WO2008105930A2

WO2008105930A2 - Supercavitation weapons launcher

Info

Publication number: WO2008105930A2
Application number: PCT/US2007/078504
Authority: WO
Inventors: Chris Weiland; Pavlos Vlachos
Original assignee: Virginia Tech Intellectual Properties, Inc.
Priority date: 2006-09-14
Filing date: 2007-09-14
Publication date: 2008-09-04
Also published as: WO2008105930A3

Abstract

A projectile launch opening is submersed in water, a projectile ejector ejects the projectile from the projectile launch opening, and a gaseous cavity ejector ejects a gas to form a gaseous launch cavity covering the launch opening, synchronized with the projectile ejection, such that a leading surface of the projectile initially impacts the water at an inner surface of the gaseous launch cavity spaced above the launch opening, at an impact velocity initiating a supercavitation, the supercavitation substantially encapsulating the entire projectile within the water.

Description

SUPERCAVITATION WEAPONS LAUNCHER

FIELD OF THE INVENTION

[0001] The embodiments relate generally to launching projectiles and missiles from a submersed launch opening.

BACKGROUND OF THE INVENTION

[0002] Launching projectile weapons from a submersed launch position to travel through the water, and arrive with suitable velocity at a target position distant from the launch point, has multiple problems.

[0003] One problem is that a projectile traveling through water, unless it is moving faster than its supercavitation speed, encounters very high hydrodynamic resistance. The resistance is so high that the projectile cannot, generally, have a useful velocity after traveling through the water more than a very short distance.

[0004] Another problem is that, in order for the projectile to naturally reach its supercavitation speed, it becomes so unstable that it cannot impact a selected target position with a useful probability.

[0005] Another problem is that launching a projectile from a submerged projectile launcher tube introduces a certain kind of water turbulence, termed a

"vortex ring," at the tube opening, which may significantly alter the trajectory of the projectile. The present inventors have identified that this vortex ring often causes extreme and unpredictable changes in projectile trajectory, even if the projectile is launched at greater then its supercavitation velocity.

[0006] Self-propelled weapons, such as torpedoes, either do not have these problems or have solutions that are not practical or useful for projectiles. For example, stabilizing surfaces, e.g. fins and rudders, may be used with torpedoes, but are generally not effective or practical for stabilizing projectiles.

[0007] However, with respect to submerged launch of projectiles that are not self-propelled problems exist, generally preventing supercavitation from being a feasible option. One problem is that the projectile must be accelerated to exit the launch tube at a velocity exceeding the supercavitation velocity. Depending on the mass of the projectile, this may impose structural requirements on the launch tube, and the launch platform, or impose limits on the maximum projectile mass, such that a system is infeasible. Still another problem, identified by the present inventors, is that even if a launch tube and ejection system could launch a projectile at higher than a supercavitation velocity, such ejection inherently forms a turbulence at the launch opening, termed a "vortex ring," described in further detail below.

[0008] Similar problems exists with respect to existing submerged missile launch methods, wherein the missile is ejected "cold" from the launch tube, i.e., without its rocket motor providing any real thrust and, until the missile rises vertically through the water, exits the surface and fully ignites its rocket engine, the missile is simply a projectile. In a conventional cold launch, the ejection is typically performed by injecting high-pressure gas into the launch tube by means of a gas generator device, under the missile base, urging the missile upward in a piston fashion via expanding gases. The launch depth is limited, though, because the missile must be ejected with enough force to overcome the hydrodynamic resistance of the water and the missile weight, and to exit the water. Since all of the ejection force is applied in the launch tube, structural limits constrain the maximum launch depth. Another shortcoming is potential water seepage into the missile due, at least in part, to the extreme force at which water contacts the surface of the missile.

[0009] One prior proposed method for launching a missile from a submersed platform arranges a missile in a platform launch tube, the launch tube having a missile restraining and release structure. The method includes a missile exhaust gas redirection structure, arranged to receive the rocket exhaust at a location proximal the rocket nozzle (at the missile base), redirect the exhaust approximately 180 degrees, to an ejection location at or proximal to the launch tube opening. The prior proposed method adjusts the submerged depth of the platform to a given launch depth under the surface, and ignites the missile's rocket motor with the missile restrained, by the restraining and release structure, from exiting the launch tube. While the missile is restrained the nozzle of the ignited rocket motor, at the base of the missile, ejects rocket exhaust at high velocity, and the missile exhaust gas redirection structure then ejects the rocket exhaust from a location proximal the rocket nozzle. The ejection creates a vapor column extending all the up from the launch opening to the surface. The missile is then released, allowing the rocket thrust to lift the missile through the vapor column and to the surface, substantially unimpeded by water. [0010] This method has certain shortcomings. One is that the missile must be "hot launched," i.e., the rocket motor must operate and eject into the launch tube massive amounts of high velocity, high temperature exhaust gas. This may pose structural requirements unsuitable for some applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Fig. 1 is a graphical representation of one example of supercavitation of one object traveling through water;

