Abstract:
A stabilizing device for a supercavitating vehicle that isolates re-entrant jet flows of liquid from its cavity. The device has a receiving means positioned on the supercavitating vehicle where the re-entrant jet flow impinges on the supercavitating vehicle. An exit means is joined to the receiving means for carrying the received re-entrant jet flow out of interference with the cavity. The exit means includes an exhaust nozzle joined to the aft of the supercavitating vehicle and a re-entrant jet nozzle positioned in communication between the receiving means and said exhaust nozzle transferring said received re-entrant jet flow into the exhaust nozzle. This stabilizes the cavity and improves controllability and maneuverability of the supercavitating vehicles while also reducing the gas ventilation required to maintain the cavity. Furthermore, this reduces self-generated noise allowing improved operation of acoustical sensors incorporated in the vehicle.

Description:
STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 

   BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The present-invention relates generally to high-speed underwater vehicles. More particularly, this invention relates to stabilization of cavitating flows past high speed underwater vehicles to improve performance. 
   (1) Description of the Prior Art 
   Currently, high-speed underwater vehicles can be used in offensive and defensive roles. Often they may be designed to reduce drag by generating enough gas to envelope them in a gas filled cavity. These vehicles have been referred to as supercavitating vehicles, and enveloping them in a gas-filled cavity improves speed and maneuverability, and provides other favorable capabilities.  FIG. 1  schematically shows a representative rocket-propelled, supercavitating body, or vehicle  10  capable of operating in the re-entrant jet regime. Supercavitating vehicle  10  has a forebody  12  and midbody  14 , and nose portion  16  of forebody  12  has a cavitator  18  that is associated with cavity  20 . Cavity  20  starts at the low-pressure point. In the case shown, this is at the salient edges of cavitator  18 . Cavitator  18  is sized to generate cavity  20  at the design speed, design depth and design cavity pressure of supercavitating vehicle  10 . Consequently, cavity  20  almost completely envelops vehicle  10  to reduce the total drag of vehicle  10  by significant reduction of the drag component attributed to skin friction. For most practical cases of interest, maintenance of the designed cavity pressure of cavity  20  will require ventilation of the cavity by an internal gas source (not shown) that vents gas through ventilation ports  22  in forebody  12  at nearly the same hydrostatic pressure as the ambient fluid, or water  100 , at the designed operating depth of vehicle  10 . 
   The configuration of vehicle  10  incorporates nozzle extender, or blast tube  26  that locates exit plane  28  of propulsion nozzle  30  in some optimal location with respect to the aftermost point, or transom  14   a  of midbody  14 . It is important that cavity  20  be maintained large enough to envelope fore and midbodies  12  and  14  of vehicle  10  for satisfactory operation of supercavitating vehicle  10 . Entrainment of vented gases by propulsion plume  34  expelled through propulsion nozzle  30  tends to stabilize dimensions of cavity  20  over an expected range of operating conditions. Moreover, impingement of re-entrant jet  102  of ambient water  100  on aftward face, or transom  14   a  of midbody  14  can result in additional drag reduction beyond that already associated with operation in the supercavitation regime. 
   The configuration of supercavitating vehicle  10  may be subject to variation. These variations can be in the relative lengths of forebody  12 , midbody  14 , and nozzle extender  26 . Variations can also be made in the transverse dimensions of cavitator disc  18 , midbody  14 , nozzle extender  26 , and propulsion nozzle  30 , and the profiles of forebody  12  and propulsion nozzle  30 . In addition, nozzle extender  26  could be boat-tailed, and appropriate tailoring can be performed with respect to the configurations and arrangements of the cavitator  18 , ventilation ports  22 , the dimensions of cavity  20 , the operational conditions, and other design dimensions and parameters, as part of the design of vehicle  10 . Such variations of these parameters are not significant for the invention to be described below, nor are any variations associated with the shapes of control surfaces, appendages, sensors, and any geometrical features intended to account for gravitational effects on the shape or extent of cavity  20 . 
