Implementation of a Finite-Element Based Mesh Motion Technique in an Open Source CFD Code

Abstract

Nowadays, Computational Fluid Dynamic (CFD) codes are widely used in different industrial fields. Although hardware and numerical model improvements, the mesh generation remains one of the key points for a successful CFD simulation. Mesh quality is influenced by the adopted mesh generator tool and, after all, by the designer’s experience and it becomes very important when moving meshes are required. In fact, mesh skewness, aspect ratio, and non-orthogonality have to be controlled during the deforming process since their wrong evolution could produce an unphysical behavior of the computed flow field. Mesh motion could be performed by different strategies: dynamic smoothing operation and dynamic re-meshing operation, are, today, two of the mainly used approaches. All of them can be combined to guarantee the correct reproduction of motion profile and a good mesh quality level. In this context, the authors have implemented a moving mesh methodology in the Open Source CFD code OpenFOAM®. A multiple number of meshes is used to cover the whole simulation period, and the grid point motion is accommodated by an automatic mesh motion techinque with polyhedral cell support. The Laplace equation is chosen to govern mesh motion. This guarantees that an initial valid mesh remains valid for arbitrary boundary motion. Mesh to mesh interpolation is performed by using a cell based, distance weighted interpolation technique. The proposed approach was tested on a real IC-engine geometry. In particular, the mesh quality evolution during motion, the numerical results and the computational costs were evaluated.