Towards the LES Simulation of IC Engines with Parallel Topologically Changing Meshes

The implementation and the combination of advanced boundary conditions and subgrid scale models for Large Eddy Simulation (LES) in the multi-dimensional open-source CFD code OpenFOAM® are presented. The goal is to perform reliable cold flow LES simulations in complex geometries, such as in the cylinders of internal combustion engines. The implementation of a boundary condition for synthetic turbulence generation upstream of the valve port and of the compressible formulation of the Wall-Adapting Local Eddy-viscosity sgs model (WALE) is described. The WALE model is based on the square of the velocity gradient tensor and it accounts for the effects of both the strain and the rotation rate of the smallest resolved turbulent fluctuations and it recovers the proper y₃ near-wall scaling for the eddy viscosity without requiring dynamic procedure; hence, it is supposed to be a very reliable model for ICE simulation. Validation of the implemented models has been performed separately on two steady state flow benches, where experimental data were available: a backward facing step geometry and a simple IC engine geometry with one axed central valve. A method to evaluate the turbulence resolution of LES simulation based on a Length Scale Resolution (LSR) parameter has been proposed and a discussion about the completeness of the LES simulation (i.e., LES simulation quality) is presented. Finally, the implementation of a fully parallel algorithm for the management of topologically changing meshes in the OpenFOAM®-2.1.x technology is described. The aim is to implement a reliable framework to perform LES simulation of internal combustion engines by the OpenFOAM® technology.