Experimental Study of Deep Cavity Noise Suppression by Surface Compliance

This study investigates a novel passive control technique for suppressing tonal noise in deep cavities, focusing on the strategic use of surface compliance. An experimental setup was designed, featuring a deep cavity with an elastic panel flush-mounted at the cavity bottom. The primary goal is to verify and extend the findings of the previous numerical study by Naseer, et al. [1], which explored the potential of leveraging aero acoustic-structural interactions for noise suppression. Pressure measurements of cavity flow and farfield noise, along with Particle Image Velocimetry (PIV), were utilized to capture the interactions between flow dynamics and the cavity acoustic response. The experimental results demonstrated that the panel effectively altered the aero acoustic pattern inside the cavity, leading to a noticeble reduction in tonal noise up to 16.1 dB, particularly at specific flow velocities, 20 and 30 ms^-1,where the interaction between shear layer oscillations and cavity acoustic modes typically strengthens aero acoustic resonance. The study provides a detailed analysis of the modified aero acoustic feedback mechanisms due to the introduction of the elastic panel. A comparison of acoustic spectra between the baseline rigid cavity configuration and the modified cavity panel setup revealed that the panel not only reduced the peak noise levels but also shifted the dominant acoustic frequencies, suggesting a disruption in the typical aero acoustic coupling processes. These findings highlight the potential of using compliant surfaces to passively control aero acoustic emissions in practical applications, offering a promising alternative to more invasive noise mitigation strategies.