USRE16001E - Screw propeller and similar - Google Patents

Description

v J. H. w. e 1

SCREW PROPELLER AND SIMILAR APPLIANCE Original Filed June 5 1920 Reissued Fa. 17, 1925.

UNITED STATES GREAT BRITAIN. 1

To all whom it may ooncem:

Be it known that I, JAMES HERBERT WATNWRIGHT GILL, a subject of the King of England,and residing at Norfolk, in 6' England, have invented certain new and useful Improvements in Screw Propellers and Similar Appliances, of which the following is a specification.

This invention relates to screw propellers and similar appliances of the axial flow type such as are employed to impart energy to fluid streams or to develop propulsive reaction.

Acoording'to this invention the blades of v the propeller are disposed within and carry on them a curved shroud whose inner surface hasacontour which is substantially that of a nozzle designed so as to give to the fluid stream on which the ropeller acts such rate of increase in velocity of flow as corresponds to a uniform progressive increase in the dynamical equivalent of head (herein referred to by the word head) per unit axial distance through the shroud, i. e. so that there 'is a. constant rate of increase in the square of the velocity of the fluid stream or unit axial distance through the shroud. EVhen the propeller acts on a liquid the quantity of liquid passing any cross-section 0 in a given time must be constant, and the velocity of flow is therefore inversely proportional to the cross-sectional area and therefore also to the uarepf the radius of the shroud The con ition above stated is thus equivalent to the condition that the fourth power of the radius of any section of the shroud is inversely proportional to the axial distance to that section. Expressed mathe- 40 is a surface of revolution generated by the rotation of a part of the curve ya1=constand v v The pitch of the blades increases in the direction of flow through the shroud, the pitch bein inversely proportional to the diametero the shroud, so that it conforms torthe acceleration of the fluid stream pass- .ing through the shroud. The "blades are carried on asuitably shaped hub which may conveniently be cylindrical though in some cases shaped otherwise and the shroud is formed integral with or is attached to the ends of the blades so that these are posimatically the internal contour of the shroud,

efiectfl conse uent on cavitation.

PATENT ;OFFICE.

.TAuEs HERBERT wArNwnronT GILL, or NORFOLK, ENGLAND, .AssIoNoR To GILL PIBO-PELLEB COMPANY, LIMITED, or xr es LYNN, ENGLAND, A' COMPANY or scBEw PROPELLER AND SIMILAR ArPLIANcE.

original 1i'o.1,454,967, dated May 15, 1923, Serial 170. 389,195, filed June 15, 1920, Application for reissue filed September 30, 1924. Serial No. 740,818.

tioned within the shroud preferabl otherwise than at the centre of the lengt of the latter and nearer to the larger end. The axial length of the shroud is such that it is less than the diameter of the propeller velocity impressed thereon and also to mini- 1 mize discontinuity of flow and its contingent effects. These objects are attained by controlling velocities and pressures in the fluid stream during its forced acceleration.

The design of the nozzle-shaped shroud should be such as to assist in the formation of vortex action resembling that of a free spiral vortex and thus to minimize dissipation of energy in the fluid which is directly acted upon by the propeller. In the case of a'fluidsuch as water the area of the stream which is acted upon by the propeller contracts under the increasing velocity and this natural contraction is assisted and controlled by the vortex shaped shrouding ring. True cavitation depends on the stream velocity at which the fluid acted upon will follow up the propeller blades, and while there is a limit .to this velocity, incipient (I cavitation, which is largely due to radial flow and local eddies, and tends to occur at velocities of flow below the above mentioned limit, can be practically eliminated by means of a shrouding ring shaped as described.

The present invention has various advantages when compared with other known types of propeller more particularly when the invention is applied to ship propulsion. By promoting steady blades and boss of the propeller the improved construction reduces the erosive ployment o strengthens the propeller and permits of higher speeds of revolution while minimizflow and preventing cavities from collapsing in -contact with the The cm the nozzle .shrouding 'ring.

ing vibration. Eddy losses and radial flow are reduced: as also is the out of pitch effect which occurs wit ordinary propellers when mounted onincline shafts. Further the efl'ect of threshing which occurs when a vessel pitches is lessened and the shrouding ring also obviates fouling of the propeller by ropes or nets When employed for going astern a propeller provided with the improved shroud acts as an ordinary propeller but as if it was of less diameter and thus it afl'ords'an advantage as compared with a turbine pro-peller fitted with guide vanes.

The accompanying drawings illustrate by way. of example one construction of propeller in accordance with this invention, the propeller being more particularly adapted for marine use. v

In these drawings Figure 1 is a longitudinal sectional elevation of the improved propeller.

Figure 2 is an end view from the forward or inlet end.

Figure 3 is a. similar view from the after or delivery end.

