WIND ENERGY TRANSFORMATION
The present invention relates to the efficiencies to be gained in renewable energy power generation. More particularly but not exclusively it relates to the use of a plurality of wind turbines in a wind dam arrangement.
Wind power is a renewable but opportunistic resource - it must be collected when available, or lost.
There are a number of inherent difficulties associated with the use of wind power as an energy source.
While it is generally realised that the wind energy resource varies from day to day, the short (1 minute) and medium (15 minute) fluctuations can be severe as well.
These variations create problems for other generation systems running in parallel which are expected to even out the supply.
Wind energy collection systems are not cheap to build or connect to a local or national electrical power grid. Without storage of the energy collected they will tend to be relegated to, or restricted to, total installed capacities below the system base load.
To invest in such expensive equipment and to then turn it off due to lack of instantaneous demand is an ultimate inefficiency, so this limit is understandable.
The high cost elements are subject to rapid obsolescence/high wear.
The avoidance of such restrictions requires a realistic high density energy storage system of low cost. While the most cost effective system currently appears to be water stored for future hydropower generation; the mating of wind power to water recirculation on a hydro scheme of significant proportions has proved difficult.
Wind turbines and hydrodynamic pumps (centrifugal, mixed flow and axial flow) can have complementary power available/power required characteristics and can be pair-optimised. The practicalities of suction lift restrictions; getting enough turbines adjacent to a tailrace; etc - have tended to make this ideal direct-coupling difficult.
Workers in this field have often resigned themselves to the cost and complexity of wind- driven generators powering electric pumps (or turbines of the water variety which can be reversed as pumps). Costs and compromises are built in.
Wind turbines in general have become part of the high tech arena with a great proportion of their cost in the high stress, high wear rate, rapid obsolescence components. Total life of only 20 years appears as the accepted norm.
OBJECT OF THE INVENTION
It is an object of the invention to provide an alternative to the abovementioned systems, and/or to overcome some of the abovementioned disadvantages.
STATEMENTS OF THE INVENTION
According to a first aspect of the invention there is provided a wind dam comprising or including the elements of:
- a plurality of wind turbines,
- a support macrostructure which a) supports the wind turbines b) provides all of: i) service access space, ii) conformal ducts for conformal ducted air flow for one or more of the wind turbines, iii) wind velocity augmentation in the ducts, iv) space or channels for fluid and electrical conduits below and/or through and/or above the structure.
Preferably the macrostructure provides conformal ducts for all of the wind turbines. Preferably the wind turbines are fixed axis orientation units and air flow is bi-directional
through the conformal ducts.
Preferably the conformal ducting reduces turbine blade tip losses in comparison to unducted turbines.
Preferably the macrostructure allows an increased turbine density relative to conventional wind turbine farms (which have a minimum separation between turbines generally between 2-6 turbine diameters; down to about 1.3 turbine diameters). Preferably there is no wind or air leakage between the turbines.
Preferably the pressure drop characteristics through the plurality of turbines increases or improves the normality of vertical velocity profile of the wind. More preferably the pressure drop characteristics through the plurality of turbines reduces the abnormality effects of local wind gusts.
Preferably the wind turbine driven outputs are coupled in one or both of series and/or parallel couplings thereby allowing the total output of the wind dam to be configured as required.
Preferably the wind turbines are arranged into an array, more preferably the array comprises a plurality of cells.
Preferably each of the wind turbines is constructed or sited within its own support microstructure, the turbine together with its microstructure comprising or part forming a cell in the array.
Preferably the array comprised a plurality of layers in a substantially vertical structure; each of the layers comprising a plurality of cells.
Preferably the microstructure may be rectangular or square or hexagonal in profile.
Preferably the microstructure is hexagonal in profile and the macrostructure comprises a plurality of interlocked hexagonal cells each containing a turbine.
Preferably the macrostructure and/or microstractures includes one or more fluid and/or electrical conduits.
Preferably the macrostructure and/or microstractures includes one or more ducting means to allow ducting of the airflow through the turbines.
Preferably the ducting means includes or allows in-duct silencing.
Preferably some or all of the inlets and/or outlets are fitted with a bird exclusion mesh cover. Preferably the configuration of the inlet and outlets of the plurality of ducting means is so shaped or configured to control inlet velocity. More preferably the inlet and outlets are hexagonal, square or rectangular shaped or intermediate between these extremes.
Preferably the macrostructure and/or microstractures includes augmentation means for wind velocity augmentation in the conformal ducts.
Preferably the augmentation means comprises duct inlet and duct outlet transitions between inlet/outlet shape and that required to conform to turbine shroud requirements.
Preferably each wind turbine has one or more rotors.
Preferablyone or more of the turbines possess one or more rotors of a sailwing configuration.
Preferably the conformal ducts may be rigid. Alternatively the conformal ducts may be constructed of a tensioned substantially flexible membrane or fabric. In this embodiment preferably the tensioned membrane or fabric has a rectangular or hexagonal configuration or profile.
Preferably the wind turbines are fixed venturi ducted turbines.
In one form all of the turbines are vertical axis turbines. Alternatively all of the turbines are horizontal axis turbines. Alternatively the wind dam includes a mixture of vertical axis and horizontal axis turbines.
Preferably the horizontal axis turbines are single or bi or multi directional rotation turbines.
Preferably the horizontal axis wind turbines include sail type rotors. Alternatively the wind turbines may be pitch changing turbines or "Wells" turbines.
Preferably the horizontal axis wind turbines for bi-directional rotation include sail type or
fixed blade rotors.
Preferably the horizontal axis rotors are single or multistage units on a common shaft with multiple blades in each stage.
Preferably the horizontal axis turbines direct drive water pumps or other users. Alternatively a mechanical or hydraulic means of shaft speed adaption is included. Preferably the horizontal axis turbine driven pumps are single or multi stage fixed displacement or hydrodynamic units of the centrifugal, mixed or axial flow type.