   Closures of hydrodynamic cavities in flows of liquids for which the freestream velocity has a horizontal component fall generally into one of three categories: (1) oscillating re-entrant jets; (2) toroidal vortex shedding; and, (3) twin-vortex flow systems. The type of closure that is observed for a particular flow depends on the cavitation number (the flow parameter characterizing the tendency to maintain a cavity) and the Froude number (the flow parameter characterizing the relative importance of fluid inertia and gravitational acceleration). Vehicles, such as vehicle  10 , that are designed to run in a supercavitating condition for reduced drag are often provided with a gas ventilation system to maintain a cavity of sufficient dimensions to envelope most of the body. The rate of ventilation required to maintain the cavity is dependent on the cavity closure type: high flow rates are required in the twin-vortex regime in which gas easily exits the cavity via the vortex system, moderate flow rates are required in the toroidal vortex shedding regime in which gas is entrained by the ambient liquid in a series of coherent vortices, and relatively low flow rates are required in the oscillating re-entrant jet regime in which gas entrainment by the main flow of liquid is impeded by the complicated interaction between the liquid flowing through the re-entrant jet and the liquid just outside the boundary of the cavity. Even in the oscillating re-entrant jet regime, the required ventilation rate can be significant since the re-entrainment of liquid is associated with a secondary re-entrainment of the ventilation gases. 
   For many applications, supercavitating vehicles are restricted to operations in the re-entrant regime due to constraints on the cavitation and Froude numbers. However, re-entrant jet flows of liquid are inherently unsteady, because liquid entering the gas cavity via the jet must disturb the cavity boundary to exit the system back into the main flow. Such unsteadiness can cause control problems, can limit the maneuverability of the vehicle, and can be associated with increased self-generated noise levels for any onboard acoustical sensors. 
   Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a device to stabilize the cavitating flows past self-propelled high-speed supercavitating vehicles, such as torpedoes and other supercavitating high-speed bodies for improving controllability and maneuverability, reducing gas ventilation rates needed to maintain cavities, and reducing self-generated noise for incorporated acoustical sensors. 
   SUMMARY OF THE INVENTION 
   A first object of the invention is to provide improved speed and control for supercavitating vehicles. 
   Another object of the invention is to provide a device to stabilize caviting flows past self-propelled supercavitating torpedoes and other supercavitating high-speed bodies. 
   Another object of the invention is to improve controllability and maneuverability of supercavitating vehicles and to reduce their gas ventilation rates required to maintain a cavity, and their self-generated noise for on-board acoustic sensors. 
   Another object of the invention is to provide a device to stabilize cavitating flows past self-propelled supercavitating torpedoes and other supercavitating high-speed bodies and use redirected liquid to further improve performance thereof. 
   Another object of the invention is to stabilize the impingement of the liquid jet of re-entrant fluid on the boundary of the cavity enveloping a supercavitating vehicle by providing an alternative path for the exit of this fluid from the cavity that is associated with reduced disturbance to the boundary of the cavity. 
   Another object of the invention is to re-entrain the entry of liquid of the re-entrant jet into the main flow to reduce secondary re-entrainment of ventilation gas. 
   Another object of the invention is to redirect the flow of re-entrant jet liquid for use in supercavitating vehicles as a diluent, coolant, lubricant, or some combination of thereof. 
   Another object of the invention is to distribute pressure over the aft end of a supercavitating vehicle to provide for further reduced drag beyond that already associated with operation in the supercavitation regime. 
   Another object of the invention is to reduce disturbances by redirecting the re-entrant jet of the liquid flowing into a cavity to inside the vehicle hull and to an exit point located well aft in the flow to reduce disruptive impingement on and disturbance of the boundary of the cavity. 
   Another object of the invention is to improve controllability and maneuverability of the vehicle by reducing disturbances to the boundary of the cavity to stabilize overall flow and reduce forces on control surfaces. 
