Numerical investigation of the impact of tailored driver gases and driver inserts on shock tube flows

Presented is a numerical study of the effects of imperfect driver gas tailoring and the use of a driver section insert on the flow field within the shock tube. Two-dimensional axisymmetric simulations of a shock tube are conducted with pure argon as the driven gas and four mixtures representing different tailoring conditions. The second part of the study investigates the use of a profiled driver insert with two driver gas mixtures to minimize the pressure rise in the test section such as that resulting from over-tailored driver mixtures. The chemical kinetic implications of imperfectly tailored driver gas mixtures on the interpretation of shock tube experiments are explored through simulations of propanol ignition with pressure and temperature changes prescribed based on the simulation results. The simulations show that imperfect tailoring toward under-tailored mixtures is more detrimental to kinetic studies in the post-reflected shock region than over-tailoring. The least compromising situation in test conditions is observed for a mildly over-tailored condition with 25% of nitrogen as opposed to the tailored value of 20%. The numerical results further show that the combination of the driver insert and slightly over-tailored driver mixture leads to longer test times. The study seeks to address problems of available test times and accuracy of shock tube reactor conditions that are crucial to the use of shock tube data for validation of chemical kinetic models.