On the Flow-Excited Acoustic Resonance of Isolated Cylinder(s) in Cross-Flow

The flow-excited acoustic resonance of single and multiple cylinders in cross-flow is investigated experimentally. The effect of the cylinder(s) proximity to the acoustic particle velocity nodes of the first three acoustic cross-modes is presented. During the experiments, the acoustic cross-modes of the duct housing the cylinders are self-excited. For the case of a single cylinder, it is observed that although the cylinder’s location doesn’t significantly affect the vortex shedding process, it affects the mechanism of the flow-excited acoustic resonance and the levels of the generated acoustic pressure. When the cylinder is shifted away from the acoustic particle velocity anti-node of a specific acoustic cross-mode, a combination of cross-modes is excited with intensities that seem to be proportional to the ratio of the acoustic particle velocities of these modes at the cylinder’s location. For the case of two and three isolated cylinders positioned simultaneously side-by-side in the duct, it is observed that when the cylinders are positioned at different acoustic particle velocity anti-nodes of different cross-modes, the intensities of the excited acoustic resonance of these cross-modes are amplified compared to those with single cylinder. Nevertheless, when one cylinder is positioned at the acoustic particle velocity anti-node for a specific cross-mode and another cylinder is positioned at its acoustic particle velocity node, i.e. a cylinder that should excite the resonance and another one that should supress it, respectively; the excitation always takes over and the resonance occurs. Moreover, as the cylinder moves closer to the duct’s wall, the Strouhal number value decreases due to the interference between the wake of the cylinder and the wall. Therefore, the acoustic resonance for this case occurs at slightly higher flow velocities.