Abstract
Underbody aerodynamic noise has become a critical high-speed Noise, Vibration and Harshness (NVH) challenge in electric vehicle (EV), especially in the low-frequency range where conventional acoustic treatments are cumbersome. To address this issue, the acoustics on the underbody of Tongji Electric Vehicle (TJEV) standard model are first revealed by wind tunnel tests and hybrid Large Eddy Simulation (LES) and Acoustic Perturbation Equations (APE) method, and a mechanism of peak noise generation is clarified via acoustic modal analysis in this study. A novel control strategy is then proposed, employing neck-embedded Helmholtz resonator (NEHR) arrays integrated into the vehicle underbody panel to reduce low-frequency noise. Results show that under high-speed conditions, surface pressure fluctuation energy on the underbody is concentrated below 500 Hz with higher energy upstream than downstream. Within both the wheel housings and the underbody panel, the flow-acoustic composition shifts from turbulent-pressure dominance upstream to acoustic-pressure dominance downstream. Furthermore, peak noise at 340 and 480 Hz on the underbody are identified as originating from acoustic resonances inside wheel housings. Based on this insight, resonator arrays of sub-wavelength scale (installed thickness of only λ/28) are arranged in the sound propagation path on the underbody panel, achieving a peak sound pressure level reduction of up to 4.8 dB(A) at the target frequency of 340 Hz. This work demonstrates the first application of ultra-thin acoustic metastructure units into an automotive underbody for targeted low-frequency aerodynamic noise suppression, offering a lightweight and compact solution aligned with EV trends.
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