Prediction of Flow-Induced Noise of Automotive HVAC Systems

Nowadays vehicle quality is rated for noise and vibration and the interior sound levels have become a major target of automotive companies. Strides have been made in reducing power train, tire and external wind noise over the years. However, HVAC and blower fan flow-induced noise reaches the interior cabin without any sound isolation and can strongly impact customer comfort. In the early stage of vehicle design, it is experimentally difficult to get an estimate of the flow pattern and sound levels. The goal of this study is to develop and validate a numerical noise prediction tool for complete HVAC systems noise, defined as the arrangement of sub-systems such as air intake duct, thermal mixing unit, blower, ducts and outlet vents. This tool can then be used during the development of vehicles to evaluate and optimize the aeroacoustics performances of the system without additional or belated experiments. The sound transmission through the dash or wall is not considered in this study and the focus is made on the primarily flow-induced noise contribution. The CFD/CAA numerical method use a time explicit, unsteady and compressible method based on the Lattice Boltzmann Method (LBM) during which flow and acoustics are calculated at the same time. The numerical method is used to estimate the noise from two productive HVAC systems mounted on a Simplified Vehicle Cabin (SVC) and real Production Vehicle Cabins (PVC). Results in term of flow and noise are compared and validated through experiments. The influence of the cabin structural modes and absorption on the broadband noise levels is also discussed.