Measurement of rotational temperatures near surfaces in hypersonic flow

Rotational temperatures of NO in hypersonic flow have been measured by Laser-Induced Fluorescence (LIF) at low densities. In undisturbed free jet expansions, the experimental results are in good agreement with the theory of isentropic flows. Near a hot surface in the flow, the rotational temperature of the reflected molecules were determined at nearly free molecular conditions. Testing parameters were the surface temperature, the kinetic energy of the incoming molecules, and the Knudsen number. The Direct Simulation Monte Carlo method (DSMC) has been applied to study the flow conditions near the surface. The experimental results show a significant deviation from total accommodation at high surface temperatures and the translational energy of the incoming molecules has to be taken seriously.