Numerical and Experimental Investigation and Refinement of Automotive HVAC Flow Induced Noise

Automotive heating ventilating and air conditioning (HVAC) noise is a very big concern for original equipment manufacturers (OEM) and suppliers. It turns out to be more challenging as the demand for acoustic comfort is increasing day by day. Many times an existing HVAC with some minor changes (mostly the vehicle fitment points) is proposed for face-lift vehicle but the performance expectation is far beyond the existing one due to market demand. One of the critical requirements is enhanced sound quality. To achieve that either experimental testing or numerical simulation is adopted. In either of these cases, it ends up with high number of experiments or increased simulation cost due to aero-acoustic simulation.

Hence a combined approach is followed in order to investigate and improve the noise sources of an existing HVAC. The present paper describes this approach in details by doing numerical flow simulation followed by experimental investigation. HVAC was modeled using computational fluid dynamics (CFD) and a detailed flow simulation was performed. Areas with flow separation, flow vortices and high turbulent kinetic energy (TKE) were identified in the flow domain. After having deep investigation into those areas, existing HVAC was modified to streamline and eliminate the secondary flows. Experiments were carried out on modified HVAC in a semi-anechoic chamber and noise data was captured. It is observed that a substantial improvement is achieved in overall airborne noise level by doing changes as per the suggestions from flow simulations. Thus a combined methodology is developed to improve the sound quality of an automotive HVAC - a novel approach which can be applied even at the design stage and other similar application for airborne noise.