GB2489522A

GB2489522A - A water jet propulsion device having a duct with an inflatable portion

Info

Publication number: GB2489522A
Application number: GB1105556.3A
Authority: GB
Inventors: Paul Fletcher; Paul John Newton; John Richard Webster
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2011-04-01
Filing date: 2011-04-01
Publication date: 2012-10-03
Also published as: GB201105556D0

Abstract

There is disclosed a water jet propulsion device 10 for a water vehicle, comprising a main duct 12 having a main inlet 14 that is arranged to be submerged in use and a main outlet 16. The device also comprises a pump disposed between the main inlet 14 and the main outlet 16 and an inflatable portion 32 disposed in a position such that the geometry of, or in the region of, the main duct can be altered by the inflation or deflation of the inflatable portion between at least a first configuration and a second configuration. The inflatable portion may form a part of an inclined upper wall 28 of the main duct or may form part of the duct lip 24.

Description

I

WATER JET PROPULSION DEVICE

The invention relates to a water jet propulsion device for a water vehicle such as a boat.

Water jet propulsion devices are often used to power water vehicles such as boats. They are also sometimes known as pump-jets or hydro-jets. Water jet propulsion devices typically comprise a pump having an inlet that is submerged in use and an outlet that is generally located above the water level. In use, the pump ejects a jet of water rearwards out of the outlet which provides a propulsive force to the boat to drive it forwards.

A previously considered water jet propulsion device 1 is shown in Figure 1.

The propulsion device I comprises a duct 2 having an inlet 3 and an outlet 4.

The duct 2 defines a duct lip 7 which has a forward-facing edge 8. A ducted impeller 9 is disposed in the duct 2 and is driven by a motor.

When the boat is travelling at low-speed, the pump sucks water in through the inlet 3. For optimum performance it is desirable to have a relatively large inlet throat area so that the necessary volume of water can be sucked through the inlet 3 by the pump. However, when the boat is travelling at high-speed, water is forced into the inlet 3 due to the speed of the boat. This usually results in too much water being forced into the inlet 3 and therefore it is desirable to have a smaller inlet 3. The dimensions and design of the inlet 3 and duct 2 are therefore a compromise for both low-speed and high-speed operation.

However, the inlet 3 is usually still too small for low-speed operation and too large for high-speed operation. This can result in separation and cavitation occurring at various positions around the inlet at both low-speed and high-speed operation. Flow separation reduces the effective intake area and therefore the thrust capability of the propulsion device I. Cavitation is undesirable since it creates pressure pulses which impact the impeller which may cause excessive noise, erosion and potential damage.

When the water jet propulsion device I operates at low speed, water is drawn from behind the inlet 2 and is turned around the duct lip 7 into the main duct 2. This can lead to flow separation at A which is a position on the upper surface of the duct lip 7 rearward of the edge 8. In turn, this flow separation can lead to cavitation if the pressure of the liquid falls below its vapour pressure and gas bubbles form.

When a conventional water jet propulsion device 1 operates at high speed, excess water can flow into the duct 2, leaving an absence and hence cavitation at B which is a position on the lower surface of the lip 7 towards the edge 8.

Furthermore, flow separation can occur at C which is a position upstream of the impeller 9 close to the upper wall of the duct 2, and at D which is a position on the rearward ly-inclined upper wall of the duct 2 towards the inlet 2. The flow separation and cavitation can lead to excessive drag, low efficiency of the water jet propulsion device and damage to the pump.

It is therefore desirable to provide a water jet propulsion device having an improved water inlet design.

In a broad aspect the invention relates to an inflatable portion that can be inflated and deflated so as to change the geometry of a main duct of a water jet propulsion device.

