EP3002208A1

EP3002208A1 - Improved air introduction device

Info

Publication number: EP3002208A1
Application number: EP15185083.1A
Authority: EP
Inventors: Daniele Maria Bertin
Original assignee: Calzoni SRL
Current assignee: Calzoni SRL
Priority date: 2014-10-03
Filing date: 2015-09-14
Publication date: 2016-04-06
Anticipated expiration: 2035-09-14
Also published as: KR20160040430A; AU2015227468A1; KR102408925B1; US20160096603A1; EP3002208B1; AU2015227468B2

Abstract

Described is a device for introducing an air flow (F) into a submarine (1), comprising a first duct (3) which is fixed relative to the hull of the submarine and a second duct (4) which is telescopically movable relative to the first duct (3), for emerging from the water with its upper end (4a) and allowing the air above to be sucked in while the submarine (1) is running at periscope depth, the first and second ducts (3, 4) being in fluid connection with air sucking means and being at least partly housed in a tower (5) of the submarine.

Description

This invention relates to a device for introducing air.
The invention applies generally to the naval (or nautical) sector and, more specifically, to the production of military submarines, where these devices are universally known as snorkels.
In this description the term "snorkel" and its definition as "air intake device" will be used without distinction.
Submarines are equipped with snorkels since it is necessary to provide them with an atmospheric air exchange intake in order to reduce the rate of CO2 present inside them.
In the case of the so-called conventional submarines, this air exchange is necessary for the operation of the internal combustion engines used for the propulsion and the electricity generation.
For the introduction of air inside the submarine when the vessel is submerged, a duct is generally used, known as snorkel, which is extended by the submarine towards the surface of the sea in order to collect the air from above the surface.
A relative upper end of the snorkel is equipped with a servo-contolled valve which is closed if it necessary to prevent the entry of water. This may occur when the sea level increases due to wave motion.
The introduction of the air from the outside towards the inside of the submarine occurs by the negative pressure created by the internal combustion engine (in its suction stage) and generally speaking by the apparatuses inside the submarine.
The sizing of the ducts depends on the requirements, in terms of flow rate and pressure, of the submarine and typically must minimise the pressure head losses compared with the atmospheric pressure.
In order to minimise head losses, snorkel ducts are commonly made with large diameters.
However, the large dimensions of the snorkels result in significant drawbacks for operation of the submarine in a military context.
A first drawback in the use of large snorkels is its visibility at sea level by observers of enemy forces.
The visibility relates basically to the emerged part of the snorkel which may be observed visually by visible spectrum and infrared video cameras and also by radar.
However, the visibility relates indirectly to the mass of raised water, the foam, and the consequent wake produced.
Further drawbacks depending on the significant dimensions of the snorkel concern its movement, which requires lifting power and implies high strength requirements for its supporting structure. This resistance is due mainly to the load produced by the water on the duct when the submarine is moving.
In order to overcome the above-mentioned drawbacks of the prior art, attempting, therefore, to obtain reduced dimensions of the snorkel, consideration has been given to the on-board system, providing an additional suction system in the submarine designed to increase the flow of air drawn inside.
This system supplies the diesel engine and supplies air to the inside environment of the submarine at atmospheric pressure. A solution of this type is described in patent application No. AU 2013100080 .
Basically, this solution is applied in the air introduction system of the submarine by inserting one or more air ventilation or compression stages and thus increasing the suction capacity of the snorkel, which can consequently have a smaller cross section.
Even though the solution according to the above-mentioned document at least theoretically allows a greater air flow rate to be obtained, it implies considerable complications both of a constructional type and with regards to its operation.
In effect, in order to obtain the above-mentioned increase in air flow rate, operations are planned on the air treatment system, thus making not only the design and management more complex and articulated but also any modernisation of unit which are already equipped with an on-board system.
The aim of this invention is to provide a device for introducing an air flow inside a submarine which is free of the above-mentioned drawbacks and is, at the same time, structurally simple and practical and effective to use. A further aim of this invention is to provide a method for controlling the air flow introduced inside a submarine through a snorkel which is practical and inexpensive to implement.
The technical features of the invention according to the above-mentioned objects may be easily inferred from the contents of the appended claims, especially claims 1 and 6, and, preferably, any of the claims that depend, either directly or indirectly, on these claims.
The advantages of the invention are more apparent from the detailed description which follows, with reference to the accompanying drawings which illustrate a preferred, non-limiting example embodiment of the invention and in which:

