Amplitude Modulation Mechanism of the Dual-Stream Hot Jet-Flap Interaction Tonal Noise

Multiple tones were observed in the jet-flap interaction noise spectra. The tonal frequencies can be accurately predicted and it was revealed that tonal noise is generated by the coupling between the downstream-travelling Kelvin-Helmholtz wavepackets and a family of trapped, upstream-travelling acoustic modes in the potential core. However, the inherent temporal features and the relationships between multiple tones are rarely researched. In this study, the experimental investigation of jet-flap interaction noise was conducted on dualstream hot jets. The continuous wavelet transform method was introduced to analyze the farfield acoustic signals for the dual-stream hot jet-flap interaction tonal noise, aiming at revealing the temporal features and excitation rules of these multiple tones. In contrast to the existing studies, this work demonstrates that multiple weak tones are produced by the amplitude modulation phenomenon of the primary and strongest tones, which indicates that mode switching mechanism and amplitude modulation mechanism are coexisting in the generation of jet-flap interaction tonal noise.