Three-Dimensional Simulation of a Complete Vertical Axis Wind Turbine Using Overlapping Grids

Three-dimensional simulations of the aerodynamic field around a three-blade straight-axis Vertical Axis Wind Turbine (VAWT) are presented for two values of the Tip Speed Ratio λ (TSR), namely λ=1.52 and λ=2.5. Numerical simulations were carried out using the over-set grid solver ROSITA (ROtorcraft Software ITAly). The Reynolds-Averaged Navier-Stokes equations are completed by the Spalart-Allmaras turbulence model. A strong interaction between the blade and the blade wakes is evidenced. Dynamic stall is observed in the case λ=2.5. The computed flow-field presents diverse three-dimensional effects, including the interaction between the blades and the tip vortices and the aerodynamic disturbances from the turbine shaft and the support arms. Three-dimensional effects are more relevant for λ=2.5. The comparison to experimental data confirms the general features of the flow.