[0012] Fig. 2A is a side, partial cut-way view of an example system having one embodiment of a supercavitating projectile launch system;

[0013] Fig. 2B is a front view, from the projection 1-1 on Fig. IA, of the Fig. IB example arrangement of gas ejection ports;

[0014] Fig. 3 illustrates one example time sequential operation of one example supercavitating projectile launch, on the example system of Fig. 2A-2B;

[0015] Fig. 4 is a graphical representation of one example of a vortex ring formed from ejecting a projectile from a tube directly into water without forming a gaseous launch cavity at the launch tube opening;

[0016] Fig. 5 is a perspective view of an example system having one embodiment of a supercavitating missile launch system; [0017] Fig. 6 is cross-sectional view of the Fig. 5 example supercavitating missile launch system;

[0018] Fig. 7 illustrates one example time sequential operation of one example supercavitating missile launch system, on the example of system of Fig. 6; [0019] Fig. 8 illustrates one prototype construction and arrangement to effect and measure one example of a supercavitating projectile launch; [0020] Fig. 9 illustrates the acrylic rod launch structure of the Fig. 8 construction and arrangement;

[0021] Fig. 10 shows an average of the projectile velocity in one example of a supercavitating projectile launch, observed at a distance from the launcher; [0022] Fig. 11 shows an average of the kinetic energy in one example of a supercavitating projectile launch, observed at the same distance from the launcher as Fig. 9.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0023] The following detailed description of the invention is in reference to accompanying drawings, which form a part of this description. The drawings are illustrative examples of various embodiments and combinations of embodiments in which the invention may be practiced. The invention is not limited, however, to the specific examples described herein and/or depicted by the attached drawings. Other configurations and arrangements can, upon reading this description, be readily seen and implemented by persons skilled in the arts. [0024] In the drawings, like numerals appearing in different drawings, either of the same or different embodiments of the invention, reference functional or system blocks that are, or may be, identical or substantially identical between the different drawings.

[0025] Various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a feature described in or in relation to one embodiment may, within the scope of the invention, be included in or used with other embodiments. Various instances of the phrase "in one embodiment" do not necessarily refer to the same embodiment.

[0026] Unless otherwise stated or made clear from its context, labeling used herein is not limiting; it is for consistency in referencing illustrative examples. [0027] This description enables persons of ordinary skill in the art relating to the invention to practice the invention, such persons having experience and knowledge in hydrodynamics of bodies traveling through water, supercavitation relating to bodies traveling through water, supercavitation effects relating to bodies traveling through an interface between a gaseous and liquid medium, and in structures and mechanics of submarine missile launch systems and methods. [0028] Unless otherwise stated or clear from the description, drawings are not necessarily to scale.

[0029] Unless otherwise stated or clear from their context in the description, various instances of the terms "arranged on" and "provided on" mean only a spatial relationship of structure(s) and, unless otherwise stated or made clear from the context, do not limit any sequence, type, or order of fabrication.

[0030] GENERAL OVERVIEW AND EMBODIMENTS

[0031] Disclosed embodiments significantly reduce viscous interactions on the surface of a body, either a projectile or missile, ejected from a launched point submerged in water by providing a cavitation at a leading surface of the body concurrent with the ejection, which quickly initiates a state of natural supercavitation encapsulating the entire body, at a velocity much lower than required for pure hydrodynamic supercavitation. The encapsulation minimizes the amount of wetted surface on the body by enclosing it in a low-density gas bubble thereby decreasing the factional drag.

[0032] According to the disclosed embodiments, the initiating cavitation is provided by establishing a gaseous cavity covering the launch opening when the object is ejected. According to the disclosed embodiments, the first impact between the leading surface of the object and the water is at an upper surface of the gaseous launch cavity, spaced above the launch opening. [0033] Therefore, in systems and methods according to the disclosed embodiments, even though the object is ejected from a submersed launch opening, it enters the water by passing through an interface (at the upper surface of the gaseous launch cavity) between a gaseous medium and a liquid medium. The disclosed embodiments thereby exploit and further, in a novel manner and arrangement, a theory that a velocity for a body to supercavitate in a liquid is lower if the body enters the liquid through an interface between a gaseous medium and the liquid medium.

