A measurement method for simulating the acoustic-solid coupling response characteristics of solid rocket motors

Abstract

The present invention provides a measurement method for simulating the acoustic-solid coupling response characteristics of a solid rocket engine. The method adopts a rubber material to simulate a propellant, and can effectively study the acoustic-solid coupling response characteristics of a rocket engine under the premise of ensuring the safety of the test, and has the characteristics of low test cost. By designing a main body fixing component, a shell is hoisted on a test bench by adopting a support frame and a spring component, and the influence of the constraint of the support frame on the vibration characteristics of the test model is reduced. The shell is hoisted "relatively freely", and the free boundary conditions of the rocket engine when working are accurately simulated, so that it can be experimentally verified that the structural oscillation can indeed induce the pressure oscillation inside the combustion chamber under the right conditions, and a more accurate transfer function from the structural oscillation to the pressure inside the combustion chamber and a transfer function from the pressure oscillation in the combustion chamber to the engine structure oscillation are obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of solid rocket engines, and in particular relates to a measurement method for simulating acoustic-solid coupling response characteristics of a solid rocket engine. Background Art

[0002] In recent years, solid rocket engines have repeatedly experienced unstable combustion, mostly in the middle and late stages of engine operation, especially when the thickness of the grain in the combustion chamber becomes smaller and the thickness of the engine casing is at the same order of magnitude, unstable combustion occurs suddenly, while in the early stages of operation, it is relatively stable. This is probably because the pressure oscillation of the combustion chamber gas and the casing vibration are directly coupled and affect each other in the late stage of operation due to the decrease in propellant, which plays a resonance role, thus forming a positive feedback, further strengthening the oscillation of the pressure in the combustion chamber, and then serious unstable combustion occurs at the end of the operation, leading to the failure of the mission. Therefore, it is urgent to use experimental methods to determine the coupling between the combustion chamber acoustic cavity and the structural solid. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a measurement method for simulating the acoustic-solid coupling response characteristics of a solid rocket engine, which can accurately simulate the free boundary conditions of the rocket engine when it is working.

[0004] A measurement method for simulating the acoustic-solid coupling response characteristics of a solid rocket motor, comprising:

[0005] The solid rocket engine combustion chamber is simplified into a cylindrical tube cavity with openings at both ends, which serves as a shell (4); according to the pouring form of the propellant in the solid rocket engine combustion chamber, a rubber with the same structure and thickness is arranged on the inner surface of the shell (4) to simulate the propellant (8);

[0006] The shell (4) is mounted on a test bench (10), and a sound source is provided at each end of the shell (4);

[0007] A plurality of sound pressure sensors are arranged axially inside the housing (4), and a plurality of acceleration sensors are arranged inside and outside the housing (4);

[0008] When the sound source is turned on, the acceleration sensor will record the vibration information of the housing (4) and the sound pressure signal recorded by the sound pressure sensor as the output signal of this test;

[0009] The openings at both ends of the shell (4) are closed, and a white noise signal is generated by a signal generator and applied to the outer wall of one end of the shell (4) as an input signal; the vibration information of the shell (4) recorded by the acceleration sensor and the sound pressure signal recorded by the sound pressure sensor are used as output signals of this test;

[0010] The data collected from the above two tests were processed to obtain the transfer function from the structural oscillation to the internal pressure of the combustion chamber and the transfer function from the pressure oscillation in the combustion chamber to the engine structure oscillation, respectively, to analyze the acoustic-solid coupling response characteristics of the solid rocket engine.

[0011] Preferably, two main body fixing components (5) are used to mount the housing (4) on the test bench (10);

[0012] The main body fixing assembly (5) comprises a supporting frame (51), two sets of spring assemblies and two second springs (57);

[0013] The support frame (51) is a hollow structure, and the shell (4) can pass through the middle of the support frame (51); four evenly distributed hanging points are arranged on the same circumference of the outer wall of the shell (4);

[0014] The spring assembly comprises an adjusting screw (52), a nut (53), a tension sensor (54) and a first spring (55); the upper end of the adjusting screw (52) passes through a through hole of the supporting frame (51) and is tightened by the nut (53); the lower end is connected to one end of the tension sensor (54); the other end of the tension sensor (54) is connected to one end of the first spring (55); the other end of the first spring (55) is connected to a hanging point of the housing (4); the two first springs (55) of the two spring assemblies are respectively connected to the hanging points located at the upper part of the housing (4);

[0015] One end of the two second springs (57) is connected to the inner wall of the support frame (51), and the other end is connected to two hanging points at the lower part of the shell (4);

[0016] The pulling forces of the first springs (55) and the second springs (57) respectively opposite to each other in the two spring assemblies are on the same straight line, and the two straight lines formed are perpendicular to each other.

