Ass. Prof. Michael Liverts, Deaprtment of Mechanics, KTH

Title: On the limiting temperatures of spherical shock wave implosion in gases

Abstract: Spherical shock wave implosion in argon is studied both experimentally and numerically. Spherical shocks are produced inside a conventional gas-dynamic shock tube facility where initially plane shocks are smoothly transformed into spherically shaped shocks which then implode inside a conical segment.  As the converging shock reflects at the cone tip the conditions become extreme so that the gas intensively glows. Focal temperatures of the order of 30 000 K are then deduced from the registered radiation spectrum. 2D axisymmetric numerical simulation is employed to study the details of the shock implosion. Accounting for multiple-level ionization, excitation, Coulomb interaction and radiation effects, the limiting equilibrium temperatures to be achieved during the shock implosion are estimated. It is shown that the nonideal gas effects play a significant role in attenuation of the converging shock. Among others, ionization presents a dominant energy sink, resulting in substantially reduced equilibrium temperatures at the focal point as compared to a perfect non-ionizing case.