Thrust Augmenter

Abstract

A device for augmenting the thrust from the prime thrust unit of a vessel wherein the thrust unit is surrounded by a shroud having a flared entrance placed in close proximity to the hull of the vessel so that the velocity of fluid being drawn into the shroud increases thus reducing the pressure of fluid acting on the leading face of the flared entrance to augment the thrust of the prime thrust unit.

Description

Propulsion of objects, such as ships and airplanes, is achieved by jetting a stream of fluid to the rear. The force involved in this momentum change is conveyed to the vehicle generating it. The jet stream can be effected by a propeller as in most ships and some aircraft, or by high pressure nozzles fed by hydrodynamic pumps or compressors, as the case may be.

For such a single jet unit high velocities are required to produce the necessary thrust. This involves a large proportionate loss of energy and efficiency due to the velocity head in the fluid on exit. Optimum efficiency for a given input is obtained from a large discharge at a low velocity, controlled by the fact that thrust is determined by the difference between the discharge velocity and the speed of the craft. On ships this implies large propellers rotating at slow speeds. The optimum has been reached in these for large bulk carriers in terms of manufacture and providing adequate flow conditions to the propeller. To augment the thrust due to the propeller on ships, shrouds have been used surrounding the propeller. The water drawn by the propeller also drags surrounding water through the entrance of the shroud. The velocity induced into the water on the forward face of the shroud reduces the pressure on it. The differential between this and the static pressure existing at the level of the unit provides additional thrust in the direction of ship motion. Such augmenters are useful for vessels of slow speed, such as tugs and large bulk carriers.

Where the prime thrust unit is smaller in diameter and of relatively high velocity as for example in the case of a driving nozzle, a similar shroud can be used to that referred to above with the addition of a rearward cylindrical extension to the shroud, the extension serving as a mixing tube. Thus when for example, the shroud surrounds a driving nozzle, the diameter of the nozzle is some fraction of that of the mixing tube, this ratio determining the proportion of fluid drawn through the flared entrance to that issuing through the driving nozzle. The length of the mixing tube should be several times its diameter in order to optimize efficiency of what is essentially an ejector or water jet-pump.

The augmentation of the thrust in the case of the mixing tube derives from the reduced pressure on the flared entrance of the shroud through the momentum given to the water drawn into the tube and expelled at some velocity between that of the driving nozzle and the suction fluid. As is the case with the first mentioned shroud, the augmented thrust decreases with any increase in vessel speed due to the initial momentum already contained in the fluid on entry to the mixing tube, plus the increased wake and friction losses of the unit.

Any shrouds of mixing tubes employed to date on ships or planes have necessarily been open to the force of the water or air as the craft moves forward. As speed increases so is it more difficult to give momentum to the fluid as any point is passed. As noted above this is not a great problem for slow moving vessels with high speed jet streams.

It is therefore an object of the present invention to provide a thrust augmenter which is efficient for both fast moving and slow moving vessels having either high speed or low speed prime thrust units.

Accordingly the present invention resides in a thrust augmenter for a vessel or craft provided with a prime thrust unit comprising a shroud surrounding said a prime thrust unit of the vessel or craft, and having a flared entrance placed in close proximity to the hull or wall of the vessel or craft such that fluid enters the shroud substantially radially thus augmenting the thrust of the prime thrust unit by reducing the pressure of fluid acting on the leading face of the flared entrance, the hull or wall of the vessel being roughened so as to reduce the velocity of the fluid entering the flared entrance immediately adjacent said hull or wall.

The advantage derived from placing the flared entrance of the shroud in close proximity to the hull of a vessel is that the velocities of fluid being drawn in are increased, particularly at the outer diameter of the flared entrance.

This increase in velocity is greater on the flared edge than on the wall or the hull of the craft or vessel. This will result in a greater differential in pressure which will result in a higher augmented thrust.

An added advantage of the fluid having to enter the shroud substantially radially or normal to its axis is that the fluid will initially be moving forward at the speed of the vessel. This represents a momentum which the vessel must provide, but this sternward force is present in any case unless the stern area of the vessel is streamlined. When this water with forward momentum is ejected from the stern of the shroud, the change in momentum provides the thrust. This thrust is much greater than that available when the suction water is static before entry, and it therefore does not decrease greatly as the speed of the vessel increases.

