Flow tagging velocimetry in a superorbital expansion tube

A non-intrusive laser-based method for direct velocity measurements has bee n demonstrated in a superorbital flow facility. The method is based upon la ser enhanced ionisation velocimetry in which a tagged region is created by two step excitation of sodium and subsequent collisional ionisation. The ac hieved depletion of neutral atoms is then interrogated by planar laser indu ced fluorescence. The velocities were measured in the freestream at a super orbital condition yielding 9.20 +/- 0.11 km/s. These results compare favour ably with the measured shock speeds in the facility.