Magnetohydrodynamic propulsor

Abstract

Magnetohydrodynamic propulsor (1 ) comprising a first electrode (2) and a second electrode (7) extending around an axis (4) to generate an electric field directed substantially radially in an active cavity (3) delimited by the first electrode (2) and the second electrode (7); - a conductive coil (8) wound around the first electrode (2) to generate in the active cavity (3) a magnetic field directed substantially parallel to the axis (4); and - an outlet cavity (9) positioned downstream of, and adjacent to, the outlet mouth (6), having extension around the axis (4) and having a maximum radius (R) greater than a radius (r) of the outlet mouth (6).

Description

[0001] DESCRIPTION

[0002] Title: MAGNETOHYDRODYNAMIC PROPULSOR

[0003] Technical field of the invention

[0004] The present invention relates to a magnetohydrodynamic propulsor, for example for propulsion of vessels both of surface and of immersion.

[0005] State of the art

[0006] Patent US5352139A shows an apparatus for magnetohydrodynamic propulsion of an aquatic vehicle.

[0007] Summary of the invention

[0008] In the context of magnetohydrodynamic propulsion, the Applicant has addressed the problem of producing a high propulsion thrust, in the presence of limited supply powers of generators of electric field and magnetic field and / or of limited physical overall dimensions of the propulsor and / or of limited acoustic emissions.

[0009] According to the Applicant, the above problem is solved by means of a magnetohydrodynamic propulsor in accordance with the appended claims and / or according to any one of the following embodiments.

[0010] According to one aspect, the invention relates to a magnetohydrodynamic propulsor. The propulsor comprises:

[0011] - a first electrode extending around an axis;

[0012] - a second electrode having a main extension along said axis, said first electrode and second electrode delimiting between first electrode and second electrode an active cavity having extension around said axis and having an inlet mouth and an outlet mouth at axially opposite parts, said first electrode and second electrode being structured to generate an electric field in said active cavity directed substantially radially;

[0013] - a conductive coil wound around said first electrode to generate in said active cavity a magnetic field directed substantially parallel to said axis in at least a central portion of said active cavity; and

[0014] - an outlet cavity positioned downstream of, and adjacent to, said outlet mouth of the active cavity, said outlet cavity having extension around said axis and having a maximum radius greater than a radius of said outlet mouth.

[0015] According to one aspect, the invention relates to a vessel (of immersion or of surface) comprising the magnetohydrodynamic propulsor according to the present invention. For “substantially parallel / orthogonal” (or similar expressions), with reference to aspatial relationship between two geometric elements (e.g. lines, planes, etc), it is intended that such elements form with respect to each other an angle of 0°+ / -15°, preferably of 0°+ / -10°, or, respectively, 90°+ / -15°, preferably 90°+ / -10°.

[0016] The expressions “radius”, “radial”, “axial”, “internal”, “external” and similar are referred to said axis.

[0017] The term “adjacent” implies a direct contact.

[0018] The expression “maximum radius” of an element indicates the maximum value of the radius considering the sections of the element orthogonal to the axis taken at all points of the axis. In the case of a cylindrical element, the radius is the same on all the orthogonal sections.

[0019] The terms “upstream”, “downstream”, “head”, “bottom” and similar refer to the direction of the flow generated in the active cavity of the propulsor.

[0020] The expressions “axial section” and “orthogonal section” refer to a section on a plane containing the axis and on a plane orthogonal to the axis, respectively.

