Ice accretion compositions in ice crystal icing

Ice crystal icing is a major hazard in aviation from the perspectives of aerodynamic deterioration, flight safety and operability. To counter this challenge, existing ice prediction tools require more accurate modeling of sticking efficiency of glaciated ice crystals on heated substrates. As part of the present study, icing wind tunnel experiments have been performed to quantify the volumetric liquid water fraction in the ice layers, the sticking efficiency of impacting ice crystals and the maximum thickness of ice layers accreted on a dedicated test article for a wide range of experimental conditions. To achieve this objective, two measurement techniques, calorimetry and capacitive measurements, have been employed to quantify the average liquid water content and the distribution of liquid in the ice layers. The experiments show that when switching from negative to positive wet bulb temperatures, the sticking efficiency and maximum thickness of ice layers increase significantly. A similar trend is observed for increasing substrate heat flux, which results in an increasing liquid fraction in the ice layer measured by calorimetry, as well as increasing sticking efficiency and maximum thickness of the ice layers. Increasing the ice water content does not have a significant influence on the liquid content, but leads to more pronounced erosion effects. The conducted experiments provide an unprecedented insight into the liquid distribution in ice accretions and its effect on the sticking efficiency. These results provide a sound basis for more accurate modeling of sticking efficiency and enhances the understanding of ice accretion processes.