US3656450A

US3656450A - Fluid propulsion mechanisms

Info

Publication number: US3656450A
Application number: US850003A
Authority: US
Inventors: James A Farman
Original assignee: Dunlop Holdings Ltd
Current assignee: Dunlop Holdings Ltd
Priority date: 1968-08-20
Filing date: 1969-08-14
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18
Also published as: NL6912657A; DE1942450A1

Abstract

Fluid propulsion mechanism, for example, a marine craft propulsion mechanism, a pump or turbine, comprising a drivable impeller for partial immersion in the fluid. The impeller is substantially free of transverse fluid thrust formations and utilizes the friction between the fluid and the impeller for the transference of kinetic energy therebetween. The impeller has formed in a fluid-contacting surface thereof a groove into which fluid can enter, the depth of the groove being equal to or greater than the width thereof.

Description

O llite States atent [151 3,656,459 I lFarman Ar. 18, 1972 [54] FLUID PROPULSION MECHANISMS 2,605,146 I 7/1952 Allen ..305/38 x 2,734,476 2 1956 M rsh ..ll5 l [72] Invent James Farm, Eshe" surrey England 3,180,305 4i1965 Ggwer-Rempel ..115i1 73 A' 1D! l-lold'n L'itd Lodo,E- Sslgnee glbiiti l gs "n e n n n FOREIGN PATENTS OR APPLICATIONS 22 Filed: Aug. 14,1969 489,062 12/1952 Canada ..305/35 EB [21] Appl. No.: 850,003 Primary Examiner-Andrew H. Farrell Attorney-Stevens, Davis, Miller & Mosher [30] Forelgn Application lfllflllly Data [57] ABSTRACT Aug, 20, 1968 Great Britain ..39,680/68 Fluid propulsion mechanism for example a marine craft propulsion mechanism, a pump or turbine, comprising a drivag 15/63 4 3: ble impeller for partial immersion in the fluid. The impeller is substantially free of transverse fluid thrust formations and util- [58] Field M Search 15/63 ggg g gg g izes the friction between the fluid and the impeller forthe transference of kinetic energy therebetween. The impeller has formed in a fluid-contactin surface thereof a groove into [56] References Cited which fluid can enter, the d pth of the groove being equal to UNITED STATES pATENTS or greater than the width thereof.

2,091,958 9/1937 Braga .....115/0.5 10 Claims, 12 Drawing Figures FLUID PRQPULSION MECHANISMS This invention relates to fluid propulsion mechanisms in the operation of which kinetic energy is transferred between a body and a fluid. Such a mechanism may constitute a propulsion mechanism for driving a ship through water, a mechanism for pumping fluid from one place to another, or amechanism for harnessing a flow of fluid so as to obtain mechanical power, as does a conventional fluid turbine.

An object of the invention is to provide an improved fluid propulsion mechanism of the kind referred to above.

According to one aspect of the invention a fluid propulsion mechanism comprises a drivable impellor arranged to be mounted for partial immersion in a fluid, the impellor being substantially free of transverse fluid thrust formations and having at least one groove formed in a fluid-engaging surface thereof, the groove extending around at least part of the periphery of the impellor, wherein the depth of said groove is greater than or equal to the width thereof.

According to another aspect of the invention a fluid propulsion mechanism comprises a drivable impellor arranged to be mounted for partial immersion in a fluid, a substantially continuous fluid-contacting surface being provided on and extending around the impellor, the said fluid-contacting surface being substantially free of transverse fluid thrust formations and having at least one groove into which fluid can enter defined by a pair of side walls formed in the said fluid-contacting surface, the side walls extending around at least part of said fluid-contacting surface of the impellor and being in height equal to or greater than the distance by which said side walls are spaced apart.

In this specification, the expression partial immersion" as used in relation to a drivable impellor means that the impellor is of the kind which is intended, at any given time during use, to be only partially immersed in the fluid. Successive portions of the impellor are successively immersed in and emerge from the fluid but at any given time only a portion of the impellor is immersed.