[0034] According to the disclosed embodiments' novel initiating of a natural supercavitation at a velocity much lower than required for pure hydrodynamic supercavitation, at speeds as low as, for example, approximately ten to fifteen meters per second, hydrodynamic forces induce vaporization of the surrounding fluid and generate a vapor bubble that envelops the body and travels with it, significantly reducing viscous drag.

[0035] One illustrative example structure and method for forming the gaseous launch opening is a compressed gas system having a controllable on/off valve connected to outlet nozzles proximal to the launch opening. This is only one illustrative example; embodiments may be implemented using any means constructed and arranged to eject a gas, with a timing, and at an adequate pressure and volume, such that a cavity forms a gaseous space between the plane and the water, the space having a given height, when the ejecting projectile reaches the plane of the launch opening.

[0036] The present inventors have identified that this supercavitation substantially and markedly increases range and stability of the projectile, compared to launching a projectile directly into water.

[0037] The present inventors have identified that the substantial and marked increase in range and stability of the projectile contemplates a wide range of applications relating to underwater launched projectiles, which may have been infeasible through launching a projectile directly into water. [0038] The present inventors have identified that, through and according to the methods, arrangements and embodiments disclosed, the minimum ejection velocity required by the embodiments to instantiate the embodiments' supercavitation is only a fraction the velocity required to effect supercavitation of body accelerated through water without impacting the water through the embodiments' gaseous launch cavity formed at the launch opening. [0039] One embodiment relates to missiles and, for example, may be implemented as a structure and method arranged to eject the missile from the launch tube as a projectile and, prior to igniting the rocket motor and, synchronized with ejecting the missile, forming a gaseous launch cavity at the launch tube opening. Systems and methods according to the disclosed missile related embodiments are arranged to synchronize forming the gaseous launch cavity and ejecting the missile such that the launch cavity fully covers the plane of the launch opening, establishing a gaseous space between the plane and the water, the space having a given height, when the ejecting missile reaches the plane. The ejecting missile therefore, instead of immediately impacting water at the launch opening, first travels a distance through the gaseous cavity whereupon a leading or nose surface of the missile impacts the water, at an extreme surface of the cavity.

[0040] Systems and methods according to the disclosed missile-related embodiments may be arranged to form the gaseous launch cavity and to eject the missile such that the nose surface of the missile impacts the water at the extreme surface of the gaseous cavity at a velocity equal or greater to a supercavitation initial velocity, whereupon a supercavitation is initiated that expands and encapsulates the entire missile upon and after exiting the launch opening. The supercavitation initial velocity is a predetermined minimum velocity at which the nose surface of the missile, when striking the phase interface between the gaseous state within the gaseous cavity and the liquid state of the water, forms sufficient vaporization bubbles to initiate the supercavitation. This supercavitation initial velocity is only a fraction the velocity required to effect pure hydrodynamic supercavitation.

[0041] Through and according to the embodiments disclosed, after the missile strikes the phase interface at the upper surface of the gaseous cavity (between the gaseous state within the gaseous cavity and the liquid state of the water), at the supercavitation initial velocity, the supercavitation expands and encapsulates the missile, and continues to encapsulate the entire missile for a an entire time or travel distance at which the missile velocity is maintained above a velocity equal or approximately equal to the supercavitation initial velocity. As described in greater detail below, depending on the particular application and type of missile, a cavitator may be provided on the missile to further lower the velocity required to maintain this encapsulation. As will be understood, this velocity is a fraction of the velocity required for pure hydrodynamic supercavitation.

[0042] As will be understood by a person of ordinary skill in the art based on this disclosure, through and according to the disclosed embodiments, the missile may be propelled at this velocity maintaining the supercavitation by the missile's rocket motor. Further, as will be understood by a person of ordinary skill based on this disclosure, since the embodiments' supercavitation maintaining velocity is a fraction of the velocity required for pure hydrodynamic supercavitation, the very low viscous resistance benefit of supercavitation is obtained, while avoiding the high thrust requirement and the instability problem due to the high speed requirement inherent to pure hydrodynamic supercavitation. As will be understood by a person of ordinary skill in the art base on this disclosure, through and according to the embodiment, the missile may be readily propelled at this supercavitation maintaining velocity by, for example, the missile's rocket motor.

