Search Results (15)

Supercooled droplets that collide with the windward surface of the aircraft will freeze, which results in icing on both stationary and rotating components. The ice accretion on rotating surfaces is physically different from those on stationary components. The icing phenomenon on the surface of a rotating intake cone was investigated in an icing wind tunnel, and the influence of icing conditions of supercooled large droplets on the experimental results was analyzed. In the experiments, the ice accretion of the intake cone was studied under various conditions, including rotational speed, wind speed, icing temperature, droplet diameter, and icing time. The ice shape on the surface of the intake cone is notably unique due to the influence of centrifugal force, which produces a longer feather-like ice structure that has a significant effect on the performance of the engine. The process of ice shedding caused by centrifugal force is also critical for the engine anti-icing process. Therefore, it is essential to study the icing characteristics under rotational effects during the design and verification process of engine anti-icing systems. Full article

With the advancement of science and technology, wind power generation has been widely adopted globally. However, ice accretion severely limits the operational efficiency and structural safety of wind turbines in cold regions, while existing research primarily focuses on the impact of supercooled droplets on blade icing, the influence of ice crystals in cold environments on the blade icing process has been largely overlooked. This study systematically simulated the accretion of ice crystals and supercooled droplets under clear ice conditions. It evaluated the effects of various ice crystal parameters on the icing process using Fensap-Ice, which is an advanced icing simulation tool. The results indicate that ice accretion, driven by the combined action of ice crystals and supercooled droplets, weakened ice corners, making the ice shape smoother and fuller. When the angle of attack of the ice-covered airfoil exceeded 15°, a separating vortex formed on the suction side of the blade, leading to a reduction in the lift coefficient. The findings of this study highlight the critical role of ice crystals in the icing process and provide a scientific foundation for understanding the icing mechanism under complex meteorological conditions. Full article

Computational results of aircraft icing and predictions of ice shape are not only determined by the solutions of air-supercooled droplet two-phase flow and icing thermodynamic models of surface water film, but are also influenced by the growth mode of the ice layer. Two ice growth modes were established in a two-dimensional (2D) icing process simulation framework to calculate the ice thickness and ice shape, depending on whether surface deformation of the icing process was considered. Ice accretion simulations were performed with the two ice growth modes for an NACA0012 airfoil under rime ice and mixed ice conditions, and the results of ice amount, ice thickness, and ice shape were compared and analyzed. Under the same amount of ice formation, the ice thickness and ice shape obtained using different ice growth modes vary. The ice thickness and the ice shape size are relatively large without considering surface deformation, whereas the results with growth correction show a certain degree of reduction, which is more noticeable around the leading edge and the ice horns. However, the degrees of difference in ice thickness and ice shape are not the same, and the deviation in ice thickness is more obvious. Furthermore, the ice thickness and ice shape obtained using the ice growth correction mode are more consistent with experimental data and commercial software results, verifying the accuracy of the ice simulation method and the necessity of considering ice surface deformation. This paper is an essential guide for understanding the icing mechanism and accurately predicting two-dimensional ice shape. Full article

With the rapid development of the general aviation industry in China, the influence of high-impact aeronautical weather events, such as aircraft icing, on flight safety has become more and more prominent. On 1 March 2021, an aircraft conducting weather modification operations crashed over Ji’an City, due to severe icing. Using multi-source meteorological observations and atmospheric numerical simulations, we analyzed the meteorological causes of this icing accident. The results indicate that a cold front formed in northwestern China and then moved southward, which is the main weather system in the icing area. Based on the icing index, we conducted an analysis of the temperature, relative humidity, cloud liquid water path, effective particle radius, and vertical flow field, it was found that aircraft icing occurred behind the ground front, where warm-moist airflows rose along the front to result in a rapid increase of water vapor in 600–500 hPa. The increase of water vapor, in conjunction with low temperature, led to the formation of a cold stratiform cloud system. In this cloud system, there were a large number of large cloud droplets. In addition, the frontal inversion increased the atmospheric stability, allowing cloud droplets to accumulate in the low-temperature region and forming meteorological conditions conducive to icing. The Weather Research and Forecasting model was employed to provide a detailed description of the formation process of the atmospheric conditions conducive to icing, such as the uplifting motion along the front and supercooled water. Based on a real case, we investigated the formation process of icing-inducing meteorological conditions under the influence of a front in detail in this study and verified the capability of a numerical model to simulate the meteorological environment of frontal icing, in order to provide a valuable reference for meteorological early warnings and forecasts for general aviation. Full article

