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

Abstract: This licentiate thesis deals with the ow in pipe bends and radial turbines inan internal combustion engine environment. Looking into the engine bay of apassenger car one cannot avoid noticing all the pipe bends and splits. Duringthe development of internal combustion engines the engine manufacturers arestarting to focus more on simulations than on experiments. This is partly becauseof the reduction in cost but also the reduction in turn around time. This isone of the reasons for the need of more accurate and predictive simulations.By using more complex computational methods the accuracy and predictivecapabilities are increased. The downside is that the computational time isincreasing so the long term goal of the project is to use the results to improvethe 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 simulationmethods can be established. The advantages of using LES over RANS for the ows under consideration stems from the unsteadiness of the ow in the enginemanifolds. When such unsteadiness overlaps the natural turbulent spectrum,general RANS models cannot handle the problem specic ow. The thesisconsiders this eect on the chosen numerical model. The LES results have beenshown to be more accurate than the RANS simulations both for global meanvalues and for the uctuating components. The LES calculations have provento predict the mean