Nozzle for solid rocket motor and solid rocket motor with the nozzle

Abstract

To provide a nozzle for a solid rocket motor, which can smoothly discharge thermal decomposition gases of a liner insert while avoiding the occurrence of a thinning phenomenon on a downstream side liner due to deflection of a combustion gas flow, which is caused by thermal deformation of a throat insert.SOLUTION: A nozzle consists of: an upstream assembly comprising a throat insert that has an inner surface forming the portion of a combustion gas flow path, which includes a throat, and a liner insert made of CFRP arranged on the outer periphery of the throat insert; and a downstream assembly that has an inner surface forming a divergent portion of the combustion gas flow path and comprises a liner in which an inner peripheral surface at the front end is a cylindrical surface. The inner peripheral surface at the front end of the liner comprises a plurality of protrusions that face the outer surface at the rear end of the throat insert and protrude inward. Between the protrusions adjacent in the circumferential direction, a flow path is formed to provide communication between the liner insert and a combustion gas flow path. The inner peripheral surface of the protrusions is a cylindrical surface having the same diameter as the outer peripheral surface at the rear end of the throat insert.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a nozzle for a solid rocket motor. [Background technology]

[0002] A solid rocket motor has a motor case and a nozzle as its main components.

[0003] The motor case is a roughly cylindrical pressure vessel made of, for example, CFRP (Carbon Fiber Reinforced Plastic), and is filled with propellant grains (solid fuel, oxidizer, and binder mixed and molded). The nozzle is attached to the rear end of the motor case (the direction of flight of the solid rocket motor is considered to be the forward direction; the same applies below), and provides thrust to the solid rocket motor by ejecting combustion gases produced by the combustion of the propellant grains rearward.

[0004] FIG. 1 is a schematic cross-sectional view showing the structure of a nozzle of a solid rocket motor.

[0005] The nozzle N is formed as a convergent-divergent nozzle in order to accelerate and eject the combustion gas to supersonic speed, and the cross-sectional area of ​​the combustion gas flow path FC is smallest at the transition section from the upstream convergent section to the downstream divergent section, i.e., at the throat TH.

[0006] Structurally, the nozzle N consists of an upstream assembly NU that forms the convergent section, through the throat TH, to the most upstream part of the divergent section, and a downstream assembly ND that forms the most upstream to most downstream part of the divergent section, and both assemblies NU and ND are fastened together by a plurality of fasteners (not shown) arranged at equal intervals around the circumference.

[0007] The upstream assembly NU includes an upstream holder HU, a throat insert IT disposed inside the upstream holder HU, and a liner insert IL interposed between the upstream holder HU and the throat insert IT. The upstream holder HU, the liner insert IL, and the throat insert IT are all annular members that are continuous in the circumferential direction.

[0008] The upstream holder HU is a structural member made of metal and having a substantially hollow cylindrical shape, and holds the liner insert IL and the throat insert IT inside.

[0009] The throat insert IT is a component whose inner surface forms the combustion gas flow path FC, from the converging section through the throat TH to the most upstream part of the diverging section. Because the inner surface is exposed to combustion gas at approximately 3000°C and is subjected to extremely high thermal loads, the throat insert IT is made from carbon / carbon (C / C), which has excellent heat and corrosion resistance.

[0010] The liner insert IL is a component made of CFRP that functions as an insulator to suppress heat transfer from the throat insert IT, which becomes hot due to heat transfer from the combustion gas, to the upstream holder HU. The presence of the liner insert IL, which functions as an insulator, prevents the temperature of the metal upstream holder HU from rising excessively, which could damage its structural strength.

[0011] The downstream assembly ND is composed of a downstream holder HD and a downstream liner LD disposed inside the downstream holder HD. Both the downstream holder HD and the downstream liner LD are annular members that are continuous in the circumferential direction.

[0012] The downstream holder HD is a metal member having a generally hollow truncated cone shape, and holds the downstream liner LD inside.

[0013] The downstream liner LD is a component that functions as a heat insulator to suppress heat transfer from the high-temperature combustion gas to the downstream holder HD. In the illustrated example, the downstream liner LD is made of a type of FRP (Fiber Reinforced Plastic) that is suitable for the temperature of the portion. The downstream liner LD, which functions as a heat insulator, prevents the temperature of the metal downstream holder HD from rising excessively, which would damage its structural strength.

