Research on aerodynamic performances of the vertical-axis wind turbines under different wind gust configurations: comparative numerical modeling

Vertical Axis Wind Turbines (VAWT) offer a viable sustainable alternative, with improved efficiency at moderate to low wind speeds. However, the lower starting of VAWTS, with vibration and stability issues is still significant challenging for large-scale utilization development. The present work investigates the performance of a VAWT under different gust shapes (step and sine-wave) at steady and unsteady wind conditions. Computational Fluid Dynamics (CFD) simulations are performed to analyze the aerodynamic performance of the distinct VAWT prototype under varying wind gusts. The local wind data for Dhahran, Saudi Arabia, is used to identify the representative gust profiles and evaluate the wind turbine performance. Moreover, the effects of time period variation of the gust, gust frequency, and azimuthal angle on the wind turbine performance are also investigated. The study is also extended to compare the performance of the proposed wind gusts against a standard gust model defined by the International Electrotechnical Commission (IEC) to provide a better understanding of its dynamic response in actual wind gust conditions. The results demonstrated that as wind velocity during the gust increases, the effective tip speed ratio reduces, whereas the aerodynamic moment of the turbine increases. This increase is directly proportional to the amplitude of the gust. Unsteady simulations also revealed a coupled behavior between the wind velocity and wind turbine power coefficient. It is found that when the wind velocity during the gust increased by 12%, the turbine power coefficient increased by 12%, and the energy coefficient of the turbine reduced by 22%. A further analysis of three frequencies (0.36, 0.46, and 0.56 Hz) at constant amplitude showed that higher-frequency gusts cause faster wind changes, affecting dynamic stall and reducing power output. The peak power from the 0.36 Hz sine-wave gust was 1.36% lower than that from the 0.56 Hz step gust. Ultimately, the study yielded new insights into VAWT aerodynamics, contributing to the advancement of turbine design and optimization of wind farm performance.