AU2008101143A4 - Spinfoil aerodynamic device - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT SPINFOIL AERODYNAMIC DEVICE The invention is described in the following statement: 00 SPINFOIL AERODYNAMIC DEVICE

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The need for high performance and versatile airfoils for commercial, industrial and recreational purposes persists, and is particularly relevant in the area of renewable energy in which increasing attention is being given to generation of power from the wind. One device offering significant potential as a generator of lift force is the spinning rotor, which when placed in a moving air stream, experiences a sideways force, a phenomenon known as the Magnus effect, so named after Heinrich Gustav Magnus, a German scientist who investigated and described the effect in 1853. Theoretical analysis of inviscid flow past a rotating cylinder, for example, shows that high lift is developed without generation of a drag force. Further, unlike the common airfoil shape which loses lift, or stalls, when 00 inclined beyond relatively small angles to the air stream, the rotating cylinder has no stall O angle, developing lift for all directions of the stream. In real fluids, however, the significant drag forces developed by the cylinder have proven to be a major factor impeding the practical use of such devices, as discussed below.

The Magnus effect was utilized in the 1920's by Flettner who used rotating cylinders to provide the driving power for ocean going vessels, and in another application, as the blades of a prototype wind turbine. It was, however, found that the deck- mounted rotating cylinders or "funnels" could not compete with submerged propellers, and in the case of the wind turbine, development was not pursued because of the machine's low efficiency which arose mainly because of the significant drag forces that were generated and which opposed motion as the rotational speed of the turbine increased from rest. In 1926 researchers in the Netherlands investigated the effects of incorporating a rotating cylinder at the front of an aircraft wing, but the resulting performance did not compare favorably with that of a good conventional wing although the maximum lift coefficient was appreciably higher. Several other proposals to utilize the potential of the rotating cylinder or other surface of revolution have been investigated over the years but all seem to have been considered as curiosities rather than as having the merit to warrant serious development. The main reasons for this include: Inability tojudiciously minimize the drag- causing low pressure region at the rear of the cylinder Inability to move the forward stagnation point to a position such as to engender contribution to lift rather than drag Inability to provide useful operation without rotation of the cylinder Extreme complexity These problems are overcome by the present invention which provides an aerodynamic device named herein a "spinfoil" comprising a rotor which may be made to rotate, or spin, about it's longitudinal axis, and an adjacent vane, or foil, which has a sharp trailing edge and which resembles the rear portion of an aircraft wing. This device combines the high lift capability and directional versatility of the spinning rotor with the low drag benefit of the rear section of the common airfoil shape.

00 c' In one form of the invention the rotor is a circular cylinder with constant diameter, in other forms the diameter of the cylinder may vary or the rotor may be a more general 0 Z form of surface of revolution. In all forms of the invention discs may be provided along or at the ends of the cylinder or both, and the rotor surface may be made rough. The components of the spinfoil may be made of any suitable material, such as metal, or plastic.

Cc To assist with explanation of the invention, reference is made to the accompanying drawings which show one example of the invention.

In the drawings: 00 FIG. I shows one example ofa spinfoil device according to this invention; FIG. 2 shows a sectional view of the device to highlight the positions of the main components and to indicate the relative geometry of the device and the surrounding air stream.

FIG. 3 shows a typical pattern of streamlines for airflow relative to the spinfoil.

Referring to FIG. I it can be seen that the spinfoil device according to this invention comprises a cylinder I which may spin about it's longitudinal axis 2 when driven by the mechanism 3. Closely fitted to this cylinder is a cambered foil 4 having an upper surface and lower surface 6. Clearances between the cylinder 1 and the foil 4 are small to minimize fluid leakage between the upper surface 5 and lower surface 6 but of sufficient size to allow free rotation of the cylinder 1. Item 7 indicates a support bracket by means of which the aerodynamic forces developed by the spinfoil are transmitted to the intended device.

FIG. 2 indicates the angle of attack 11 between the chord line 12 of the spinfoil and the air stream 13. As depicted, the angle of attack i I is measured clockwise from the direction of the air stream 13. The direction of spin 14 of the cylinder is shown as clockwise. The foil 4, where it is nearest to the cylinder, covers approximately one quarter of the circumference of the cylinder 1, it's upper surface 5 has convex curvature, it's lower surface 6 has concave curvature and it's trailing edge is sharp. The upper surface 5 of the foil is arranged relative to the cylinder 1 so that air flows from the cylinder 1 to the surface 5 tangentially with minimal disturbance. Exterior surfaces of the foil's upper surface 5 and lower surface 6 are smooth to minimize drag forces. The foil terminates at the sharp trailing edge FIG. 3 shows a typical case of a uniform stream of air 13 flowing from the left, and the cylinder I with clockwise rotation 14; a forward stagnation point 20 occurs as shown.

This stagnation point 20 is located in an anticlockwise direction from the front of the cylinder 1, in a position dependent upon the spin ratio, that is, the ratio of the peripheral speed of the cylinder I to the upstream speed of the air stream 13, the stagnation point moving further anticlockwise as the spin ratio increases. Rotation of cylinder 1 in the air 00 stream 13 produces upflow of fluid 21 as flow approaches the cylinder. In the region above the stagnation point 20 velocities combine to produce high speed and the resulting 0 region of low pressure 22 whilst below the stagnation point 20 velocities oppose to produce the high pressure region 23. This high pressure region 23 assists in forming a favorable pressure gradient which causes the air to expand into the space underneath the foil and so maintain continuous flow with minimal separation on the lower surface 6 of the foil. As mentioned above, the upper surface 5 of the foil is arranged relative to the Mc, cylinder 1 so that the flow of air from the cylinder to this surface is tangential with minimal disturbance. Momentum of the fluid stream and the influence of the Coanda effect ensure that fluid flows over the upper surface 5 of the foil with minimal separation 0 and the consequent formation of a dead air region, over a wide range of variation of the 0angle of attack 11 (see FIG. The rear stagnation point 25 is located at the sharp 00 trailing edge 15 of the foil, this sharp trailing edge ensuring that a well defined region of 0downflow 24 is established. Pressure differences around the spinfoil produce a lift force 26 which acts on the spinfoil in a direction at right angles to the air stream 13.

Adjustment of the spin ratio by means of the cylinder drive mechanism 3 (see FIG. 1) provides control of the position of the stagnation point 20 and allows the position to be established such that drag force exerted by the air stream on the spinfoil may be kept to a minimum.

It will be realized that: The rotor, or cylinder, may be any surface of revolution such as a cone or portion of a cone, and that it's surface may be corrugated, roughened or otherwise formed to assist with the development of aerodynamic circulation Actual details of the drive mechanism 3 and support bracket 7 will depend upon the particular use for which the spinfoil is employed The spinfoil may operate in fluids other than air The spinfoil has many practical applications including blades for wind turbines and VTOL aircraft, "sails" for small sea craft, lift devices for hang gliders, ultra light aircraft and pilot less aircraft, and low energy- loss turning vanes for ducted gas flows.