Abstract

A computational study of the aerodynamics of the straight-bladed VAWTs was performed by RNG k − ε and S-A turbulence models. Three different rotor types with NACA0022, NACA0018, and S1223 blade profiles were studied. The main objective was to numerically analyze the torque and the highly unsteady wake dynamics of the VAWTs by RANS turbulence models. The effect of increasing the blockage of the free-stream wind by the rotor on the generated torque, the influence of different turbulence models on the results, and the performance of the downwind rotor in a row of two VAWTs were analyzed as well. The results indicate that the ducted VAWTs are more efficient than the regular VAWTs. The efficiency of the rotor is overestimated by the 2-D geometry. This is mainly related to the negative influence of the tip vortices on the torque. The velocity magnitude in the wake recovers 50 % of its inlet value within 2D downstream distance. In a row of 2 VAWTs, due to the disturbances in the flow generated by a turbine placed 15D upwind, the efficiency of the downstream VAWT varies in each revolution of the rotor. Comparison between the values of torque obtained by the RNG k − ε and S-A turbulence models reveals that the RNG k − ε model reports higher values of torque. In a direct relation, the values of torque obtained by the second-order-accurate solver are generally higher than those given by the first-order solvers. It can be argued that although the RANS turbulence models overestimate the efficiency, they can be appropriately used as CFD design tools.