Synchronous vortex shedding from aerodynamically isolated side-by-side cylinders imposed by flow-excited resonant acoustic modes

The flow-excited acoustic resonance of aerodynamically isolated side-by-side cylinders is experimentally investigated to identify the influence of the resonant acoustic field on the dynamics of vortex shedding in the wake of the cylinders. Self-excitation of the acoustic cross-modes inside the duct housing the cylinders is achieved when the vortex shedding from the cylinders occurs at locations away from the acoustic particle velocity node of an acoustic cross-mode, with acoustic pressure amplitude dependence on the cylinders’ proximity to the acoustic particle velocity antinode of the excited resonance mode. Phase-locked particle image velocimetry measurements indicate that the acoustic resonance excitation synchronizes the isolated wakes of the cylinders according to their relative phase with the acoustic particle velocity at the cylinder axis plane. Notably, such effect is absent for cylinders with wakes shed at the acoustic particle velocity nodes of a resonant mode. Investigation of the phase between cylinders’ wakes during resonance excitation for individual instants shows that the synchronization is not a perfect lock-in, but a statistical tendency of the wakes to shed vortices at a preferred phase, suggesting that the strong acoustic field engages in constructive or destructive interference with the shed vortices according to their phase. The results presented in this paper prove that the effectiveness of cylinder removal from certain locations in a tube bundle as a method to suppress resonance excitation may be reduced as other cylinders at large spacing may act in sync to excite acoustic cross-modes.