Computational Aeroacoustic Analysis of noise mitigation potential of complex exhaust systems

The necessity to improve the Noise Vibration Harshness (NVH) performance and, in particular, to reduce the flow noise produced by turbulent exhaust gases is requiring automotive manufacturers to optimize Internal Combustion Engines (ICE) exhaust systems from the early design phases. Computational Aeroacoustics Analyses (CAA) can be seen as a promising tool to support engineering design and optimization, enabling the evaluation of system performance and allowing the selection of effective noise reduction strategies.

This work deals with the application of a CAA methodology for the assessment of noise mitigation potential of two heavy-duty exhaust system designs. Firstly, the mean flow field is obtained with a steady RANS simulation performed with the 3D-CFD code Star-CCM + . Then, the acoustic software ACTRAN SNGR is used to synthetize the noise sources and compute the radiated acoustic field. Flow noise level predicted with the hybrid approach has been compared with the results of a Direct Noise Calculation (DNC) performed in 3D-CFD for the baseline design, to determine absolute levels. It follows a fast optimization loop with the hybrid approach to evaluate the noise attenuation obtained thanks to a design modification in the exhaust diffusor. The proposed methodology significantly reduces the timeframe required to assess exhaust system’s performance, reducing the need of 3D-CFD DNC simulations, and is compatible with the development of new products in a commercial context.