Experimental Study of Boundary-Layer Response to Laser-Generated Disturbances at Mach 6

Surface-mounted pressure sensors were used to investigate the response of a hypersonic conical boundary layer to artificial disturbances. A pulsed high-power laser was focused to a spot about 5 mm above the model. When a certain intensity threshold is exceeded, the air is no longer transparent, the laser energy is absorbed, and a plasma ignites. This plasma very quickly reassociates and an expanding shock wave and a volume of heated gas in the disturbance center remain. Because this center was some distance above the model, only the shock wave interacted with the boundary layer and, as a result of this interaction, a second-mode-like wave train evolved. The wave’s behavior is compared with uncontrolled natural waves, which originated from freestream disturbances. The measurements yield the spatial extensions, the frequency content, and the wave structure. Furthermore, the effects of changing the Reynolds number and applying multipulses to affect the frequency content were investigated.

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