Abstract

Ice accretion on aerofoils has been researched for many years for aircraft, rotorcraft and wind turbine blades using experimental and numerical techniques. While each method has some distinct advantages, it is the combination of the two strategies that is suggested to be the best way to understand and combat the icing challenge. However, both experimental and numerical techniques have certain limitations which can affect the droplet behavior and the resulting ice profiles. Therefore, when comparing numerically predicted ice shape with experimental data for validation purposes, it is important to account for the limitations of both techniques and identify how the two profiles were compared and deemed acceptable even when the two ice shapes appear to have geometrical discrepancies. Although most of the studies highlight the sources of error in their data, almost none of them explain the strategy employed to validate and verify their results. Furthermore, while the anti/de-icing is involved, energy consumption will be one key factor to consider. There should be a criteria to compare ice shapes from the same icing wind tunnel or results from different test facilities which can further help with comparison of numerical and experimental ice shapes. It would aid to set a standard to improve the quality of our research and make progress in the industry. The aim of the present study is to propose criteria that could be used to compare experimental and numerical ice profiles on an aerofoil surface. Therefore, thorough, and meaningful discussion will be conducted in academic world and relevant industries. The main features of the article are outlined as follows. A brief review on some of the experimental and numerical studies on ice accretion have been presented to discuss the methods used, highlight the technological advancements, and discuss key results and sources of error. Research shows that, in addition to the geometrical comparison, the performance of iced aerofoil must also be considered as a comparison strategy. Based on this analysis, the aim of comparing the ice shapes will be discussed. Following this, numerical results from current study are compared with experimental results to illustrate the necessity and importance of having the criteria. Next section will be devoted to proposing the preliminary criteria. Finally, the conclusion will be provided.

Abstract

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.