High-fidelity computational assessment of the performance of a vertical axis wind turbine

Even though the Vertical Axis Wind Turbines (VAWT) are known to have lower efficiencies than the Horizontal Axis Wind Turbines (HAWT), their simple construction and the inherent design features qualify them as a viable and cheap options for low cost wind energy systems. Hence the VAWT proves extremely useful in rural sectors where it can be used extensively for electricity generation, pumping water and so on. Computational modeling of the flow fields in the vicinity of a VAWT for four different tip speed ratios of the turbine blade is the focus of this work. Here the flow is numerically computed using two different turbulence modeling approaches namely the Reynolds Averaged Navier-Stokes (RANS) with the Spalart-Allmaras turbulence model, which is popularly used for external aerodynamic analysis and the Large Eddy Simulation (LES) with the Wall-Adapting Local-Eddy Viscosity (WALE) model. The primary focus of this study is on the LES approach for turbulence modeling, where large scale motions are computed explicitly and the small scales of motion are modeled. This approach can accurately capture turbulent flow structures and effects of the large scale motions. Examination of the computed flow shows that the aerodynamic force coefficients are more accurately predicted by the LES flow models compared to those predicted by the RANS flow models. Although the computed variation of the aerodynamic force coefficients at different angular positions of the VAWT during a single revolution appears to be similar for both the flow models, noticeable differences in their magnitude are clearly observed. This work aims to support future studies such as the design optimization of a VAWT, layout of VAWT in a wind farm and extensive study of the effect of the turbine-wake interactions on the efficiency of the wind farm systems.