Velocity Determination in High Enthalpy Ground Testing Facilities

Abstract

The flow velocity is of significant importance in plasma wind tunnels, because the enthalpy and hence the chemical reaction processes in the boundary layer near the surface consist mainly of the high velocity. In real re-entry scenarios, the plasma is resulting from the strong bow shock in front of the vehicle which is again the result of the high velocity. In this paper, a comparison is made between the theoretically estimated velocity from basic equations for hypersonic flow conditions and experimentally gained velocities using Fabry-Perot-Interferometry. This optical diagnostic means is used in the present investigation to measure the translational temperature and velocity of nitrogen atoms. Depending on the ambient pressure, velocities between 1000m/s and 4000m/s have been measured. The detectability limit is the emission spectra of the flow which is influenced by the oxygen mass flow and the input power of the generator. Under the assumption of chemical equilibrium, several possible comparisons are made leading to the result that the pure nitrogen flows are considerably in non-equilibrium.