This paper aims to investigate phenomena that are related to SLD conditions in aircraft icing including gravity, non-spherical droplets, droplet breakup and droplet splash using an in-house computational tool. The in-house computational tool involves four modules for the computation of the flow field, droplet trajectories, convective heat transfer coefficients and ice growth rates. Droplet trajectories are computed using the Lagrangian approach, while ice growth rates are calculated using the Extended Messinger Model. In order to extend the capabilities of the computational tool to include SLD-related phenomena, empirical models that represent SLD physics are implemented. An extensive study has been performed using MS317 and NACA0012 airfoils, that aims to bring out the relative importance of the SLD-related phenomena, particularly on water catch rates and ice formation. The results of the study pointed to some important new conclusions that may shed further light on SLD physics. For example, multiple droplet breakup has been observed under certain conditions and droplet breakup emerged as a more important effect than previously reported. It was also seen that droplet splash influences both the energy balance and the mass balance in the icing process, which has been shown to have an important effect on the final ice shape, especially for very large droplets. Full article

Many applications in the life science and food industries require (semi-)crystalline oil-in-water (O/W) dispersions. Unfortunately, high supercooling and, thus, low temperatures are often needed to induce the crystallization of droplets. As low molecular weight emulsifiers (LMWEs) are able to act as nucleation templates, they might help to decrease the required level of supercooling. Furthermore, proteins and LMWEs are frequently co-formulated to improve the colloidal stability of emulsions and dispersions. Hence, choosing a suitable protein and LMWE mixture would allow for achieving specific product properties for controlling the solid fat content (SFC) and take advantage of the stabilization mechanisms of both emulsifiers. Therefore, this study focuses on the impact of the co-existence of β-lactoglobulin (β-lg) and phospholipids (PLs) LMWEs on the SFC of triglyceride (TAG) droplets at isothermal conditions using a thermo-optical method. When β-lg alone was used as an emulsifier, a maximum SFC of 80% was obtained at a supercooling of 32 K and 42 K for trilaurin and tripalmitin, respectively. The SFC could be increased to 100% using a PL containing saturated fatty acids (FAs) and a small hydrophilic headgroup. At the same supercooling, a PL containing saturated FAs and a large hydrophilic headgroup led to a maximum SFC of 80%. At lower supercooling, the SFC was reduced with this PL by 10% compared to β-lg alone. In addition, when the PLs had more time to adsorb and rearrange with ß-lg at the interface, even lower SFCs were observed compared to cooling directly after emulsification. Full article

Slippery liquid-infused porous surfaces (SLIPS) have received growing attention as promising icephobic materials. In this study, SLIPS were prepared on aluminum alloys by combining anodization and infusion of common silicone oil. An SLIPS with low ice-adhesion strength (6 kPa) was obtained by optimizing the anodizing time parameters (10 min). In addition, the frosting process and freezing of water droplets on the as-prepared SLIPS at −10 °C were delayed for 2000 s and 4800 s, respectively. Simultaneously, the as-prepared SLIPS also exhibited excellent anti-icing performance in glaze ice, since the supercooled water drips/ice slipped from the surface. The ice weight of the as-prepared SLIPS was significantly lower than that of the bare aluminum surface and the anti-icing-fluid-coated aluminum surface, which was reduced by 38.2%–63.6% compared with the bare aluminum surface. The ice weight increased with decreased temperature and inclination angle. This work proposes a method suitable for large-area preparation of SLIPS that achieves excellent anti-icing performance and significantly reduces the weight of glaze ice. Full article

In order to compare and analyze the similarities and differences between normal droplet icing shapes and supercooled large droplet icing shapes, SADRI carried out normal droplet and supercooled large droplet icing wind tunnel tests in the NRC−AIWT icing wind tunnel. Taking the typical glaze ice in normal droplet icing conditions as the reference, the freezing drizzle and freezing rain icing tests under the supercooled large droplet conditions were carried out. The test results show that compared with normal droplets, the ice horn height of supercooled large droplets decreases with the increase in droplet particle size, and even the ice horn characteristics are not obvious when the icing condition is freezing rain. At the same time, the range and height of rough element ice shape after the main ice horn of supercooled large droplets are significantly larger and higher than those of the normal droplets, while the difference in the rough element in different supercooled large droplet icing conditions is small. Full article