The term transverse fluid thrust formations as used in this specification is intended to refer to formations such as paddle wheels, the spoon or cup-like formations of prior art water turbines and indeed to any formation provided on a fluid-engaging partial immersion impellor which in use prevents fluid flowing past the formation in the general direction of movement of the fluid relative to the impellor.

When relative movement takes place between a body and a fluid, friction causes the volume of fluid nearest the body to move relatively more slowly than the remainder of the fluid. This volume of fluid is known as the boundary layer."

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein:

FIG. 1 shows a diagrammatic plan view of a ship;

FIG. 2 shows a section taken on the lines 11-11 in FIG. 1;

FIG. 3 shows an enlarged cross-sectional view of the fluid propulsion mechanism of the ship of FIGS. 1 and 2, illustrating an impellor in the form of a mechanical belt;

FIGS. 4 and 5 show cross-sectional views of portions of two different belt constructions which may be used as impellors in the fluid propulsion mechanism of FIG. 3, the sections being taken in the direction of the transverse width of the belt in each case;

FIG. 6 shows a cross-sectional view of a sidewall gascushion vehicle the section being taken in a direction transverse to the sidewalls of the vehicle;

FIG. 7 shows a side axial view of a further impellor construction;

FIG. 8 shows another view of the impellor of FIG. 7, in a direction at right angles to that of FIG. 7;

FIGS. 9 and 10 show further fluid propulsion mechanisms according to the invention;

FIG. 11 shows a plan view of a portion of a further belt construction for a fluid propulsion mechanism according to the' invention;

ran:

FIG. 12 shows a cross-sectional view on the line XII-XII in FIG. 11.

With reference to FIGS. 1 to 3, a ship 1 is propelled through water 2 and creates a boundary layer 3 of water moving in the direction of motion of the ship. FIG. 3 shows a portion of the ships boundary layer 3 which engages an endless belt 4 of flexible form extending between

rollers

5,6. Roller 6 is driven by a variable-speed engine 7.

The boundary layer 3 is formed by friction between the immersed surfaces of the ship 1 and the water 2 which causes water nearest the immersed surfaces to move relatively more slowly than the remainder. The characteristics of the boundary layer follow known laws and can easily be determined by calculations based on a non-dimensional coefficient known as Reynolds Number.

The width of the boundary layer 3 based on Reynolds Number is a function of the length and speed of the ship 1. It is zero at the bow of the ship and extends progressively in width to the stern of the ship, as shown in FIG. 1.

With reference once again to FIG. 3, the lower run of the belt 4 is disposed within an aperture8 formed in the bottom 9 of the ship and the belt is positioned so that the bottom surface of the bottom run is in contact with the water. Seals (not shown) are provided to restrict inward leakage of water between the belt 4 and the peripheral parts of the aperture 8. The seals may be of the labyrinth type or may comprise flexible components.

In operation, the belt is driven so that the bottom run moves stemwards. This causes the boundary layer of water surrounding the bottom run of the belt to be accelerated in the same direction. The characteristics of the boundary layer of water in contact with the belt can be obtained by calculation in a manner similar to that referred to above in connection with the boundary layer around the ship. However, the boundary layer in contact with the belt moves sternwards, that is, in the opposite direction to the boundary layer around the ship. The work done in accelerating stemwards the boundary layer of water in contact with the belt produces a reaction force on the belt which is transmitted to the ship in the form of propulsive thrust therefor.

The required effective area of the belt 4 per unit thrust horse power is smaller as the speed of the ship 1 increases and it has been discovered that even for high-speed operation the use of a single plane-surfaced belt would introduce engineering problems, principally those of bulk and weight. With reference to FIGS. 4 and 5, the belt 4 is formed with a series of laterally spaced longitudinally extending grooves 10 and these give the belt a high area to width ratio and reduce or overcome the aforementioned disadvantages.

The depth of each groove is greater than the maximum width thereof, as shown in FIG. 5, or is equal to the maximum width thereof as shown in FIG. 4. It has been found that both the depth and the width of the grooves critically affect the ability of an impellor to transmit power efficiently.