Preferably the vertical axis turbines are single directional rotation turbines; more preferably they are of "Darius" or "Savonius" or "split Savonius" style.
Preferably the vertical axis wind turbines have fixed blade or sailwing rotors. More preferably the rotors are twisted axially to at least partially direct air downwards to equalise and/or avoid noise arising from pulsations due to duct exit interactions with the rotor. Preferably the vertical axis wind turbines have two or more blades on the rotors. Preferably the vertical axis wind turbines of the split savonius type have inner blade or sail edge supports of torsional rigidity to substantially eliminate the need for a centre shaft.
Preferably the drive effort for vertical axis turbines is taken from the base of the rotor by direct drive, right angle drive or a system using mechanical or hydraulic means of shaft speed adaptation.
Preferably the vertical axis turbine drive pumps are single and/or multistage fixed displacement and/or hydrodynamic units of the centrifugal, mixed or axial flow type.
Preferably the wind dam is employed in water pumping applications.
Preferably the macrostructure includes an aqueduct, preferably along the top surface of the dam to convey the water to storage and user points.
Preferably the water pumping includes pumping water to an elevated level for storage, and subsequent power generation, crop irrigation, or domestic/town supply.
Preferably each level pumps water to a lateral water main, which feeds the next level.
Preferably check valving and/or shut-off valving are employed to allow individual cell service.
Preferably or alternatively lateral water mains are isolatable for each selected number of cells
(for example every 10 cells) to allow section commissioning, decommissioning and servicing.
Preferably the wind dam is sited to take advantage of topographical/geographical features. Preferably the topographical/geographical features enhance wind flow incident upon the wind dam.
According to a second aspect of the invention there is provided a wind turbine cell for use in the construction of a wind dam, wherein the cell includes: a wind turbine, microstructure for supporting the turbine, a conformal duct for the turbine having inlet and outlet transitions, and wherein the features of the cell are such to allow each conformal duct of the cell with its inlet and outlet transitions to be prefabricated as interlocking modular construction blocks of the wind dam.
Preferably the conformal ducts may be rigid. Alternatively the conformal ducts may be constructed of a tensioned substantially flexible membrane or fabric. In this embodiment preferably the tensioned membrane or fabric has a rectangular or hexagonal configuration or profile.
Preferably the cell also includes means to enable access to the turbine. Preferably the profile of the cell may be rectangular, square or hexagonal.
According to a third aspect of the invention there is provided a method of constructing a wind dam, the dam comprising or including the elements of:
- a plurality of wind turbines arranged in an array and
- a support macrostructure to support and/or order the wind turbines,
the method comprising or including the steps of: a) preparation of a wind turbine cell as described previously; b) stepwise placement of each wind turbine cell in accordance with or as required to complete the array, wherein the placement ensures each cell interlocks with an adjacent cell.
Preferably the method is accomplished via sectional completion and commissioning, preferably with linear advance of construction.
Preferably the method includes one or more or all of the following steps:
- construction of foundations as a first step;
- construction or provision of a supply water canal and/ or feed pipe;
- construction of a construction straddle crane trackway;
- construction of a straddle crane;
- lifting of prefabricated cell structure modules into place with compliant jointing material.
Preferably each cell is prefabricated, either in full or as subassemblies. Preferably the method includes erection of a trackway either side of the dam macrostructure to support a crane. More preferably the trackway crane comprises, in the finished dam, an external service access way and/or wind block.
According to a fourth aspect of the invention there is provided a method of constructing a wind dam comprising or including the elements of:
- a plurality of wind turbines arranged in an array, and
- a support macrostructure to support and/or order the wind turbines, the method comprising or including the steps of: a) preparation of a wind turbine cell as previously described wherein the conformal ducting is constructed of a tensioned substantially flexible; membrane or fabric, b) stepwise placement of each wind turbine cell in accordance with or as required to complete the array,
wherein placement ensures each cell interlocks/engages with an adjacent cell.
Preferably the macrostructure is constructed of or includes lightweight and/or slender structural elements.
Preferably the conformal ducts are hexagonal or rectangular in profile or confirmation.
Preferably the wind dam further includes an aqueduct containing water the weight of the water in the aqueduct improves stabilisation of the wind dam against wind pressure loading.
Preferably the membrane or fabric ducts allow greater porosity of the wind dam without comprising access or conduct space requirements within.
According to a fifth aspect of the invention there is provided a wind dam prepared substantially according to one or both of the method previously disclosed.
According to a sixth aspect of the invention there is provided a wind dam substantially as described herein with reference to any one or more of the accompanying drawings.
According to a seventh aspect of the invention there is provided a sailwing turbine rotor for bidirectional wind flow incorporating:
• a double surface filled aerofoil sail, and
• shear plane in fill and split trailing edge for bidirectional setting of sail boom, and
• rotatable leading edge fill with setting angle at the base geared to the boom setting angle.
Preferably the turbine is adapted for incorporation into a wind dam as claimed in claim 1.
According to a seventh aspect of the invention there is provided a sailwing turbine rotor substantially as herein described with reference to Figure 9.
To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.
DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the drawings in which:
Figure 1: illustrates a cross-sectional view of a wind dam of the invention in which the turbines are horizontal axis. Figure 2: illustrates a face view of the dam of Figure 1. Figure 3 : illustrates a sectional plan view of an alternative wind dam of the invention in which the turbines are horizontal axis. Figure 4: illustrates a face view of the dam of Figure 3. Figure 5 : illustrates a plan view of a wind dam of the invention in which the turbines are vertical axis. Figure 6: illustrates a face view of the dam of Figure 5. Figure 7: illustrates a cross-format as one possible wind dam arrangement. Figure 8: illustrates a graphical representation of wind velocity upstream, at the site of, and downstream from a wind dam of the invention at the optimum (Betz) condition. Figure 9: illustrates the prefeπed sailwing rotor design of the turbines; Figure 10: illustrates the choke test;
Figure 11: illustrates rotor RPM vs Rotor Power (W) at different valve settings; Figures 12 (a to f): illustrate Tip Speed Ratio vs COP;
Figure 13 illustrates Duct Speed Ratio vs COP; Figure 14 illustrates Velocity vs COP; Figure 15 illustrates Velocity Points; Figure 16 illustrates a side perspective view of the rig set up for simulation testing; Figure 17 illustrates a side view of the rig of Figure 16;
Figure 18: illustrates the outputs of the rig set up of Figure 16;
Figure 19: illustrates the hydraulic ancillaries for the test rig of Figure 16;
Figure 20: illustrates the turbine duct for the test rig of Figure 16.
DETAILED DESCRIPTION OF THE INVENTION A. General - The Wind Dam Concept
Our invention of the wind dam has been intended to ease some of the technical issues associated with the use of wind power, increase the density of turbines (reduce the land use), and change the investment strategy in favour of more permanent structures with cheaper wearing parts (turbines and driven equipment) which also allows ongoing optimisation and performance increase of these elements with each refurbishment.
As discussed herein, a "wind dam" includes any straight or curved wall or dam structure, in this case consisting of or penetrated by an array of multiple ducts. Most or potentially all the ducts will contain a wind turbine. An "aπay" is used to describe any pattern of ducts, having at least some semblance of order.
The wind dam stracture of the invention is a departure from current wind turbine thinking. A robust semi permanent (200yr) stracture provides an infrastructure that will have its capital value grown by the generational developments of aerodynamics, hydrodynamics and multidisciplinary optimisation applied to the elements it supports. This is in contrast to modern wind turbines where obsolescence and wear erode the total capital in approximately 20 years.
The wind dams are potentially large structures of 80- 120m high by kilometres long incorporating the following features:
A wall dam or wall which provides an array of wind turbines in a cellular aπangement along with:
1. service access
3. conformal ducted airflow
4. Wind velocity augmentation
5. fluid and electrical conduits throughout its structure
The turbines of the wind dam then cooperatively transform the wind energy to shaft energy which can be used in a range of applications (discussed below).
The dam macrostructure is a substantial stracture designed to withstand gale force winds. The multiplicity of the dam macrostructure functions contributes to an efficient use of space and materials.
Two options exist for the wind dam which are not available to other turbine mounting systems. These are the possibility of in-duct passive silencing and duct entrance screens to eliminate birds. The latter could be important in coastal areas particularly since these are also often locations of a prevailing wind direction energy resource.
B. General Construction Considerations
Visual impact is unavoidable but may be more positive than the equivalent power in discrete wind farm turbines because the dam emulates a natural land form (cliff face or rampart).
Locating a wind dam system next to a large power consuming industrial site could service as a useful visual barrier as well as providing power directly on the site, avoiding transmission losses.
In the case of a horizontal axis turbine dam with hexagonal cellular module stracture on flat terrain a permanent trackway either side of the dam can support a large travelling structure which is initially configured as a crane to lift and place the prefabricated construction (cell) modules, or parts thereof.
When complete this would be used for external service access and to block the wind from
sections of cells for internal service. This approach allows extendable structures and stage- wise commissioning as sections are complete.
The dam does not require wind directly onto the face. Prior art work with single-cell generators of this fixed type indicate 45° either side of perpendicular is effective. Our studies have shown no quantifiable reduction in coefficients of performance at up to 30° off-axis. This factor is combined with the containment provided by the dam structure and additional containment by utilizing existing hills/ranges, then the workability of the fixed turbines can be appreciated. Wind flow up/down a broad valley orientated to prevailing winds is an obvious (simple) application of the concept.
For horizontal axis wind turbines and water pumping applications it is envisaged that the cells will be set up with "sail" type rotors which turn the pump the same way regardless which way air flows through the venturi tube. A tube diameter of 3.75 metres fed by a hexagonal inlet/outlet conical end of 5.4 metres point to point is envisaged. Using this size is intended to allow an expendable sail blade system which doesn't have to be shut down in high winds. Equipment is light enough and accessible for manual maintenance.
Fluid entering a contracting tube can be subject to "vortexing". Very little inlet pre-rotation (from wind gust/eddy effects) is required to start this but it can wind up quite rapidly unlessguided to eliminate it. However our sample duct area ratio tested (of 2.18), with a diffuser length at each end of 2 times the diameter of the throat, vortexing has not been observed (tufts) under any conditions.
One approach is to guide the pre-rotation to suit your application. In this instance a two stage turbine may be required to handle this plus bi-directional flow. This process would be favoured, since the pressure drop over outlet straightening vanes (prevented vortex) would be an unproductive loss.
Wind turbine element and pump optimisation can continue for the life of the structure:- perfection in year one is not a viable target. The stracture and water channels need to be
adequately sized for 100% aero and aqua foil efficiency sized at 95% upper wind velocity (only exceeded 5% of time) to allow generations of future evolution in design and optimisation.
There are many ways the dam structures can be laid out in place to utilize natural features to aid wind intensification. In preferred forms the top of the dam provides an aqueduct to transfer the water to a new or existing water storage dam, lake or tower. External canals or positive head conduits below are required to return it.
In certain cases, a flat wind swept area, even without prevailing directions of wind could still utilize, for instance a cross structure in plan with central water storage tower and power house. Linear developments along a river bank can return water to a previous dam or be equipped with powerhouses at discrete intervals, using only the top aqueduct for storage. Coastal developments using seawater will need lining of any natural storage facility at the upper level to avoid salinity problems.
