Icing Environments Research Articles

Scalable robust photothermal superhydrophobic coatings for efficient anti-icing and de-icing in simulated/real environments

Photothermal superhydrophobic coatings are supposed promising to prevent ice accumulation on infrastructures but often experience significant performance degradation in real icing conditions and lack mechanical robustness. Here, we report design of robust photothermal superhydrophobic coatings with three-tier hierarchical micro-/nano-/nanostructures by deposition of nanosized MOFs on natural attapulgite nanorods, fluorination, controlled phase separation of a hydrophobic adhesive and spraying assembly. Phase separation degree and adhesive content significantly influence the coatings’ properties by regulating the structural parameters and morphology. In simulated/real icing environments, the coatings simultaneously show (i) high superhydrophobicity and stable Cassie-Baxter states due to their low-surface-energy, three-tier micro-/nano-/nanostructure, (ii) excellent photothermal effect primarily due to nanosized MOFs, and (iii) good mechanical robustness by the phase-separated adhesive, reinforcement with attapulgite and the coatings’ self-similar structure. Accordingly, combined with low thermal conductivity, the coatings exhibit remarkable anti-icing/frosting (e.g., no freezing in at least 150 min and almost free of frost in 25 min) and de-icing/frosting performances (e.g., fast de-icing in 12.7 min and fast de-frosting in 16.7 min) in such environments. Furthermore, we realize large-scale preparation of the coatings at reasonable costs. The coatings have great application potential for anti-icing and de-icing in the real world by efficiently using natural sunlight.

Efficient and Controllable Preparation of Super-Hydrophobic Alumina-Based Ceramics Coating on Aviation Al-Li Alloy Surface for Corrosion Resistance and Anti-Icing Behavior

Al-Li alloys have been widely applied in aircraft structural component and shell material. However, Al-Li alloys are prone to corrosion failure, which leads to a considerable safety risk in the aerospace field and greatly limits their industrial application. Herein, a simple, low-cost, and large-scale air-spraying technique is developed for the preparation of an alumina-based ceramics coating with enhanced corrosion resistance and anti-icing behavior. The results show that the static contact angle of the as-prepared coating is 157.2 ± 0.4°, and the rolling angle is only 9.8°, suggesting a super-hydrophobic surface. Meanwhile, the electrochemical corrosion potential of the coating is 70 mV higher than that of the substrate, and the corrosion current density of the coating also decreases by 1 order of magnitude, indicating a significantly improved corrosion resistance. In addition, the fabricated super-hydrophobic coating also shows excellent anti-pollution and anti-icing characteristics. This work provides positive guidance for expanding the application of hydrophobic coating in the aerospace industry, especially in some complex corrosion, icing, and pollution environments.

Challenges in Detecting Clouds in Polar Regions Using a Drone with Onboard Low-Cost Particle Counter

It is expected that uncrewed aerial vehicles (UAVs) will be used increasingly for operational atmospheric soundings to cover a broader area of the lower troposphere, including that in the polar regions and over the oceans. During the Japanese Antarctic Research Expedition of 2022/2023, 172 vertical profiles up to a maximum height of 1000 m a.s.l. were conducted from mid-December 2022 to mid-March 2023 using a commercially available inexpensive drone launched from the icebreaker RV Shirase. Over a quarter of the flights encountered clouds and snow, of which half produced icing on the body and blades of the drone. The onboard aerosol counter detected an increase in the particle number concentration in the cloud layers, which was synchronized with an increase in the attenuated backscatter coefficient of a shipboard lidar ceilometer. In the presence of icing, the concentration of particles >1.0μm exceeded 5000 particles L−1 as a median value, while the concentration was <1000 particles L−1 for cases without icing. Using an onboard aerosol counter and/or land-based ceilometer would be useful for detecting the icing environments.

Sturdy oil-impregnated polyurethane coatings with long-lasting and high-efficient deicing performance

Icing on exposed surfaces can cause serious problems for aircraft, radar, highways, etc. Passive anti-icing surfaces with delicate surface structures show ultralow ice adhesion strength, but they suffer from stability and durability issues when facing the complex icing environments. Here, we show that oil-impregnated polyurethane coatings (OIPs) with gradient distribution of nanoscale oil droplets along the coating depth simultaneously exhibit reduced ice adhesion strength, improved stability and durability, and enhanced substrate adhesion compared with polyurethane (PU) coatings. This heterogeneous structure of OIPs not only leads to the formation of a stable oil/PU composite surface on the top surface but also induces slip pulse at the ice/coating interface at a lower critical shear force, both of which greatly reduce the effective ice/coating contact area. The deicing efficiency of OIPs can last >130 days without degradation, covering the whole winter in most temperate-zone countries.

