CO2 laser absorption measurements of temperature and density in the shock-induced Richtmyer-Meshkov mixing zone.

Abstract

The aim of this paper is to discuss the interest of using spectroscopic diagnostic methods to study shock-induced Richtmyer-Meshkov mixing as a complement to other experimental techniques, numerical simulations, and theoretical studies. Using a ${\mathrm{CO}}_{2}$ laser absorption technique, the average temperatures and densities are experimentally determined through a high velocity gaseous mixing zone. This mixing is originated from a shock-induced acceleration of a plane interface, materialized by a thin plastic membrane, that initially separates two gases of different densities. Two gas combinations have been tested: ${\mathrm{CO}}_{2}$-Ar and ${\mathrm{CO}}_{2}$-He. Temperature and density are determined within the shock accelerated mixing zone from infrared absorption measurements of two characteristic vibrational-rotational lines of the ${\mathrm{CO}}_{2}$ bending mode, using a ${\mathrm{CO}}_{2}$ continuous wave laser as a diagnostic probe. The absorption coefficient is a function of the temperature and density of the ${\mathrm{CO}}_{2}$ for a known linewidth profile. Thus, temperature and density profiles within the mixing region are calculated from two measurements. For this, a ${\mathrm{CO}}_{2}$ absorption coefficient model, assuming the Voigt linewidth profile in the mixing region and taking into account the contribution of the hot bands, has been developed. It is shown that the technique is well applicable to this type of study, and that there is a strong correlation between the Atwood number and the shape of the mixing zone.