GB2548330A - Vertical axis wind turbine - Google Patents

Abstract

A lift type vertical axis wind turbine comprises a plurality of wing structures or blades. The multi-portion wing structures comprise a main wing device 1, a leading edge slat device 2 and a trailing edge slat device 3. The main wing device has a convex lift surface 20 facing the axis of rotation, and a trailing edge 4 near the trailing edge slat device. There is a funnel channel 12 between the leading edge slat device and the main wing device. The leading edge slat device further comprises a convex leading surface 10, a lift surface 18, and a concave trailing surface 11. The leading surface and lift surface continue into an elongated portion 19. A plurality of cross channels [13, fig. 5] pass through the leading surface and trailing surface of the leading edge slat device, and a plurality of micro-vortex channels [14, fig. 5] confluent with the cross channels extend from the leading edge over the lift surface. The cross channels and micro-vortex channels may be tapered to reduce drag. The main wing device and the two slat devices of each wing structure may be rigidly held together by end fixing plates [5, fig. 3].

Description

Vertical Axis Wind Turbine.

This invention relates to a lift type vertical axis wind turbine that is able to self start

Harnessing the winds energy to generate electricity with wind turbines is a significant contributor to the global attempt to generate green energy and move away form fossil fuels. At present the majority of energy captured is with 3 blade horizontal axis wind turbines, these can be of considerable size with rotor diameter in the region of 130m across. The rotors are connected to a nacelle via with a yaw system which is then connected to a tower which supports the whole structure, generally at a significant height to raise the rotor out of turbulent air flow found close to the ground. The yaw system enables the rotor to be turned into the wind. There is further complexity in that the rotor blades on large devices need to have their pitch adjusted to match the in coming wind speed to reduce the risk of damage.

Wind however, can change in direction and in speed significantly and rapidly which is difficult to respond to quickly enough in terms of adjusting the turbine rotor direction or the blade pitch to limit extremes of strain and torsional forces. Due to this limitation it is necessary to engineer considerable strength into a horizontal axis wind turbine to enable it to with strand these unpredictable and unavoidable forces, which adds to production cost. Furthermore a horizontal axis wind turbine has many moving parts such as the yaw system and the variable blade pitch system which add to the opportunities for structural failure and the need for maintenance. Because these components are so critical to the operational and structural survival of the wind turbine, triple redundancy is generally built into the systems further adding to the production and maintenance costs.

Horizontal axis wind turbines generate noise, with large devices generating an unpleasant droning sound while smaller devices generate a high pitch whizzing sound. This has lead to the large devices being deployed generally away for built up areas and even off-shore where this adds to the implementation costs further. Small devices due to the noise are generally not welcomed in urban areas.

Vertical axis wind turbines accept the wind from any direction and hence do not need to track the wind and therefore do not require a yaw system. The blades also do not need to alter pitch and hence can be a fixed structure. The advantage of the vertical axis wind turbine over the horizontal axis counterpart is that they are less complex to make and can operate in turbulent and gusty wind. This means that they can be deployed in locations where turbulent wind is likely to be present and do not require tall towers to get them out of turbulent wind that is typically found closer to the ground. The vertical axis turbine can therefore be deployed in more confined spaces and in urban environments. A further significant advantage is that Vertical axis wind turbines are virtually silent in operation and hence acceptable in urban areas.

They can be of drag type which typically present a concave surface to the wind. The drag type design however is not regarded as particularly effective at extracting energy from the wind as they essentially cannot rotate faster than the wind.

This invention however relates to the lift type vertical axis wind turbine which is able to rotate faster than the wind speed due the lift generated by the aerodynamic wing shaped profile.

The lift type vertical axis wind turbine is able to extract useful energy at lower wind speeds than the similarly sized horizontal turbine and thus have wider range of wind speed operation.

However lift type vertical axis wind turbines suffer from the problem of difficulty with self starting since they rely on rotation for the lift force to be generated which is the force that causes the rotation. The vertical axis wind turbine can therefore have difficult self starting even when moderate wind gusts are present. Contained within the existing art designed to over come this start up problem are multiple examples that can be categorised into two types. Firstly those that include a fixed drag surface within the design so that they are both lift and drag at the same time, the drag components of this style of existing art act to counter the lift vector and are thus limited by design. The second type attempt to overcome this limitation with moving parts such as mechanisms to adjust the angle of attack of the blade or wing as the turbine rotates and other designs have deployed swinging flaps to catch the wind when moving with the wind direction but lift up when travelling into the wind. While others have opted for motorisation to set the turbine spinning when the wind speed reaches a suitable speed. This second type with moving parts all introduce complexity and are considerably less robust for any given level of engineering strength.

