Fluid reaction surfaces (i.e. – impellers) – Rotor having flow confining or deflecting web – shroud or... – Axially extending shroud ring or casing
Patent
1997-12-29
2000-08-15
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, 416192, 416194, 416195, 416228, 416237, 416247A, B63H 116
Patent
active
061026611
DESCRIPTION:
BRIEF SUMMARY
This application has been filed under 35 U.S.C. 371 and claims foreign priority benefits under 35 U.S.C. 119 of PCT/AU95/00826, filed Dec. 6, 1995, which is based upon Australian patent, Serial#: PM 9879, filed Dec. 6, 1994.
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 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.
One such propeller is disclosed in International Patent Application No. PCT/AU91/00582. The propeller described in that document includes an annular ring which joins the tips of the blades of the propeller and leaves free a region only on the high pressure side of the blades. It has been found in practice that this propeller has some disadvantages.
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 provide in one aspect an improved propeller, particularly suited to marine applications which functions efficiently and which is safe in operation. The present invention also aims in a preferred aspect to provide a propeller which prevents excessive vortex formations, particularly at the tips of the blades of the propeller. Other objects and advantages of the invention will become apparent from the following description.
The present invention thus provides in a first preferred aspect a propeller having a central hub, a plurality of blades spaced around said hub and extending outwardly of said hub and having outer tips, and annular connecting means joining said tips of respective said blades, said annular connecting means joining adjacent said blades on the leading and trailing sides thereof respectively and leaving a region of each said blade at said tips on the leading and trailing sides free for outward flow of liquid.
The annular connecting means may be in the form of part annular connecting elements having leading and trailing edges, relative to the normal forward direction of movement of the propeller, the annular connecting elements extending around and lying on or substantially on the surface of imaginary cylinder arranged concentrically with the propeller hub. In one form, the trailing edge of each annular connecting element may extend between the trailing edge of one blade at its tip and a first relief point on the pressure side or back face of the adjacent blade at the blade tip, the relief point being disposed intermediate the leading and trailing edges of the blade at the tip. The pressure side or back face of the blade is the side of the blade facing rearwardly with respect to the direction of forward movement of a water craft with which the propeller is used. The leading edge of each connecting element may extend from a second relief point on the negative pressure or suction side of a blade intermediate the leading and trailing edges of the blade at its tip and the leading edge of the adjacent blade at its blade tip. The negative pressure or suction side of the blade is the side of the blade facing forwardly relative to the direction of movement of the water craft with which the propeller is used.
In one preferred fo
REFERENCES:
patent: 5096382 (1992-03-01), Gratzer
patent: 5405243 (1995-04-01), Hurley et al.
patent: 5413465 (1995-05-01), Daniel
Hofmeister Eddie
Robson Martin
Look Edward K.
Rost Kyle W.
Shanley Matthew T.
SPI LTD
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