An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces. The multiphase flow simulation results of the wind-driven water runback (WDWR) flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow. The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface. To the best knowledge of the authors, the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows. It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.

An experimental study was conducted to characterize the dynamic ice accretion process and icing-induced aerodynamic penalties to offshore wind turbines under highly wetted icing environments during sea spray icing events. A turbine blade model was exposed to frozen-cold airflows with the Liquid Water Content levels up to 10.0 g/m3 and ambient temperatures down to −15.0 °C. Ice accretion characteristics under highly wetted icing environments were found to be significantly different from those of the onshore turbine icing scenarios with much lower Liquid Water Content levels. While a typical rime icing process was found to be experienced by onshore wind turbines at the cold temperature of −15.0 °C, mixed or even glaze icing processes occurred over the blade surfaces of offshore wind turbines due to the much higher wetted icing environments. The aerodynamic penalties induced by the mixed and glaze ice accretion were found to be significantly greater (i.e., up to 15 % more accreted ice mass, 85 % less lift, and 150 % more drag) than the rime icing scenario. However, at a "warmer" icing temperature of −5.0 °C, the glaze icing process over blade surfaces under highly wetted icing environments was accompanied by significant runback of unfrozen water, causing smaller aerodynamic penalties to offshore wind turbines. © 2025 Elsevier Ltd

Atmospheric icing on aircraft surfaces represents a significant aviation hazard that compromises flight safety and aerodynamic performance in cold weather conditions. Precise measurement of supercooled water droplets and ice crystal characteristics in cold environments is essential for accurate ice formation prediction. This study presents a comprehensive experimental investigation to develop an advanced digital inline holography (DIH) system capable of differentiating and characterizing supercooled water droplets and ice crystals within an icing research tunnel. The DIH system measures critical particle characteristics including liquid water content (LWC), median volume diameter (MVD), ice water content (IWC), and particle size/shape distribution. System validation was performed using standard NIST particles. Additionally, we propose a novel method for distinguishing between supercooled water droplets and ice crystals based on DIH measurements. © 2025, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

This study investigates the dynamic behavior of wind-driven water droplets over a flat plate, focusing on the interactions between runback water droplets/rivulets, water surface tension, and boundary layer airflow, which are critical for understanding aircraft icing phenomena. Using an integrated experimental setup combining Digital Image Projection (DIP) and Particle Image Velocimetry (PIV) techniques, time-resolved measurements were obtained to capture the deformation, movement, and flow characteristics of water droplets on a test plate under varying free stream velocities. The measurement results reveal that droplet motion is strongly influenced by both droplet size and airflow speed, with larger droplets exhibiting slower oscillations and a more stable motion compared to smaller droplets. The study highlights the complex interplay between aerodynamic forces and surface tension, which induces periodic oscillations in the front contact line of the droplets/rivulets. Furthermore, the PIV results show how the presence of the droplet disturbs the local airflow, altering boundary layer characteristics. These findings provide new insights into the important micro-physical processes of wind-driven droplet/rivulet runback and its effects in dynamic ice accretion, offering valuable database to validate/verify theoretical models and numerical simulations for more accurate prediction of aircraft icing phenomena. © 2025, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.