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 several millimeters in diameter, with the size dependent on the ow density. Optimal formationof the perturbation is achieved with large-F-number focusing systems. To date, the disturbancehas been used as a freestream perturbation for supersonic receptivity experiments as well as forward-facing cavity and blunt-body shock oscillation studies.

Numerical Study of Hypersonic Boundary-Layer Receptivity with Freestream Hotspot Perturbations

“…Schmisseur et al [12,13] studied the receptivity of a freestream laser spot over an elliptical cone in a Mach 4 flow. Salyer et al [14,15] characterized the laser-generated hotspot and used it in a boundary-layer receptivity experiment for a hemisphere-cylinder model in Mach 4 freestream.…”

“…The schematic explanation of the laserspot and cone setup in the experimental studies is demonstrated in Fig. 1 [12,13]. The hotspot is initially generated at a location upstream from the cone on the centerline.…”

“…Then, the spot moves along with the hypersonic freestream toward the cone nose, interacts with and passes through the bow shock, and eventually travels further downstream around the cone. Schmisseur et al [12,13] and Salyer et al [14,15] completed benchmark tests for generating laser spots in their wind tunnel, and they measured the responses of the perturbed boundary layers. However, there was no detailed analysis of the receptivity mechanisms in their work.…”

“…They also performed an experimental study Fig. 1 Schematic of the experimental laser spot and cone scenario in Schmisseur et al [12].…”

Measurements of Resonance in a Forward-Facing Cavity at Mach Six

“…This thermal disturbance is surrounded by a weak spherical shock propagating at the speed of sound away from the core [24,25]. More information on this apparatus can be found in [26][27][28].…”