Rime Ice Research Articles

Atmospheric icing measurement and online ice type recognition for aircraft utilizing optical fiber sensor and machine learning algorithms

For the detection of atmospheric icing process, an ice type recognition and thickness measurement method based on optical fiber sensor is proposed and evaluated. Finite element models based on different structures are built for the four corresponding typical ice types in the atmospheric icing environment. Finite element analysis results show the characteristics of sensor response for different ice types and the potential of real-time ice type recognition using optical fiber sensor. In the laboratory test, under the atmospheric icing conditions, 1655 sets of valid data including glazed ice, mixed ice, rime ice and frost are collected. Cascade models based on machine learning algorithms are built and evaluated using a round-robin leave-one-out method. The model realizes instant ice type recognition and thickness measurement without relying on time-domain curve information. The evaluation results show that the proposed method achieves 92.8 % ice type recognition accuracy and 0.27 mm RMSE for ice thickness measurement.

Experimental Study of Dynamic Ice Accretion Process over Rotating Aeroengine Fan Blades

An experimental campaign was conducted to study dynamic ice accretion on rotating aeroengine fan blades and evaluate the icing-induced performance degradation to the fan rotor. The experiments were performed in an icing research tunnel with a scaled spinner-fan model exposed to typical dry rime and wet glaze icing conditions. Although the accreted ice layers were found to conform well with the shapes of the fan blades under the rime icing condition, the performance of the fan rotor was found to degrade substantially due to the much rougher blade surfaces, causing up to 60% reduction in the pressure increment after 360 s of the rime icing experiment. More complicated, needlelike icicles were found to grow rapidly over the rotating spinner and fan blades under the glaze icing condition due to the combined effects of the aerodynamic forces and the centrifugal forces associated with the rotation motion. The irregular-shaped glaze ice structures were found to induce tremendous detrimental effects on the fan rotor, making the airflow depressurized, instead of pressurized, after passing the iced fan rotor. The iced spinner-fan model was always found to consume more power, regardless of rime or glaze ice structures accreted on the fan blades.

Design optimization of a blunt trailing-edge airfoil for wind turbines under rime ice conditions

A new optimization method is developed for the design of a blunt trailing-edge airfoil for wind turbines under rime ice conditions. The parametric representation of the airfoil is given using the profile integration theory and B-spline function. The rime ice shape from wind tunnel tests is fitted using a linear interpolation algorithm with equidistant and equiangular steps to preserve the same number of ice shape feature points. The blunt trailing-edge thickness and distribution ratio on the upper side of the middle arc are included in the design variables. The optimizer, based on the Bare-Bones Multi-Objective Particle Swarm Optimization (BB-MOPSO) algorithm integrated with ICEM-CFD and FLUENT software, seeks the solutions maximizing the lift coefficient and lift-drag ratio. A new airfoil NACA0012BT (with BT denoting the blunt trailing-edge) with the trailing-edge thickness of 2.2004 %c (with c denoting the chord length) and distribution ratio of 1:55.8482 is obtained, and the lift and drag coefficients, lift-drag ratios, pressure distributions, and flow characteristics are investigated using the Computational Fluid Dynamics (CFD) method. Significant improvements of the NACA0012 airfoil design are achieved in this process, confirming that the developed method constitutes a valuable tool for designing and optimizing the wind turbine airfoil operating in icing conditions.

Dynamic Mitigation Mechanisms of Rime Icing with Propagating Surface Acoustic Waves.

Ice accretion on economically valuable and strategically important surfaces poses significant challenges. Current anti-/de-icing techniques often have critical issues regarding their efficiency, convenience, long-term stability, or sustainability. As an emerging ice mitigation strategy, the thin-film surface acoustic wave (SAW) has great potentials due to its high energy efficiency and effective integration on structural surfaces. However, anti-/de-icing processes activated by SAWs involve complex interfacial evolution and phase changes, and it is crucial to understand the nature of dynamic solid–liquid–vapor phase changes and ice nucleation, growth, and melting events under SAW agitation. In this study, we systematically investigated the accretion and removal of porous rime ice from structural surfaces activated by SAWs. We found that icing and de-icing processes are strongly linked with the dynamical interfacial phase and structure changes of rime ice under SAW activation and the acousto-thermally induced localized heating that facilitate the melting of ice crystals. Subsequently, interactions of SAWs with the formed thin water layer at the ice/structure interface result in significant streaming effects that lead to further damage and melting of ice, liquid pumping, jetting, or nebulization.