Figure 1 shows a schematic side elevation view, with some parts in cross section, of a portion of a submarine equipped with a device for introducing an air flow made according to this invention;
Figure 2 shows a schematic graphical representation of a relationship between quantities described herein;
Figure 3 shows a schematic side elevation view, with some parts in cross section, of a portion of a submarine equipped with a variant embodiment of the device of Figure 1;
Figure 4 shows a schematic side elevation view, with some parts in cross section, of a portion of a submarine equipped with a further variant embodiment of the device of Figure 1;
Figure 5 shows a schematic plan view from below of the portion of Figure 4;

As illustrated in Figure 1, the reference numeral 1 denotes a submarine navigating at periscope depth, moving forward in the direction indicated by the arrow D.
The submarine 1 is equipped with a device 2 for introducing an air flow F.
The device 2 is therefore designed to introduce an air flow F inside the submarine 1 and comprises a first duct 3 fixed relative to the hull of the submarine 1 and a second duct 4 which is telescopically movable relative to the first duct 3 along a direction X substantially perpendicular to the direction of travel of the submarine 1.
The second movable duct 4 is designed to emerge from the water with a relative upper end 4a and allow suction of the air above, during the above-mentioned navigation of the submarine 1 at periscope depth.
The submarine 1 comprises a tower 5 and the first fixed duct 3 and the second movable duct 4 are housed inside the tower 5.
With regard to this specification, when the first and second ducts 3, 4 are considered together, they are also known as snorkels and are labelled with reference numeral 6.
The tower 5 also houses an actuator, schematically illustrated in Figure 1 with a rod 7, for lifting the second movable duct 4 relative to the first fixed duct 3.
The first fixed duct 3 and the second movable duct 4 are put in fluid connection with air suction means present in the submarine, of substantially known type and not illustrated in the accompanying drawings or described in further detail.
The second movable conduit 4 has a transversal cross section A1.
The cross section A1 substantially represents the working section of the second duct passed through by the air flow F.
The device 2 comprises a fan 8 operating on the above-mentioned snorkel 6 and acting on an air flow F entering from the outside towards the inside of the submarine 1 through the snorkel 6.
Advantageously, according to the preferred embodiment illustrated in Figure 1, the fan 8 is of the axial type.
According to variant embodiments not illustrated, the fan is of the helico-centrifugal type.
The fan 8 is advantageously positioned at the first fixed duct 3 basically since the fixed duct 3 normally has a transversal cross section which is greater than A1 of the movable duct 4 which slides telescopically inside it and this greater cross section is without doubt useful for the purposes of housing the fan 8 without excessively feeling the effects, for reasons of aerodynamic efficiency, of the central nose-piece which these fans 8 normally have.
The fan 8 is advantageously positioned at the first fixed duct 3, due also to the fact that in this way no movement of the fan 8 is required. Alternatively, according to variant embodiments, not illustrated, the fan 8 is positioned at the second movable duct 4, with the drawback, however, of having to move the fan together with the movable duct 4, with a consequent increase in size and costs resulting from the complication of the apparatus.
The fan 8 is operatively separate from the above-mentioned and not illustrated air suction means present in the submarine 1 and, in terms of fluid connection, positioned in series relative to them.
Advantageously, in other words, the control of the fan 8 is independent of the user system positioned downstream.
Moreover, the control of the fan 8 is advantageously rendered automatic by setting up a suitable control law depending on the operation of the snorkel 6.
In effect, since in general the different modes of operation of the submarine 1 can result in the need for different values of the flow rate of the air flow F passing through the snorkel 6, a law which depends on the flow rate may render the snorkel 6 available for operation for any user system.
The introduction device 2 also comprises a sensor 9 indicating operating parameters of the air flow F flowing through the snorkel 6. Advantageously, in the preferred embodiment illustrated in Figure 1, the sensor 9 is a pressure sensor and is positioned close to a lower end 4b of the movable duct 4.
The device 2 comprises a command and control unit 10 which is connected to the sensor 9 and to the fan 8.
Downstream of the fan 8, in the direction of the air flow F introduced through the snorkel 6, the device 2 comprises a water sealing valve 11, designed to prevent the entry of water inside the submarine 1 with the air flow F.
Advantageously, the management (or control) of the fan 8 is automatic, linked to measurements of pressure (or flow rate), in such as way as to reproduce the operation with a larger intake duct and, therefore, with lower pressure losses.
In other words, the fan 8 is controlled in terms of number of revolutions, in such a way that a user system located downstream (suction means and air treatment not illustrated) perceives a flow F of air introduced, equivalent to that coming from a larger snorkel, that is to say, with the flow rate/pressure link of the latter.
Advantageously, in the preferred embodiment illustrated in Figure 1, the command and control unit 10 operates the fan 8 as a function of the pressure values measured by the sensor 6.
The operation of this command is described below.
Reference is made to a generic duct comprising a plurality of stretches and various narrowings to obtain a relationship, along the duct, of the pressure/flow rate link.
The loss of pressure along a generic stretch of the duct, with the simplifying assumption of incompressible fluid in consideration of the low pressure jumps and the low fluid speed, can be described as follows: $δ P_{i} = \frac{1}{2} ρ \frac{K_{i}}{A_{i}^{2}} Q^{2}$
Where:

