3D CFD simulation of the flow field generated by a rotating blade of an H-Darrieus VAWT

In this work, the results of a first 3D analysis of an H-Darrieus rotor performed with the structured multi-block finite volume COSA research code of the Lancaster University are presented and discussed. Based on the above consideration, the key features were the reduction of the computational cost while maintaining the same accuracy of the 2D calculations. A single blade configuration having an aspect-ratio of 8.7 was chosen in order to minimize the grid size, since a three-bladed rotor would have required an excessively large number of elements. The 3D grid was generated starting from an existing 2D structured mesh with a fine discretization level, which was able to provide mesh independent results. The airfoil profile was discretized with 580 nodes with a first element height chosen to guarantee y+ ~ 1, resulting in a global size of 4.3×105 quadrilateral cells. To achieve a good spanwise resolution, the blade is discretized with 80 layers along its height. The final mesh size is 63.9×106 hexahedral cells (Figure 1). The calculations were performed on a large cluster able to handle very large MPI jobs. The available resources were 1024 nodes with 16 cores each, thus the grid was split into 16384 blocks. In the authors’ intents, the primary motivation was a more in depth investigation of the real functioning of the turbines by the analysis of the unsteady loads and 3D patterns of the flow, which can not be detected through a 2D model. The attention will be focused on three-dimensional phenomena as the tip vortex structures and efficiency losses along the blade span. In particular, 2D slices of the vorticity contours (Figure 2) and other flow quantities will be shown at different span locations and will be compared to the results of the 2D computations, to assess the applicability of such approach. At the same time, the present results represent the basis for a future extension of the analysis to full-rotor 3D models.