According to an aspect of the invention there is provided a water jet propulsion device for a water vehicle, comprising: a main duct having a main inlet that is arranged to be submerged in use and a main outlet; a pump disposed between the main inlet and the main outlet; and an inflatable portion disposed in a position such that the geometry of, or in the region of, the main duct can be altered by the inflation or deflation of the inflatable portion between at least a first configuration and a second configuration. There may be a plurality of inflatable portions that are each inflatable and defiatable between at least first and second configurations. The or each inflatable portion may be a bag. The or each inflatable portion may be located near the main inlet. The or each inflatable portion may form or constitute at least part of a wall of the main duct. The or each inflatable portion may form part of an inclined rear wall. The first configuration may be an inflated configuration and the second configuration may be a deflated configuration. The inflatable portion may be inflated to the first configuration when the water vehicle is operating at high speed, for example more than 20 knots, and the inflatable portion may be deflated to the second configuration when the water vehicle is operating at low speed, for example less than 20 knots. When the inflatable portion is in the first configuration the dimensions, for example a cross-sectional area, of the main duct may be less than when the inflatable portion is in the second configuration. The or each inflatable portion may be inflatable and deflatable between a range of configurations between the first and second configuration. The or each inflatable portion may have a variable volume. The or each inflatable portion may be inflatable with a gas or a liquid.

The inflatable portion may be disposed upstream of the pump towards, or at, the main inlet.

The main duct may be at least partially inclined. The main duct may comprise an inclined upper wall, and may comprise a lower inclined wall. An inflatable portion may form at least part of the inclined upper wall of the main duct and/or an inflatable portion may form at least part of the inclined lower wall of the main duct. An inflatable portion may be disposed adjacent to a wall of the main duct, such as an inclined upper or lower wall, for example. The main duct may comprise an inclined portion and a substantially horizontal portion.

An inclined portion of the main duct may define a main duct lip. The main duct lip may have an upper wall and/or a lower wall and may have a lip edge therebetween. The inflatable portion may form at least part of the main duct lip.

The inflatable portion may form, or may be disposed adjacent to, at least part of the lower wall or the upper wall, or the lip edge of the main duct lip.

The pump may comprise an impeller disposed within the main duct between the main inlet and the main outlet. The impeller may be rim driven.

The pump may comprise a drive shaft arranged to drive the impeller. At least part of the drive shaft may be substantially horizontal or may be inclined, for

example.

The main duct may comprise an impeller duct portion, which may be substantially horizontal, within which the impeller may be disposed. The main duct may further comprise first and second duct portions disposed either side of the drive shaft and having first and second main inlets respectively. The first and second duct portions may be located side-by-side. The first and second duct portions may lead to the impeller duct portion. An inflatable portion may be disposed within each of the first duct portion and the second duct portion. Each of the inflatable portions may be inflatable and deflatable between at least first and second configurations.

The water jet propulsion device may further comprise a pressure pick-up arranged to be submerged in use. The pressure pick-up may be in fluid communication with the inflatable portion so as to be capable of inflating the inflatable portion. The pressure-pick up may be located at or near the main duct lip, such as at or near the lip edge, for example. The use of a pressure-pick up would allow the inflatable portion to be passively inflated.

The inflatable portion may be arranged to be inflated or deflated on the basis of a detected parameter. Sensors may be provided to measure or detect a parameter such as vehicle speed or shaft speed. A controller may be provided that is connected to the sensors and that is arranged to control the inflation or deflation of the or each inflatable portion based on the detected parameter. The inflatable portion may be inflated to the first configuration if the parameter, such as speed, is over (or under) a predetermined threshold, and may be deflated to the second configuration if the parameter, such as speed, is under (or over) a predetermined threshold.

The inflatable portions may comprise a synthetic rubber such as polyethylene, chlorosulfonated polyethylene, polychloroprene, polyvinylchloride, or polyurethane, for example. The inflatable portions may comprise a laminated structure of chlorosulfonated polyethylene and polychloroprene.

The inflatable portion may be inflated with a fluid. The fluid may be a liquid or a gas.