[0043] Systems and methods according to the disclosed missile-related embodiments may include conventional "cold launch" submarine missile launch systems and methods without substantial modification other than a system or method to form the gaseous cavity covering the launch tube opening in a manner synchronized with ejecting the missile such as, for example, a gas compressed gas system having a controllable on/off valve connected to outlet nozzles proximal to the launch opening.

[0044] Systems and methods according to the disclosed missile-related embodiments are contemplated as including conventional "cold launch" submarine missile launch systems and methods because the supercavitating initial velocity at which the missile nose surface must strike the water at the extreme surface of the gaseous launch cavity is sufficiently low to be attainable with such conventional cold launch methods.

[0045] Systems and methods according to the disclosed missile-related embodiments, by their providing a supercavity encapsulating the missile as it is ejected from the launch tube, and maintaining the encapsulating supercavity to obtain substantial decrease in viscous drag, at a low, readily attainable travel velocity through water, substantially and markedly increases the range of depths from which cold launch may be practical.

[0046] Pure hydrodynamic supercavitation is known and described in various publications. In brief summary, supercavitation refers to a single bubble or gas cavity which envelops the moving object and continues for many lengths after the body has passed, as shown in Fig. 1. As known, cavitation is the formation of gas or vapor filled microbubbles which rapidly grow in response to a decrease in pressure below a critical point. The degree of cavitation is quantified by the cavitation index:

σ₌ £ — PJL Equation (1) Where p is the static pressure in the ambient fluid, p_c is the cavity pressure, D is the density of the liquid, and U is the body speed.

[0047] As known, to reach the supercavitating state in pure hydrodynamic supercavitation, high-speed bodies must transition from a first stage of cavitation inception to partial cavitation to the fully developed supercavitation. With slender axisymmetric bodies, supercavities take the shape of elongated ellipsoids, beginning at the point of separation and trailing behind, with the length dependent on the speed of the body. The resulting elliptically shaped cavities soon close and detach under the pressure of the surrounding water. [0048] The flow over a supercavitating projectile thus involves intrinsically complicated flow structures and the interaction of an unsteady cavity with the surrounding fluid. Maneuvering and control of a supercavitating body presents a difficult problem. The projectile rotates inside the cavity, striking the cavity wall as it translates (tail- slapping).

[0049] The inception of cavitation corresponds to the first event where nuclei (i.e. microbubbles) grow explosively in response to a local pressure field. The lower the cavitation index, the greater degree of cavitation exists. A primary factor influencing cavitation inception is the nature of the viscous flow past the body. Boundary layer characteristics such as flow separation and reattachment points are significant to cavitating flows because they characterize the local pressure field. Regions of separated flow that are turbulent will initiate cavitation due to the large pressure fluctuations seen. Therefore, cavitation is often first seen in the centers of vortices, which have pressures lower than that of the ambient.

[0050] The present inventors observe, related to cavitation in the center of vortices, but without any statement of theoretical conclusion, direct submersed launch of a projectile into a liquid generates a vortex ring when the piston impulsively drives the projectile down the bore. Fig. 1 shows an example representation of such a vortex ring development. The present inventors observe, without any statement of theoretical conclusion, that absent the present embodiments' generation of a gaseous cavity covering the launch opening, interaction of the projectile with the leading vortex ring may cause the projectile to turn and become unstable. Further, the present inventors observe, without any statement of theoretical conclusion, that the vortex ring may precede the projectile and becomes asymmetric as it propagates, which may cause the projectile to become unstable.

[0051] The present inventors observe, without any statement of theoretical conclusion, that the present embodiments' generation of a gaseous cavity covering the launch opening eliminates the formation of the vortex ring. [0052] Relating to the vortex, systems and methods according to the disclosed embodiments preferably inject the gas forming the gaseous launch cavity to completely fill a "dead-water" located near the launch exit where the injected gases, due to buoyancy and the jet action, do not normally occupy. [0053] The present inventors further observe, without any statement of theoretical conclusion, that high gas injection proximal to the launch opening according to the disclosed embodiments may increase stability because the moment of yaw is proportional to the product of a geometric shape factor and the dynamic pressure. The dynamic pressure is several orders of magnitude smaller in the cavitation bubble, where the density is very low. Therefore the onset and development of yaw takes place at a lower rate, and the projectile is more stable in its flight.

