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

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. Still, complexities arise from water droplets freezing at supercooled levels. A proposed approach uses the structure's vibration to induce atomization, an active 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, 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 atomization involved adjusting the frequency applied (as a single and a sweep) to the PZT attached to an aluminum flat plate at a constant AC voltage supply, and variation of droplet velocity parameters.

The effect of frequencies on the droplet is studied by analyzing 3 quantities: the Spread factor, Volume ejected per ms (Vatomized), and total energy (E_atomized) of the atomized droplets. The three help understand the dynamics of the droplet, the change in dynamics, and the most effective atomization. During atomization, Wenzel state pinning becomes more prevalent as opposed to a non-vibrating surface. Vibration also promotes spreading, meaning thinner lamella and more surface area contact, thereby higher wetting. Also, the more it spreads, the larger the volume of water ejected. It was observed that the total energy (sum of KE and PE) of ejected droplets is inversely related to an increase in Re number. As the Re number increases from ≈ 548 to ≈4797, the E_atomized reduces. Most likely, due to pinning, suggesting an increase in surface energy that promotes hydrophilic behavior. Higher energy is required to eject a droplet from a wider cross-sectional area (spreading increases with an increase in Re). Swept frequencies exhibited less spatial dependency on droplet deposition while maintaining atomization rates, volumes, and energy levels similar to those of single frequencies. It explores the effects of combining atomization with a superhydrophobic surface, further improving the anti-icing characteristics.