Measurements of the Interaction of an Upstream Laser Perturbation with a Forward-Facing Cavity

摘要

The laser perturber is a tool to be used for receptivity studies in the Boeing/AFOSR Mach-6 Quiet Tunnel. To demonstrate that the laser perturber is functioning correctly, it is tested with a forward-facing cavity. Results are similar to previous studies by Ladoon and Segura in a Mach-4 quiet tunnel. The cavity base pressure fluctuations are nearly quiescent at shallow cavity depths. When a freestream perturbation interacts with the forward facing cavity, the cavity base pressure experiences oscillations that decay exponentially. The measured cavity resonance frequency matches the theoretical cavity resonance frequency to within 6%. The measured cavity response appears to be initiated by the acoustic disturbance that results from the laser-generated perturbation. The damping characteristics of the forward-facing cavity are also examined. For cavities with similar resonant frequencies, the damping constants can differ by almost an order of magnitude. However, cavities with similar non-dimensional depths have similar damping constants.