GB2187154A

GB2187154A - Magnus effect rotor for ship propulsion

Info

Publication number: GB2187154A
Application number: GB08703757A
Authority: GB
Inventors: Ewan Christian Brew Corlett; Brian James Corlett
Original assignee: Hydroconic Ltd
Current assignee: Hydroconic Ltd
Priority date: 1987-02-18
Filing date: 1987-02-18
Publication date: 1987-09-03
Also published as: GB8703757D0; GB2187154B

Abstract

A Magnus effect rotor for ship propulsion is provided constructed as a series of cylindrical sections 11 increasing stepwise in diameter from section to section up the height of the rotor so that the rotor can be retracted telescopically into a well 17 in the ship's deck. A central non-rotating support post 13 inside the rotor is fitted with a top bearing 14 that carries the rotor, the post also being telescopic. The top most rotor section has a boundary layer fence 16 projecting radially around its top end, and the step increase in diameter between each of the sections below and the section above it provides a respective boundary layer fence 12 for the rotor section below in each case. <IMAGE>

Description

SPECIFICATION Improvements in and relating to the propulsion of ships This invention relates to the propulsion of ships by means of Magnus effect rotors.

The Magnus rotor has been used for the propulsion of wind-driven ships, the original development installation being by Flettner in the 1 920(s. The principle is well known and is currently under development and of interest due to high fuel prices which improve the economic prospects of wind-driven propulsion. However, all wind assistance devices, e.g. windmill propellers, wingsails, sails and even Magnus effect rotors, are necessarily large and interfere with the arrangement and operation of ships four normal commercial use.

Of the various devices one of the easiestto accommodate isthe Magnus rotor because of its simpleshape and relatively small size arising from the very large lift coefficients that can be developed. Even the Magnus rotor, however, can present difficulties as the considerable vertical projection interferes with cranes and both ship and shore mounted loading/unloading apparatus as well as giving potential air draft problemswhen transisting bridges, etc. It is an object of the invention to overcome this problem.

According to the present invention, a Magnus rotor is provided for ship propulsion which can be extended for use and retracted for storage. Preferably, the rotor is constructed as a succession of cylindrical sections that can be retracted telescopically.

Another problem with any lifting surface is a tendency towards spanwise flow thereby reducing achievable lift coefficients and producing trailing tip vortices. Flettnerfound that is was necessary with the Magnus effect rotor to fit large end plates, both top and bottom, to inhibit spanwise flow and such end plates are now an accepted standard part of any ship propulsion Magnus rotor. In previous work we have shown thatthese end plates are more effective at model scale than at ship scale because of increased centrifugal effect on the air at the tip plates flinging the air out radially and thereby making spanwiseflow more liable to occur on a large version than on a small, e.g. more likely on a ship rotorthan on a model.

Another object ofthe invention therefore is to provide means whereby spanwise flow is inhibited more effectively.

According to this aspect of the invention, boundary layer fences are provided not only at the ends ofthe rotor but also at one or more intermediate positions up its height.

It will be appreciated that it is easy to provide a large ground plate or fence at the bottom of the rotor,this being in effect the ship's deck. It is the top of the rotor that is subject to significant spanwise (axial) flow as distinctfrom the desirable chordwise flow of the two-dimensional airfoil.

A conventional Magnus rotor is constructed as a cylinder of constant diameter with tip plates top and bottom, but particularly at the top, rotating about a fixed post which may extend up to the top of the rotor, or only partway up depending upon the design, and which is fitted with bearings about which the rotor rotates.

A characteristic of the Magnus effect rotor is that some degree of automatic reefing facility is provided by virtue ofthefactthatthe lift and drag produced by the rotor are proportional in a non-linearwaytotheratioof the peripheral velocity of the rotorto the wind velocity (u/v). However, the drag ofthe rotor with zero peripheral velocity will still be equal to that of a cylinder ofthe same dimensions exposed to the incidentwind flowandthis can be considerable in a high wind. This drag is much less than that of normal sailing ship masts and rigging to provide the same thrust when underway, but nevertheless is appreciable.The arrangement according to the invention preferably provides for the stowing of the rotor substantially completely out ofthe incidentwindflow or completely out of the way of cargo handling in port or of bridges over inland waterways.

One arrangement according to the invention is shown diagrammatically byway of example, in the accompanying drawing. The rotor 10 consists of a set of cylinders 11 nesting one insidethe other,thesmallest diameter being at the bottom ofthe rotor and the largest at the top. Thus, the diameter atthe bottom is appreciably less than that at the top and between the cylinders at ascending vertical levels of the rotorthere are step changes in the diameter 12, the width of each step being, as a minimum, sufficient to accommodate one cylinderwithin another and, as an optimum, sufficientto provide a significant barrier two spanwise (axial) flow from the lower to the upper cylinder.

