Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Aerospace Engineering

Major

Aerospace Engineering

First Advisor

Hui Hu

Abstract

Aircraft icing is widely recognized as a significant hazard to aircraft operations in cold weathers. Bio-inspired water- and ice-phobic coatings are currently being investigated for use as viable strategies for aircraft in-flight icing mitigation. The objective of this study is to evaluate the anti-/de-icing performance of a number of bioinspired hydro-/ice-phobic coatings and explore their potentials for aircraft in-flight icing mitigation.

In the present study, the bioinspired hydro-/ice-phobic coatings examined include the lotus-leaf-inspired super-hydrophobic surface (SHS), the pitcher-plant-inspired slippery liquid-infused porous surface (SLIPS) and the goose-feather-inspired textured surface. Firstly, a comprehensive experimental study was conducted to investigate the dynamics of impacting water droplets onto the test plates with SHS, SLIPS and goose feather surface, in comparison with that of over a conventional hydrophilic aluminum surface. A novel wind tunnel was built to accelerate the droplets to the Weber number up to 3,000, in the range relevant to aircraft in-flight icing phenomena. A high-speed, high-resolution system was used to reveal the droplet impact dynamics at the high Weber number regimes. Secondly, a new anti-/de-icing strategy with icephobic soft materials (e.g., made from PDMS gels) was also explored for aircraft anti-icing applications. The effects of surface stiffness on the dynamics of droplet impingement at high Weber numbers were investigated in great details. The soft surface was also applied to an airfoil/wing model to demonstrate its effectiveness for in-flight icing mitigation in the unique icing research tunnel of Iowa State University (i.e., ISU-IRT). Thirdly, the durability of various surface coatings due to spray erosion pertinent to aircraft icing mitigation scenario was also experimentally investigated and compared for the bio-inspired hydro-/ice-phobic surface coatings. Surface morphology, wettability, and ice adhesion strength were compared quantitatively after different spray erosion testing durations. A theoretic wettability-based lifetime model was developed following the Cumulative-Fatigue-Damage theory to predict the spray erosion characteristics of the bio-inspired hydro-/ice-phobic surface coatings. Fourthly, Particle Image Velocimetry (PIV) technique was used to measure the flow fields around wind-driven droplets on surfaces with various wettabilities. A theoretical model based on force balance analysis was developed to predict the critical wind speed which dislodges the droplet from the solid surface. Finally, wind-driven droplet motion on SLIPS was provided with more details by measuring the flow field inside and outside of the droplet simultaneously using the PIV technique. It showed that wind-driven droplet internal circulation is related to the droplet viscosity and it will influence the prediction of the droplet moving speed. The findings derived from this study could be very helpful to explore/optimize design paradigms for the development of innovative, low-power anti-/de-icing strategies by leveraging the bio-inspired hydro-/ice-phobic materials/surfaces for aircraft in-flight icing mitigation.

Copyright Owner

Liqun Ma

Language

en

File Format

application/pdf

File Size

169 pages

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