[0054] One method provides a projectile launch tube arranged to accommodate a projectile, the projectile launch tube having a projectile launch opening submersible in a water environment, and includes ejecting a gas, concurrent with the projectile launch opening being submersed in a water environment, to form a gaseous launch cavity proximal to the projectile launch opening, and includes ejecting a projectile, wherein ejecting the gas forms the gaseous launch cavity to have an inner surface at a given supercavitation start position at a given supercavitation start time. [0055] According to one aspect, ejecting the gas and ejecting the projectile are performed in relation to each other, the relation being such that, at approximately a given supercavitation start time, a leading surface of the projectile impacts the inner surface of the gaseous launch cavity, at a velocity to initiate a supercavitation event proximal to the leading surface [0056] According to one aspect, the projectile includes a cavitator structure such as, for example, according to a conventional cavitator structure as known in the art of pure hydrodynamic supercavitation.

[0057] According to one aspect where the projectile has a cavitator structure, ejecting the gas and ejecting the projectile are performed in relation to each other such that the supercavitation event expands to form a supercavitation encapsulating the entire projectile, for up to a given maximum distance, until the projectile reaches a given position or target. As will be understood by persons of ordinary skill in the art based on this disclosure, the given maximum distance is readily determined based on, for example, the projectile shape and mass, and the velocity and means by which it is ejected. Through and according to the embodiments' encapsulation of the projectile at significantly lower velocity than required for pure hydrodynamic supercavitation, and significantly reduced viscous drag is obtained, without loss of stability and, therefore, the maximum of this given maximum distance is markedly higher than generally attainable with prior art submersed ejection of a projectile.

[0058] One method provides a missile launch tube arranged to accommodate a missile, the missile launch tube having a launch opening submersible in a water environment, and includes ejecting a gas, concurrent with the launch opening being submersed in a water environment, to form a gaseous launch cavity proximal to the projectile launch opening, and includes launching the missile through the tube and through the launch opening, wherein the ejecting the gas forms the gaseous launch cavity to have an inner surface at a given supercavitation start position at a given supercavitation start time. [0059] According to one aspect, ejecting the gas and launching the missile are performed in relation to each other, the relation being such that, at approximately a given supercavitation start time, a nose surface of the missile impacts the inner surface of the gaseous launch cavity, at a velocity to initiate a supercavitation event proximal to the leading surface.

[0060] According to one aspect, the missile includes a cavitator structure such as, for example, according to a conventional cavitator structure as known in the art of pure hydrodynamic supercavitation. The cavitator structure may be fixed. The cavitator structure may be releasably attached to the missile. The cavitator structure may include means for releasing and detaching from the missile at, for example, a controllable or predetermined time or missile position. [0061] According to one aspect, ejecting the gas and launching the missile are performed in relation to each other such that the supercavitation event expands to form a supercavitation encapsulating the entire missile, wherein the encapsulating is continuing until the missile reaches a given target location in the water.

[0062] According to one aspect, the encapsulating is such that no substantial interference between the water and the missile surface occurs; from a given launch time until the missile exits the surface.

[0063] EXAMPLES ACCORDING TO ONE OR MORE EMBODIMENTS

[0064] Fig. 2A is a side, partially cut-away view of one example system according to the disclosed embodiments. Referring to Fig. 2A, the example system has a launch tube body 2, having a bore 4, accommodating a projectile 6. Gas ejection ports 8 are formed proximal to the launch opening 4A. A gas ejection unit 10 connects to the ports 8 through tube 12. The Fig. 2A example system may be used with conventional means (not shown), or equivalent, for ejecting the projectile out through the launch opening 4A. [0065] The projectile may include a cavitator such as, for example, cavitator known in the art of pure hydrodynamic supercavitation. [0066] With continuing reference to Fig. 2A, the gas ejection unit 10 may include a compressed gas source (not separately shown), a preferably fast- switching gas flow control valve (not separately shown), and a controller (not separately shown) for controlling the gas control valve. Various implementations of the gas ejection unit 10 will be readily apparent to persons of ordinary skill in the art upon reading this disclosure, based on the mass and diameter of the projectile 6, the type of projectile ejection means, and the desired size, shape and time history of the gaseous launch cavity (not shown in Fig. 2A, but examples described in reference to Fig. 3).