Numerical Investigation of Ice Formation on a Wing with Leading-Edge Tubercles

This work numerically investigates the influence of sinusoidal leading-edge characteristics, often described as wavy leading-edge wings or wings with tubercles, on aircraft icing. Initially, the flow prediction of clean wavy wings is compared to experimental data for model validation. A series of test cases based on the experimental geometry is subsequently established with varying wave amplitudes and lengths. The icing assessment is conducted numerically using the three-dimensional PoliMIce ice accretion toolkit. Firstly, the influence of the three-dimensional flow behavior on the collection efficiency is evaluated. The simulations demonstrate that wavy leading edges with shorter wave lengths and higher wave amplitudes increase the localized impingement of super-cooled water droplets during impact. Secondly, the influence of the wavy leading-edge profile on the ice shapes is assessed for both the rime and glaze ice regime. The results show that the maximum ice thickness is in the vicinity of the wave peaks and troughs; meanwhile, the midsections of the waves have significantly lower levels of ice accretion. The future perspective of this work is to assess the potential for improving the efficiency of anti-icing and de-icing systems using wavy leading edges.

Effect of curvature on durable ice-phobic surfaces based on buckling metallic plates

Degradation in system performance due to ice accretion on curved surfaces remains a decades-old challenge. We recently reported that Buckling Elastomer-like Anti-icing Metallic Surfaces (BEAMS) exhibit a low ice adhesion strength and extreme durability in realistic icing conditions. BEAMS consist of thin, flat metal sheets suspended on strips or dots of adhesive, and this partial confinement facilitates buckling of the metal sheet, causing ice to dislodge from the surface at a low applied force. The mechanism of ice detachment from curved BEAMS has not been investigated. Here we study how curvature affects the shear ice adhesion strength of BEAMS, using both glaze- and rime-type ice at −20 °C. For glaze, it was observed that increasing the radius of curvature increased the ice adhesion strength regardless of whether the curvature was positive or negative. For rime ice a high radius of curvature, R = 17.3 mm, was used inside an icing wind tunnel. When the compliance of the material used to suspend the metallic sheet was increased, the rime ice adhesion strength was as low as τice≈3 kPa. Further, the confinement configuration of BEAMS was studied to understand its effect on lateral torsional buckling. Lateral torsional buckling altered the radius of curvature of both the suspension material and metal sheet, initiating cracks due to the unchanged curvature of the accreted ice. Accordingly, the extremely low ice adhesion strength of BEAMS, even on curved surfaces, was due to buckling instabilities either within the thin metal plates or the suspension material. Overall, BEAMS would appear to be a durable, low-ice-adhesion candidate material even for complex and curved surface geometries such as the leading edges of aircraft wings, wind turbine blades, or power transmission lines.

Influence analysis of rime icing on aerodynamic performance and output power of offshore floating wind turbine

Wind turbine blades are prone to icing under cold conditions, and the associated changes of blade airfoil geometry have a substantial impact on the aerodynamic characteristics and output power of an offshore floating wind turbine. Taking a 5 MW offshore floating wind turbine as the research object, and with consideration of marine meteorological conditions in a cold region, this study used fluid mechanics to predict icing on wind turbine blades. The influence on the aerodynamic performance of the blade airfoil by rime icing-related changes in its geometric shape was investigated, and the associated change in power production of a floating wind turbine was analyzed using blade element momentum theory. When the wind turbine blade condensed rime ice, the results showed that iced airfoil geometry was reasonably regular over a short period, and that icing was concentrated primarily in the tip area of the NACA64_A17 airfoil. The change of wind speed has a certain influence on the rime icing, and the temperature variation has little effect. Airfoil geometry change after icing had little effect on the lift coefficient (maximum decrease: ∼34%) but had greater impact on the drag coefficient (increase: 36%–200%). The power production of a wind turbine with an iced airfoil was approximately 17% lower than that of a wind turbine with a clean airfoil.

