HVAC noise predictions using a Lattice Boltzmann Method

For the automotive industry, the quality and levels of the airborne noise contribution from HVAC systems has a growing importance and has to be addressed as early as possible in the development process. Airborne noise is generated by the turbulent flow circulating in the ducted system and by the vents flow. Flow detachments and separations, strong mixing and duct resonances are typical mechanisms related to the noise production. An automotive HVAC system is usually composed of different parts such as air intake, ducts, mixing unit, face feet, rear and defrost outlets and each of them contributes to the overall noise perceived in the cabin. Previous investigations have shown the possibility to use transient CFD/CAA simulations based on Lattice Boltzmann Method to predict the noise from face ducts, vents, mixing units and blowers as well as complete production configurations. In this paper, our attention is focused on the defrost outlets located below the windshield and on top of the dashboard. Those outlets are usually relatively small in size and potentially represent a significant source of annoyance depending on the HVAC system operating condition. Three configurations are acoustically characterized experimentally and compared to transient and compressible aeroacoustics simulations based on the Lattice Boltzmann Method simulations. The effect of the pseudo-noise contribution at the virtual microphones is investigated using an acoustic analogy based on the resolution of the Ffowcs-Williams and Hawkings equation.