An experimental study on the coupling between adjacent Hartmann whistles

Abstract

An experimental study has been conducted to examine interactions between two Hartmann whistles placed in close proximity. Microphone measurements of acoustic emission from the whistles, in addition to high-speed flow field visualizations, were used to assess the physical mechanisms present. A strong coupling mode has been identified that results in frequency locking between the resonators. Observed for only one set of parameters in the experimental matrix, the frequency-locked coupling requires sufficient spacing between the nozzle exit and resonator cup of each whistle to establish the acoustic-driven feedback loop. The visualization results show this coupling to arise due to acoustic excitation from the adjacent resonator, inducing hydrodynamic perturbations that grow sufficiently to alter the flow field around the perturbed resonator. The study indicates that coupling dynamics can play a primary role in dual-whistle resonance and frequency output.