An Investigation of Aerodynamic Noise from Standard Ground Vehicles using Computational Aeroacoustics

The noise radiating from ground vehicles and its detrimental effects on occupants, pedestrians, and the environment have spurred vehicle manufacturers to seek effective noise prediction methods and mitigation strategies. This thesis focuses on predicting aerodynamically generated noise from vehicles using a hybrid Computational Aeroacoustics (CAA) method. This study aims to explore how geometrical features influence noise generation and provide valuable insights for noise reduction. A hybrid CAA approach is proposed, employing Stress Blended Eddy Simulation (SBES), and Ffowcs-Williams and Hawkings (FW-H) acoustic analogy to predict noise radiation from standardised vehicle geometries. Initially, SBES is validated against experimental data for scaled notchback geometry, followed by assessing SBES coupled with FW-H to predict noise radiated by half-round mirrors. Subsequently, the methodology is applied to full-scale vehicle geometry with a bluff mirror mounted on one side. The SBES predictions indicate that the flow behaviour behind the backlight of notchback becomes increasingly asymmetric with a higher backlight angle, which is consistent with the experimental findings. As the backlight angle increased, the strength of the vortex generated from the lateral edges of the backlight decreased on one side and increased on the other side, leading to an asymmetrical flow. The hybrid CAA approach predicts the flow and noise radiated from the half-round mirror in agreement with experiments and reveals increased noise radiation with higher aspect ratios but reduced noise when the mirror is inclined towards the mounting plate. Notably, the radiated noise from the half-round mirror exhibited a dipole-like structure near the plate and a monopole-like structure away from it. This observation is consistent for both variations introduced into the half-round mirror. For the full-scale vehicle model, the absence of the A-pillar is identified as the primary contributor to overall noise radiation. However, in the presence of a side-view mirror, the side window becomes a significant contributor to noise. Additionally, when the mirror is inclined, a linear reduction in the radiated noise is observed, although the vehicle's overall drag becomes nonlinear and highly dependent on the flow behaviour past the mirror. The proposed hybrid CAA approach provides valuable insights into noise prediction for ground vehicles. By considering the impact of mirror inclination and geometric factors on noise radiation, this research contributes to the development of quieter and more aerodynamically efficient vehicles, thus fostering a comfortable and sustainable transportation environment.