Aero-Acoustic Characterization of a Commercial Vehicle Configuration Using CFD

Noise pollution from automotive vehicles is a significant concern in urban areas, emphasizing the need for improved vehicle engineering of automotive vehicles to reduce noise levels. The necessity for automotive vehicles to have a low acoustic signature may further be emphasized by local regulatory requirements, such as the EU's regulation 540/2014, which sets sound level limits for commercial vehicles at 82 dB(A). In addition to this the external noise may propagate inside the cabin affecting the overall wellbeing of the driver. To address the issue vehicles are observed to measure noise levels at various locations, including inside and outside the cabin. These testing facilitate noise source identification and categorization of noise into structure-borne noise and air-borne noise. The air-borne noise, which can be either broadband or tonal in nature, is particularly discomforting and may require mitigation. To analyse these complex aero-acoustic behaviour of the vehicle, CFD can be used to complement experimental observation. Although studies have been conducted on actual vehicle configurations, most of them focus solely on capturing broadband noise levels rather than tonal noise behaviour. This study explores the phenomenon of external tonal noise generation caused by aero components, such as the A-pillar turning vane (APTV) on a commercial vehicle configuration using both the compressible and incompressible transient CFD approaches. The results are compared with critical tonal frequencies in previous observation for similar vehicle configurations. The comparison reveals that CFD tends to overpredict the critical tonal frequency although the overall deviation within 5% of the expected Strouhal no. frequency data. The source of sound is identified as the coherent vortex shedding from the APTV which exhibits a dipole acoustic behaviour. The developed method can be further refined for accuracy and integrated with a Vibro-acoustics tool to propagate the noise inside the cabin.