DOUBLE NOZZLE

Abstract: Double nozzle consisting of a main nozzle (1) and a flap nozzle (2), coaxially located and operating in conjunction with main nozzle (1), comprising an opening (6) formed between the two nozzle profiles by the thin part (1a) of main nozzle (1) and the front part (2a) of flap nozzle (2), said opening (6) extending rearwardly and inwardly. Main nozzle (1) and flap nozzle (2) may be interconnected by extended parts of the nozzle construction, such as radial stiffening plates.

Description: Double nozzle. This invention relates to the propulsion of waterborne vessels employing propellers surrounded by one or more shrouds. Shrouded propellers, sometimes referred to as nozzle propellers or propellers in so-called Kort nozzles are known since several decades. Two types can be distinguished. One type in which the shroud is connected to the blade tips and therefore rotates with the propeller - this type is known as ring propeller - and the other type in which the shroud is stationary and fixed to the hull of the ship. In British Patent Specification No.1,324,356 is described that the propulsion of ships can be improved by fitting a first ring surrounding the propeller along with a second ring coaxial with the first one, such that a slot is formed between the two rings, the two rings together forming a single foil shape with, in any axial section, the inner surfaces of the two rings lying approximately on a common smooth curve, and the slot extending inwardly and rearwardly and being shaped in such a way that, in use, the lift produced by the foil is larger than without the slot. It is also mentioned that both rings may be made stationary, the propeller rotating in one of the rings. Britishwatent SpeciticationT%:rl.1,215,136 deFcrlnes a concept known in the art as the so called "Hannon slot". Its purpose is to improve the astern performance of a nozzle. Thus the Hannon slot does improve the astern performance but does not improve the efficiency in the ahead condition as is achieved by the present invention. Fundamental differences of the Hannon slot in comparison with the present invention are (a) that the direction of the slot with respect to the flow is approximately perpendicular to that of the present invention resulting in een improvement of the astern performance by the Hannon slot but without improvement of the efficiency in the ahead condition: (b) the Hannon slot does not yield any increase of the effective diffusor angle whereby the efficiency improvement of the present invention is achieved; (c) the openings of the Hannon slot cover the circumference of the nozzle only in part - mentioned is 25% - whereas the present invention envisages an opening over the complete circumference. Thus it has been found according to the present invention that the disadvantages of the above state of the art can be overcome, and an improvement of the propulsive efficiency can be achieved, by fitting a double nozzle around the propeller. This double nozzle consists of a main nozzle, in which the propeller rotates, and a second nozzle rearward of the main nozzle viewed in the ahead direction, and acting as a flap to the main nozzle, whereby the opening between the main nozzle and the flap extends inwardly and rearwardly, which in effect causes the improvement of the propulsive efficiency. In contrast the state of the art, especially as discussed above, it is not neceesary for the double nozzle according to the present invention that the inner surfaces of the two nozzle parts are lying on a common smooth curve. Both parts of the double nozzle, i.e. the main nozzle and the flap nozzle, are preferably connected to each other, although they may be independently connected to the hull of the ship by known means. The connection may consist, for instance, by entended radial stiffening plates of the main nozzle reaching into the construction of the flap nozzle. It has appeared from tests that providing a jump in the inner surfaces of both nozzle parts by selecting a larger inside diameter for the flap nozzle yields an improvement of the propulsive efficiency. This is analogous to the known improvement of efficiency due to an increase of the diffusor angle, which however is limited to about 7 degrees or flow separation will occur. This limitation is removed in the present invention by the interaction of the two nozzle profiles. The invention will now be illustrated by way of example with reference to the accompanying drawings, wherein: Figure 1 shows a longitudinal section of a double nozzle according to the invention; and Figure 2 shows a similar section in more detail. Figure 1 shows the double nozzle, consisting of a main nozzle 1 and a flap nozzle 2, which are connected to a hull 3 of a ship by appropriate means (not shown). Inside the main nozzle operates a propeller, having blades 4 mounted on a hub 5, driven by a shaft (not shown) in a known manner. Seen in the axial direction, the main nozzle has a circular shape. The thickness of the profile of main nozzle 1 is reduced towards its rear end and its thinner part overlaps in part the front part of flap nozzle 2, the opening 6 between the two nozzle profiles extending rearwardly and inwardly. Further detail of the latter is shown in Figure 2, wherein main nozzle 1 and flap nozzle 2 are shown (without applied connecting parts) and the opening 6 between the two nozzle profiles. Said opening is formed by the thin part la of main nozzle 1 and front part 2a of flap nozzle 2. The double nozzle according to the invention can be applied in various combinations with the propeller. The most usual one is to locate the propeller inside main nozzle 1, but in special cases the propeller may be located aft of main nozzle 1. It will be obvious that the propeller can be fixed pitch or of controllable pitch type. In the case of a propeller with fixed pitch, the double nozzle may be attached to the blade tips so that both rings will rotate with the propeller.

Claims: Claims: 1. A double nozzle, consisting of a main nozzle (1) and a flap nozzle (2), coaxially located and operating in conjunction with the main nozzle (1), an opening (6) being formed between the two nozzle profiles by the thin part (la) of main nozzle (1) and the front part (2a) of flap nozzle (2), opening (6) extending rearwardly and inwardly. 1. A double nozzle according to claim 1, characterised in that main nozzle (1) and flap nozzle (2) are connected by extended parts of the nozzle construction. 3. A double nozzle according to claim 1 or 2, characterised in that the connection consists of radial stiffening plates. 4. A double nozzle according to one or more of the foregoing claims, characterised in that the inside of flap nozzle (2) shows an outward jump (larger diameter) with respect to the inside of main nozzle (1) 5. A double nozzle according to one or more of the foregoing claims, characterised in that it is connected to the fixed pitch propeller blade tips.

Inventors: GELLING JACON LOURENS, VAN GUNSTEREN LEONARD ANTHONIE, GELLING, JACON, LOURENS, VAN GUNSTEREN, LEONARD, ANTHONIE
Applicants: GUNSTEREN & GELLING MARINE PRO, VAN GUNSTEREN & GELLING MARINE PROPULSION DEVELOPM
Application year: 1989
Main classification: B63H5
IPC codes: B63H5