Large-Eddy Simulation in IC Engine Geometries

The computation of flows in IC engines is very challenging due to the variety of phenomena taking place. The well-known RANS methods often fail in both qualitative (dynamic of vortex breakdown...) and quantitative (swirl number, discharge coefficient...) predictions of these unsteady flows. The increasing power of computers now allows to investigate these flows using Large Eddy Simulation, which is a very promising technique. In order to explore the capability of LES in engine configurations, two simple IC engine geometries have been treated with a LES code, called AVBP, developed at CERFACS. This code is massively parallel and uses both unstructured and structured grids. First, the academic configuration of Dellenback was tested. It consists of an axisymmetric sudden expansion, which has been computed both with swirl (S=0.6) and without swirl. The LES results are compared to experimental data in terms of both mean and RMS, axial and tangential velocities. Besides, an unstationnary motion called the precessing vortex core is shown in the LES calculation. The influence of the swirl number on the PVC has been studied and compared to experimental data. Then, a more complex configuration with a valve is investigated. This steady state flow bench shows the capability of the code to handle complex geometries, close to a typical IC engine. Again, LES results are compared to experimental LDA measurements. The discharge coefficient is calculated and compared to experimental data. An analysis of the valve jet has been carried out. Finally, the influence of the scheme order (2 nd versus 3 rd order) and of the mesh type (structured versus unstructured) was investigated on both configurations. The results of this parametric study give more insight into the methodology for the computation of engine configurations with LES.

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