Self-excited shear-layer oscillations are observed in the cavity flows of a multi-cavity channel when the mean velocity through the channel exceeds a critical value. These coherent shear-layer oscillations appear as one or sometimes two selectively-amplified frequencies in the Fourier-analyzed signals of hot-film gauges that are sintered into the channel walls. At a constant velocity above the critical velocity, the self-excited oscillations are present in only a few cavities. Downstream from these cavities there are oscillations in the cavity flows but one or two selectively-amplified frequencies are not observed. The self-excited oscillations move upstream and the selectively-amplified frequency increases as the mean velocity through the channel is increased.

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