Multi-Physics Simulations of a Wind Turbine in Icing Conditions

Wind turbines in cold climates are likely to suffer from icing events, deteriorating the aerodynamic performances of the blades and decreasing their power output. In this work, a 3-hour rime ice accretion event is numerically simulated on five significant sections of a wind turbine blade operating in steady wind using a high-fidelity procedure based on the Blade Element Momentum Theory. The onshore NREL 5MW reference wind turbine is studied. Ice accretion is simulated through a fine multi-step process, adding ice layers approximately 0.5 mm thick; each step consists of the successive coupling of a CFD simulation, a Lagrangian particle-tracking of the cloud droplets, an ice accretion step, and re-meshing of the new geometry. Ice roughness is modelled with an equivalent sand-grain approach. After computing the aerodynamic coefficients of ice-contaminated airfoils, power losses are obtained considering the aeroelastic response of the wind turbine in turbulent winds as defined by the Design Load Case 1.1. The effect of the extension of roughness on the surface of the blade is also assessed. In the considered operating conditions and accretion times, a strong dependence between the decrease in power output and the tip-speed ratio and a small dependence on surface roughness are found.