Freestream Velocity in a Shock-Tunnel Nozzle Flow using Diode Laser Absorption Spectroscopy

Abstract

Diode laser absorption spectroscopy has been used to make time-resolved velocity measurements in the freestream of a large free piston shock tunnel. A small probe was used to sample a uniform region of the flow at the nozzle exit. Experiments were conducted with air and nitrogen test gases, however, only the nitrogen case produced velocity measurements during the shock-tunnel test time. Rubidium was seeded into the flow and employed as the probe species. The results are consistent with chemical reactions reducing the concentration of atomic Rb in the freestream and increasing it in the high-temperature boundary layers formed on the probe during flow establishment.