[0017] Preferably, two mounting brackets (56) are fixed on the inner wall of the support frame (51), and the second spring (57) is connected to the support frame (51) through the mounting brackets (56).

[0018] Preferably, the main body fixing assembly (5) is fixed on the test bench (10) symmetrically relative to the center of the shell (4).

[0019] Preferably, the main body fixing assembly (5) is fixed and supported by a triangular support frame (6).

[0020] Preferably, the shell (4) is made of structural steel.

[0021] The present invention has the following beneficial effects:

[0022] The present invention provides a measurement method for simulating the acoustic-solid coupling response characteristics of a solid rocket engine. The method uses a rubber material to simulate the propellant, and can effectively study the acoustic-solid coupling response characteristics of the rocket engine under the premise of ensuring the safety of the test, and has the characteristics of low test cost.

[0023] By designing the main fixing components and using the support frame and spring assembly to hoist the shell on the test bench, the influence of the constraint of the support frame on the vibration characteristics of the test model can be reduced. The shell is lifted "relatively freely" to accurately simulate the free boundary conditions of the rocket engine when it is working. It can be verified experimentally that structural oscillations can indeed induce pressure oscillations inside the combustion chamber under suitable conditions, and more accurate transfer functions from structural oscillations to internal pressure of the combustion chamber and from pressure oscillations in the combustion chamber to engine structural oscillations can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1( a ) is a schematic diagram of a measuring device for simulating the acoustic-solid coupling response characteristics of a solid rocket engine according to the present invention;

[0025] Figure 1(b) is a schematic diagram of the structure of the support structure and the spring suspension housing;

[0026] Figure 2 It is a schematic diagram of the distribution of the sound pressure sensor in the housing;

[0027] Figure 3 Schematic diagram of the measurement method.

[0028] Among them, 1-three-coordinate slide; 2-speaker shell; 3-treble and bass speakers; 4-shell; 5-main body fixing assembly; 6-triangular support frame; 7-movable support; 8-propellant; 10-test bench; 51-support frame; 52-adjusting screw; 53-nut; 54-tension sensor; 55-spring assembly; 56-mounting bracket; 57-second spring assembly. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0030] According to the actual situation of the solid rocket engine, the combustion chamber is simplified into a cylindrical tube cavity with openings at both ends as the shell 4, and the openings at both ends of the shell 4 are sealed. In order to simulate the real solid rocket engine, according to the pouring form of the propellant in the combustion chamber of the solid rocket engine, the rubber with the same structure and thickness is set on the surface of the shell 4 to simulate the propellant 8, and then the device for the acoustic-solid coupling experiment is built.

[0031] The present invention uses rubber material to simulate the propellant 8, because the actual propellant is a pyrotechnic product, which is flammable and explosive. For the safety of the test, it is necessary to use a rubber material with similar physical parameters to replace it. Although the physical parameters of the rubber sold on the market are different from those of the actual propellant, the elastic modulus of the two are still on the same order of magnitude as a whole, and the elastic modulus of the same engine shell is still several orders of magnitude different, so the rubber sold on the market is used to replace the propellant. At the same time, the purpose of this experiment is to explore the transmission law of vibration excitation after passing through two layers of materials with large differences in mechanical properties, and the combustion chamber of a solid rocket engine belongs to this situation. Therefore, as long as the difference in elastic modulus of the material used in the experiment is not significantly different from that of the actual solid rocket engine combustion chamber in terms of order of magnitude, it can be guaranteed that the same law is obtained. Therefore, the experiment will use structural steel to process the shell and use rubber to replace the propellant.