Self-Driven Droplet Motions Below their Icing Points.

Liquid fluidity is a most key prerequisite for a broad range of technologies, from energy, fluid machineries, microfluidic devices, water, and oil transportation to bio-deliveries. While from thermodynamics, the liquid fluidity gradually diminishes as temperature decreases until completely solidified below icing points. Here, self-driven droplet motions are discovered and demonstrated occurring in icing environments and accelerating with both moving distances and droplet volumes. The self-driven motions, including self-depinning and continuous wriggling, require no surface pre-preparation or energy input but are triggered by the overpressure spontaneously established during icing and then continuously accelerated by capillary pulling of frosts. Such self-driven motions are generic to a broad class of liquid types, volumes, and numbers on various micro-nanostructured surfaces and can be facilely manipulated by introducing pressure gradients spontaneously or externally. The discovery and control of self-driven motions below icing points can greatly broaden liquid-related applications in icing environments.

Experimental Study on the Noise Evolution of a Horizontal Axis Icing Wind Turbine Based on a Small Microphone Array

In recent years, the global energy mix is shifting towards sustainable energy systems due to the energy crisis and the prominence of ecological climate change. Wind energy resources are abundant in cold regions, and wind turbines are increasingly operating in cold regions with wet natural environments, increasing the risk of wind turbine blade icing. To address the problem of noise source distribution and the frequency characteristic variation of wind turbines in natural icing environments, this paper uses a 112-channel microphone array to acquire the acoustic signals of a horizontal axis wind turbine with a diameter of 2.45m. Using the beamforming technique, the wind turbine noise evolution law characteristics under natural icing environment were studied by field experiments, and the noise source distribution and noise increase in different frequency bands under different icing mass and positions and different angles of attack were analyzed in detail. The results show that under the leading-edge and windward-side icing, the noise source gradually moves toward the blade tip along the spanwise direction with the increase in ice mass. In addition, the total sound pressure level at 460 r/min, 520 r/min, 580 r/min, and 640 r/min are increased by 0.82 dB, 0.85 dB, 0.91 dB, and 0.95 dB, respectively for the leading-edge icing condition in comparison with the uniform icing over the windward side of the blade.

Icing on Full-Scale Swept Wings in Flight and Icing Wind Tunnel

Inflight ice accretion on aircraft wings has been critically important for development and certification of transport category aircraft. With recent efforts toward certification by analysis, it is becoming increasingly important to characterize ice accretions in icing wind tunnels, the primary source of validation data for higher-fidelity three-dimensional ice shape analysis codes to be used in aircraft certification, in comparison with those in natural icing environments. In this study, a series of natural icing flight tests and icing wind tunnel tests were conducted on a transport category aircraft. The results were compared at similar test conditions on protected and unprotected surfaces of swept wings and empennage. For unprotected surfaces, both tests resulted in scallop ice, with natural icing flight test resulting in significantly smaller ice accretions. For protected surfaces, runback ice was formed on the lower wing surface in both tests, with natural icing flight test resulting in significantly less and sparser runback ice. Differences in scallop ice structures, limitations of icing wind tunnels, and scaling methods are considered the potential contributing factors to the differences. The results indicate a need for further studies on case-to-case comparison of ice accretions in the two test methods focusing on full-scale aircraft conditions.

Propeller-integrated airfoil heater system for small multirotor drones in icing environments: Anti-icing feasibility study

