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

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dc.contributor.authorThomas Fernandez, Kevinen
dc.contributor.committeechairCoutier-Delgosha, Olivieren
dc.contributor.committeechairPhilen, Michael Keithen
dc.contributor.committeememberLowe, Kevin T.en
dc.contributor.departmentAerospace and Ocean Engineeringen
dc.date.accessioned2025-03-22T08:00:32Zen
dc.date.available2025-03-22T08:00:32Zen
dc.date.issued2025-03-21en
dc.description.abstractStructural 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.en
dc.description.abstractgeneralAircraft icing, a major engineering obstacle to economic and safe transportation, has promoted in-depth research into thermal and mechanical preventive measures. General solutions involve spraying chemicals and high-power consumption heating systems for large aircraft and minimum measures for small aircraft, but the challenge resides in water droplets freezing at supercooled levels, leading to increased weight, drag, and de-icing power requirements. A novel approach is attempted using high-frequency Piezoelectric Transducer (PZT) atomization in combination with the fabricated superhydrophobic surface to tackle structural icing while also exploring the effect of surface roughness. The study spans various drop impact heights (∆d) and chosen resonant frequencies (6 kHz to 25.6 kHz) to determine the optimal range. Atomization creates smaller easily broken droplets, with a timescale similar to and smaller than ice nucleation, making it an effective anti-ice and or de-ice method. The experimental methodology involves adjusting frequency and droplet velocity to draw relevant effectiveness parameters as volume ejected per ms (Vatomized) and total atomization energy (Eatomized) using an aluminum substrate. The most effective actuators are selected and determined through the analysis of frequency response, where the range of frequencies and magnitude of their amplitudes allow selections that produce the best atomization. The use of mechanical vibrations to expel liquid more effectively addresses challenges faced with earlier larger PZTs that consumed greater power and significant voltage amplification. Single and sweep frequencies' effect on the droplet dynamics are studied in 3 parameters: the droplet Spread factor, the Vatomized, and the Eatomized. Vatomized is approximated from the rate of number of droplets ejected per ms (Ratomized) using ImageJ, the Eatomized is estimated using Track Mate, also in ImageJ, to detect and track the atomized droplets based on a search radius of 0.2 mm and the advanced Kalman filter applied. The combination of the 3 items helps achieve 3 key objectives: the dynamics of the droplet, the change in dynamics due to atomization, and the most effective method. The droplet dynamic is studied through the Wenzel/Cassie-Baxter state and the spreading of the droplet over the substrate. It is observed that the Atomizations induce more of a Wenzel state (hydrophilic) pining as opposed to a static surface. It promotes spreading, meaning the droplet has more surface area contact with the substrate, and the pining effect increases, therefore suggesting an increase in surface area energy. The localized effects of the vibration amplitude can help in both anti-icing and de-icing as observed through atomized these atomized droplets carry as they move away. As the droplet Re increases, the energy of the atomized droplet decreases. The total energy (Eatomized) reduces as a result of an increase in contact area and pining (hydrophilic nature) due to increased attraction of fluid particles to the substrate surface. Additionally, sub-objectives such as the drawbacks in current mathematical equations on atomization, the construction of a supercooled chamber, and the basis for finite element method analysis of a PZT attached to the aluminum substrate using ABAQUS, are discussed.en
dc.description.degreeMaster of Scienceen
dc.format.mediumETDen
dc.identifier.othervt_gsexam:42528en
dc.identifier.urihttps://hdl.handle.net/10919/125065en
dc.language.isoenen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectAnti-icingen
dc.subjectPiezoelectric Transduceren
dc.subjectAtomizationen
dc.subjectHigh frequencyen
dc.subjectImpacten
dc.subjectSuperhydrophobic surfaceen
dc.titleAircraft Anti-Icing Analysis: Water Droplet Dynamics Under High-Frequency Atomization and Superhydrophobic Effectsen
dc.typeThesisen
thesis.degree.disciplineAerospace Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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