AEROACOUSTICS ANALYSIS OF AUTOMOTIVE SIDE VIEW MIRROR

Abstract

The aerodynamic noise generated by car side view mirrors is a significant contributor to overall vehicle noise, particularly at highway speeds, impacting passenger comfort and the perception of vehicle quality. This thesis presents a comprehensive aeroacoustics analysis of a generic car side view mirror, focusing on the influence of varying mirror angles on noise generation mechanisms. Computational Fluid Dynamics (CFD) simulations are employed to model the complex turbulent flow field around the mirror at these different orientations. A broadband noise model is utilized to predict the acoustic characteristics emanating from the unsteady flow structures. This approach allows for the identification and quantification of dominant noise sources and their behaviour as the mirror's angle relative to the oncoming flow is altered. The study investigates changes in flow separation, vortex shedding, and pressure fluctuations on the mirror surface and in its wake, and correlates these aerodynamic phenomena with the predicted broadband noise spectra. Key objectives include understanding the fundamental aeroacoustics phenomena associated with different mirror positions, characterizing the directivity and intensity of the radiated sound, and identifying optimal mirror angles for potential noise reduction. The findings of this research aim to provide valuable insights for automotive designers seeking to optimize side view mirror designs for improved aeroacoustics performance and enhanced driving experiences. This work contributes to the ongoing efforts in vehicle noise, vibration, and harshness (NVH) refinement by systematically analysing a critical aeroacoustics component. This analysis focuses on understanding and mitigating aeroacoustic noise generated by automotive side view mirrors, a critical concern in modern vehicle design, especially for Electric Vehicles (EVs) where other noise sources are diminished. The study highlights the application of Computational Aeroacoustics (CAA) methodologies within ANSYS Fluent, emphasizing the role of turbulence models and acoustic analogies, and discusses the impact of side mirror geometry and orientation on noise generation. The outside rear view mirror (OSRVM) is a major contributor to wind-induced noise due primarily to its non-streamlined, "bluff body" design, which leads to significant flow separation and turbulent wake formation Aeroacoustic noise from side mirrors is primarily driven by flow separation, vortex shedding, and the resulting unsteady pressure fluctuations. Periodic vortex shedding from bluff bodies like side mirrors creates distinct "Aeolian tones". Optimal Mirror Base Orientation: A significant finding indicates that an optimal orientation of the mirror's base (the arm connecting the mirror to the vehicle body) at approximately 35 degrees relative to the horizontal axis yields minimal acoustic noise and favorable aerodynamic performance. This optimal orientation can lead to a substantial reduction of up to 3 dB in sound pressure level by redirecting turbulent flow away from the side window, allowing a more linear airflow path between the vehicle side and the mirror.