Innate Immune Responses of Pulmonary Epithelial Cells to Burkholderia pseudomallei Infection

10.1371/journal.pone.0007308PLoS ONE410

Assessment of Flow Noise Mitigation Potential of a Complex Aftertreatment System through a Hybrid Computational Aeroacoustics Methodology

Flow noise produced by the turbulent motion of the exhaust gases is one of the main contributions to the noise generation for a heavy-duty vehicle. The exhaust system has therefore to be optimized since the early stages of the design to improve the engine's Noise Vibration Harshness (NVH) performance and to comply with legislation noise limits. In this context, the availability of reliable Computational Aero-Acoustics (CAA) methodologies is crucial to assess the noise mitigation potential of different exhaust system designs. In the present work, a characterization of the sound generation in a heavy-duty exhaust system was carried out evaluating the noise attenuation potential of a design modification, by means of a hybrid CAA methodology. In a first step, a steady state 3D-CFD simulation of the exhaust system in its baseline configuration was carried out with a RANS approach, to gather an analysis of the flow inside the diffusor and to obtain the turbulence intensity distribution necessary to localize and quantify the noise sources. Then, in a second step, the Stochastic Noise Generation and Radiation (SNGR) method was employed to synthetize the noise sources for the subsequent computation of the radiated acoustic field. A sensitivity analysis on the far field noise to the main method parameters was also performed, especially on the noise source region extension. Moreover, the baseline design of the exhaust system was also studied with a Direct Noise Calculation (DNC) approach, providing absolute flow noise levels to be compared with the results obtained by the means of the hybrid CAA approach. Then, a modified version of the exhaust diffusor was analysed with the proposed hybrid CAA methodology, highlighting the impressive potential in terms of noise attenuation of the new design configuration. The adoption of proposed hybrid CAA methodology was therefore demonstrated to allow a dramatic downscaling of the computational cost compared to DNC simulations, being fully compatible with the limited time available for the development of a new product in the automotive industry

Development of a Numerical Methodology for the Assessment of Flow Noise in Complex Engine Exhaust Systems

Worldwide regulations concerning noise emissions of road vehicles are constantly demanding further reductions of acoustic emissions, which are considered a major environmental health concern in several countries. Among the different sources contributing to noise generation in vehicles equipped with internal combustion engines, exhaust flow noise is one of the most significant, being generated by turbulence development in the exhaust gases, and robust and reliable numerical methodologies for its prediction in early design phases are currently still needed. To this extent, Computational Aero-Acoustics (CAA) can be considered a valuable approach to characterize the physical mechanisms leading to flow noise generation and its propagation, and it could therefore be used to support exhaust system development prior to the execution of experimental testing campaigns. This paper describes the development of a CAA methodology suitable for automotive applications that can be used to support the design of new exhaust system components in their early phases. In particular, the work focuses on the flow noise generated in a complex heavy-duty exhaust system, featuring three tailpipes located next to the ground. Firstly, the near-field acoustic field is obtained with a Direct Noise Computation (DNC) approach from an unsteady compressible 3D Computational Fluid Dynamics (3D-CFD) simulation, carried out by means of the commercially available 3D-CFD software STAR-CCM+. A Detached Eddy Simulation (DES) technique is implemented to reduce the high computational cost of the DNC approach and it has been initialized by a steady-state converged solution. The steady-state simulation has been also exploited to extract qualitative predictive indexes, as a preliminary characterization of the system in terms of mean flow and broadband noise generation. Finally, predicted near-field noise levels are evaluated to obtain an assessment of engine exhaust system acoustic performance