The invention also concerns a water vehicle comprising a water jet propulsion device in accordance with any statement herein.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 schematically shows a previously considered water jet propulsion device; Figure 2 schematically shows a first embodiment of a water jet propulsion device having an inflatable portion which is shown in an inflated configuration; Figure 3 schematically shows the water jet propulsion device of Figure 2 with the inflated portion in a deflated configuration; Figure 4 schematically shows a second embodiment of a water jet propulsion device; Figure 5 schematically shows a third embodiment of a water jet propulsion device; Figure 6 schematically shows a fourth embodiment of a water jet propulsion device; Figure 7 schematically shows a fifth embodiment of a water jet propulsion device; Figure 8 schematically shows a sixth embodiment of a water jet propulsion device having an inflatable portion shown in an inflated configuration; and Figure 9 schematically shows the water jet propulsion device of Figure 8 with the inflatable portion in a deflated configuration.

Figures 2 and 3 show an embodiment of a water jet propulsion device 10 which is integrally part of a water vehicle which in this embodiment is a boat. It should be appreciated that in other embodiments the water jet propulsion device 10 could be a separate device arranged to be attached to a water vehicle. The propulsion device comprises a main duct 12 having a main inlet and a main outlet 16. The main inlet 14 lies in a substantially horizontal plane and is formed in the lower surface of the hull of the boat. In use, the main inlet 14 is submerged underwater. The main outlet 16 lies in a substantially vertical plane and is formed in a rear surface of the hull 18 of the boat. In use, the main outlet 16 is located above the waterline. In the embodiment, the main outlet includes a nozzle.

The main duct 12 comprises an inclined portion 20 and a substantially horizontal portion 22. The inclined duct portion 20 extends from the main inlet 14 rearwards (downstream) and upwards and transitions into the horizontal portion 22 that extends rearwards to the main outlet 16. In other embodiments the main duct 12 may be entirely inclined along its length. The main duct 12 defines a main duct lip 24, the lower surface of which forms part of the hull 18.

The duct lip 24 has a forward-facing lip edge 26 which is also part of the edge of the main inlet 14.

The main duct 12 in this embodiment has a substantially rectangular cross-section and therefore comprises an upper wall, a lower wall and first and second side walls. It should be appreciated that in other embodiments the cross-section of the main duct 12 may be another shape such as circular or oval, for example.

The inclined portion 20 of the main duct 12 comprises an upper wall 28 that is rear-facing and inclined. A recess 30 is formed in this wall 28 and an inflatable portion, which in this embodiment is an inflatable bag 32, is disposed within this recess 30 and is fixedly attached thereto. The inflatable bag 32 can be manufactured from any suitable material. Examples of suitable materials include, but are not limited to, synthetic rubber such as polyethylene, chlorosulfonated polyethylene (CSPE) -Hypalon ®, polychloroprene -Neoprene ®, polyvinylchloride (PVC), or polyurethane (PU), for example. The inflatable portions may comprise a laminated structure of Hypalon ® and Neoprene ®. The inflatable bag 32 has a variable volume which can be inflated and deflated between at least a first high-speed configuration (as shown in Figure 2) in which it has a first high-speed volume, and a second low-speed configuration (as shown in Figure 3) in which it has a second low-speed volume.

The inflatable bag 32 may be inflated or deflated to a volume between the high-speed and low speed configurations. For example, there may be a "standard" configuration that is midway between the high-speed and low-speed configurations. Further, the inflatable bag 32 may be inflated to a volume in excess of the high-speed configuration and deflated to a volume below the low-speed configuration.

The inflation and deflation of the inflatable bag 32 in this embodiment is controlled by a reversible pump (not shown) that is arranged to inflate and deflate the inflatable bag 32 to a particular volume (or pressure). The reversible pump (not shown) can therefore inflate and deflate the inflatable bag between at least the first high-speed configuration (Figure 2) in which it has a first high-speed volume, and the second low-speed configuration (Figure 3) in which it has a second low-speed volume. Although it has been described that a reversible pump is used to inflate and deflate the inflatable bag 32, other methods may be used. For example, the bag 30 may be inflated using a cylinder of gas and deflated by discharging gas from the bag 30 through a valve. Alternatively, the bag 30 could be passively inflated by using a pressure pick-up disposed in the region of the lip edge 26, for example.