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.

Design of Capacitance and Impedance Dual-Parameters Planar Electrode Sensor for Thin Ice Detection of Aircraft Wings

An ice types recognition and ice thickness detection system was designed based on capacitance and impedance double parameters. By studying the influence of electrode structure on sensor performance based on finite element simulation, the finger electrode was selected with better performance, and a planar electrode sensor was designed suitable for wing thin ice detection. After the thin ice (2.5 mm) making experiment, the capacitance and impedance spectra of three ice types (glaze ice, rime ice and mixed ice) were obtained. Among them, capacitance can reflect the growth of ice well, and the impedance spectra of different ice types are significantly different. Therefore, a capacitance-based regression model and an impedance-based classification model were built. The results of regression model show that about 90% of the calculation error of thin ice thickness is concentrated in the range of [−0.2 mm, 0.2 mm]. Finally, a field test was conducted in the ice wind tunnel to preliminarily determine the system effectiveness.

Numerical Modeling of Atmospheric Rime Ice Accretion on an Airfoil Using an Eulerian Approach

AbstractThis paper presents an approach to numerically simulate the inherently unsteady rime ice accretion problem on a two-dimensional airfoil and elucidate the associated variations under different icing conditions. The airflow field and the water impingement on the airfoil are obtained based on an Eulerian two-phase model. A dynamic mesh strategy is employed to unsteadily account for the changes in the ice profile and its impact on the air and droplet flow by continuously reconstructing the computational grid at each time-step through smoothing and layering mechanisms. All main icing modules including the airflow field, droplet trajectory, icing thickness profile, and mesh management are fully coupled within the same computational framework without resorting to any external tools. Classical icing theory is employed to model the rime ice roughness, and it is assumed that the ice accretes in a direction normal to the airfoil surface. The governing Reynolds-averaged Navier–Stokes (RANS) conservation equations along with the energy and continuity equations are solved to produce the velocity and temperature fields. A convective film heat transfer coefficient is computed based on the surface heat flux and a recovery temperature which takes into account the dissipative heat release in the boundary layer in the vicinity of the airfoil surface. With the implemented strategy and calculating the convective heat transfer coefficient, the water film thickness is also calculated along with the ice shape. The model is validated by comparing the local collection efficiency distribution and ice shape with experimental data, and the results show that the implemented approach provides acceptable predictions of ice accretion profiles and rates.

Thermal characteristic and spatial morphology between electrode and phase changing ice during de-icing process of dielectric barrier discharge and critical behavior of the surface charge density

Dielectric barrier discharge (DBD) plasma recently has been demonstrated as an effective in situ heating methodology in anti-ice and de-ice applications of the aircraft. However, the thermal stability of this special heat source during the interactions between the plasma and the ice block may pose serious concerns. In this paper, it is found that when the ice blocks of different characteristic locations covered the DBD device with alternative current (AC) power, two different kinds of interaction processes can be resulted: First, the concentration of the heat flow through the local enhancement of the streamers between the electrode and the ice, long-lasting for the glaze ice ended with the partial evaporation of the melted ice block with larger separations, or short-lived intermittent for the rime ice until the boundary is beyond the reach. Second, sparks, very likely to be generated between the electrode and the ice block when the separation and electric field meet the transition conditions, resulting in the fast evaporation of the melted ice block and the severe aging or on-sight burning of the devices, even at the operation voltage safe for the AC-DBD plasma without ice blocks. It is emphasized that the coexistence or the number of the ice blocks of different separations does not alter such behavior. Supported by the calculation of the streamer-to-spark transition criterion, and affected by ice phase change, it is argued that the de-icing AC-DBD plasma is a strong nonlinear heat source, resulting from the surface charge accumulation, melting of the ice blocks, and the enhancement of ionization collision frequency due to the mixing of the evaporated water molecules. A new critical condition, the critical surface charge density was proposed for the initiation of spark, ρsc: Densities higher than ρsc will lead to the catastrophic spark, while the lower will lead to the selective concentration of the heat flow for the faster de-icing process. Due to the random distribution nature of the electrode-to-ice separations during the real-world practice of an AC-DBD heat source for de-icing, the existence of ρsc may be under further scrutiny and considered as a crucial factor for the stable operation of the plasma heat sources for de-icing.