Atmospheric icing is one of the most common and hazardous environmental challenges for aircraft operations. So far, only large passenger aircraft, a few general aviation aircraft, and specialized rotorcraft are equipped with ice protection systems because of their additional energy consumption and weight. The emerging markets of small electric aircraft like Urban Air Mobility and Unmanned Aerial Vehicles for transportation, logistics, search and rescue, and other specialized operations will require efficient, lightweight and all-electric ice protection systems in order to allow operations in ice and snow conditions. In this work, an electrothermal ice protection system with an average heat power density of 1Wcm−2 was designed and developed for use on small multirotor drones. Commercially available propeller blades with diameters of 33cm were retrofitted with lightweight multilayer heating foils independently powered by super-capacitors. The heated propellers were tested in close-to-real icing conditions in a small-scale icing wind tunnel. Thrust, rotational speed, and power consumption of a non-heated reference propeller and a heated propeller were compared. In glaze ice conditions at air temperatures > −5°C the thrust of the non-heated propeller fluctuated between 60 and 90% with frequent cycles of ice accretion and shedding for the entire duration of the test. The heated propeller maintained a thrust of >95% in the same icing conditions. In rime ice conditions at air temperatures < −8°C the heating was not sufficient and the thrust of the non-heated and heated propellers similarly decreased over time. Heat flux calculations along the span of the propeller were made for different icing conditions and compared to the heat power density distribution of the tested ice protection system.

Coral-like silicone nanofilament coatings with extremely low ice adhesion

Passive icephobic surfaces can provide a cost and energy efficient solution to many icing problems that are currently handled with expensive active strategies. Water-repellent surface treatments are promising candidates for this goal, but commonly studied systems, such as superhydrophobic surfaces and Slippery Liquid Infused Porous Surfaces (SLIPS), still face challenges in the stability and durability of their properties in icing environments. In this work, environmental icing conditions are simulated using an Icing Wind Tunnel, and ice adhesion is evaluated with a Centrifugal Adhesion Test. We show that superhydrophobic coral-like Silicone Nanofilament (SNF) coatings exhibit extremely low ice adhesion, to the point of spontaneous ice detachment, and good durability against successive icing cycles. Moreover, SNFs-based SLIPS show stably low ice adhesion for the whole duration of the icing test. Stability of surface properties in a cold environment is further investigated with water wettability at sub-zero surface temperature, highlighting the effect of surface chemistry on superhydrophobicity under icing conditions.

Experimental investigation on the performance degradation of helicopter rotor due to ice accretion

Helicopter rotor performance can be significantly altered by ice accretion which directly degrades the handling qualities and safety during flight. To obtain understanding into the effect of ice accretion on a helicopter rotor in forward flight under different icing environments, an experimental campaign was conducted in an icing wind tunnel using a rotor model with diameter at 2 m. Research was emphasized on revealing effect of liquid water content and static temperature on the rotor performance degradation. The dynamic thrust and torque of the rotor were measured by a six-component balance. Ice shape of the airfoils at specific rotor blade spanwise locations was obtained through the ice cutting process; meanwhile, the entire ice topology on the blade was scanned by means of the three-dimensional scanning technique. Results showed that ice was mainly accreted on the leading edge and lower surface of the blade. The static temperature of a icing cloud has a noticeable effect on the regime of accreted ice. The ice formation was transparent glaze at −8°C and transformed to milky rime when changed the static temperature to −20°C. Comparing to rime ice, the glaze ice on the blade is more influential to the rotor performance degradation. Particular attention is given to the fact that under extreme icing conditions, over 30% degradation of transient rotor thrust was observed.

Potential of slippery liquid infused porous surface coatings as flashover inhibitors on porcelain insulators in icing, contaminated, and harsh environments

Humidity and pollution deposition on the surface of porcelain insulators affect the electrical field distribution and their performance which may lead to partial discharge and decreasing flashover voltage. Thereby one essential aspect of insulator designing is their surface science and surface wettability. To address these challenges, in this study robust omniphobic coatings were designed which can repel water and oil droplets as well as other contaminant particles from the porcelain insulators surface. In this regard, slippery liquid infused porous surface (SLIPS) coatings were applied on the porcelain substrate by infusing perfluorinated liquid lubricants into 200 %-stretched Teflon tape cover or fluoro-silanized porcelain. The surface of the designed transparent coatings repelled water, olive oil, kaolin, sodium chloride microparticles, and ice. The applied coatings exhibited low contact angle hysteresis (Δθ ≤ 5°) and a low sliding angle (α ≤ 7°) for water and olive oil droplets. SLIPS coatings showed good stability to extreme environments like immersion into acid, base, brine solutions, UV radiation and withstood at 4.5 kV inclined plane test without failure after 6 h. So, the modified SLIPS can be used as effective coatings in the porcelain insulators surface engineering.

