Supercooled Large Droplet Research Articles

Unsteady numerical simulations of aircraft icing based on the dynamic grid method

In this study, an unsteady numerical simulation method based on dynamic grids was established to solve unsteady aircraft icing processes. The dual-time step method was used to achieve the time advancement of the transient airflow and droplets fields. The droplets trajectory was calculated using the Euler method, which incorporates a supercooled large droplets model. The transient evolution of the water film and ice layer on the substrate surface was considered in the icing thermodynamic model. The accuracy of the unsteady method for ice-shape prediction was verified via comparison and analysis of numerical examples. Additionally, the rime and glaze ice formation processes were explored, and the coupling effects of ice horn growth and the air convective heat transfer coefficient, water collection coefficient, and water film flow on the substrate surface were studied. The ice shapes calculated by unsteady and quasi-steady methods were compared. The results indicated that the latter predicts a larger icing range than the former. Moreover, there may be more obvious distinctions between these two methods in predicting glaze ice.

Modeling of Supercooled Large Droplet Physics in Aircraft Icing

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.

Numerical and experimental investigation of the supercooled large droplets icing of rotating spinner

The icing of aero-engine rotating components is more complex than traditional aircraft icing. A three-dimensional numerical method was developed based on the Eulerian method to study the supercooled large droplets icing of a rotating spinner. Typical dynamic behaviours of supercooled large droplets, such as deformation, breakup, rebound, and splashing, were considered. An icing thermodynamic model applicable to a rotating spinner was established by considering the effects of pressure gradient, air shear force, and centrifugal force on the flow of the water film. Meanwhile, an ice wind tunnel experiment on supercooled large droplets icing of a rotating spinner was carried out. The results showed that the maximum relative deviation of the simulated icing thickness at the cone tip is no more than 15% compared with the experimental result, and the icing thickness on the surface of the rotating spinner is basically consistent with the experimental result. Based on the three-dimensional numerical method developed in this study, the effects of the rotational speed, inflow velocity, and inflow temperature on the supercooled large droplets icing of a rotating spinner were investigated. As the rotational speed increases, the rebound and splashing of supercooled large droplets becomes more obvious, leading to an increase in the mass loss coefficient and a decrease in the collected mass of water droplets on the surface of the rotating spinner. Consequently, the icing thickness at the tail of the rotating spinner decreases with an increase in the rotational speed. Since the liquid water content in the environment is relatively low, water droplets freeze immediately after impacting the surface of the rotating spinner and rime ice is usually formed. When the inflow temperature is relatively high, overflow water exists and glaze ice is formed near the tip of the rotating spinner. The findings of this study can provide valuable support for the design and verification of anti-icing systems for aero-engine rotating spinner.

Supercooled large droplet size distribution effects on airfoil icing: A numerical investigation based on a new coupled Eulerian method

Supercooled large droplets (SLDs) under natural icing conditions have the characteristics of easy deformation in motion and easy splashing on impact, and a bimodal droplet size distribution that has received less attention. The modified form of the Rosin-Rammler function was improved to achieve a more accurate nonlinear fitting of the SLD distribution curve. The droplet size distribution was divided into non-equipartition continuous multiple components. The drag source term of each component was coupled with the overall droplet size distribution, and the Eulerian equations of each component of SLDs were solved simultaneously. A new coupled Eulerian method for non-equipartition continuous multi-size droplets was proposed to simulate the impact characteristics of SLDs, and the SLD collection coefficients were validated. Effects of the ratio between the number of large and small droplet components and the number of all components on the simulation results were investigated to select a better combination based on stable convergence calculation steps and the calculation time. This new method was added to the multi-step icing numerical method, and the accuracy and robustness of the method in icing shape prediction were verified based on the freezing drizzle, median volume diameter < 40 μm (FZDZ, MVD < 40 μm) icing condition. Airfoil icing characteristics based on the bimodal and monomodal distribution were compared, and the icing shapes at the leading edge were similar. Still, the upper and lower limits of the icing shapes with the bimodal distribution were nearer to the trailing edge and the ice layer was thicker there.

