A comparison of molecular vibration modeling for thermal nonequilibrium airflow

This paper discusses modeling of molecular vibration in thermal nonequilibrium airflow. The effects of high-temperature thermodynamic states were investigated using an explicit, first-order, Roe scheme. Various molecular vibration models were examined: perfect gas, one-temperature model (equilibrium), and two-temperature model (nonequilibrium). Relaxation rates were compared to experimental data from a shock tube. The Roe scheme was then modified for axisymmetric flow and a general coordinate system. The solution over the forward portion of a sphere, at Mach numbers from 5-8, was computed and analyzed to provide a more comprehensive check on the accuracy in computing flows around more physically realistic geometries. Agreement with experimental relaxation rates was obtained. The first-order Roe scheme accurately predicted inviscid flow about a sphere, and converged thermal nonequilibrium solutions were obtained in less than 1000 iterations (41 x 81 grid). One-temperature and two-temperature models predicted very similar surface conditions for the blunt-body. 27 refs