Like letters-indicate. like parts throughout the drawings. i

In the construction shown the propeller has four blades A-mounted on a cylindrical hub B whose after end is ta ered off at B with a stream-line form. n the ends of the blades A is mounted a nozzle-shaped shroud C which is either formed integral with the blades or separate and. attached thereto in some suitable manner. The blades A have a gaining pitch so as to con form' with the acceleration of the water passing through the shroud C. I

The length of the shroud C may vary in accordance with requirementsv and the con ditions under which the propeller is to be used. In the construction shown the len h of the nozzle measured in the axial direction is about three-quarters-of the smaller diameter of the propeller. The smaller and outlet end C has a diameter which is about .8 of the small diameter of the propeller. It will be noted that the blades A are not positioned at the centre of the shroud C but to one side of thiscentre and somewhat towards the larger end C of the shroud.

In some cases the hub B may be split and handed to allow for uniform contraction of the shroud C where the latter is made integral with the blades.

The leading edge C at the inlet end of the shroud may be enlarged with an outside bulb whilethe after edge C is fined off from the inside, but if the ropeller is likely to encounter ice or ot er -obstructions through which it is desirable to cut the edge C may be serrated.

The contour of the shroud is a surface of revolution generated by a suitable portion of the curve ywzconstant, and thus approximates to that of a portion of a free spiral vortex, so that the shroud conforms approximately to the path which is naturto secure by Letters Patent is tlirough the shroud to conform with the acally followed by thewater acted on by the propeller blades. at any cross-section is inversely proportional to the internal diameter of the shroud at that section and thus conforms to the acceleration of the water assing through the shroud. When a propel er thus formed and shrouded is operating against a dead pull, as in towing, the radial effect and eddy losses are reduced and the propeller operates efiiciently as an axial flow pump. The propeller will act efficiently when going astern but it then functions as an ordinary propeller of less diameter.

What I'claim as my invention and desire 1. In a screw propeller the combination of a hub, blades radiating from 'the hub, and a shroud mounted on the ends of the blades, the inner surface 'of the shroud having approximately the contour of a nozzle designed so as to give to-the fluid stream'on w hich the propeller acts such rate of increase in velocity of flow as corresponds to a uniform progressive increase in the dynamical equivalent of head per unitaxial distance through the shroud, and the blades having axial increase of pitch in the direction of flow through the shroud to conform with the acceleration of the water passing through the shroud.

2. In a screw propeller the combination of a hub, blades radiating from the hub, and a shroud mounted on the ends of the blades, the inner surface of the shroud havin approximately the contour of a nozzle desi ned so as to give to the fluid stream on w ich the propeller acts such rate of increase in velocity of flow as corresponds to, a uniform progressive increase in the dynamical equivalent of [head per unit axial distance through the shroud, the length of the shroud in the axial direction being less than the diameter of the propeller but greaterthan the axially projected width'pf the propeller blades, the blades havin axial increase of pitch in the direction of ow through the shroud to conform with the acceleration of the water passing through the shroud.

3. In a screw propeller the combination of a hub, blades radiating from the hub,

and a shroud mounted on the ends of the blades, the inner surface of the shroud having approximately the contour of a nozzle designed so as to ive to the fluid stream on which the propel er acts such rate of increase in velocity of flow as corresponds to a uniform progressive increase in the dynamical equivalent of headp'er unit axial distance through the shroud, and the blades being positionedintermediate the ends of the shroud but otherwise than at the centre of its length, the blades having axial in crease of pitch in the direction of flow The pitch of the blades 'of pitch in the direction 0 moiceleration of the water passing through the shroud.

4. In a screw propeller the combination of a hub, blades radiating from the hub, and a shroud mounted on the ends of the blades, said shroud having a length which measured in the axial direction is less than the diameter of the propeller but is greater than the axially pro ectedwidth of the blades,

the inner surface of the shroud being curved to an a roximately conical form and being outwa i flared toward one end "so as to give to t e fluid stream -on,;which the propeller acts such rate of increase in velocity 1 of flow as corresponds to a uniform progressive increase in the dynamical equivalent of head per unit axial distance through the shroud, and the blades having afixial ificrease ow is rough the shroud to conform with the acceleration of the water passing through the shroud.

5. In a screw propeller the combination.

of a hub, blades radiating from the hub, and a shroud mounted on the ends of the blades, the shroud being curved to an approximately conical form and bein outwardly flared toward one end, the blades being positioned within the shroud intermedii ate the ends of the latter but otherwise than at the centre of its len h and said blades having-axial increase 0 pitch in theidirection offlow through the shroud toconform with the acceleration of the water passing through the shroud.

In testimony whereof I have signed my name to this specification.-

I .muzs HERBERT muawlucur cm.

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