Aircraft Anti-Icing Analysis: Water Droplet Dynamics Under High-Frequency Atomization and Superhydrophobic Effects

Abstract

Structural icing is a significant engineering challenge that has prompted extensive research into thermal and mechanical preventive measures. Common solutions involve the spraying of de-icing chemicals and high-power consumption heating systems for larger aircraft that add to the weight. Still, complexities arise from water droplets freezing at supercooled levels. A novel approach uses the structure's vibration to induce atomization, a proposed active anti-icing method using high-frequency Piezoelectric Transducer (PZT) vibration and combines it with the passive method of surface roughness variation by fabricating superhydrophobic surfaces. The study analyzes the droplet impact at 3 speeds. The impact is recorded with high-speed imaging using selected resonant frequencies (between 6 kHz and 25.6 kHz) to determine the optimal range for atomization. The study of the active method of atomization involved adjusting the frequency applied (as single and a sweep of frequencies) to the transducer material attached to an aluminum flat plate at a constant AC voltage supply, and variation of droplet velocity parameters. The best actuators are selected and determined through the analysis of frequency response and the magnitudes of the amplitude of vibration that are generated.

The effect of single and sweep frequencies on the droplet dynamics is studied by analyzing 3 quantities: the Spread factor, the Volume ejected per ms (Vatomized), and the total energy (Eatomized) of the atomized droplets. The combination of the three helps to determine three key outcomes: The dynamics of the droplet, the change in dynamics due to vibrations, and the most effective atomization. It is observed that during atomization, Wenzel state (Hydrophilic) pining becomes more prevalent in the droplet as opposed to a non-vibrating static surface. Vibration also promotes spreading, meaning thinner droplet lamella (droplet height on the surface) and more surface area contact, thereby higher wetting. Furthermore, the more it spreads, the larger the volume of water is ejected. It was observed that the total energy (sum of Kinetic and potential energies) of ejected droplets have an inverse relation with the increase in Reynolds number. As the droplet speed increases in Re from ≈ 548 to ≈4797, the Eatomized reduces. Most notably, due to pinning, suggesting an increase in surface energy that promotes hydrophilic behavior and also the higher energy required to eject a droplet from a wider cross-section area (as the spreading increases with increase in Re). This research examines droplet interaction using parameters from both single-frequency and swept-frequency atomization, including the spread factor, Vatomized and Eatomized, to study droplet interaction. Here, swept frequencies exhibited less spatial dependency on droplet deposition while maintaining atomization rates, volumes, and energy levels comparable to those of single frequencies. Additionally, it explores the effects of combining atomization with a superhydrophobic surface, further improving the anti-icing characteristics. The study also establishes protocols for Abaqus FEA to simulate the frequency response of a PZT attached to a flat plate and outlines the design and construction of a supercooling chamber.