阅读说明：本技术 一种发动机地面试验pogo激发方法 (Engine ground test POGO excitation method ) 是由 李大海 唐斌运 刘洋 郭立 王薇 梁永鹏 吉展阳 郭玉凤 于 2019-08-28 设计创作，主要内容包括：本发明提供了一种发动机地面试验POGO激发方法,解决现有地面试验未能有效真实模拟火箭飞行时POGO振动产生的环境,导致在试验时无法通过对POGO激发后推力振动测试确定相关影响,并针对影响进行POGO控制及抑制方法的研究的问题。该POGO激发方法包括以下步骤：1)建立液氧煤油发动机POGO测试环境,按照一定梯度规律改变推进剂的供应压力,激发POGO激振；2)分别对推进剂不同供应压力下的POGO激振环境关键特性参数进行功率谱密度激振分析,若POGO激振环境关键特性参数共同出现某一个或多个峰值,则确定该峰值对应的频率点为易产生低频振动的频率点；POGO激振环境关键特性参数包括推力、氧入口压力和点火路压力。(The invention provides a POGO excitation method for an engine ground test, which solves the problems that the related influence cannot be determined through a thrust vibration test after POGO excitation in the test and the POGO control and inhibition method is researched aiming at the influence because the environment generated by POGO vibration in rocket flight cannot be effectively and truly simulated in the conventional ground test. The POGO excitation method comprises the following steps: 1) establishing a POGO testing environment of a liquid oxygen kerosene engine, changing the supply pressure of a propellant according to a certain gradient rule, and exciting POGO to vibrate; 2) performing power spectral density excitation analysis on key characteristic parameters of the POGO excitation environment under different supply pressures of a propellant, and if the key characteristic parameters of the POGO excitation environment jointly have one or more peak values, determining a frequency point corresponding to the peak value as a frequency point easy to generate low-frequency vibration; key environmental parameters for POGO excitation include thrust, oxygen inlet pressure and ignition circuit pressure.)

1. a POGO excitation method for an engine ground test is characterized by comprising the following steps:

1) establishing a POGO testing environment of a liquid oxygen kerosene engine, changing the supply pressure of a propellant according to a gradient rule, and exciting POGO to vibrate;

2) performing power spectral density excitation analysis on key characteristic parameters of the POGO excitation environment under different supply pressures of a propellant, and if the key characteristic parameters of the POGO excitation environment jointly have one or more peak values, determining a frequency point corresponding to the peak value as a frequency point easy to generate low-frequency vibration;

The POGO excitation environment key characteristic parameters comprise thrust, oxygen inlet pressure and ignition circuit pressure.

2. The POGO excitation method for the engine ground test according to claim 1, wherein the supply pressure of the propellant is changed according to a gradient law in the step 1), specifically:

a) After the engine is started at the normal inlet pressure, slowly reducing the pressure to 0.5-0.7 times of the normal inlet pressure value, keeping the pressure for a certain time, and then recovering the pressure to the normal inlet pressure;

b) after the engine is started at the normal inlet pressure, slowly increasing the pressure to 2.6-3 times of the normal inlet pressure value, keeping the pressure for a certain time, and then recovering the pressure to the normal inlet pressure;

c) Starting the engine at normal inlet pressure and maintaining for a certain time;

The certain time is determined according to the time required to be tested.

3. The POGO excitation method for the engine ground test according to claim 2, wherein the supply pressure of the propellant in the step 1) is changed according to a gradient law, specifically:

a) after the engine is started at the normal inlet pressure, the pressure is slowly reduced to 0.6 time of the normal inlet pressure value, the pressure is kept for a certain time, and then the pressure is restored to the normal inlet pressure;

b) after the engine is started at the normal inlet pressure, the pressure is slowly increased to 2.86 times of the normal inlet pressure value, the pressure is kept for a certain time, and then the pressure is restored to the normal inlet pressure;

c) The engine is started at normal inlet pressure and held for a certain time.

4. the engine ground test POGO excitation method of claim 1, 2 or 3, wherein:

in the step 1), the key characteristic parameters of the POGO excitation environment are obtained through a water test.

5. the POGO excitation method for the engine ground test according to claim 4, wherein in the step 2), the power spectral density is obtained by: and setting a time window of 100s to intercept the POGO excitation environment key characteristic parameter signals.

Technical Field

the invention relates to a POGO excitation method for an engine ground test.

