Background of the Invention

[0001 ] This invention relates to a vortex generator and has been devised particularly though not solely for generating vortices at the wing tips of aircraft to reduce or counter the naturally occurring wing tip vortices.

[0002] There are many applications where it is desirable to generate vortices in fluids, for example in many pneumatic conveying situations, but one particular application is the need to ameliorate or eliminate the vortices naturally generated from the wing tips of aircraft. As an aircraft moves through the air, vortices are typically created at the wing tips which not only increase the drag of the aircraft through the air but also result in dangerous air movement during the takeoff of aircraft necessitating large time gaps between aircraft takeoff frequency at busy airports in order to provide reasonably safe and clear air for a following aircraft.

[0003] Many attempts have been made to reduce the vortices shed from the wing tips of aircraft including the use of upturned winglets, loops of rigid ribbon material attached to each wing tip, the use of wing tip vortex turbines located on the wing tips and other similar devices all intended to either reduce the size of the vortex being shed from each wing tip or to provide an artificially created counter-rotating vortex to ameliorate the naturally occurring vortex at each wing tip.

[0004] The present invention aims to provide a simple apparatus which can be used in the last mentioned application to create a counter-rotating vortex at the wing tip of an aircraft to significantly ameliorate or eliminate the naturally occurring vortex in a simple and cost effective manner.

Summary of the Invention

[0005] Accordingly, in one aspect, the present invention provides a vortex generator including a nozzle having an axial inlet, an axial outlet and a midsection therebetween, arranged so that primary fluid can be drawn in through the inlet, passed through the midsection and exit through the outlet, a toroidal chamber encompassing the midsection, a narrow circumferential slit communicating between the toroidal chamber and the inner surface of the midsection, and fluid supply means arranged to supply secondary fluid under pressure tangentially into the toroidal chamber such that the secondary fluid accelerates through the narrow circumferential slit and issues into the midsection in a spiral flow, inducing a vortex in the primary fluid at the axial outlet.

[0006] Preferably, the midsection of the nozzle incorporates a venturi with converging and diverging surfaces, located immediately downstream of the circumferential slit.

[0007] Preferably, the circumferential slit is axially aligned relative to the nozzle such that the secondary fluid issues from the slit parallel with the adjacent converging surface of the venturi.

[0008] Preferably, the diverging surface of the venturi makes a shallower angle with the axis of the nozzle than the converging surface.

[0009] Preferably, the width of the narrow circumferential slit is variable to control the intensity of the spiral flow.

[0010] In a further aspect, the invention provides a method of generating a vortex using a vortex generator as described in any one or more of the preceding four paragraphs, comprising the steps of supplying secondary fluid under pressure tangentially into the toroidal chamber, and drawing primary fluid into the axial inlet due to a Bernouilli effect.

[001 1 ] In one form of the invention, the primary and secondary fluids comprise air with the mass flow rate of air draw into the axial inlet being an order of magnitude greater than the mass flow rate of secondary air supplied to the toroidal chamber.

[0012] In one preferred use of the invention, a pair of vortex generators as described above are mounted on the wing tips of an aircraft, one to each, and arranged such that the rotation of the vortex issuing from the axial outlets is opposite in direction to the rotation of the vortices naturally issuing from the wing tips as the aircraft moves through the air.

[0013] Preferably the magnitude of the vortex issuing from the axial outlets is sufficient to significantly ameliorate the vortices naturally issuing from the wing tips.

[0014] In one form of the invention, the secondary air is provided from intakes positioned on the leading edge of the aircraft wing, increased in pressure if needed by a mechanical driven blower before being fed to the toroidal chamber.

[0015] Alternatively, the secondary air is provided by compressed air bled from the aircraft engines.

[0016] In a still further form of the invention, the primary and secondary fluids comprise water with the vortex generator used to pump water under pressure through the nozzle.

[0017] Preferably the vortex generator is applied in use as a propulsion unit on a water craft.

