| The high intensity noise generated by fluid flow over a cavity is the result of the receptivity between the instabilities of the cavity shear layer and the hydrodynamic and acoustic pressure fluctuations generated at the downstream edge or trailing edge of the cavity. In addition to unacceptable noise levels, cavity oscillations can lead to a significant increase in aerodynamic drag due to the presence of the cavity, destruction of internal cavity components, and sonic fatigue. In spite of substantial efforts in the past, a clear understanding of the dependence of cavity noise on the cavity width, flow temperature, and upstream boundary layer is seriously lacking. The goal of this research was to assess and quantify the aforementioned cavity noise parameters with the intent of providing benchmark data for validation of CAA codes, presently being developed by numerous researchers, and a physical basis for effective control techniques. Measurements were made to characterize the shear layer spanning a cavity and to link these characteristics to the measured acoustics. The measurements consisted of nearfield sound pressure levels, instability-wave coherence distribution within the cavity, turbulence energy spectra, wave number spectra, and instability wave growth rates. In addition, the first-ever detailed farfield acoustic measurements were made. The major contributions of this research are a better understanding of the influential parameters of cavity noise, effective control techniques, and documentation of a substantial amount of flow and acoustic data for CAA validation. |
