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This paper introduces a passive protrusions to reduce undesirable structural loading and high-amplitude noise radiation in axisymmetric cavities, are common in industries, including pipelines and aerospace. A comprehensive experimental investigation of the pipe-cavity noise control system is conducted, exploring various protrusion locations and lengths at different Nozzle Pressure Ratios (NPRs). The study examines protrusions placed at the leading, trailing, and both leading and trailing edges of the axisymmetric cavity. Additionally, detailed experiments are performed to analyze the impact of protrusion lengths on unsteady cavity pressure and far-field noise radiation. Cavity pressure fluctuations and far-field noise levels are measured for both cases: with and without protrusions in the pipe-cavity setup. The Proper Orthogonal Decomposition (POD) technique is applied to the time-resolved Schlieren images to show the effect of passive protrusions on the exit jet flow structure. Results demonstrate that a protrusion located at the trailing edge yields superior noise reduction compared to other configurations. The efficacy of this protrusion in mitigating cavity noise is attributed to its ability to efficiently alleviate the feedback mechanism responsible for cavity noise generation and break down the recirculation region within the cavity system. Significant noise reduction, approximately 4 dB, is achieved at lower NPRs, and substantial noise reductions are also observed for the underexpanded jet condition. [ABSTRACT FROM AUTHOR]

Understanding the occurrence of various feedback mechanisms of an under-expanded impinging supersonic jet is a crucial task in research. The presence of several jet modes is examined in this study for the flat and corrugated impinging plate geometries. The behavior of impinging plate configurations during mode switching is investigated by varying the flow state, such as the jet Mach number. The staging behavior at various jet Mach numbers is observed using acoustic spectral plots and schlieren flow visualization. To explore the presence of various types of modes during the jet impingement due to the modification of jet Mach number, ensemble averaging and Proper Orthogonal Decomposition of schlieren images are carried out. In the majority of situations, the corrugated design shows a reduction in tonal noise and overall sound pressure level. In exceptional cases, for the corrugated plates, the enhanced overall sound pressure level is caused by the existence of axisymmetric instability (A1, A2). [ABSTRACT FROM AUTHOR]