[0021] According to the Applicant, the electric field and the magnetic field generated in the active cavity respectively by the pair of electrodes and by the coil in the above configuration impart to the electrically conductive fluid that fills the cavity (e.g. sea water) a (volumetric) Lorentz force directed azimuthally with respect to the axis. Such force initially induces a circular motion of the fluid around the axis (assuming for simplicity that the fluid is initially at rest). The circular motion in turn exerts on the fluid a centrifugal force. In such situation, the fluid that is located at the outlet mouth of the active cavity acquires a radial component of motion (away from the axis) under the effect of the centrifugal force, thanks to the fact that the outlet cavity, which develops immediately downstream of the outlet mouth, has a radius greater than a radius of the outlet mouth (that is the outlet cavity has a development along the radial direction that externally exceeds a radial development of the outlet mouth). In other terms, the outlet cavity allows the fluid present at the outlet mouth a motion along a trajectory having a radial component and away from the axis, since the outlet cavity is radially wider than the outlet mouth of the active cavity. Such motion induces a displacement of fluid from the active cavity towards the outlet cavity through the outlet mouth and therefore a recall of new fluid in the active cavity through the inlet mouth. The propulsor thus triggers a flow having an axial component.

[0022] The Applicant has further verified, by means of numerical simulations on the basis ofmulti-physics models, that the flow of fluid thus triggered and under the effect of the electric field and of the magnetic field evolves during a transient phase, partly in turbulent motion, to finally settle in a steady-state or quasi-steady-state condition in which the flow of fluid is almost axial in the region of the active cavity around the axis (with direction from the inlet mouth to the outlet mouth) and substantially radial in the outlet cavity. Such suction flow induced by the propulsor on the fluid in which the propulsor is immersed produces a reaction thrust by the fluid on the propulsor (and therefore on the vessel in which the propulsor is incorporated) directed in opposite direction with respect to the direction of the incoming fluid flow. The steady flow can be stabilized and regulated with a control system on the intensity of the electric field and / or of the magnetic field, optionally by means of further generators of magnetic field dedicated thereto.

[0023] In conclusion, the Applicant has surprisingly found that the above configuration of the propulsor achieves a high flow of fluid, in the presence of contained supply voltages and / or currents and without the need of a propeller in the active cavity to exert a thrust on the vessel, as for example described in US5352139A, with consequent advantages in terms of structural simplicity and / or greater thrust efficiency and / or reduction of noise (e.g. produced by impact on the propeller or by rotation of the propeller or by strong pressure variations / cavitation). Preferably said active cavity does not house any propeller.

[0024] The present invention in one or more of the above aspects may present one or more of the following preferred features.

[0025] Preferably said propulsor has radial symmetry with respect to said axis.

[0026] Preferably said active cavity and / or said outlet cavity has radial symmetry with respect to said axis. The propulsor is thus simple and rational.

[0027] With the expression “radial symmetry with respect to the axis” it is intended the property of invariance with respect to a rotation around said axis different from 360° (and multiples thereof). In an embodiment such invariance is verified for any angle (that is the section orthogonal to the axis is circular at each point of the axis), although the present invention also contemplates non-circular shapes of the orthogonal section, such as elliptical shapes, lenticular shapes, polygonal shapes, etc. For the purposes of symmetry, negligible elements are not considered, such as for example electrical connections.A particular and preferred case of radial symmetry in the present invention is the cylindrical shape (characterized by invariance of the shape on the section orthogonal to the axis at each point of the axis), although any other shape of the cavities is possible, once the respective surface does not hinder the flow of fluid.

[0028] Preferably said first electrode has an internal surface of cylindrical shape around said axis, said internal surface delimiting externally said active cavity.

[0029] In an embodiment said second electrode has an external surface, more preferably of cylindrical shape around said axis, which delimits internally said active cavity.

[0030] In other terms, the first and / or second conductor, preferably coaxial, is / are in contact with said active cavity, respectively radially externally and internally to said active cavity. In such manner the electric field in the active cavity is optimized.

[0031] The cylindrical configuration of the resulting active cavity allows a high uniformity of the electric field and of the magnetic field inside the cavity at each point of the axis, with advantages in terms of intensity of the resulting Lorentz force.

[0032] Preferably said conductive coil comprises a conductive longiform element, such as for example a conductive wire or a conductive tape, wound as a solenoid in one or more layers with respect to said axis or wound in one or more adjacent pancakes.