Wind turbine performance in natural icing environments: A field characterization

Over 30% worldwide installations of wind turbines in cold climate regions are threatened with icing risks. The current study presents a systematic characterization of the turbine operation, power production, and blade/tower structural responses of a utility-scale wind turbine (2.5 MW, variable-speed variable-pitch regulated) under natural icing environments, by leveraging the unique facilities at the Eolos Wind Energy Research Field Station. A representative icing event that lasts 51 h is selected and divided into pre-icing, operational-icing, stopped-icing, and post-icing phases based on the variation of turbine operational conditions (i.e., power, rotor speed, and pitch angle) for the detailed evaluation. The results show that ice accretion can lead to appreciable reductions in the rotor speed and pitch angle before the turbine reaches its operational limits. Such reductions increase correspondingly as the inflow wind speed increases, which may accelerate the airfoil stall process and result in more severe power loss. The 51-h icing event yields a total energy loss of ~25 MWh, and the post-icing phase contributes a second-largest share of 17%, on the heel of the stopped-icing phase of 71%, associated with the long duration of natural ice melting process. Besides, blade structural response is highly sensitive to the ice accretion due to its fast reaction to the ice-induced lift penalties. The tower response also provides concrete evidence for the increase of the structural imbalance with ice accretion. Our findings can provide insights into the development of advanced control strategies for a more efficient and safer operation of wind turbines in natural icing environments.

Acoustic Characterization of Glaze and Rime Ice Structures on an Oscillating Airfoil via Fully Unsteady Simulations

The development of low-cost and simple technologies to improve pilot awareness of icing environments is crucial to improve the safety of rotorcraft, and especially those with limited icing clearance which are admittedly operating within icing environments without full icing clearance. An acoustic characterization of glaze and rime ice structures is hereby introduced to begin to quantify different ice shape noise signatures which directly transcend from the iced performance characteristics to develop acoustic ice detection technologies. The feasibility of the detection technique is assessed for fully unsteady simulations of ice accretion on an oscillating, two-dimensional airfoil. This work focuses on the computational modeling of the experimental database of a rotor airfoil with pitching motion during icing conditions from the NASA Glenn Icing Research Wind Tunnel and computing the resultant noise signals and analyzing their topology.

Self-lubricating icephobic elastomer coating (SLIC) for ultralow ice adhesion with enhanced durability

A durable, self-lubricating icephobic elastomer coating (SLIC) was realized by systematic optimization of silicone oil infusion levels within a robust, weather-resistant silicone elastomer matrix for ultra-low ice adhesion, targeting high durability levels for a variety of applications operating in harsh icing environments such as in aviation. This coating combines multiple properties that synergistically enhance the ice release effect, i.e., hydrophobicity, low surface roughness, coating elasticity and lubrication enabled interfacial slippage. Supercooled drop impact icing experiments on rotating fan blades at rpms of same order of magnitude as commercial aircraft engines showed that the SLIC repeatedly reduced more ice on the coating than other commercial hydrophobic and superhydrophobic surfaces. In addition, the SLIC displayed long-term self-replenishing lubrication – after repeated mechanical abrasion of the surface, lubricants stored within the bulk of the coating could continuously migrate to the surface to replace the lost lubricants, thus promoting low ice adhesion. Durability tests also showed that the SLIC could withstand long-term micron-sized droplet impact at 25 m/s and acceleration loading up to 276 g without coating degradation. This study is the first to demonstrate a lubricated, self-replenishing coating material capable of repeated ice removal from the coating surface in harsh environmental conditions.

A Numerical Weather Model’s Ability to Predict Characteristics of Aircraft Icing Environments

Abstract Recent advances in high-performance computing have enabled higher-resolution numerical weather models with increasingly complex data assimilation and more accurate physical parameterizations. With respect to aircraft and ground icing applications, a weather model’s cloud physics scheme is responsible for the direct forecasts of the water phase and amount and is a critical ingredient to forecasting future icing conditions. In this paper, numerical model results are compared with aircraft observations taken during icing research flights, and the general characteristics of liquid water content, median volume diameter, droplet concentration, and temperature within aircraft icing environments are evaluated. The comparison reveals very promising skill by the model in predicting these characteristics consistent with observations. The application of model results to create explicit forecasts of ice accretion rates for an example case of aircraft and ground icing is shown.

