Laser-Generated Localized Freestream Perturbations in Supersonic and Hypersonic Flows

Abstract

An optical method for generating localized, controlled perturbations has been developed for use in supersonic and hypersonic ow elds. The thermal spot disturbance is generated when the pulsed beam from a laser is focused at the desired origin and a small region of the gas is ionized. After recombination, the thermal spot persists as a region of heated gas that convects with the local ow velocity. The perturbation is approximately spherical and severalmillimeters in diameter,with thesize dependenton the owdensity.Optimalformationof theperturbationis achievedwith large-F-numberfocusing systems.Todate, the disturbancehasbeenused asa freestream perturbation for supersonic receptivity experiments as well as forward-facing cavity and blunt-body shock oscillation studies.