Wavelet analysis of multiple tonal phenomena generated from a simplified nose landing gear and a ring cavity

Abstract

Discrete tones exist in the airframe noise spectra. For landing gear components, some cavities may generate multiple tones. The tonal frequencies can be accurately predicted and two different tonal noise generation mechanisms have been already proposed, namely fluid-acoustic feedback loop and acoustic resonance. However, the inherent temporal features and the relationships between multiple tones are rarely researched. This paper introduces the continuous wavelet transform method to analyze the acoustic signals from a simplified nose landing gear model and a ring cavity model, aiming at revealing the temporal features and excitation rules of these multiple tones. For the landing gear model, the wavelet analysis results show the mid-high frequency tones generated from the acoustic resonance phenomenon are randomly excited in time and the excitation states are independent of one another. For the ring cavity model, the low frequency tones generated from fluid-acoustic feedback loop are excited alternately and the primary acoustic energy switches from one to another in time, namely the mode switching mechanism. While among the high frequency tones generated from acoustic resonance, the second to the fourth tones satisfy the amplitude modulation mechanism and the other tones are randomly excited.