The whole of the stepped rotor, which is very like a telescope in concept, is arranged to rotate around a non-rotating post 13 which may extend to a point in the top cylinder remote from the top end of the rotor, but as shown extends to the top of the top cylinder, the top bearing 14thereon providing a hanging pointforthe entire set of nested cylinders when extended. The bottom bearing 15, it will be appreciated, needs only to be a steadying bearing preventing movement in the horizontal plane.

The central non-rotating post is itselftelescopicand able to provide enough force on extension to liftthe entire set of cylinders from the stowed collapsed position to the extended position. The extension mechanism employed can be similarto that of many extensible hoists and therefore does not need to be here described.

When stowed, the set of cylinders is equal to the length of the uppermost cylinder plus its tip plate 16 and this collapsed length may, if desired, be arranged to fit into a vertical-well 17 in the bow, stern or other partof the vessel so that in this coilapsed position only the top cone and tip fence of the uppermost cylinder project.

By this means, the rotor can be stowed completely out of the way of cargo handling operations, oralternatively, at sea in extremeweathercan be stowed similarly to avoid the aerodynamic drag of the extended cylinders, or it can be stowed when the ship passes under low bridges.

Thus the arrangement achieves first a means of stowing or reefing the rotor completely out of the way of cargo handling operations, bridges, etc. and/or high winds, and second, a means of counteracting the axially upwards spanwise flow which is a natural tendency on a lifting surface such as a rotor.

Afurther benefit isthatthe arrangement makes it possible to keep the ratio u/v substantially constant atall levels of the rotor. Due to ground orwaterfrictional effects the wind close to the surface ofthe sea or land travels at a velocity different from the free-stream velocity dependent upon the height above the ground or sea surface. The general form ofthevelocity gradient is as follows: V ~ (h)1/n Vo (ho) where Vo is the velocity at zero height, h is the height above the ground or sea surface, and n varieswith the surface and also with the time over which the interval is to be considered. Generally, however n is approximately 6 or 7 orthereabouts.

This means that the velocity near the surface ofthe sea or the deck is lower than the velocity at the top ofthe rotor. Typically, if the bottom of the rotor is 6 metres above the sea surface and the height of the rotor is 26 metres then the velocity atthetop of a parallel-sided rotor or pure cylinder will be 28% greaterthanthe velocityatthe bottom of such a rotor.

As a conventional rotor is atall points rotating at the same peripheral velocity, being at a constantangular velocity and having a constant diameter, it is impossible forthe ratio u/vtp be optimised at any otherthan one height on the cylinder. This is detrimental to design efficiency and the control of the system. However, ifthe peripheral velocity is lower atthe lower end of the rotor and higher at the higher end then it is possible by choice of the actual values to retain a more constant ratio u/v at the different heights up the rotorfora constant angular velocity. This the stepped arrangementdescribed provides automatically, conditional upon the diameters being chosen suitably.

In the example of a conventional rotor given above, the ratio u/v mayvaryfrom a value of say 4to 5.12 fora particularvalue of V and constant u. For the same value of V the ratio can be kept substantially constant, as is most desirable, if the diameter at the top ofthe rotor is 28% greater than that at the bottom and the intermediate steps in the diameter ofthe rotor are suitably chosen.

Thus the arrangement described according to the invention provides, in addition to the advantages previously set out, the ability to achieve a substantially constant ratio u/v and accordingly optimise the propulsion capability of the rotor.

Claims

1. A Magnus effect rotor for ship propulsion which can be extended for use and retracted for storage.

2. A Magnus effect rotorforship propulsion with radial boundary layer fences at at least one end and also at one or more intermediate positions up its height

3. A rotor according to Claim 1 or Claim 2, comprising a succession of cylindrical sections with diameters that increase up the rotor and which can be retracted telescopically.

4. A rotor according to Claims 2 and3, wherein each step change in diameter from one cylindrical section of the telescopic rotor to the next constitutes an intermediate boundary layerfence.

5. A rotor according to Claim 3 or Claim 4, supported on a non-rotating post which is itselftelescopic.

6. A rotor according to Claim 5, wherein the post is substantially the same height as the rotor and carries a bearing forthe rotor at its top end from which the rotor is supported.

7. A rotor according to any one of Claims 3 to 6, wherein the diameter of the top section of the rotor is about28% greaterthan the diameterofthe bottom section.

8. A rotor according to any one of Claims 3 to 7, designed to have a substantially constant u/v up its height for a constant angular velocity, where u is the peripheral velocity ofthe rotor and v is the wind velocity.

9. A rotor according to any one of the preceding claims installed on a ship and arranged to retract into a well in the ship's deck.

10. A Magnus effect rotor for ship propulsion substantially as described with reference to the accompanying drawing.