Deicing strains and stresses of iced substrates

The performance of low ice adhesion or icephobic coatings might be improved by adding a mechanical energy component via an underlying low powered electro-deformable substrate. The strain could be generated with many types of smart actuators consisting of piezoelectric devices, shape memory alloys (SMAs), conductive polymers, or ionic membrane polymer composites (IMPCs). An important step in designing a new electromechanical deicing system would consist of measuring the level of strain needed within an iced substrate to break and shed ice at the interface. In this paper are presented the results of an experimental investigation, in which new set-ups were built and used to simulate the behaviour of an active iced electromechanical substrate generating three types of strains: tensile, torsion, and bending. A total of 174 icing/deicing tests were conducted with aluminum and polyamide test specimens covered with hard rime ice deposits 2, 5 and 10 mm thick and stressed at −10°C at various strain rates in the brittle ice regime. Real time strains and forces were precisely monitored using strain gages and load cells. The stress was calculated from the deicing strain ϵ deicing and force measured at time of deicing corresponding to an interfacial failure between ice and substrate and/or cohesive failure of ice. Under test conditions used, strains were found to be very similar in torsion and in tension but about ten times lower in bending. Moreover, stresses and strains at deicing were found to increase with increasing substrate roughness and decrease with increasing ice thickness

A laboratory simulation of wet icing build-up On H.V. insulators

The objective of the present study is to propose a practical laboratory method to simulate wet atmospheric ice accretion on H.V. insulators. The method developed is based on first accumulating a low density soft rime on energized insulators and then to heat the produced deposits. The liquid water fraction of the ice accretion is then determined using a centrifuge. This approach makes it possible to determine the performance of insulators under wet-snow-like conditions with relatively simple, low cost equipment

Modèle d'accrétion de glace sur un objet bidimensionnel fixe appliquable aux pales d'éoliennes

Le LIMA (Laboratoire International des Matériaux Antigivre) en collaboration avec le CIRA (Italian Aerospace Research Centre) a développé un logiciel simulant l'accrétion de la glace en régime sec et humide sur un objet bidimensionnel fixe. Le modèle thermodynamique de l'accrétion de glace est similaire aux modèles existants, LEWICE aux États Unis, TRAJICE en Grande Bretagne, ONERA en France ou CANICE au Canada, où les corrélations empiriques ont été remplacées par des analyses physiques. La hauteur des rugosités dépend de l'état de l'eau en surface qui peut exister sous forme d'un film, de gouttes ou de ruisselets et elle est calculée à partir de l'équation d'équilibre entre les forces de tension de surface, aérodynamique et gravitationnelle. Les masses d'eau liquide résiduelle, de ruissellement et d'arrachement sont calculées à partir de modèles analytiques basés sur la hauteur des rugosités, tandis que la nouvelle position de la surface est calculée à l'aide d'une méthode géométrique basée sur les bissectrices entre les panneaux définissants la surface. Le modèle d'accrétion a été validé pour les régimes sec et humide avec des formes de glace obtenues expérimentalement en soufflerie par Shin et Bond. Les formes de glace prédites numériquement sont similaires à celles mesurées expérimentalement et le modèle a été en mesure de générer les formes complexes de glace observées comme les cornes et les cannelures. Les particularités du modèle développé font qu'il pourrait être appliqué aux cas où les vitesses sont faibles ou élevées, ou encore pour les objets tournants par rapport au sol comme pour les pales d'éoliennes ou d'hélicoptères

Heat and mass transfer during ice accretion on aircraft wings with an improved roughness model

This paper presents the thermodynamic model used in the numerical simulation of ice accreted on an airfoil surface in wet and dry regimes developed at AMIL (Anti-Icing Materials International Laboratory), in a joint project with CIRA (Italian Aerospace Research Center). The thermodynamic model combines mass and heat balance equations to an analytical representation of water states over the airfoil to calculate the surface roughness and masses of remaining, runback, and shedding liquid water. The water state on the surface is represented in the form of beads, film or rivulets, each situation corresponding to a particular roughness height which has a major impact on the heat transfer coefficients necessary for the heat and mass balances. The model has been tested for severe icing conditions at six different temperatures corresponding to dry, mixed and wet accretion. Water mass, roughness and heat transfer convection coefficients over the airfoil surface are presented. The thermodynamic model combined with an air flow, water trajectory, and geometric model provides accurate results. It generates the complex ice shapes observed on the wing profile, and the numerical ice shapes profiles agree well with those obtained in wind tunnel experiments

Aircraft take-off laboratory simulation for de/anti-icing study

A wind tunnel investigation of a 2-D airfoil covered with various aircraft ground de-icing/anti-icing fluids at subfreezing temperatures has been conducted in the laboratory of the 'Groupe de Recherche de l'Ingenierie de l'Environnement Atmospherique' at Universite du Québec a Chicoutimi. The main objective of this investigation was to simulate take-off conditions in order to evaluate the behavior of these fluids on the airfoil surface, and to determine their effects on the aerodynamics of the model. The fluids tested include six products, some of which are similar to the fluids previously tested in flight (Boing 737) and with 2-D and 3-D models in the NASA Lewis Research Center. Calibration and development tests were then performed with the cruise airfoil model available in the laboratory (NACA 662-415 with a 30 cm chord and a 60 cm span). The profile was modified, by flap and slat additions, in order to obtain an aerodynamic performance approaching that of a large aircraft wing during take-off and to reproduce the flow-off of the fluid observed in flight tests. The experimentations confirmed the existence of a significant lift loss at all rotation angles. This phenomenon was found to be similar to that of a roughness element, placed at the leading edge of the wing model, and to be dependent on the presence of a fluid wave moving after rotation from underneath the wing leading edge. De-icing fluids exhibit lower lift loss than anti-icing fluids. Comparison with previous laboratory and flight tests showed general agreement in terms of fluid behavior with respect to lift loss. In particular, the study shows that, in the present generation of de/anti-icing fluids, the aerodynamic behavior deteriorates as the basic ice holdover endurance improves

