Effect of atmospheric turbulence on the aerodynamics of wind turbine blades: a review

As Wind Turbines (WTs) operate in the atmospheric boundary layer, the atmospheric turbulence may have a significant effect on their overall aerodynamic forces distribution. Therefore, the resulting flow pattern varies, and it becomes complex to weight up simultaneous presence of inflow turbulence and other issues, such as unsteadiness, three dimensionality or rotation. Steady wind condition is an off-design condition, but it is habitually used in both design and research. This paper aims to give a review of the research about the effects of turbulent inflow experienced by WT blades. A first introduction to the broad subject of WT aerodynamics is proposed, with particular reference to the stall mechanism that is recognized as the leading phenomenon for the comprehension of turbulent effects on the flow pattern, as separation point position, critical angle of attack and the onset itself vary strongly with level of atmospheric turbulence. A brief introduction to the nature of turbulence found within the urban environment further clarifies the major role of inflow unsteadiness, as many attempts are currently made to enhance Urban Wind Energy. A review of state-of-the-art research is then given, in order to underline current limits of research, highlighting eventual role of possible concomitant issues, such as rotation or rotor yaw angle. In particular a critical review of the used turbulence intensities and length scales is given, for their variation strongly affects significance of experiments and simulation. To fulfil this purpose a quick summary to the methodology, especially to Computational Fluid Dynamics analysis, is convenient, with special reference to possible ways of generating artificial inlet turbulent flow field. It has turned out that a “back to basics” approach is needed in order to provide thorough understanding of the effect of turbulence on the stall mechanism and the aerodynamics of the wind turbine, to overcome actual gaps in research.