[0014] Here, the detailed structure of the fastening portion between the upstream assembly NU and the downstream assembly ND, that is, the portion enclosed by the dashed circle J in FIG. 1, will be described below with reference to FIG.

[0015] FIG. 2 is a schematic cross-sectional view showing the discharge path of pyrolysis gas of the liner insert IL formed at the joint between the upstream assembly NU and the downstream assembly ND in the nozzle N of a conventional solid rocket motor.

[0016] The liner insert IL is in contact with the outer surface of the throat insert IT, whose inner surface is exposed to combustion gases at approximately 3000°C, and therefore becomes extremely hot. As a result, the resin contained in the CFRP that makes up the liner insert IL thermally decomposes, generating gas, and this pyrolysis gas is also very hot. Therefore, to prevent the temperatures of the upstream holder HU and downstream holder HD, both made of metal, from rising excessively and damaging their structural strength, it is necessary to release the pyrolysis gas generated in the liner insert IL directly into the combustion gas flow path FC without contacting the upstream holder HU and downstream holder HD.

[0017] For this reason, in the nozzle of a conventional solid rocket motor shown in Figure 2, an annular gap C extending in the axial direction (left-right direction in the figure) is provided between the rear end of the throat insert IT and the front end of the downstream liner LD. In other words, the outer peripheral surface of the rear end of the throat insert IT and the inner peripheral surface of the front end of the downstream liner LD are both formed as cylindrical surfaces, and the diameter of the former is smaller than the diameter of the latter by an amount corresponding to the radial dimension of the gap C. Then, as shown by arrow GP in the figure, pyrolysis gas generated in the liner insert IL flows axially through the annular gap C and is released into the combustion gas flow path FC. Summary of the Invention [Problem to be solved by the invention]

[0018] Here, the rear end of the throat insert IT, i.e., the portion facing the annular gap C described above, forms the most upstream portion of the diverging section of the nozzle N, and therefore the diameter of its inner peripheral surface gradually increases toward the rear. Meanwhile, the diameter of the outer peripheral surface of the rear end of the throat insert IT is constant in the axial direction. As a result, the rear end of the throat insert IT has a cross-sectional shape whose thickness decreases toward the rear. The rear end of the throat insert IT having such a shape is deformed by the influence of the heat of the combustion gas, bending radially outward as shown by the two-dot chain line in the figure.

[0019] In a hypothetical state where such deformation does not occur, the combustion gas flows smoothly along the inner surface of the throat insert IT and the inner surface of the downstream liner LD, as indicated by the solid arrows GC.

[0020] However, in the state where the above-described deformation occurs, the flow of combustion gas is bent radially outward along the inner surface of the curved throat insert IT (shown by the two-dot chain line), as indicated by the two-dot chain arrow GC', and impinges on the periphery of the edge LDe of the downstream liner LD. As a result, starting from the periphery of the edge LDe, erosion by the combustion gas occurs on the inner surface of the downstream liner LD aft of the edge LDe, causing the inner surface of the downstream liner LD to gradually recede radially outward. In other words, the thickness of the downstream liner LD gradually decreases (thinning phenomenon) in the area aft of the edge LDe, and eventually perforation may occur. This phenomenon must be avoided because combustion gas entering through the perforation causes an excessive rise in the temperature of the downstream holder HD, which can damage its structural strength.

[0021] The present invention has been made in consideration of the above problems, and aims to provide a nozzle for a solid rocket motor that can smoothly release thermal decomposition gases from the liner insert while avoiding the occurrence of thinning of the liner due to deflection of the combustion gas flow caused by thermal deformation of the throat insert. [Means for solving the problem]

