Tonal noise investigation of automotive HVAC systems : a hybrid method

There is no need to recall how the electrification trend of transport facilities has tightened the requirements around acoustic comfort. Within the automotive industry, these targets are more challenging for Heating, Ventilation and Air Conditioning systems for which passengers are in the foreground of noise emissions. The complexity of the requirements and specifications set by car manufacturers and suppliers stems from a dual aspect. First is quantitative based on the sound pressure level, whether it's the overall level or 1/3 octave band spectra. The second is purely subjective based on the perceived noise quality by stakeholders and final customers worldwide. During development phases, low frequency tone noises are frequently encountered on these systems which might induce discomfort to the passengers. The experimental investigations usually point to an aerodynamic origin, which prompted this research activity. The purpose of this work is to analyze and understand the mechanism of low frequency tonal noise creation using simulation and experimental correlations. This paper discusses all of the post-processing steps, which involve several methodologies such as spectral analysis, wall pressure FFT, filtered wall pressure and flow analysis. Cross-referencing this data allows us to identify the flow patterns responsible for the noise. Finally, this paper introduces a corrective technique based on the phase shift of noise sources that was implemented on this system analysis which demonstrates the relevance of the source location method.