Aeroacoustic Analysis of the Automotive Ventilation Outlets Using Extended Proper Orthogonal Decomposition

Abstract

Extended Proper Orthogonal Decomposition based on snapshot POD is used to investigate the correlation between the aerodynamic quantities of interest in an automotive ventilation outlet and the associated sound pressure field. A 3D simulation of the flow and the associated sound field of a real engineering application is obtained thanks to a Direct Noise Calculation. The flow field on a 2D measurement plane is decomposed on three components using the POD decomposition : The large and small scale coherent structures and the background quasi-Gaussian fluctuations. Based on this POD flow partitioning, the far-field acoustic pressure is used to calculate the extended modes. We exhibit that each part of the far-field acoustic pressure spectrum can be related to each POD aerodynamic flow partitioning. I. Introduction Noise is a major concern in modern automotive industry due to the car manufacturers wish to reduce the noise level for passengers. The purpose of this study concerns the analysis of noise generation mechanisms occuring in automotive ventilation outlets. Historically, fifty years ago, Lighthill 1 reformulated the momentum and the mass conservation equations in the form of a wave equation. While this equation provides an analytical expression for the aerodynamic sound generation, the understanding of the underlying physics and the noise production mechanisms still needs further investigations. Experimental studies have been contributing to a better understanding of the governing mechanisms but they are usually hindered by the complexity of the acoustic sources, requiring the measurement of the fluctuating quantities in a highly resolved space-time extent. The recent progresses in the numerical simulations facilitate the access to the reliable data in those zones where the sound generation is concentrated. The flow simulation and its related acoustic field could be simultaneously performed thanks to the Direct Noise Calculation (DNC). The DNC of compressible flows provides a spatio-temporal database for a particular case. This database can be employed to check the theoretical models and to investigate the phenomena involved in the sound production. The