence.

Support legs are pre-assembled on site and are pinned to their connection points on the 20 primary diffuser prior to lifting. The cross bracing between the legs can be fitted when the support legs are in final position or the cross bracing can be fitted prior to final lift position.

The lifting sequence is undertaken upon the reinforced concrete circular foundation/yaw ring.

Example 2 In this example illustrated in figures 21-24, the space frame structure is used to assemble a 25 diffuser having an entry slot, and multiple exit slots Thus there is only a "primary diffuser T703UCA1 300/JP/ld section" in contrast to the earlier drawings, and the segments are used to lift the centre body, i.e. the nacelle which supports the turbine blades.

Figures 21-24 show a lifting sequence using tower crane sections as supports. Diffuser segments 115 can be assembled together, covered with cladding such as long run roofing (see 5 below), and lifted into position starting at the centre top of the diffuser shape. The central location of the centre top diffuser segment 115A can be located relative to a support beam 120 positioned on the ground 121.

As in the previous example, additional segments, either singly or in multiples can be assembled together on-site, and then attached to the ends of the segments already lifted into 10 place, and in this case supported by tower crane sections 130-131 shown in figure 22 as being attached to the insides of the left diffuser segment 1151 and the right segment 1151, and shown in figure 23 as being attached to the outside of the left diffuser segment 115K and the right segment 115K, (the diffuser segments being labelled from the central segment 115A, counting either right or left alphabetically). The intervening sections have not been labelled, 15 simply the central section and the two end points of figure 22. As with the previous example, it will be convenient to lift one end at a time to attach segments, and then go back and lift the other end and attach additional segments However if the team is large enough, and the tower crane sections 130, 131 are used correctly, it will be possible to raise the entire structure further off the ground by raising the tower crane sections, to allow space for the 20 attachment of the additional segments.

Conveniently, when the diffuser has been erected, to the half way position, or just beyond the half way position, shown in figures 22 and figures 23, the diffuser structure can be used to suspend and thereby lift the centre body 140. The centre body includes the nacelle which support the turbine blades, and the electrical generator to be driven by the turbine. The 25 centre body 140 can be positioned in the centre of the ring 120, and suspended by appropriate cables 150 from the diffuser segments directly above. In this case, the slings are attached to the structure below segments 115B, 115C to the right and left of the central segment 115A. As the tower crane sections 130, 131 continue to rise, the sling 150 will tighten and will commence to lift the centre body 140 off the ground, as shown in figure 23.

T703UCAI 300/JP/ld Also in figure 23, the tower crane sections have been repositioned from the inside position of figure 22 to the outside position of figure 23 once the diffuser structure passes the half way point.

Figure 24 is a cross-sectional view, from the side showing the almost complete assembly of 5 the diffuser wing 160 made up of the multiple segments 115, and shows a cross-sectional view through a portion of the diffuser wing 160 aerofoil shape of the wing when viewed in section, in this case having an entry slot 161 and multiple exit slots 162 on the inside surface of the diffuser wing.

The centre body 140 is now suspended in the centre of the diffuser wing by the support 10 cables 150.

The position of the support legs 170 are shown towards the bottom of figure 24, and these can be swung into position and pinned together, preferably in groups of three, whilst the diffuser wing 160 is supported on the tower crane sections. Similarly the centre body supports 180 can be swung into position and attached to the centre body to support it in 15 place. The support links are attached to the concrete base ring 120, so that the resulting structure will correspond closely to the overview shown in figures 1-3, the only difference being that in this case there is only a modified primary diffuser wing 160 in contrast to the primary and secondary diffuser wings 10 and 12 shown in those earlier views.

Example 3 A Diffuser Augmented Turbine 200 can be positioned and supported on a floating platform 201 using the technique set out in Examples 1 and 2, the floating platform can be moored close to shore, and the diffuser ring erected on the platform 201. Indeed this could be carried out in deep water some distance from shore, although it is more convenient to be close to a shore based installation, so that the diffuser segments can be assembled, and conveyed a 25 short distance to the floating platform.

