FR2787876A1 - Procedure and installation for testing effect of water jet impact on rear end of propulsion unit, e.g. of submarine launched missile - Google Patents

Abstract

The procedure consists of producing a coherent water jet and directing it through a nozzle (62) against the rear end of a test module (40). The ignition of the propulsion unit is simulated by increasing the pressure inside a chamber separated from the module outlet by a seal, using a pressurised gas, and the resultant forces received by the outlet pipe are measured. The water jet is deviated away from the propulsion unit by a deflector (72) which is removed to direct the jet against the test module. The water jet impact simulator consists of a variable-position supporting frame (12) for the test module, force metering sensors, and a stationary water jet generator with a nozzle (62) connected to a tank (64) of water under pressure.

Description

Field of the Invention The invention relates to a method and an installation

  test to study the effects of the impact of a jet of water entering the rear area of a thruster, in particular the effect of such an impact when it is

  concomitant with the ignition of the propellant in an underwater environment.

  The invention also relates to a test installation for setting up

process work.

  BACKGROUND OF THE INVENTION Failures of missile shots from submerged submarines have been explained by the so-called "water plug" effect. After a missile has been ejected from its housing by a hunting pressure, a reduction in the volume of flushing gas at the rear of the missile can allow water to enter the nozzle, before ignition of the propellant. The water thus introduced into the nozzle forms a plug which can disturb

  ejection of gas on ignition and causing the firing to fail.

  A known solution consists in providing the outlet of the nozzle with a closing part, or re-entering anti-water jet cap, which prevents the water from rising into the nozzle and is expelled by the pressure of the gases admitted into the nozzle. after ignition. However, it is then the closing part which can be exposed to the impact of a water jet. Such an impact is likely to hinder the expulsion of the closure part. In addition, it induces forces on the nozzle directed upstream of the nozzle, forces which may be damaging for the stop which is disposed between the

  nozzle and the bottom of the propellant and which allows an orientation of the nozzle.

  It is therefore desirable to simulate a returning jet of water impact, including in a nozzle configuration provided with an expelling closure part, in order to be able to assess the effects and to find the means of overcoming them, for example search

  the most suitable form for the closure part.

  Objects and Summary of the Invention The object of the invention is to provide a test method for simulating such an impact and for measuring and / or visualizing its effects. The object of the invention is also to provide a test method making it possible to simulate the impact of a returning jet of water and the ignition

concomitant of the propellant.

  Another object of the invention is to provide an installation

  test for implementing the method.

  According to a first aspect of the invention, it relates to a test method comprising the steps which consist in: - providing a test specimen comprising a nozzle with a diverging part, - generating a substantially coherent water jet according to a direction of impact directed towards the downstream end part of the nozzle, - simulating a ignition of propellant by increasing the pressure inside a chamber separated from the diverging part of the nozzle by a cover, and

  - measure the forces exerted on the nozzle.

  The generation of a substantially coherent water jet preferably comprises the steps which consist in: - supplying pressurized water to a nozzle having an outlet axis directed in the direction of impact, - initially deflecting the outgoing jet of the nozzle, with respect to the direction of impact, and -remove the deflection of the jet after it has reached a state

consistent stationary.

  The initial deflection of the jet is advantageously achieved by interposing a deflector on the path between the nozzle and the downstream end portion of the nozzle, the elimination of the deflection of the jet being

  performed by moving the deflector.

  Advantageously also, the deflector is oriented so that it has a deflection surface of the jet making a determined angle with respect to the direction of impact and the deflector is moved to eliminate the deflection of the jet with a speed of displacement as a function of the speed of the water jet, so as to give it a predetermined shape front, preferably a flat front substantially perpendicular to the direction of impact. The deflector is integral with a mobile assembly propelled at high speed, for example by being subjected to the action of a gas

under pressure.

  The ignition simulation can be carried out by admitting a pressurized gas into the chamber or by controlling a choke located in the chamber. The ignition simulation can be ordered before or after the arrival of the water jet at the downstream end of the nozzle, or concomitantly with this arrival. In the latter case, the ignition simulation can be controlled by moving the

water jet deflector.

