Sound Radiation From Two Side-by-Side Rectangular Cylinders With Slightly Different Aspect Ratios

Sound radiation from two side-by-side rectangular cylinders, one of which had a square cross-section and the other had a rectangular cross-section with aspect ratio AR = 1.2 to 1.5, was examined experimentally at Reynolds numbers Re = 1.0 × 10⁴ - 3.3 × 10⁴ in low Mach number flows. The center-to-center distance between two cylinders T/D was 3.6, 4.5 and 6.0. When the center-to-center distance was small, T/d = 3.6, vortex streets from two different cylinders were synchronized with the same frequency as that for a pair of identical square cylinders, even for the cylinder pair of ARs = 1.0 and 1.5. Sound radiation was dipole-like (planar-anti-symmetric), unlike in the case of square-cylinders-pair where sound radiation was in-phase. For larger cylinder spacing T/d = 6, highly modulated sound was radiated with two different frequencies due to non-synchronized vortex shedding from two cylinders.