Laser Velocimetry in the Supersonic Regime: Advancements, Limitations, and Outlook

Laser Velocimetry (LV) is often utilized as an off-the-shelf nonintrusive measurement technique for low speed, steady state flows. However, in complex, supersonic flows, the application of LV becomes highly specialized. Setups must often contend with limited optical access, poor signal-to-noise ratios, and limited tunnel run times. Furthermore, seeding particles must survive large ranges of flow temperatures and pressures, and extensive data analysis and interpretation are required to ascertain whether measured particle velocities are representative of the fluid flow. Several examples of LV studies in the supersonic regime demonstrate recent advancements and the current state-of-the-art of this measurement technique. Results are included from three wind tunnel facilities, operating at freestream Mach numbers of 1.9, 3, and 6, and track an evolution of applications from flat plate boundary layers to the complex flowfield of a supersonic inlet. Results demonstrate that further development of collection, seeding and analysis techniques will continue to extend the range of LV applications and measurement statistics, but the overall limiting factor will continue to be the ability of LV seed to model the discrete motion of fluid molecules.