The width of the groove is closely connected with the tendency of the impellor to produce turbulence and other parasitic energy losses in the fluid in the region of the boundary layer of fluid surrounding the impellor. It has been found that there is an upper limit to the width of the grove, beyond which gross turbulence in the region of the boundary layer can develop under operating conditions. This limit is related to the thickness of the boundary layer of fluid produced when the impellor is in use and also to the operating velocity of the impellor relative to the fluid, the pressure, temperature and density of the fluid, and the effective immersed length of the impellor and is determined experimentally for any given application or duty.

Further, it has been found that the depth of the groove formed in an impellor according to the invention is related to the ability of the impellor to transmit kinetic energy to the fluid with which it is in contact. Broadly, it has been found that the deeper the grooves are the more power the impellor can effectively handle.

However, taking into account both power and streamline flow requirements, it has been discovered that for practical purposes the dimensions of the groove of an impellor must lie within the field defined by the following expression in order for success to be achieved and ensured:

depth of groove width of groove That is to say the depth of the groove must be greater than or equal to the width of the groove.

The belt 4 comprises a flexible polymeric composition based on natural rubber having embedded therein a composite reinforcement (not shown) including at least one ply of natural or synthetic textile material serving to provide the belting with tensile strength, the composit reinforcement imparting a degree of transverse stiffness to the belting. Alternative belt constructions, particularly for arduous duty such as in amphibious vehicles or marine vessels for use in shallow water, make use of metallic materials either alone or as a reinforcement for a polymeric composition.

In FIG. 6, a sidewall" gas-cushion vehicle is shown operating over the water surface 2. It is believed that it is not necessary to include here a full description of a sidewall gas-(for example, air-)cushion vehicle, since such vehicles are well known, having been fully described in, for example, the article entitled The First Production Sidewaller published in the Air-cushion Vehicles supplement to the issue dated 26th Dec., 1967 of the journal entitled Flight International. Briefly, however, the vehicle 15 comprises a vehicle body 16 supported above the surface of the water 2 by a cushion of pressurised air 17 formed beneath the vehicle body. The sides of the vehicle-supporting cushion 17 are contained by a pair of side" walls of rigid construction extending lengthwise along the sides of the vehicle body and depending therefrom to dip into the water 2 and provide a seal. The ends ofthe cushion 17 are contained by flexible skirts 19 extending laterally between the sidewalls 18. Air forming the cushion 17 is drawn in a duct 21 and air is discharged by the unit into the space occupied by the cushion 17 by way ofthe duct 21.

The sidewalls 18 are hollow and endless belts 22 of the form shown in FIG. 4 (or, alternatively, FIG. 5) are located therein. The belts 22 are supported by rollers 23 rotatable about axes 24 and the bottom runs of the belts extend lengthwise along and a little below the bottom edges of the sidewall 18 so as to be in contact with the water. Seals are provided (not shown) to restrict in-leakage of water past the belts 22.

In operation, the belts 22 are rotated by means not shown but similar to the arrangement shown in FIG. 3 so as to accelerate boundary layer water in contact with the belts rearwards whereby a propulsive thrust is imparted, through reaction, to the vehicle 15.

As shown in FIGS. 7 and 8 the impellor of a fluid propulsion mechanism according to the invention may comprise an assembly of rotatable fins or discs mounted in axially spaced portions about a common axis of rotation. Such a mechanism may provide motive power for ships, boats or gas-cushion vehicles. In a ship, for example, the impellor may be mounted on the ship so as to project below the bottom of the ships hull so as to be in contact with but only partially immersed in the water. Seals are provided to restrict in-leakage of water past the impellors.

Preferably, however, the impellor of FIGS. 7 and 8 is employed as the impellor of a fluid pump. FIG. 9 shows such a pump 40. The pump comprises a cylindrical casing 41, a pump inlet 42, a pump outlet 43 and a boundary layer accelerator member or impellor 44 disposed within the casing. The impellor 44 is identical in form to the member 31 of FIGS. 7 and 8 comprising a series of discs 45 mounted on a shaft 46 and spaced apart by spacers 47. The pump is provided with glands 48 to restrict outleakage of pumped fluid. The depth of the grooves defined by the discs is greater than or equal to the width of the grooves.