   These and other objects of the invention will become more readily apparent from the ensuing specification when taken in conjunction with the appended claims. 
   Accordingly, the present invention provides a device for stabilizing re-entrant jet flows of liquid for a supercavitating vehicle. Annular structure mounted on an aft wall of a supercavitating vehicle defines an annulus-shaped inlet to absorb the re-entrant jet of liquid. An annular plenum receiving the annulus-shaped re-entrant jet captures it and sprays captured liquid from the plenum into a passageway for propulsion gases of the supercavitating vehicle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention and many of the attendant advantages thereto will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein like reference numerals refer to like parts and wherein: 
       FIG. 1  is a schematic cross-sectional view of an exemplary supercavitating vehicle having a cavitator producing a gas filled cavity during high speed transit underwater; 
       FIG. 2  schematically shows a cross-sectional view of a portion of a first embodiment of a stabilizing device of this invention on a supercavitating vehicle; 
       FIG. 3  schematically shows a cross-sectional view of a portion of a second embodiment of a stabilizing device of this invention on a supercavitating vehicle; 
       FIG. 4  schematically shows a cross-sectional view of a portion of a third embodiment of a stabilizing device of this invention on a supercavitating vehicle; 
       FIG. 5  shows distribution of captured liquid in accordance with this invention; and 
       FIG. 6  is a cross-sectional view showing other structure for redirecting re-entrant jet flow of water. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 2 , stabilizing device  50  of this invention is shown mounted on an aft-most transom  14   a  of a supercavitating vehicle  10  of the type shown in FIG.  1  and described, above. A ring-shaped portion  52  of stabilizing device  50  extends from hull  24  of mid-body  14 . Ring-shaped portion  52  may be integral with, or can be separate and attached by conventional means to hull  24 . Annular wall  54  extends inwardly from ring-shaped portion  52  and has a flared section  56  that reaches aft of transom  14   a  and terminates in annular lip portion  58 . Annular wall  54 , flared section  56 , and annular lip portion  58  are disposed in gas-filled cavity  20  that envelops nearly all of supercavitating vehicle  10 . 
   Annular lip portion  58  extends a short distance and is spaced apart from outer surface  26   a  of nozzle extender  26  to define annular duct, or inlet  60  between annular lip portion  58  and outer surface  26   a  of nozzle extender  26 . Annular inlet  60  captures liquid (water  100   a ) flowing into the volume of cavity  20  via an annulus-shaped re-entrant jet  102  of ambient water  100  (shown as arrow  102   a  in FIG.  2 ). Liquid  100   a  of annulus-shaped re-entrant jet  102  is directed to and captured in annular plenum  62  bounded by aft-most transom  14   a,  ring-shaped portion  52 , and annular wall  54 . The dynamic pressure of liquid  102   a  is recovered and converted to static pressure via a reduction in velocity that occurs through plenum  62  and plenum nozzles  64  that are mounted to extend through nozzle extender  26 . In the preferred embodiment, plenum nozzles  64  are equidistantly spaced apart from one another around the circumference of nozzle extender  26 ; however, other configurations are envisioned. Also in the preferred embodiment, aft nozzles  66  are mounted to extend through propulsion nozzle  30 . Liquid  100   a  that is captured in plenum  62  is thereby redirected from plenum  62  through plenum nozzles  64 , and into passageway  34   a  channeling the flow of propulsion gases  34   b.  This redirected liquid  100   b  acts as a diluent in passageway  34   a  where it becomes a vapor and is vented via propulsion nozzle  30  as a vaporized part of propulsion plume  34 . Liquid  100  near the outer part of re-entrant jet  102  of ambient water additionally may be fed to passageway  34   a  through aft nozzles  66 , and into passageway  34   a  providing additional diluent for propulsion gases  34   b,  becoming vapor and being vented via propulsion nozzle  30  as part of propulsion plume  34 . 
