Flow structure and aerodynamic forces of finned cylinders during flow-induced acoustic resonance

Abstract

This experimental study investigated the impact of self-excitation of acoustic resonance on the fluctuating lift force, flow structure, and aeroacoustic energy transfer of spirally finned cylinders with crimps in cross-flow. Three different finned cylinders with varying fin pitch-to-root diameter ratios (p/Dr) were compared with their equivalent diameter (Deq) bare cylinders. The study found that self-excitation of acoustic resonance occurred at a lower reduced flow velocity for the finned cylinders. During acoustic resonance excitation, finned cylinders with lower p/Dr experienced an abrupt increase in the fluctuating lift force coefficient and acoustic pressure. The decomposition of the fluctuating lift force with respect to the acoustic pressure showed that the earlier onset of resonance and the abrupt increase in the lift force and acoustic pressure were due to the increased susceptibility to flow-induced acoustic resonance. Phase-locked particle image velocimetry (PIV) measurements of the vorticity field supported this finding by showing a well-organized vorticity field in the wake of these finned cylinders. However, the fins and crimps had a significant effect on the distribution of the acoustic particle velocity field compared to the bare cylinder. The presence of the fins and crimps caused the acoustic particle velocity magnitude to be concentrated within the fins and rapidly decline away from the cylinder base. As a result, the acoustic power generated was lower in the case of the finned cylinders. This ultimately resulted in a lower peak acoustic pressure and fluctuating lift force being generated in the case of the crimped spirally finned cylinders.