Diaphragm rupturing processes by a ram accelerator projectile

摘要

Fluid dynamic processes of diaphragm rupturing by a conically-nosed projectile were experimentally studied. The experiments were conducted using a 25-mm-bore ram accelerator. The projectile was launched by a powder gun which was the pre-accelerator of the ram accelerator. Either air or nitrogen was used as the test gas. Through framing photography using a high-speed image converter camera, it was observed that in the processes of the diaphragm rupturing a radiating region developed between the diaphragm and the approaching sabot. Thsi region corresponded to the shock-heated gas which originated from a precursory shock wave driven by the accelerating projectile. With this precursory shock wave eliminated by a gasdynamic method, flow field around the projectile which was entering the test section by rupturing the diaphragm was visualized by holographic interferometer. During the rupturing, the system of oblique shock waves around the conical nose of the projectile was seen undisturbed on the fore side of the diaphragm. Under hte same condition, numerical simulation was conducted using a GRP (Generalized Riemann Problem) scheme which was extended for computign fluid dynamci problems with movign boundaries. Two extreme models were examined; one assumed that the diaphragm deformed in the same way as the projectile piercing the diaphragm. The other assumed that the diaphragm was rutpured instantly at the moment that the tip of the nose hit the diaphragm. Comparing these models with the experimentally visualized result, the former was concluded to better express the diaphragm rupturing process under the present sutudy.