Title: A Practical Approach towards Reducing the HVAC Flow Noise
text: Automotive heating ventilating and air conditioning (HVAC) noise is becoming a big concern area as the demand for acoustic comfort increases day by day. Vehicles are manufactured in recent years with quieter powertrain, reduced body leakage, better suspension. The other quieter technologies like electrification, hybridization of vehicle further complicate the whole subject of vehicle cabin noise issue. The HVAC noise is the major noise source inside the cabin. Hence designing a HVAC with very low sound pressure level is quite challenging and poses many difficulties in meeting other basic performances due to certain trade-off while meeting the noise requirement. However in recent years engineers have done extensive research and come up with various feasible and non-feasible solutions in order to reduce the HVAC noise significantly. Most commonly used tools and techniques are numerical simulation and experimental investigation or combined numerical simulation followed by experimental investigation. The present paper describes the way an existing HVAC noise is reduced by extensive experimental investigations. First the HVAC was dismantled and the flow path inside the HVAC was examined in details along with special features. Areas with chances of flow separations, vortices and high turbulent kinetic energy (TKE) were identified. Smoke tracing was also used in order to actually understand that phenomenon. After having deep investigation into those areas, existing HVAC was modified and series of experiments were carried out on this modified HVAC in a semi-anechoic chamber and noise data was captured at different voltages. In all these changes it is always aimed at keeping the airflow same or better than existing HVAC. It is observed that a significant improvement upto 3-4 dB(A) is achieved in overall noise level both at bench level and vehicle level. So this study provides a deeper insight into how HVAC overall noise level is reduced and hence further it can be very well applied at initial stage of design to make the noise level within desired limit.