In terms of cost, the intention of this wind dam invention is to focus the investment on the long term structural life elements and allow cheap and cheerful mechanical" systems to be used at the outset. Over time replacement of these systems can be carried out substantially without need to alter the structural elements.
Turbine selection is discussed below, but the choice of turbines (horizontal or vertical axis, or a combination) is a significant consideration in the design of the wind dam.
The cellular horizontal axis turbine stracture tends to favour mechanised construction with preformed cellular components lifted into place by a travelling gantry crane astride the dam structure riding on rails along each side. This in turn favours areas of higher labour cost. The towers of the vertical axis dam can be built in situ using semi-continuous casting methodology where the preform is raised and poured at (for instance) 1m per day so that the development load is within the limits for the cure out all points of height. Similar results
could be achieved with double skinned block or brick and reinforced concrete infill (in place of advancing formwork). These are labour intensive systems favouring lower labour costs.
C. Conformal Ducting
To maximise the useful work done by the wind passing through the wind dam it is important to ensure that the maximum amount of air actually passes through the turbine. For horizontal axis turbines with axis parallel to airflow, the circular blade sweep is confined in a circular duct with practical minimum clearance between blade tip and duct.
Since in face aspect, an assembly of round ducts (even in the closest hexagonal stacking pattern) never completely intercepts all the incident wind, it is necessary to develop duct transitions from the face configuration (hexagonal, square, rectangular or other) to the round shape of the duct conforming to the turbine blade tip sweep - and back out to the similar geometrical configuration of the other side of the dam. These transitions are best smooth curves but may also incorporate some point-to-point twist for inlet vortex control.
The resulting shapes can involve fairly complex compound curvature which lend themselves to moulding on formers or by use of tensioned membrane "socks" affixed to the geometrically patterned dam face at one end, and the round duct in the centre.
The vertical axis turbines require a totally different type of duct in which to operate. Like any fixed rotating blade mechanism, the extremity prescribes a circular path, but in our design the vertical tower sides are only required to conform with practical clearance to two 90° segments of the rotation.
Because the tower sides are vertical and the curves are only in one direction, this favours many types of rigid simple construction.
D. Turbine Selection
The choice of turbine (horizontal or vertical axis, or a combination of both) is a primary
determining feature in structural considerations of the stracture of the invention.
The arrangement of our wind turbines may be solely of the horizontal axis, axial flow type or solely of the vertical axis, cross flow type, or a combination of both.
These two kinds create a separate array of vertical compared with horizontal axis turbines, or they can be used in combination, generally adjacent to one another.
The individual wind turbines are fixed axis orientation units and air flow is bi-directional through the ducts. The design of the dam is such that it can be orientated across prevailing winds and can be used in conjunction with other topographical features and even shelter belt plantings to augment the inflow.
Previous works have shown that even single ducted wind turbines can produce acceptable performance up to 45° off alignment with the wind. Prevailing wind energy resources are often confined to a limited directional spectrum.
Dl. Horizontal Axis Turbines
A horizontal axis turbines can be a multi directional type (fixed blade) which reverses rotation with reversing wind direction or single direction rotation type (blade incidence changing; sail wing or Wells turbine. A Wells turbine is a proprietary fixed rotation direction device.
D2. Vertical Axis Turbines
A vertical axis cross flow turbine can be of "Darius" or "Savonius" style. It is expected that the "split Savonius" will respond best to the augmentation available from the wind dam structure. These are single rotational direction turbines.
The shaft power generated from the system could be applied in any number of applications including:
- pump water - for irrigation, domestic and town supply, hydropower or hydropower storage
- generate DC or AC electricity
- compress air or other gases
- compress vapour in a heat pump
- circulate a thermal fluid for heating by mechanical energy input
- drive a vacuum pump system.
It will be appreciated by those skilled in the art that other applications are possible, without departing from the scope of the invention.
The prefeπed applications and aπangements relate to:
I) water pumping for irrigation ii) water pumping for hydro-electric generation from stored water a) at existing hydro sites to better use limited water supply on under-utilised generation equipment and infrastructure. b) at existing hydro sites with additional generation capacity (increases in head and/or volume from the wind dam) c) new wind-dam hydro systems
F. Preferred Configuration and Structure
The prefeπed application is, as previously discussed, water pumping for irrigation or hydro generation of power with water storage.
The prefeπed aπangement is a multi-cell aπangement of fixed venturi ducted wind turbines with multi stage water pumping for subsequent hydro power generation or irrigation.
The advantages of the water pumping system are:
- smoothing out short-term and medium term wind variations.
- storage of the elevated water is possible to delay the power generation till required
- in some cases under utilised hydro generation can be uprated.
- reduced number of individual generators (to be controlled and synchronised) to a few large units. Reduces "high Tech" maintenance requirements in the same way.
Actual use patterns with the daily power demand peaks make storage and timely smooth generation more important than the inefficiency introduced by an extra conversion stage (water pump to water powered generator) in the process.
"Augmentation" is a process by which the wind is forced to speed up using converging nozzles out the inlet to the dusting and/or diverging nozzles at the outlets. Various claims for this process have been made; but in the case of the wind dam the area ratio [inlet: turbine throat] is a function of structural necessity and not the subject of power enhancement claims for the horizontal axis machines.
For the vertical axis, wind turbines; sheltering the back coming blade is beneficial and requires an area ratio of 2 in comparison with an open field unit. The finite wall thickness limit gives a minimum area ratio of around 2.1 which is similar to the hexagonal cell, horizontal axis turbine case.
Based upon our own proof of concept results, using a reference free- field velocity of 8m/sec (similar to that used to max-rate the generator on a free field electrical generation turbine) gives the accumulated shaft power at COP = 0.23 (dam face area reference) of 22 Mw per kilometre at 80m high. The overall area ratio will be increased by the height of the top aqueduct, but for conservative figures this can be ignored.
