Simulation of Exterior Powertrain Acoustic Transfer Functions using IFEM and other Deterministic Simulation Methods

This article is a follow-up of a companion article published at the Automotive Acoustics Conference in 2011. It documents the last part of a numerical/experimental activity aimed at assessing the capabilities of deterministic numerical methods in relation to the simulation of exterior powertrain Acoustic Transfer Functions (ATFs). The motivations at the basis of such activity are linked to the foreseen update of the ISO 362 standard in a more restrictive sense that is likely to make powertrain exterior noise become again a relevant issue in the automotive industry, after many years during which OEMs have been able to achieve pass-by targets and solve issues related to the acoustic radiation from the engine bay simply on the basis of experience and good practices. The more restrictive limits foreseen by the exterior noise regulation will be again a real challenge for OEMs and this will lead to a strong focus on the design of the acoustic trim parts positioned inside the engine bay. In turn, the possibility of designing in an efficient and cost-effective way such parts will call for reliable simulation methods. In this article, in particular, the focus is on the use of the Infinite Finite Elements Method (IFEM), that has been used to simulate the exterior ATFs of a simplified (while not trivial) test case consisting of an engine bay mock-up that includes all the topological difficulties typical of the problem, i.e. the coupling between an almost-closed cavity characterized by small gaps between its walls with the exterior, through relatively small apertures. On top of this, the capability of the method to assess the effect of simple absorbers was tested. Last but not least, the simulation frequency range considered was quite wide, up to 3.5 kHz. The article, after documenting in detail all the results obtained with the IFEM, compares them with the ones (already shown in the 2011 paper) previously obtained with other deterministic methods (Boundary Elements and Automatically Matched Layer), both in terms of quality of the results and in terms of computational efficiency.