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An experimental investigation was conducted to explore the noise generation mechanism of polygonal cylinders within a Reynolds number range of ���� = 2. 0 × 10⁴ to 8 × 10⁴. Far-field noise measurements were performed on polygonal cylinders with side numbers �� = 4, 7, 8, 10 and circular cylinder. Additionally, a specific polygonal cylinder, a heptagonal cylinder (�� = 7), was equipped with surface microphones to measure near-field pressure synchronously with far-field noise. Planar particle image velocimetry was employed to examine the flow field and provide insights into the noise generation mechanism of the heptagonal cylinder. Analysis of far-field noise revealed that all tested polygonal cylinders exhibited a prominent tone at the vortex shedding frequency, similar to the circular cylinder. However, in the case of the heptagonal cylinder, dual tones were observed, with frequencies slightly lower and higher than the vortex shedding frequency of the circular cylinder. Flow field measurements elucidated that these dual tones are attributed to two types of vortex shedding in the case of the heptagonal cylinder.
Zhang et al. (Thu,) studied this question.
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