Tonal noise generation from tandem cylinders of unequal diameter in cross-flow

The flow around two parallel cylinders arranged in a tandem configuration is a major source of aerodynamically induced noise and vibrations that can be found in a variety of technical applications. Although this configuration has already been the subject of many past investigations, the effect of unequal cylinder diameters on the resulting far-field tonal noise has not been fully addressed yet, especially for varying streamwise distances between the two cylinders. The present paper describes an experimental acoustic study on tandem cylinder configurations with varying diameters and normalized spacings, where special emphasis was placed on the identification of basic scaling approaches. Additional two-dimensional flow simulations were performed to enable a better qualitative understanding of the flow phenomena. The resulting dataset shows that in most cases, the vortex shedding tonal noise scales with the upstream cylinder diameter. However, for small spacings and large ratios of downstream cylinder diameter to upstream cylinder diameter, the vortex shedding scales with the downstream cylinder diameter. The dominant tonal peak essentially shows a classical dipole-like directivity.