Numerical investigation of Reynolds number and pitch ratio effect on lock-in ability of an aeroacoustic field in ducted flows

Abstract

Tube arrays in ducted flow often experience aeroacoustic resonance. This phenomena is initiated through a mechanism of lock-in during which, the flow induced acoustic field modifies the frequency of vortex shedding not only at a single frequency but over a range of frequencies, when the flow periodicity approaches, but is not equal to, the acoustic frequency of the duct. Predicting the flow velocity at which lock in starts is not yet possible as the factors that may influence the mechanism are not yet clear. Experimental studies have demonstrated that the lock-in depends on the amplitude of the acoustic field and its frequency ratio to the vortex shedding frequency. However, the impact of other factors such as turbulence and the typology of the flow patterns, which strongly characterise the fluid dynamics, have not been extensively investigated. The objectives of this research are to gain a better understanding of the fluid dynamic characteristic of the flow in which lock-in initiates and to determine if simplified cylinders arrangement can be utilised to investigate multiple cylinders resonance. This is pursued considering scenarios where lock-in is fulfilled, while the structure of the flow is altered. The flow is modifies by varying the Reynolds number and the convective velocity of the vortices.