Background

the physical process that POGO vibration produced is that the pressure of propellant in the conveying pipeline causes engine thrust pulsation, leads to arrow body structure vibration, and then aggravates pressure fluctuation in the pipeline, forms positive feedback and causes structural vibration to enlarge to make thrust pulsation increase. Under a ground test, due to the reasons that the working state of an engine is different from that of the engine during rocket flying, a propellant supply system is far away from the engine and the like, the environment generated by POGO vibration during rocket flying cannot be effectively and really simulated, at present, a vibration exciter form is adopted, taking a piston as an example, the structure is complex, the dynamic characteristic is poor, and excitation under a low-temperature medium is difficult to realize (the piston of the low-temperature medium is difficult to seal, and gasification is easy to occur during the movement process to influence the excitation effect); therefore, the POGO vibration cannot be effectively tested in the test, namely, the relevant influence cannot be determined through the thrust vibration test after the POGO is excited, and the research on the POGO control and inhibition method can be carried out according to the influence.

disclosure of Invention

The invention aims to overcome the defects that the related influence cannot be determined through a thrust vibration test after POGO excitation in the test due to the fact that the existing ground test cannot effectively and really simulate the environment generated by POGO vibration in rocket flying, and the POGO control and inhibition method is researched aiming at the influence.

in order to achieve the purpose, the technical solution provided by the invention is as follows:

a POGO excitation method for an engine ground test is characterized by comprising the following steps:

1) Establishing a POGO testing environment of a liquid oxygen kerosene engine, changing the supply pressure of a propellant according to a certain gradient rule, and exciting POGO to vibrate;

2) Performing power spectral density excitation analysis on key characteristic parameters of the POGO excitation environment under different supply pressures of a propellant, and if the key characteristic parameters of the POGO excitation environment jointly have one or more peak values, determining a frequency point corresponding to the peak value as a frequency point easy to generate low-frequency vibration; when POGO excitation occurs, one or more abnormal peaks can occur together in key characteristic parameters of the POGO excitation environment;

the POGO excitation environment key characteristic parameters comprise thrust, oxygen inlet pressure and ignition circuit pressure.

Further, the step 1) of changing the supply pressure of the propellant according to a gradient law specifically includes:

a) After the engine is started at the normal inlet pressure, slowly reducing the pressure to 0.5-0.7 times of the normal inlet pressure value, keeping the pressure for a certain time, and then recovering the pressure to the normal inlet pressure;

b) after the engine is started at the normal inlet pressure, slowly increasing the pressure to 2.6-3 times of the normal inlet pressure value, keeping the pressure for a certain time, and then recovering the pressure to the normal inlet pressure;

c) starting the engine at normal inlet pressure and maintaining for a certain time;

The certain time is determined according to the time required to be tested.

Further, the step 1) of changing the supply pressure of the propellant according to a gradient law specifically includes:

a) after the engine is started at the normal inlet pressure, the pressure is slowly reduced to 0.6 time of the normal inlet pressure value, the pressure is kept for a certain time, and then the pressure is restored to the normal inlet pressure;

b) After the engine is started at the normal inlet pressure, the pressure is slowly increased to 2.86 times of the normal inlet pressure value, the pressure is kept for a certain time, and then the pressure is restored to the normal inlet pressure;

c) the engine is started at normal inlet pressure and held for a certain time.

further, in the step 1), the key characteristic parameters of the POGO excitation environment are acquired through a water test.

further, in step 2), the power spectral density is obtained by: and setting a time window of 100s to intercept the POGO excitation environment key characteristic parameter signals.

the invention has the advantages that:

the supply pressure of the propellant is changed according to a certain gradient rule, the environment generated by POGO during rocket flying can be truly simulated on the ground, the POGO excitation is excited, and meanwhile, key characteristic parameters of the POGO excitation environment obtained by a water test are analyzed and compared, and the frequency point which is easy to generate low-frequency vibration is determined; the excitation method can adopt the existing pressure precise control and gradient regulation system, is simple and rapid, has a reliable test result, and is precise and reliable; can establish the experimental test basis for the subsequent rocket POGO research.

drawings

FIG. 1 is a diagram showing the variation of key characteristic parameters of the POGO excitation environment under low inlet pressure;

FIG. 2 is a power spectral density contrast plot of key characteristic parameters of the POGO excitation environment at low inlet pressure;

FIG. 3 is a graph I of power spectral density versus pressure for a low inlet pressure with a signal truncated for a set 100s time window;

FIG. 4 is a graph II of power spectral density versus pressure for a low inlet pressure with a signal truncated for a set 100s time window;

FIG. 5 is a graph of amplitude for a low inlet pressure POGO condition;

FIG. 6 is a variation diagram of key characteristic parameters of the POGO excitation environment under high inlet pressure;

FIG. 7 is a power spectral density contrast plot of key characteristic parameters of the POGO excitation environment at high inlet pressure;

FIG. 8 is a plot of power spectral density versus pressure for a signal intercepted at a high inlet pressure setting a 100s time window;

FIG. 9 is a diagram showing the variation of key characteristic parameters of the POGO excitation environment under normal inlet pressure;

FIG. 10 is a power spectral density contrast plot of key characteristic parameters of the POGO excitation environment at normal inlet pressure;

FIG. 11 is a graph of amplitude during normal inlet pressure POGO conditions;

FIG. 12 is a graph of low inlet pressure and its ascending gradient control;

FIG. 13 illustrates high inlet pressure and its ramp control.

