Acoustic Resonance Mechanism for Screech Modes of Supersonic Sweeping Jets

Supersonic sweeping jets (SWJs) have promising prospects for high-speed flow control applications. In this work, an experimental investigation using schlieren imaging and microphone measurements is conducted to examine the screech of supersonic SWJs and their acoustic resonance mechanisms. Nozzle pressure ratio (NPR) ranges from 1.75 to 6. Acoustic results show that multiple discrete tones at specific frequencies are generated when [Formula: see text], and the frequency differences between adjacent tones are always equal to the frequency of the jet sweeping motion. With increasing NPR, the frequencies of the tones remain almost constant, indicating the absence of mode-staging behavior. Time–frequency spectra show that these multiple tones coexist at all NPRs, suggesting the stability of the SWJ screech generation process. Flow structures at the screech frequency, extracted via SPOD, show that the high-amplitude regions are associated with interactions between instability waves and shock structures. The wavenumber spectra of the selected SPOD modes suggest that the dominant and adjacent secondary screech modes are generated by interactions between the Kelvin–Helmholtz (KH) waves and the primary shock wavenumber peaks at different phases. Instantaneous far-field schlieren visualizations provide insight into the generation mechanism and acoustic feedback loop of the multiple screech tones.