Description

Nautical propulsion system for surface and/or underwater navigation

Technical Field

The present invention relates to a nautical propulsion system for surface and/or underwater navigation.

In more detail, the invention relates to a propulsion system of said type, with the direction of the primary flow at a right angle to the direction of the induced secondary flow, having a thrust which can be angled through 360° in the azimuth plane for surface and/or underwater navigation.

Background Art As is known, obtaining a propulsive thrust force derived as a reaction from the action of expulsion of a fluid jet in conformity with the third principle of dynamic systems, has for more than fifty years allowed the construction of jet propulsion systems and in the naval sector the construction of water jet propulsion systems, in the various forms with axial pumps, with acceleration of the immersed jet for small and medium flow rates, with high-powered centrifugal pumps with the discharge nozzle out of the water.

Such systems have allowed high navigation speeds to be achieved. In particular, use of these propulsion systems in the naval sector brings many advantages, including the absence of bottom projections, reduced system weight, greater manoeuvrability and high speed efficiency with greater accelerations.

However, the solutions produced until now for propulsion with water jet propulsion systems have several disadvantages, including extensive generation of very considerably vorticose washes, with the possible formation of abnormal waves which spread even a long way from the boat.

Moreover, the water jet propulsion system requires water intakes with a very large intake cross-section, intakes close to the surface which, in certain navigation conditions, may suck in air, thus compromising system efficiency. Moreover, good operating efficiency can only be achieved within a very limited range of speeds. Finally, due to their intrinsic operating features, water jet propulsion systems have a high acoustic signature.

Disclosure of the Invention

The aim of the present invention is therefore to provide a nautical propulsion system which allows the above-mentioned disadvantages to be completely or partly overcome.

In the solution proposed according to the present invention the water delivery flow rate for the pumps consists only of a fraction of the flow rate coming out of the diffuser, due to the significant amplification effect between the two flows.

With the solution disclosed, propulsion is characterised by the absence of vorticose washes and the lack of cavitation phenomena, with low acoustic signature. The propulsive thrust may be angled between 0° and 360° in the azimuth plane, making the boat highly manoeuvrable even without rudders. The technical features of the invention according to the above-mentioned aim may be easily inferred from the contents of the claims herein, especially claim 1, and any of the claims that depend, either directly or indirectly, on claim 1.

Therefore, the present invention relates to a nautical propulsion system for surface and underwater navigation, comprising a unit for feeding a delivery or primary flow which comprises an internal combustion engine, a pump driven by the internal combustion engine, and which sucks the fluid directly from the propulsion system by means of an intake through a rotary joint positioned on a foot of the nautical propulsion system. The thrust force is generated by the delivery or primary flow, having a flow rate which is a fraction of the flow coming out of the nautical propulsion system, the delivery flow inflow duct being able to

rotate along a 360° arc in the azimuth plane perpendicular to the nautical propulsion system thrust axis.

In accordance with the invention, said internal combustion engine is preferably a diesel engine or a turbine engine. Also according to the invention, the intake is an annular water intake, in particular downstream of the infeed edge for the fluid current which passes through the propulsion system.

According to the invention, the intake flow passage is coaxial with the primary flow inflow passage. Also according to the invention, there are, in series, along the duct between the pump and the propulsion system, a hydraulic accumulator with floating piston, a valve with modulating opening, and an elastic joint device for damping the oscillation of the fluid passing through.

Also according to the invention, the system for primary flow inflow is regulated by a sliding shutter, the shutter sliding axially between two positions, respectively close to the infeed edge and close to the throat of the duct for the passage of the propulsive thrust.

In particular, the inflow angle through the sliding shutter in the position close to the infeed edge varies between 90° and 20°, preferably between 70° and 30°, and even more preferably 45°.

Moreover, the inflow angle through the sliding shutter in the position close to the throat section of the propulsion system varies between 50° and 10°, preferably between 40° and 20°, in particular 30°.