   An optional ducting system  84  can be provided in communication with transom  14   a.  Ducting system  84  draws liquid  100   a  from plenum  62  for providing to other systems of the supercavitating vehicle, as will be discussed with reference to FIG.  5 . 
   Referring to  FIG. 3 , stabilizing device  150  is an alternative geometry of the invention to optimize performance for supercavitating vehicle  110  that has only propulsion nozzle  130  extending behind it and not a nozzle extender. Inlet geometry of stabilizing device  150  is modified so that it can be mounted on aft-most transom  114   a  of supercavitating vehicle  110 . A ring-shaped portion  152  of stabilizing device  150  extends from hull  124  of mid-body  114 . Annular wall  154  extends inwardly from ring-shaped portion  152 . A ring shaped wall portion  156  can be included to add structural integrity and reduce the size of plenum  162 . Annular lip portion  158  extends a short distance toward aft-most transom  114   a  and is spaced apart from outer surface  130   a  of propulsion nozzle  130 . Annular wall  154  and annular lip portion  158  are disposed in gas-filled cavity  120  that envelops nearly all of supercavitating vehicle  110 . 
   Annular duct, or inlet  160  is defined between annular lip portion  158  and outer surface  130   a  of propulsion nozzle  130  to capture liquid (water  100   a ) flowing into the volume of cavity  120  via an annulus-shaped re-entrant jet  102  of ambient water  100  shown as arrow  102   a  in FIG.  3 . Liquid  100   a  of annulus-shaped re-entrant jet  102  is directed to and captured in annular plenum  162  that is bounded by ring-shaped portion  152 , aft-most transom  114 a and annular wall  154  (or ring shaped wall portion  156 ). The dynamic pressure of liquid  100   a  of jet  102  is recovered and converted to static pressure via a reduction in velocity that occurs through plenum  162  and plenum nozzles  164  that are mounted to extend through propulsion nozzle  130 . Plenum nozzles  164  can be equal-distantly spaced apart from one another around the circumference of propulsion nozzle  130 . Liquid  100   a  that is captured in plenum  162  is redirected from plenum  162  through plenum nozzles  164  and into chamber, or passageway  134   a  that channels the flow of propulsion gases  134   b.  Redirected water  100   b  acts as a diluent that flashes to vapor and is vented from propulsion nozzle  130  as a vaporized part of propulsion plume  134 . 
     FIG. 4  shows another embodiment of the invention in stabilizing device  250  that has an annular inlet  260  to plenum  262  that is shaped to reduce flow losses while maintaining static pressure well below stagnation pressure at the operating speed and depth of a supercavitating vehicle  210 . A ring-shaped portion  252  of stabilizing device  250  extends from hull  224  of midbody  214 . Annular wall  254  extends inwardly from ring-shaped portion  252  and has an inwardly tapered portion  256  that extends toward transom  214   a  in annular lip portion  258 . Annular wall  254 , inwardly tapered portion  256 , and annular lip portion  258  are disposed in gas-filled cavity  220  that envelops nearly all of supercavitating vehicle  210 . 
   Annular lip portion  258  extends along and is spaced apart from outer surface  226 a of nozzle extender  226 , and creates a tapered, streamlined annular inlet  260  between annular lip portion  258  and outer surface  226   a.  Annular duct, or inlet  260  captures liquid (water  100   a ) flowing into the volume of cavity  220  via an annulus-shaped re-entrant jet  202  of water  100 . Liquid  100   a  of annulus-shaped re-entrant jet  202  is directed to and captured in annular plenum  262  bounded by ring-shaped portion  252 , transom  214   a,  and annular wall  254 . Optionally, ring-shaped wall portion  270  can be included to add structural integrity and help reduce the size of plenum  262 . The dynamic pressure of liquid  100   a  is recovered and converted to static pressure via a reduction in velocity that occurs through plenum  262  and spray heads, or nozzles  264  that are mounted to extend through nozzle extender  226 . Nozzles  264  can be equal-distantly spaced apart from one another around the circumference of nozzle extender  226 . Liquid  100   a  that is captured in plenum  262  is thereby redirected from plenum  262  through nozzles  264  and into chamber, or passageway  234   a  that channels the flow of propulsion gases  234   b.  Sprayed liquid  100   b  thereby enters passageway as diluent where it flashes to vapor and is vented via propulsion nozzle  230  as a vaporized part of propulsion plume  234 . 
