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Licentiate seminar

Unsteady simulations of the turbulent flow in the exhaust system of an IC-engine for optimal energy utilization


Defendant Main Advisor Extra Advisor Date
Johan Fjällman Laszlo Fuchs Mihai Mihaescu 2013-06-14

Opponent
Dragos Moroianu, Lund University

Evaluation committee

Abstract

This licentiate thesis deals with the flow in pipe bends and radial turbines in an internal combustion engine environment. Looking into the engine bay of a passenger car one cannot avoid noticing all the pipe bends and splits. During the development of internal combustion engines the engine manufacturers are starting to focus more on simulations than on experiments. This is partly because of the reduction in cost but also the reduction in turn around time. This is one of the reasons for the need of more accurate and predictive simulations. By using more complex computational methods the accuracy and predictive capabilities are increased. The downside is that the computational time is increasing so the long term goal of the project is to use the results to improve the predictive capability of the lower order methods used by the industry. By comparing experiments, Reynolds Averaged Navier-Stokes (RANS)simulations, and Large Eddy Simulations (LES), the accuracy of the simulation methods can be established. The advantages of using LES over RANS for the flows under consideration stems from the unsteadiness of the flow in the engine manifolds. When such unsteadiness overlaps the natural turbulent spectrum, general RANS models cannot handle the problem specic flow. The thesis considers this effect on the chosen numerical model. The LES results have been shown to be more accurate than the RANS simulations both for global mean values and for the fluctuating components. The LES calculations have proven to predict the mean field and the fluctuations very well as compared to the experimental data.