[0067] Fig. 2B shows an illustrative example arrangement of the gas ejection ports 8, seen from Fig. 2A projection 1-1. The Fig. 2 B arrangement of gas ejection ports 8, with respect to the quantity, shape, dimension, and relative position to the launch opening 4A is only one example. Various implementations and arrangements of the gas ejection ports 8 will be readily apparent to persons of ordinary skill in the art upon reading this disclosure based on, for example, the type of projectile ejection means, the diameter of the launch opening 4A, and the desired size, shape and time history of the gaseous launch cavity (not shown in Fig. 2A, but examples described in reference to Fig. 3).

[0068] Fig. 3 illustrates one example time sequence, as four arbitrary snapshots labeled a, b, c, and d, of one example method for supercavitating launch 20 of a projectile such as, for example, projectile 6 shown in Fig. 2A. For ease of understanding, the Fig. 3 example supercavitating launch is depicted in reference to the example system illustrated in Fig. 2A. However, the Fig. 2A example system is not a limitation as to the operation 20. The supercavitating launch 20 may be performed by any system having means for ejecting a body through a submersed launch tube opening combined with means for ejecting a gas to form a gaseous launch cavity, synchronized with the body ejection, as described herein. [0069] Referring to Fig. 3, the example launch 20 begins at (a) showing the projectile 6 in one arbitrary example pre-launch position. Image (b) shows the projectile 8 after being accelerated by a projectile ejection means (not shown), at a position just prior to reaching the launch opening 4A. Prior to the time instant represented at (b) the gas ejecting unit 10 ejects a gas to form a gaseous launch cavity 24 covering the launch opening, the cavity 24 having an upper surface 26. Preferably, the gas ejecting unit 10 ejects the gas such that a diameter (not separately labeled) of the gaseous launch cavity 24 covering the launch opening 4A is larger than the launch opening diameter.

[0070] With continuing reference to Fig. 3, at the time instant represented by image (b) the upper surface 26 extends an approximate mean distance, arbitrarily labeled as DL, into the water. Stated differently, at the time instant represented by (b) the gaseous launch cavity 24 covering the launch opening has an approximate mean height DL.

[0071] With continuing reference to Fig. 3, at the time instant represented by image (c) the projectile 8 is partially exiting the launch opening 4A, and a cavity surface 26' represents a cavitation boundary (not separately labeled) between a surface of the projectile and the water 22. At time instant represented by image (d) projectile 8 has fully exited the launch opening 4A and is traveling through the water 22, with a supercavity 24' encapsulating the entire projectile body. [0072] Fig. 5 is a perspective view of an example system 30 having one embodiment of a supercavitating missile launch system.

[0073] With continuing reference to Fig. 5, the example launch system 30 may be a conventional, currently deployed, cold launch missile launch system having a launch tube, generically represented in cross section as 32, through a launch tube opening, generically represented in cross section as 32A, and a currently deployed missile cold launch ejection means, or equivalent, such as that represented as 38, modified only by adding a gas ejection unit, such as item 10 of Fig. 2A, exiting at gas ejection ports proximal to the launch tube opening 32A, such as the example ports 34. [0074] With continuing reference to Fig. 5, the missile, represented as 36 may, for example, be a currently deployed tactical (e.g., surface-to-air) missile equipped for conventional cold launch from a current cold launch system of a currently deployed submarine. The missile 36 may, for example, be a known, currently deployed intercontinental ballistic missile equipped for conventional cold launch from a submerged submarine.

[0075] Fig. 6 is a cross-sectional view of the Fig. 5 example supercavitating missile launch system.

[0076] Fig. 7 illustrates one example time sequence, as four arbitrary snapshots labeled a, b, c, and d, of one example method for a supercavitating launch 40, performed on the Fig. 6 example system 30, of a missile such as missile 36 from a depth LD under a surface WS of water 42.

[0077] Referring to Fig. 7, the example launch 40 begins at (a) showing the missile 36 in one arbitrary example pre -launch position. Image (b) shows the missile 36 after being accelerated by, for example, the ejection means 38 of the conventional cold launch system 30, at a position just prior to reaching the launch tube opening 32A. Prior to the time instant represented at (b) a gas ejecting unit, which may be the gas ejection unit 10, ejects a gas through, in this example, ports 34, to form a gaseous launch cavity 44 covering the launch opening, the cavity 44 having an upper surface 46. Preferably, the gas ejecting unit, such as item 10, ejects the gas such that a diameter (not separately labeled) of the gaseous launch cavity 44 covering the launch opening 32A is larger than the launch opening diameter.