If we have pumps of 66% efficiency this equates to 3.78m3 / sec per kilometre at 100m head (increased for losses in conduits and check valves).
More normal average wind velocities of 6m/sec but COP = 0.27 reduce these to 2.8Mw/km and 1.85m 3 / sec per kilometre at 100m head respectively. Siting wind dams to complement existing hydro schemes may not necessarily coincide with optimum wind sites, but a lot more
sites become usable if better density and utilization allows lower wind speeds to suffice.
Again, detailed construction principles depend upon choice of turbine.
FI. Horizontal Axis
The wind turbines are direct coupled to multistage hydrodynamic water pumps on common shafts. Wind turbine and pump turn at the same speed. Relatively large O.D pump impellers can be accommodated within the 25-30% tip diameter turbine hub.
The wind turbines are preferably of limited diameter so that tip speeds of 25-70 m/sec result in usable shaft RPM for direct pump drive and avoid gear boxes.
The pumps are preferably set up for single direction rotation and the turbines will be 2 or 3 blade sail wing types to provide this rotation regardless of wind direction.
Pumps are preferably low head, high volume aπangements to take the water from the conduit below the cell and deliver it to the one above via a check valve.
Lowest level pumps may require flooding from an elevated canal; check valves at the foot and external priming; or self priming recirculation vessels.
A major aqueduct on top of the wind dam flows the water to the water dam or water reservoir. If the aqueduct is above the hydro water reservoir intermediate water turbines will be required to convert this to electrical energy.
Figures 1 and 2 illustrate one form of wind dam of the invention incorporating solely (or predominantly) horizontal axis wind turbines. Figure 1 illustrates a cross sectional view whilst Figure 2 illustrates a face view. With reference to these Figures the individual turbine cells are shown (such as a typical cell X), along with the features of service access A, wind turbine support B, conformal ducted airflow C (which may be rigid or a tensioned membrane), wind velocity augmentation D, fluid and other service conduits over under and
through the dam E, optional silencing F and optional bird screens G.
Figures 1 and 2 show such a wind dam in a substantially triangular configuration (when viewed on the face), though it will be appreciated that other configurations such as rectangular for example, are possible without departing from the scope of the invention.
Figures 3 and 4 show a wind dam (plan and face views, respectively) with vertical towers supporting horizontal axis turbines in slot ducts between with a rectangular aπay. In Figure 4 particularly a possible aqueduct above and water conduit or canal below the stracture are shown E. The duct throat Y is illustrated as is the inlet area Z.
F2. Vertical Axis
The vertical axis split Savonius type rotors, even when augmented in the manner provided by the wind dam, still work at tip velocities 1.5 times the upstream velocity or less and therefore require some form of gearing.
In one form, a reinforced concrete "millstone" at the base of the vertical axis turbine may ride on pneumatic tyres and wheels on truck rear axles. Drives to pumps would be taken off the differential input via the standard articulated drive shafts. In this manner critical height and pump alignment set ups are eliminated. The use or re-use of mass produced gear equipment keeps this more complex drive train within the reach of basic economies.
An advantage of this aπangement is that the output drives can be angled down (right to vertical if necessary) so that first stage pumps can be below the low reservoir level. The pumps will most likely be in series to develop the full 80- 150m static head.
In this system the additional option is available such that the axle can be adjusted by a screw or ram in its axial direction to alter the gearing ratio. In this manner the pneumatic tyre taking the drive from the millstone alters it position with respect to the millstone axis, changing the driver radius. This would only be adjustable in the range allowed by the limits
of the articulated drive shaft universals and length adjustment.
At least four power take-off wheels may be used for each millstone on a full sized circuit.
Other idler wheels may be required for stability, alignment, and periodic tyre replacement on the driven elements. As above, where the driven outputs are pumps for a water elevation and/or storage system the pumps can be in series or parallel as befits the actual application head (pressure) and flow.
As in the horizontal axis turbine wind dam; the vertical axis system in this prefeπed development incorporates a horizontal aqueduct on top of the dam structure to provide some storage in itself, plus the ability to transfer water to the required site (hydrodam or irrigation reservoir).
The vertical tower elements support the aqueduct; provide internal pipe, service and access conduits; plus location bearing systems for the rotor axis.
The Savonius turbines may incorporate a twinned, vertical-torsion member system at the turbine blade inner points rather than a vertical centre shaft. Intermediate bearing supports will then take the form of rings encompassing the torsional risers riding within a minimum of four pneumatic tyred wheels at each bearing support. Commonality with millstone base support idlers is prefeπed.
It is envisaged that a minor axial twist may be built into the turbine to direct air downward slightly for equalisation, with the added benefit of reducing pulsation noise which could occur with the entire height of outside blade edge passing duct inlet and outlet points simultaneously.
Figures 5 and 6 illustrate one form of wind dam (plan and face views, respectively) in accordance with the invention incorporating solely or predominantly vertical axis wind turbines. Again the features of service access A, wind turbine support B, conformal ducted
airflow C (which may be rigid or a tensioned membrane), wind velocity augmentation D, fluid and other service conduits over and under the dam E. Optional silencing F and optional bird screens G, are not considered to be required or effective with the low tip speed ratio of these turbines.
Figure 7 illustrates one of innumerable variations of wind dam structure in accordance with the invention. This structure is a cross-format with central control water tower and powerhouse.
F3. Sailwing Rotor
The design of the turbines of the invention incorporates the sailwing rotor as discussed below. The rotor is designed for bi-directional flow; possible auto regulation in pitch, ease of construction and maintenance; and natural compliance allowing aerofoil pitch/camber change which allows a high tip-speed ratio turbine to self start.
Ideally materials used to form a sail can be found in any location with the use of natural or synthetic fibre or leathers, man-made foams, and natural fibre or cork type fills. The simplicity of design and materials is intended to allow manufacture and maintenance of sails in any cultural and production environment, not excluding recycled materials.
