Interaction of sound from supersonic jets with nearby structures

We numerically solve a model of sound generated in an ideally expanded two-dimensional supersonic (Mach 2) jet. Two configurations are considered: 1) a free jet and 2) an installed jet with a nearby array of flexible aircraft type panels. In the later case the panels vibrate in response to loading by sound from the jet, and the full coupling between the panels and the jet is simulated, accounting for panel response and radiation as well as the jet acoustics. We consider the long time behavior of the jet/panel system and present results for the flowfield and far-field pressure and the vibration of, and radiation from, the panels. The pressure within the jet changes from a nearly discrete spectrum peaked at a preferred frequency f*, which depends on properties of the jet, to a continuous spectrum as downstream distance increases. The far-field pressure is characterized by a highly directional beaming of sound with a spectral peak at f*, within the Mach line and a lower-level breakup into small-scale structures away from the Mach line. We show that the location of the panels relative to the Mach line is critical in determining panel response. Panels located upstream of the Mach line are subject to a low-level continuous spectrum loading and exhibit a comparable response. In contrast, panels located within the Mach line are subject to a high-level loading due to the intense Mach wave radiation of sound peaked at f*, and exhibit a comparable response. The panels radiate in a similar fashion to the sound in the jet. In particular, there is a strong beaming of sound waves at frequency f* from the excited panels within the Mach angle from the bounding wall, indicating a significant effect of Mach wave radiation on both interior sound levels and spectral content in the supersonic regime.