[0022] In order to solve the above problems, a solid rocket motor nozzle according to a first aspect of the present invention comprises an upstream assembly and a downstream assembly fastened together with a fastener, the upstream assembly having an inner surface that forms the portion of the combustion gas flow path from the convergent portion through the throat to the most upstream portion of the divergent portion, and the outer peripheral surface of the rear end is formed as a cylindrical surface, an annular throat insert, an annular CFRP liner insert arranged on the outer periphery of the throat insert, and an annular metallic upstream holder that holds the throat insert and the liner insert inside, and the downstream assembly having an inner surface that forms the portion of the combustion gas flow path from the most upstream portion of the divergent portion through the throat to the most downstream portion of the divergent portion. and an annular downstream liner made of FRP, the inner circumferential surface of the front end of which is formed as a cylindrical surface, and an annular downstream holder made of metal that holds the downstream liner inside, wherein the inner circumferential surface of the front end of the downstream liner faces the outer circumferential surface of the rear end of the throat insert, and a plurality of circumferentially arranged protrusions protrude radially inward from the inner circumferential surface, thereby forming a flow path between each two circumferentially adjacent protrusions that connects the liner insert to the flow path of the combustion gas, and the inner circumferential surfaces of the protrusions are formed as cylindrical surfaces having the same diameter as the cylindrical surface that forms the outer circumferential surface of the rear end of the throat insert.

[0023] A second aspect of the present invention is a solid rocket motor equipped with the solid rocket motor nozzle of the first aspect of the present invention, comprising a motor case having a star-shaped hollow portion and an internal combustion type propellant grain loaded inside, the star-shaped hollow portion having a plurality of rays arranged at equal intervals in the circumferential direction, and the protrusions of the solid rocket motor nozzle being positioned at the same circumferential phase as the rays.

[0024] A third aspect of the present invention is a solid rocket motor equipped with the solid rocket motor nozzle of the first aspect of the present invention, comprising a motor case having a star-shaped hollow portion and an internal combustion type propellant grain loaded inside, the star-shaped hollow portion having a plurality of rays arranged at equal intervals in the circumferential direction, and the protrusion of the solid rocket motor nozzle being located at a circumferential phase midway between two adjacent rays. [Effects of the Invention]

[0025] According to the present invention, it is possible to obtain the excellent effect of smoothly releasing the thermal decomposition gas of the liner insert while avoiding the occurrence of thinning of the liner due to deflection of the combustion gas flow caused by thermal deformation of the throat insert. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the structure of a nozzle of a solid rocket motor. [Figure 2] FIG. 1 is a schematic cross-sectional view showing a discharge path of pyrolysis gas of a liner insert formed at a joint portion (portion J in FIG. 1) between an upstream assembly and a downstream assembly in a nozzle of a conventional solid rocket motor. [Figure 3] FIG. 1 is a schematic cross-sectional view showing a discharge path of pyrolysis gas of a liner insert formed at a fastening portion (part J in FIG. 1) between an upstream assembly and a downstream assembly in a nozzle of a solid rocket motor according to an embodiment of the present invention. [Figure 4] FIG. 1 is a schematic explanatory diagram showing the relative positional relationship in the circumferential direction between the release path of pyrolysis gas from a liner insert in a nozzle of a solid rocket motor according to an embodiment of the present invention and the ray of light from a propellant grain. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0028] FIG. 3 is a schematic cross-sectional view showing the discharge path of pyrolysis gas of the liner insert IL formed at the fastening portion between the upstream assembly NU and the downstream assembly ND in the nozzle N of the solid rocket motor according to an embodiment of the present invention.

[0029] The downstream liner LD has a front end portion, which faces the rear end portion of the throat insert IT in the radial direction, on its inner periphery, and is provided with a plurality of protrusions P arranged at equal intervals in the circumferential direction.

[0030] The protrusion P is a roughly rectangular parallelepiped portion that protrudes radially inward from the inner circumferential surface LDi, which is formed as a cylindrical surface at the front end of the downstream liner LD, and has a front surface Pf and a rear surface Pr that extend on a plane perpendicular to the central axis CL of the nozzle N (see Figure 1), a pair of side surfaces Ps (see the view in the Z direction arrow) that extend on a plane including the central axis CL of the nozzle N, and an inner circumferential surface Pi (see the view in the Z direction arrow) that is formed as a cylindrical surface having the same diameter as the outer circumferential surface ITo, which is formed as a cylindrical surface at the rear end of the throat insert IT.

[0031] Between the two opposing side surfaces Ps of two circumferentially adjacent protrusions P, a groove-like flow passage FP is formed, which connects the liner insert IL to the combustion gas flow passage FC (see the view from the Z direction arrow). The pyrolysis gas generated in the liner insert IL flows in the axial direction through multiple groove-like flow passages FP arranged at equal intervals in the circumferential direction, as shown by arrows GP in the figure, and is released into the combustion gas flow passage FC.

