Fluid reaction surfaces (i.e. – impellers) – Rotor having flow confining or deflecting web – shroud or... – Axially extending shroud ring or casing
Patent
1992-02-26
1994-05-17
Look, Edward K.
Fluid reaction surfaces (i.e., impellers)
Rotor having flow confining or deflecting web, shroud or...
Axially extending shroud ring or casing
416228, 416237, B63H 116
Patent
active
053122283
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a ship's propellar provided with propeller blades with end plates at the end remote from the propeller hub and on both sides of the blade.
Such a ship's propeller is known. The end plates at the tip of the propeller blades aim to distribute the free vortices coming from the tip of the blade transversely of the end plate, so that the kinetic energy losses incurred by these free tip vortices remain as low as possible. The end plates however have an important disadvantage. Since they are moved with relatively large speed by the liquid, they tend to have a large friction resistance. The energy losses incurred by this friction resistance can be so large that the mentioned energy profit is counteracted. It is also known to provide the blades of a ship's propeller at one side of the tip with an end plate. In order to distribute also in this case the tip vortices in the same direction, the width of this endplate must be equal to the sum of the widths of the plates present on both sides of the tip. Also in this case the friction resistance with respect to the water will be considerable.
The invention aims to provide a propeller with end plates at the blade tips, which has a lower friction resistance with respect to the water than the known propeller.
This is obtained, in that at the attachment to the blade the end plates have a chord length less than the chord length of the blade end and are overlapping each other partly, whereby one end plate is extending to one blade edge and the other end plate is extending to the other blade edge.
Since the bound vortices in chord direction are distributed over the blade tip, the whole blade tip must be covered by one or two end plates in order to obtain the desired effect.
According to the invention these vortices are not always distributed over two end plates, such as in the prior art, but substantially over one end plate. The bound vortices present in chord direction at the front side of the blade are namely discharged by the end plate extending to the front edge and the vortices at the back side of the blade by the end plate extending to the back edge. By equalizing the sum of the widths of the end plates with that of both known end plates or with the width of the single end plate the same favourable distribution of the discharge vortices transversely is obtained. Since however the width of each end plate according to the invention is smaller than that of the known single end plate, and its chord length is smaller than the chord length of the known double end plate, a considerable surface decrease is obtained by the end plates according to the invention with about a factor of 0.4. Since moreover the end plates in the intermediate area of the blade tip overlap each other, it is obtained that in this area the vortex of the blade tip can be distributed over both end plate halves, in such a way that on the front and back edges of these halves the bound vortex strength can go smoothly to zero to avoid danger of cavitation.
The ship's propeller can be carried out in such a way that at the attachment the chord length of each end plate is between 90% and 45% of that of the blade tip. It is preferred however that at the attachment the chord length of each end plate is between 70% and 45% of that of the blade tip.
The smallest surface area of both end plates is obtained if at attachment the chord lengths of both end plates are the same.
An especially favourable effect can be obtained if the form of the propeller is optimalized in the way as disclosed in International Ship building Progress, part 34, July 1987 Nr. 395, (An optimum screw propeller with end plates) by J. A. Sparenberg and J. de Vries. The there determined optimal circulation distribution with respect to a propeller provided with end plates can now be applied to determine the further form of the end plates according to the invention. The chord lengths of the end plates are chosen proportional to said optimal circulation distribution, so that danger of cavitation owing to too large underpr
REFERENCES:
patent: 1515268 (1924-11-01), Morrow
patent: 1703412 (1929-02-01), Thompson
patent: 2086307 (1937-07-01), Stewart
patent: 2104306 (1938-01-01), McLeod
patent: 4875831 (1989-10-01), Fetiveau
"Flugtechnik Mehr Auftrieb-weniger Winderstand", Technische Rundschau, vol. 73, No. 10, Mar. 3, 1981, By V. S. Iselin, pp. 26-27.
De Jong Karel
De Vries Jacob
Sparenberg Johan A.
Larson James A.
Look Edward K.
Stichting Voor De Technische Wetenschappen
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