  According to a particular feature of the method according to the invention, the test specimen is provided with a closure element at the downstream end of the nozzle, in order to simulate a re-entrant anti-jet plug, and we observe

  Ejection of the closing element after the ignition simulation.

  Several tests can be carried out by varying the shape of the

  surface of the closure element exposed to the water jet.

  Several tests can also be carried out by varying the

  center of impact of the water jet on a radius of the re-entrant anti-jet cap.

  Several tests can still be carried out by varying

  the angle between the direction of impact and the axis of the nozzle.

  According to another aspect of the invention, it relates to a test installation making it possible to implement the method defined above. According to the invention, such an installation comprises: - a support frame for a test specimen comprising a nozzle with a diverging portion, - an envelope carried by the frame and containing a chamber, - means for pressurizing the chamber, - means provided with force sensors for connecting the casing to a nozzle with interposition of a cover between the chamber and the diverging part of the nozzle, - a device for generating a stationary coherent water jet, comprising a nozzle having an outlet opening with a vertical axis and connected to a pressurized water tank, - means for pressurizing the chamber, - a deflector movable between an initial position in which it is interposed on the path between the nozzle and a nozzle carried by the frame, and a position in which it frees this path, and

  - means for moving the deflector.

  Advantageously, the support frame is orientable to vary the angle between the vertical direction of exit from the nozzle and the axis of a nozzle carried by the frame. It can also be movable transversely by

  relative to the vertical direction of exit of the nozzle.

  The means for pressurizing the chamber may include at least one source of pressurized gas or a choke, the

  volume of the chamber being advantageously variable.

  Advantageously also, the deflector is secured to a movable assembly along a guide ramp, the latter being inclined,

  for example at 45, relative to the horizontal.

  The means of movement of the deflector are

  advantageously designed in the form of a pressurized gas cannon.

  Other peculiarities of the test process and installation

  according to the invention will emerge on reading the description made below

  indicative but not limiting with reference to the accompanying drawings.

Brief description of the drawings

  In the drawings: FIGS. 1A to 1C illustrate very schematically the phenomenon of water jet returning when a missile is fired in an underwater environment; - Figure 2 is a general schematic view of an embodiment of a test installation according to the invention; Figure 3 is a detail view of the test specimen mounted in the installation of Figure 2; FIG. 4 is a detail view in elevation and in section showing the jet deflector of the installation of FIG. 2 and its associated propellant system; - Figure 5 is a partial top view of the jet deflector and its associated propellant system; - Figure 6 is a sectional view along the plane VI-VI of Figure 5; FIGS. 7A to 7C schematically illustrate the formation of a water jet with a flat front by means of the deflector of FIG. 4; - Figures 8A and 8B show two test configurations of the installation of Figure 2; and - Figures 9A to 9C schematically show different types of re-entrant anti-jet caps that can be associated with the specimen

  installed in the installation of figure 2.

  Detailed description of preferred embodiments

  Before describing in detail a test installation in accordance with the invention, reference will be made to FIGS. 1A to 1C which illustrate the

incoming water jet phenomenon.

  In FIG. 1A, a missile 1 is expelled from its housing 2 of a submarine while diving by a hunting pressure. The missile 1 has a nozzle 3 the downstream end of which is closed by a re-entrant anti-water jet plug 4. A constriction of the volume of flushing gas expelled with the missile can occur (Figure 1B), providing access to a column of water towards the downstream part of the nozzle. Upon ignition of the missile's propellant, and after rupture of a seal which isolated the combustion chamber from the nozzle, the combustion gases produced cause the plug 4 to leave (FIG. 1C). This departure can be disturbed by the incoming water jet 5 which rushes in or has rushed into the space provided by the necking of the

volume of flushing gas.

  The object of the invention is to propose a test method and installation making it possible to simulate the impact of a water jet entering the downstream part of a nozzle, whether or not fitted with an anti-plug incoming jet, in order to measure its effects. An embodiment of such

  installation is shown diagrammatically in Figure 2.