In operation, the shaft 46 is rotated and fluid, such as water, enters the pump by way of the inlet 42 so as to flow over the discs 45. Rotation of the discs 45 accelerates boundary layer fluid whereby the latter imparts, by drag, a propulsive force to the remainder of the fluid so as to displace it in the same direction of rotation as the discs and cause it, eventually, to be discharged from the pump outlet 43.

The pump 40 may also be used as a turbine by causing a flow of fluid through the casing 40 whereby boundary layer fluid imparts, by drag, a propulsive thrust to the discs 45 so as to rotate them, and in so doing, rotate the shaft 46 also, in the direction of fluid flow.

In a (non-illustrated) modification the disc-spacers 47 comprise thin-walled cylinders disposed co-axially between the discs 45.

FIG. 10 shows a further fluid propulsion mechanism according to the invention, in the form of a pump 50.

The pump 50 comprises an endless belt member 51 of substantially the same form as the belt 4 of FIGS. 3 to 5 mounted for rotation on rollers 52 and disposed in a casing 53. The casing 53 has an inlet 54 and an outlet 55 in line with each other and with the lower run of the belt member 51. Seals 56 restrict a carry over of accelerated boundary layer fluid by the belt member 51. The pump 50 may be used for marine propulsion.

FIGS. 11 and 12 illustrate a modified groove configuration for the impellor of a fluid propulsion mechanism according to the invention. The impellor is in the form of an endless flexible belt 57 having a single longitudinally extending groove defined by sidewalls 58 formed therein. At intervals along the length of the groove there is provided a reduced width portion of the groove comprising, at the leading end of the said portion with respect to the normal direction A of fluid flow relative to the impellor, a throat portion 61 in which the sidewalls are inclined in opposite senses with respect to their direction in the preceding portion of their length so that the groove progressively decreases in width. At the end of the throat portion, in the region 59 where the ribs on each side of the groove are of maximum width, the sidewalls 60 defining the groove in the said region sharply diverge and return to their normal separation. The inclination of the sidewalls of the groove in the throat portion 61 relative to the longitudinal axis of the impellor is such as to minimize parasitic energy losses and is determined experimentally having regard to the intended use of the impellor.

The modified groove configuration illustrated in FIGS. 11 and 12 amounts to the provision in the groove of the impellor of a venturi-type restriction resisting the flow of fluid along the groove.

The modified groove construction results in the production by the impellor of augmented thrust and permits, for a given thrust requirement of a particular installation the use of a smaller impellor while maintaining streamline fluid flow in the region of the impellor.

The number of restrictions in groove width in a given impellor is a matter of choice, having regard to the particular use intended for the impellor. Further, the minimum groove width and the inclination of the sidewalls relative to the side edges of the impellor in the restricted portion are chosen having regard to the requirements to be made of the impellor such as the power to be transmitted the normal operating velocity of the impellor, the pressure temperature, density and viscosity of the fluid and the area of the fluid-contacting surfaces of the impellor.

It is to be noted that in FIG. 12 the depth/maxumum width ratio of the groove is apparently less than 1. However, for the purpose of the present invention FIG. 12 has been drawn thus in order to illustrate more clearly the modified groove construction and it is to be understood that the embodiment of the invention illustrated in this particular Figure is intended to be constructed, as are all other embodiments of the present invention, with the depth of the groove equal to or greater than the width thereof.

Where, in this specification including the claims thereof, reference is made either directly or indirectly to the ratio of the depth to the width of the groove or grooves formed in the impellor it is to be understood that where, as in the embodiment of FIGS. 11 and 12, the width of the groove varies along its length, the width to be used for the purpose of computing the depth/width ratio is the maximum width of the groove.

A fluid propulsion mechanism according to the invention wherein the impellor is in the form of mechanical belting may conveniently be provided with a ratio-changing device, for example a train of gears located within a drive drum around which the belt is driven. The provision of such a ratio-changing device allows the propulsion mechanism to be easily matched to the requirements of the source of motive power (for example the engines of a ship) or to the requirements of the power-absorbing system (for example a dynamo) to which the propulsion mechanism is to be connected.

