基于测力系统一体化设计的高精度脉冲型天平技术研究

Shock tunnel has the advantages of high Mach number and high enthalpy, which can be used for simulating the flowfield in real flight altitude, for the force test. Therefore, due to the instantaneous flowfield and the short test time, the mechanical vibration of the balance system is generated and cannot be damped when the measurement of aerodynamic force is carried out in hypersonic shock tunnel. The inertial forces lead to low frequency vibrations of the model and its motion cannot be addressed through digital filtering. Therefore, the result’s accuracy of force test is decreased. Based on the difficulties encountered by the measurement of aerodynamic force, the integrated design approach for the force measurement system was proposed in order to increase the stiffness of MBSS (model-balance-support system). The balance signal frequency f≥2/t Hz is used as a design criterion, where at least the two cycles can be found in some balance signal. The optimized design improves the system stiffness as well as increases the measuring sensitivity. The strain-gauge sensor is used for the force measurement in hypersonic shock tunnel because of its mature technology, simple structure, and low cost. At the same time, according to the result of the integrated design, the pulse-type balances are optimized further to resolve contradictions between the stiffness and sensitivity of the balance. Three shock tunnels, JF8A, JF10, and JF12, will be used in this study due to the wide ranges of the enthalpy, the scale, Mach number, and the test duration. It also implies that the results of the research have extensive use for the force test in hypersonic shock tunnel.

激波风洞测力的独特优势在于马赫数及焓值高，可模拟飞行高度真实来流。但其由于流场瞬时建立，巨大冲击载荷激起模型、天平、支撑系统的振动，形成惯性干扰力。其与真实气动力混杂在一起，极大降低试验精准度。本项目针对激波风洞测力技术难题和发展现状，提出测力系统一体化设计概念，以试验时间t内天平某分量信号频率f≥2/t Hz为系统及天平结构设计准则。提高测力系统整体刚度的同时，增大输出灵敏度，提高测力精准度。基于应变计技术成熟、结构简单、成本低廉等优点，天平形式选为应变天平，并依据一体化设计准则，探索新型天平结构。基于有限元优化技术有效化解天平的刚度与灵敏度之间矛盾。应用力学所JF8A、JF10和JF12三座激波风洞开展脉冲型天平的试验应用研究。其焓值范围宽、喷管尺寸跨度大，有效试验时间范围2～130毫秒，马赫数涵盖5～15，因此本项目研究具有普遍性应用价值和意义。

高焓条件测力试验对高超声速飞行器气动外形设计和优化起决定性作用。通常采用脉冲风洞产生高温高压驱动气体以模拟高焓试验气流。在脉冲风洞测力试验时，输出结果无法摆脱惯性干扰影响，其低频振动干扰对短试验时间测量产生严重影响，传统风洞天平结构设计及其静态校准技术已经出现发展瓶颈问题。发展脉冲风洞测力技术，切实提高测量精度是促进我国高超飞行器发展中亟待解决的关键问题之一。本研究对脉冲风洞测力技术开展了深入研究和探索。一方面，通过测力系统结构设计和优化，提高刚度和频率性能，得到高精准度测力结果。本研究提出了冲击测力系统概念并进行了大量的测试验证。对尖锥和HB-2测力准模开展的激波风洞气动力测量试验结果充分验证了目前冲击测力系统的可靠性和精度性能。另一方面，为实现短试验时间（毫秒量级）高性能气动力测量，从性能影响因素的根源出发，动态校准研究凸显其重要性和必要性，其也是高性能测力系统中亟需重点关注和开展研究的最关键技术之一。研究中提出一种新的基于人工智能深度学习技术的单矢量动态自校准方法和智能测力系统概念，并应用于目前脉冲风洞测力试验中。该动态校准技术摆脱了传统砝码加载阶跃载荷的束缚，实现风洞内即可对同一测力系统开展高精度动态校准。其中，引入AI（人工智能）技术，对测力系统结构振动特征进行深度学习动态建模，实现对测力系统结构振动特性的高精度识别，实现风洞天平输出不带有惯性振动干扰（或干扰基本可忽略）的“纯”气动力，进而实现智能测力系统技术。通过采集样本和风洞试验的综合验证，智能测力系统智能数据处理技术得到了较为理想的效果，大幅度低频振动干扰基本被消除，脉冲风洞测力的精度和可靠性得到了大幅提高。高焓条件瞬态测力技术的智能化发展将有助于对高超飞行器在“复现”飞行条件下的高温效应问题开展更深入研究，揭示流动物理规律。同时也将为我国高超声速飞行器研发提供更可靠试验数据，具有现实意义和工程实践意义。