Time-frequency analysis of acoustic signals from a high-lift configuration with two wavelet functions

- The continuous wavelet transform method is introduced to analyze far-field acoustic signals of high-lift configuration with two wavelet functions (Morlet wavelet function and Mexihat wavelet function).
- The Morlet wavelet function is more appropriate to analyze the oscillatory behaviors of far-field acoustic signals.
- The multiple tones radiated from slat cove is related to the mode-switching phenomenon, while the multiple tones radiated from flap-main element gap is related to the amplitude modulation phenomenon.

This paper introduces the continuous wavelet transform method to analyze different multiple tonal phenomena of the high-lift configurations, aiming at revealing the time-frequency information of these multiple tones simultaneously. Two types of multiple tones can be respectively observed in the far-field noise spectra at landing and cruise configurations, but their inherent physical mechanisms are different. Two wavelet functions are applied in this paper. The Morlet function as a complex wavelet function returns both amplitude and phase information for capturing oscillatory behaviors, so that it can clearly distinguish the mode switching mechanism and the amplitude modulation mechanism of different multiple tonal phenomena. While the Mexihat function as a real wavelet function returns only amplitude information, so that it is usually to isolate peaks or discontinuities of signals and cannot reveal the mechanisms of different multiple tonal phenomena. In summary, the Morlet function is more appropriate to analyze the periodical oscillatory acoustic tonal signals from multiple tonal phenomena.