The flow over aircraft bays exhibits many characteristics of cavity flows, namely resonant pressures that can create high structural loading. An extensive dataset of pressure measurements within both simple and complex cavities was previously obtained and analyzed using power-spectral densities, coherence levels, and cross correlations between sensor pairs within the cavity. More in-depth analysis of the flow structure is studied here using modal decomposition techniques. Both Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) were applied to the experimental and computational results within a simple rectangular cavity. POD was able to show that the cavity modes are coherent across the cavity width. Only higher modes that were associated with more turbulent fluctuations exhibited spanwise variations. These were concentrated at the aft end of the cavity. DMD was able to isolate structures associated with single frequencies in the flow. At the Rossiter frequencies, coherent structures across the front cavity width were found, while more complex shapes were observed at the cavity rear, consistent with the POD analysis. Additional DMD modes in between the dominant Rossiter frequencies also appeared. These additional modes were associated with a low-frequency modulation of the cavity tones.
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