Investigation of the do minant Rossiter modal tones at the locked-on state

Abstract

Rossiter resonance noise, which is flow driven cavity noise involving fluid dynamics processes, was investigated in a low-speed wind tunnel. The experiments include near-field and far-field acoustic field measurements of the rectangular cavity at different depths as well as velocity measurements of the shear layer. The rectangular cavity geometry was also designed to enable the Rossiter mode to interact with the first-order depth resonant mode in a locked-on state. The experimental results showed the variation of frequency and overall sound pressure level (OASPL) when the self-sustained oscillation was in the locked-on state. When the self-sustained oscillatory mode is in the unlocked state, the frequency of the self-sustained oscillatory mode can be predicted well by using the Rossiter formula, whereas the frequency of the dominant Rossiter mode in the locked-on state will be predicted inconsistently. Moreover, the corresponding selection of the dominant mode also depends on the resonant mode, and there are local variations in the OASPL. The results indicate that the ratio of the resonant mode frequency to the self-sustained oscillatory fundamental frequency, Rd, plays a key role in the locked-on state. In this paper, the Rossiter model is modified using the parameter Rd for the prediction of the dominant mode frequency in the locked-on state. The difference between the current formula and previous studies is that the variation of the phase delay coefficient γ with velocity is considered, and γ is related to Rd. Finally, the accuracy of the formulation is verified with experimental data from different models.