Essential Elements of the Sailwing Rotors: a) Frame Spar The frame spar must be rigid. We have found the best results have been with tubular steel, kinked forward to even up trailing edge tension. The light solid (eg balsa) leading edge covers the front surface of the spar and its semicircular conformal groove allows it to rotate within the confines of pins at either end. The outer pin through a tip plate holds the leading edge tip static while the inner pin rotates with the boom to align the leading edge with sail pitch and aerofoil camber.
The boom pivots around the inner spar to allow bidirectional wind rotation and may allow different amounts of pitch during rotation as consequence of centrifugal forces applied in more complex form.
In such form the boom pitch and trailing edge tension would be regulated with the force from springs or other such devices to favour a neutral or unpitched position windless, allow boom pitching, aerofoil cambering and trailing edge pitching at start, ease back to lower camber and pitch while running; then lower the trailing edge tension in overspeed.
b) Sail The sail membrane with fill is designed for ease of local manufacture and maintenance. The prefeπed features of construction are:
- made of lightweight, strong, resilient local resources or those that are commonly found, ideally fabrics or leathers, with fill by natural fibre, cork type material or foams and leading edges in lightweight wood or synthetic substitute (since in remote locations where wind dams may be used local communities need to be able to fix them easily). Recycled reconstituted materials for fills and leading edges waπant special consideration.
- the membrane material must allow some tensioning to generate a smooth and aerodynamic sail, especially at the tip end, and must also be able to produce pockets so the tensioning cord can run through them.
- The leading edge material needs to be strong in compression but have some torsional compliance.
- The centre fill must also be a lightweight material with the coπect balance of rigidity and compliance, suitable to stop/inhibit air flowing through the centre of the sail outer membrane, as well as have the properties to generate a smooth outer surface. However the centre must be in two symmetrical sections to allow shear movement so the dual trailing edge can move in accordance with the pitch controlling arm.
- The membrane needs to be fixed or adhered to the leading edge material and fill.
- The sail must be able to auto-rotate to start up using a combination of boom pitch, aerofoil camber compliance and trailing edge pitching.
- the construction must be such that local people if required, can repair or replace the sails without high tech skills, materials or equipment.
d) Tensioning of trailing edge cord and membrane The tensioning must be continual, dependent on material and setup, with turnbuckles or any other adjustable method used and possible accommodation of an autotensioner made for start up/braking that slackens the cord of the trailing edge.
The material used here for tensioning (ie the cord) must be again commonly and locally available, have reasonably high loading, (so that it won't snap when tension is applied), and it must be able to fit into the pockets along the trailing edge. We have used nylon fishing line in experiments which meets these criteria and comes in various weights.
The sailwing rotors may successfully be made from a wide range of materials. Emphasis should be on
- local availability
- constractability in the local environment using existing skills and equipment where possible
- recycled material and environmentally sustainable processes.
Sail membrane and fill materials are expected to be replaced regularly such as on a 2 yearly rotation which encourages and allows generational refinement.
With reference to Figure 9 there is illustrated one blade of a sailwing rotor, generally A which includes - the frame 1 which is tubular or solid, kinked to put the tip pivot point of the boom geometry on the boom pivot centre-line to maintain constant trailing edge tension in the cords 9. The tip plate 2 retains the leading edge piece 4 against centrifugal displacement and anchors the trailing edge tension cord 9 at the extended centreline of the boom pivot. The boom 3 is articulated to allow the sail A to set for constant rotation in bidirectional wind (from either side). The boom 3 pivots about frame 1 by means of radial bearings which can be plain or frictionless. The boom 3 is positioned radially by either thrast bearings, a tension mechanism 13 (eg a cable, wire or spring), compression member(s) 14, or any combination thereof. Tension mechanisms tend to favour neutral setting whereas compression members tend to favour full setting in either direction. The leading edge of the sail 4 is a shaped
rotatable leading edge sail support material which can pivot about frame member 1 in a manner controlled by mechanism 5 but restrained by locator 6. The leading edge 4 material requires compressive strength, minimum weight and torsional elasticity. The aerofoil profile can be blended from low to high speed, base to tip.
The gearing mechanism 5 is illustrated, which is used to pivot the leading edge at base (lower air/blade relative velocity) to a greater angle displacement increment than that of boom 3 which drives the mechanism. With the kinked frame 1 the simplest mechanism uses different radii of boom pin loci about frame centre lines to multiply motion. This creates a more cambered aerofoil suitable for high lift at the relatively low ai^lade relative velocity experienced on the inner sailwing radii. In the simplest mechanism R^R^, where R (Figure 9) is the pin locus radius about the inner part of frame 1, and R2 is that of the same pin about the kinked part of the frame.
At the tip 6, the leading edge 4 is pinned to maintain a symmetrical aerofoil at zero or low incidence angle which can be the best compromise for bidirectional flow and the higher relative air/blade velocity experienced at the tip.
The sail external membrane 7 is prepared of suitable fabric or natural material which encapsulates the leading edge 4 and fill 8. The material may be further treated or impregnated to improve longevity and/or aerodynamic damping. The said membrane 7 is wrapped around frame and fills, but trailing edges are deliberately not joined to allow shear movement for alternative direction setting. Trailing edge pockets are formed, or the equivalent cord 9 retention is created by sewing, gluing or similar means at both the trailing edges. In rotation R, the aft suction of the aerofoil tends to close any static gap between the trailing edges. Resistance to aerodynamic flapping of the membrane is dependent on
- membrane weight/area;
- membrane internal damping;
- fill 8 effects on the above;
- trailing edge cord 9 tensions.
