Aerodynamically Excited Acoustic Oscillations in Cavity Resonator Exposed to an Air Jet

Experimental and theoretical results are presented for a cavity resonator driven by an air jet. Cavity sound spectra have been investigated to found a dependence of sound frequency and amplitude versus jet speed. Two ranges of the jet speed were distinguished. In the stage I, identified with low speed range, the frequency increased fast with jet speed and a frequency increment was proportional to jet speed as in the edge–tones phenomenon. In a stage II, corresponding to higher jet speeds, an increase in the frequency was still observed, but a frequency growth was much smaller. A correlation of experimental data has shown that the observed oscillation amplitudes are within moderate–range. A theoretical model based on moving compact vortices was presented to describe flow–acoustic interaction in a resonator opening and find an aerodynamic force driving a resonator. A response of resonator was modelled by equivalent impedance circuit with added nonlinear term. From final equations a frequency and an amplitude of oscillation were calculated. A support for the proposed theory is provided by favourable comparison between theoretical predictions and experimental data.