[0033] Preferably said coil (e.g. said longiform element) is made of superconducting material, more preferably high-temperature superconducting material (HTS, that is with critical temperature greater than or equal to 38K or 77K), such as for example a cuprate or MgB2. Preferably said propulsor comprises a cryostat which houses said coil. In such manner losses in the coil are reduced or almost cancelled, with consequent reduced consumption of electric energy, and / or the intensity of magnetic field is increased, for the same volume of the coil, with respect to a coil in conventional conductor (e.g. copper).

[0034] Preferably said propulsor has a bottom wall (preferably closed and continuous, that is free of through openings for the fluid), extending around said axis, more preferably having radial symmetry with respect to said axis, the bottom wall delimiting downstream said outlet cavity. Preferably (at least an axially central portion of) said bottom wall, in an axial section, forms with the axis an angle directed downstream greater than or equal to 45°, more preferably greater than or equal to 60°, and / or less than or equal to 90°, for example right or less than or equal to 80°.

[0035] Preferably said propulsor has an annular wall (preferably continuous), extendingaround said axis, more preferably having radial symmetry with respect to said axis, which extends from said outlet mouth radially outward. Preferably said annular wall faces a crown portion of the bottom wall. In an embodiment, said annular wall is parallel to the crown portion of the bottom wall.

[0036] Preferably said annular wall, in an axial section, forms with the axis an angle directed downstream greater than or equal to 45°, more preferably greater than or equal to 60°, more preferably greater than or equal to 70°, and / or less than or equal to 90°.

[0037] In case of a curvilinear bottom wall and / or annular wall (in orthogonal section), the above relative angle is defined by the tangent line to the wall.

[0038] Preferably said outlet cavity comprises a central portion, extending around said axis, more preferably having radial symmetry with respect to said axis, delimited upstream by said outlet mouth and downstream by said bottom wall and extending radially up to a maximum radius equal to said radius of the outlet mouth. Such central portion of the outlet cavity connects the outlet mouth with the annular portion described below. Preferably said outlet cavity comprises an annular portion, extending around said axis, more preferably having radial symmetry with respect to said axis, radially adjacent to said central portion and extending radially from said central portion away from said axis up to said maximum radius of the outlet cavity. Preferably said annular portion of the outlet cavity is delimited upstream by said annular wall and downstream by (a crown portion of) said bottom wall. Such annular portion facilitates the radial motion of the fluid exiting from the active cavity.

[0039] Preferably said outlet cavity, more preferably said annular portion, comprises an expulsion mouth, more preferably having radial symmetry with respect to the axis, extending along a radial end line of (said annular portion of) said outlet cavity. The flow of fluid, once having radially crossed the annular portion, exits from the outlet cavity through the expulsion mouth.

[0040] According to the Applicant the bottom wall, which closes downstream the outlet cavity, favors the deflection of the fluid exiting from the outlet mouth radially outward, and the conveying of the fluid first from the central portion towards the annular portion of the outlet cavity and then radially through the annular portion up to the expulsion mouth. Preferably said first electrode terminates axially at the outlet mouth (to favor the radial widening of the outlet cavity with respect to the outlet mouth).

[0041] Preferably said inlet mouth has a radius smaller than a maximum radius of (at least afront portion of) said active cavity. Preferably the propulsor comprises a head wall, extending around said axis, more preferably having radial symmetry with respect to the axis, provided with an opening, preferably circular, corresponding to said inlet mouth, the head wall delimiting upstream said active cavity. Preferably said head wall (or a tangent thereof), in an axial section, forms with the axis an angle directed downstream greater than or equal to 60°, more preferably greater than or equal to 70°, and / or less than or equal to 90°, for example right.

[0042] The Applicant has found that in such manner, in steady-state condition the flow of fluid presents in an annular zone downstream of the inlet mouth (at the head wall) flow lines that recirculate with retrograde motion (e.g. the lines bend radially outward and then return axially upstream, then bend radially inward and continue axially downstream). Such vortices of fluid favor the confinement of the flow of fluid in the axially central zone, and consequently the stability and the intensity of the flow of fluid (and therefore the intensity of the thrust of the propulsor).

