Acoustic Performance Analysis of Automotive HVAC Duct Designs Using a Lattice-Boltzmann Based Method and Correlation with Hemi-Anechoic Chamber

Acoustic comfort of automotive cabins has progressively become one of the key attributes of passenger comfort within vehicle design. Wind noise and the heating, ventilation, and air conditioning (HVAC) system noise are two of the key contributors to noise levels heard inside the car. The increasing prevalence of hybrid technologies and electrification has an associated reduction in powertrain noise levels. As such, the industry has seen an increasing focus on understanding and minimizing HVAC noise, as it is a main source of noise in the cabin particularly when the vehicle is stationary. The complex turbulent flow path through the ducts, combined with acoustic resonances can potentially lead to significant noise generation, both broadband and tonal. In order to avoid time-consuming and expensive late stage design changes, or avoid being hit by low consumer rating for ignoring the issues, it is important to identify potential problems early in the design process and take appropriate measures to rectify them. In this study, the noise characteristics of three HVAC duct designs are studied using a commercial Computational Fluid Dynamics (CFD) code based on the Lattice-Boltzmann method. The noise spectra for each duct is predicted using simulation tools, and the ducts are ranked in terms of their overall noise levels. The predicted spectra are shown to have good correlation with experimental results measured in a hemi-anechoic chamber in addition to the rankings being properly ordered. The noise generating flow mechanisms for each duct are identified using a proprietary patented flow noise source detection method.