Also according to the invention, the movement of the shutter which slides axially between two positions is obtained by means of two actuator pistons connected to a disk cam which transmit the motion to the shutter through a closed hydraulic circuit.

Also according to the invention, the diffuser has a cone angle of between 4° and 30°, preferably equal to 10°. Again according to the invention, the diffusion cone from the throat section

towards the outfeed edge has Riblet surface working, consisting of a plurality of small axial channels separated by small radial grooves, which promote the adherence of the boundary layer of the flow passing through.

Also according to the invention, at the end zone close to the outfeed edge the surface of the propulsion system diffuser skirt has a configuration with micro- holes in it.

Also according to the invention, there is a modulating valve with proportional opening between the end zone boundary layer intake duct and the propulsion system delivery pump intake duct.

Brief Description of the Drawings

The present invention is now described, by way of example and without limiting the scope of the invention, with reference to the accompanying drawings which illustrate preferred embodiments of it, in which: Figure 1 is a schematic view of an embodiment of the nautical propulsion system apparatus in accordance with the invention;

Figure 2 shows a detail of the propulsion system apparatus of Figure 1; Figure 2a is an enlarged cross-section of a portion of the detail from Figure 2; and Figure 3 shows a second embodiment of the detail from Figure 2.

Detailed description of the preferred embodiments of the invention

With reference to Figure 1, the numeral 100 denotes as a whole a nautical propulsion system apparatus made in accordance with the present invention. Figure 1 is a schematic overview of the nautical propulsion system apparatus

100 comprising a propulsion system body 101 and a unit 1 for feeding a delivery or primary flow to the propulsion system body 101.

The feed unit 1, comprises an engine 2 which drives the axial rotation of a pump 3 which sucks water directly from the propulsion system body 101 through the annular intake 4, by means of the rotary hydraulic joint 5.

In the preferred embodiment illustrated in Figure 1, the engine 2 is a diesel internal combustion engine but, in alternative embodiments not illustrated, without departing from the scope of the inventive concept, the engine 2 may be a turbine internal combustion engine or an electric motor. The pump 3 delivery flow, indicated in Figure 1 with arrows Fl, passes through a filter 6 which serves the dual purpose of filter, to avoid any blockages in the circuit, and acoustic insulation element.

The apparatus 100 also comprises an accumulator device 7 positioned downstream of the filter 6 relative to the direction of flow Fl, the accumulator device 7 acts as a damper, levelling out pressure peaks, varying the stroke A of the floating piston 102, based on the counter-pressure Pk in a pressure chamber 103 filled with nitrogen.

The unit 1 is suspended by an apparatus, not illustrated, with elastic joints, rubber supports and steel springs, so that the system impedance prevents resonance.

Then the delivery flow Fl enters a chamber 8 in which there is a pin 9 which, with a modulated stroke along its longitudinal axis, regulates the flow rate Qm at the pressure Pm.

The delivery flow Fl, with flow rate Qm, then passes through a special chamber 10, having one wall consisting of an elastic membrane integral with the core 11 on which the pulsing electromagnetic force of a solenoid 104 acts. The solenoid 104 is driven, by a computerised control unit 105, with opposite timing to that of the vibrations emitted by the propulsion system body 101 at the outfeed end U and detected by an acoustic sensor 12, cancelling out the amplitude of vibration. Longitudinally opposite the outfeed end U, the propulsion system body

101 has a second, infeed end E.

An elastic joint 13 guarantees that the propulsion system is isolated from the downstream devices.

Downstream of the elastic joint 13 there is a curved connecting element 106 at the end of which there is a rotary joint 14 for connecting the curved element 106

and a straight duct 107, extending longitudinally according to a substantially vertical axis X. The stretch of straight duct 107 is connected to the propulsion system body 101 and is integral with it.

