Quantification of air compressibility on large wind turbine blades using Computational Fluid Dynamics

Current simulations of wind turbines routinely use an incompressible flow solver which assume a constant air density, while the development of large wind turbines increases the blade tip speed, which breaks the incompressible flow assumption. The present paper aims to investigate the effect of air compressibility on large wind turbine blades and examine the Prandtl-Glauert correction on air compressibility. Based on the IEA 15 MW wind turbine, Computational Fluid Dynamics is used to study the effect of air compressibility on the aerodynamic performance under various operating conditions, including different pitch angles and rotor speeds. Results show that the air compressibility can increase both normal and tangential forces at 70%-95 % radii with 2.3 % and 1 % at the rated wind speed, respectively. In addition, the effect of compressibility on tangential force and power becomes significant at high wind speeds when the blades are pitched. The Prandtl-Glauert correction can predict the blade normal force with a good accuracy but can't accurately predict the blade tangential force, which indicates the necessity of a better correction for wind turbine blade forces in designing and controlling large wind turbines.