Assessment of stress-blended eddy simulation model for accurate prediction of three-straight-bladed vertical axis wind turbine performance

The performance of a three-straight-bladed vertical axis wind turbine at low tip speed ratio has been evaluated by detached eddy simulation (DES) with stress-blended eddy simulation (SBES) turbulence model. Two grid topologies around the blades, i.e. O-type (OG) and C-type (CG), and three sets of grids from coarse, medium to fine meshes are generated for grid sensitivity studies. For the same mesh type (either OG or CG), simulation results have shown better predictions by the DES/SBES turbulence model than that of unsteady Reynolds Averaged Navier-Stokes (URANS) realizable k-e turbulence model with enhanced wall treatment regarding to power coefficient (Cp). Moreover, simulation by the CG mesh predicted Cp distributions in better agreement with the experimental data than that by the OG mesh. It is mainly because that the CG mesh has a higher grid density in region near the blade than OG mesh, despite they have same number of cells around the blade surface. Furthermore, the simulation with the OG mesh predicts earlier flow separation at 130° azimuthal position while with the CG mesh, it occurs at 150° azimuthal position. The predicted flow reattachments are at similar position (around 190° azimuthal position) for both meshes, indicating that simulation with the OG mesh will produce lower Cp than the experimental data.