Experimental Investigation of Upstream Geometry Effects on Screech Feedback Mechanisms in Twin Supersonic Jets

This paper investigates the impact of upstream nozzle geometry on screech generation mechanisms in twin supersonic jets. Through detailed acoustic and flow-field experiments, evidence is presented that demonstrates higher screech production and multimodal behavior along with broadband shock associated noise in nozzles featuring a plug-type design. Although the optimal nozzle design exhibits slightly higher broadband shock-associated noise in design operating condition, the plug nozzle’s pronounced screech tones dominate the overall sound pressure levels, exceeding by approximately 3–5 dB across nearly all tested conditions, including over expanded (2.5,2.7,3.0) and design nozzle pressure ratios NPR of 3.67. Additionally, a notable increase in high-frequency noise accompanies the screech tones in plug-type nozzles, suggesting the presence of smaller-scale turbulent structures upstream of the nozzle exit. This high-frequency acoustic signature is especially pronounced at lower observer angles, consistently appearing stronger in plug nozzles compared to their optimal counterparts across all measurement angles. Observations suggests the jet turbulence characteristics changes not just because of its design parameters rather the way the design is inculcated.