In-Flight Icing of UAVs - The Influence of Reynolds Number on the Ice Accretion Process 2011-01-2572

The intensive deployment of UAVs for surveillance and reconnaissance missions during the last couple of decades has revealed their vulnerability to icing conditions. At present, a common icing avoidance strategy is simply not to fly when icing is forecast. Consequently, UAV missions in cold seasons and cold regions can be delayed for days when icing conditions persist. While this approach limits substantially the failure of UAV missions as a result of icing, there is obviously a need to develop all-weather capabilities. A key step in accomplishing this objective is to understand better the influence of a smaller geometry and a lower speed on the ice accretion process, relative to the extensively researched area of in-flight icing for traditional aircraft configurations characterized by high Reynolds number.

Our analysis of the influence of Reynolds number on the ice accretion process is performed for the NACA0012 airfoil. Analytical analysis of the integrated mass and energy balance equations along the airfoil surface allows the identification of regimes of rime and glaze formation, as well as the ice accretion extent as a function of static air temperature and liquid water content. For each Reynolds number, a CFD solver computes the airflow field, and the distributions of Stanton number and static air pressure along the airfoil surface. Next, a drop trajectory solver computes the distribution of collection efficiency along the airfoil for a given drop size. Finally, a morphogenetic model is used to predict the ice accretion shape and its extent over the entire Reynolds number range under consideration. Our analysis highlights the differences between ice accretions on components of traditional aircraft and UAVs, arising from their differences in cruising speed and airfoil dimensions.