Acoustic experimental investigation of the acoustic resonant influence on Rossiter modal tones at the locked-on state

Abstract

In this work, the complex interactions of the inherent instability of the separated shear layer and an acoustic mode of the cavity noise at the locked-on state are studied within a low-speed wind tunnel. Experimental results for near- and far-field acoustics in rectangular cavities with varying widths and depths are provided for flow velocities ranging from 10 to 35 m/s. The geometry of the rectangular cavity is specially designed with an excited tone related to the first depth mode of acoustic resonance. Differences between the locked-on and non-locked-on states are highlighted. At the non-locked-on state, the tonal frequency is well predicted by the Rossiter formula; whereas, at the locked-on state, it is found to deviate from the Rossiter formula and the dominant mode selection behavior of Rossiter tones is inconsistent with those reported at the non-locked-on state. However, the mode switching behavior can be observed with similar results by the wavelet analysis method for both states, showing a week influence of the acoustic resonance on the intermittency behavior of the sustained oscillation due to the inherent instability of the separated shear layer.