     FIG. 5  schematically shows several exemplary uses that captured liquid  100   a  can be put to in the embodiments herein described. Dynamics associated with inception  80  of cavities  20 ,  120  and  220  permitted capture  82  of portions of liquid  100   a  which can be fed to a ducting system  84  located on-board the host supercavitating vehicle. From ducting system  84  the captured liquid is distributed to dilution, cooling, and lubrication subsystems  86 ,  88 , and  90  before exiting the vehicles hull. Ducting system  84  may incorporate a pump  84   a  for increasing the total head of captured fluid  100   a  beyond stagnation pressure at the operating speed and depth of the vehicle. 
     FIG. 6  shows another embodiment of the invention. In this embodiment, a redirecting structure  98  receives at least part of a re-entrant jet flow  92  of water  100  at a mouth  98   a.  Redirection region  98   b  is shaped to turn re-entrant jet flow  92  from a forward flow direction to an aftward flowing direction. Conduit  98   c  carries the redirected jet flow to an annular region  94  located radially outwardly from nozzle extender  326 . By providing this redirection well away from the boundary of cavity  96  distubances to the cavity are reduced. Structure  98  for redirection of re-entrant flow  92  can be combined with stabilizing devices  50 ,  150 , and  250  described above or can be applied separately to reduce the problems associated with disturbances to the boundary of a cavity. 
   The stabilizing devices  50 ,  150 , and  250  of the inventions of  FIGS. 2 ,  3 , and  4  respectively reduce the disturbances to boundaries of cavities  20 ,  120 , and  220  by providing alternative paths for the exit of fluids from the cavities. This capability helps reduce underlying causes of unsteadiness of re-entrant jet flows, i.e., impingements of the liquid jets of re-entrant liquids on the boundaries of the cavities. By controlling the process by which liquids entering the cavities via the re-entrant jets are re-entrained into the main flow of ambient liquid  100 , secondary re-entrainment of ventilation gas  20  from vents, or ventilation ports  22  will also be reduced, see FIG.  1 . 
   Many variations of constituents discussed herein may be made within the scope of this invention. These variations can be, but are not limited to changes in the relative lengths of fore and midbodies of any supercavitating vehicle. Furthermore, such variations also can be made to selections and dimensions of any nozzle extender, cavitator, midbody, nozzle extender, and nozzle, as well as the forebody and nozzle profiles and any boat-tailing of the nozzle extender, and still be within the scope of this invention. Configurations of the ventilation ports (vents), cavities, the operational conditions and other design dimensions and parameters, are free to be chosen in accordance with this disclosed and claimed invention. In addition, variations may be made within the scope of this invention that are associated with configurations of control surfaces, appendages, sensors, and any geometrical features (including asymmetry of the vehicle or the re-entrant jet inlet) intended to account for gravitational effects on the shape or extent of the cavities or the re-entrant jets themselves. 
   Having the teachings of this invention in mind, therefore, modifications and alternate embodiments of this invention may be fabricated to have a wide variety of applications in other systems. The disclosed components and their arrangements as disclosed herein all contribute to the novel features of this invention. Stabilizing devices  50 ,  150 , and  250  of this invention are intended to provide a reliable and cost-effective means to stabilize cavitating flows past self-propelled supercavitating vehicles as they pass through the water. Therefore, stabilizing devices  50 ,  150 , and  250  as disclosed herein are not to be construed as limiting, but rather, are intended to be demonstrative of this inventive concept. 
   It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.