Brief Description of the Drawings

[0018] Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0019] Fig. 1 is a frontal and plan view of a jet aircraft showing the vortices typically generated at the wing tips;

[0020] Fig. 2 is a cross-sectional view through a vortex generator according to the invention;

[0021 ] Fig. 3 is a perspective view of a vortex generator of the type shown in Fig. 2 mounted on the wing tip of an aircraft; [0022] Fig. 4 is a diagrammatic elevation of the configuration shown in Fig. 3;

[0023] Fig. 5 is a chart of the thrust generated by a vortex generator according to the invention against supply pressure showing the increase in thrust when the axial inlet is open compared with the situation when it is blocked;

[0024] Fig. 6 is a chart of lift against angle of attack showing the variation between different operating conditions of the vortex generator;

[0025] Fig. 7 is a chart of drag or thrust against angle of attack over the same variation in conditions as shown in Fig. 6;

[0026] Fig. 8 is a perspective view of a vortex generator according to the invention mounted on the wing tip of an aircraft showing variable angle of attack of the vortex generator relative to the wing;

[0027] Fig. 9 is a perspective view of a vortex generator mounted on the upturned wing tip of an aircraft;

[0028] Fig. 10 is a similar view to Fig. 2, showing variations for adjustable slit with and the optional use of inclined holes from the toroidal chamber to the midsection of the vortex generator;

[0029] Fig. 1 1 is a perspective view of a portion of the vortex generator using the inclined holes shown in Figure 10;

[0030] Fig. 12 is a diagrammatic cross section through the outer periphery of the toroidal chamber showing an optional secondary fluid supply point;

[0031 ] Fig. 13 is a diagrammatic view showing two vortex generators according to the invention arranged in series in a pneumatic conveying situation;

[0032] Fig. 14 is a diagrammatic view of a vortex generator according to the invention showing the use of variable angle supply of the secondary fluid; and [0033] Fig. 15 is a perspective view of a particular pneumatic conveying application of the vortex generator according to the invention using the variable angle secondary fluid supply as shown in Fig. 14.

Preferred Embodiments of the Invention

[0034] In the preferred form of the invention, a vortex generator will now be described for use in generating counter-rotating vortices on the wing tips of aircraft, although it will be appreciated that there are many other applications for a vortex generator of this type as will be referred to broadly later in the specification.

[0035] With reference to Figure 1 , a passenger jet aircraft 1 having wings 2 and wing tips 3 and 4 typically generates a large vortex 5 at the wing tip as the aircraft moves through the air. Many attempts have been made to reduce the size of this vortex, for example, by providing an upturned winglet 6 as shown for demonstration purposes at the port wing tip 4 of the aircraft 1 , which has been found to result in a reduced vortex 7. The present invention however aims to further reduce or ameliorate the vortex 5 or 7 by providing a counter-rotating induced vortex at each wing tip in a simple manner which has also been found to reduce the drag of an aircraft and therefore the fuel efficiency, as well as providing benefits in possible reduced spacing between aircraft on takeoff and therefore an increase in takeoff frequency at airports.

[0036] In order to achieve this aim, a vortex generator 8 (Figure 2) is formed in a tubular configuration defining a nozzle 9 having an axial inlet 10, an axial outlet 1 1 and a midsection 12 therebetween. The nozzle is arranged so that primary fluid, and typically air in the case of an aircraft, can be drawn in through the inlet 10, pass through the midsection 12 and exit through the outlet 1 1 .

[0037] The vortex generator further includes a toroidal chamber 13 encompassing the midsection 12 and incorporating a narrow circumferential slit 14 communicating between the toroidal chamber 13 and the inner surface 15 of the midsection 12.

[0038] The invention further provides fluid supply means (not shown) arranged to supply secondary fluid, and typically air under pressure, tangentially into the toroidal chamber 13 such that the secondary air accelerates through the narrow circumferential slit 14 and issues into the midsection in a spiral flow 16, inducing a vortex in the primary fluid at the axial outlet 1 1 .

[0039] The effect is enhanced by providing a venturi 17 at the midsection of the nozzle immediately downstream of the circumferential slit 14. The venturi comprises a converging section 18 and a diverging section 19 arranged to induce a Bernouilli effect by accelerating the airflow through the venturi 17 and thus reducing the pressure in the air at this point.