  This installation essentially comprises - a test specimen 10 which is supported by a gantry 12 and which comprises a model, preferably on a reduced scale, of a nozzle, and a propellant ignition simulator 40, - a jet generator 60 comprising a nozzle 62 connected to a water tank 64 by a pipe 66 provided with a valve (not shown) surmounting the nozzle 62, and - a movable assembly 70 which comprises a jet deflector 72 and a lifter 74 (integral with ejectable pistons 74a and 74b) and which is

  associated with a guide ramp 80 and with propulsion means 90.

  The test specimen 10 (Figures 2 and 3) is mounted in a generally circular frame 14 which is fixed by an upper flange 14a to support rails 16 in an arc, which can also

  slide laterally in gantry rails 12.

  The nozzle 20 comprises a divergent 20a which is connected to a convergent 20b by a neck 20c. The divergent 20a is constituted by an egg-shaped wall and a fixing base. The neck 20c is formed by an annular piece. The convergent 20b is also formed by an annular piece 26 which has a circular base 26a connected

by screw at divergent 20a.

  The passage between the converging element 20b and the diverging element 20a is closed by a cover 30 constituted by a resilient elastic membrane. The cover 30 is held in a sealed manner around its periphery between two rings 28a, 28b interposed between the part 26 and the divergent a. The ring 28a is connected by screw to the ring 28b, while the ring 28b is connected by screw to the divergent 20a with the interposition of a thin ring 28c which rests both on the divergent 20a and on the part 20c forming the collar. Seals are interposed between the part 26 and the ring 28a, between the ring 28b and the ring 28c and between the latter

and divergent 20a.

  The cover 30 reproduces that which normally exists in a storage missile, to isolate the combustion chamber from the diverging portion of the nozzle, in order to avoid pollution or deterioration of the propellant contained in the chamber by humid air or the like. . Such a seal is usually placed in the upstream part of the nozzle, at the level of the neck (the terms upstream and downstream are used here with reference to the normal direction of flow of gases in a nozzle). The nozzle 20 can also be provided with a closure part 32 at its downstream end, simulating a re-entrant anti-jet plug. The part 32 is for example formed from two aluminum sheets between which is placed a block 34 of rigid foam. The sheets are joined at their periphery 32a o are formed holes allowing the centering of the part 32 on pins 35 fixed at the end of the diverging, around the outlet thereof. The part 32 is connected to the divergent by means for example of copper wire ligatures (not shown) capable of being broken by the overpressure in the nozzle after the ignition simulation. A leakage section is provided between the part 32 and the nozzle 20, as there is in reality between a re-entrant anti-jet plug and a nozzle diverging element, in order to avoid too great an overpressure in the diverging element after ignition of the

  propellant and before departure of the re-entering anti-jet plug.

  The ignition simulator 40 comprises an axisymmetric chamber 42, of the same axis A as the nozzle, located inside an envelope 44. In its downstream part, the chamber 42 has a frustoconical shape whose diameter decreases to its end which is connected with the convergent 20b of the nozzle. At this level, the casing 44 has a flange 44a which engages on the part 26 with the interposition of a seal. This separation is representative of the separation area between the propellant fixed part and the movable nozzle part. In its upstream part, the chamber 42 is delimited by a bottom 46 movable axially inside the envelope. The bottom 46 has a U-shaped piston shape, the position of which in the casing 44 is adjusted by means of rods 45 which

  cross the bottom 44b of the envelope 44.

  In Figure 3, the bottom 46 is in its most downstream position, defining a chamber 42 of smaller volume. Other positions of the

  bottom 46 are shown in phantom.

  The head of the piston 46 has an injection nozzle 48 which can be connected by a line 50 to an inflation circuit under pressure, of neutral gas, for example nitrogen gas. Another injection nozzle 52 is provided through the head of the piston, which communicates with a nipple 54. The injection of neutral gas under pressure through the line 50 or the ignition of the nipple 54 cause an increase in pressure in chamber 42, simulating a propellant ignition. It is possible to install a second neutral gas inlet at the location of the choke on

nozzle 52.

