Effects of sand grain roughness height on the performance of wind turbine blade section under extreme weather conditions

Wind turbine blades are prone to icing and their performance is affected significantly by the roughness caused by icing and erosion. Numerical models are constructed to simulate the effects of sand grain roughness on the mass of accreted ice and aerodynamic performance. The sand grain roughness height is considered by applying the NASA and Shin et al. models, and the cloud characteristics studied are the liquid water content (LWC), median volume diameter (MVD) and air temperature covering freezing drizzle and in-cloud icing conditions resulting in glaze ice and rime ice, respectively. The numerical model applied the multi-shot approach, and the effects of the number of shots on the ice accretion and aerodynamic performance was examined to determine the optimum number of shots which can be used in the simulation in order to minimize the computational time without affecting the accuracy. The relationship between the sand grain roughness height and aerodynamic performance is studied, revealing that the shallowest roughness heights cause less performance degradation_. The mass of ice increases with increasing LWC from 0.05g/m³ to 0.3g/m³ and MVD from 20 µm to 100 µm, which results in a reduction in the lift-to-drag ratio (C_L/C_D).