Hybrid Technique for Underbody Noise Transmission of Wind Noise

Wind noise has become an important indicator for passenger automobile quality. Several transmission paths can be related to different parts of the vehicle exterior. While the greenhouse (side glasses, windshield, seals & others) often dominates the interior noise level above 500 Hz, the contribution coming from the underbody area usually dominates the interior noise spectrum at lower frequencies. This paper describes a framework of numerical tools which is capable of determining realistic underbody turbulent and acoustic loads being generated for typical driving conditions, as well as performing the noise transmission through underbody panels and the propagation of sound to the drivers ear location. Different numerical tests are performed to demonstrate the ability of a Statistical Energy Analysis model updated with Finite Element Method properties to predict accurately the noise transmission through the underbody of simplified car vehicle in the mid frequency range under aero acoustic excitation. Parameters of the hybrid technique and the use of finite element modeling to estimate them are discussed. Transfer function comparisons between pure FEM and the hybrid technique are performed involving various load types to demonstrate the consistency of these methods. Cabin sound pressure level comparison for a simplified vehicle with wind noise excitation shows good correlation to FEM calculations performed with adequate statistical treatment. In addition, sensitivity analysis for several underbody parameters involving stiffness, mass, damping and geometry design change is applied to show further the utility of the technique for wind noise design.