US 3499412 A
Description (OCR text may contain errors)
March 1o, 1970 J, ,ANTHES En.. 3,499,412
` KORTNOZZLIE Filed Feb. 8, 1968 MS2/@fha @w ATTORNEYS.
United States Patent O U.S. Cl. 11S-42 7 Claims ABSTRACT OF THE DISCLOSURE This application discloses the combination of a screw propeller surrounded by a Kort type nozzle where an added flow of water is induced along the inside wall of the nozzle to relieve cavitation at the tips of the propeller blade. This is effected by discharging water around the forward end of the nozzle through a slit so arranged that water forced through the slit flows under influence of the so-called Coanda effect along the inner wall of the nozzle. The ow may be adjusted by controlling the water supply to the slit and additional thrust may be obtained from the added flow of water.
BACKGROUND OF THE INVENTION Field of the invention The present invention relates to improvements in propulsion devices of the propeller type in which the propeller works in a surrounding nozzle.
Description of the prior art It is known in the art of ship propulsion to surround the propeller with an annular nozzle structure which is of substantially airfoil section with the passage therethrough of a venturi-like contour with the propeller being positioned in the passage at the place of greatest restriction and with the propeller blade tips having a working clearance with the inner wall of the nozzle structure. Such a nozzle arrangement is shown in U.S. Patent 2,030,-
375', issued Feb. 11, 1936 and is now generally known in the art as a Kort-type nozzle. Such an arrangement is most widely used on river tow-boats where the maximum diameter of the propeller is restricted by the relatively shallow channels and thrust cannotbe increased by increasing the diameter of the propeller, so that any increase in thrust is important, and is also of importance for increasing rudder response for manuvering the boat and its tow along a winding course.
One of the things which now limits the maximum thrust for any given diameter of propeller is cavitation in the region of the propeller tips. Due to drag or friction of the water along the walls of the nozzle,'the velocity of the water entering the nozzle is diminished in the region immediately adjacent to the interior wall of the nozzle s O that it is different from the ow of the water elsewhere through the passage, resulting in cavitation at the propeller blade tips. In order to avoid'or reduce this effect, it is the usual practice to design the propeller blades in such manner that the propeller blades have a reduced pitch at their tip regions rather than a constant pitch throughout. This reduces the maximum power absorption, and complicates the propeller design.
SUMMARY Briefly, the present invention provides a nozzle in combination with a screw-like propeller for increasing the propulsive efficiency of the propeller and for producing a thrust in addition to that produced by the propeller.
According to this invention, the nozzle isprovided at its forward end with a substantially annular radially di- ICC rected opening or slit through which a controlled flow of water is discharged from an annular duct inside the nozzle. A pipe opening into this duct, which may also be the supporting post for the nozzle, is connected with a pump. The slit is so formed between front and rear lip portions arranged to increase the flow of water through the nozzle adjacent to its interior wall by a phenomenon known as the Coanda effect and thereby relieve the cavitation at the propeller blade tips. This Coanda effect which in a crude way is evidenced by the flow of water down the outside of a glass of water when the glass is tipped for pouring, is discussed in the .lune 1966 issue of Scientific American, pps. 84-92.
Accordingly, with the improved Kort nozzle of this invention, it is possible to counteract the drag effect of the walls of the nozzle on the water owing through the nozzle and thus reduce or eliminate cavitation and enable the use of a propeller with a uniform pitch throughout, thus simplifying its design and provide a propeller having greater thrust for a given diameter over propellers heretofore used in conjunction with nozzles.
It is therefore a primary object of the present invention to provide an improved Kort nozzle and propellerl arrangement wherein cavitation in the tip region of the propeller blades is substantially eliminated, thus allowing use of a propeller of constant pitch throughout, and to provide a Kort nozzle of unique construction.
These and other objects of the present invention will become more apparent by referring to the following detailed specification and claims.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation of a partially shown stern of a vessel and the propeller, with the improved Kort nozzle of the present invention being shown in longitudinal section.
FIG. 2 is a longitudinal section through the improved Kort nozzle shown in FIG. l on a larger scale with the propeller being shown in dotted line.
FIG. 3 is a fragmentary longitudinal sectional view on a larger scale to more clearly show the lip arrangement defining the slit.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, 10 designates schematically the stern of a ship with a propeller shaft 11 and a propeller 12. The propeller is positioned in the passage 13 in a Kort-type nozzle of the usual contour, in which the nozzle comprises an annulus 14 of generally airfoil contour, thickest at its forward or entering end 15 and tapering to the rear or trailing end 15. The passage 13 is of a venturilike shape with the propeller in the region of greatest restriction. Asv shown in the drawing and as customary in the art for the reason hereinbefore explained, the propeller has a diameter such that there is only a good working clearance between the tips of the propeller blades and the inside wall of the nozzle.
