Synergistic noise reduction in cylindrical shell structures using porous materials and Helmholtz resonators

Broadband vibroacoustic control in cylindrical shell cavities, particularly for aerospace applications, remains a critical challenge due to the performance limitations of single-mode treatments, space constraints and complex modal interactions. To address this, the acoustic modal characteristics of the cylindrical cavity are first investigated via theoretical derivations and numerical simulations to identify dominant noise behaviors clarifying the noise reduction requirements. Guided by these modal insights, a synergistic noise reduction strategy is proposed integrating porous materials and internally extended-neck Helmholtz resonators (HRs) to balance broadband attenuation and compact integration. A comprehensive validation framework is then established to verify the feasibility and performance of the strategy. First, the applicability of classical acoustic models for porous media is evaluated, identifying the Johnson–Champoux–Allard model as the most accurate for characterizing melamine foam. Second, an analytical formulation for the resonance frequency of internally extended-neck HRs is derived and validated. Third, component-level experiments on a small-scale cylindrical shell individually confirm the broadband mid-to-high frequency absorption of the porous material and the tunable low-frequency suppression of the HRs. Building on these foundational analyses, a system-level integrated testing platform featuring a large cylindrical shell is developed. Concurrently, an acoustic finite element model is constructed and validated against experimental data, demonstrating excellent agreement in predicting dominant peak frequencies. Experimental results indicate that the melamine foam lining achieves substantial noise reduction in the mid-to-high-frequency range while inducing a downward shift in the dominant low-frequency modal peak. By specifically targeting this shifted peak with embedded HRs, additional low-frequency suppression is attained. This work provides a validated, robust framework for broadband acoustic protection in aerospace structural systems, where space efficiency, weight control, and wide-frequency noise attenuation are mutually critical design objectives.