[0043] Preferably the propulsor comprises an inlet cavity positioned upstream of, and adjacent to, said inlet mouth of the active cavity, said inlet cavity having more preferably radial symmetry (e.g. cylindrical shape) with respect to said axis, and having more preferably maximum radius equal to a radius of said inlet mouth. In an embodiment said inlet cavity has ogive shape in axial section (with the tip directed upstream). In such manner the flow at the inlet of the active cavity is stabilized, favoring the operation of the propulsor.

[0044] Brief description of the figures

[0045] Figure 1 shows schematically and partially a perspective view in axial section of a propulsor in accordance with the present invention;

[0046] Figure 2 shows schematically and partially a view in axial section of a propulsor in accordance with the present invention, with some flow lines shown;

[0047] Figure 3 shows schematically and partially a view in axial section of a propulsor in accordance with the present invention, with some flow lines shown.

[0048] Detailed description of some embodiments of the invention

[0049] The features and the advantages of the present invention will be further clarified by the following detailed description of some embodiments, presented by way of example and not limiting the present invention, with reference to the attached figures.

[0050] With reference number 1 a magnetohydrodynamic propulsor according to the presentinvention is indicated. The same reference number will indicate identical or similar elements in the various embodiments.

[0051] The magnetohydrodynamic propulsor 1 can be advantageously coupled to a vessel (not shown), of immersion or of surface.

[0052] The propulsor 1 comprises a first electrode 2 having an internal surface of cylindrical shape with respect to an axis 4 and a second electrode 7 having a main extension along the axis 4 and having an external surface of cylindrical shape around the axis 4. The first electrode and second electrode are coaxial with each other and delimit between first electrode and second electrode an active cavity 3 of cylindrical shape (tubular) and having an inlet mouth 5 and an outlet mouth 6 at axially opposite parts. The inlet mouth 5 and the outlet mouth 6 are exemplarily circular and orthogonal to the axis 4.

[0053] Preferably the first electrode 2 terminates axially at the outlet mouth 6 and at the inlet mouth 5, while the second electrode 7 can continue downstream also beyond the outlet mouth 6 (figures 1-3) and / or upstream beyond the inlet mouth 5 (figures 1 and 3). The propulsor 1 comprises, not shown, a voltage generator to apply a voltage difference between the two electrodes and thus generate an electric field in the active cavity, directed (substantially) radially.

[0054] The propulsor 1 comprises a conductive coil 8 (shown schematically only in figure 2) wound around the first electrode 2 to generate, when crossed by an electric current (e.g. direct current) induced by a current generator (not shown), a magnetic field directed (substantially) parallel to the axis at least in the central portion of the active cavity (as known, in the peripheral portions of the active cavity the magnetic field lines deviate from the axial condition to be able to close on themselves).

[0055] Preferably the coil 8 comprises a conductive longiform element, for example a conductive wire or a conductive tape, wound as a solenoid coaxial to the axis. Preferably the longiform element is made of high-temperature superconducting material (HTS), such as for example BSCCO, YBCO, ReBCO or MgB2 (critical temperature equal to about 38K). In such case the propulsor comprises a cryostat 20 (shown only schematically in figure 1, for example cooled with liquid nitrogen) in which the superconducting coil is housed.

[0056] The propulsor 1 comprises an outlet cavity 9 positioned downstream of, and adjacent to, the outlet mouth 6 of the active cavity, the outlet cavity 9 having radial symmetrywith respect to the axis 4 (e.g. disk-shaped configuration) and having maximum radius R (indicated by the double arrow) greater than the radius r (indicated by the double arrow) of the outlet mouth 6.

[0057] Preferably the propulsor has a bottom wall 10, closed and continuous, having radial symmetry with respect to the axis 4, which delimits downstream the outlet cavity 9. In the exemplary embodiments shown in figure 1 and 2, the bottom wall 10 is a flat disk orthogonal to the axis 4.

