Aircraft Icing: Modeling and Simulation

This paper reviews the background to and the current status of analyses developed to address the problem of icing on aircraft. Methods for water droplet trajectory calculation, ice accretion prediction, aerodynamic performance degradation and an overview of ice protection system modelling are presented. The paper addresses the issues involved in the development of icing analyses including problem formulation and assumptions, solution techniques, validation and the incorporation of empirical inputs where a purely theoretical approach is not feasible. Results are presented to illustrate the capabilities of the analyses when applied to practical design problems. Recommendations are made for further research.

A IRCRAFT icing is widely recognized as a significant hazard to aircraft operations. For this reason, aircraft and ice protection systems must be certified for flight into icing conditions. The aircraft certification and icing research communities rely on icing wind tunnels as an efficient way to produce ice accretions in a controlled environment. The aerodynamic performance of aircraft with these ice accretions contributes to the certification of aircraft. It is therefore critical to ensure that the ice accretions are simulated within a known aerodynamic uncertainty. The aerodynamic performance of an airfoil containing an ice accretion is highly dependent on the geometry of the ice accretion, which is in turn dependent on icing conditions such as temperature, liquid water content (LWC), and median volume diameter (MVD). Icing wind tunnels have the capability to vary LWC and MVD, however, the accuracy in LWC and MVD required to create an aerodynamically representative ice accretion is not known. This research addressed the problem of “how good is good enough” by determining the relationship and sensitivity of iced-airfoil performance to these icing cloud parameters. In addition, these data were placed in perspective by relating measurable or significant aircraft performance changes to the underlying changes in airfoil aerodynamic performance. Recent NASA studies [1,2] in the Icing Research Tunnel (IRT) measured the effect of icing parameter variations on ice-accretion geometry. These studies showed that small variations in LWC and MVD corresponded to distinct changes in ice-accretion geometry. In addition, the effect of ice-accretion geometry on aerodynamic performance has been recently investigated [3–6]. Papadakis et al. [3,4] used spoilers to simulate horn ice and showed that Clmax degradation was related to the horn height (k=c). Kim and Bragg [5], and Broeren et al. [6] showed that k=c and surface location (s=c) had the biggest impact on airfoil performance degradation. This study used ice tracings from theNASA studies [1,2] as a basis to examine the sensitivity of aerodynamic performance to icing parameter variations. Eleven ice-accretion tracings were selected from the 39measured byMiller et al. [2] to reasonably span the range of LWC andMVD tested. The selected ice tracings were modeled as two-dimensional smooth simulated ice shapes for wind-tunnel testing. The experiments for this research were performed in the Illinois subsonic, low-turbulence, open-return wind tunnel. The airfoil model was an aluminum NACA 0012 airfoil with an 18 in. chord, 33.6 in. span, and a removable leading edge to facilitate installation of the ice simulations. Testing was performed at a Reynolds number of 1.8 million, and a Mach number of 0.18. The results of the aerodynamic testing were related to the corresponding icing parameters in the form of two sensitivities: airfoil performance to icing parameter variations, and derived aircraft performance to icing parameter variations. More details can be found in Campbell et al. [7,8].

I CE accretion on cold surfaces is a topic of great concern for a number of engineering applications. Ice formation and accretion on power cable and radio masts have been found to cause significant damage or completely destroyed the electric equipment on numerous occasions [1]. Aircraft icing is widely recognized as one of the most serious weather hazards to aircraft operations [2]. The importance of proper ice control for aircraft operation in cold climates was highlighted by many aircraft crashes in recent years, like the Continental Connection Flight 3407, which crashed in Buffalo, New York due to ice buildup on its wing, killing all 49 people aboard and one person on the ground, as the plane hit a residential home on 14 February 2009.Wind-turbine icing represents themost significant threat to the integrity of wind turbines in cold weather. It has been found that ice accretion on turbine blades would decrease power production of the wind turbines significantly [3]. Ice accretion and irregular shedding during wind-turbine operation would lead to load imbalances, as well as excessive turbine vibration, often causing the wind turbine to shut off [4]. Icing was also found to affect the reliability of anemometers, thereby leading to inaccuratewind-speed measurements and resulting in resource estimation errors [5]. Advancing the technology for safe and efficient operation of numerous functional devices in atmospheric icing conditions requires a better understanding of the icing physics. While a number of theoretic and numerical studies have been conducted in recent years to develop ice prediction tools for improved ice protection system designs [6–9], many details of important microphysical processes that are responsible for the ice formation and accretion on frozen cold surfaces are still unclear. Fundamental icing physics studies capable of providing accurate measurements to quantify important microphysical processes associated with icing phenomena are highly desirable in order to elucidate the underlying physics. In this study, we report an experimental icing physics study to quantify the transient behavior of the phase-changing and heattransfer processes within small water droplets impinging onto a frozen cold plate. It should be noted that this is a fundamental icing physics study. Instead of reproducing every detail of the icing phenomena for a specific engineering application, the present study was aimed to elucidate underlying fundamental physics to improve our understanding about the important microphysical processes pertinent to various icing phenomena found in nature, which include power cable icing, wind-turbine icing and aircraft icing. To the best knowledge of the authors, this is the first effort of its nature. The new findings derived from the icing physics studies, as the one reported here, will lead to a better understanding of the important microphysical processes, which could be used to improve current icing accretion models for more accurate prediction of ice formation and accretion on frozen cold surfaces, as well as the development of effective icing mitigation and protection systems for various engineering applications.