[0078] With continuing reference to Fig. 7, at the time instant represented by image (b) the upper surface 46 extends an approximate mean distance, arbitrarily labeled as DX, into the water 42. The distance DX must be synchronized with the ejection of the missile 36 such that the missile tip impacts the surface 46 at a minimum speed for supercavitation inception. [0079] With continuing reference to Fig. 7, at the time instant represented by image (c) the missile 36 is partially exiting the launch opening 32A, and a cavity surface 36' represents a cavitation boundary (not separately labeled) between a surface of the projectile and the water 42. At time instant represented by image (d) missile 36 has fully exited the launch opening 32A and is traveling through the water 42, with a supercavity 44' encapsulating the entire missile 36 body. The supercavity 44' very significantly reduces the viscous drag of the missile body.

[0080] With continuing reference to Fig. 7, after the missile 36 has reached a given distance (not labeled) from the launch tube opening 34A, i.e., from the submarine, the rocket motor may be started. Due to the supercavitation 44' provided by the method and system, the missile 36 is sufficiently stable for such a rocket motor starting. Based on analyses and simulations performed by the present inventors, thrust of various conventional missile motors is sufficient to maintain the supercavitation 44', all the way from the launch opening 32A up the water surface WS, for a launch depth LD markedly greater than the maximum launch depth LD possible with conventional cold launch systems. Further, based on analyses and simulations performed by the present inventors, the present [0081] Referring to Fig. 7, a cavitator (not shown) such as, for example, a "bluff forebody" may optionally be placed or arranged on the nose of the missile 36. As known in the art, in pure hydrodynamic supercavitation over a bluff forebody includes large pressure fluctuations that come from flows. Selecting a specific cavitator is readily understood by persons of ordinary skill in the art based on this disclosure, the selection based on launch depth and other performance requirements. The cavitator may include means (not shown) for releasing and detaching from the missile at, for example, a controllable or predetermined time or missile position. For example, as will be understood by persons skilled in the art based on this disclosure, if the missile trajectory subsequent to launch includes an air flight, the cavitator release and detachment means may release and detach the cavitator concurrent with the missile nose entering the air. Various implementations for releasing and detaching a cavitator from a missile are readily identified by persons skilled in the art based on this disclosure and, therefore, detailed description is omitted.

[0082] With continuing reference to Fig. 7, a booster motor (not shown) may be added to the missile 36. It will be understood that a booster motor is not necessary but, as readily understood by persons of ordinary skill in the art based on this disclosure, depending on launch depth, parameters of the particular rocket motor of the missile, and other system performance requirements.

TEST OBSERVATION OF CONSTRUCTED SAMPLES

[0083] Fig. 8 depicts one example construction for observing and measuring a supercavitating launch. Using the Fig. 8 construction, cylindrical Teflon® slugs approximately 50.5 mm x 12.6 mm were fired into a 152 mm x 152 mm x 1.5 m tank filled approximately 0.6 m with water. The cylindrical Teflon slugs had no guidance or control surfaces of any kind. The cylindrical Teflon slugs were ejected by means of an air cylinder rod, depicted in greater detail in Fig. 9, with a 152 mm stroke that pushed the projectiles out of an acrylic rod bored to accept the projectiles. As depicted in Fig. 9, the acrylic rod contained four air injection ports 6 mm (1/4 inch) in diameter approximately equally spaced around the surface of the rod. The maximum ejection velocity was approximately 15 m/s. A ground glass sheet was placed in front of two 500 Watt lights to generate shadowgraph images of the test section. An IDT XS-3 high speed camera capable of a maximum resolution of 1280x1024 pixels was used to photograph the interrogation region at 700 Hz with reduced resolution of 328x960 pixels. [0084] A timing circuit controlled the time delay between the gas injection pulse and the projectile launch. The gas injection period was kept constant at 0.11s and the injected gas pressure was varied between 0.03 MPa (5 psig), 0.1 MPa (15 psig), and 0.17 MPa (25 psig). Immediately after the gas injection period the cylindrical Teflon slug projectile was fired.

[0085] The cylindrical Teflon slug projectiles were automatically tracked using a customized image processing program to record the instantaneous position and projectile trajectory. Second order central difference scheme was used to compute the velocity and a 3-point digital filter was used to smooth the extracted data for analysis.

