Acoustic performance analysis of automotive HVAC duct designs using a Lattice-Boltzmann based method and correlation with Semi-anechoic chamber.

Acoustic comfort of automotive cabins has progressively become one of the key attributes of vehicle design, with wind noise and HVAC noise being two of the key contributors to noise levels heard inside the car. With the increasing prevalence of hybrid technologies and electrification and the associated reduction in powertrain noise levels, the industry has seen an increasing focus on understanding HVAC noise, as it is a main source of noise in the cabin if not the single one when the vehicle is stopped. 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 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 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 semi-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. Next, a methodology to enable the rapid evaluation of the acoustic performance of duct designs is discussed. This method is used to quantify the variation in flow noise sources associated with changes in duct design, allowing for the exploration and acoustic ranking of multiple designs in a short period of time. This method is demonstrated using one of the ducts previously studied, and a potential improvement in the design is presented.