A 3D icing simulation code is developed in the open-source CFD toolbox OpenFOAM. A hybrid Cartesian/body-fitted meshing method is used to generate high-quality meshes around complex ice shapes. Steady-state 3D Reynolds-averaged Navier-Stokes (RANS) equations are solved to provide the ensemble-averaged flow around the airfoil. Considering the multi-scale nature of droplet size distribution, and more importantly, to represent the less uniform nature of the Super-cooled Large Droplets (SLD), two droplet tracking methods are realized: the Eulerian method is used to track the small-size droplets (below 50 $\mathsf{\mu }$m) for the sake of efficiency; the Lagrangian method with random sampling is used to track the large droplets (above 50 $\mathsf{\mu }$m); the heat transfer of the surface overflow is solved on a virtual surface mesh; the ice accumulation is estimated via the Myers model; finally, the final ice shape is predicted by time marching. Limited by the availability of experimental data, validations are performed on 3D simulations of 2D geometries using the Eulerian and Lagrangian methods, respectively. The code proves to be feasible and accurate enough in predicting ice shapes. Finally, an icing simulation result of the M6 wing is presented to illustrate the full 3D capability. Full article

This article describes the development of a machine learning (ML)-based algorithm for snowfall retrieval (Snow retrievaL ALgorithm fOr gpM–Cross Track, SLALOM-CT), exploiting ATMS radiometer measurements and using the CloudSat CPR snowfall products as references. During a preliminary analysis, different ML techniques (tree-based algorithms, shallow and convolutional neural networks—NNs) were intercompared. A large dataset (three years) of coincident observations from CPR and ATMS was used for training and testing the different techniques. The SLALOM-CT algorithm is based on four independent modules for the detection of snowfall and supercooled droplets, and for the estimation of snow water path and snowfall rate. Each module was designed by choosing the best-performing ML approach through model selection and optimization. While a convolutional NN was the most accurate for the snowfall detection module, a shallow NN was selected for all other modules. SLALOM-CT showed a high degree of consistency with CPR. Moreover, the results were almost independent of the background surface categorization and the observation angle. The reliability of the SLALOM-CT estimates was also highlighted by the good results obtained from a direct comparison with a reference algorithm (GPROF). Full article

Icing is a hazard which is important for the aerospace industry and which has grown over the last few years. Developing sensors that can detect the existence not only of standard icing conditions with typically small droplet size, but also of Supercooled Large Droplet (SLD) conditions is one of the most important aims in order to minimize icing hazards in the near future. In the present paper a study of the Fiber Bragg Grating Sensors’ (FBGSs) performance as a flight icing detection system that predicts the conditions of an icing cloud is carried out. The test matrix was performed in the INTA Icing Wind Tunnel (IWT) with several icing conditions including SLD. Two optic fibers with 16 FBGS in total were integrated in the lower and upper surface of an airfoil to measure the temperature all over the chord. The results are compared with a Messinger heat and mass balance model and the measurements of the FBGS are used to predict the Liquid Water Content (LWC) and Ice Accretion Rate (IAR). Finally, the results are evaluated and a sensor assessment is made. A good correlation was observed between theoretical calculations and test results obtained with the FBGS in the IWT tests. FBGS proved to detect the beginning and end of ice accretion, LWC and IAR quickly and with good precision. Full article

The homogeneous freezing of water is important in the formation of ice in clouds, but there remains a great deal of variability in the representation of the homogeneous freezing of water in the literature. The development of new instrumentation, such as droplet microfluidic platforms, may help to constrain our understanding of the kinetics of homogeneous freezing via the analysis of monodisperse, size-selected water droplets in temporally and spatially controlled environments. Here, we evaluate droplet freezing data obtained using the Lab-on-a-Chip Nucleation by Immersed Particle Instrument (LOC-NIPI), in which droplets are generated and frozen in continuous flow. This high-throughput method was used to analyse over 16,000 water droplets (86 μm diameter) across three experimental runs, generating data with high precision and reproducibility that has largely been unrepresented in the microfluidic literature. Using this data, a new LOC-NIPI parameterisation of the volume nucleation rate coefficient (J_V(T)) was determined in the temperature region of −35.1 to −36.9 °C, covering a greater J_V(T) compared to most other microfluidic techniques thanks to the number of droplets analysed. Comparison to recent theory suggests inconsistencies in the theoretical representation, further implying that microfluidics could be used to inform on changes to parameterisations. By applying classical nucleation theory (CNT) to our J_V(T) data, we have gone a step further than other microfluidic homogeneous freezing examples by calculating the stacking-disordered ice–supercooled water interfacial energy, estimated to be 22.5 ± 0.7 mJ m⁻², again finding inconsistencies when compared to theoretical predictions. Further, we briefly review and compile all available microfluidic homogeneous freezing data in the literature, finding that the LOC-NIPI and other microfluidically generated data compare well with commonly used non-microfluidic datasets, but have generally been obtained with greater ease and with higher numbers of monodisperse droplets. Full article

