Aeroacoustics of square finite wall-mounted cylinders with different aspect ratios in pressure-gradient flows

This study examines square finite wall-mounted cylinders (FWMCs) across a broad range of aspect ratios (from 0.25 to 20 in increments of 0.25), focusing on the combined effects of aspect ratios and pressure gradients in shaping their aeroacoustic behaviour. Simultaneous far-field noise and unsteady surface pressure measurements were conducted for square FWMCs immersed in flows with favourable pressure gradient (FPG), near-zero pressure gradient (ZPG), and adverse pressure gradient (APG). Under ZPG, three regimes are identified based on aspect ratio: R0 (no Aeolian tone), RI (single Aeolian tone), and RII (two Aeolian tones). APG generally shifts the transitions between different regimes to larger aspect ratios and promotes the upward convection of vortical structures. Further, the convection effect decorrelates the pressure fluctuations near the cylinder base junction, attenuating the Aeolian tone in RI. In contrast, FPG promotes the early onset of Aeolian tones and drives vortical structures to convect downward. A new regime, RI', emerges within the transitional aspect ratio range between RI and RII under FPG, where the pressure fluctuations along the entire cylinder sidewall become decorrelated, leading to complete suppression of Aeolian tones.