The water jet propulsion device further comprises a pump having a ducted impeller 34 which is disposed in the horizontal portion 22 of the main duct 12.

The impeller 34 is mounted to a substantially horizontal rotational drive shaft 36 that passes through the upper wall of the main duct 12 into the interior of the boat. The drive shaft 36 is coupled to a motor (not shown) which is arranged to rotationally drive the drive shaft 36 and hence the impeller 34 about a horizontal axis.

In use, the hull 18 of the boat is partially submerged in water so that the main inlet 14 is submerged. The impeller 34 is rotated about a horizontal axis by the drive shaft 36 and water in the main duct 12 is accelerated by the impeller 34 and forced out of the main outlet 16 as a jet of water which causes the boat to be propelled forwards. The speed of the impeller 34 can be increased or decreased in order to increase or decrease the propulsive force generated by the water jet propulsion device 10.

During use, the inflatable bag 32 can be inflated and deflated between at least the first high-speed configuration (Figure 2) and the second low-speed configuration (Figure 3) in order to alter the geometry of, or in the region of, the main duct 20.

When the boat is travelling at high-speed, which may be considered to be greater than 20 knots, the inflatable bag 32 is inflated to the first high-speed configuration that is shown in Figure 2. This reduces the overall intake area of the main duct 12 and changes the geometry of the upper rearwardly-inclined wall 28. The smaller overall intake area of the main duct 12 results in less water being forced into the main duct and also allows the flow of water to more closely follow the inclined wall 28 (including the outer surface of the inflatable bag 32).

This may reduce the tendency for separation and hence cavitation to occur at position D which is a position in the region of the inclined wall 28 towards the main inlet 14. This may also reduce the tendency for separation and cavitation to occur at position B which is a position on the lower surface of the lip 24 towards the edge 26, and a position C which is a position on the upper wall of the main duct 12 towards the impeller.

When the boat is travelling at low-speed, which may be considered to be less than 20 knots, the inflatable bag 32 is deflated to the second low-speed configuration that is shown in Figure 3. This increases the overall intake area of the main duct and changes the geometry of the upper rearward ly-inclined wall 28. The larger overall intake area of the main duct 12 allows the pump to suck more water into the main duct. This may reduce or eliminate the flow turning of water around the lip 24, this reducing the tendency for separation and hence cavitation to occur at A which is a position on the upper surface of the lip 24 towards the main inlet 14.

The provision of at least one inflatable portion may allow the water jet propulsion device to avoid separation, cavitation and pump face distortion at both low and high speeds. This may extend the operating range of the device, providing improved thrust capability at low and high speeds whilst avoiding damage and low efficiency performance.

Further, the use of an inflatable portion to dynamically change the geometry of the main duct may mean that the inlet design is less of a compromise between high speed and low speed operation. This may allow other areas of the intake to be redesigned to improve the performance at high or low speed.

The inflation and deflation of the inflatable bag 32 (or portion) may be fully externally controlled. The means for inflating and deflating the inflatable bag may be connected to control circuitry (not shown) which in turn is connected to one or more sensors (not shown) that are arranged to detect or measure various parameters. The parameters could be boat speed, pressure levels at a particular point, differential pressure, impeller speed or shaft power, for example.

The control circuitry could be arranged to inflate or deflate the inflatable bag 32 in response to the detected parameter values. For example, if the boat speed is detected as "low" (e.g. less than 20 knots) the inflatable bag 32 could be deflated to the second configuration shown in Figure 3, and if the boat speed is detected as "high" (e.g. greater than 20 knots) the inflatable bag 32 could be inflated to the first configuration shown in Figure 2.

An inflatable portion 32 may be disposed or located at any position in the region of the main duct 12 so that the geometry of the main duct, or in the region of the main duct, can be changed. The or each inflatable portion 32 may be located at positions where cavitation conventionally occurs so that the geometry can be changed depending on the operating condition in order to reduce or prevent cavitation from occurring.