Ki is a coefficient - relative the i-th stretch - which depends on Re (Reynolds number) and the geometrical shape
p is the air density
Ai is the area of the cross section of the i-th stretch
Q is the volumetric flow rate.

In a duct A consisting of a certain number of stretches, the pressure may be expressed as follows: $δ P_{A} = \frac{1}{2} ρ \sum_{i} \frac{K_{i}}{A_{i}^{2}} Q^{2} = H_{A} Q^{2}$
A duct B characterised by a smaller cross section in at least a part of its stretches will have a greater head loss due to: $δ P_{B} = H_{B} Q^{2}$
The characteristic of a duct C with the addition of a fan relative to the duct B may illustrated as follows: $δ P_{C} = H_{B} Q - f (N_{f}, Q)$
Where f is the characteristic pressure/flow rate of a fan which depends on the parameter Nf, number of revolutions.
To reproduce the characteristics of a duct A, the number of revolutions Nf of the fan must be controlled as a function of the flow rate Q, in such a way that the following equation is satisfied for each Q: $δ P_{C} = H_{B} Q^{2} - f (N_{f}, Q) = H_{A} Q^{2} = δ P_{A}$
Thus, the law which the fan must satisfy is the following: $f (N_{f}, Q) = (H_{B} - H_{A}) Q^{2}$
A graphical representation of this relation is illustrated in Figure 2 in which the effect of the fan is schematically shown.
Figure 2 illustrates two columns: the one on the right represents the duct A (with the arrow indicating the pressure drop from the point with the lowest pressure, the suction negative pressure to that of greater pressure, the atmospheric pressure), whilst the column on the left represents the set "C" of the duct B and of the fan (with the relative arrows indicating the reaching of the same pressure jump of A, obtained, however, by combining the effects of the duct B and of the fan).
Again in simplified terms, the diagram below, referred to a plurality of different operational curves of the fan with variations in the control unit typically comprising the number of revolutions Nf, illustrates the concept of combination of the effects of duct B and the fan: for each flow rate value Q: $δ P_{B} = f (N_{f}, Q) = δ P_{A} .$
In practical terms, with reference to the above-mentioned diagram, the flow rate Q can be conveniently measured from the pressure difference between two points of a duct with known characteristic H with the following formula: $Q^{2} = \frac{δ P_{m}}{H}$
The procedure illustrated graphically may also be represented by a table of numbers (or map) in which Nf corresponds to relative pressure measurements, and the table or map is then inserted in a control system. $Nf = g (δ P_{m})$
Considering by way of an example that the simplified operation of a fan in the region of normal operation (denoted in the following diagram with a closed dashed line) can be approximated by a quadratic law of the following type: $f (N_{f}, Q) = K_{f 1} N_{f} Q - K_{f 2} Q^{2}$
Equations (6) and (7) result in $K_{f 1} N_{f} Q - K_{f} Q^{2} = (H_{B} - H_{A}) Q^{2}$
and thus the law for controlling the revolutions is $N_{f} = \frac{(H_{B} - H_{A}) + K_{f 2}}{K_{f 1}} Q$
or even $N_{f} = G \sqrt{δ P_{m}}$
where G is a constant which depends on the characteristics of the system. In other words, to sum up the above, the law for operation of the fan can be identified both as a linear function of the flow rate and as a function which depends on the root square of the pressure drop measured in the duct.
For real features of the fan 8, the law will be advantageously derived in points in a tabular form.
In light of the above, with the control law indicated for the behaviour of the duct formed by the snorkel 6 it is possible to reproduce a duct of any equivalent resistance less than the resistance of the duct without the fan, provided the resistance is greater than zero.
It is possible to emulate a "passive" duct, with a sufficiently low resistance which, according to the laws of physics, does not cause a pressure increase compared with that of introduction (delta P positive relative to the atmospheric pressure).
There is, therefore, always the presence of an introduction of air by the system supplying the submarine, referred to as air suction means.
This is consistent with the common embodiment of submarines and allows the device according to this invention to remain completely autonomous from the remaining on-board systems.
With regard to the preferred embodiment described above in simplified terms, this invention comprises numerous variants.
In a first variant embodiment, not illustrated, of the device 2 according to this invention, the fan 8 is positioned at the lower end 4b of the second movable duct 4.
