Aeroacoustics prediction of simplified and production automotive HVAC ducts and registers

For the automotive industry, acoustic comfort is of increasing importance and changes in the market make the HVAC system noise quality a question to be addressed as early as possible during the vehicle development process. On one hand, the so-called traditional sources of annoyance such as engine, road-tires contact, exhaust systems and wind-noise have been significantly reduced for most traditional combustion engine vehicles. On the other hand, the rapid expansion of both hybrid and electric vehicles and idling stop systems increases the importance of sources such as HVAC systems considered in the past as secondary. At high mass flow rate, the flow-induced contribution from ducts and registers is the main source of noise in the mid to high frequency ranges and is more important than the HVAC structure borne and blower contributions. In this paper, our attention is focused on flow-induced noise contribution related to the turbulent flow generated by elbowed ducts and outlets vents of HVAC systems. Some flow and noise measurements are performed in a reverberant room for five configurations including simplified and production geometries and are compared to transient and compressible CFD/CAA simulation results based on the Lattice Boltzmann Method.