Ice accretion is a phenomenon whereby super-cooled water droplets impinge and accrete on wall surfaces. It is well known that the icing may cause severe accidents via the deformation of airfoil shape and the shedding of the growing adhered ice. To prevent ice accretion, electro-thermal heaters have recently been implemented as a de- and anti-icing device for aircraft wings. In this study, an icing simulation method for a two-dimensional airfoil with a heating surface was developed by modifying the extended Messinger model. The main modification is the computation of heat transfer from the airfoil wall and the run-back water temperature achieved by the heater. A numerical simulation is conducted based on an Euler–Lagrange method: a flow field around the airfoil is computed by an Eulerian method and droplet trajectories are computed by a Lagrangian method. The wall temperature distribution was validated by experiment. The results of the numerical and practical experiments were in reasonable agreement. The ice shape and aerodynamic performance of a NACA 0012 airfoil with a heater on the leading-edge surface were computed. The heating area changed from 1% to 10% of the chord length with a four-degree angle of attack. The simulation results reveal that the lift coefficient varies significantly with the heating area: when the heating area was 1.0% of the chord length, the lift coefficient was improved by up to 15%, owing to the flow separation instigated by the ice edge; increasing the heating area, the lift coefficient deteriorated, because the suction peak on the suction surface was attenuated by the ice formed. When the heating area exceeded 4.0% of the chord length, the lift coefficient recovered by up to 4%, because the large ice near the heater vanished. In contrast, the drag coefficient gradually decreased as the heating area increased. The present simulation method using the modified extended Messinger model is more suitable for de-icing simulations of both rime and glaze ice conditions, because it reproduces the thin ice layer formed behind the heater due to the runback phenomenon. Full article

Icing simulations involving super-cooled large droplets (SLDs) on a NACA0012 airfoil and a commercial axial fan were performed considering the characteristic behavior of SLD icing (i.e., splash-bounce, deformation, and breakup). The simulations were performed considering weak coupling between flow field and droplet motion. The flow field was computed using the Eulerian method, wherein the droplet motion was simulated via the Lagrangian method. To represent the ice shape, an extended Messinger model was used for thermodynamic computation. The ice shape and collection efficiency of the NACA0012 airfoil derived using the icing simulation exhibited a reasonable agreement with the existing experimental data. The icing simulation results for the axial fan, in terms of distribution of ice on the blade and its influence on the flow field, indicated that flow separation occurred, and the mass flow rate of the flow passage decreased. Moreover, the splash and bounce phenomena considerably influenced the icing process; however, the effect of the deformation and breakup phenomena was negligibly small. In terms of the effect of the SLDs on the icing phenomena, it was noted that, with the decrease in the SLD temperature (from −5 °C to −15 °C), the number of adhering SLDs increased, whereas the number of splashing and bouncing SLDs decreased. Full article

In the present work, an investigation of stagnation flow imposed on a supercooled water drop in cold environmental conditions was carried out at various air velocities ranging from 0 (i.e., still air) to 10 m/s along with temperature spanning from −10 to −30 °C. The net effect of air flow on the impacting water droplet was investigated by controlling the droplet impact velocity to make it similar with and without air flow. In cold atmospheric conditions with temperatures as low as −30 °C, due to the large increase of both internal and contact line viscosity combined with the presence of ice nucleation mechanisms, supercooled water droplet wetting behavior was systematically affected. Instantaneous pinning for hydrophilic and hydrophobic surfaces was observed when the spread drop reached the maximum spreading diameter (i.e., no recoiling phase). Nevertheless, superhydrophobic surfaces showed a great repellency (e.g., contact time reduction up to 30% where air velocity was increased up to 10 m/s) at temperatures above the critical temperature of heterogeneous ice nucleation (i.e., −24 °C). However, the freezing line of the impacting water droplet was extended up to 2-fold at air velocity up to 10 m/s where substrate temperature was maintained below the aforementioned critical temperature (e.g., −30 °C). Full article