In a second variant embodiment, illustrated in Figure 3, of the device 2 according to this invention, a centrifugal type fan 8 is used, which basically forms a curve in the fixed duct 3.
In other words, the centrifugal fan 8 is located at a lower portion of fixed duct and constitutes, in practice, a terminal end 3a.
According to a further variant embodiment, not illustrated, the device 2 according to this invention comprises a fan with blades which can be adapted to reduce the head loss created by the fan in the event of a fault.
The axial fan is in effect equipped with blades which are arranged in a radial position during operation by the effect of the centrifugal rotation force. With the fan switched off, possibly following a fault, the blades are positioned along the axis. In this way, the loss of pressure, with the fan not active, is minimised and ensures a sufficient flow for low flow rate uses or guarantees an operation of the diesel engine in the event of a fault of the fan.
In a further variant embodiment, illustrated in Figures 4 and 5, the forced suction is achieved through a duct 40 parallel to the movable duct 4 and then introduced into the fixed duct 3 through a diffuser nozzle 41 having a circular crown cross section.
The circular ring (or annular) nozzle 41 is conveniently positioned at the zone of connection between the fixed duct 3 and the movable duct 4, where a sudden change of cross section occurs.
In this case, the parallel duct 40 is advantageously made with reduced diameter, so as not to increase the size of the part of the snorkel 6 moved and the change in air pressure must be greater.
Depending on the circumstances, it may prove necessary to adopt a compressor instead of the fan 8.
The introduction of air occurs through the circular ring nozzle 41 outside the movable duct 4, by guiding the flow leaving the fan 8. The fan 8 and fan are made conveniently in the stretch for inserting the movable duct 4 in the fixed duct 3.
The high speed air introduced by the annular nozzle 41 is guided from the downstream surface which expands and joins with the fixed duct 3 with a larger cross-section. The air adheres to the surface due to the "Coanda" effect and expands. The Coanda effect is basically the tendency of a flow to follow the boundary of a nearby surface.
The high speed on the perimeter drags by viscosity the air which is in the central part of the duct 3 and which adds to the flow rate of the air in the duct at high speed.
A similar principle is shown in patent applications MI2006A001759 or US 2009/0060710 , even though in different contexts.
The free duct remains available in the case of low flow rates or a fault of the fan/compressor 8.
According to the preferred embodiment of the device 2 described above, during the management (or control) of the automatic fan 8, the fan 8 is controlled in terms of number of revolutions. According to alternative embodiments not illustrated nor described further, the control unit 10 acts on the fan by modifying different characteristic parameters. For example, a parameter which can be modified is the inclination of the blades in those fans where this function is provided.
The axial fan, the centrifugal fan and the compressor described above are as a whole identifiable as aeraulic machines.
This invention achieves the preset aims and brings important advantages. In general terms, thanks to the device according to this invention and the introduction of the fan as described above, it is, in effect, possible to reduce the dimensions of the snorkel, also concentrating the modifications in the snorkel itself, to annul undesired impacts on the existing air treatment system of the submarine.
The suction in the most common submarines is achieved in effect by the diesel engine itself without further elements and this invention besides not limiting the design of the system also allows the existing snorkel (that is, already present on submarines) to be replaced without having to make modifications to the system of the submarine.
The reduction of the cross section of the duct defining the snorkel brings considerable advantages, including, as mentioned above, in general terms, a reduced visibility of the submarine by enemy forces during navigation.
Conveniently, only the movable cross section of the duct may be particularly reduced. In this way, the minimum dimension is obtained on the part of the snorkel outside the vessel, which ensures all the effects of improvement of the visual signature and minimisation of the resistance of the water.