From the foregoing description, it will be appreciated that the invention provides a new marine vessel propulsion system quite apart from the uses of the inventionin relation to fluid pumps and turbines. The invention is equally applicable to ships, boats, hydrofoils, amphibious craft and other types of water-traversing vehicles, and is particularly suitable for shallow draft vessels and for high speed travel over a water surface at high propulsive efficiencies.

Normal methods of screw propulsion are reasonably adequate for certain marine vessels, but this is usually achieved only in large slow to medium speed vessels after extensive testing has been carried out to match the screw propeller with the requirements to be made of it in service. In other applications a screw propeller is less satisfactory and, particularly in high speed vessels, incorrect matching leads to the formation of large areas of cavitation over the screw surfaces and consequent low efficiency.

The impellor of a fluid propulsion mechanism according to the invention simply ejects stemwards the layer of water around it and is more easily matched to the requirements of a particular application. Further, in contrast to impellors employing paddles or other transverse fluid thrust formations, the impellors described in the above embodiments of the invention minimise the production of vortices, gross turbulence and cavitation in the fluid.

It is to be understood that although the present invention has been described above with reference to impellors having grooves of generally rectangular transverse cross section, the invention is by no means restricted thereto. The grooves may have other cross-sectional shapes, for example they may be wedge-shaped. That is to say, the shape of the groove when viewed in transverse cross section is such that the groove is narrowest at its base and diverges outwardly therefrom. lrrespective of the cross-sectional shape of the groove, it may be formed so as to restrict the flow of fluid along the groove as for example is shown in FIGS. 11 and 12 so as to augment the thrust obtainable from the impellor.

lclaim:

1. A fluid propulsion mechanism comprising a drivable impellor arranged to be mounted for partial immersion in a fluid, the impellor being substantially free of transverse fluid thrust formations and having at least one groove formed in a fluid engaging surface thereof, the groove extending around at least part of a periphery of the impellor, wherein the sidewalls define a reduced width portion of the length of the groove, said reduced width portion comprises a throat portion at the leading end thereof with respect to the normal direction of fluid flow relative to the impellor, the sidewalls being inclined in said throat portion in opposite senses with respect to their direction in the preceding portion of their length.

2. A fluid propulsion mechanism according to claim 1, wherein the impellor is constituted by mechanical belting.

3. A fluid propulsion mechanism according to claim 2, wherein the belting is arranged to be driven around a pair of pulleys so as to travel in two spaced-apart runs, one of said runs being located so as to bring the outer surface of the beltingconstituting said run into engagement with the fluid.

. A fluid propulslon mechanism according to claim 2,

wherein the belting comprises a flexible polymeric composition having embedded therein a composite reinforcement comprising at least one ply of natural or synthetic textile material serving to provide the belting with tensile strength, said composite reinforcement imparting a degree of transverse stiffness to the belting.

5. A ship or boat comprising a fluid propulsion mechanism according to claim 1.

6. An air cushion vehicle comprising a fluid propulsion mechanism according to claim 1.

7. A sidewall air cushion vehicle comprising a fluid propulsion mechanism according to claim 2, wherein the belting is mounted in the sidewalls of the vehicle.

8. A fluid propulsion mechanism as in claim 1, wherein the height of the sidewalls is at least equal to the greatest distance between the sidewalls forming a groove.

9. The mechanism of claim 1, including a boat hull in which said impellor is mounted, the total effective area of said impellor being no more than 50 percent of the area of said boat bottom.

10. The combination of claim 9, in which said impellor is mounted with a substantial portion forward of the mid-ship section of said hull.

Claims

3. A fluid propulsion mechanism according to claim 2, wherein the belting is arranged to be driven around a pair of pulleys so as to travel in two spaced-apart runs, one of said runs being located so as to bring the outer surface of the belting constituting said run into engagement with the fluid.

4. A fluid propulsion mechanism according to claim 2, wherein the belting comprises a flexible polymeric composition having embedded therein a composite reinforcement comprising at least one ply of natural or synthetic textile material serving to provide the belting with tensile strength, said composite reinforcement imparting a degree of transverse stiffness to the belting.

5. A ship or boat comprising a fluid propulsion mechanism according to claim 1.