All these examples can be seen to compromise on the inherent advantages of the lift type vertical axis wind turbine.

This invention addresses these limitations as the start up drag surface by design develops negligible drag once rotating and does not require moving parts to accomplish this, and the whole wing structure is optimised further by generating micro-vortices to reduce drag. It take inspiration from a leading edge slat device that would typically be seen on a short take off and landing aircraft. The existing art for leading edge slat devices is that of a wing profile.

This device is however geometrically more complex than the existing art with a number of specific design characteristics that take into account the varying aerodynamics of the wing structure as it rotates, which thus requires consideration of the aerodynamic properties as it presents into the wind, moves across the wind and than away for the wind.

Further specific design consideration has been given to the aerodynamic properties that prevail at different speeds of rotation including at start up when there is no rotation taking place and at low rotation speeds when the air flow reverses across the wing structure during the rotation cycle. At high rotation speeds the air flows In just one direction. The leading edge slat developed for aircraft do not have to take into account such considerations. Special attention has also been given to the intentional development of micro vortex generation both within and across the structure which reduces drag and optimises performance.

Firstly there are some general feature to describe.

The turbine unit is constructed utilising a plurality of wings structures. A development prototype has been constructed and tested with 3 such wings however this number is illustrative and not specified in this invention. Connection of the turbine unit to a power generation unit is an obvious component of a wind turbine and this element will not be described in any detail as there is much existing art in relation to this.

Figure 1 shows the overall wing structure, which is comprised of a main wing device 1 with a lift surface 20, a leading edge slat device 2, and a trailing edge slat device 3. There is a secondary trailing edge device 4, at the trailing edge of the main wing device which is known as a passive Gurney flap.

The main wing device 1, is presented with an asymmetric wing design as this demonstrates beneficial start up capability however other wing profiles can be used.

The leading edge slat device 2, comprises a convex leading surface 10, which is continuous with a lift surface 18, this lift surface is continuous with an elongated portion 19 which terminates at 15. Also provided is a concave trailing surface 11 which is continuous with the elongated portion 19 which also terminates at 15.

The trailing edge slat device 3 is presented with an asymmetric design as this demonstrates beneficial start up capacity along with beneficial aerodynamic lift during the initial rotation after start up, however other wing profiles may be used. The angel of attack of this device may be off set against the chord of the main wing. This angle requires optimisation dependent upon the chosen main wing profile.

Figure 2 shows an end fixing plate 5 along with the relative positions of the main wing device 1, the leading edge slat device 2, and the trailing edge slat device 3. On the development prototype a fixing plate has been provided for at both ends of each wing structure. The shape and size of this fixing plate Is shown for Illustrative purposes only and are a convenient method of fixing the three component parts of the wing structure together. Other methods of fixing the structure together are entirely possible but not specified herein. That said it should be noted that by having a fixing plate as Illustrated this provides an additional function of limiting an undesirable aerodynamic effect which occurs at the wing tip referred to a parasitic drag.

Figure 3 shows the relative position of a three winged turbine around a central axis from a plan view. The wind direction has been Indicted by arrow 6 for illustrative purposes with the resultant lift vector demonstrated at 7. For clarity of function the lift surface 20 is the inner surface of the wing and the lift vector trajectory can be seen ahead of or In front of the central axis. It is for this reason that the lift type vertical axis wind turbine rotates. The optimum angle of attack of the overall wing structure is a balance of the trajectory of the lift vector against the drag vector. It is necessary to optimise the wing angle of attach dependent upon the precise geometry of wing design chosen.

Figure 3 additionally shows bearings 8 which are provided for along the central axis, with fixing arms 9 between the bearings and the wings. These supporting arms 9 are shown for simple illustration as a multitude of connection methods would be suitable.

Figure 4 shows an elevation of the overall wing from the external facing aspect, with the main wing device 1, the leading edge slat device 2, the trailing edge slat device 3 and the end fixing plates 5. This elevation is the surface presented to the wind as identified by the arrow 6 on figure 3.

For the sake of clarity it should be stated that the structures described above may be constituted from a wide range of construction materials, including but not limited too, metals, plastics, composite materials such as glass reinforce plastic or carbon fibre and other carbon derived construction materials, including wood and multilayered wooden materials. Foam core and other light weight core materials may be bonded to outer skin materials made from a wide range of metals plastics and any combination of the above. The specification provided for herein specifies construction from anything ranging between a singular building material to a plurality of material and is not limited to those describes above and is meant to include any acceptable construction material that has the suitable physical properties of strength and resilience required for a structure as described above to operate as a wind turbine in potentially harsh turbulent wind environments.

