随机激励下受热翼面的模态频率特性试验研究

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 of Modal Frequency Characteristics of Heated Wing Surface under Random Excitation Condition

Experimental study of thermal modal frequency characteristics of modern high-speed aircraft structure is very important to the design and verification of this kind of aircraft and flight safety. A transient thermal environment simulation system was designed based on the aerodynamic heating characteristics during flight. At the same time, according to the characteristics of high temperature environment, the excitation and measurement ways in measurement were redesigned, and an ordinary vibration exciter was successfully applied to high temperature structure modal experiment. Finally, both thermal environment simulation system and vibration test system were combined to form a thermal modal experimental system which takes into account the transient thermal effects. Thus, the ground test of structure mode in transient thermal environment is realized. Temperature variation with heating time in each heated region was measured for a cutting tip delta wing, which verifies the accuracy of temperature control during heating. By using short time Fourier transformation (STFT), the time-varying modal parameters were identified for measured excitation and vibration response signals under the condition of pure random excitation. The variation of first four order of modal frequencies along with the heating time was obtained and compared with the results from finit element numerical simulation. Both results are in good agreement, which verifies the effectiveness and correctness of this experimental method. Through analysis of experimental and computational results obtained from transient and steady state thermal environment respectively, influence mechanism of the transient temperature field on the modal frequency was explored. Results show that the variation of thermal stress and material properties existed in internal structure is the intrinsic cause of thermal modal frequency variation with heating time.