[0032] The specific test steps are as follows:

[0033] (1) Placement of test pieces

[0034] like Figure 1(a) and 1(b) As shown, the housing 4 is mounted on the test bench 10 by two main body fixing assemblies 5. The two main body fixing assemblies 5 are fixed on the test bench 10 symmetrically relative to the center of the housing 4 and are fixed and supported by a triangular support frame 6 respectively. The main body fixing assembly 5 includes a support frame 51, two sets of spring assemblies and two second springs 57;

[0035] The support frame 51 is a hollow structure, and the shell 4 can pass through the middle of the support frame 51; four evenly distributed hanging points are arranged on the same circumference of the outer wall of the shell 4;

[0036] The spring assembly includes an adjusting screw 52, ​​a nut 53, a tension sensor 54 and a first spring 55; the upper end of the adjusting screw 52 passes through the through hole of the support frame 51 and is tightened by the nut 53, and the lower end is connected to one end of the tension sensor 54, the other end of the tension sensor 54 is connected to one end of the first spring 55, and the other end of the first spring 55 is connected to the hanging point of the housing 4; the two first springs 55 of the two spring assemblies are respectively connected to the hanging points located at the upper part of the housing 4;

[0037] One end of the two second springs 57 is connected to the inner wall of the support frame 51, and the other end is connected to two hanging points at the lower part of the shell 4; wherein, two mounting brackets 56 are fixed on the inner wall of the support frame 51, and the second springs 57 are connected to the support frame 51 through the mounting brackets 56.

[0038] The tension of the first spring 55 and the second spring 57 in the two spring assemblies are on the same straight line, and the two straight lines formed are perpendicular to each other. The spring can effectively reduce the rigid constraint of the support frame 51 on the shell 4, and reduce the influence of the constraint of the support frame 51 on the vibration characteristics of the test model. As a result, the shell 4 is suspended "relatively freely", simulating the free boundary condition of the rocket engine when working, but it is impossible to achieve a completely free boundary on the ground, so it is called a "relatively free" boundary condition.

[0039] (2) Arrangement of sensors.

[0040] A certain number of sound pressure sensors are placed axially inside the housing 4 to measure the pressure oscillation data excited by the vibration of the sound source. Figure 2 The position distribution of the sound pressure sensor (the number and arrangement of the sensors will be modified according to actual needs in later experiments). The sensitivity of the sound pressure sensor is 50mv / pa, and the range is 20-146db; taking the 2m long shell 4 as an example, a certain number of acceleration sensors are set along the busbar on the inside and outside of the shell 4, and the number and arrangement of the sensors will be adjusted according to actual needs in later experiments. The position of the acceleration sensor can be calculated by the standing wave equation. The measurement point should avoid being placed at the location of the vibration node, and try to choose a location with a large deformation, otherwise the measured result will be very small, thereby reducing the accuracy of the measurement result.

[0041] (3) Experiment on structural response under the disturbance of acoustic cavity pressure

[0042] In the acoustic-solid coupling measurement test, a tweeter and woofer 3 of the same specification is placed at both ends of the shell 4 as a sound source to emit sound waves of specified frequency and amplitude to generate continuous sound pressure vibration in the cavity of the shell 4, and the sound pressure signal is measured by the sound pressure sensor. The sound shell 2 of the tweeter and woofer 3 is fixed on the three-coordinate slide 1, which is set on the test bench 10 and can drive the tweeter and woofer 3 to move forward and backward to adapt to shells 4 of different sizes.

[0043] Under the action of the internal standing wave sound field, the shell 4 will vibrate, and the acceleration sensor will record the vibration information of the shell 4. The acceleration signal and the sound pressure signal are used as the output signals of the system. The signals are transmitted to the computer via the data acquisition system, and the test data is recorded at this time.

[0044] (4) Experiment on acoustic pressure response of acoustic cavity under structural vibration

[0045] First, remove the sound source at both ends of the sound cavity shell 4, and use a disc consistent with the shell material to close the openings at both ends. Then use a signal generator to generate a white noise signal, which is then amplified by a power amplifier and acts on the outer wall of one end of the shell 4 as the input signal of the system. The structural vibration of the shell 4 is measured by an acceleration sensor, and then the data acquisition system analyzes and collects the sound source signal, acceleration signal, and sound pressure signal. Finally, the software in the computer is used to record and analyze the response.