An overview of icing scaling parameters for supercooled large drop icing conditions in icing wind tunnels

Aircraft icing is a serious threat to flight safety, especially the abnormal ice accumulation on the wing surface under the icing conditions of supercooled large droplets (SLD). Icing wind tunnel test is one of the main means of conducting research on aircraft icing, and the icing scaling law is the theoretical basis for selecting the similarity of characteristic parameters. In order to deeply understand the problems related to icing similarity in icing wind tunnel test under SLD icing conditions, the test capabilities on SLD icing conditions for the existing ice wind tunnel and the common similar parameter scaling methods were reviewed. The icing similarity transformation of SLD icing test was emphasized and the advantages, disadvantages, and applicability of each icing scaling law were analyzed. It can provide some references for the SLD icing wind tunnel test for large civil aircraft.

Numerical Investigation of Supercooled Large Droplets Impingement Characteristics of the Rotating Spinner

Aircraft engine icing caused by supercooled large droplets (SLD) poses a significant threat to flight safety. In this paper, the SLD impingement characteristics of the rotating spinner were investigated using FLUENT UDS and the governing equations for water droplet motion were solved based on the Eulerian method. The droplet breakup was simulated using the number density equation, while the droplet rebound and splashing were simulated using a semiempirical model. The effects of rotational speed, droplet diameter, and inflow velocity on the SLD impingement characteristics of the rotating spinner were studied. Some new valuable insights have been found for the SLD impingement. The results indicated that as the rotational speed increases, the local collection efficiency of the rotating spinner decreases. Higher rotational speed results in reduced droplet impingement angle and stronger droplet rebound and splashing. For the droplets with diameters smaller than 111 μm, the local collection efficiency increases with the increase of the droplet diameter. However, when the droplet diameter exceeds 111 μm, the local collection efficiency decreases near the leading edge of the rotating spinner. Additionally, the local collection efficiency decreases as the inflow velocity increases near the leading edge of the rotating spinner. However, higher inflow velocities lead to larger droplet impingement angles, resulting in higher local collection efficiency near the tail of the rotating spinner. The critical impingement angle increases with the increase of the inflow velocity, leading to a more pronounced rebound and splashing of SLD. The research in this paper provides useful help for ice shape prediction and anti-icing system design of rotating spinner in SLD environment.

The choice of an anti-icing system to expand the possibilities of using the aircraft in instrumental meteorological conditions

This article provides a comprehensive overview of past studies of aircraft icing. Special attention is paid to the following aspects. First, the causes, types, severity and natural parameters of aircraft icing are introduced. Then the various effects of icing on the aerodynamic characteristics of the aircraft, stability, controllability, as well as existing evaluation methods are generalized and analyzed. The following is a simple introduction to the recent problem of icing with supercooled large droplets, and whose nature is carefully described in the article (SLD). Finally, a series of aviation accidents that have occurred in recent years due to icing is analyzed. Previous lessons should be adopted and disseminated by subsequent generations in order to avoid accidents due to icing of aircraft. Based on the consideration of such a wide range of issues related to icing, ways to prevent it using various methods and devices are considered, and the effectiveness of such methods to prevent icing of specific aircraft units is compared.

Research on Icing Classification Method Based on Wind Tunnel Test with Double Impact Surface Probe

Facing supercooled large water droplet environment, an effective ice detection method is a prerequisite to implement the avoidance strategy and get out of the icing environment of SLD as soon as possible. Fiber-optic icing sensors were arranged on the double impact surface probe. The probe was used for icing wind tunnel test. Different machine learning algorithms were used to establish the classification method of icing conditions based on multi-sensor ice thickness information fusion. An appropriate algorithm was selected for the classification method to detect icing conditions. The icing classification method based on SVM could effectively distinguish the conventional water droplet icing condition from the SLD icing condition, and it has significant potential on aviation industry application.

