Analytical and experimental determination of airfoil performance degradation due to ice accretion

A physics-based, empirical correlation between icing conditions and corresponding drag coefficient was developed for NACA 0012 airfoil and compared to other three existing prediction methods. The correlation was developed based on experimental aerodynamics database of iced airfoils and derived using statistical methods. The correlation model also provides drag coefficients for varying angles of attack under a given icing condition. The calculated drag coefficients matched (33.40% mean absolute deviation) with 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 Center were reproduced on a 21-inch chord, 4.5-feet 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. Performance degradation was compared between the four iced models and the clean airfoil. 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 prior to stall. Comparison between the proposed analytical determination method and experimental results from both rotor ice testing and icing wind tunnel testing showed to be satisfactory, ranging from 25% to 6% depending on the icing condition.