Airfoil-Performance-Degradation Prediction Based on Nondimensional Icing Parameters

Abstract

A physics-based empirical correlation between icing conditions and the corresponding drag coefficient was developed for NACA 0012 airfoils, and compared to other three existing prediction methods. The correlation was developed based on experimental aerodynamic databases of iced airfoils, and derived using statistical methods. The correlation model also provides drag coefficients for varying angles of attack for a given icing condition. The calculated drag coefficients resulted in 33.40% mean absolute deviation with respect to reference data from three different experimental databases. To validate the proposed degradation model and to further extend the database for helicopter-rotor performance degradation, rotating ice-accretion experiments were conducted. Four ice shapes obtained at the NASA Icing Research Tunnel were reproduced on a 53.34-cm-chord, 1.37-m-radius NACA 0012 rotor blade at the Adverse Environment Rotor Test Stand facility. Ice-shape molding and casting techniques were introduced to capture delicate ice features, such as ice feathers. The iced-airfoil castings were tested in a dry-air wind tunnel. The drag-coefficient comparison between the proposed analytical determination method and the experimental results from both rotor ice testing and icing-wind-tunnel testing showed to be satisfactory, ranging from 5 to 25% depending on the icing condition. The effect of ice feathers on drag degradation was investigated. Ice-feather formation can account for up to 25% of the drag introduced by ice accretion before stall.