Linking Acoustic Simulation Tools for Efficient Computation of Exterior Noise in Vehicles
Résumé
Due to legislation, exterior noise targets have been continuously reduced in the last decades and a new normalsation for pass-by noise is expected. Thus, a numerical tool to predict the noise radiated from a vehicle in an early design stage is needed. Due to the large frequency range to be taken into account [100Hz-2.5kHz], the complexity of the domain to be simulated (partial enclosures, exterior field) and the number of DOFs to be considered, exterior noise simulation reaches the limits of standard deterministic method like FEM or BEM. In the frame of the European project VISPeR, a benchmark of several numerical methodologies aiming at exterior noise simulation has been conducted by the partners Centro Ricerche Fiat (CRF), INSA Lyon, Ecole Centrale de Lyon (ECL) and Rieter. Simple test cases with different treatment configurations, the mock-up of an engine comprtment as well as a real engine compartment have been considered. Deterministic LF methods like indirect BEM and FEM/FEM were tested for their potential to be extended to higher frequencies with a descretisation criterion of lambda/6 and a realistic number of DOFs. The Patch Acoustic Impedance PAI method, developed at INSA Lyon and applied together with CRF, is aiming at coupling two uncoupled calculations (one interior, one exterior), thus offering a potential for optimisation. Energetic methods adapted rather for the HF range, like incoherent ray-tracing, applied by Rieter, and the "simplified energy method" SEM method, developed and applied at ACL-LTDS, have been tested. In the case of ray-tracing, the influence of various parameters (e.g. phase and diffraction) has been checked. The sensitivity to acoustic treatment configurations has also been evaluated.