The rotary joint 14 allows the propulsion system body 101 to rotate about the axis X through an angle ω (from 0° to 360°), the angle and the rotation of the body 101 providing the direction of navigation. The rotation is driven by the motor 15 by means of gears 16 and 17, of which the wheel 16 is integral with the motor 15 whilst the wheel 17 is integral with the straight duct 107.

Figure 2 shows a first embodiment with variable geometry of the propulsion system body 101, in which the delivery flow Fl, or inductor primary flow, enters the propulsion system body 101 whose parts labelled 101a, 101b, 101c and lOle are fixed, whilst the shutter 101d can be moved by a hydraulic device 18, between two limit positions Cl and C2, depending on the speed of navigation.

The movement of the shutter 101d which slides between its two positions Cl, C2 is obtained by means of two actuator pistons Dl, D2 connected to a disk cam D3 which transmit the motion to the shutter 101d through a closed hydraulic circuit.

As illustrated in Figure 2, the shutter 101d can move between the forward position Cl, illustrated in the lower section of the body 101, and the back position C2, illustrated in the upper section of the propulsion system body 101.

Figure 2 therefore illustrates in a single drawing, for the sake of simplicity, two different shutter 101d positions.

With the shutter 101d in the position C2, the port 01 is open and the delivery flow Fl inflow is into an annular area of the body 101, at an angle α to the axis CL of the propulsion system body 101.

With the shutter in the position Cl, the port 02 is open, and the delivery flow Fl inflow occurs at an angle β in the intermediate positions between Cl and C2.

The delivery flow Fl enters partly at the angle a. and partly at the angle β, with a hydrodynamic behaviour equivalent to that of a delivery flow Fl at an

intermediate angle φ between Oi and β.

The angle φ is therefore defined as α≤ φ ≤β.

The optimum shutter 101d position is determined by the instantaneous value of the navigation speed V _n . For any inflow angle φ value, the delivery flow Fl is positioned in such a way that it is adherent to the wall, applying a pulling action for the rest of the fluid current in the throat area φg. The vacuum zone -P induced by the primary flow draws the induced secondary flow Qe at the speed Ve.

Inside the propulsion system body 101 there is a diverging duct 108, delimited by a propulsion system body 101 inner skirt 109.

The diverging duct 108 is set at an angle θ to CL and constitutes a diffuser duct for the total flow (flow rate of the delivery flow Qm + flow rate of the induced flow Qe) at outfeed at the speed Vu at the pressure +P which generates the propulsive thrust Nw. As illustrated in Figure 2a which shows, in a cross-section according to a plane transversal to the axis CL, a portion of the inner skirt 109, at the end part 10 Ie of the body 101, the skirt 109 has ribbing formed by a plurality of longitudinal grooves 110.

The grooves 110 have a depth h with average pitch π and radii of curvature at the top pe. Said ribbing is known in modern fluid-dynamics with the name "riblet", and keeps the inductor primary flow layer adherent as far as the outfeed of the diffuser duct 108, increasing the gain of the propulsive thrust Nw.

The propulsion system body 101 thrust, as well as rotating through the azimuth angle ω, can oscillate with a round angle in the plane perpendicular to it. In other words, the propulsion system body 101 may advantageously be allowed to oscillate according to two straight lines between perpendicular lines lying in a plane perpendicular to the axis X whose line in the plane of the drawing is represented by the longitudinal axis CL.

Figure 3 shows a second embodiment of the nautical propulsion system disclosed, in which the delivery flow Fl with flow rate Qm enters the propulsion system at a right angle to the longitudinal axis CL and comes out in the annular area Ig with a fixed angle of inclination α, positioned so that it adheres along the wall 19 which, in the stretch 19', similarly to what was described above relative to Figure 2, is worked with riblets, that is to say, has longitudinal grooves 110.

In such conditions, the primary delivery or inductor flow Fl, remaining adherent to the wall 19, applies a pulling action for the rest of the fluid current in the throat 20 area. The vacuum zone -P, induced by the primary flow, draws the induced secondary flow Fe with flow rate Qe.