Numerical analysis of impingement characteristics of supercooled large droplets on the surface of a rotating hood

The authors of this study numerically analyze the characteristics of impingement of supercooled large droplets on the surface of the rotating hood of an aircraft. We use the secondary development function of Fluent software to first compare the prevalent models of impinging supercooled large droplets and then develop a modified model to numerically simulate their characteristics of impingement on the surface of a rotating hood in order to examine the effects of the diameter of the droplets, the speed of rotation, and the corresponding velocity of inflow on them. The results showed that the efficiency of the loss of mass of the droplets caused by their splashing and rebounding was low on the top of the cone, while the efficiency of local droplet collection was the highest. The efficiency of mass loss quickly increased, while that of droplet collection sharply decreased in the area of transition from the top to the side. The efficiencies of mass loss and droplet collection were nearly constant on the side of the cone, while that of the latter decreased to zero on the tail of the cone. When the median volumetric diameter of the droplets was increased from 79 to 250 µm, the efficiency of the loss of mass increased by about 15% on the side of the cone, but that of local droplet collection changed only slightly. The efficiency of the loss of mass decreased by about 20%, while that of local droplet collection increased by about 2.6% on the top of the cone under this condition. When the speed of rotation was increased from 1200 to 4300 r/min and the corresponding velocity of inflow was increased from 30 to 140 m/s, the efficiency of mass loss increased by about 15% on the side of the cone, while that of local droplet collection changed little. The efficiency of mass loss on the top of the cone decreased by about 37.5%, while that of local droplet collection increased by about 8% in this case.

Lagrangian and Eulerian algorithms for water droplets in in-flight ice accretion

A particle tracking framework for the computation of the collection efficiency for in-flight ice accretion is presented. Algorithms for the computation of the collection efficiency are presented for both Lagrangian and Eulerian descriptions of the droplets equations. Strengths and weaknesses of each method are analyzed and possible solutions are described and implemented. For the Lagrangian solver, a method for automatic resolution adaptation is introduced, and a strategy for exploiting parallelism is described. In the Eulerian frame a scheme is presented for the solution of the equations on unstructured 3D grids using a relaxation approach. An hybrid Lagrangian Eulerian approach for the computation of the collection efficiency is also introduced which is relevant for Super-cooled Large Droplet condition. All presented algorithms are thoroughly verified, and a comprehensive validation is performed.

A dendritic freezing model for in-flight supercooled large droplets impingement and solidification

Supercooled large droplets (SLD) solidification is a complex multi-physics process of great importance for assessing in-flight icing problems. In this work, a multiphase smoothed particle hydrodynamics (SPH) formulation of SLD impingement and solidification is further enriched by incorporating a freezing model for dendrites growth. The solver is validated against available experimental data of SLD impingement on ice surfaces at low speeds and then applied to test cases with various supercooling degrees and impact speeds to explore their effects on residual ice layers. This work completes a comprehensive toolset for parametric studies of single SLD impingement and solidification and paves the way for macroscopic models that can enrich in-flight icing CFD codes.

Quasi-Steady Simulation of Glaze Ice Accretion and Heat Transfer in the Supercooled Large Droplet Regime in Atmospheric Turbulent Air Flow

