The mitigation of duct noise while allowing airflow is an important but challenging task in mechanical systems such as HVAC systems, data center cooling facilities, and power plant intake systems. Acoustic metamaterials have been actively investigated to address this trade-off between airflow and noise reduction. However, most previous studies assume ducts with uniform cross sections and unchanged flow velocity profiles, limiting their applicability. This study presents a metaliner—an acoustic metamaterial designed to achieve effective noise reduction even in flow ducts with non-uniform cross sections. The metaliner comprises multiple unit cells, each individually designed for local flow characteristics. A theoretical model is established to predict the effect of locally varying flow velocity profiles on the effective impedance of each unit cell. By incorporating friction velocity as a key physical parameter, the model enables accurate calculation of effective impedance even in flow ducts with non-uniform cross sections. Based on this theoretical model, each unit cell is designed to account for the effect of locally varying flow. Experimental results validate the performance of the designed metaliner, demonstrating its effectiveness in reducing noise within a flow duct featuring non-uniform cross sections.
Kim et al. (Wed,) studied this question.