GB2097478A - Magnus effect rotor - Google Patents

Abstract

The rotor has end plates 18 to minimise spanwise flow of the boundary layer, which end plates are not secured to the rotor drum 15 to rotate therewith but are fixed against rotation on a stationary axle 17. The rotor may be used for lifting surfaces such as wings, propeller blades and rudders, and for the propulsion of ships using incident winds. <IMAGE>

Description

SPECIFICATION Improvements in magnus effect or flettner rotors This invention relates to Magnus effect or Flettner rotors.

The Magnus effect rotor is basically a cylinder rotating in a stream of fluid. Due to the distortion of the stream-lines produced by the tangential frictional forces resulting from the rotor rotation, the stream-line are concentrated to one side of the cylinder rather than the other and hence generate a powerful lift coefficient. The effect is well known and has been investigated both practicaily and theoretically.

In particular embodiments of the effect where the high lift characteristics of the rotor are exploited, it has been found from model tests that it is highly desirable to fit end plates to the rotor so that the spanwise flow that inevitably accompanies the higher pressure on one side and the lower on the other is minimised and the flow becomes more two-dimensional. These end plates have been shown in model tests to be very effective and to give lift coefficients which approximate to the theoretical limit of 4err.

Such rotors may be used for lifting surfaces such as wings, propeller blades and rudders, and for the propulsion of ships using incident winds. A particular example was in the so-called Flettner rotor ships where model tests were highly encouraging and the final large ship built unimpressive. The development was not proceeded with.

The present invention relates to the nature of the end plates. If the rotors are large, then because of scaling difficulties it is found that model tests do not give reliable indications of the lift and drag characteristics and indeed the drag coefficient is very much higher than predicted from the model tests while the lift coefficient is lower.

According to the present invention, there is provided a Magnus effect or Flettner rotor with end plates, wherein the end plates do not rotate with the rotor drum but are fixed.

The invention will now be further explained with reference to the accompanying drawings, in which Figures 1 and 2 are, respectively, a diagrammatic part-elevation and plan view of a conventional Flettner rotor and Figure 3 is a sectional part-elevation of a Flettner rotor according to the invention.

Referring to Figures 1 and 2, showing the conventional Flettner rotor 1 , the boundary layer on the end discs 12, when they rotate, is subject to a radial centripetal force and as a result flows outwards, as indicated by the arrows 1 3. The space thereby evacuated is filled by the boundary layer from the rotor drum 11 itself, as indicated by the arrows 14, the net effect being that there is a loss of the boundary layer on the rotor.

The intention of end plates on any lifting surface is to reduce spanwise flow and thereby increase the effective aspect ratio. Due to this centripetal shedding from the rotating end disc on such a rotor the effectiveness of the disc as an end plate is destroyed, indeed it acts as a pump increasing the spanwise flow rather than reducing it and thereby reducing the aspect ratio rather than increasing it.

This effect is not apparent at small model scale due to viscosity effects but when the size of the rotor has reached a level where the centripetal forces are sufficiently high the radial shedding of the boundary layer starts. There is a considerable increase in drag due to the disc of air being shed by an end plate in effect being dragged through the air, but also there is a reduction of aspect ratio to less than the geometric aspect ratio of the rotor.

The rotor according to the invention, as shown in Figure 3, consists of a drum or cylinder 1 5 with closed flat ends 1 6 rotating around a fixed axle 1 7 on which axle are borne immovably fixed end plates 1 8. There is now no centripetal effect from the end plates and they act in the true sense as tip plates preventing spanwise flow parallel to the rotor axis. This being so, there are no scaling problems as between the rotor drum 1 5 and the disc 18, both being scaled on Reynolds number. If both were rotating at the same speed the scaling laws for the drum and the tip plates would be different.However, if the disc is not rotating, there is no difficulty in scaling its effect from model to full size using the same principles as in scaling the lift and drag of the rotor itself.

The invention may be used on a range of devices as described above but, in particular, on rotor ships, i.e. vessels using the natural winds as their main source of propulsion.

Claims

1. A Mangus effect or Flettner rotor with end plates, wherein the end plates do not rotate with the rotor drum but are fixed.