  The nozzle 20 is connected to the casing 44 with the interposition of a force sensor 36 of annular shape provided with several piezoelectric devices making it possible to measure the forces tending to approach or separate the nozzle 20 from the casing 44 during the test, under the effect of the impact of a water jet on the nozzle and after ignition simulation. The sensor 36 comprises for example a balance such as the table supplied by the Swiss company Kistler under the reference Z14398. The nozzle 20 is connected to the balance 36 by screwing the divergent 20a by means of screws 39, while the casing 44 is connected to the balance 36 by screws 49 at a lower flange 44c of the casing. The envelope 44 rests on an internal recess of the frame 12 by means of an external rim. At its lower part, the envelope 44 is extended by a skirt 21 which surrounds the upstream part of the divergent a.

  The nozzle 62 of the water jet generator 60 is located above

  below the test specimen 10. It has a vertical J-axis outlet orifice which is aligned with the axis A of the test specimen when the latter is in the vertical position (FIG. 2). The outlet section of the nozzle 62 determines the diameter of the jet 65, so as to be able to simulate jets of diameters

different.

  The water tank 64 is pressurized, the pressure level in the tank regulating the speed of the jet leaving the nozzle 62. The pressurization is produced by a source 63 of compressed gas connected to the upper part of the tank 64, while the pressure regulation of the tank is carried out by the opening of two dischargers 67. The speed of the water jet leaving the nozzle 62 is adjusted to a value representative of the speed of a returning water jet, for example from 10 to 50 m / s. This speed can be calculated by measuring the flow rate in line 66 and by measuring the pressure difference between the top and the bottom of the tank.

  of water 64 by means of a differential pressure sensor 69.

  The deflector 72 of the moving element 70 (FIGS. 2 and 4 to 6) is a rigid metal blade whose initial position is on the path of the water jet between the outlet of the nozzle 62 and the downstream part of the nozzle 20 At its front part, the deflector 72 is connected to the lifter 74 by a cable 76. At its rear part, the deflector 72 has a housing 72a for a finger of a trigger 92 controlled by an electromagnet 94 carried by the ramp 80. This is inclined relative to the horizontal by an angle ca. The lifter 74 has two parallel lateral rods 74a, 74b which can slide in tubular guides 84a, 84b carried by the ramp 80. The lifter 74 is also provided with a strip 78 pierced with holes 78a (Figure 4) at regular intervals and passing in front of a photoelectric sensor, or light barrier, 88 carried by the ramp 80. At its rear end, each rod 74a, 74b is sealingly engaged on an outlet orifice of a connecting piece 96 (FIG. 4) provided buffer capacities 98a, 98b and which has inlet ports 99 connected to one or more sources of pressurized gas, for example nitrogen sources, provided with valves (not shown). The system

  propellant 90 thus constitutes a compressed gas cannon.

  A detector 86 (Figure 5) carried by the ramp 80 is placed on

  the path followed by the spreader 74 when it was propelled by the barrel 90.

  The detector 86 which can be of the photoelectric or frangible type produces a signal at the time of the passage of the spreader 74. This signal is used to control the ignition simulation by a pin 54. The operation of the test installation is as follows. A test specimen 10 with a nozzle 20 whose shape reproduces that of an actual nozzle concerned by the tests to be carried out is mounted. The position of the bottom 46 adjusts the volume of the chamber 42, thus making it possible to simulate a drain law comparable to the ignition to be simulated. A slight pressurization of the chamber 42, for example at a pressure of 1.1 MPa,

  is carried out in order to reproduce the usual real conditions.

  The deflector 72 is placed between the nozzle 62 and the downstream part of the nozzle 20 by engaging the trigger 92 in the housing 72a, the pistons 74a, 74b of the spreader 74 being inserted in the guides 84a, 84b and having their rear ends connected to connecting pieces 96a, 96b. The barrel 90 is pressurized by connection of the part 96 and the buffer capacities 98a, 98b to the gas source or sources under

  pressure to which or to which the part 96 is connected.

  The water jet is then generated by opening the valve 68 and emptying the reservoir 64, the diameter and the speed of the jet being

  determined by the choice of nozzle 62 and the pressurization of reservoir 64.

  The deflector 72 being in its initial position (FIGS. 2 and 7A),

  the jet 65 is deflected and does not reach the nozzle 20.