Abstract To avoid the use of a computationally intensive full unsteady simulation while providing an accurate solution, a quasi-steady simulation has been performed to study glaze and mixed ice accretion in the supercooled large droplet (SLD) regime in turbulent flow of atmospheric air. We have attempted to find the minimum time-step necessary to adequately simulate the icing process on an airfoil surface. Based on node displacement, a mesh morphing scheme has been adopted in the computations to account for the moving boundaries that are caused by the continuous ice buildup. We have modeled ice accretion on an airfoil surface for a time period of 232 s using several time steps. At each time-step we solved the steady-state conservation equations for the air and droplet phases and then used the results as initial conditions for the next time position. The magnitude of the time-step ranged from a least accurate two-shot simulation (where the time-step is 116 s) to a most accurate 2320-shot simulation (where the time-step is 0.1 s). In-between these two extreme time steps, we have performed a three-shot simulation (where the time-step is 77.33 s), a four-shot simulation (where the time-step is 58 s), a six-shot simulation (where the time-step is 38.67 s), a 46-shot simulation (where the time-step is 5 s), and a 232-shot simulation (where the time-step is 1 s). We have done so to find out the degree of accuracy (or inaccuracy) of the multishot simulation approach and to find out the appropriate time-step needed for a successful and valid quasi-steady simulation. A valid quasi-steady simulation needs to use a time-step that is small enough to reproduce the full time-dependent solution within a very small error band. We have found that both the 1 s and the 0.1 s time steps produce virtually identical results. This is the primary litmus test that proves the validity of the quasi-steady-state assumption. The results adopted in this paper are thus all based on the more conservative 0.1 s time-step. In the process of performing the simulations, remeshing was required in order to maintain the grid density in zones of high curvature to be able to capture the full physics in those zones. After successfully modeling glaze ice accretion over the airfoil surface using the 0.1 s quasi-steady simulation approach, the effects of supercooled large droplets (SLDs) impacting the surface have been examined and presented in terms of the variation of the local collection efficiency, the water film thickness, and the heat transfer rate. Examination of the variation of the angle that the ice horn makes with the airfoil chord line demonstrated a 20% improvement in angle prediction when the time-step is reduced from 116 s to 0.1 s. The analysis also reveals a 12% or 8.5% increase in the maximum collection efficiency, βmax, depending on whether the value of the liquid water content (LWC) has been doubled from 0.5 g/m3 to 1 g/m3, or the value of the freestream velocity has been doubled from 75 m/s to 150 m/s, respectively. Because of the need to monitor the local collection efficiency and convective heat fluxes at each shot (regardless of the number of shots employed), the approach adopted here was found to be effective in successively and successfully reproducing the curvature of the glaze ice horn.

Icing wind tunnel measurements of supercooled large droplets using the 12 mm total water content cone of the Nevzorov probe

Abstract. Supercooled large droplet (SLD) icing can occur behind the protected surfaces of an aircraft and create severe aerodynamic disturbances, which represent a safety hazard for aviation. Liquid water content (LWC) measurements in icing conditions that contain SLDs require instruments that are able to sample unimodal and bimodal droplet size distributions with droplet diameters from 2 to 2000 µm. No standardized detection method exists for this task. A candidate instrument, which is currently used in icing wind tunnel (IWT) research, is the Nevzorov probe. In addition to the standard 8 mm total water content (TWC) collector cone, a novel instrument version also features a 12 mm diameter cone, which might be advantageous for collecting the large droplets characteristic of SLD conditions. In the scope of the two EU projects, SENSors and certifiable hybrid architectures for safer aviation in ICing Environment (SENS4ICE) and ICE GENESIS, we performed measurement campaigns in SLD icing conditions in IWTs in Germany, Austria and the USA. We obtained a comprehensive data set of measurements from the LWC sensor, the 8 mm cone sensor and the 12 mm cone sensor of the Nevzorov probe, and from the tunnel reference instrumentation. In combination with measurements of the particle size distribution, we experimentally derive a collision efficiency curve that is based on a suitable functional form for the new 12 mm cone for median volume diameters (MVDs) between 12 and 58 µm and wind tunnel speeds from 40 to 85 m s−1. Knowledge of this curve allows us to correct the LWC measurements of the 12 mm cone (LWC12) in particular for the inevitably high decrease in collision efficiency for small droplet diameters. In unimodal SLD conditions, with MVDs between 128 and 720 µm, LWC12 generally agrees within ±20 % with the tunnel LWC reference values from a WCM-2000 and an isokinetic probe. An increase in the difference between LWC12 and the WCM-2000 measurements at larger MVDs indicates better droplet collection properties of the 12 mm cone. Similarly, the favorable detector dimensions of the 12 mm cone explain a 7 % enhanced detection efficiency compared to the 8 mm cone; however this difference falls within the instrumental uncertainties. Data collected in various bimodal SLD conditions with MVDs between 16 and 534 µm and LWCs between 0.22 and 0.72 g m−3 also show an agreement within ±20 % between LWC12 and the tunnel LWC, which demonstrates the suitability of the Nevzorov sensor head with the 12 mm cone for measurements of LWC in Appendix O icing conditions.

Contrast Icing Wind Tunnel Tests between Normal Droplets and Supercooled Large Droplets

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.