The floating platform is preferably an open bottom flotation cell, and line 210 shows the external water level, and line 211 shows the internal water level as the air within the cell is compressed Attached to the underside of the flotation cell 201 are support legs 203, T703UCA1 300/JP/ld supportmg a keel ballast 204. The length of the legs, and the mass of the ballast will be varied to suit the expected wind loads on the turbine. The diffuser ring 220 is supported by legs 221 on a yaw control ring 225, so that when the floating platform 201 is anchored to the sea bed in a fixed orientation, the diffuser ring 220 can be turned to face the wind by suitable 5 control means associated with the yaw control ring 225.

Figure 26 shows a side view of figure 25 As shown there are four legs 203 supporting a cylindrical ballast 204, but the number of legs could be varied, as could be the size or shape of the ballast. The anchoring means, and the tethering arrangement between the floating platform, ballast, and the sea bed is not shown. Indeed in some versions, it maybe desirable to have the platform provided with its own motive means such as powered propellers, so that it can either move under its own power, or can have its position changed, so that the untethered platform can be rotated to face the wind, and it propellers can be used to maintain it in the desired position. In which case the yaw control ring 225, need not be rotatable with respect to the floating platform, the entire platform can itself then be manoeuvred or rotated into position, and/or the diffuser legs could be attached directly to the top of the platform.

CLADDING Any suitable cladding can be used, however we prefer to use long run steel roofing material, as this is of low cost, it is substantially weatherproof, and is usually provided with corrugations or ribs so to provide additional strength to the material.

In its most preferred form, the invention makes use of long run steel roofing material that is turned inside out so that the bulk of the corrugations face towards the space frame, and the exterior of the cladding is left substantially smooth. This cladding can be attached to the space frame by appropriate fasteners or by welding, brazing or the like. Fabric cladding can also be fixed to the frame with the addition of a proprietary fabric fixing system.

ADVANTAGES OF THE PREFERRED EMBODIMENT The design of the DAT, and the method for erecting such a DAT as shown in the preferred embodiment, has a number of advantages including: T703UCAI 300/JP/ld A specifically designed space frame which offers advantages in weight reduction for any given size No large cranes are necessary for the assembly of the DAT according to these examples (the crane alternative for a large installation of this type will be in excess NZ$1 million dollars).

By using the lifting means in accordance with examples 1 or 2, the invention allows for a much wider site selection than is possible with any other DAT construction. For example, hill tops can be utilised where higher mean wind speeds occur than on flat land. As a general rule, the increase in wind speed in an elevated site could mean an extra 25% of available energy than a site on a flat plain.

A specifically designed space frame which is capable of providing a variety of different diffuser shapes.

A specifically designed space frame that provides a structural integrity to design and construct a diffuser to be scaled up or down to any size.

A specifically designed space frame that is fabricated in a completely knocked down (CKD) 15 form to provide transportability in standardised transport containers internationally.

A specifically designed space frame that provides a means for site installation that allows erection of large diffusions without requiring heavy cranes.

This type of construction allows the machine to be de-mounted with the system operating in the reverse sequence from that shown in the examples. Also without the need for using heavy cranes.

The system also allows for multiples of this type of space frame construction machine to be erected simultaneously on a site, as there is no need for a heavy crane to concentrate on erecting the diffuser ring, as low cost lifting means such as tank jacks, or tower crane support sections can be used as shown in the examples 1 and 2.

A specifically designed space frame that is suited to an erection technique that allows for a plurality of installations to be undertaken simultaneously.

* T703UCA1 300/JP/ld A specifically designed space frame that is skimmed or cladded with either a fabric type material or rigid cladding VARIATIONS Note especially that the dimensions which are shown in the drawings for the purpose of 5 illustration only, will be varied depending upon the size or shape of the resulting space frame construction. The dimensions are in no way limiting to the definition or operation of this invention.