Light weight fill 8 prevents the sailwing rotor A from "pumping" air out through the otherwise hollow trailing section which can potentially "blow-up" and destroy the tip aerofoil section, plus absorb power in a useless fashion, detracting from efficiency. To allow sail bi-directional setting with associated camber change, particularly at the base, the fill 8 is unconnected via a deliberate shear plane on the centre line with half the fill material adhered or otherwise attached to each membrane side.
Tensioning cords, wires or similar 9 are attached or retained in the trailing edge of each membrane 7 half to stretch the membrane 7 in a catenary or similar shape to keep the membrane material as smooth as possible in both static and rotating situations. Separate turnbuckles 10 or other tensioning devices attach cords 9 to the boom 3 directly or by an offset frame extension.
The sailwing rotor benefit is compliance, allowing wind pressure-induced pitch and camber changes conducive to self-starting high tip speed ratio rotors. Further enhancements are possible by articulating the aft portion of the tip plate 2 (see 11) to reduce trailing edge tension under low or zero rotational speeds, then increase this tension by centrifugal force on the articulated portion of the tip plate 2 as speed increases. Real world windmill type operations benefit from ease of starting and maximising acceleration since they work in continually changing wind conditions.
Note that these are not constant speed rotors, they are intended for the maximum rotational speed wind conditions will produce, up to structural limits.
Overspeed may be limited by material selection which allows aerodynamic instability of the membrane at excessive airspeeds (major increase in drag); using a centrifugal device at the base to deliberately part the trailing edge cord anchor points (creates air breaking); allowing boom pivot or flex under high centrifugal loads (see 12) to de-tension cords 9 (de-pitch
plates); any combination of the above; and/or addition of non-novel centrifugal air brake mechanisms from prior art.
In extreme conditions, light membrane and fill systems can be allowed to destruct without significant hazard. In reality, sail dislocation due to major overspeed brings it in contact with the duct, producing severe breaking action - protecting the mechanism for the cost of a 1.2m x 0.5m sail wrap.
G. Aerodynamics and Performance
In one sense, a wind dam may be taken as a single large turbine, regardless of the number of individual turbine elements it contains, or the area ratio of the velocity - augmenting conformal ducts.
An exhaustive literature survey, for horizontal axis turbine, has turned up much theoretical work on augmentation by downstream diffusers. Experimental papers have failed to report any device in which the power augmentation equals, let alone betters, the area ratio between that inlet/outlet and the turbine blade swept area.
Our own experimental work is all referenced to the duct intake area condition, as a portion of dam face area.
The case is a little different for the Savonius turbines, as there is obvious benefit in sheltering the side of the turbine moving into wind. Although experimental work to hand suggests an augmentation for the Savonius in excess of the area ratio, this needs to be viewed in perspective as the baseline unducted, unaugmented performance coefficient is low. The reported ducted/augmented figure is more respectable and similar to the ducted/augmented performance coefficient expected for a sailwing turbine in horizontal axis mode.
The experimental results for horizontal axis machinery tends to favour minimum area ratio and theoretical cases can be made to support this conclusion. In the wind dam however,
there is a practical minimum area ratio for construction, access and fluid conduit considerations which gives a lower limit of approximately 2: 1 for a hexagonal aπay and 3:1 for a square aπay.
A conservative figure of COP = 0.27 based on dam frontal area and an "equivalent turbine- plane" wind velocity of 0.55x upstream free field wind velocity have been used in the big picture calculation even though the embedded turbines see localised higher velocity because of the area ratio.
With reference to Figure 8 the wind velocities at the Betz optimum condition have been shown wherein the wind dam is treated as single large turbine of inlet area equal to its projected face area. Yx indicates the free field upstream wind velocity; the optimum condition is V2 at face where V2 = choked flow fraction x 2/3 V}.
The "choked flow fraction" (0.8 for our testing)
= V2/V1 with all features complete but no blades on the turbine;
= 0.7-0.9 for a wind dam;
= slightly less than 1 for a free field turbine (because of tower effects) is proportional to (1/area ratio)2 where the area ratio = face area/ ∑throat area - nacelle area. This optimum condition is still a relevant reference to less than optimum real life situations where the pressure across the turbine blade plane is less than theoretical and further inefficiency occurs translating air mass flow to turbine rotation.
H. Development Life cycles & Investment Strategies
The construction disclosed here uses "cheap and cheerful" expendable/replaceable parts to actively encourage evolutionary development at minimum costs. This is facilitated by a semi permanent support and utility structure intended to be capable of capital gains.
The long term elements require good design, selection at the required service factors and reliable suppliers. Life cycle rather than lowest first cost is the criteria.
The life cycle basis to use is the structure life even when reviewing the shorter life span elements. How many lives, at what cost.
This whole concept is designed to be applicable to both undeveloped and developed countries so the cell moving elements need to be low cost, robust, simple to set up and maintain. These criteria are important considerations for any environment.
I. Experimental Simulations
The performance of the turbine system has been simulated by testing in a rig set up for mobile or static operation (See Figures 16 and 17). The rig has a 24V DC datalogging system to record ambient airspeed, duct entry airspeed wind direction in relation to rig axis, turbine RPM, turbine torque and five air temperatures.
The airspeeds, turbine speed and turbine torque are signal conditioned to 4-20mA signal loops through 0-100% scale indicator gauges. These visual indicators are used to drive the rig at the coπect airspeed and give a quick indication of parameters to aid decisions on
manual torque settings. (See Figure 18, which indicates a pre-start condition).
The turbine rotor (for the test rig) drives a hydraulic motor converted to pump use to circulate fluid through a manual needle valve for torque control, then an oil cooler to dissipate the energy. The pump circuit is flooded from a pressurized header tank to prevent suction cavitation. (Figure 19).
The geometry of the test rig involves a 5m long duct with compound cuπent transitions from the 1 m diameter turbine duct throat to the 1.55 (point to point) hexagonal inlets/outlets. This gives an area ratio of 2.18 with an 0.3m diameter nacelle, (see Figure 20).
