Numerical investigation of whistling sound in narrow-gap flow of automobile side mirror

• Published in: Applied acoustics 2022-08, Vol.197, p.108893, Article 108893
• Main Authors: Lee, Kwongi, Lee, Songjune, Lee, Sangheon, Cheong, Cheolung
• Format: Article
• Language: English
• Subjects: Aerodynamic noise; Cavity noise; Narrow-gap flow noise; Vortex sound source; Whistling sound
• ISSN: 0003-682X; 1872-910X
• DOI: 10.1016/j.apacoust.2022.108893

•The generation mechanism of the narrow gap whistling of a side mirror was investigated.•A wind tunnel test was performed to find the flow conditions for the onset of the whistling sound.•The generation mechanism of the whistling sound was captured using compressible LES techniques with high-resolution grids.•The main aerodynamic sources were identified using the vortex sound sources.•The generation mechanism of the whistling sound based on the feedback mechanism was revealed.•The standing wave pattern in the narrow gap was shown to be coupled with the identified vortex sound sources. It is frequently reported that a high-frequency whistling noise is generated by airflow through the narrow gap of a vehicle’s side mirror under certain driving conditions. The aim of the present study is to identify the generation mechanism of the narrow gap whistling of a side mirror, which is considered one of the most challenging problems due to too the small dimensions and complex geometry of the gap. A wind tunnel test was performed to find the flow conditions where the whistling sound is generated. The relative directions and speeds of the airflow were identified for the onset of the whistling sound and its frequency. A numerical analysis of the external and internal flows of the side mirror was then conducted using compressible Large Eddy Simulation (LES) techniques with high-resolution grids to capture the generation mechanism of the whistling sound, which is generally based on a feedback mechanism between the vortex and sound waves. The numerical result was validated through a comparison of the predicted sound pressure spectrum with the measured ones. The main aerodynamic sources were identified using the vortex sound sources, and a generation mechanism of the whistling sound based on the feedback mechanism was revealed. This was done by visualizing the standing wave pattern in the narrow gap, which was coupled with the identified vortex sound sources.