Experimental study of shock facility's test time extension and application to force measurement

Abstract

The shock facility is a ground test facility that can generate test flows with high temperature and high pressure by heating and compressing the test gas through the propagation and reflection of a strong incident shock wave. Using the shock facility, a relatively wide range of high enthalpy test flows can be simulated with a small degree of contamination, but the test time is generally limited to several milliseconds. Because of the short test time, several constraints and limitations arise in ground tests using the shock facility. For example, it is challenging to measure physical quantity using a measurement system with a slow reaction rate, and it is difficult to test large and complex test models with long flow development times around the test model. Therefore, in the present work, in order to overcome the limitations caused by the short test time of the shock facility, the test time extension techniques of the shock facility were theoretically and experimentally investigated. The techniques considered in the present work were the contact surface tailoring technique through the driver gas tailoring and the expansion wave delaying technique through the staged driver tube filling. The contact surface tailoring technique suppresses the flow disturbance induced after the interaction between the reflected shock wave and the contact surface. The driver gas tailoring technique is a representative technique of the contact surface tailoring technique that changes the composition and filling pressure of the driver gas to satisfy the contact surface tailoring condition without changing the test flow conditions. The expansion wave delaying technique delays the propagation of expansion waves reflected from the end of the driver tube to the test flow, and in the present work, the staged driver tube filling technique that fills a low-acoustic speed gas near the end of the driver tube was investigated. The driver tube staging valve was designed and applied to prevent the mixing of the driving gas and the low-acoustic speed gas. The variation in the test time and the flow conditions according to the application of the test time extension techniques was confirmed through the pressure measurement at the end of the driven tube. As a practical application example of extending the test time of the shock facility, the force measurement in the shock facility was also performed. At first, free-flight, movable-support force balance, and stress-wave force balance technique systems were developed and investigated, and the simple cone model's drag measurements were performed to evaluate each technique's characteristics. Among them, using the stress wave force balance technique, the drag measurement was performed in the shock facility with the application of the test time extension techniques. Through the present work, the test time of the shock facility could be efficiently and significantly extended. In addition, the practicality of the test time extension of the shock facility was experimentally confirmed by confirming that the effective measurement time was extended for the drag measurement through the test time extension of the shock facility.