基于时频变换的激波风洞天平信号分析与处理

SIGNAL ANALYSIS AND PROCESSING OF SHOCK TUNNEL BALANCE BASED ON TIME-FREQUENCY TRANSFORM

在激波风洞中开展测力试验时,测力系统在风洞流场起动瞬间会受到冲击激励,从而对天平的输出信号产生惯性干扰.天平输出信号中叠加有动态气动力信号和惯性振动信号,有可能无法直接分辨出气动力信号的规律性,信号处理结果与真实气动力之间会产生较大的误差,导致处理结果不可靠.由于模型测力天平系统结构的复杂性,在极短的有效试验时间(毫秒级)内,天平信号中部分高频率分量(由结构高阶模态振动、非定常气动载荷或其他流场干扰等因素引起的高频干扰)有可能无法完全衰减,此时对信号直接进行传统的滤波处理和傅里叶变换分析反而有可能增大处理结果的误差.本文采用小波变换和希尔伯特-黄变换,针对尖锥标准模型的激波风洞天平信号,开展降噪和时频变换分析处理,旨在有效辨识出天平信号中的不同干扰成分,输出可靠的气动力结果.本文将时频变换方法应用于风洞天平冲击阶跃载荷的信号处理,对结果进行对比分析,验证了该方法在脉冲风洞测力试验数据处理中的有效性和可靠性,得到了比较理想的结果.

Shock tunnel ground test is usually used to study the high-enthalpy aerodynamic characteristics of new hypersonic vehicles. As one of the basic researches of high-temperature aerodynamics, high-precision aerodynamic force measurement is the key technology of shock tunnel ground test. When a force test is conducted in the shock tunnel, the vibration of force measurement system is excited during the starting process of shock tunnel, which causes inertial interference to the output signal of the balance. The balance signals, with dynamic force and inertial-vibration,may not directly show regularity of the real dynamic force, resulting in a big error between the processed balance forces and the real loads, and making the results unreliable. Due to complex structure of the force measurement system, part of the high-frequency components of the balance signal(high-frequency interference caused by structural high-order modal vibration, unsteady aerodynamic load or other flow field interference) may not be fully attenuated within the extremely short-duration(millisecond level). At this time, traditional filter processing and Fourier transform may increase the error of results. In order to solve the problem of aerodynamic force measurement fast and accurately,wavelet transform and Hilbert-Huang transform are used in this study to carry out noise reduction and time-frequency transform analysis for the balance signal in a cone’s force test of shock tunnel, to effectively identify the different interference components and output reliable force results. In this paper, the time-frequency transform is applied to the signal processing of the step-load and balance output. The force results are compared and analyzed to verify the effectiveness and reliability of the current method in the data-processing of the shock tunnel test, and obtain good results. At the same time, the time-frequency processing method of signal in this study will be used in the sample data pre-processing of the shock tunnel balance intelligent research.