[0040] This effect is enhanced by axially aligning the circumferential slit 14 such that the secondary fluid issues from the slit parallel with the adjacent converging surface 18 of the venturi 17 so that the secondary fluid tends to cling to the curved surface of the throat of the venturi 17 by the Coanda effect. In this manner, spiral motion is produced by Coanda effect and the primary air is drawn into the nozzle through the axial inlet 10 due to the Bernouilli principle. The intensity of the swirl or spiral flow 16 can be adjusted by varying the supply pressure of the secondary fluid into the toroidal chamber 13, and changing the width of the circumferential slit gap 14.

[0041 ] It has been found that the mass of primary air that is drawn in through the axial inlet 10 can be forty times or more than that of the compressed air supplied through the circumferential slit 14. This produces a large exit velocity (in addition to the swirl) from the nozzle which yields an extremely large thrust compared to the thrust generated when the axial inlet 10 is blocked. This can be clearly seen in Fig. 5 where the upper line (circular points) shows the thrust generated relative to the supply pressure when the axial inlet 10 is open compared with the lower line (square points) showing the thrust generated when the axial inlet 10 is blocked.

[0042] In this manner, the vortex generator according to the invention when used on the wing tip of an aircraft can not only suppress the tip vortex formation, but also increase lift, decrease lift-induced drag, and generate a significant thrust.

[0043] It has been noted that even with the axial inlet 10 blocked, the spiral jet 16 issuing out of the outlet 1 1 produces a reasonable amount of thrust, but an extremely large increase is obtained when the inlet 10 is open. This can be clearly seen in Fig. 5. [0044] Fig. 3 shows one possible configuration of a vortex generating nozzle 20 mounted on the wing tip 21 of an aircraft wing 22. This embodiment also shows that the secondary fluid can be provided from an air intake 23 on the leading edge of the wing 22 through a conduit 24 where it can be pumped up or increased in pressure through a blower 25 before being fed into the toroidal chamber 13 of the vortex generator as previously described. Alternatively compressed air can be bled from the aircraft engines, or even high enthalpy, high pressure gas can be bled from the combustion chamber and fed into the toroidal chamber 13 to produce high kinetic energy at the nozzle outlet.

[0045] As can be seen in Fig. 4, the spiral flow 26 induced in the wing tip vortex generator can be arranged to rotate in the opposite direction to the direction 27 of the naturally occurring vortex shed by the wing tip and thus counter or significantly ameliorate the wing tip vortex.

[0046] In order to optimize the effect of the vortex generator on the wing tip of an aircraft, the vortex generator 20 may be mounted on the tip of the wing 22 at a variable angle of attack as shown in Fig. 8. The angle of attack can be controlled either manually or automatically and rotated through various angles as shown by arrow 27 in order to allow variation in the angle of presentation between the wing and the wing tip nozzle defining the optimum operating angle at different stages of flight. For example, the angle of attack of the vortex generator 20 on the tip of the wing 22 may be set to be different during takeoff than it is at cruise level.

[0047] It is also possible to fit the wing tip nozzle vortex generator as a retrofitted hybrid on an existing winglet of the type shown at 6 in Fig. 1 as can be seen more clearly in Fig. 9. In this configuration, the vortex generator 20 is mounted on the upper tip of the winglet 6 in order to further ameliorate the already reduced wing tip vortices 7 (Fig. 1 ). In this application, it is envisaged that the size of the vortex generator could be reduced compared to that typically required on the wing tip of a conventional wing 22.

[0048] The vortex generator according to the invention has the advantage that it has no moving parts and operates using compressed air only. It can be adjusted, e.g. by varying the width of the circumferential slit 14 to produce various different swirl intensities. The device has a streamlined shape and can be easily retrofitted to an existing wing tip.

[0049] One way of adjusting the width of the circumferential slit 14 will now be described with reference to Fig. 10, where the tubular configuration of the vortex generator 8 is formed in two parts 28 and 29. The two parts are joined together by a screw thread 30 such that when part 29 is rotated relative to part 28, it moves axially toward or away from part 28 causing the circumferential slit 14 to narrow or widen accordingly. Rotation of one part relative to the other can either be performed manually as a "set and forget" feature, or alternatively may be performed automatically using a suitable drive motor (not shown) to allow continuous variation of the width of the circumferential slit 14.