[0058] In the exemplary embodiment shown in figure 3, the bottom wall 10 is of conical shape which, in axial section (fig. 3), forms with the axis 4 an angle 11 directed downstream exemplarily equal to about 75°.

[0059] Preferably the propulsor 1 has an annular wall 12, continuous, having radial symmetry with respect to the axis 4, which extends from the outlet mouth 6 radially outward. The annular wall 12 faces a crown portion of the bottom wall 10. In the example of figure 3 the annular wall 12 is parallel to the (crown portion of the) bottom wall 10.

[0060] In the exemplary embodiment shown in figure 1, the annular wall 12 is a flat annular disk orthogonal to the axis 4.

[0061] In the exemplary embodiments shown in figure 2 and 3, the annular wall 12 is of conical shape which, in axial section (fig. 2 and 3), forms with the axis 4 an angle directed downstream exemplarily equal to 86° and 75°, respectively.

[0062] Preferably the outlet cavity 9 comprises a central portion 13, having radial symmetry with respect to the axis 4, delimited upstream by the outlet mouth 6 and downstream by the bottom wall 10, and extending radially from the axis 4, or from the second electrode 7 in case the second electrode 7 is also present in the outlet cavity 9 (as exemplarily shown in the figures), up to a maximum radius equal to the radius r of the outlet mouth. In other terms the central portion 13 has an extension in a view orthogonal to the axis 4 equal to the extension of the outlet mouth 6. In the exemplary embodiments shown in figure 1 and 2, such central portion 13 has, in axial section, rectangular shape (the bottom wall 10 being flat), while in figure 3 such central portion 13 has shape (on each side of the axis 4) of a right triangle with hypotenuse coincident with the bottom wall 10.

[0063] Preferably the outlet cavity 9 comprises an annular portion 14, having radial symmetry with respect to the axis 4, radially adjacent to the central portion 13 and extending radially from the central portion 13 away from the axis 4 up to the above maximumradius R of the outlet cavity. In practice the annular portion 14 is delimited upstream by the annular wall 12 and downstream by the bottom wall 10, or more precisely by a crown portion thereof.

[0064] In the embodiment shown in figure 1 , such annular portion 14 has, in axial section (on each side of the axis 4), rectangular shape, in figure 2 such annular portion 14 has shape of a right trapezoid and in figure 3 such annular portion 14 has shape of a parallelogram.

[0065] Preferably the annular portion 14 of the outlet cavity comprises an expulsion mouth 15, having radial symmetry with respect to the axis, extending along a radial end line of the annular portion 12.

[0066] The propulsor 1 can further comprise, as shown in figures 1 and 2, an expulsion cavity 16 delimited upstream by the expulsion mouth 15 and extending mainly parallel to the axis. In such manner the fluid is expelled from the propulsor with axial direction downstream (that is in direction opposite to the motion of the propulsor in the fluid) with advantages in hydrodynamic terms.

[0067] Preferably the propulsor comprises a head wall 17, having radial symmetry with respect to the axis, provided with a circular opening corresponding to the inlet mouth 5 and delimiting upstream the active cavity 3. In the illustrated examples, the head wall 17 is a flat annular disk, but in other embodiments, not shown, the head wall 17, in an axial section, can form (on each side of the axis) with the axis an angle directed downstream acute, for example between 70° and 90°.

[0068] Preferably the inlet mouth 5 has a radius smaller than the maximum radius r of the active cavity, at least in the upstream portion thereof.

[0069] Preferably the propulsor 1 comprises an inlet cavity 18 positioned upstream of, and adjacent to, the inlet mouth 5 of the active cavity 3, having radial symmetry with respect to the axis 4, and having maximum radius equal to a radius of the inlet mouth. In the embodiments shown in figures 1 and 3 the inlet cavity 18 has ogive shape directed upstream, while in figure 2 the inlet cavity 18 is cylindrical.

[0070] Exemplarily, the axial length of the active cavity 3 is equal to 23 cm, the total axial length of the propulsor is equal to about 85 cm and the radius R of the outlet cavity is equal to about 17 cm.

