Publications Details

High Temperature Gladstone-Dale Coefficient Measurements in a Free-Piston Shock Tube

Wang, Gwendolyn T.; Daniel, Kyle; Lynch, Kyle P.; Guildenbecher, Daniel R.; Mazumdar, Yi C.

Accurately measuring aero-optical properties of non-equilibrium gases is critical for characterizing compressible flow dynamics and plasmas. At thermochemical non-equilibrium conditions, excited molecules begin to dissociate, causing optical distortion and non-constant Gladstone-Dale behavior. These regions typically occur behind a strong shock at high temperatures and pressures. Currently, no experimental data exists in the literature due to the small number of facilities capable of reaching such conditions and a lack of diagnostic techniques that can measure index of refraction across large, nearly-discrete gradients. In this work, a quadrature fringe imaging interferometer is applied at the Sandia free-piston high temperature shock tube for high temperature and pressure Gladstone-Dale measurements. This diagnostic resolves high-gradient density changes using a narrowband analog quadrature and broadband reference fringes. Initial simulations for target conditions show large deviations from constant Gladstone-Dale coefficient models and good matches with high temperature and pressure Gladstone-Dale models above 5000 K. Experimental results at 7653 K and 7.87 bar indicate that the index of refraction approaches high temperature and pressure theory, but significant flow bifurcation effects are noted in reflected shock.