Whenever the military parade is performed, the attention is nothing more than the wonderful aerobatic performance, in addition to the thrilling aerobatic action, the formation of aircraft pulling the colored smoke tail also brings the audience a visual beauty enjoyment. Through various aerobatic actions, the air show can not only fully display the performance of the aircraft, but also highlight the national military strength and show the national spirit and culture. However, the thrilling aerobatic actions in the air show may bring "danger" to the aircraft, in order to ensure the safety of the aircraft during the aerobatic performance, it is necessary to develop some "secret weapons", and the aerodynamic instability prediction technology of the aero engine is one of them.
Aircraft formation for national day celebration training (Source: China News Network)
The air show consists of a variety of basic movements, such as rolling, rib fighting, Inmaman tendon fighting, and the famous cobra movement. Under these actions, the aircraft engine will suffer from intake air distortion, engine stability margin attenuation, at this time monitoring the aerodynamic stability of the aircraft engine is the key to ensure the safe flight of the aircraft. The so-called intake air distortion, that is, the inlet flow field parameters of the aircraft engine are inconsistent with the assumptions of its design, if the inlet flow field parameters are different, it can be divided into total pressure distortion, total temperature distortion, static pressure distortion and so on. In the actual operation of the aero engine, the aircraft's large angle of attack flight or high maneuvering flight and crosswind intake will cause total pressure distortion due to air intake separation; shipborne catapult aircraft take off to inhale steam and air exhaust gases discharged by missiles when the aircraft launches missiles will cause total temperature distortion. Intake aeration is the main cause of aircraft engine instability, easy to cause the loss of compressor stability, at this time the turbine load and thermal stress increase, compressor blade forced vibration, it is very likely to cause irreversible damage to the engine, affecting the aircraft flight safety, so it is necessary to develop timely and reliable compressor instability forecasting technology to ensure the safe and stable operation of the aircraft engine under the condition of intake distortion.
Aircraft engine suffers intake aberration (image from the Internet)
Serious consequences of aero engine instability (image from the Internet)
During the flight of the aircraft, we can monitor the operating state of the engine by measuring the pressure, vibration and other signals, for the pressure or vibration of this type of discrete time signal, how to extract the disturbance signal that characterizes the instability characteristics of the compressor? At present, there are many aero-engine instability prediction methods reported in the literature, such as correlation analysis, root mean square analysis, rapid wavelet analysis and nonlinear feature extraction methods, but most of them are only applicable under uniform flow conditions. In order to solve the problem of instability prediction under the condition of intake aeration distortion, researchers from the Institute of Engineering Thermophysics of the Chinese Academy of Sciences have conducted in-depth research on several existing instability prediction methods in the world, and innovatively proposed a practical engineering "rapid wavelet" instability prediction method with the help of "wavelet", which is widely used in the analysis of seismic waves and brain waves.
"Wavelet", as the name suggests, is a small waveform. Compared to the sine waves used in Fourier analysis, the energy of the "wavelets" is limited and very concentrated in the time domain. This "wavelet", which can effectively analyze the instantaneous signal through telescopic translation operation, can split the signal (for the aircraft engine, the dynamic static pressure signal obtained by the measurement of the wall surface of the compressor receiver) from the time-frequency characteristics, extract the disturbance component, and then extract the aircraft engine instability characteristic signal.
"Wavelet"
Fast wavelet decomposition process (citation 1)
The researchers first carried out relevant experimental studies on the multistage axial compressor experimental bench, and systematically compared the reliability of fast wavelet analysis and other instability prediction methods under intake aeration distortion conditions. The results show that under the condition of total circumferential pressure distortion, rapid wavelet analysis can sensitively feel the influence of intake aberration on stability, and the requirements for the location of the measurement point are low, which is more advanced and engineering practical than other forecasting methods. Subsequently, the researchers achieved a destabilization prediction of the multistage compressor under the condition of radial total pressure distortion by predicting the stability of the first instability stage.
Reliability of instability prediction under weekly total pressure distortion (citation 2)
Reliability of instability forecasting under radial total pressure distortion (citation 1)
Based on the laboratory verification results, the rapid wavelet instability prediction method was applied to the aero engine model for field application verification, and the results of the insertion plate distortion and asthma test at different speeds showed that the rapid wavelet analysis can quickly and accurately predict the instability signal within 20 milliseconds, which can effectively avoid the phenomenon of blade vibration exceeding the standard and stress overload caused by the compressor for a long time.
Aero engine instability forecasting instrument
A certain type of aircraft engine instability forecast test verification
bibliography:
1. Yang Liu, Jichao Li, Juan Du, Hongwu Zhang, Chaoqun Nie. Stall warning strategy based on fast wavelet analysis in multistage axial compressor [J]. ASME Journal of Engineering for Gas Turbine and Power, 2022, 144: 044501.
2. Yang Liu, Jichao Li, Juan Du, Hongwu Zhang, Chaoqun Nie. Realiability analysis for stall warning methods in an axial flow compressor [J]. Aerospace Science and Technology, 2021, 115:106816.
3. HU Jun. Aerodynamic stability analysis method of aeronautical compressor[M]. Beijing: National Defense Industry Press, 2015.
4. "How do you enjoy the military parade air show?" https://www.zhihu.com/question/348481104/answer/840750863
Source: Institute of Engineering Thermophysics, Chinese Academy of Sciences