基于载荷辨识的脉冲燃烧风洞模型测力方法研究

Pulse combustion wind tunnels are important facilities in ground tests of hypersonic aircraft models, which possess virtues of low construction costs and low use-cost. However the duration of pulse combustion tunnels are relatively short (about 300ms), and it's necessary for the test system to have a very high response rate. But the models are becoming larger and havier. The largest model now being tested is more than 4 meters in length and near 1 ton in mass. As a result, the response time of the system is raised and the structural vibration of the system is hardly damped. So it's more difficult for the measurement technique used in the continuous wind tunnels to get good results when applied to massive models in impulse wind tunnels. In this study, identification method will be employed to force measurements on models in pulse combustion wind tunnels. This novel technique will release the restrictions on response rate of the system and the mass of models. And also the stiffness of the measurement elements of the balances can be reduced to improve the sensitivity of the balance. The aerodynamic loads on the model will be determined by the deconvolution of the strain signals of the balance. This technique will allow larger models to be tested, and will fully exploit the superiorities of the pulse combustion wind tunnels. The main research contents include modeling of the test system, design of force balance, force identification method and validation by experiments. The key scientific problems involved is how to build accurate structural dynamic model of the test system with small number of freedoms and how to identify the aerodynamic forces on the model with sufficient precision using the strain signals of the balance.

脉冲燃烧风洞是高超声速飞行器地面试验的重要设备，具有建造和试验成本低廉等优点。脉冲燃烧风洞工作时间很短（300ms左右），对试验系统的响应速度提出了较高的要求。随着试验模型尺度不断增大（目前长度超过4米），质量随之增大（已接近1吨），试验系统的响应速度降低，结构振动也难以衰减，连续式风洞所用的常规测力方法越来越难以获得良好的测力结果。本项目拟采用载荷辨识的方法，利用天平输出信号和系统动力学方程反算试验模型所受气动载荷，此方法不需要试验系统有很高的响应速度，对试验模型的质量大小没有限制，同时可以适当降低天平测量元件的刚度，提高天平灵敏度，进而提高测量精度，适用于在脉冲燃烧风洞中开展大尺度模型的测力试验，充分发挥脉冲燃烧风洞的优势。本项目主要研究内容包括：试验系统动力学建模、天平设计、载荷辨识方法研究以及风洞试验验证。要解决的关键科学问题为试验系统的高精度建模和基于结构应变响应的载荷辨识方法。

本项目以脉冲型风洞（有效试验时间在二三百毫秒）的模型测力系统为对象，研究了如何由天平信号反求试验模型气动载荷的问题。主要研究内容是测力系统的结构动力学模型建立方法和模型载荷辨识方法。建模方法方面分别研究了基于有限元与子结构模态综合相结合的数值建模方法和通过系统动态标定的试验建模方法，前者导出微分方程描述，后者给出系统脉冲响应函数矩阵描述。模型载荷辨识方法方面，针对动态载荷研究了Krylov子空间投影与Tikhonov正则化相结合的混合正则化方法和先用参数辨识法得到载荷主分量再用正则化方法求解剩余分量的两步法，针对稳态载荷研究了参数化辨识方法。正则化参数确定是反问题正则化求解的关键，针对载荷辨识问题的Tikhonov正则化方法提出了确定正则化参数的虚拟载荷方法，针对一般性反问题的Tikhonov正则化方法提出了通过隐式地对离散Picard曲线进行平滑而确定正则化参数的新方法。本项目的研究成果可直接应用于脉冲型风洞模型测力试验，提高载荷精度，还可推广应用于诸如爆震发动机等新型脉冲式发动机的推力测量；本项目研究提出的正则化参数确定方法也为其它反问题的求解提供了新的有效工具。