[0032] Thus, in the nozzle N of the solid rocket motor according to the embodiment of the present invention, the inner circumferential surfaces Pi of the multiple protrusions P provided on the inner periphery of the forward end of the downstream liner LD are in intimate contact with the outer circumferential surface ITo of the aft end of the throat insert IT. Therefore, unlike the nozzle N of the conventional solid rocket motor shown in Figure 2, the aft end of the throat insert IT is not deformed by bending radially outward due to the heat of the combustion gas, and the flow of combustion gas is smooth along the inner surface of the throat insert IT and the inner surface of the downstream liner LD. Therefore, it is possible to avoid thinning of the inner surface of the downstream liner LD.

[0033] The shape of the groove-like flow path FP formed by the multiple protrusions P arranged at equal intervals in the circumferential direction is not limited to that described above with reference to FIG. 3. For example, in the flow path FP shown in FIG. 3, its radial outer surface is formed as a cylindrical surface having the same diameter as the inner circumferential surface LDi of the front end of the downstream liner LD. However, the radial outer surface may be formed as a cylindrical surface having a smaller diameter than the inner circumferential surface LDi of the front end of the downstream liner LD, or as a plane perpendicular to the radial direction and located radially inward from the cylindrical surface constituting the inner circumferential surface LDi of the front end of the downstream liner LD. Furthermore, although the pair of side surfaces Ps of the protrusions P have been described above as extending on a plane including the central axis CL of the nozzle N, the side surfaces Ps may also be formed as planes perpendicular to the radial outer surface of the flow path FP at their connection portions with the radial outer surface.

[0034] Furthermore, the dimensions or number of groove-shaped flow paths FP formed by a plurality of protrusions P arranged at equal intervals in the circumferential direction can be appropriately set, for example, so that the pyrolysis gas released from the flow paths FP flows smoothly along the inner surface of the downstream liner LD without excessively disturbing the flow of combustion gas in the flow paths FC. In addition, although the protrusions P are shown in this embodiment as being arranged at equal intervals in the circumferential direction, they may be arranged at appropriate unequal intervals (non-uniform intervals) so that the flow of combustion gas in the flow path FC flows smoothly along the inner surface of the downstream liner LD without excessively disturbing it.

[0035] The pyrolysis gas discharged into the combustion gas flow path FC as described above flows in a film shape along the inner surface of the downstream liner LD, which is formed as a conical surface, and this prevents the inner surface of the downstream liner LD from being directly exposed to the high-temperature combustion gas. That is, the pyrolysis gas flowing out from the groove-shaped flow path FP functions as a heat shield that suppresses heat transfer from the combustion gas flowing through the flow path FC to the downstream liner LD. Therefore, it is preferable to provide the groove-shaped flow path FP in the flow path FC at a circumferential position where the temperature of the combustion gas is particularly high.

[0036] In solid rocket motors, internal combustion propellant grains are often used as the propellant grains loaded into the motor case. Internal combustion propellant grains are generally formed into a hollow cylindrical shape, but the cross section of the hollow portion is often star-shaped. This star-shaped hollow portion consists of a central circular space and a plurality of equally spaced circumferential spaces, i.e., rays, that protrude radially outward from the circular space. It is empirically known that the circumferential temperature distribution of combustion gases generated by the combustion of propellant grains having star-shaped hollow portions has a local peak (maximum value) at the same circumferential phase as the rays or at the midpoint between two adjacent rays.

[0037] A preferred arrangement of the groove-shaped flow paths FP, which has been set based on this, will be described below with reference to FIG.

[0038] FIG. 4 is a schematic explanatory diagram showing the relative positional relationship in the circumferential direction between the pyrolysis gas release path (groove-shaped flow path FP) of the liner insert in the nozzle of a solid rocket motor according to an embodiment of the present invention and the ray of light of the propellant grain.

[0039] In the illustrated example, the hollow portion of the propellant grain has seven rays HSb protruding radially outward from a central circular space HSc.

