Detecting the Inherent Modulation Phenomenon of High-Lift Configuration Noise Using the Hilbert–Huang Transform.

The phenomenon of multiple tones is a typical feature of high-lift configuration noise, and the underlying nonlinear and nonstationary features need to be revealed through time-frequency analysis. This paper introduces the Hilbert–Huang transform method to detect the inherent amplitude modulation and frequency modulation phenomena of multiple tones from 30P30N three-element high-lift configuration with both slat and flap completely stowed. The acoustic modes are extracted from the multiple tones firstly and then the variation features of amplitude and instantaneous frequency are analyzed. The results show that the acoustic energy concentrates on the primary mode with much larger amplitude. Moreover, both the amplitude and instantaneous frequency are periodically varied in time and the predicted modulation frequencies are equal to the frequency intervals between nearby tones, confirming that the inherent temporal features of multiple tones are amplitude modulation and frequency modulation. [ABSTRACT FROM AUTHOR]