Diaphragm rupture. Impingement by a conically-nosed, ram-accelerator projectile

The effect of diaphragm rupture by a conically-nosed projectile on the gasd ynamics related to ram accelerator operation was experimentally and numeric ally studied. The experiments were conducted using a 25-mm-bore ram acceler ator. Either air or nitrogen was used as the test gas. Using a high-speed i mage converter camera, it was observed that during the process of the diaph ragm rupture a region with strong radiation developed between the diaphragm and the approaching projectile/sabot. This radiating region corresponds to the shock-heated gas which is originated from a precursory shock wave driv en by the accelerating projectile/sabot. The flow around the projectile upo n entering the test section by rupturing the diaphragm was visualized by ho lographic interferometry. During the diaphragm rupture, the system of obliq ue shock waves around the conical nose of the projectile was seen undisturb ed on the downstream side of the diaphragm. Under the same condition as the experiment, numerical simulation was conducted using GRP (Generalized Riem ann Problem) scheme which was extended to the computation of compressible f low fields bounded by moving surfaces. Two diaphragm rupture models were ex amined: (1) the diaphragm deformed by wrapping tightly around the moving pr ojectile; (2) the diaphragm was ruptured instantly at the moment the projec tile touched the diaphragm. Comparing these models with the experimentally visualized flow, the former was found to express the diaphragm rupture proc ess much better than the latter.