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Published: 2001

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A cavity was inserted into a 20 m/s subsonic flow. The flow had a freestream turbulence level of 0.5%. The cavity had an aspect ratio of 2.0 and was capable of reaching depths from 0.0 to 2.35L. Velocity and turbulence measurements were acquired in the shear layer over the cavity and upstream of the cavity in the approaching boundary layer using hotwire anemometry. These measurements showed that the approaching boundary layer approximated a universal fully turbulent boundary layer. The hotwire was also used to acquire energy spectra in the boundary and free shear layers as well as in the freestream in order to examine the frequency content of the flow. Finally condenser microphones were installed into the cavity and used to acquire energy spectra by measuring the unsteady pressure inside the cavity at various locations. Significant effort was made to identify the causes for each mode. The author has found evidence to suggest that tones generated by the cavity can be driven either acoustically or fluid dynamically. However, acoustics appear to dominate in the current cavity geometry and the current flow speed. The data acquired agrees well with past experiments. However, several new trends were noted that the author has not found mentioned in past work. First, shear layer velocity and turbulence profiles indicate the presence of a recirculation region at the upstream cavity lip. Second, relative sound pressure levels indicate that the total energy inside the cavity decreases as depth increases from D/L = 0.5 to 2.1. This loss of energy coincides with an increase in energy in the shear and boundary layers at the same depths. However, at cavity depths greater than D/L = 2.1 the trend reverses itself as a second vortex cell begins to form beneath the primary vortex.