[0046] (5) The collected data are processed to produce pressure oscillation frequency and structural vibration frequency diagrams under the two tests, and numerical analysis is performed to draw conclusions.

[0047] In order to use the cylindrical cavity to simulate the actual situation of the actual solid rocket engine in the test, the test designed by the present invention will use rubber of different thicknesses to simulate the propellants 8 of different thicknesses (i.e., different working times). It is also possible to conduct acoustic-solid coupling tests of two groups of acoustic cavities of different lengths (2m and 3m), each group of acoustic cavities of different lengths simulating the test of propellants 4 of 4 different rubber thicknesses, so it is expected that 8 groups of tests will be conducted, and each group of tests will be measured using two different fixing methods. Therefore, 8 groups of test equipment with different lengths and thicknesses were processed in the test.

[0048] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A measurement method for simulating the acoustic-solid coupling response characteristics of a solid rocket engine, characterized in that: include: The solid rocket motor combustion chamber is simplified into a cylindrical tube cavity with openings at both ends as a shell (4); According to the pouring form of the propellant in the combustion chamber of the solid rocket engine, a rubber with the same structure and thickness is arranged on the inner surface of the shell (4) to simulate the propellant (8); The shell (4) is mounted on a test bench (10), and a sound source is provided at each end of the shell (4); A plurality of sound pressure sensors are arranged axially inside the housing (4), and a plurality of acceleration sensors are arranged inside and outside the housing (4); When the sound source is turned on, the acceleration sensor will record the vibration information of the housing (4) and the sound pressure signal recorded by the sound pressure sensor as the output signal of this test; The openings at both ends of the shell (4) are closed, and a white noise signal is generated by a signal generator and applied to an outer wall at one end of the shell (4) as an input signal; the vibration information of the shell (4) recorded by the acceleration sensor and the sound pressure signal recorded by the sound pressure sensor are used as output signals of this test; The data collected from the above two tests were processed to obtain the transfer function from the structural oscillation to the internal pressure of the combustion chamber and the transfer function from the internal pressure oscillation of the combustion chamber to the engine structure oscillation, respectively, to analyze the acoustic-solid coupling response characteristics of the solid rocket engine; The housing (4) is mounted on a test bench (10) using two main body fixing assemblies (5); The main body fixing assembly (5) comprises a supporting frame (51), two sets of spring assemblies and two second springs (57); The support frame (51) is a hollow structure, and the shell (4) can pass through the middle of the support frame (51); four evenly distributed hanging points are arranged on the same circumference of the outer wall of the shell (4); The spring assembly comprises an adjusting screw (52), a nut (53), a tension sensor (54) and a first spring (55); the upper end of the adjusting screw (52) passes through a through hole of the support frame (51) and is tightened by the nut (53); the lower end is connected to one end of the tension sensor (54); the other end of the tension sensor (54) is connected to one end of the first spring (55); the other end of the first spring (55) is connected to a hanging point of the housing (4); the two first springs (55) of the two spring assemblies are respectively connected to the hanging points located at the upper part of the housing (4); One end of the two second springs (57) is connected to the inner wall of the support frame (51), and the other end is connected to two hanging points at the lower part of the shell (4); The pulling forces of the first springs (55) and the second springs (57) respectively opposite to each other in the two spring assemblies are on the same straight line, and the two straight lines formed are perpendicular to each other.

2. A method for measuring the acoustic-solid coupling response characteristics of a simulated solid rocket engine as claimed in claim 1, characterized in that: Two mounting brackets (56) are fixed on the inner wall of the support frame (51), and the second spring (57) is connected to the support frame (51) through the mounting brackets (56).

3. A method for measuring the acoustic-solid coupling response characteristics of a simulated solid rocket engine as claimed in claim 1 or 2, characterized in that: The main body fixing assembly (5) is fixed on the test bench (10) symmetrically relative to the center of the shell (4).

4. A method for measuring the acoustic-solid coupling response characteristics of a simulated solid rocket engine as claimed in claim 1 or 2, characterized in that: The main body fixing assembly (5) is fixed and supported by a triangular support frame (6).

5. A method for measuring the acoustic-solid coupling response characteristics of a simulated solid rocket engine as claimed in claim 1 or 2, characterized in that: The shell (4) is made of structural steel material.

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