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.