To reveal the acoustic radiation mechanism of mixing layer under supersonic flow

and enhance the understanding

the parabolized stability equations (PSE) were performed to investigate the sound generation by sideband instability in a supersonic mixing layer. The nonlinear evolution of two initial disturbances and the fluctuation of difference component were analyzed. Mach wave radiation was quantified by an integral derived by Wu

which representd the detail of sound generation mechanism in far field. The results showed that the spectral broadening was due to the excitation of difference component and its sideband interaction. The generation of the difference component broadened the scope and enhanced the strength of Mach wave radiation. For fast mode

the difference component increases more rapidly with its frequency getting smaller

and the scope of Mach wave radiation gets wider in the meantime. However

for slow mode

the influence of frequency of difference component on Mach wave radiation is not obvious.