Conditions favorable for secondary ice production in Arctic mixed-phase clouds

Abstract. The Arctic is very susceptible to climate change and thus is warming much faster than the rest of the world. Clouds influence terrestrial and solar radiative fluxes and thereby impact the amplified Arctic warming. The partitioning of thermodynamic phases (i.e., ice crystals and water droplets) within mixed-phase clouds (MPCs) especially influences their radiative properties. However, the processes responsible for ice crystal formation remain only partially characterized. In particular, so-called secondary ice production (SIP) processes, which create supplementary ice crystals from primary ice crystals and the environmental conditions that they occur in, are poorly understood. The microphysical properties of Arctic MPCs were measured during the Ny-Ålesund AeroSol Cloud ExperimENT (NASCENT) campaign to obtain a better understanding of the atmospheric conditions favorable for the occurrence of SIP processes. To this aim, the in situ cloud microphysical properties retrieved by a holographic cloud imager mounted on a tethered balloon system were complemented by ground-based remote sensing and ice-nucleating particle measurements. During the 6 d investigated in this study, SIP occurred during about 40 % of the in-cloud measurements, and high SIP events with number concentrations larger than 10 L−1 of small pristine ice crystals occurred in 4 % of the in-cloud measurements. This demonstrates the role of SIP for Arctic MPCs. The highest concentrations of small pristine ice crystals were produced at temperatures between −5 and −3 ∘C and were related to the occurrence of supercooled large droplets freezing upon collision with ice crystals. This suggests that a large fraction of ice crystals in Arctic MPCs are produced via the droplet-shattering mechanism. From evaluating the ice crystal images, we could identify ice–ice collision as a second SIP mechanism that dominated when fragile ice crystals were observed. Moreover, SIP occurred over a large temperature range and was observed in up to 80 % of the measurements down to −24 ∘C due to the occurrence of ice–ice collisions. This emphasizes the importance of SIP at temperatures below −8 ∘C, which are currently not accounted for in most numerical weather models. Although ice-nucleating particles may be necessary for the initial freezing of water droplets, the ice crystal number concentration is frequently determined by secondary production mechanisms.

Fiber Bragg Grating Sensors ice detection: Methodologies and performance

New Researches have been done recently in order to create and adapt new systems to the recent Appendix O FAR 25 Aeronautical aircraft icing regulations. One important issue are the Supercooled Large Droplets (SLD) that are an important hazard in many cases. Novel sensor technologies for aircraft are being developed in order to assess the ice severity and to discriminate between large size droplets and small size droplets ice accretions. The European SENS4ICE project gives founding for the research and development of several aeronautical ice detection systems that can discriminate between Appendix C and Appendix O conditions. In the present paper, the strengths and weaknesses of the Fiber Optic ice Detector (FOD) developed by INTA are discussed using a test matrix from the Canadian National Research Council (NRC). The FOD has presented good performance at the NRC ice wind tunnel tests in the ice detection time, detecting ice in most cases earlier than required by the actual standard (ED-103). Its lightness, low intrusiveness and small size, makes the FOD ideal for aeronautical applications. It measures indirectly the icing cloud characteristics, such as the liquid water content (LWC) and the ice accretion rate, so only an approximate severity assessment could be done. • FBG sensors are useful for fast detection. • The Optic Fiber sensors can estimate the icing conditions in rime conditions • The optic fiber sensor can provide of information about the type of ice and its location

Development of a 3D Eulerian/Lagrangian Aircraft Icing Simulation Solver Based on OpenFOAM

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 m) for the sake of efficiency; the Lagrangian method with random sampling is used to track the large droplets (above 50 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.