[0050] In one form of the invention, and particularly in various pneumatic conveying applications, it may be found desirable to bleed some of the secondary fluid from the toroidal chamber 13 into the midsection 12 of the nozzle 9 by means other than via the narrow circumferential slit 14. This can be achieved by providing a number of inclined holes 31 between the toroidal chamber 13 and the interior of the midsection 12 as can be seen in cross section in Fig. 10 and is as more clearly shown in the perspective view of part 28 in Figure 1 1 .

[0051 ] The inclined holes are drilled around the tip of the nozzle part 28 at an inclination in the direction of the swirl vortex 32 as seen in Fig. 1 1 . The swirl direction as shown at 32 is for illustration only and could be either clockwise or anticlockwise depending on the application.

[0052] The thrust produced by the vortex generator can augment the main thrust produced by the jet engine or propeller of the aircraft resulting in improved fuel efficiency, which is further enhanced due to the reduction in drag when the wing tip vortices are ameliorated.

[0053] Although there are no moving parts, this device needs a continuous supply of compressed air unlike winglets which are readily attached to wing tips. However, the device according to the invention has the important added advantage of producing additional thrust. [0054] In experimental testing, a vortex generating nozzle according to the invention was attached to the tip of a model wing (NACA 2412) and the configuration placed in a wind tunnel to measure lift and drag, using a lift and drag balance, with and without the nozzle in operation at different angles of attack of the wing.

[0055] Four different operating conditions were used:

• The nozzle axial inlet open; no spiral flow

• The axial inlet blocked; no spiral flow

• Axial inlet open; spiral flow induced

• Axial inlet blocked; spiral flow induced

[0056] The measurements were performed at different air speeds in the wind tunnel and the main results are shown in Figs. 5, 6 and 7 with the following outcomes:

• Without the spiral flow, there was no significant change in the lift and drag values; the drag was slightly higher when the nozzle inlet was blocked (no axial entrainment).

• When the spiral flow (swirl) was introduced, significant increase in lift and a reduction in drag was observed with the nozzle inlet blocked; however when the nozzle inlet was open, there was an extremely large increase in lift and a large thrust was obtained. This phenomenon was observed at several wind tunnel air speeds and inlet supply pressure of the nozzle. These increases occur essentially due to a large entrainment of secondary, axial flow air at the front inlet of the nozzle.

• Simple flow visualisation experiments using smoke and by attaching a string to the wing tip indicate the suppression of the wing tip vortex. The reduction in the intensity of the tip vortex depends on the air speed and the nozzle inlet pressure. Another factor of significance is related to whether the nozzle inlet is open or blocked.

• With the inlet open, the spiral flow nozzle not only increases the lift but also produces a significant thrust component. [0057] Although the main application described here is to improve the aerodynamic efficiency of aircraft, the type of nozzle developed by the inventors can potentially be used in a number of applications such as:

• Condensing vapour from air. The nozzle is intrinsically safe and therefore suitable for separating combustible vapours from air (e.g. kerosene based mill coolant used in aluminium strip rolling mills)

• Transport of grains in agricultural industries to eliminate the dependence on augers (Archimedes screw type grain transporters - from ground level to a silo, for example). It is well known that use of augers results in several serious accidents in farm environments.

• Development of nozzles for pneumatic transport of mineral particles, sand, plastic, cables etc and to minimise pipe and pipe-bend erosion.

• Fluid mechanic scrubber; cleaning of inside of pipes.

• Design of efficient and compact combustion chambers; under certain operating conditions, the nozzle according to the invention can produce a bi-directional spiral flow. This feature can be used in a greater and more efficient mixing of fuel and oxidant. Remotely varying the swirl intensity may yield improved combustion and/or mixing applications without any moving parts.

• The nozzle can be used in water, for example, to augment the thrust developed by a jet ski.

• Control of large wind turbine blades and propellers

• Can be used in UAV (Unmanned Aerial Vehicle) that are used for surveillance and rescue operations. A small compressed air tank in the miniature UAV can supply the air to a small nozzle that produces thrust. Alternatively, high pressure gas can be produced through chemical reactions in a small tank in the aircraft which can be used by the nozzle for producing thrust. Such a miniature UAV can even be used in space applications within the earth's atmosphere.

