Design and Simulation of Acoustic Metamaterials for Noise Reduction in Open- Flow Systems

Abstract

The growing demand for larger and more efficient cooling systems in heavy-duty trucks has led to increased noise levels, particularly from cooling fans, which poses challenges to both environmental standards and user comfort. Conventional techniques for sound absorption typically restrict particle motion, which will also impede flow and increase temperature in a situation when fans are present. Acoustic metamaterial (AMM) solutions have been explored to address these problems. A systematic methodology for designing a single metamaterial cell is presented, encompassing four stages: specification of geometrical parameters, parametrization, parametric design, and optimization. Noise characterization of a vehicle’s cooling fan, based on Lu’s study[20], revealed broadband noise and tonal harmonics centred on the blade passing frequency (BPF). In response, a double-layer micro-perforated panel (DLMPP) structure was designed to reduce noise over a broad frequency range; a space-coiling structure was created to target specific tonal noise. Theoretical calculations show that both structures have excellent noise absorption performance. Simulations of the space-coiling cell with a flow field were then conducted. Although the absorption coefficients show slight deviations from theoretical calculations, the results remain promising for this study and warrant further investigation. A simulation of an under-cab environment was also studied by applying the acoustic impedance of DLMPP on target surfaces under conditions with and without flow. The results demonstrate that the present AMMs can significantly reduce cooling fan noise while maintaining thermal management efficiency.