The Influence of Unsteady Wind on the Performance and Aerodynamics of Horizontal Axis Wind Turbines

This study elucidates the work which has been undertaken in the field of horizontal axis wind turbine (HAWT) aerodynamics and performance. The main aim of the study is to obtain a better understanding of the characteristics of HAWTs operating with unsteady flow conditions. The literature review found that most research on the HAWT has not taken this unsteadiness into account and that will be the general objective of the current study. The effects of steady and unsteady wind velocity upon the horizontal wind turbine performance have been studied numerically. Using a mesh independent CFD model, the NREL phase VI wind turbine was built utilising Ansys ICEM CFD and then simulated using FLUENT. Firstly, steady wind simulations at 6 m/s were implemented, with a maximum power coefficient Cp of (0.4245) at the tip speed ratio of 6. Then, this process was repeated to test the performance of the scaled–down wind turbine. The effect of the sinusoidal oscillating flow on the wind turbine performance was investigated using a user-defined function, or UDF. Initially a (1Hz) wind frequency was chosen to carry out this study. Then, the performance of the wind turbines was investigated in the flow of upstream mean velocity of Ū=6 m/s and four different oscillating amplitudes (7%, 15%, 25% and 45%) of the mean upstream wind velocity. Moreover, various additional wind speed frequencies (0.5, 2, 5 and 10Hz) and their effects on the wind turbine’s performance and aerodynamics were investigated. Similarly, the small scale wind turbine was also investigated to examine the performance of these sizes of machines. The various wind speed performance trend was well-matched a previous experimental data trend. The constant wind speed performance trend also showed a good agreement with the QBlade data and CFD data of previous researchers. The results generally showed that the unsteady flow caused the performance to a relative drop compared to steady flow. Moreover, the findings revealed that small amplitudes improved the performance marginally. The small-scale rotor also presented high performance at small amplitudes whereas, high amplitudes could cause negative impact to its performance.