Claims

A device for introducing an air flow (F) into a submarine (1), comprising a first duct (3) which is fixed relative to the hull of the submarine and a second duct (4) which is telescopically movable relative to the first duct (3), for emerging from the water with its upper end (4a) and allowing the air above to be sucked in while the submarine (1) is running at periscope depth, said first and second ducts (3, 4) being in fluid connection with air sucking means and being at least partly housed in a tower (5) of the submarine, characterised in that it comprises an aeraulic machine (8) operating along one of said first or second ducts (3, 4), said aeraulic machine (8) being designed to at least partly compensate for pressure losses in the air flow (F) passing through at least said second duct (3).
The device according to claim 1, characterised in that said aeraulic machine (8) is operatively separate from said sucking means and is positioned in series relative to them.
The device according to claim 1 or 2, characterised in that it comprises at least one sensor (9) indicating operating parameters of said air flow (F), said sensor (9) being positioned along one of either the first or the second ducts (3, 4).
The device according to claim 3, characterised in that it comprises control means (10) for controlling the operating parameters of said aeraulic machine (8), said control means (10) being operatable depending on a signal detected by said sensor (9).
The device according to any one of claims 1 to 4, characterised in that said aeraulic machine is an axial fan.
The device according to any one of claims 1 to 4, characterised in that said aeraulic machine is a helico-centrifugal fan.
The device according to any one of claims 1 to 4, characterised in that said aeraulic machine is a compressor.
A method for managing the air flow (F) introduced into a submarine (1) through a snorkel (6) whose upper end (4a) emerges from the water, comprising the steps of:
- preparing an aeraulic machine (8) acting on said snorkel (6),

- detecting along said snorkel (6) at least one of either the flow rate or pressure values of said flow (F),

- adjusting at least one operating parameter of said aeraulic machine (8) depending on said value detected.
The method according to claim 8, characterised in that said step of adjusting at least one parameter is carried out by adjusting the speed (Nf) of rotation of the aeraulic machine (8) depending on said value detected according to a predetermined law.
The method according to claim 8 or 9, wherein said second, movable duct has a predetermined working cross-section (A1), characterised in that said step of preparing an aeraulic machine (8) comprises the step of selecting an aeraulic machine (8) able to modify the operating parameters of said air flow (F) so as to make it correspond in terms of flow rate to the flow which, in the absence of said aeraulic machine (8), would pass through at least said movable duct (4) if the movable duct were to have a working cross-section greater than said predetermined working cross-section (A1).
Use of a device according to any one of claims 1 or 6, with said movable duct (4) having a predetermined working cross-section (A1), for modifying the operating parameters of said air flow (F) so as to make it correspond in terms of flow rate to the flow which, in the absence of said aeraulic machine (8), would pass through at least said movable duct (4) if the movable duct were to have a cross-section greater than said predetermined working cross-section (A1).