The effect of Mach number on flow over an isolated shallow open-type cavity was investigated experimentally. Measurements at Mach numbers 0.3, 0.5 and 0.6 were performed. Boundary layer was naturally developed along flat plate upstream the cavity. During the experiments, two plates of different lengths were employed. Static pressure and velocity fluctuations near the wall were measured by pressure transducers and MEMS thermal film sensors, respectively. In order to get only fluctuating characteristics of the turbulent flow, MEMS sensors were integrated with an AC signal amplifier. Strong resonance was observed in the pressure signals obtained at M = 0.5 and M = 0.6 for the test configuration with the short plate upstream. Instantaneous oscillating characteristics were studied by the Wavelet and Hilbert-Huang transforms of the obtained signals. These data analysis techniques allowed one to see how a shallow cavity flow got resonant intermittently in time. The results of Wavelet and Hilbert-Huang transforms were compared with respect to the same set of experimental data. Moreover, comparing the results reduced from the signals of the pressure and MEMS sensors allows one to estimate the highest frequency response of the MEMS sensors under the high subsonic velocity conditions.

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