• Can be used in gliders and helicopters (at the blade tips). • Can be used as a submersible thruster without the need for propellers thus avoiding the entanglement of underwater objects.

• Can be used in turbomachinery to control blade tip flow and tip noise.

• Removal of hazardous snow from runways and roads by using suction (Bernoulli effect) through the nozzle inlet instead of using powerful vacuum pumps.

[0058] One of the most significant of these applications is the use of the vortex generator to improve pneumatic conveying of particulate material, or combined fluids and gases in various different applications. Such applications often call for the ability to vary the swirl intensity and the exit velocity through the outlet 1 1 . One way of achieving this is shown diagrammatically in Fig. 12 where circle 32 represents the outer circumference of the toroidal chamber 13. Typically the secondary fluid would be introduced tangentially as shown by port 33, but it is also possible to introduce the secondary fluid at an optional inlet port 34 which is non-tangential and offset closer to the radius of the circle 32 than the tangential port 33.

[0059] When compressed air is used as the secondary fluid, the intensity can be altered by simply moving the compressed air supply from port 33 to port 34 as required by the operator. In some situations, it is envisaged that compressed air could be supplied to both ports 33 and 34 simultaneously and the ratio of pressure between the two supplies adjusted to fine tune the exit velocity and swirl intensity from the vortex generator.

[0060] In some pneumatic conveying applications, it is envisaged that the vortex generator can be used to mix different materials such as granules, or gases in various ways that are also used for controlling the swirl vortex. One way of achieving this is to run two separate vortex generators 35 and 36 in tandem as shown in Fig. 13 with the main inlet shown at 37 and the outlet at 38. Various different effects can be obtained by introducing a first compressed fluid into the toroidal chamber of vortex generator 35 through port 39 and a second fluid similarly into vortex generator 36 through port 40. In this manner, different fluids may be introduced at different points and mixed in different manners. It is also possible to introduce an optional suction port at 41 allowing further variations in the overall outcome. Alternatively compressed air can be supplied tangentially and liquid, or liquid mixed with particles or powder can be drawn in at the inlet, producing a strong jet at the exit.

[0061 ] Although Fig. 13 shows the swirl direction from the vortex generators 35 and 36 as being in the same direction, they can also be arranged to be in opposite directions, for vortex cancellation, in certain applications.

[0062] One other variation in the vortex generator design can be seen in Fig. 14 where the vortex generator diagrammatically shown at 41 and having a suction inlet 42 and a vortex outlet 43 is provided with secondary fluid through tangential port 44. In this embodiment, the angle of the tangential port 44 may be varied as shown at 45 in order to optimize the suction through the inlet 42. It has been found in practice, that small angles of variation can result in a noticeable improvement in the suction through the inlet 42.

[0063] The features shown in Fig. 14 can be utilised in a particular application of the vortex generator as shown in Fig. 15. In this embodiment, the vortex generator 46 has a suction inlet through a hose 47 and an outlet through a nozzle 48, which can be used to propel particulate material such as granules into the atmosphere in a vortex spiral 49.

[0064] The device may be designed to be handheld by a handle 50 and also to have a secondary fluid inlet through a hose 51 adjustable through the angle 45 as previously described with reference to Fig. 14.

[0065] In this manner, the vortex generator may be used to form a cannon or gun for the projection of granular materials in a very effective spiral pattern as shown at 49. One particular use of this apparatus is to disperse oil absorbing polymers onto the surface of contaminated water where it is desired to soak up oil spills. Compressed air can be supplied at 52 into the secondary port 51 while polymer granules are sucked through a hose at 53 into the inlet 47. The vortex generator 46 has been found particularly effective in mixing the polymer granules with the compressed air supply and projecting them through the outlet nozzle 48 in a vortex pattern 49. This has been found to result in improved projection distance and spread characteristics compared with conventional ways of projecting granules over a large surface area. [0066] Although this particular application has been described for the use of polymer granules in absorbing oil spills on water, it will be appreciated that a similar apparatus could be used for distributing other granular materials over large surface areas, for example to distribute fertiliser over paddocks.