Numerical Analysis of Nonuniform Flow Around a Large Wind Turbine Operating at Variable Speeds

Abstract

The increasing reliance on wind energy necessitates a deeper understanding of the unsteady aerodynamic behavior of wind turbines operating under variable speed conditions. This study employs computational fluid dynamics (CFD) simulations to investigate the flow dynamics around a large wind turbine subjected to height-dependent wind speed variations common within the atmospheric boundary layer (ABL). Utilizing a fine computational mesh and the k-ω shear stress transport (SST) turbulence model, we explored the interaction between wind turbine rotor aerodynamics, wake structures formation and evolution, and power performance under nonuniform operational conditions. The obtained numerical results highlight the nonlinear relationship between power output and angular velocity, demonstrating peak power generation at an optimal rotational speed (1.25 rad/s) before aerodynamic losses reduce performance. Additionally, the study examines variations in power and thrust coefficients, emphasizing their dependence on tip speed ratio and wind inflow characteristics. The computed power coefficient curve matches closely the corresponding experimental one, thus validating the adopted numerical setup as well as the assigned boundary conditions. Velocity contour analyses reveal critical regions of flow deceleration and separation, intensive turbulence, and wake interactions, providing insights for optimizing turbine design and control strategies. The findings underscore the importance of accurate inflow conditions and turbulence modeling in improving the reliability of estimated wind turbine.