Numerical investigation into the blade and wake aerodynamics of an H-rotor vertical axis wind turbine

Abstract

Blade aerodynamics is of critical importance in the design of an isolated vertical axis wind turbine (VAWT). In contrast, wake aerodynamics plays a crucial role in the optimum placement of multiple VAWTs. In this study, both the blade and the wake aerodynamics of a straight-bladed VAWT are investigated using a three-dimensional computational fluid dynamics (CFD) model. The algebraic wall-modeled large eddy simulation (LES) was used for turbulence modeling. The LES predictions were compared with and had good agreement with the published experimental data. A semi-empirical method was proposed to estimate the convergence time of CFD calculations. Further, guidelines for the LES modeling of VAWTs were provided. Relatively thick airfoils are recommended for VAWTs to reduce fatigue loading on blades. Torque analysis suggested that winds in built environments would benefit the self-starting performance. Comparisons between transient and time-averaged velocity fields indicated a statistically stable wake. Moreover, the blade speed ratio effect on the development of wake velocities was assessed. The underlying causes of the significant wake asymmetry were addressed. The periodical vortex-ring structures, counter-rotating vortical motions, and wake asymmetry were analyzed and concluded as the signature features of H-rotor VAWTs' wake.