2. A rotor according to claim 1, comprising a rotor drum in the form of a cylinder with flat ends, and a fixed axle on which the cylinder is mounted for rotation, and wherein the non-rotary end plates are borne on the fixed axle.

3. A Magnus effect or Flettner rotor substantially as described with reference to Figure 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in magnus effect or flettner rotors This invention relates to Magnus effect or Flettner rotors. The Magnus effect rotor is basically a cylinder rotating in a stream of fluid. Due to the distortion of the stream-lines produced by the tangential frictional forces resulting from the rotor rotation, the stream-line are concentrated to one side of the cylinder rather than the other and hence generate a powerful lift coefficient. The effect is well known and has been investigated both practicaily and theoretically. In particular embodiments of the effect where the high lift characteristics of the rotor are exploited, it has been found from model tests that it is highly desirable to fit end plates to the rotor so that the spanwise flow that inevitably accompanies the higher pressure on one side and the lower on the other is minimised and the flow becomes more two-dimensional. These end plates have been shown in model tests to be very effective and to give lift coefficients which approximate to the theoretical limit of 4err. Such rotors may be used for lifting surfaces such as wings, propeller blades and rudders, and for the propulsion of ships using incident winds. A particular example was in the so-called Flettner rotor ships where model tests were highly encouraging and the final large ship built unimpressive. The development was not proceeded with. The present invention relates to the nature of the end plates. If the rotors are large, then because of scaling difficulties it is found that model tests do not give reliable indications of the lift and drag characteristics and indeed the drag coefficient is very much higher than predicted from the model tests while the lift coefficient is lower. According to the present invention, there is provided a Magnus effect or Flettner rotor with end plates, wherein the end plates do not rotate with the rotor drum but are fixed. The invention will now be further explained with reference to the accompanying drawings, in which Figures 1 and 2 are, respectively, a diagrammatic part-elevation and plan view of a conventional Flettner rotor and Figure 3 is a sectional part-elevation of a Flettner rotor according to the invention. Referring to Figures 1 and 2, showing the conventional Flettner rotor 1 , the boundary layer on the end discs 12, when they rotate, is subject to a radial centripetal force and as a result flows outwards, as indicated by the arrows 1 3. The space thereby evacuated is filled by the boundary layer from the rotor drum 11 itself, as indicated by the arrows 14, the net effect being that there is a loss of the boundary layer on the rotor. The intention of end plates on any lifting surface is to reduce spanwise flow and thereby increase the effective aspect ratio. Due to this centripetal shedding from the rotating end disc on such a rotor the effectiveness of the disc as an end plate is destroyed, indeed it acts as a pump increasing the spanwise flow rather than reducing it and thereby reducing the aspect ratio rather than increasing it. This effect is not apparent at small model scale due to viscosity effects but when the size of the rotor has reached a level where the centripetal forces are sufficiently high the radial shedding of the boundary layer starts. There is a considerable increase in drag due to the disc of air being shed by an end plate in effect being dragged through the air, but also there is a reduction of aspect ratio to less than the geometric aspect ratio of the rotor. The rotor according to the invention, as shown in Figure 3, consists of a drum or cylinder 1 5 with closed flat ends 1 6 rotating around a fixed axle 1 7 on which axle are borne immovably fixed end plates 1 8. There is now no centripetal effect from the end plates and they act in the true sense as tip plates preventing spanwise flow parallel to the rotor axis. This being so, there are no scaling problems as between the rotor drum 1 5 and the disc 18, both being scaled on Reynolds number. If both were rotating at the same speed the scaling laws for the drum and the tip plates would be different. However, if the disc is not rotating, there is no difficulty in scaling its effect from model to full size using the same principles as in scaling the lift and drag of the rotor itself. The invention may be used on a range of devices as described above but, in particular, on rotor ships, i.e. vessels using the natural winds as their main source of propulsion. Claims

1. A Mangus effect or Flettner rotor with end plates, wherein the end plates do not rotate with the rotor drum but are fixed.

2. A rotor according to claim 1, comprising a rotor drum in the form of a cylinder with flat ends, and a fixed axle on which the cylinder is mounted for rotation, and wherein the non-rotary end plates are borne on the fixed axle.

3. A Magnus effect or Flettner rotor substantially as described with reference to Figure 3 of the accompanying drawings.