Wind tunnel study on lift reduction on a wing section covered with anti-icing fluid in supercooled precipitation

Residues of de-icing or anti-icing fluid, applied to aircraft on the ground, may produce, in some instances, lift loss at takeoff. The main objective of this work is to provide introductory information on the possible increase of lift loss in the case of supercooled droplets precipitation (freezing rain, drizzle, and fog) during taxi and ground acceleration. The study is performed on a 2D airfoil model set in the icing wind tunnel at the Universite du Quebec a Chicoutimi. The work concentrates on the lift measurement of a wing model subjected to wind acceleration and rotation, simulating those of a B737 aircraft. The fluids tested include three experimental anti-icing fluids. The supercooled precipitation is generated at a rate of 6.5 g/dm 2/hr with 33μ MVD droplets for contamination levels equivalent to 15% and 30% dilution of the fluid. The experimentations are performed at -10°C and -20°C. At low temperature, when exposure time is large enough to induce high fluid dilution (about 30%), the additional lift penalty may be enough to exceed the temporarily acceptable level of takeoff lift loss for large aircraft. This effect seems to correspond to the formation of a viscous mixture of fluid and ice that is similar to wet snow. Further work is recommended to confirm these findings for currently certified type I and type II fluids

Cold and humid environment simulation for de/anti-icing fluids evaluation

New recommendations regarding the performance of de/anti-icing fluids used on aircraft parked on the ground have been presented by various international organizations such as the Association of European Airlines (AEA) and the Society of Automative Engineers (SAE), and evaluation of fluid behaviour under cold and highly humid conditions is now required. An experimental simulation corresponding to AEA specifications is described as performed in the cold chamber of the Groupe de Recherche de l'Environment (GRIEA) at the Université du Québec à Chicoutimi. The methods to insure a high relative humidity level and an appropriate frost deposition rate are demonstrated. A description of the fluid behaviour is offered from a simple numerical analysis supported by results drawn from several anti-icing fluid experiments

State-of-the-art on power line de-icing

This paper presents a detailed review of the different de-icing techniques, already developed and in development, which could be applied to the conductors and wires of electric power lines. After a bibliographical search in various data banks, on de-icing processes, more than 30 techniques at different stages of development, capable of removing ice and assuring anti-icing protection, have been identified in different fields such as air and rail transport, electrical networks, telecommunications, etc. Although many techniques have not yet made it beyond the concept stage, some are used in several of the sectors previously mentioned. The following is a comparative evaluation of all these techniques, thermal, mechanical and passive, based on energy efficiency and practicability. It is recommended to favor the mechanical techniques over thermal methods that have been developed, but require more energy. Specific development projects and feasibility studies on the most attractive techniques have finally been identified as steps for progress in power line de-icing

Introductory analysis of boundary-layer development on de/anti-icing fluid

When aircraft are kept on the ground for a significant period of time under cold precipitation, anti-icing fluids are used to prevent ice buildup. Unfortunately, at the time of takeoff, the residual fluid on wings modifies the boundary layer of the air and causes lift loss. The purpose of this work was to study the boundary-layer development of the air flowing above a horizontal flat plate covered with a de/anti-icing fluid film. The objective was to find the relationship between the air boundary layer and the geometric and dynamic characteristics of the air/fluid interface. This work consists of numerical and experimental studies. The experimental work contains a rheological study of the fluid and wind-tunnel tests on flat plates in order to describe the movement of the fluid during airflow acceleration. The numerical modeling is used for the prediction of the wave characteristics at the interface and for the determination of the integral relationships for rough boundary-layer conditions. The model of stability gave a good correlation between theory and experiment for the waveform at the air/fluid interface. A simple integral model determines an equivalent flat plate roughness that produces the same boundary layer as with the fluid. This equivalent roughness corresponds, in general, to the waveform, which indicates that the influence of the fluid seems to be only geometrical in nature

Experimental evaluation of flat plate boundary layer growth over an anti-icing fluid film

Since 1987, de-icing procedures for aircraft on the ground have been increasingly modified to account for longer queuing time before take-off. New fluids that exhibit long-lasting ice protection have been introduced. These anti-icing fluids are non-Newtonian (pseudo-plastic) in order to be highly viscous when the aircraft is at rest while losing viscosity during acceleration before take-off rotation. The objective of the present work is to implement an improved standard testing procedure recommended by the Aerospace Industries Association (AIA) and the Association Europeenne des Constructeurs de Materiel Aerospatial (AECMA) that defines aerodynamic acceptance of de-icing/anti-icing fluids for large aircraft. The experimental set-up consists of a rectangular duct, 1.5 m long, with a 30 cm by 10 cm cross-section, which is fitted in a cold recirculated wind tunnel and instrumented to measure temperatures and boundary layer displacement thickness (BLDT) during a wind acceleration that simulates ground acceleration of a type B-737 aircraft. Previous work (Carbonaro, 1985-87) demonstrated that the BLDT was well-correlated to the lift loss induced by the fluid remaining on the wing at take-off. Consequently, the BLDT that is produced by accelerating air over a 2 mm fluid layer on the bottom of the test duct can be used to identify acceptable levels of lift reduction for a given fluid. A reference fluid is used to present and validate the overall procedure, and five leading commercial fluids that exhibit acceptable behaviour above -20°C are evaluated