It may be particularly beneficial to locate the inflatable portion 32 at a position within the main duct 12, for example on the upper rearwardly-inclined wall. In such a position the inflatable portion 32 would be protected from damage by debris that the boat may encounter.

Figure 4 shows a water jet propulsion device 10 in accordance with a second embodiment of the invention. The only difference between the first and second embodiments is that the pump comprises a rim-driven impeller 34 and therefore there is no drive shaft. The radially outer ends of the blades of the impeller 34 are provided with permanent magnets 38 and stationary windings 40 are provided on a stationary part of the water jet propulsion device 10. In use, the electromagnetic field generated by the windings 40 interacts with the magnetic field of the permanent magnets 38 which causes the impeller 34 to rotate. The rotational speed of the impeller 34 can be altered by changing the current supplied to the wind ings 40. One of the main benefits of using a rim-driven pump is that a drive shaft is not required. As can be seen from the first embodiment illustrated in Figures 2 and 3, if a drive shaft 36 is used it may extend through the area within which the inflatable bag 32 is disposed. This increases the complexity of the design. Therefore, the use of a rim-driven impeller 34 avoids such complexities.

Figure 5 shows a third embodiment of a water jet propulsion device 10. In this embodiment the drive shaft 36 for the impeller (not shown in this Figure) of the pump is angled such that it extends through the upper wall of the main duct 12 is a position away from the inflatable bag 32. This reduces the design complexity of the inflatable bag 32.

Figure 6 shows a fourth embodiment of a water jet propulsion device 10. In this embodiment there is a bifurcated intake. The main duct 12 comprises an impeller duct portion 42 which is substantially horizontal and within which the impeller (not shown) is disposed, and first and second duct portions 44, 46 that are inclined. The first and second duct portions 44, 46 each comprise a main inlet 14 that is arranged to be submerged in use. The first and second duct portions 44, 46 are located side-by-side and each feed into the impeller duct portion 42. The first and second duct portions 44, 46 each have a rearwardly-inclined wall 28 having a recess 30 within which is disposed an inflatable bag 32.

Each of the inflatable bags 32 is similar to the inflatable bag 32 of the first embodiment and each can be inflated and deflated between at least a first high-speed configuration and a second low-speed configuration. The inflatable bags 32 may be connected to the same control circuitry so that they inflate and deflate in unison or they may be separately controlled.

As in the first embodiment, the impeller (not shown) of the pump is driven by a substantially horizontally extending drive shaft 36. In this embodiment the drive shaft 36 is disposed between the first and second duct portions 44, 46 and therefore unlike the first embodiment, the drive shaft 36 does not have to pass through an inflatable bag 32. This may reduce the complexity of the design.

Figure 7 shows a fifth embodiment of the invention which is similar to that of the first. As in the first embodiment the water jet propulsion device 10 comprises a main duct 12 having a main inlet 14 and a main outlet 16. The main duct 12 comprises a rearwardly-inclined upper wall 28 having a recess 30 formed therein. However, unlike the first embodiment an elastically deformable member 48 covers the recess 30, thereby defining a variable volume inflatable portion 32. The deformable member 48 is sealed to the walls of the main duct 12 and is moveable between at least a first high-speed position (shown in a solid line in Figure 7) and a second low-speed position 48' (shown by a dotted line in Figure 7). The deformable member 48 is moveable between at least these two positions by inflation and deflation of the inflatable portion 32. This allows the geometry of the rearwardly-inclined wall 28 of the main duct 12 to be changed.

As discussed in respect of the first embodiment, this can help to prevent cavitation at various positions in the region of the main duct.

Figures 8 and 9 show a sixth embodiment of the invention which is also similar to that of the first embodiment. As in the first embodiment, the water jet propulsion device comprises a main duct 12 having a main inlet 14 and a main outlet 16. The main duct comprises an inclined portion 20 and a substantially horizontal portion 22 within which is disposed an impeller 34. A drive shaft 36 is arranged to rotationally drive the impeller about a substantially horizontal axis.