Study of the icing growth characteristic and its influencing factors for different types of insulators

Icing poses a serious threat to power transmission in many countries. Various studies on the icing mechanism and icing growth process of transmission lines have been carried out all over the world, whereas there are few reports about the icing growth mechanism and its inuencing factors on insulators to date. In this paper, articial tests of insulator icing were carried out; the inuences of temperature, median volumetric diameter (MVD), and wind velocity on the icing accretion process, ice shape, and ice type on the surface of insulators were analyzed systematically; and the icing growth performance of different types of insulators were also analyzed. Test results show that under different icing environments, the icing growth of insulators is always nonlinear; the growth rates of icicles and ice layers increase with the decrease of temperature; with the increase of wind speed, all of the ice thicknesses and the length and diameter of icicles increase signicantly; for wet growth, the impact of MVD on icing growth of insulators is not signicant; the structure of the insulator has some inuence on the icing growth process; and with the increase of length and diameter of icicles, the growth rate of the ice layer on the insulator surface decreases signicantly.

Mountain hydrometeorology

Mountain hydrometeorology

Ultrasonic De-Icing Bondline Design and Rotor Ice Testing

The use of ultrasonic excitation has shown the ability to promote ice shedding of impact ice (less than 2 mm thick) during prior wind-tunnel testing efforts. The ultrasonic de-icing technology is implemented to structures representative of rotorcraft blade leading edges and tested under impact icing and centrifugal environments (). Finite element models are experimentally validated and used to predict the ultrasonic ice shedding transverse shear stresses responsible for ice shedding. The finite element models tools are then used to guide the design of a robust bondline between the lead zirconate titanate actuators and the host structure. The novel bondline approach is implemented to a rotor blade leading-edge erosion cap representative structure (0.813-mm-thick stainless-steel leading edge). The system is tested under centrifugal loads and icing conditions generic to helicopter operational envelopes. Details on the de-icing system fabrication and integration are provided. The bondline configuration does not degrade during operation and increases the ice interface transverse shear stresses by 15% with respect to prior bonding approaches. To promote ice shedding of impact ice, a system control to identify and excite optimum de-icing modes during rotor ice testing is also implemented and described in this paper. The power consumption of the de-icing system is quantified to average . The de-icing system is able to promote shedding of ice layers ranging from 1.4 to 7.1 mm in thickness for varying icing conditions representative of helicopter icing environments.

Reply to “Comments on ‘Characterization of Aircraft Icing Environments with Supercooled Large Drops for Application to Commercial Aircraft Certification'”

Cober et al. (2009) and Cober and Isaac (2012) characterized aircraft icing environments that contained supercooledlargedrops (SLD).100mm indiameteron the basis of data collected during 134 research flights into winter storms in three geographic regions of North America. The characterization was designed to be supplemental to existing aircraft icing certification envelopes, given that existing envelopes do not explicitly incorporate SLD conditions. The U.S. Federal Aviation Administration is considering using the results from Cober et al. (2009) and Cober and Isaac (2012) as the basis for new certification regulations. Marwitz (2013) has suggested that the results of Cober and Isaac (2012) are deficient with respect to their application to the proposed new certification regulations, and he provided some criticisms. The purpose of this response is to address these criticisms. Marwitz (2013) suggested that the use of median volume diameter (MVD) and maximum diameter (Dmax) by Cober and Isaac (2012) as part of their characterization method is invalid because MVD and Dmax are not related to performance measurement. Cober and Isaac (2012) made no attempt to measure performance degradation of the research aircraft. Rather the intent was to collect and analyze a sufficiently large dataset to characterize icing environments that included SLD at the 99% and 99.9% levels (i.e., extreme values) so that manufacturers could subsequently determine the associated performance degradation on their instruments, aircraft components, or engines. A justification for using MVD and Dmax follows. MVD is the 50% mass diameter, and hence large MVD values (i.e., .40mm) specifically identify icing conditions that are outside the existing certifications standards and for which the majority of the mass is incorporated in drops that have higher collision efficiency (and corresponding performance degradation) with aircraft surfaces. Aircraft, instrument, and engine manufacturers use different combinations of MVD (or other drop diameter characteristics), temperature, and liquid water content (LWC) to evaluate performance losses primarily through their use in wind-tunnel, naturalicing, and numerical simulation experiments. Aircraft icing envelopes have been based in part on MVD since their inception in the 1950s. It is an industry standard to correlate the analysis of icing conditions against performance degradation, and MVD is one of the primary

Comments on “Characterization of Aircraft Icing Environments with Supercooled Large Drops for Application to Commercial Aircraft Certification”

Comments on “Characterization of Aircraft Icing Environments with Supercooled Large Drops for Application to Commercial Aircraft Certification”