<div class="section abstract"><div class="htmlview paragraph">Aircraft icing has been a focus of the aviation industry for many years. While regulations existed for the certification of aircraft and engine ice protection systems (IPS), no FAA or EASA regulations pertaining to certification of ice detection systems existed for much of this time. Interim policy on ice detection systems has been issued through the form of AC 20-73A as well as FAA Issue Papers and EASA Certification Review Items to deal mainly with Primary Ice Detection Systems. A few years ago, the FAA released an update to 14 CFR 25.1419 through Amendment 25-129 which provided the framework for the usage of ice detection systems on aircraft.</div><div class="htmlview paragraph">As a result of the ATR-72 crash in Roselawn, Indiana due to Supercooled Large Droplets (SLD) along with the Air France Flight 447 accident and numerous engine flame-outs due to ice crystals, both the FAA and EASA have developed new regulations to address these concerns. These new regulations are focused on aircraft-level ice protection certification and do not require a new type of ice detection technology. However, they do imply the need for ice detection systems which can detect and differentiate 14 CFR Part 25 Appendix C from Appendix O (SLD) as well as the ability to detect and differentiate Part 25 Appendix C or O from 14 CFR Part 33 Appendix D (ice crystals).</div><div class="htmlview paragraph">To meet these evolving industry needs, many new ice accretion and icing conditions detector technologies are being developed. Designing an ice detection system which has the sensitivity to detect and differentiate these different types of icing environments can be challenging enough, but integration with the aircraft systems, installation effects and freezing fraction differences between the ice detector technology and the aircraft surface of interest must be considered as well. This paper will review the regulation changes that impact ice detection system design and certification and discuss the necessary analyses and testing required to demonstrate the ability of ice detection technologies to meet these requirements and achieve successful Primary Ice Detection System certification.</div></div>

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

Aircraft icing and ice accretion pose great threat to the safety as the accumulated ice affects the aerodynamic profile of the airfoil hence extensive investigation is being done to understand ice accretion on airfoils. These studies help us understand how lift, drag, pressure and the velocity control is affected due to accumulated ice and how certain measures can be taken to ensure an efficient flight while minimizing risks posed to the safety. This paper focuses on the differences in the aerodynamic parameters on different NACA profiles and how each airfoil is affected by the ice accretion. The computational analysis of this research concentrates on the performance parameters of airfoils of NACA four, NACA five and NACA six digit series on conditions with clear ice, rime ice and without ice for different values of angle of attack. The key research objective of the paper was to investigate how each airfoil is affected under the different icing conditions and compare the results to study ice accretion on different airfoils, namely, NACA0012, NACA23012 and NACA643218. The 2D model of the airfoils was developed with Solid works and Standard K-€ model was used for CFD analysis.

