Experiments were performed to study the characteristics of compressible cylindrical cavity flows. The diameter-to-depth ratio is an important parameter in determining the characteristics inside a cylindrical cavity and its vicinity. Closed-type cavity flow has lower amplitude of mean surface pressure behind the front wall and higher one ahead of the rear wall of the cavity. The amplitude of surface pressure fluctuations increases toward the rear face for an open-type cavity, whereas an additional peak near the middle of cavity floor is observed for a closed-type cavity. The diameter-to-depth ratio affects the characteristics of pressure distribution of a cavity, while the freestream Mach number effect is less significant. By taking Fourier transform analysis of the data near the trailing edge of a cavity, resonant modes are observed in open- and transitional- cavity flows. These modes are well-predicted by the Rossiter's empirical equation developed for rectangular cavities. Furthermore, the dominant mode switches to a higher mode as Mach number increases.
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