Hybrid flow control method for supersonic jet noise suppression: a Mach number effect

Abstract This study examines the noise reduction potential of the proposed hybrid flow control nozzle for designs with Mach numbers 1.4 and 1.8. The Schlieren image indicates that jets exiting the hybrid flow control nozzle (DS-CHN) exhibit two notable changes: a reduction in the dimensions of the supersonic core jet and an increase in the thickness of the shear layer owing to the enhanced mixing within the shear layer. The improved mixing aims to diminish the convection velocity of the large-scale structures that generate low-frequency mixing noise. Furthermore, the controlled jets also show significant asymmetry across all NPRs. Acoustic far-field data indicate that the DS-CHN demonstrated a significant reduction in dominant low-frequency mixing noise compared to the baseline nozzle (BSN), with attenuation intensity increasing in parallel with a surge in NPR. The magnitude of the overall sound pressure level (dB) (OASPL) shows that the DS-CHN reduces dominant low-frequency mixing noise ranging between 0.5 to 4 dB for Mach 1.4 (NPR 2.25–6.25) nozzle and 0.5 to 5.2 dB for Mach 1.8 (NPR 2.75–6.75) nozzle. Similarly, the DS-CHN also reduces screech noise at both Mach numbers. At Mach 1.8, the reduction in screech noise intensity is substantial, while at Mach 1.4, it is moderate. Furthermore, the DS-CHN also moderately reduces the intensity of shock noise for both investigated Mach numbers. Therefore, it is obvious that combining an active deflecting seal with a passive chevron produces a synergistic effect for superior noise suppression. Statistical techniques, such as autocorrelation and cross-correlation, are employed to evaluate jet noise radiation features.