[0071] Figures 2 and 3 show some flow lines of the fluid in steady-state condition. As can be seen the flow in the axially central portion of the active cavity is substantially axial (witha modest azimuthal component, to realize a helical trajectory), while in the radially more external and front (that is upstream) portion of the active cavity the flow lines form axial vortices due to the presence of the head wall 17.

Claims

CLAIMS1. Magnetohydrodynamic propulsor (1 ) comprising:- a first electrode (2) extending around an axis (4);- a second electrode (7) having a main extension along said axis (4), said first electrode (2) and second electrode (7) delimiting between first electrode and second electrode an active cavity (3) having extension around said axis (4) and having an inlet mouth (5) and an outlet mouth (6) at axially opposite parts, said first electrode (2) and second electrode (7) being structured to generate an electric field in said active cavity (3) directed substantially radially;- a conductive coil (8) wound around said first electrode (2) to generate in said active cavity (3) a magnetic field directed substantially parallel to said axis (4) in at least a central portion of said active cavity; and- an outlet cavity (9) positioned downstream of, and adjacent to, said outlet mouth (6) of the active cavity, said outlet cavity (9) having extension around said axis (4) and having a maximum radius (R) greater than a radius (r) of said outlet mouth (6).

2. Propulsor (1) according to claim 1, wherein said first electrode (2) has an internal surface of cylindrical shape around said axis (4) which delimits externally said active cavity (3) and said second electrode (7) has an external cylindrical surface around said axis (4) which delimits internally said active cavity.

3. Propulsor (1) according to claim 1 or 2, wherein said conductive coil (8) comprises a conductive longiform element wound as a solenoid with respect to said axis, wherein said conductive longiform element is made of high-temperature superconducting material, and wherein said propulsor comprises a cryostat (20) which houses said coil (8).

4. Propulsor (1) according to any one of the preceding claims, comprising a bottom wall (10), closed and continuous, extending around said axis and delimiting downstream said outlet cavity (9).

5. Propulsor (1) according to the preceding claim, wherein at least an axially central portion of said bottom wall, in an axial section, forms with the axis an angle (11) directed downstream greater than or equal to 45°, and / or less than or equal to 90°.

6. Propulsor (1 ) according to claim 4 or 5, comprising an annular wall (12), continuous, extending around said axis, and extending from said outlet mouth (6) radially outward, wherein said annular wall (12) faces a crown portion of the bottom wall (10), andwherein said annular wall, in an axial section, forms with the axis an angle directed downstream greater than or equal to 45°, and / or less than or equal to 90°.

7. Propulsor (1) according to any one of claims 4 to 6, wherein said outlet cavity (9) comprises a central portion (13), extending around said axis, delimited upstream by said outlet mouth (6) and downstream by said bottom wall (10) and extending radially up to a maximum radius equal to said radius (r) of the outlet mouth, wherein said outlet cavity (9) comprises an annular portion (14), extending around said axis, radially adjacent to said central portion (13) and extending radially from said central portion away from said axis up to said maximum radius (R) of the outlet cavity, wherein said annular portion (14) of the outlet cavity is delimited upstream by said annular wall (12) and downstream by a crown portion of said bottom wall (10).

8. Propulsor (1 ) according to any one of the preceding claims, wherein said inlet mouth (5) has a radius smaller than a maximum radius of at least a front portion of said active cavity, wherein the propulsor comprises a head wall (17), extending around the axis, provided with an opening corresponding to said inlet mouth (5), the head wall delimiting upstream said active cavity (3), and wherein said head wall, in an axial section, forms with the axis an angle directed downstream greater than or equal to 60°, and / or less than or equal to 90°.

9. Propulsor (1) according to any one of the preceding claims, further comprising an inlet cavity (18) positioned upstream of, and adjacent to, said inlet mouth (5) of the active cavity, said inlet cavity (18) having radial symmetry with respect to said axis, and having maximum radius equal to a radius of said inlet mouth.

10. Vessel of immersion or of surface comprising the propulsor (1) according to any one of the preceding claims.

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