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现代高速飞行器结构热模态频率特性试验研究,对这类飞行器设计校核和飞行安全具有重要意义。根据飞行过程中遭受的气动加热特性设计了瞬态热环境模拟系统,同时,根据高温环境的特点对测试中的激励和测量方式进行了重新设计,成功地将普通激振器应用于高温结构模态试验,最终将热环境模拟系统与振动测试系统组合,形成一套考虑瞬态热影响的热模态试验系统,实现了瞬态热环境下结构模态的地面测试。对一个切尖三角翼测量了各个加热区的温度随加热时间的变化,验证了加热温度控制的精确性;在纯随机激励下对测得的激励和振动响应信号采用短时傅里叶变换(Short Time Fourier Transformation,STFT)进行时变模态参数辨识,获得了前四阶模态频率随加热时间的变化,并与结构有限元数值计算结果进行了比较,试验与计算结果吻合得很好,验证了该试验方法对热模态测试问题的有效性和准确性。通过分别对瞬态和稳态热环境下结构模态频率试验和计算结果的分析,探讨了结构瞬态温度场对模态频率影响的机理,揭示了结构内部存在的热应力和材料属性的变化,是决定模态频率随加热时间变化趋势的内在原因。
Experimental study on the thermal modal frequency characteristics of modern high-speed aircraft structures is of great significance for the design verification and flight safety of such aircraft. According to the characteristics of aerodynamic heating during flight, a transient thermal environment simulation system is designed. At the same time, the excitation and measurement methods in the test are redesigned according to the characteristics of high temperature environment. The conventional vibration exciter is successfully applied to high temperature structural mode State experiment. Finally, the thermal environment simulation system and the vibration test system are combined to form a thermal modal test system that considers the transient thermal effects, and realizes the ground test of the structural modal in the transient thermal environment. The temperature of each heating zone was measured for a cutting edge triangle wing with heating time, and the accuracy of heating temperature control was verified. Under the pure random excitation, the measured excitation and vibration response signals were analyzed by using the short-time Fourier transform Short Time Fourier Transformation (STFT) was used to identify the time-varying modal parameters. The first four modal frequencies with heating time were obtained and compared with the finite element numerical results. The experimental results agree well with the calculated results, The validity and accuracy of the test method for the thermal mode test problems are verified. Through the analysis of modal frequency and experimental results under transient and steady state thermal environment respectively, the mechanism of the effect of transient temperature field on the modal frequency is discussed. The thermal stress and the change of material property are revealed , Is to determine the modal frequency with the heating time changes in the internal causes.