The critical performance parameters are:- (see also Figure 15, illustrating the velocity points):
• COP -co-efficient of performance - the fraction of wind energy extracted.
• TSR -tip speed ratio of the turbine blade which is the ratio of the air (throat) speed (V3) to the rotation of velocity of the tip. V3 = V2 x area ratio (calculated; Vt and V2 are measured).
The area ratio = (area of hexagonal inlet/outlet)/(area of throat - frontal area of nacelle
• Duct speed ratio - the ratio of the upstream free-field velocity to the hexagon entrance velocity (V2/N .
• Choked flow - particular duct speed ratio that occurs with duct and nacelle only - turbine removed. This then defines a theoretical maximum COP for each duct speed ratio if turbine effect enhancements of inlet duct diffusion are ignored. Choked flow duct speed ratio is theoretically and practically constant, iπespective of ambient speed VI (see Figure 10 graph V1 vs V V .
Our cuπent duct choke condition is V V^ = 0.8. At this condition COP is theoretically zero since all the energy is absorbed in duct pressure and diffusion losses. These losses are proportional to the square of the throat air velocity (V3), which obviously favours a minimum area ratio.
• Angle Group - ambient wind direction relative to duct. The results graphed and discussed here are for our proof of concept stage. It is obvious (and intentional) that refinement and development potential exists. The duct area ratio of a full sized horizontal hexagonal aπay wind dam will be lower than the 2.18 we have tested at this point.
Figure 11 shows the power output vs RPM for the turbine - hydraulic pump combination. The different curves show the effects of the hydraulic needle valve settings. There is a small area of cavitation effect at high RPM on the sample ran used, (and as a result we subsequently use higher static pressurization).
Figures 12 a, b, c, d, e, f show the classic COP vs tip speed ratio for the angle groups tested. Figure 12a is angle group 1 through to Figure 12e is angle group 5. These indicate virtually no performance degradation for off-axis inflow under these conditions. With the proper inflow direction at the actual turbine that only an extended inlet transition can provide, the benefits of this approach can be appreciated. These particular tests were mobile rather than static so the degree of off-axis misalignment is limited (up to 25 degrees either side of full alignment). Figure 12f provides all the a to e points combined.
These figures also indicate some transitional points at lower TSR and COP which are startups (automatic, unpowered) caught by the 5 second scan time on the data logger package. This is a majorly beneficial peculiarity of the compliant sailwing geometry. Normally TSR = 5 turbines are difficult to self start.
The peak COP figures for this test were found to occur at 4.5 to 5, which is where we need
them for a (nominal) 3.6 to 3.8m diameter turbine to drive a multistage hydrodynamic pump direct drive on a common shaft (without a gearbox) in a 1.1m diameter nacelle.
Figure 13 illustrates COP vs duct-speed ratio with the theoretically COP limit over-plotted for this duct geometry (0.8 choked flow). Where the actual results come close to or exceed this limit, we have a clear indication that the rotating turbine slip stream and tip vortices are actually enhancing the diffusion of the air in the outlet transition. That particular sailwing blade may exceed 75% efficiency at some conditions but the remainder of the performance enhancement comes from duct reduction of blade tip losses, and tip residual vortices effect on outlet transition diffusion.
Figure 14 shows COP vs ambient wind speed for all the tested angle conditions. The wind speed is the greatest influence variable. With a constant TSR the RPM and actual tip speed vary with the ambient wind speed. At high RPM there are centrifugal and air velocity effects which can distort the aerofoil shape to the point where performance drops off and an RPM limit is established. Sail development allows tailoring of this condition to occur at excessive wind speed, preferably without any permanent distortion.
For the test sail shown the COP at 7.5m/sec is approximately 0.27. The 0.27 used in performance indications at 6m/sec is thus deliberately conservative. This is the 8th sail tested. The pair take approximately one day to handmake on a one-off basis.
J. Advantages of the System
The advantages of the wind dam claimed include the practical advantages of: a) a long life structure of sufficient integrity to handle major storms, b) a stracture potentially higher than the ground - boundary layer is thick, c) a tendency to redistribute the wind velocity profile to favour more uniform velocity of face incidence and increase dynamic pressure at the base. d) conformal ducting to reduce tip losses, especially on the limited (direct drive pump)
horizontal axis turbine diameters. Normally such turbines (approximately 4m dia) would suffer performance losses with the blade aspect ratios envisaged for the sail- wings. e) unlike the super large free field turbines required to extend to these heights (horizontal axis type) where the uppermost blade is in a different velocity environment to the lower one(s); each ducted unit sees a relatively uniform velocity due to cellularising on the horizontal axis dam. Even on the vertical axis structure c) above assists velocity redistribution in the vertical slot ducts. f) a turbine installed density much higher than any free field wind farm system.Normally the tip losses on free field mills are such that a minimum spacing of 1.3 x rotor diameter is required for adjacent (side x side) machines. The ducts containing each turbine eliminate turbine tip interaction in a wind dam. g) ducting the rotors will significantly reduce the "flicker" of light which has been cited as a nuisance in open field wind farms. For the same reason; UV light falling directly on rotor blade/sail will also be reduced. h) A true "investment" when compared with present free field turbines in which the 20- 25 year replacement cycle costs tend to follow an "expense" line (200 year scale). i) Available through simple local construction and ownership to the bulk of the world's potential users who are not catered for by cuπent high tech offerings requiring 100% imported content/service and overseas funds for both. j) Produces a robust system which benefits from ongoing development rather than high tech free field turbine mechanisms with high R& D amortisation costs, the benefit of which is immediately undermined by any new developments. k) Has the capacity of keeping the mechanical development, parts supply and service for most elements within control of the wind dam owners and operators rather than with potentially unreliable offshore contractors (or their subcontractors) who require payment in overseas funds.