An Extension of the Dynamic Mesh Handling with Topological Changes for LES of ICE in OpenFOAM
The paper focuses on the development of a mesh moving method based on non-conformal topologically changing grids applied to the simulation of IC engines, where the prescribed motion of piston and valves is accomplished by rigidly translating the sub-domain representing the moving component. With respect to authors previous work, a more robust and efficient algorithm to handle the connectivity of non-conformal interfaces and a mesh-motion solver supporting multiple layer addition/removal of cells, to decouple the time-step constraints of the mesh motion and of the fluid dynamics, has been implemented as a C++ library to extend the already existing classes for dynamic mesh handling of the finite-volume, open-source CFD code OpenFOAM®. Other new features include automatic decomposition of large multiple region domains to preserve processors load balance with topological changes for parallel computations and additional tools for automatic preprocessing and case setup. Finally, a transient solver for compressible viscous flows based on the transient SIMPLE algorithm has been implemented in order to enhance conservation of mass and energy for domains sliding over dynamically attached/detached boundaries. The advantages are significant: mesh changes in terms of topology and deformation are fully managed by the mesh motion solver without remeshing, with a consequent reduction of the overall simulation time. Most important, the method allows to preserve the quality of the mesh initially defined by the user (skewness, non-orthogonality and aspect ratio) during the whole engine cycle, favoring a faster convergence of the solver and a very accurate fluid-dynamic solution. Used in conjunction with LES turbulence modeling, the method allows to decouple mesh motion by LES filter operation, since the filter width is kept constant during the entire cycle. Validation tests have been performed on the full-cycle simulation of a Transparent Combustion Chamber (TCC) engine, whose experimental data are available through the Engine Combustion Network database (ECN). The implementation of the described methodology is absolutely general, it works on any number of processors and it can be applied to any application where moving parts and non-conformal interfaces are involved.