长试验时间激波风洞测力技术研究

中国科学院力学研究所复现飞行条件高超声速激波风洞JF12的落成突破了毫秒级试验时间的瓶颈,有效试验时间超过100ms.因此,对于JF12长试验时间激波风洞的测力试验,基于应变天平技术较为成熟、结构简单等优点,我们考虑采用传统的应变计天平.但是,激波风洞来流冲击所带来的惯性力干扰导致天平测力系统产生低频振动,传统内置应变天平的结构刚度很难保证信号有足够的处理周期,这大大限制了激波风洞测力模型的尺寸和重量.针对这个难题,基于JF12激波风洞的运行特点及对测力天平刚度特性的特殊要求,优化设计了应变天平的测力单元结构以适用于这种脉冲动态测力试验,相应加工制造了大刚度、低干扰、高灵敏度的系列脉冲型应变天平,结构形式包含了杆式和盒式,最大载荷(法向力)从1kN到30kN,以满足不同尺度飞行器的测力试验需求.同时,我们应用不同尺度的测力模型对研制的脉冲型天平在JF12激波风洞进行了一系列动态气动力测量试验,以进一步评估JF12系列脉冲型应变天平的结构特性和测力性能. 

STUDY ON FORCE MEASUREMENT IN LONG-TEST DURATION SHOCK TUNNEL

JF12 hypersonic shock tunnel has been designed and built in Institute of Mechanics, CAS. The performance tests demonstrated that this facility is capable of reproducing the pure airflow with Mach numbers from 5-9 at altitude of 25-50 km with at least 100 ms test duration. Therefore, a sti construction balance, that is the traditional internal strain-gaged balance (SGB), was considered to use in this long-test duration impulse facility due to its mature technology, simple structure and low cost. However, when the force test is carried out in shock tunnel, the inertial forces lead to low frequency vibrations of the model and its motion cannot be addressed through digital filtering since enough cycles cannot be found during a shock tunnel run. This implies restriction on the model's size and mass as its natural frequencies are inversely proportional the length scale of the model. Therefore, there are still many problems for the force measurement in a shock tunnel, especially for the large and heavy model. In order to overcome the technical di culties, JF12 series SGBs were designed and fabricated. The maximum loads are from 1 kN to 30 kN for the test models with di erent scale. The di erent structures were proposed and optimized for two types of balance, i.e., the sting and cassette balances. The finite element method was employed for the analyses of vibration characteristic of the model-balance-support system in order to ensure enough cycles, especially axial force signal during 100 ms test duration. In addition, the force tests were carried out using several large-scale test models. JF12 series pulse-type SGBs show good performances and the frequency of the model-balance-support system increases due to the sti construction of the SGB.