[0086] The two data sets showed that cylindrical Teflon slug projectiles launched with no gas injection consistently developed slight cavitation behind the flow separation point at the blunt corner and a small cavitating vortex ring in the wake of the cylindrical Teflon slug projectile. The data showed that in the case of the cylindrical Teflon slug projectiles launched as described above with gas injection, a gas cavity consistently formed surrounding the cylindrical Teflon slug projectiles and was consistently fully developed and consistently appeared as a cavitation, in the experience and opinion of the present inventors, as that occurring with bodies traveling at much greater speeds in pure hydrodynamic cavitation. Fig. 10 shows a recorded average of the projectile velocity observed at a distance from the launcher and Fig. 11 shows a recorded average of the kinetic energy of the cylindrical Teflon slug projectiles observed at the same distances. The distances were normalized by the projectile diameter (D = 12.61 mm). [0087] While certain embodiments and features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will occur to those of ordinary skill in the art, and the appended claims cover all such modifications and changes as fall within the spirit of the invention.

Claims

reby claim:

1. A supercavitating projectile launch system, comprising: a projectile launch tube arranged to accommodate a given projectile, the projectile launch tube having a projectile launch opening submersible in a water environment; a projectile ejector arranged to eject the given projectile from the projectile launch opening; a gaseous cavity ejector arranged to eject a gas, concurrent with the projectile launch opening being submersed in a water environment, proximal to the projectile launch opening to form a gaseous launch cavity in the water, wherein the projectile ejector and the gas cavity ejector unit are arranged to eject the projectile and to eject the gas to form the gaseous launch cavity, respectively, such that a leading surface of the given projectile initially impacts the water at an inner surface of the gaseous launch cavity, at an impact velocity initiating a supercavitation substantially encapsulating the entire projectile within the water.

2. A supercavitating projectile launch method, comprising: providing a projectile launch tube having a projectile launch opening submersed in a water having a top surface, at a launch depth relative to said top surface; ejecting a gas to form a gaseous launch cavity covering the projectile launch opening and having a surface spaced from said launch opening; ejecting a given projectile from the projectile launch opening into the gaseous launch cavity, such that a leading surface of the given projectile travels through the gaseous launch cavity and initially impacts the water at said surface of the gaseous launch cavity.

3. The method of claim 2, wherein the ejecting a given projectile is such that the leading surface of the given projectile initially impacts the water at said surface of the gaseous launch cavity with an impact velocity initiating a supercavitation substantially encapsulating the entire projectile within the water.

4. The method of claim 3, wherein the given projectile is a missile having a rocket motor and having a nose structure having a surface forming said leading surface.

5. The method of claim 4, further comprises an igniting of the rocket motor, wherein the igniting is performed after supercavitation substantially encapsulates the entire missile within the water.

6. The method of claim 5, wherein the igniting the rocket motor is performed such that the rocket motor generates a thrust sufficient to propel the missile through the water, at a velocity maintaining the supercavitation substantially encapsulating the missile until the missile reaches the top surface of the water.

7. The method of claim 4, further comprising providing a cavitation structure proximal to the nose structure.

8. The method of claim 4, further comprises an igniting of the rocket motor, wherein the igniting is performed after the missile reaches the top surface of the water.

9. The system of claim 1 wherein the given projectile includes a cavitator structure.

10. The system of claim 1, wherein the given projectile is a missile having a nose surface and a rocket motor.

11. The system of claim 10, wherein the missile includes a cavitator attached to the missile proximal to the nose surface.

12. The system of claim 11, wherein the cavitator is releasably attached to the missile by an attachment arranged to secure the cavitator to the missile until the missile reaches a predetermined event in its trajectory and, response to the event, to release and detach the cavitator from the missile.

13. The method of claim 3, wherein the ejecting a gas is performed, based on a characteristic of the projectile, such that the impact velocity initiating a supercavitation is less than approximately 15 meters-per-second.

14. The method of claim 4, further comprises an igniting of the rocket motor, wherein the ejecting a gas is performed, based on a characteristic of the missile, such that the impact velocity initiating a supercavitation is less than approximately 15 meters-per-second, and wherein the igniting is performed to propel the missile through the water at a velocity maintaining the supercavitation substantially encapsulating the missile until the missile reaches a given target position.

15. The method of claim 14, wherein the given target position is a top surface of the water.

16. The method of claim 15, further comprising: providing a cavitator on the missile proximal to the nose surface; securing the cavitator to the missile from prior to ejecting the missile until missile reaches approximately the top surface of the water; and releasing the cavitator from missile.