On the reduction of the flow-induced noise using porous material plates with high acoustic transmissibility

This study investigates the efficacy of closed-structure porous materials for reducing flow-induced noise, given their high acoustic transmissibility and low fluid permeability. A multifaceted approach encompassing wind tunnel experiments, numerical simulations, and practical applications to heating, ventilation, and air-conditioning (HVAC) systems in commercial electric vehicles was adopted. Wind tunnel experiments demonstrated a significant reduction, over 20 dB, in the tonal noise generated from a rectangular cylinder and an increase in its frequency, attributable to changes in the vortex structure and velocity fluctuations in the wake of the cylinder. The numerical simulation of fluid permeation and pressure wave conditions on the surface of the porous material as a boundary condition aligned with the experimental outcomes, suggesting that such permeation conditions could lead to noise and drag reduction. Practical testing showed a 5 dB noise reduction at the driver's ear position when porous materials were attached to a portion of an electric vehicle's HVAC system. The noise reduction was associated with changes in velocity fluctuations in the flow field, aligning with the wind tunnel experimental findings. This study provides promising insights into the development of effective noise reduction strategies using porous materials.