Interferometry analysis and CARS measurements of nonequilibrium in hypersonic oxygen/argon and pure oxygen flows

In this article we explore (a) optical and (b) thermochemical properties of reactive hypersonic flows, with an emphasis on oxygen dynamics and time resolved measurement capabilities. First, we discuss experimental and numerical analysis of reactive hypersonic flows of an argon–oxygen mixture over a blunt wedge geometry. The experimental campaign for that geometry uses Michelson interferometry to determine the refractive index of the shock layer. Numerical analysis of these cases reveals that there is dissociation of molecular oxygen in the shock layer. Excellent comparison between numerically predicted and nanosecond sampled experimentally observed refractive index serve as verification of non-equilibrium refractive index theory and the thermochemistry models used in the simulation. Uncertainties and limitations of the interferometry technique are discussed. In addition, we perform subnanosecond sampled femtosecond/picosecond hybrid Coherent anti-Stokes Raman scattering (CARS) spectroscopy behind a hypersonic Mach stem configuration in a pure oxygen flow to demonstrate capabilities to enhance understanding of nonequilibrium vibrational mode contributions to the refractive index. Hybrid CARS gives instantaneous vibrational populations and relevant vibrational temperatures at specific locations downstream of the shock.