The inclined portion 20 of the main duct defines a duct lip 24 having a forward-facing edge 26 which also forms part of the main inlet 14.

The propulsion device 10 further comprises an inflatable portion 32 in the form of an inflatable bag 32 that is attached to, or forms part of, the lower surface of the lip 24. The inflatable bag 32 is disposed towards the lip edge 32 and is inflatable and deflatable between at least a first low-speed configuration (Figure 8) and a second high-speed configuration (Figure 9). The inflatable bag 32 may be inflated and deflated in a similar manner to that described with respect to the first embodiment.

When the boat is operating at low-speed, the inflatable bag 32 may be inflated to a first low-speed configuration (Figure 8) in which it has a first volume.

The inflatable bag 32 therefore changes the geometry of the duct lip 24 in the region of the main inlet 14 of the main duct 12. In this example, the curvature of the lip edge 26 is changed which may reduce the water flow turning around the edge 26, thereby reducing separation and potential cavitation. When the boat is operating at high-speed, the inflatable bag 32 may be deflated to the second high-speed configuration as shown in Figure 9, so as to reduce the volume of water forced into the main duct. This may also reduce or prevent separation and cavitation.

Although it has been described that the inflatable portion is inflated by a gas, it should be appreciated by one skilled in the art that the inflatable portion could be inflated with a liquid. Further, the geometry of or in the region of the main duct can be altered by disposing an inflatable portion in an appropriate position. For example, the side walls of the duct could be changed by the use of appropriately positioned inflatable portions.

Although it has been described that the main outlet is above the water line in use, in some applications the main outlet may be submerged in use.

Claims

CLAIMS: 1. A water jet propulsion device for a water vehicle, comprising: a main duct having a main inlet that is arranged to be submerged in use and a main outlet; a pump disposed between the main inlet and the main outlet; and an inflatable portion disposed in a position such that the geometry of, or in the region of, the main duct can be altered by the inflation or deflation of the inflatable portion between at least a first configuration and a second configuration.
2. A water jet propulsion device according to claim 1, wherein the inflatable portion forms at least part of the wall of the main duct.
3. A water jet propulsion device according to claim 2, wherein the inflatable portion is disposed upstream of the pump towards the main inlet.
4. A water jet propulsion device according to any preceding claim, wherein the main duct is at least partially inclined and comprises an inclined upper wall.
5. A water jet propulsion device according to claim 4, wherein the inflatable portion forms at least part of the inclined upper wall of the main duct.
6. A water jet propulsion device according to claim 4 or 5, wherein the inclined main duct defines a main duct lip having an upper wall, a lower wall and a lip edge therebetween.
7. A water jet propulsion device according to claim 6, wherein the inflatable portion forms at least part of the main duct lip.
8. A water jet propulsion device according to claim 6 or 7, wherein the inflatable portion forms at least part of the lower wall of the main duct lip.
9. A water jet propulsion device according to any preceding claim, wherein the pump comprises an impeller disposed within the main duct between the main inlet and the main outlet.
10. Awaterjet propulsion device according to claim 9, wherein the pump comprises a drive shaft arranged to drive the impeller.
11. A water jet propulsion device according to claim 10, wherein the main duct comprises an impeller duct portion within which the impeller is disposed and first and second duct portions disposed either side of the drive shaft and having first and second main inlets respectively.
12. A water jet propulsion device according to claim 11, wherein an inflatable portion is disposed within each of the first duct portion and the second duct portion.
13. Awaterjet propulsion device according to any preceding claim, further comprising a pressure pick-up arranged to be submerged in use and in fluid communication with the inflatable portion so as to be capable of inflating theinflatable portion.
14. Awaterjet propulsion device according to any preceding claim, wherein the inflatable portion is arranged to be inflated or deflated on the basis of a detected parameter.
15. A water vehicle comprising a water jet propulsion device in accordance with any preceding claim.
16. A water jet propulsion device or a water vehicle substantially as described herein with reference to the accompanying drawings.