In order, however, that the invention may be better understood, it will now be described with reference to the accompanying drawings, but it will be appreciated that the invention is not intended to be limited to the particular embodiments shown therein.

In the drawings:

FIG. 1 is a diagrammatic sectional elevation of one form of thrust augmenter;

FIG. 2 is an enlarged fragmentary section of the augmenter shown in FIG. 1;

FIG. 3 is a diagrammatic sectional elevation of a second form of augmenter;

FIG. 4 illustrates suggested layouts for the augmenters at the stern of a vessel;

FIG. 5 illustrates a suggested layout for the augmenters along the hull of a vessel; and

FIG. 6 illustrates the mounting of variable direction augmenters for use in propulsion and maneuvering of a vessel.

In the embodiment shown in FIG. 1, the augmenter is provided with a shroud 11 having a flared entrance 12, the shroud surrounding a driving nozzle 13, the flared entrance 12 of the shroud being placed close to the wall or hull 14 of the vessel such that fluid enters the shroud substantially radially or normal to its axis. Preferably the rear end of the shroud 11 is provided with a rearwardly extending cylindrical tubular extension 15 which serves as a mixing tube, the length then of the shroud together with extension being much greater than the inner diameter of the flared entrance 12. Because the flared entrance 12 is placed close to the hull 14, as explained above, the velocity of fluid being drawn into the shroud is increased, the increase in velocity being greater on the flared edge than on the hull 14. To reduce any possible high velocity near the hull 14, which would make for a sternward force, the hull 14 may be hydraulically roughened by the use, for example, of protuberances 16 as seen in FIG. 2, so as to reduce velocities adjacent to the hull 14. The outer periphery of the flared entrance 12 is preferably sharp edged as at 17, or alternatively provided with a slight forward projection 18 in order that the boundary layer of fluid is swiftly widened over the curved surface of the flared entrance 12. This increases the thrust force developed.

The prime thrust unit as shown in FIGS. 1 and 2 is, as stated, a nozzle 13 fed by a pump from within the vessel to provide high velocity. An alternative to the nozzle 13, is a conventional or specially designed propeller 23, as shown in FIG. 3, the propeller 23 being provided with a shroud 21 having a flared entrance 22 placed close to the hull 24 of the vessel. In this embodiment however, instead of the mixing tube 25 being an extension at the rear end of the shroud, it is a separate integer having a flared entrance 20 which is located adjacent and in close proximity to the flared entrance 22 of the shroud 21, the length of the tube 25 being much greater than the inner diameter of its flared entrance 20. In this embodiment, augmentation of the initial propeller thrust is obtained through suction at the leading face of the shroud 21 and additional suction at the flared entrance 20. Preferably the rear face of the flared entrance 22 of the shroud 21 is hydraulically roughened in a manner and for the reasons similar to that of the hull 14 in the embodiment shown in FIGS. 1 and 2. By principles of hydrodynamics it can be shown that, for lamina conditions near the flared entrances, a swirl motion given to the inward radial flow will increase the velocities adjacent to the surfaces of the flared entrances. This would probably apply to turbulant flow so that vanes 26 (FIG. 3) placed around the periphery of the flared entrance 20 adjacent the rear face of the flared entrance 22 also increase further the pressure differential over it. Similar further vanes or blades 27 between the flared entrance of the shroud and the hull of the vessel in both embodiments shown in FIGS. 1 and 2 and FIG. 3 may be so directed as to improve the efficiency of the prime thrust units.

It might be considered that the system described with reference to FIG. 3, with the small clearance or spacing between the flared entrance 20 and the flared entrance 22, represents the cascade mixing system proposed in the past. However, the similarity breaks down due to the long length of the mixing tube 25 required in the present instance. Were a cascade system to be adopted the length overall would become excessive.