Detailed Description

The invention is described in further detail below with reference to the following figures and specific examples:

a POGO excitation method for an engine ground test comprises the following steps:

1) identifying POGO characteristic parameters of an engine oxygen pump by using a water test to obtain key characteristic parameters of a POGO excitation environment, wherein the key characteristic parameters of the POGO excitation environment comprise thrust, oxygen inlet pressure and ignition path pressure;

2) Establishing a POGO testing environment of a liquid oxygen kerosene engine, changing the supply pressure of a propellant according to a certain gradient rule, and exciting POGO to vibrate;

The above-mentioned supply pressure of propellant that changes according to certain gradient law specifically means: testing the engine by respectively adopting low inlet pressure, high inlet pressure and normal inlet pressure;

2a) low inlet pressure

after the engine is started at a normal inlet pressure of 0.42MPa, the pressure is slowly reduced to 0.25 +/-0.03 MPa, the pressure is maintained for 20s, and then the pressure is restored to 0.42MPa, wherein a specific control mode is shown in figure 12;

2b) High inlet pressure

After the engine is started at the normal inlet pressure of 0.42MPa, the pressure is slowly increased to 1.2 +/-0.03 MPa, the pressure is kept for 20s, and then the pressure is restored to 0.42MPa, wherein the specific control mode is shown in figure 13;

2c) Normal inlet pressure

The engine was started at normal inlet pressure 0.42MPa and maintained for 20 s.

3) respectively carrying out power spectral density excitation analysis on the thrust (Fe), the oxygen inlet pressure (Pio) and the ignition circuit pressure (Pigc) under the three conditions of the low inlet pressure, the high inlet pressure and the normal inlet pressure, and if one or more peak values of the three parameters appear together, determining a frequency point corresponding to the peak value as a frequency point which is easy to generate low-frequency vibration;

3a) POGO excitation analysis at low inlet pressure

the change diagram of the key characteristic parameters of the POGO excitation environment under low inlet pressure is shown in figure 1, and the power spectral densities among thrust (Fe), oxygen inlet pressure (Pio) and ignition circuit pressure (Pigc) are compared, as can be seen from figure 2, the power spectral densities are the frequencies of the common occurrence peaks of the three parameters at 4.15Hz and 5 Hz;

setting a 100s time window to intercept the POGO excitation environment key characteristic parameter signal, wherein a power spectral density and pressure comparison diagram at 4.15Hz is shown in figure 3, and a power spectral density and pressure comparison diagram at 5Hz is shown in figure 4;

As shown in FIG. 5, the maximum amplitude of POGO excitation was 2.6 g. This peak is generated after the engine inlet pressure enters the low inlet pressure region, and therefore, 4.15Hz and 5Hz are frequency points at which the engine is prone to low frequency vibrations at low inlet pressures.

3b) POGO excitation analysis at high inlet pressure

the variation graph of the key characteristic parameters of the POGO excitation environment under the high inlet pressure is shown in FIG. 6, and the power spectral density among the three parameters is compared, as shown in FIG. 7, so that the frequency of the common peak of the three parameters is shown at 11 Hz;

a 100s time window is set to intercept the signal, and a power spectral density and pressure comparison graph at 11Hz is shown in FIG. 8;

3c) POGO excitation analysis under normal inlet pressure

Fig. 9 shows a variation diagram of key characteristic parameters of the POGO excitation environment at normal inlet pressure, and by comparing power spectral densities of the three parameters, see fig. 10, and an amplitude diagram of the POGO excitation environment at normal inlet pressure, see fig. 11, it can be seen that the POGO excitation phenomenon does not occur at normal inlet pressure, and the maximum amplitude is 0.8 g.

Through the POGO excitation method for the engine ground test, the ground excitation system can realize a thrust test environment not lower than 11Hz, and the amplitude is larger than 0.25 g.

While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications or substitutions can be easily made by those skilled in the art within the technical scope of the present disclosure.