There is an annular duct 16 in the annulus, and a water supply pipe 17, which may also be a supporting post for the nozzle which opens into duct 16. The pipe 17 is connected to a source of water, indicated by pump 18 on the ship and a conduit 19 leading from the pump to the pipe 17. A restricted substantially annular passage leads forwardly from the duct 16 to a substantially annular discharge opening 20. This opening is a slit formed between confronting annular lip portions 21 and 22 constituting part of the forward end of the nozzle. The opening is directed substantially radially inward and communicates with the passageway 13, and the rear lip 21 is formed with a step or relief 23 immediately adjacent the slit and arranged to increase the Coanda effect by which the water,
flowing radially from the slit, travels rearwardly in a layer like stream adjacent to the inner wall or surface of nozzle. Its rate of flow can be controlled and adjusted by controlling the output from the pump 18 or otherwise throttling it. By this arrangement the drag against the interior surface of the nozzle is relived, and a stream flow is induced around the inner wall of the nozzle by means other than the propeller itself. As a result, there is adequate velocity to relieve cavitation at the propeller blade tips. While energy of course is required to operate the pump, it is utilized by decreasing the drag of water through the nozzle and water issuing from the slit and moving rearwardly along the nozzle produces some forward thrust which is added to the thrust of the propeller thereby adding to the thrust without increasing the propeller size.
While the invention has particular application to ship propulsion it may be used elsewhere where a venturi-like nozzle is employed in combination with a propeller type means which induces a main flow of fluid through the nozzle and it is desirable to induce an additional ow of fluid adjacent to the interior surface of the nozzle to reduce drag resulting from contact of the main flow of lluid with the interior surface of the nozzle.
It is to be further understood that the above described embodiment of the invention is simply illustrative and numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof and within the scope of the following claims.
1. The combination comprising:
(a) a nozzle comprising an annulus of substantially air foil section with the forward end of the annulus being thicker than the trailing end such that a venturilike passageway is defined therethrough,
(b) a screw propeller about which the nozzle is positioned for inducing a main ow of water through the passageway,
(c) means located at the forward end of the annulus for inducing a flow of water through the passageway adjacent to the interior surface of the annulus in addition to the main flow of water induced by the propeller through the passageway, and
(d) means independent of an external to the nozzle for supplying water under pressure to said last-named means.
2. A Kort-type nozzle having entering and trailing ends with a substantially annular radially-directed opening in the entering end thereof with a substantially annular Coanda surface therearound adjacent the outlet of said opening, a screw propeller having pitched blades about which the nozzle is positioned for inducing a main flow of water through the nozzle and means comprising a source of water under pressure for discharging water through the radially-directed opening in a stream along the interior surface of the nozzle in addition to the main flow of water induced by the propeller through the nozzle to reduce drag resulting from contact of the main flow of water with the interior surface of the nozzle and thereby relieve cavitation producing conditions at the tips of the screw propeller blades.
3. The combination comprising:
(a) a nozzle comprising an annulus of substantially air' foil section with the forward end of the annulus being thicker than the trailing end such that a venturi-like passageway is defined therethrough, the forward end of the annulus having a substantially annular radially-directed opening therein communicating with the passageway, the annulus having an internal duct opening into said annular radially-directed opening,
(b) a screw propeller having pitched blades about which the nozzle is positioned for inducing a main ow of water through the passageway, and
(c) means comprising a source of water under pressure independent of the nozzle for supplying water to said internal duct for discharge through the radially-directed opening along the interior surface of the passageway between the main flow of water induced by the propeller through the passageway and the interior wall of the passageway.
4. The combination as set forth in claim 3 wherein the opening in the forward end of the annulus is provided between spaced forward and trailing annular lip portions defining between them a radially-directed slit-like opening, the trailing lip having an annular step immediately adjacent the slit-like opening in a position to increase the Coanda elfect of the water emerging from the slit-like opening.
5. The combination as set forth in claim 4 wherein said means for supplying water to the internal duct includes a pipe constituting also a supporting post for the nozzle.
6. The combination as set forth in claim 4 wherein the means for supplying the water to the internal duct is adjustable for varying the pressure of the tluid supplied thereto whereby the velocity of the water emerging from the radially-directed opening may be adjusted.
7. In the combination of a nozzle member having a venturi-shaped passageway therethrough with a powerdriven screw propeller positioned transversely in the area of greatest restriction of the passageway with a working clearance between the periphery of the propeller and the interior of the nozzle, the invention comprising:
(a) means in the nozzle arranged to induce a substantially annular llow of fluid through the nozzle along and in contact with the interior wall of the nozzle and independently of the llow induced through the nozzle by the rotation of the propeller in the nozzle, and- (b) means for supplying uid under pressure from a source externally of the nozzle to said first-named means.
References Cited UNITED STATES PATENTS 1,730,748 10/ 1929 Schmidt 230--122 2,864,236 12/1958 Toure et al 230-114 3,179,081 4/ 1965 Backhaus et al 114--166 FOREIGN PATENTS 893,489 4/ 1962 Great Britain. 935,340 2/ 1948 France.
ANDREW H. FARRELL, Primary Examiner U.S. Cl. X.R.