[0040] If the circumferential temperature distribution of the combustion gas generated by the combustion of the propellant grains has a local peak (maximum value) at the same circumferential phase as the light beam HSb, as shown in (A), the above-mentioned groove-shaped flow paths FP can be arranged so that they are each located at the same circumferential phase as the light beam HSb (in other words, the protrusions P can be arranged so that they are each located at a circumferential phase midway between two adjacent light beams HSb).

[0041] On the other hand, if the circumferential temperature distribution of the combustion gas generated by the combustion of the propellant grains has a local peak (maximum value) at the circumferential phase midway between two adjacent beams HSb, then as shown in (B), the above-mentioned groove-shaped flow paths FP can be arranged so that they are each located at the circumferential phase midway between the two adjacent beams HSb (in other words, the protrusions P can be arranged so that they are each located at the same circumferential phase as the beams HSb).

[0042] By arranging the grooved flow passages FP in this manner, the circumferentially phased portions of the inner surface of the downstream liner LD that are exposed to locally high-temperature combustion gases are covered with pyrolysis gases from the throat insert IT that are discharged from the grooved flow passages FP located in the same circumferential phase, preventing excessive temperature rise due to heat transfer from the combustion gas flowing through the flow passages FC. As a result, it is possible to prevent wall thinning from occurring over the entire circumferential area of ​​the inner surface of the downstream liner LD. [Explanation of symbols]

[0043] C Gap CL Central axis of nozzle for solid rocket motor FC Combustion gas flow path FP flow path HD downstream holder A ray of light from the star-shaped hollow of an HSb propellant grain The circular space in the center of the HSc propellant grain HU upstream holder IL liner insert IT Throat Insert ITo Outer surface of the rear end of the throat insert LD downstream liner LDe Downstream liner edge LDi Inner surface of the forward end of the downstream liner N Solid rocket motor nozzle ND Downstream Assembly NU Upstream Assembly P protrusion Pf Front of protrusion Pi Inner surface of protrusion Pr Rear surface of protrusion Ps Side of protrusion TH throat

Claims

1. 1. A nozzle for a solid rocket motor, comprising: an upstream assembly and a downstream assembly fastened together by fasteners; The upstream assembly includes: an annular throat insert having an inner surface that forms a portion of a combustion gas flow path from the convergent portion through the throat to the most upstream portion of the divergent portion, and an outer peripheral surface of a rear end portion formed as a cylindrical surface; an annular liner insert made of CFRP arranged on the outer periphery of the throat insert; an annular upstream holder made of metal that holds the throat insert and the liner insert inside; Equipped with The downstream assembly includes: an annular downstream liner made of FRP having an inner surface that forms the combustion gas flow path from the most upstream portion of the diverging section to the most downstream portion of the diverging section, and the inner circumferential surface of a front end portion is formed as a cylindrical surface; a downstream side holder that is an annular metal member and that holds the downstream side liner therein; Equipped with an inner peripheral surface of the forward end portion of the downstream liner faces an outer peripheral surface of the aft end portion of the throat insert, and a plurality of circumferentially arranged protrusions protrude radially inward from the inner peripheral surface, whereby a flow path is formed between each two circumferentially adjacent protrusions, the flow path connecting the liner insert to a flow path of the combustion gas; a nozzle for a solid rocket motor, wherein the inner peripheral surface of the protrusion is formed as a cylindrical surface having the same diameter as the cylindrical surface that constitutes the outer peripheral surface of the rear end of the throat insert.

2. A solid rocket motor comprising the nozzle for a solid rocket motor according to claim 1, A motor case is provided with a star-shaped hollow portion and an internal combustion propellant grain loaded therein, The star-shaped hollow portion has a plurality of rays arranged at equal intervals in the circumferential direction, A solid rocket motor, wherein the protrusion of the solid rocket motor nozzle is positioned at the same circumferential phase as the beam of light.

3. A solid rocket motor comprising the nozzle for a solid rocket motor according to claim 1, A motor case is provided with a star-shaped hollow portion and an internal combustion propellant grain loaded therein, The star-shaped hollow portion has a plurality of rays arranged at equal intervals in the circumferential direction, A solid rocket motor, wherein the protrusion of the solid rocket motor nozzle is located at a circumferential phase midway between two adjacent beams.

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