Experimental and Numerical Analysis of an Expansion Flow in Chemical and Thermal Nonequilibrium

Results of a basic experiment on a high-expanding nozzle flow in hot gas conditions are presented and discussed. Gas flow temperatures and velocities at various locations at the inlet and the exit of a hypersonic nozzle designed for a hydrogen burning ramjet model were determined. The flow velocity was measured by laser two-focus velocimetry,detecting seeded TiO2-particles whose behavior in fast expanding flows was examined experimentally and numerically. CARS was applied to measure nitrogen single pulse spectra from which vibrational and rotational temperatures were determined. The flow at the exit of the nozzle shows a market thermal nonequilibrium because of the molecular exchange processes, which cannot keep pace with the expansion. The experimental results are compared to a numerical computation by a 2D FEM code solving the Navier-Stokes equations for a chemically reacting mixture of gases, using a reduced chemical kinetic scheme and modeling the vibrational energy and its relaxation by the Landau-Teller theory. Experimental and numerical results are in excellent agreement