Fluid reaction surfaces (i.e. – impellers) – Rotor having flow confining or deflecting web – shroud or... – Axially extending shroud ring or casing
Patent
1993-08-12
1995-04-11
Look, Edward K.
Fluid reaction surfaces (i.e., impellers)
Rotor having flow confining or deflecting web, shroud or...
Axially extending shroud ring or casing
416191, 416237, 416247A, B63H 116
Patent
active
054052432
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
THIS INVENTION relates to improvements to propellers and in particular to improved marine propellers.
BACKGROUND ART
Many different propeller constructions have been proposed in the past and are presently available. Some propellers which have been proposed incorporate a ring or shroud which surrounds the propeller let blades and is fixed thereto so as to be rotatable with the blades. The aim of such shrouds is to direct energy rearwardly from the propeller, rather than losing energy as a result of centrifugal action. Such propellers have not proved particularly effective and often have substantially decreased efficiency compared to normal unshrouded propellers. In particular, excessive pressure can build up within the ring and furthermore, viscous drag which occurs about the ring as it rotates builds up a rotational boundary layer about the ring increasing the effective drag area of the propeller.
Other propellers have been provided with tip or end plates at the end of the propeller blades for distributing the vortices from the blades so that minimum kinetic energy losses occur. Current tip and end plate designs have had limited success.
DISCLOSURE OF THE INVENTION
The present invention aims to overcome or alleviate the above disadvantages by providing in one aspect an improved ring-type propeller, particularly suited to marine applications which has greater efficiency than known ring propellers and substantially the same efficiency as conventional propellers whilst retaining the benefits of a ring shrouding the propeller blades. The present invention in a further aspect aims to provide a propeller having tip or end portions at the ends or tips of the propeller blades which functions more efficiently than propellers having known tip or end plate configurations. Other objects and advantages of the invention will become apparent from the following description.
The present invention thus provides in a first aspect a propeller having a central hub portion, a plurality of blades fixed to said hub portion and spaced therearound to extend outwardly of said hub portion, an annular ring or shroud joining the tips of said blades, a portion of each said blade tip being free of said annular ring on the trailing side of said blade to define a region permitting outward flow of liquid along said blades.
Preferably, each said region of said ring is adjacent the trailing edge of said blade.
The trailing edge of said ring suitably intersects each blade at a relief point intermediate the leading and trailing edges of the blade tip and follows the profile of the blade tip from said relief point to or adjacent the trailing edge of said blade tip.
Preferably, the ring tapers in its dimension axially of said propeller from a maximum at said trailing edge of each blade to a minimum at the relief point.
The ring on the leading side of said blade preferably joins said blade tips along the full width thereof.
The region free of the ring may be defined by a slot in the ring, the s lot being bounded on one side by the tip of the blade.
In a second aspect, the present invention provides a propeller having a central hub portion, a plurality of blades fixed to said hub portion and spaced therearound to extend outwardly of said hub portion, said blades having at their free tips, end portions on opposite sides of said blades and extending generally axially of said propeller, a portion of each said blade tip being free of said end portions on the trailing side of said blade to define a region permitting outward flow of liquid along said blades, said blade tip being joined to said end portions along the full width thereof on the leading said of said blade.
Preferably, said end portion on the trailing side of each blade is joined to said blade tip up to a relief point.
said region being disposed between said relief point and the trailing edge of the blade.
Propellers according to the present invention have a similar external diameter (D) to the diameter of a conventional open propeller. Most preferably the diameter is i
REFERENCES:
patent: 834624 (1906-10-01), Littlejohn
patent: 855131 (1907-05-01), Preidel
patent: 1438012 (1922-12-01), Bauer
patent: 3224509 (1965-12-01), Thompson
patent: 4331429 (1982-05-01), Koepsel et al.
patent: 4505641 (1985-03-01), Tsuchikawa et al.
patent: 4836748 (1989-06-01), Church
Hurley Norman R.
Mirfin Russell D.
Morgan Rhys W.
Tunstill Michael B.
Larson James A.
Look Edward K.
Stealth Propulsion Pty. Ltd.
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