Transient analysis of blade-vortex interaction noise.

In this work, we propose the using of a transient acoustic imaging technique to analyze blade-vortex interaction (BVI) noise, which is considered as one of the dominant noise sources from rotorcraft. A simplified but representative set-up with a two-bladed rotor in the presence of a moving flow is considered herein. First, we conducted a delayed detached-eddy simulation to reveal the associated flow physics and to identify the distinctive flow structures during the BVI process. The numerical analysis complements the physical understanding gained from the following acoustical imaging analysis, where a recently developed phase-averaged wavelet-based beamforming method in the time-frequency domain is adopted. Compared to transient flow structures, which have been visualized in the numerical study, the acoustic imaging results clearly demonstrate the transient analysis capability of the proposed approach. It is impossible to achieve such a transient analysis capability by simply using the classical beamforming method. In particular, the transient analysis shows that the dominant noise sources would move along the blade in the radial direction, by essentially following the corresponding BVI positions on the blade, which is also consistent with the numerical results. Overall, the proposed method can help achieve a deepened physical understanding of transient aerodynamic and aeroacoustic process and could find applications in low-noise rotorcraft designs. [ABSTRACT FROM AUTHOR]