Symmetry and Time Delayed Boundary Condition for CFD Simulation and its Application in a Two-Cylinder Two-Stroke Engine

Computational Fluid Dynamic (CFD) is the state of the art tool for the development of an internal combustion engine (IC engine), especially for the scavenging process, internal mixture preparation, and combustion. CFD simulation is apt for the detailed simulation of the processes inside the IC engine and consequently it consumes a lot of computer resources. The time for a calculation can be decreased by a reduction of the full three-dimensional (3D) calculated domain. The omitted domain parts can be either replaced by a simplified model or by the smart exploitation of symmetry-conditions. The corresponding boundary conditions for the 3D domain often stem from one dimensional (1D) calculation, measurement data, or corresponding boundary values.

In this paper, a new symmetry and time delayed boundary condition is introduced together with its application in a simulation of an internal combustion engine. The boundary conditions are calculated during the simulation and are set on the corresponding faces in the calculated domain. The data are not constant over the boundary face, which is usually the case in the standard boundary conditions of all CFD applications. The data for the boundary condition do not need to come from a 1D code or measurements, which additionally reduce the pre-processing time of CFD simulation.

The presented method is generally an approach to increase the speed of CFD calculations using a new boundary condition for symmetric and/or time delayed technical problems.