AEROACOUSTIC RESPONSE OF ISOLATED CYLINDER(S) IN CROSS-FLOW AT DIFFERENT LOCATIONS INSIDE A RECTANGULAR DUCT

Abstract

ABSTRACT: The flow-excited acoustic resonance of single and multiple isolated 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 hosing the cylinders are self-excited. For the case of single cylinder, it is observed that although the cylinder′s location doesn′t significantly affect the process of vortex shedding, it affects the mechanism of the flow-excited acoustic resonance and the generated acoustic pressure. When the cylinder is shifted away from the acoustic particle velocity anti-node of a certain acoustic cross-mode, a combination of cross-modes is excited with intensities that seem to be proportional to the ratio of the acoustic particles 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 of certain cross-modes and another cylinder is positioned at it′s acoustic particle velocity node, i.e a cylinder that should excite the resonance and another one that should suppress 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 decrease due to the interference between the wake of the cylinder and the duct′s wall. Therefore, the acoustic resonance for this case occurs at slightly higher flow velosities.