Laser-Generated Localized Freestream Perturbations in Supersonic and Hypersonic Flows

An optical method for generating localized, controlled perturbations has been developed for use in supersonic and hypersonic flowfields. 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 flow velocity. The perturbation is approximately spherical and several millimeters in diameter, with the size dependent on the flow density. Optimal formation of the perturbation is achieved with large-F-number focusing systems. To date, the disturbance has been used as a freestream perturbation for supersonic receptivity experiments as well as forward-facing cavity and blunt-body shock oscillation studies

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