Quantitative comparison of ice accretion shapes on airfoils

Abstract

The need to compare quantitatively ice accretions that form on aircraft during flight in icing conditions has recently expanded from a research-oriented activity to more general applications. For example, verification of the calibration of ground-test facilities is often performed by comparing ice shapes produced at a specific icing condition. Because icing tests in ground facilities are important in the aircraft certification process, concerns about the subjectivity and consistency of these ice shape comparisons have increased. The ice accretion comparison method presented uses geometric features as well as several parameters extracted from a P-Fourier descriptor of the ice accretion profile to develop a single parameter that can be used to rank how well two ice shapes compare. The results of this automated method were found to be consistent with comparisons of ice accretions made visually and based on percent differences of geometric characteristics. Also, for comparisons of ice shapes having a calculated comparison parameter less than 0.075 (7.5%), the drag coefficient of the iced airfoils differs by less than 10%. Higher values of the comparison parameter produce greater visual differences in the ice accretions and larger variations in the drag coefficient.