WO2012041751A1

WO2012041751A1 - Propulsion unit for propelling watercrafts in general

Info

Publication number: WO2012041751A1
Application number: PCT/EP2011/066436
Authority: WO
Inventors: Aldino Testa; Annamaria Testa
Original assignee: Aldino Testa; Annamaria Testa
Priority date: 2010-09-28
Filing date: 2011-09-21
Publication date: 2012-04-05
Also published as: IT1401976B1; EP2621800A1; ITMI20101764A1

Abstract

A propulsion unit for propelling watercrafts, comprising an impulsive propulsion element (1) which is actuated from outside and is connected to a submerged diffuser (3) associated with a watercraft, the impulsive propulsion element comprising a cylindrical tube (2) provided with means (4) for injecting a dose of fluid into the diffuser, the injection of fluid being provided in alternating steps upon the actuation of pumping means adapted to supply the fluid to the injection means.

Description

PROPULSION UNIT FOR PROPELLING WATERCRAFTS IN GENERAL

Technical field

The present invention relates to a propulsion unit for propelling watercrafts in general.

Background art

As is known, watercrafts are typically provided with a directional propulsion system based on the use of rotating propellers and a rudder. This type of propulsion is undoubtedly disadvantageous, because the propeller has a relatively low efficiency, since the volume of the displaced water mass corresponds approximately to 40% of the generated disk area and depends on the movement of the watercraft.

The efficiency of a good screw, if the vessel proceeds at high speed, may be over 55%; nonetheless, the propeller is used universally because mechanizing a propeller with a rotary engine is relatively simple, whereas, despite many attempts, advantageous mechanization of an oar has never been achieved.

In the case of an oar, the volume of the mass below the oar that has a circular blade is equal to all the blade area, multiplied by 2-3 times its diameter.

Moreover, the use of propellers can have damaging effects for example in the case of watercrafts in shallow waters, or in canals, in which the rotation of the propeller causes problems to the bed and in any case creates waves which, for example in the case of narrow canals, tend to erode the banks of the canal.

As regards for example lagoon sailing, such as for example in Venice, the rotation of a propeller undoubtedly causes problems to the bed and causes erosion problems because of the fact that the mass of water that is displaced, and therefore the wave created, impacts disadvantageously on the banks of the canals, and bounces from them a certain number of times before being finally damped.

This problem is multiplied by the number of watercrafts that sail in the canals, with evident disadvantages.

Italian Patent application MI2004A000060, by the same Applicant, proposes a propulsion unit for propelling watercrafts in general that has the peculiarity of comprising an impulsive propulsion element actuated by a motor assembly and capable of operating on a large mass of water, which thus, by exiting from a submerged and flooded diffuser, deals with the external mass like a 'disposable' oar, accelerating and reacting on the associated watercraft with an equal and opposite thrust.

The diffuser is re-flooded laterally through the wall with each cycle, which wall is unidirectionally permeable from outside.

The solution proposed above, despite being undoubtedly advantageous in comparison to the use of traditional propellers, suffer however some drawbacks due to the fact that the operation on the mass of water is provided by an elastically yielding actuator, which can be compressed so as to reduce its volume by means of the external force that may derive from any type of engine or movement element. This actuator thus acts like a piston. When the speed of the piston decreases, the speed of the impelled mass may easily be higher than the mass of the piston and the mass detached from the ship can no longer react and push the ship.

Disclosure of the invention

The aim of the present invention is to provide a propulsion unit for propelling watercrafts in general that makes it possible to obtain an optimum propulsion which is particularly effective from the point of view of efficiency, where the formula of efficiency is 2VN/(VN+VE), where VN is the speed of the watercraft and VE is the speed of the external water mass measured at the outlet of the diffuser.

Within this aim, an object of the present invention is to provide a propulsion unit in which propulsion occurs in a fluid and homogeneous manner.

Another object of the present invention is to provide a propulsion unit for propelling watercraft that can be obtained easily starting from commonly commercially available elements and materials and is also competitive from a merely economic point of view both as regards the provision of the propulsion unit and as regards operating costs.

This aim, as well as these and other objects that will become better apparent hereinafter, are achieved by a propulsion unit for propelling watercrafts, comprising an impulsive propulsion element, which is actuated from outside and is connected to a submerged diffuser associated with a watercraft, characterized in that said impulsive propulsion element comprises a cylindrical tube provided with means for injecting a dose of fluid into said diffuser, said injection of fluid being provided in alternating steps upon the actuation of pumping means adapted to supply said fluid to said injection means.

Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of the propulsion unit according to the present invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a schematic view of the propulsion unit according to the present invention;

Figure 2 is a view of the propulsion unit according to the invention in the inactive step;

Figure 3 is a chart which plots, on the axis of the abscissas, the flow as a function of time;

Figure 4 is a chart related to the thrust cycle;

Figure 5 is a schematic view of the propulsion unit according to the invention, for mathematical purposes; Figure 6 is a view of a step of the operation of the propulsion unit according to the invention;

Figure 7 is a view of a further step of the operation of the propulsion unit according to the invention;

Figure 8 is a view of the inactive step of the propulsion unit according to the invention.

Ways of carrying out the invention

With reference to the figures, the propulsion unit for propelling watercrafts according to the invention comprises an impulsive propulsion element, generally designated by the reference numeral 1, which is constituted conveniently by a cylindrical tube 2 that leads into a diffuser 3 whose surface is constituted, for example, by a spirally arranged lamina, which in practice provides a one-way valve that prevents the passage of water from the inside of the diffuser body toward the outside through the lateral surface.

The cylindrical tube 2 is provided internally with at least one means for injecting water that arrives from pumping means actuated, for example, by a piston crank system. The pumping means are not shown in the figures and can be constituted, for example, by a high-pressure dosage pump. The dosage pump should be capable of providing, with a pressure of at least 15 atm, more than five liters of water at least three times per second. Each dose provided by the pump has enough kinetic energy to push, entrain and discharge all the ducted mass of water.

In practice, the divergent part (diffuser) is perfectly permeable from the outside and therefore is re-flooded in the same time during which the ducted flow is discharged. In this way the propulsion unit returns to the initial conditions at the end of each action.

The at least one nozzle is designated by the reference numeral 4.

The cylindrical tube and the corresponding diffuser 3 are designed to be arranged in a submerged position, connected to the hull of the watercraft. With the configuration described above it happens that, by injection of the dose of water with sufficient energy by means of the at least one nozzle 4, into the outflow port of the diffuser 3, which is submerged and flooded, all the water contained in the cylindrical tube 2 and in the diffuser 3 is accelerated. Since water is incompressible, by dosing the volume and speed of the injected water a propelling mass is obtained that has all the energy required to expel in a single stroke all the water contained in the diffuser, because the propelling mass, by adhering directly to the conical wall of the diffuser 3, pushes and entrails for action, as if it were an "expendable" oar, the external mass that faces the outlet of the diffuser.

The pumping means that send to the nozzle the water to be injected, actuated by a piston crank system, cause the water to be expelled cyclically at the nozzle, following only the positive half-axis of the speed, according to the trend shown in Figure 3.

A single thrust cycle is thus represented by a step of expulsion of the water jet from the nozzle and a step in which the nozzle is inactive (but the cylindrical portion and the diffuser continue to "work" in order to facilitate thrust).

In the chart of Figure 4, three steps have been highlighted which relate to three precise motion regimes that are established inside the propulsion unit and are fundamental for understanding the phenomenon:

- step I ("potential" step): this is a step of short duration, totally independent of the shape of the nozzle, in which the flow follows ideal flow lines and the motion regime contains neither viscous effects nor rotational effects.

- step II (vortical step): because of the effect of the gradients of pressure and viscous entrainment, one or more vortical recirculation structures are created proximate to the nozzle 4 and are deformed and elongated during the emission but remain substantially unchanged in their function of perturbation of the field of motion. - step III (inactive step): the entire capacity of the pump has been expelled, the flow retains its own inertia and the membranes (which form the spirally arranged lamina) on the diffuser open, facilitating the passage of the external water.

These three steps will be explained in detail hereinafter.

The motion regime that is established in the "potential" step of the propulsion unit can be fully likened to a non-rotational non-viscous flow (hence the name "potential").

It is possible to infer governing rules for this step by applying the equations of conservation of mass and momentum to the diagram of Figure 5.

The equations used start from the Navier-Stokes equation. The first is the equation for conservation of mass: p _l ' U_l ' A_l + p₂- u₂- A₂ = p_Q ' ₀'A_Q which, derived with respect to time, does not lose its meaning and leads to: p , · w, · Α_ι +ρ₂· ύ₂· Α₂= ρ₀'ΰ₀Ά₀ [ ΐ]

The second equation is the conservation of momentum, in differential form, simplified for the ID, incompressible, non-viscous case:

d t p d x ^{1 J}

Only this equation states that, for a flow that is accelerated, a pressure gradient is established in the direction opposite to said acceleration. If the tube is straight, the pressure gradient is linear, whereas inside a diffuser the pressure drop varies according to l/χ, therefore decreasing while flowing through the diffuser.

The pressure gradient along the portion 2 and 3 is given by:

By solving equation [1] using relations [3] and [4] (and the link given by [2]) it is possible to evaluate how the acceleration imparted to section 0 is distributed to sections 2 and 3. In particular:

h. t [6]

In the first step of injection of the water flow into the tube, therefore, part of the liquid will always and inevitably exit from the inlet and, with equal inlet and outlet areas, the reverse flow at the inlet will be greater (thus unfavorable for use for propulsion) as the portion from the inlet to the nozzle shortens.

