Initial conditions for Large Eddy Simulations of piston engine flows

The exact knowledge of the flow in a piston engine chamber is of vital interest in engine design. These flows feature 3D highly unsteady turbulent phenomena combined with combustion processes. Large Eddy Simulations (LES) appear to be a promising way to simulate them. However, computing several engine cycles results in excessive computational costs. Therefore, a different approach, namely the single-cycle strategy (SC), is to perform several simulations just of those parts of one engine cycle that are of interest. In this study, non-reacting LES is undertaken with a SC strategy for the injection of gas into a tumbling motion. Measured data are used for both the initialization and the validation of the computations. In addition, the initial field is varied using a proper orthogonal decomposition analysis on the experimental data to mimic realistic cycle-to-cycle variations of the tumble before the injection. Satisfactory results are obtained by using a simple procedure for creating initial conditions based on experimental data. By changing the initial field, it is demonstrated that initial conditions have a very significant influence on the LES results. This influence may restrict the use of SC strategies in favour of mutiple-cycle computations.