  When the jet has reached a stationary coherent state, the electromagnet 94 is controlled to actuate the trigger 92 and release the deflector 72. The mobile assembly comprising the deflector 72 the spreader 74 and the pistons 74a and 74b is then propelled by the barrel 90, which frees the passage for the water jet 65 towards the nozzle

(Figures 7B and 7C).

  The choice of the angle of inclination of the ramp 80 and the ratio between the speed of the deflector 72 and that of the water jet 65 makes it possible to give the front of the water jet a desired shape. Thus, to obtain a substantially flat and horizontal front, in order to best simulate a returning jet of water, it is possible to choose an angle a equal to 45 and the ratio between the speed of the deflector 72 and that of the equal jet of water 65 in Jô. The deflector 72 then acts as a "guillotine" which would cut off the water jet 65 to give it a flat front, like the

show Figures 7A to 7C.

  The water jet 65 can then reach impact on the downstream part of the nozzle 20, the nozzle being or not provided with a closure part 32 or partly on the nozzle and partly on the rear bottom of the propellant and

the skirt 21.

  The propellant ignition simulation is controlled at a selected time before or after the impact of the water jet or

concomitant with impact.

  The ignition simulation is carried out at a selected time before or after impact by injecting pressurized gas into the chamber 42 from an annex circuit of pressurization by nitrogen gas, by choosing the instants of the simulation control d ignition and

  the release of the deflector 72 by the electromagnet 94.

  A simulation of ignition concomitant with the impact is carried out by injecting combustion gases from the choke 54 in the chamber 42 by ignition of the choke 54 from the signal of the detector

  86. The position of the detector 86 on the ramp 80 is adjusted for this purpose.

  The increase in pressure in the chamber 42 causes the latching of the cover 30 then the departure of the closure part 32 with which the nozzle 20 is optionally provided by rupture of the ligatures which

connect to the nozzle divergent.

  A camera (not shown) makes it possible to view and record the departure of the closing part. The starting time of the closing part can be detected by means of one or more sensors which are interposed between the closing part and the nozzle and which deliver a signal in response to their rupture when the closing part leaves . Pressure sensors (not shown) make it possible to measure the pressure at the level of the wall of the nozzle 20, in the

  divergent, convergent, as well as the pressure in the chamber 42.

  The force sensor 36 makes it possible to measure the forces which tend to separate or bring the nozzle 20 closer to the casing 44 under the effect of the ignition simulation and the impact of the water jet. The sensor 36 being subjected to the same forces as those of a hinge abutment usually provided between an orientable nozzle and the bottom of a thruster, it makes it possible to measure the forces applied to the abutment in the event of

incoming water jet.

  The signals produced by the sensor 88 in response to the scrolling of the strip 78 carried by the mobile assembly make it possible to measure the real speed of the deflector when it is expelled, while the measurement of the flow rate in the pipe 66 makes it possible to measure the speed of the water jet 65 at the outlet of the nozzle 62. These measurements make it possible to make the necessary adjustments to obtain the desired ratio between

these speeds.

  Tests can be carried out with impacts of the water jet parallel to the axis A of the test specimen (figure 8A) and inclined with respect to the axis A (figure 8B). The inclination between the axes A and J of the test specimen and of the impact of the jet is chosen by adjusting the position of the frame 14 on the support rails 16. Tests can also be carried out by shifting the specimen laterally. direction test

  transverse to the axis J of impact of the jet.

  Tests can be carried out with the nozzle 20 with or without a closure part and with different closure parts in order to find the most favorable form. Closure pieces 321, 322, 323 simulating re-entrant anti-jet plugs having an external surface exposed to impact of planar shape, frustoconical shape or in shape of

  spherical cap, are shown in Figures 9A to 9C.