Impingement and splashing of a supercooled large droplet on a freezing water film

In the present study, we report for the first time the detailed dynamic processes of a supercooled large droplet (SLD) impacting on a freezing water film at different freezing moments. At the beginning of the experiment, the deionized water film was first set to a desired temperature and then triggered to freeze by further cooling. Then, a supercooled large droplet was released to impact the freezing water film at different freezing moments. Its impact and splashing processes were recorded by a high-speed camera. Besides, under room-temperature conditions, the impinging and splashing processes of a water droplet on the water film with different thicknesses were also measured. The results showed that, at the early stage of the water film freezing process, the dendritic ices could be pushed out of the water film surface due to the impact of the supercooled large droplet. Besides, the dendritic ices significantly affected the formation and growth of crowns, which could lead to the earlier crown breaks or the formation of the irregular crowns. Moreover, compared to its counterpart of the room-temperature droplet case, the evolution characteristics of the crown generated by the supercooled large droplet case were significantly different in terms of the crown top diameter, the crown base diameter, the crown height, the crown angle, and the crown lifetime. In addition, the correlations between the number of the secondary droplets and the dimensionless water film thickness were obtained and compared as for the room-temperature droplet cases and the supercooled large droplet cases.

Internal mixing air-assisted spray nozzle for large droplets: Experimental measurements and numerical simulations

In the present study, detailed experimental measurements of a large-droplet spray nozzle under a wide range of operating conditions have been conducted at China Aerodynamics Research and Development Center (CARDC) low-speed vertical wind tunnel facility. The droplet size distributions obtained from these measurements have been modeled using the Rosin-Rammler distribution. A multi-physics multi-phase numerical model for the simulation of the complex spray dynamics associated with the large-droplet spray nozzle has been developed in order to support the performance characterization of this device. More specifically, the primary breakup of liquid (water) in the atomizer-produced spray is modeled using a volume of fluid (VOF) to discrete phase model (DPM) transition representation. The numerical model is validated using the experimental measurements. The small relative error between the numerical predictions and experimental measurements for the droplet size distribution and for a number of characteristic droplet diameters suggest that the numerical model provides accurate high-fidelity predictions of the spray dynamics of the large-droplet spray nozzle. Moreover, it is shown that a simple modification of the spray nozzle (increasing the length of the mixing chamber by 50%) has a significant effect on the performance of the nozzle. In particular, the droplet median volumetric diameter and the spray angle are increased as the air pressure is decreased. Furthermore, an increase in the nozzle mixing chamber length results in a much broader droplet size distribution. The validated VOF-to-DPM transition model developed in this study can be used for a future redesign (involving modifications of some key geometric parameters) of the original large-droplet spray nozzle to generate reliably and robustly larger droplets required to simulate various supercooled large droplet conditions of practical relevance.

High Ice Water Content Conditions Associated with Wintertime Elevated Convection in the Midwest

AbstractAircraft flying through areas of high ice water content (HIWC) can experience engine damage and/or failure. HIWC is typically associated with convection and the microphysical properties of tropical oceanic and coastal convection are well documented as a result of several field campaigns in the past decade. HIWC appears to be less common in extratropical convection, but instances of HIWC-related aircraft issues have been recorded in extratropical weather, even during winter. The present study documents the microphysical properties of HIWC between −25° and 0°C and the meteorological and thermodynamic conditions around that HIWC from five flights from the In-Cloud Icing and Large-Drop Experiment (ICICLE) in the midwestern United States in February 2019. All five cases contained elevated convection above a strong low-level temperature inversion. Values for top-of-inversion mixing ratios and total column precipitable water were about 5 g kg−1and 20 mm, respectively, according to soundings near each case. A maximum ice water content of 2.1 g m−3was observed over a length scale of about 500 m, and ice particle size distributions had mean volume equivalent diameters around 1000μm. Supercooled drizzle droplets were also observed in the vicinity of the HIWC, raising questions about the possible role of secondary ice production via the freezing and shattering of supercooled large droplets in HIWC formation. The generalizability of these results is limited by the small number of cases, but they provide some of the first in situ observations of extratropical winter HIWC and highlight the need for continued research on these conditions.Significance StatementHigh ice water content (HIWC) conditions can cause engine damage, stall, and failure in aircraft and can cause air data probes to report erroneous values. Most research on HIWC has focused on tropical convection. This paper serves to draw more attention to the aviation hazard posed by extratropical winter HIWC and the need for additional research into these environments. The cases examined also contained supercooled precipitation-sized liquid droplets. Combined with other recent research, these observations may help to motivate laboratory experiments investigating the role of secondary ice production via droplet freezing and shattering in the formation of HIWC.