Self-sustaining oscillations of flow over ducted cavities and corrugated pipes proved to be a potential source of tonal noise and possible failure in industrial applications. Most of the recent studies focused on the flow over a single cavity to simplify the problem and establish basic understanding of the phenomenon. This paper investigates experimentally the flow over multiple cavities, specifically two and three-cavity configurations, and the results are compared with those of a single cavity. Two different categories of experiments were performed in this study. The first category of measurements quantified the aeroacoustic source of various cavity configurations as a function of Strouhal numbers and acoustic velocity of the resonant pipe mode. The cavities are situated at the acoustic pressure node of a piping system which was sufficiently long to maintain the acoustic velocity fairly constant along the test section. The second category involved self-excited oscillations where the cavities were tested in a short piping system. The flow velocity was gradually increased and the acoustic pressure amplitude and frequency were measured and the lock-in ranges for different shear layer modes were identified. A semi-empirical model is then developed to use the measured source to predict the self-excited oscillation amplitude.

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