Aerodynamic research progress in wind energy Ⅰ: Wind turbine aerodynamic characteristics

With the establishment of national policies around the world, the development of wind industry has been entering its heyday. Wind turbine systems are continuously upsized from megawatt level to multi-megawatt class, deployed for both onshore wind power and offshore wind power in diverse sea conditions, intelligentized with smart materials, structures and control strategies, and digitized with precise prediction and state-aware control system. These mainstream trends for wind energy development, in the meanwhile, raise tremendous challenging issues for wind energy research and development. Among them, wind turbine aerodynamics will face new problems and great challenges. As the first review of a sucessive work, this study is mainly focused on the aerodynamics of horizontal-axis wind turbines. An explanation for the aerodynamic complexity is addressed at first. Then, research progress on key aerodynamics issues, such as the aerodynamic characteristics of wind turbine airfoils and blades, as well as modern wind turbine design (special focus is put on the offshore wind power technology and the inevitable typhoon phenomenon, together with the experienced aeroelastic problem caused by the increasement in wind turbine size) and new flow control strategies are discussed. In this process, recent theoretical, experimental, and numerical studies that have contributed to improve our understanding of wind turbine aerodynamic performance, such as aerodynamic forces, flow fields and flow mechanism, are summarized. Additionally, the strength and limitation of these research approaches are discussed. Possible future research trend is analyzed and prospected, providing some references for large-scale wind turbine blade design.