A finite element LES methodology for anisotropic in- homogeneous meshes

Large eddy simulation techniques offer a wealth of valuable information for engineering design purposes, but in many cases the required mesh resolution is prohibitive. Combining the dynamic LES procedure with unstructured mesh adaptivity offers a robust and efficient way of capturing the inhomogeneity and anisotropy of complex turbulent flows. However, this may result in a non-vanishing commutation error due to the filter employed. The inverse Helmholtz filter is used here with a tensor definition of filter width related to the local element size and shape. The formulation, verification and validation of a finite element methodology, designed to yield maximal accuracy from moderate mesh resolution with minimal ad hoc procedures, is described. Results for the 3D backward facing step obtained using the open source CFD code Fluidity are presented. Using adaptive meshing, closer agreement to DNS was obtained compared to fixed meshes while using 60% fewer nodes.