Claims (22)

  1. Test method for simulating the impact of a water jet entering the rear part of a propellant, characterized in that it comprises the steps which consist in: -providing a test specimen comprising a nozzle with a divergent, -generate a substantially coherent water jet in an impact direction directed towards the downstream end part of the nozzle, -simulate a ignition of propellant by increasing the pressure inside d '' a chamber separated from the diverging part of the nozzle by a cover, and   - measure the forces exerted on the nozzle.   2. Method according to claim 1, characterized in that the generation of a substantially coherent water jet comprises the steps which consist in: - supplying water under pressure to a nozzle having an outlet axis directed in the direction impact, - initially deflecting the jet coming out of the nozzle, with respect to the direction of impact, and - removing the deflection of the jet after it has reached a state consistent stationary.   3. Method according to claim 2, characterized in that the deflection of the jet is carried out by interposition of a deflector on the path between the nozzle and the downstream end portion of the nozzle, the elimination of   the deflection of the jet being produced by displacement of the deflector.   4. Method according to any one of claims 1 and 2,   characterized in that the deflector is oriented so that it has a deflection surface of the jet making a determined angle with respect to the direction of impact and the deflector is moved to remove the deflection of the jet with a speed displacement depending on the speed of the water jet,   so as to give it a determined shape front.   5. Method according to any one of claims 1 to 4,   characterized in that the jet is given a substantially flat front   perpendicular to the impact direction.   6. Method according to any one of claims 1 to 5,   characterized in that the ignition simulation is carried out by admission   pressurized gas in the chamber.   7. Method according to any one of claims 1 to 5,   characterized in that the ignition simulation is carried out by command   a gas nozzle injecting gas into the chamber.   8. Method according to claim 7 depending on one   any of claims 3 and 4, characterized in that the choke is   controlled by detection of the movement of the deflector, to control the ignition simulation substantially concomitantly   with the arrival of the jet at the downstream part of the nozzle.   9. Method according to any one of claims 1 to 8,   characterized in that the test specimen is provided with a   closure at the downstream end of the nozzle, in order to simulate an anti-plug   incoming jet, and we observe the ejection of the closure element after the ignition simulation.   10. Method according to any one of claims 1 to 9,   characterized in that several tests are carried out by varying the   shape of the surface of the closure element exposed to the water jet.   11. Method according to any one of claims 1 to 10,   characterized in that several tests are carried out by varying   the angle between the direction of impact and the axis of the nozzle.   12. Test installation for simulating the impact of a water jet entering the rear part of a propellant, characterized in that it comprises: - a frame (12) for supporting a specimen test comprising a nozzle (20) with divergent, - an envelope (44) carried by the frame (12) and enclosing a chamber (42), - means (50; 54) for pressurizing the chamber (42 ), - means provided with a force sensor (36) for connecting the casing (44) to a nozzle (20) with the interposition of a cover (30) between the chamber (42) and the diverging portion of the nozzle ( 20), - a device for generating a stationary coherent water jet (65), comprising a nozzle (62) having an outlet opening with a vertical axis and connected to a pressurized water tank (64), - a deflector (72) movable between an initial position in which it is interposed on the path between the nozzle (62) and a nozzle carried by the frame (12), and a position in which it releases this path, and   - Means (90) for moving the deflector (72).   13. Installation according to claim 12, characterized in that the support frame (12) is orientable to vary the angle between the vertical direction of exit of the nozzle (62) and the axis of a nozzle (20) carried by the frame (12).   14. Installation according to any one of claims 12 and   13, characterized in that the volume of the chamber (42) is variable.   15. Installation according to any one of claims 12 to   14, characterized in that the means for pressurizing the   chamber (42) have at least one source (50) of pressurized gas.   16. Installation according to any one of claims 12 to   14, characterized in that the means for pressurizing the   chamber (42) have a choke (54).   17. Installation according to any one of claims 12 to   16, characterized in that the deflector (72) is integral with a crew   movable along a guide ramp (80).   18. Installation according to any one of claims 12 to   17, characterized in that the deflector (72) is movable according to a   inclined trajectory with respect to the horizontal.   19. Installation according to claim 18, characterized in that the deflector (72) is movable along a guide ramp (80)   making an angle of 45 relative to the horizontal.   20. Installation according to any one of claims 12 to   19, characterized in that the means for moving the deflector are   constituted by a pressurized gas cannon (90).   21. Installation according to any one of claims 12 to   20, characterized in that it comprises a detector (86) placed on the path of the deflector in order to provide a signal at a determined time after   the deflector has left its original position.   22. Installation according to any one of claims 12 to   21, characterized in that it includes means (78, 88) for measuring   the speed of movement of the deflector (72).