Applicability of Large Eddy Simulation to the Fluid Mechanics in a Real Engine Configuration by Means of an Industrial Code

3D simulations of internal combustion engines are usually based on statistical approaches (RANS) that may not allow predicting cycle-to-cycle variations (CCV) or transient speeds because part of this information is lost by the averaging procedure. To simulate such phenomena, it requires time resolved approaches. Therefore, large eddy simulation (LES), which only involves a spatial averaging, appears to be a very promising tool.

An LES approach is applied to simulate the flow field inside one cylinder taken from a real four-valve diesel engine mounted on an experimental particle image velocimetry (PIV) bench. Preliminary tests are carried out to evaluate the industrial code capabilities. A multi-cycle calculation is computed in cold flow, in order to evaluate its ability to simulate cycle-to-cycle variations (CCV). A compromise is looked for between robustness of the simulation, industrially conceivable time computation of the calculation and precision requirement of such modeling methods. Some keys are given to validate the results obtained, with the use of characteristic quantities and statistic tools.

The code used is Star-CD. Simulations are achieved with a standard Smagorinsky model. The mesh at the bottom dead center contains 1 million cells. Ten consecutive cycles are studied. Comparisons between LES simulations, RANS simulations and experimental results (PIV) are presented. The bench and the PIV results originate from a study by Deslandes [1].