Connection of the turbine unit to a power generation unit may be via a wide range of methodologies including but not limited too, direct linkage, gearing mechanisms, chain drives, continuously variable transmissions and other similar devices. It is possible to have the turbine unit at some distance from the power generation unit with the turbine at a height for example on a tower or roof structure and the power generation unit at a low level or ground level.

There will now be a detailed description of the leading edge slat device.

Returning to figure!, the basic profile of the leading edge slat device 2 is demonstrated and can be described as having a convex aerodynamic leading surface 10 that extends along the lift surface 18 and the asymmetric elongation 19, terminating at the trailing edge 15. There is also provided a concave trailing surface 11 which is continuous with the asymmetric elongated portion 19 and terminates at 15. Due to the position of the leading edge slat device ahead of the main wing device 1, a channel 12 is provided between the two structures, this channel is funnel shaped, narrowing towards point 15. This channel 12 will be referred to as the funnel channel to distinguish from other channels described in subsequent sections. These are cross channels 13 on figure 5 and micro-vortex channels 14 on figure 5 and 6.

If in figure 3 the turbine is taken to be at start up i.e. not rotating, it can be seen that the leading edge slat device 2 presents the concave trailing surface 11 into the direction of the wind. At start up it can therefore be said to present a wind capture surface to the wind, the force of which is thus captured and funnelled through the funnel channel 12 and this is sufficient to enable start up.

The geometry of the funnel channel 12 is such that it narrows towards the exit point 15 on figure 1 and thus the air flow accelerates as it passes through the channel which results in a reduction in air pressure. This accelerated air exits the funnel channel at 15 at a lower pressure which acts to pull additional air flow over the leading edge 10 of the leading edge slat device 2. This increases air flow across the entirety of the lift surfaces thus increases the lift generated.

As the speed of the turbine rotation increases the overall aerodynamic effect becomes that of the wing structure as whole so that is acts as a single unit which now limits the drag present at the concave surface as compared to the drag present at start up. Once the turbine is rotating at speed this drag factor is very much reduced and becomes negligible. As the rotation speed increases the beneficial air flow into the funnel channel 12 would be limited with air now tending to flow across the undersurface of the wing rather than through the channel. Thus to maintain the air flow through the funnel channel at 12, the leading edge slat device has a plurality of cross channels 13, which pass from the front edge at 10 to the concave trailing surface 11. These cross channels 13 are shown on figure 1 between the two dotted lines. There is provided for a plurality of these cross channels along the leading edge.

Figure 5 demonstrated a detailed view of a portion of the leading edge device in elevation view as seen from the front edge 10. It shows the arrangement of the cross channels 13 along the leading edge. In this figure the utmost front portion of the convex surface has been marked by a dotted line. These cross channels ensure that the air flow is maintained as the turbine rotates with a significant air flow passing through the cross channels at 13 and maintaining the accelerating flow effect through the funnel channel 12 and out over the lift surface at 15.

An additional and significant component of the design is that of the micro-vortex channelling 14 and the cross channeling 13 which have both been specifically designed to act as micro-vortex generators to reduce drag. These will be describe in detail below.

Continuing with figure 5, the cross channels at 13 are confluent with the micro-vortex channels shown at 14. The micro-vortex channels 14 are cut in a spiralling geometry, this has been marked with contour lines on the figure to represent the curving surface. Additionally to the spiral geometry there is a tapering of Θ degrees which occurs in the cross channels 13 between the line marked 16 at the leading edge and the line marked 17 which is situated on the inner concave aspect. This spiralling and tapering acts together to rotate the air flow leading to micro-vortex generation. This micro-vortex generation reduces the adhesion of the air flow and reduces drag as the air passes though the cross channel 13. The micro-vortices reducing drag effect, extends along the funnel channel 12, existing the channel at 15 and then extends over the lift surface 20.

Figure 6 shows a view of the lift surface of the leading edge slat device 2. Flere it can be seen that the micro-vortex channels at 14 extend across the lift surface tapering by Θ2 degrees toward the trailing edge 15 of the leading edge slat device. This tapering causes the air flow to accelerate as is passes along the channel which results in micro vortex generation where the faster moving air ο combines with slower moving air, this occurs at multiple points including along the length of the micro-vortex channels 14 and at the trailing edge 15. A further and significant micro vortex generation effect is produced by the undulating leading edge which is created by the design of the micro-vortex channelling 14. The undulation in the leading edge 10 can best be viewed on the elevation presented in figure 4. Micro-vortices are maximally produced as the wing passes across the wind, at the front of the rotation and perpendicular to the wind direction. The micro-vortices travel firstly over the leading edge slat device and then across the main wing device 1. This enables a marked reduction in drag at the same point in time as when the maximal lift is generated.