The significant total flow (Qm+Qe) which generates the propulsive thrust Nw, in high installed power propulsion systems according to the invention creates high efficiency values for much greater diverging duct angles a.

This brings the risk of possible detachment of the pulling fluid layer: to prevent that from happening, the diffuser skirt 109, at its end zone 21, has a plurality of small holes 111 with predetermined diameter and pitch.

The zone 22 of the inner skirt 109 at the back is sucked by the duct 112 connected to the pump 3, with a flow rate Qa regulated by a modulating valve, of the known type and not illustrated, with proportional opening. The modulating valve, referred to and not illustrated, is designed to guarantee in any operating condition the minimum vacuum gradient (minimum Qa) necessary to keep the current adhering to the diffuser duct 108 from which the flow Fu comes out, with flow rate Qu = Qm + Qe - Qa.

Similarly to the embodiment in Figure 2, the embodiment in Figure 3 can rotate through the angle ω about the axis X of the straight duct 107 (0° - 360° in the azimuth plane), and can oscillate with a round angle in the plane perpendicular to it.

The propulsion system apparatus with primary flow at a right angle to the induced secondary flow disclosed was tested in a cavitation channel, on test tank models and actual-size prototypes. It operates with a delivery water flow rate

which is a fraction of between 1/3 and 1/15 of the flow rate coming out of the diffuser nozzle.

In the two different embodiments illustrated, the boundary layer adheres along the diffuser duct of the propulsion system body 101. The embodiment in Figure 2, with decreasing propelling jet inflow angles, depending on the speed (variable geometry), is suitable for high navigation speeds (up to 60 - 70 knots) for low and medium installed power in the optimum range of between 20 and 600 kW.

In contrast, the embodiment in Figure 3 is advantageous for medium navigation speeds from 12 to 25 knots, with high installed power, from 300 to 3000 kW.

The propelling jet inflow angle is constant, since the nozzle is fixed. In the end part of the diffuser duct the boundary layer is sucked by a surface with holes made in it, the suction created by the pump and its flow rate modulated by a special regulating valve, not illustrated.

In both embodiments illustrated, the propulsion system operating principle is the same: the two flows, respectively the primary flow and the secondary flow, cross one another vectorially with a very high amplification ratio, and with very limited delivery pump intake water flow rate compared with the flow coming out of the propulsion system (on average 10 times less).

The advantages obtained with the propulsion system apparatus 100 disclosed may be summarised as follows:

- obtaining any angle in the azimuth plane (from 0° to 360°), with the possibility of also oscillating in the plane perpendicular to it; - absence of moving parts for creating the propulsive thrust (the induced flow passes through the delivery duct of the pump fitted);

- availability of a vast range of navigation speeds with maintained efficiency, unlike water jet and propeller propulsion systems which have a very limited optimum range; - high level of boat manoeuvrability, both two-dimensional and three-

dimensional, with the possibility of precisely maintaining hovering (which is impossible in propeller propulsion systems without the aid of control surfaces and rudders);

- absence of vorticose washes at the nozzle outfeed and drastic reduction of cavitation phenomena, with consequent low acoustic signature;

- possibility of passing from maximum thrust to null value and vice versa in a fraction of a second (impulse capacity);

- reduced weight and dimensions, with the possibility of telescopic mounting for the propulsion system; - when applying the propulsion system on underwater vehicles (underwater robots and submarines) with the installation of two propulsion systems and without the aid of any other apparatus, it is possible to achieve predetermined values for the pitching, rolling and yawing moments irrespective of the navigation speed. The present invention is described by way of example only, without limiting the scope of application, according to its preferred embodiments, but it shall be understood that the invention may be modified and/or adapted by experts in the field without thereby departing from the scope of the inventive concept, as defined in the claims herein.