Moreover, the constant acceleration of the fluid ensures that an overpressure is maintained inside the diffuser, keeping the membrane closed.

As soon as the flow that exits from the nozzle gathers speed, because of the gradient differing with the external flow, it tends to form a well- structured vortical structure.

The presence of the vortical structure interrupts the potential flow described previously, establishing a new regime which is definitely interesting: the acceleration imparted by the nozzle goes completely in the direction of the diffuser, with the addition of a "suction" contribution in the inlet given by the vortical structure, resulting in an acceleration at the outlet that is greater than the one that was introduced.

Given in any case a negative pressure Pd, the acceleration of the fluid at the inlet is:

which, together with the mass acceleration balance [1], gives an acceleration that exits from the cylindrical portion equal to: p A₂ p A₂ L_d

Again, the flow of the diffuser 3 is accelerated, keeping the membranes closed.

This condition is maintained until the vortical structure reaches the inlet of the diffuser (or if in the meantime the injection has ended); upon reaching the vortex (negative pressure) in the diffuser, the external pressure becomes higher, opening the membranes and drawing external water.

In this step, the acceleration contribution exiting from the cylindrical portion becomes greater as the portion before the nozzle becomes shorter, contrary to what happened in the "potential" step. It is necessary, therefore, to find the best compromise between these two steps.

In the step in which the pump is aspirating, the nozzle 4 is closed. The water, accelerated in the cylindrical portion 2, proceeds by inertia, while the water that leaves the diffuser 3 draws an equal flow inside it, opening the membranes, as shown in Figure 8.

It has thus been found that the water discharged suddenly, contained, compacted and directed by the inlet duct, behaves for an instant like a solid body, and exactly like an oar faces, pushes and entrains the adjacent external mass, pushing, by reaction in the opposite direction, the diffuser and the associated watercraft, with an equal and opposite force. The duration of the thrust is shorter than that obtained from an oar, but the thrust can be repeated with the most suitable frequency and intensity, so as to achieve a practically continuous thrust. In order to obtain this, the diffuser must always be available, i.e., always perfectly flooded.

The perfect one-way permeability of the diffuser 3, obtained for example by means of an elastomeric tape a few centimeters wide, anchored on one side to a steel profile, free to oscillate and vibrate, makes it possible to provide in practice a one-way valve which is integral and active over the entire surface of the wall; moreover, there are no mechanical losses and any hydraulic losses are negligible because they are discharged in the opposite direction to the motion of the watercraft.

The discharged mass flows out silently, without turbulence or cavitation and the fluid threads remain practically parallel, with the possibility of repeating the pulses frequently, thus involving a substantial water mass which, for slow watercrafts in shallow waters or in canals, when the propeller has an excessively low efficiency, gives the opportunity to obtain an energy saving of even more than 50%.

In practice it has been found that the propulsion unit according to the invention fully achieves the intended aim and objects, since it is particularly suitable for use at low speeds, with substantially no environmental impacts.

The propulsion unit thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

All the details may further be replaced with other technically equivalent elements.

In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to requirements and to the state of the art.

The disclosures in Italian Patent Application No. MI2010A001764 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A propulsion unit for propelling watercrafts, comprising an impulsive propulsion element (1) which is actuated from outside and is connected to a submerged diffuser (3) associated with a watercraft, characterized in that said impulsive propulsion element comprises a cylindrical tube (2) provided with means (4) for injecting a dose of fluid into said diffuser, said injection of fluid being provided in alternating steps upon the actuation of pumping means adapted to supply said fluid to said injection means (4).

2. The propulsion unit according to claim 1, characterized in that said pumping means are actuated by a piston crank system.

3. The propulsion unit according to claim 1, characterized in that said diffuser (3) comprises a semipermeable diverging portion.

4. The propulsion unit according to one or more of the preceding claims, characterized in that said injection means comprise at least one nozzle (4) for the injection of said dose of fluid.

5. The propulsion unit according to one or more of the preceding claims, characterized in that said diffuser (3) has a lateral surface that is adapted to allow the passage of water from the outside toward the inside of said diffuser.

6. The propulsion unit according to one or more of the preceding claims, characterized in that said diffuser (3) has a lateral surface that is constituted by a spirally arranged lamina, which substantially provides a one-way valve that is adapted to allow the passage of water from the outside of said diffuser to the inside of said diffuser and to prevent the passage of water from the inside of said diffuser toward the outside through said lateral surface.

7. The propulsion unit according to one or more of the preceding claims, characterized in that said cylindrical tube (2) that leads into said diffuser (3) is adapted to be connected in a submerged position to the hull of a watercraft.