HVAC noise predictions using a Lattice Boltzmann Method

Abstract

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.

Direct flow-induced noise prediction of a simplified HVAC duct using a Lattice Boltzmann Method

“…This contribution affects the low and high frequencies and comparisons to experiments have to be carefully analyzed particularly when low levels are involved For production cases, this importance is less significant. The same type of method has been applied on production defrost systems from automotive HVAC systems to suppress the pseudo-noise contribution from near-field microphones 33 . …”

“…In addition, such an approach represents an efficient way to reduce, and eventually optimize, the noise produced by HVAC systems 2 . Previous published studies on simplified ducts 4 , production face ducts and vents 1,4-6 , mixing units 7 , blowers 8,9 and complete HVAC systems 3,10 have shown the possibility to use LBM simulations as an engineering design solution. This type of simulation also represents an interesting diagnostic tool helping at identifying the location of flow-induced noise sources 3 .…”

“…Unlike two-steps procedure based on acoustics analogies and requiring the coupling between aerodynamics information to an acoustic propagation solver [14][15] , in this study the noise is predicted in one-step during the CFD/CAA simulations. Previous studies have shown the potential of this method at propagating acoustics waves 12,13 and accurately predict the flow-induced noise contribution from HVAC systems [1][2][3][4][5][6][7][8][9][10] . This method presents a net interest in terms of accuracy, process simplicity and turnaround times.…”

Aerodynamic noise from cooling and HVAC systems features important to land vehicles in urban traffic conditions

“…In fact, from the physical point of view, Aerodynamics and Acoustics may be considered simplifications of a unique problem of Fluid Mechanics and methods aimed at a full solution are currently under study [3]. The drawback of such methods are the large CPU requirements and computing time, which presently make such an approach unpractical for many technical applications.…”