A Simulation and Diagnosis of Flow Induced Duct Noise

For the comport quality of vehicle, reduction of noise radiated from HVAC system has been requested for years and the demands are increasing due to recent trend of electrification of vehicle which is typically quieter than that of ICE. Large contribution to the HVAC noise is typically coming from flow induced noise of which source is generated at fan(s) and/or wall(s) of the HVAC. One of the ways to predict the HVAC noise is to solve it by compressible CFD directly. However, in such case, it is difficult to diagnose the acoustic characteristics how the acoustic wave propagates through the HVAC casing and is amplified by the acoustic modes since the acoustic response is likely masked by the hydrodynamic response. Knowledge of acoustic characteristics are sometimes helpful to find countermeasure to reduce those noise. This paper therefore solves the flow induced noise of a simple duct by the acoustic BEM based simulation utilizing the fluctuating surface pressure obtained by the incompressible CFD to be able to diagnose the acoustic characteristics. Some diagnoses are then performed such as the source area contribution to SPL at a microphone to investigate relationship of source and acoustic characteristics at the frequency of interest.