Jet noise reduction and mechanism analysis for rearview mirrors and A-pillars

Aerodynamic noise generated by exterior functional protrusions significantly affects in-cabin noise levels. This study focuses on the rearview mirror, A-pillar, and roof sensing system, investigating the effects and mechanisms of jet noise reduction. The agreement between the simulation results and wind tunnel test data validates the feasibility of the numerical simulation method developed in this study. Applying jets at 0.3 times inflow to the rearview mirror, the A-pillar and roof sensing system reveal that the rearview mirror jet achieves the best noise reduction. This type can lower the total sound pressure levels of the front side window, windshield, and sunroof by 2.5, 1.3 and 0.9 dB, respectively, with the main noise reduction observed in the frequency range from 300 to 1500 Hz. The jet applied to the A-pillar has limited effects, while those on the roof sensing system produce virtually no noticeable noise reduction. Through the analysis of the improved clustering method, the jet can significantly change the temporal distribution of acoustic pressure. Further employing proper orthogonal decomposition methodology, the study analyzes the changes of the first-order modal coherent structure and total energy. Then the noise reduction mechanism is elucidated from the perspective of the flow-acoustic connection. The jet redistributes the system energy from the low-frequency large-scale coherent structure to the high-frequency small-scale structure. By reducing the structural coherence of organized flow patterns and diminishing the vortex size, this process effectively attenuates overall acoustic radiation intensity, thereby achieving noise suppression. Both jet configurations exhibit similar noise reduction mechanisms.