Multi-scale CFD modeling of intake and exhaust systems for internal combustion engines

The present work focuses on the development of computational tools for the modelling of intake and exhaust systems of internal combustion engines. Different aspects have been investigated: acoustics and fluid-dynamics of ducts and mufflers, fluid-dynamics and heat transfer in after-treatment systems, micro-scale simulations of unstructured substrates. The analysis has been conducted adopting a multi-scale approach, involving different detail levels, ranging from the largest scale represented by the entire engine to the smallest scale constituted by the micro-structure of porous media. Different approaches have been considered, in order to accomplish accuracy and computational runtime requirements for the different applications. In particular quasi-3D tools have been developed for fast simulations of the entire engine configuration, while CFD approaches have been applied for more detailed investigations. The last task included the simulation of phenomena occurring at the macro-scale in the engine components and detailed investigations of fluid-dynamic and heat transfer at micro-scale level inside porous media. The aim of the present work is to develop an integrated approach for the simulation of the internal combustion engines, which involves the modeling of phenomena occurring at different scales. In this framework, simulations are performed at the smallest scales in order to enhance the understanding of the physical phenomena, to give optimization guide-lines and to extract useful information for the macro-scale modelling. When the largest scales are considered, phenomena occurring at the smallest ones are modelled, in order to allow the full scale simulation of the device considered with an acceptable computational effort. Macro-scale models are built on the basis of the information obtained by means of numerical simulations of the micro scales, applying suitable averaging techniques for upscaling the results.

Il presente lavoro riguarda lo sviluppo di strumenti di calcolo per la modellazione dei sistemi di aspirazione e scarico per motori a combustione interna. Sono state studiate varie tematiche: acustica e fluidodinamica nei condotti e nei silenziatori, fluidodinamica e scambio termico nei sistemi di post-trattamento, simulazione CFD della micro-scala di substrati non strutturati. L'analisi è stata condotta con approccio multi-scala, studiando i fenomeni fisici con diversi livelli di approssimazione.