Quantitative Investigation into the Relationship between Ice Accretion Shape and Ambient Conditions

Abstract

The relationship between the ice accretion shape and ambient conditions is quantitatively investigated via analysis of variance (ANOVA) and is qualitatively studied using self-organization maps (SOMs). The independent variables of this study are liquid water contents (LWC), mean volumetric droplet diameter (MVD), flight speed (free stream velocity) and ambient temperature. The ranges of these variables follow appendix C of FAR part 25. The ice accretion shape is quantified through parameterization of ice accretion area, maximum thickness, ice heading and icing limits. SOMs and ANOVA can be used for parameter analysis. We determine the associated parameters, although the parameters are examined under non-linear conditions. The range of temperature, -40–0°C, is divided into 10°C intervals. Three distinctive temperature groups are found, depending on the response of the ice shape to the ambient conditions. They are rime (-40–-20°C), mixture (-20–-10°C) and glaze (-10–0°C). The ice accretion area and maximum thickness are determined by free stream velocity and LWC over the entire temperature range, while ice heading is affected by the temperature, free stream velocity and LWC. Different variables affect the icing limits on the upper and lower surfaces. On the upper surface, runback dominates the formation of icing, while on the lower surface the dominant factor is where limits are impinged.