In respect to a water medium as for ships, efficiency of operation would depend greatly upon the exclusion of air from the inducted water. Aerated water would not provide such good momentum change. For this reason, the augmenters should be located as deep as possible on the stern of the vessel. A suggested layout for a large bulk carrier is depicted on the right hand side of FIG. 4. It is possible that a multi-rudder attachment could be used on the outlets of the mixing tubes, but steering could also be effected by jets on one side of the stern being used only. If sufficient room is not available on the stern of a vessel to develop the desired thrust, jets and their augmenters could be employed in suitable indentations 29 along the sides as shown in FIG. 5 and the left hand side of FIG. 4. These units are slightly less efficient than those used in the stern for thrust purposes, because of their slightly oblique angle to the ship center line. However, they could be extremely effective in steering the vessel. When those on the bow quarter, for example, are operated alone, there is a strong turning moment exerted on the ship. A more flexible propulsion system is illustrated in FIG. 6, in which thrust units according to the invention are connected to a swivel 30 inside appropriate channels 31 along each side of the ship. The prime thrust units, which can be either of the nozzle or propeller type, can be directed astern (S), to port or starboard (P), or towards the bow (B) for purposes of reversing. Maneuvering can thus be accomplished without the use of tugs.

It will be noted that the above augmenters have been described in connection with a liquid medium, however, it will be appreciated that air can be the driving and driven fluid medium, the air being fed from compressed air tanks, compressors or fans in a vertical, inclined or horizontal direction.

In respect to aircraft the concept of a mixing tube and high speed jet or nozzle can provide the necessary large volumes of air and other advantages of differential pressure on shrouds and flared entrances. This would be mainly applicable to lift forces as required in a helicopter type operation. Units as illustrated in FIGS. 1 or 3 which are directed upwards could use the nozzle 13 or propeller 23 to draw air through the mixing tube 15 or 25. A large load carrying platform would require several such thrust units. A single unit could be designed to lift one man and the necessary hardware for providing power. He could then propel himself horizontally by tilting the platform, or by means of a subsidiary propeller.

Claims

I claim:

1. A thrust augmenter for a vessel or craft provided with a prime thrust unit comprising a shroud surrounding said prime thrust unit and having a flared entrance placed in close proximity to the hull or wall of the vessel such that fluid enters the shroud radially thus augmenting the thrust of the prime thrust unit by reducing the pressure of fluid acting on the leading face of the flared entrance, the hull or wall of the vessel or craft adjacent the flared entrance being roughened so as to reduce the velocity of fluid entering the flared entrance immediately adjacent said hull or wall.

2. A thrust augmenter as claimed in claim 1 including a swivel mechanism connecting said thrust augmenter to said vessel hull whereby thrust can be exerted by the thrust augmenters in any direction for maneuvering purposes.

3. A thrust augmenter for a vessel craft provided with a prime thrust unit comprising a shroud surrounding the prime thrust unit of the vessel or craft, the shroud having a flared entrance placed in close proximity to the hull or wall of the vessel or craft such that fluid enters the shroud radially so as to create a velocity gradient across that part of the flow path between said flared entrance and said hull or wall, the velocity of fluid being a maximum adjacent said flared entrance and a minimum adjacent said hull or wall, thus augmenting the thrust of the prime thrust unit by reducing the pressure of fluid acting on the leading face of the flared entrance, fixed or movable guide vanes being located at said flared entrance to provide radial or swirling flow to the fluid entering the flared entrance.

4. A thrust augmenter for a vessel or craft provided with a propeller as the prime thrust unit comprising a shroud surrounding the propeller forming the prime thrust unit of the vessel or craft, the shroud having a flared entrance placed in close proximity to the hull or wall of the vessel or craft such that fluid enters the shroud radially so as to create a velocity gradient across that part of the flow path between said flared entrance and said hull or wall, the velocity of fluid being a maximum adjacent said flared entrance and a minimum adjacent said hull or wall, thus augmenting the thrust of the propellor by reducing the pressure of fluid acting on the leading face of the flared entrance, and an additional or secondary shroud is located rearwardly of the shroud surrounding the propellor, said secondary shroud having a flared entrance in close proximity to the flared entrance of the shroud surrounding the propellor.

5. A thrust augmenter as claimed in claim 4 wherein the rear face of the shroud surrounding the propellor is roughened.