Flow-Excited Acoustic Resonance of Single Finned Cylinder in Cross-Flow

The flow-excited acoustic resonance of single straight finned cylinder in cross-flow is investigated experimentally in this work. This phenomenon has been investigated in some detail for the case of bare cylinders; however, the effect of adding fins to the cylinders on the flow-sound interaction mechanism is not yet fully understood. During the experiments, the acoustic cross-modes of the duct housing the cylinder are self-excited due to the vortex shedding that emerges from the cylinder’s surface. In order to determine the effect of different fin parameters on the onset and intensity of acoustic resonance, fourteen different finned cylinders with fin thickness ranging from 0.35 to 1.5 mm and fin density ranging from 4 to 13.7 fin/inch are investigated for a Reynolds number ranging from 3.2×10⁴ to 2.6×10⁵. The onset and intensity of the acoustic resonance generated from each finned cylinder are compared to those generated from an equivalent bare cylinder with the same effective diameter. It is observed that the finned cylinders experience an earlier acoustic resonance and higher levels of acoustic pressure compared to their equivalent bare cylinders. This suggests that adding fins to the cylinder enhances the flow coherence along the cylinder’s span and thus makes the flow more susceptible to acoustic excitation. Moreover, it is observed that for constant fin spacing the acoustic pressure amplitude increases and the acoustic resonance occurs at earlier velocities as the fin thickness increases. On the other hand, for constant fin thickness, as the fin spacing increases the amplitude of the acoustic pressure decreases, while the onset of the resonance is delayed. Finally, the effect of the cylinder’s aspect ratio is investigated in three different test sections. It is observed that the amplitude of the excited acoustic resonance depends on the cylinder’s aspect ratio. The acoustic resonance amplitude is weaker for finned cylinders with aspect ratio less than 5 compared to their equivalent bare cylinders. However, finned cylinders with aspect ratio higher than 6 produces stronger acoustic resonance compared to their equivalent bare cylinders.