The focus of this study is to investigate and compare the behavior of a droplet on superhydrophobic (SHS) and slippery lubricant impregnated (SLIPS) surfaces under the effect of air shear flow. In this regard, both experimental and numerical analyses have been conducted to compare their performance on droplet mobility under different air speeds. Two different lubricants have been utilized to scrutinize their effect on droplet movement. The numerical simulations have been performed based on the volume of fluid method coupled with the large eddy simulation turbulent model in conjunction with the dynamic contact angle method in addition to a model that can represent the effect of lubricants on slippery surfaces. The numerical simulations are compared with the experimental study in order to shed light on the underlying mechanisms. The results showed that under the same conditions, the critical velocity for droplet movement on the superhydrophobic surfaces is lower than that on the slippery lubricant impregnated surfaces due to the smaller droplet base diameter and the larger contact angle. The hydrodynamics of droplet mobility on superhydrophobic surfaces exhibits a rolling behavior while for the slippery lubricant impregnated surfaces a combination of rolling and sliding is observed. Beyond the critical airflow speed, a complete droplet shedding on all surfaces occurs. The wetting length and position of the droplet on superhydrophobic and slippery surfaces have been measured. On slippery surfaces, the speed of droplets is greatly affected by the lubricant properties while similar behavior in the wetting lengths is observed.

Ice formation on the aerodynamic surfaces of an aircraft is regarded as a major problem in the aerospace industry. Ice accumulation may damage parts, sensors and controllers and alter the aerodynamics of the airplane, leading to a range of undesired consequences, including flight delays, emergency landings, damaged parts and increased energy consumption. There are various approaches to reducing ice accretion, one of them being the application of icephobic coatings. In this work, commercially available polyurethane-based coatings were modified and deposited on NACA 0012 aircraft airfoils. A hybrid modification of polyurethane (PUR) topcoats was adopted by the addition of nanosilica and three-functional spherosilicates (a variety of silsesqioxane compound), which owe their unique properties to the presence of three different groups. The ice accretion on the manufactured nanocomposites was determined in an icing wind tunnel. The tests were performed under three different icing conditions: glaze ice, rime ice and mixed ice. Furthermore, the surface topography and wetting behavior (static contact angle and contact angle hysteresis) were investigated. It was found that the anti-icing properties of polyurethane nanocomposite coatings strongly depend on the icing conditions under which they are tested. Moreover, the addition of nanosilica and spherosilicates enabled the reduction of accreted ice by 65% in comparison to the neat topcoat.