Icephobic coatings for aircraft and other surfaces subjected to ice accretion have generated great interest in the past two decades, due to the advancement of nanomaterials, coating fabrication methods, biomimetics, and a more in-depth understanding of ice nucleation and ice adhesion. Icephobic coatings have demonstrated the ability to repel water droplets, delay ice nucleation and significantly reduce ice adhesion. Despite these ongoing research activities and promising results, the findings reported hereafter suggest that coatings alone cannot be used for aircraft anti-icing and de-icing operations; rather, they should be considered as a complementary option to either thermal or mechanical ice protection methods, for reducing power consumption and the ecological footprint of these active systems and for expediting ground de-icing operations. This paper will first review the state-of-the-art of icephobic coatings for various applications, including their performance and existing deficiencies. The second part of this paper focuses on aerospace anti-icing and de-icing requirements and the need for hybrid systems to provide a complete ice protection solution. Lastly, several urgent issues facing further development in the field are discussed.

Recent research is showing growing interest in low-power electromechanical de-icing systems and, in particular, de-icing systems based on piezoelectric actuators. These systems use the vibrations generated by piezoelectric actuators at resonance frequencies to produce shear stress at the interface between the ice and the support or to produce tensile stress in the ice. This paper provides analytical and numerical models enabling a better understanding of the main de-icing mechanisms of resonant actuation systems. Different possible ice shedding mechanisms involving cohesive and adhesive fractures are analyzed with an approach combining modal, stress and crack propagation analyses. Simple analytical models are proposed to better understand the effects on ice shedding of the type of mode, ice thickness, or frequency with respect to cohesive and adhesive fractures.

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a b s t r a c tThe understanding of ice shedding is of prime importance in the assessment of aeronautical ice protection systems. In this paper, the authors previously studied mechanism is extended to include adhesive debonding. It is based on pressure redistribution in the water film formed at the ice/airfoil interface. The numerical modelling of crack propagation is based on recent work on damage mechanics which provides a general framework. As for adhesive debonding an algebraic model is derived from general mechanical equilibrium relations. Numerical experiments are performed to study an adhesive-debonding/brittlefailure mode detachment, the results of which are discussed.

In the context of more electrical aircraft and reduction of fuel consumption, aircraft manufacturers are moving towards more complex and transient ice protection systems. The operating of these systems involves several unsteady heat and mass transfer phenomena. Modelling and numerical simulation play an important role in the investigation of these unsteady phenomena. In this paper, a model for unsteady ice build-up and melting is presented. The model is based on a triple layer assumption. In addition, a tailored numerical methodology for solving the governing partial differential equations is also described. It is based on a Galerkin finite element method and a Gauss-Seidel like implicit time marching scheme. The global method is validated and its capabilities are demonstrated on several cases.

Electromechanical resonant de-icing systems provide a low-energy solution against ice accumulation on aircraft. Recent researches show a growing interest towards these systems in the context of more electrical aircraft. Electromechanical de-icing systems consists in electric actuators producing stress within the ice, through micro-vibrations of the surface to be protected, leading to bulk or adhesive failure and, ultimately, ice shedding. The understanding of the mechanisms at play is of prime importance in order to design efficient ice protection systems. Despite a large number of studies in the literature, there is still a lack when dealing with fracture propagation phenomena in this context. In this work the authors propose a model based on the well established phase-field variational approach to fracture. The approach is applied to the study of crack propagation and debonding of ice under the effect of an electromechanical resonant de-icing system. Numerical experiments are performed in order to assess possible ice shedding mechanisms.

The aim of the present paper is to propose a general methodology for the numerical modelling of both anti and de-icing systems. A lubrication model is used for dealing with the dynamics of the runback water film. As regards thermal effects, in order to take into account heat conduction and unsteadiness, a parabolic temperature profile is assumed with respect to the normal coordinate for the ice layer. Heat transfers in the airfoil solid structure are described using a dedicated solver based on the unsteady heat conduction equation. The most original contribution of this work is the new technique (herein referred to as the "improved Schwarz method") which is proposed for coupling in a robust way the accretion-runback model and the solid heat conduction model. This new coupling algorithm allows to ensure fast convergence of both temperature and heat flux at the coupling interface (airfoil outer surface) and can be used either for steady state computations (anti-icing mode) or unsteady computations (de-icing mode). Numerical test cases which have been performed so far are very promising and show the relevance of this new approach for real applications and 3D extension.

This article focuses on resonant ice protection systems and studies fracture mechanisms at work for flexural modes having frequencies lower than100 kHz. The objective is to study the power required for fracture initiation and propagation in this frequency range. Two types of deicing mechanisms are studied in this paper: tensile stress dominant flexural modes and shear stress dominant flexural modes. Criteria are introduced to enable the comparison between these deicing mechanisms according to their power requirements and the selection of the most promising configurations. Eventually, the numerical results are compared to experiments to verify assumptions and computations. The contribution of this article is to put forward power-efficient de-icing configurations for resonant electromechanical de-icing systems using flexural modes. Low frequency flexural modes appear to be less power consuming for both mechanisms. Tensile stress dominant flexural modes have lower power requirements than shear stress dominant modes. The instantaneous peak power requirement to cover 90% of the area is estimated to be 5.5 kW/m². Nomenclature A = Area (m²) b = Fracture width (m) Cshear = Criterion for fracture initiation by shear stress Ctensile = Criterion for fracture initiation by tensile stress Ccoh = Criterion for cohesive fracture unstable propagation