Numerical Modeling of Ice Accumulation on Three-Dimensional Bridge Cables under Freezing Rain and Natural Wind Conditions

In order to accurately predict the ice accumulation on bridge cables under two typical freezing rain conditions, rime and glaze ice, this paper proposes a numerical simulation framework based on the three-dimensional Messinger theory. Two technical challenges of determining the flow direction of unfrozen water and solving three-dimensional Messinger equations are solved in this research. Based on the outflow, mass was calculated according to the three-dimensional Messinger theory, and the flow direction of unfrozen water in each cell was determined by the resultant force of air shear stress and water film gravity. To solve the three-dimensional equations, an iterative method without finding the stagnation line was introduced. The final iced geometries were determined when the inflow mass ratio was satisfied with the converge criteria. Moreover, this modified numerical model was programmed and embedded into computational fluid software. For both two typical freezing rain conditions, the effects of temperature and wind speed on iced geometries were studied. The aerodynamic characteristics and galloping instability of bridge cables with different iced geometries were also investigated. These preliminary aerodynamic simulations can provide the basis for the wind-induced vibration analysis of the whole structure.

Immersed Boundary Methodology for Multistep Ice Accretion Using a Level Set

The numerical prediction of in-flight ice accretion involves a sequential call to different modules including mesh generation, aerodynamics, droplet trajectories, wall heat transfer, ice accretion, and geometry update. Automation of this process is critical as these solvers are embedded in a time loop that is repeated several times to obtain an accurate ice shape prediction. The robustness of ice accretion tools is often limited by the difficulty of generating meshes on complex ice shapes and also by the geometry update that can exhibit overlaps in concave regions if not treated properly. An immersed boundary method combined with a level set has the potential to alleviate these issues. The objective of this paper is twofold: confirm the potential of this methodology and assess its accuracy against the usual body-fitted approach. The proposed methodology is tested on two-dimensional (2D) rime and glaze ice cases from the 1st AIAA Ice Prediction Workshop, showing good correspondence with the body-fitted approach. The new methodology also performs well for a 2D three-element airfoil configuration when a proper mesh refinement is used. The immersed boundary method combined with the level-set ice accretion provides a viable alternative to the body-fitted approach.

Three-Dimensional Numerical Simulation of Rime Ice Accumulation on Silicone Rubber Insulator and its Experimental Verification in the Natural Environment

Three-Dimensional Numerical Simulation of Rime Ice Accumulation on Silicone Rubber Insulator and its Experimental Verification in the Natural Environment

Cover Photograph

Front cover: Image of rime ice taken in calm conditions near Hangingstone Hill on Dartmoor, 21 January 2013 at 1400 utc, in cold continental air within a complex area of low pressure. (© David Moore.)image

An experimental study on mitigating dynamic ice accretion process on bridge cables with a superhydrophobic coating

An experimental study is conducted to evaluate the effectiveness of utilizing a superhydrophobic surface (SHS) coating to mitigate ice accretion on bridge cables and to characterize the resultant aerodynamic forces acting on bridge cables under different icing conditions. Two bridge cable models (i.e., a model with untreated hydrophilic surface and a model with SHS coated surface) were used for a comparative study. The dynamic ice accretion process and the resultant aerodynamic forces acting on the bridge models were found to change significantly after applying the SHS coating to treat the cable surface. Under glaze icing condition, the SHS coated cable model was found to have much narrower ice coverage, less amount of accreted ice mass, and smaller aerodynamic drag forces, in comparison to that with untreated cable surface. While the SHS coating was found to be less effective for icing mitigation under rime icing condition, the much rougher rime ice grains accumulated within the droplet direct impinging zone on the SHS coated cable surface caused a greater reduction of the aerodynamic drag forces acting on the cable model at the initial stage of the rime icing process. The acquired ice accretion images were correlated with aerodynamic force measurements for a better understanding of the underlying physics in the context of bridge cable icing mitigation.