The detailing shown in figure 5 & 6 represent a small section of the leading edge slat device 2 and are repeated along the entire length of the slat a plurality of times.

Additionally vane type vortex generators have been incorporated into the prototype between the leading edge slat device 2 at point 15 and the main wing device 1, and between the main wing device at point 4 and the trailing edge slat device 3. These simple vanes have the benefit of adding considerable rigidity to the structure. Figure 7 shows a plan view and figure 8 shows an elevation of these simple structures.

This invention provides for further micro vortex generators which may take the form of vane type structures attached to and protruding from the wing surface, concave dimpled surfaces or conversely convex pimpled surfaces and my cover any part or the totality of the wing structures to beneficially reduce drag and optimise performance.

Claims (17)

Claims

1. A vertical axis wind turbine comprising; a plurality of wing structures mounted around a central axis of rotation, The wing structures are each comprised of; a lift surface facing the central axis of rotation, a main wing device, a leading edge slat device, a trailing edge slat device, a secondary trailing edge device confluent with the main wing device at the trailing edge, a funnel channel between the leading edge slat device and the main wing device. The leading edge slat device comprises; a convex leading surface, a lift surface, a concave trailing surface, an elongated portion which is a continuation of the lift surface and the concave trailing surface and contributes to the funnel shape of the funnel channel, a plurality of cross channels passing through the leading edge slat device between the convex leading edge surface and the concave trailing surface, a plurality of micro-vortex channels confluent with the cross channels which extend from the convex leading edge over the lift surface of the leading edge slat device,

2. A vertical axis wind turbine as in claim 1 wherein the concave trailing surface provides for wind energy capture, enabling rotation of the device at start up and directs air flow through the funnel channel, the concave trailing surface is the front boundary of the funnel channel between the leading edge slat device and the main wing device.

3. A vertical axis wind turbine as in preceding claims wherein air that flows through the funnel channels is accelerated due to the funnel shape, resulting in a reduction in the pressure of the air, which exits the funnel channel on to the lift surface of the wing structure and contributes to the lift vector generated by the main wing device.

4. A vertical axis wind turbine as in preceding claims wherein once rotation begins, air passes through the cross channels of the leading edge slat device, flowing from the convex leading surface to the concave trailing surface, thus maintaining the air flow into the funnel channel which would othen/vise have been diminished due to the effect of the rotation.

5. A vertical axis wind turbine as in preceding claims wherein the cross channels are tapered promoting micro-vortex generation reducing drag within; the cross channels, the funnel channels, and over the lift surface of the main wing device.

6. A vertical axis wind turbine as in preceding claims wherein the micro-vortex channels have a spiralling geometry at the confluence with the cross channels to Induce rotation of the air flow and thus further promote the micro-vortex generation reducing drag within; the cross channels, the funnel channels and over the lift surface of the main wing device.

7. A vertical axis wind turbine as in preceding claims wherein the micro-vortex channels taper by Θ2 degrees as they extend over the lift surface of the lead edge slat device from the ledge edge to trailing edge, with the resultant micro-vortices travelling over the lift surface of the main wing device reducing drag.

8. A vertical axis wind turbine as in preceding claims wherein the elevation aspect, is that of an undulating profile along the leading edge due to the cut of the micro-vortex channels, this produces significant micro-vortex generation as the wing structure rotates to the front aspect moving across the wind, contributing an additional reduction in drag over the entire lift surface.

9. A vertical axis wind turbine as in preceding claims wherein the main wing device is of asymmetric profile.

10. A vertical axis wind turbine as in preceding claims wherein the trailing edge slat device is of asymmetric profile.

11. A vertical axis wind turbine as in preceding claims wherein the secondary trailing edge device is a passive Gurney flap.

12. A vertical axis wind turbine as in preceding claims wherein the leading edge slat device is connected to the main wing device by simple vane type micro-vortex generators which also contribute to structural integrity and add stiffness.

13. A vertical axis wind turbine as in preceding claims wherein the trailing edge slat device is connected to the main wing device by simple vane type micro-vortex generators which also contribute to structural integrity and add stiffness.

14. A vertical axis wind turbine as in preceding claims wherein any surface may have additional vane type micro-vortex generators attached.

15. A vertical axis wind turbine as in preceding claims wherein any surface may have concave dimples to cause micro-vortex generation.

16. A vertical axis wind turbine as in preceding claims wherein any surface may have convex pimples to cause micro-vortex generation.

17. A vertical axis wind turbine as in preceding claims wherein the leading edge slat device , the main wing device and the trailing edge slat device are all held rigidly by end plates which while providing structural integrity also reduce the aerodynamically adverse phenomena know as parasitic drag at the wing structure tips.