In its most preferred form, the invention makes use of jacking means such as tank jacks, hydraulic lifters, or tower crane sections to lift each end of the main segment (i.e. made up of 10 a number of segments attached together) Thus when one end of the main segment is being raised by jacking means the other end will be supported on the ground, as this aids in providing stability for the structure during the lifting process. However in the case of a smaller diffuser, it would be possible to lift both ends of the main segment simultaneously by appropriate jacking means and then position the additional segment or segments at each end 15 of the main segment and attach them to the main segment. This would mean that the additional segments would have to be light enough to be manhandled into place. However in most cases the segments will be large enough and the structure heavy enough that the preferred form of the invention will be carried out, namely alternately jacking the respective ends of the main segment whilst leaving the other ends supported on the ground.

The invention could also be applied to any preformed segments, which need not make use of the space frame construction, as the segments could be factory assembled, ready for attaching together on site to make use of the construction technique shown with particular reference to the figures 4-13 However the space frame construction is particularly preferred for larger structures Tliey are often required to be installed in remote locations, on hill tops, or on 25 floating off-shore islands, where it is difficult to make use of cranes. Hence the spaceframe construction, and the erection technique shown with reference to figures 4-13 is particularly suited to large diameter DAT's, to be erected in remote locations.

T703UCA1 300/JP/ld Although the examples have been described with reference to the erection of a space frame construction on the land for use as a wind turbine, it is possible that a similar technique could be used in a sub-sea application, where the turbine is to be inserted into a sub-sea current.

Although long run roofing has been mentioned as the preferred cladding, any other suitable material can be used.

Finally, various other alterations or modifications may be made to the foregoing without departing from the scope of this invention.

T703UCA1 300/JP/ld

Claims (10)

WHAT WE CLAIM IS:

1 A method of constructing a diffuser for a Diffuser Augmented Turbine, wherein an annular diffuser is assembled from arcuate segments by lifting one the end of a first segment and attaching a second segment thereto to form a main segment (larger than the first segment), lifting the other end of the main segment and attaching a third segment thereto, and continuing in this way until the annular diffuser structure is completed.

2. A method as claimed in claim 1 wherein sub-segments are pre-assembled to form a composite segment which can be attached to an end of the main segment.

3. A method as claimed in claim 1 wherein the method involves lifting each end of the first (or main) segment one at a time, so that they are lifted alternately by jacking means

4. A method as claimed in claim 3, wherein the jacking means is chosen from the group consisting of tank jacks, tower crane sections or hydraulic lifters.

5. A method as claimed in claim 1 wherein each segment is constructed as a segment of a space frame, so that the entire diffuser structure comprises a completed space frame structure.

6. A diffuser for a Diffuser Augmented Turbine where the diffuser is formed from annular segments which have been connected together.

7. A diffuser as claimed in the preceding claim wherein either the entire diffuser structure, or each diffuser segment, or both, are formed from space frame structures

8. A diffuser as claimed in the preceding claim wherein the diffuser is provided with an outer sheath or cladding

9. A Diffuser Augment Turbine constructed in accordance with the method of any one of claims 1-8. T703UCA1 300/JP/ld I - 19-

10. A method of constructing a diffuser for a Diffuser Augmented Turbine substantially as herein described with reference to any one of the accompanying drawings. 11 A diffuser for a Diffuser Augmented Turbine substantially as herein described with reference to any one of the accompanying drawings. 5 12. A Diffuser Augmented Turbine substantially as herein described with reference to any one of the accompanying drawings. Attorneys for 10 VORTEC ENERGY LIMITED T703UCA1 300/JP/ld 'NTE1.LEG IUML PHUPfcRTY OFF/CE OF NZ 1 7 MAR 2000 -J EC El \/Fn