Modeling In-Flight Ice Accretion Under Uncertain Conditions

In-flight ice accretion under parametric uncertainty is investigated. Three test cases are presented that reproduce experiments carried out at the NASA’s Glenn Icing Research Tunnel facility. A preliminary accuracy assessment, achieved by comparing numerical predictions against experimental observations, confirms the robustness and the predictiveness of the computerized icing model. Besides, sensitivity analyses highlight the variance of the targeted outputs with respect to the different uncertain inputs. In rime icing conditions, a predominant role is played by the uncertainty affecting the airfoil angle of attack, the cloud liquid water content, and the mean volume diameter of droplets. In glaze icing conditions, the sensitivity analysis shows instead that the output variability is due mainly to the ambient temperature uncertainty. Moreover, this paper exposes a challenge inherent in the approximation of the full icing model by means of standard (linear) polynomial chaos regression techniques. The complexity is related to the approximation of the model behavior in domain regions scarcely affected by ice buildup. To mitigate this issue, a nonlinear regression method is proposed and applied.

Experimental Research on the Similarity of Rime Icing on a Cylinder Rotating around Its Horizontal Axis

Ice accumulation on the blade of a wind turbine surface seriously threatens the operational safety of the turbine; therefore, the research on this problem is very important. In this paper, a new similarity criterion of icing shape for a rotational model was proposed based on the similarity criterion for translational motion models in the aviation field, and experimental studies on the similarity of the rotational model icing were carried out. To validate the similarity criterion, icing wind tunnel tests were carried out with aluminum cylinders with diameters of 40 mm and 20 mm. Key parameters for the experiment, such as wind speed, temperature, liquid water content, medium volume diameter, and test time, were selected based on the criterion. All the icing tests were carried out in a new self-designed icing wind tunnel test system based on natural low-temperature conditions. The icing shapes observed in the tests were confirmed after many repetitions. To quantitatively analyze the similarity between different sizes of ice shapes, a dimensionless method for evaluating the similarity of ice shapes of different sizes was defined based on the typical characteristics of ice shapes. The research results show that the similarity score between two sizes of ice shapes under different test conditions is 81%~90%. The accuracy and applicability of the icing shape similarity criterion were thus validated. The research results in this paper lay a theoretical and experimental foundation for exploring the icing shape similarity of a rotating model.

Rime ice growth characterized by surface acoustic wave

We propose a new theoretical method and experimental investigation to characterize the growth process of rime ice through surface acoustic waves (SAWs). The Biot theory of dual-phase porous media was employed to construct a theoretical model to describe the acoustic wave propagation in porous rime ice; the transient changes in acoustic propagation attenuation and velocity were simulated; and the icing sensing mechanism of the acoustic wave propagation attenuation (∼18 dB) and the transient change in velocity (0.8 m/s) during the icing process was obtained. A 177.5 MHz waveguide type SAW micro–nano-device with an SU8/ST-90°X quartz multilayer composite film structure and a microfluidic cavity on the top of the acoustic device were designed and fabricated, and the transient attenuation in the growth of rime ice was evaluated experimentally. The experimental results indicated that the appearance of rime ice can be monitored accurately by utilizing the transient changes in acoustic wave velocity and attenuation. Therefore, the acoustic method can aid in the early warning of the development status of rime ice.

A Wind Tunnel Experimental Study of Icing on NACA0012 Aircraft Airfoil with Silicon Compounds Modified Polyurethane Coatings.

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.