Research on Noise of Several Times Frequency of Karman Vortex Shedding from Rectangular Cylinders in Air Flow

In the present paper the attention is focused on mechanism of abnormal noise generated from rectangular cylinders in cross flow. The width-to-height ratios of was 3.0. The tube pitch ratio in the transverse direction was 8.0. We measured the aerodynamic sound radiated from the rectangular cylinders in the range of Reynolds numbers from about 103 to 104. The several high peaks were formed at the spectrum of SPL. The two peaks of the spectrum of Strouhal number of 0.08 and 0.2 were caused by vortex shedding from the two horizontal rails of 16×30 mm and rectangular cylinders of 5×15 mm, respectively. On the other hand, the various abnormal noises occurred several times at the vortex shedding frequency. We measured the natural frequencies of the rectangular cylinders by hammer tests. We have discussed the relation between the various abnormal noises, the vortex shedding frequency and the natural frequencies of the rectangular cylinders.