Comparison of hexahedral, tetrahedral and polyhedral cells for reproducing the wind field around an isolated building by LES

The wind field around a 1:1:2 isolated building was predicted by large-eddy simulation for evaluating the pedestrian-level wind environment. This study focused on the effects of cell types (hexahedral, tetrahedral and polyhedral cells) and boundary layer mesh on the time-averaged and fluctuating wind characteristics. The minimum cell size and stretching ratio were set to be the same among all cases. The case composed of hexahedral cells was found to have the best agreement with the experiment among the three cell types. The accuracies of the polyhedral cases are close to that of the hexahedral case, and better than those of the tetrahedral cases. However, the polyhedral mesh is most economical for the computational resources since the cell numbers of the polyhedral cases are less than half of that of the hexahedral case and about a quarter of those of the tetrahedral cases. It was also found that the boundary layer mesh does not improve the numerical accuracy under any circumstances. For both tetrahedral and polyhedral meshes, the boundary layer mesh can improve the numerical accuracy in the region above the flat ground by reducing the mesh non-orthogonality and skewness. However, the boundary layer mesh was found to worsen the mesh quality in the local region around the sharp corners of the building for both tetrahedral and polyhedral meshes. As a result, the boundary layer mesh did not lead to the expected improvement of numerical accuracy of wind velocity in the sensitive region of the separated flow from the sharp corners.