Comparing Experimental Ice Accretions on a Swept Wing with 3D Morphogenetic Simulations

Experimental and computational simulation of in-flight icing phenomena

Ice accretion on exposed surfaces of aero-engine components has been widely recognized as a significant hazard to aviation safety in cold weathers. Icing process due to the impingement of the supercooled water droplets suspended in the cloud onto the cold surfaces of inlet components of aeroengines have been studied extensively for decades. Since ice particles were believed to simply bounce off from the exposed surfaces of aero-engine components, ice crystals in the clouds were initially considered not to pose a threat to aviation safety. Therefore, the ice accretion process due to the impacting of ice crystals onto the surfaces of hot engine componentes has not been studied until recently. It has been found recently that, tiny ice particles in the cloud may be partial/full melting upon impacting onto the hot surfaces of aero-engine components, such as heated Inlet Guide Vanes (IGV) and various probes. The partially/fully melted ice crystals were found to stick onto the hot surfaces and form thin water film, which would intercept more oncoming ice particles and lead to significant ice accretion over the surfaces of the hot engine components. The ice crystal induced ice accumulation on the critical aero-engine components has been found to cause significant engine performance loss and erroneous data being read from the probes. In the present study, a series of experimental investigations were conducted to elucidate the underlying physics of the dynamic ice accretion process pertinent to ice crystal icing phenomena. A novel ice crystal icing test rig with the capacity of generating controllable amount of ice crystals and flying speed up to 100 m/s was developed in a temperature-controllable environment chamber for the ice crystal icing studies. By using a high-speed imaging system, a digital particle image velocimetry(PIV), and an Infrared (IR) thermal imaging system, a comprehensive experimental campaign was performed to characterize the transient impacting process of ice crystals, dynamic ice accretion and unsteady heat transfer process associated with the impacting of ice crystals onto heated surfaces, in comparison to those due to the impingement of supercooled water droplets. By using an ultra-sensitive force sensor and a high-speed image system, a comparative study is conducted to examine the differences in the transient impinging dynamics of single water droplets, supercooled water droplets, and ice crystals onto solid surfaces with different wettability and stiffness. By upgrading the unique Icing Research Tunnel of Iowa State University (i.e., ISU-IRT) with additional ice crystal icing capability, a set of explorative studies are also conducted to examine the characteristics of the dynamic ice accretion processes over the heated surfaces of an aero-engine Inlet Guide Vane (IGV) model under both ice crystal icing and supercooled droplet icing conditions. The anti-/de-icing performance of a novel hybrid strategy by integrating icephobic coatings and minimized surface heating are also evaluated under both supercooled water droplet icing and ice crystal icing conditions. The new findings derived from the present studies are very helpful to gain further insights into the ice crystal icing phenomena for the development of more effective and robust anti-/de-icing strategies to ensure safer and more efficient aircraft/aero-engine operations in cold weathers.

Multi-physics simulation of 3D in-flight ice-shedding

In-flight ice accretion poses a significant risk to aircraft safety and performance. Despite advancements in ice protection systems, aircraft must demonstrate the ability to operate safely under icing conditions, highlighting the importance of reliable ice accretion simulations. Traditional multistep simulations divide the accretion process into discrete stages, improving the accuracy of ice predictions. However, this approach increases computational costs and reduces automation, as evolving ice shapes necessitate the generation of new grids. This paper investigates the application of immersed boundary methods (IBMs) to eliminate the need for volume remeshing, thereby enhancing the automation of multistep simulations. The proposed framework, integrated into the ONERA three-dimensional (3D) icing suite IGLOO3D, uses a ghost-cell method for modeling airflow and a penalization approach for simulating droplet impingement, building upon recent work by the authors. By relying on inviscid flow simulations, the method significantly reduces computational costs; however, boundary-layer calculations are required. To address this, a 3D simplified integral boundary-layer solver based on the resolution of partial differential equations on a surface is presented. Results from three cases of the 1st Ice Prediction Workshop are presented and analyzed, demonstrating the potential of IBMs to enhance the efficiency and practicality of 3D ice accretion simulations.

Aircraft icing presents a serious threat to the aerodynamic performance and safety of aircraft. The numerical simulation method for the accurate prediction of icing shape is an important method to evaluate icing hazards and develop aircraft icing protection systems. Referring to the phase-field method, a new ice accretion mathematical model is developed to predict the ice shape. The mass fraction of ice in the mixture is selected as the phase parameter, and the phase equation is established with a freezing coefficient. Meanwhile, the mixture thickness and temperature are determined by combining mass conservation and energy balance. Ice accretions are simulated under typical ice conditions, including rime ice, glaze ice and mixed ice, and the ice shape and its characteristics are analyzed and compared with those provided by experiments and LEWICE. The results show that the phase-field ice accretion model can predict the ice shape under different icing conditions, especially reflecting some main characteristics of glaze ice.

<div class="section abstract"><div class="htmlview paragraph">This work presents a comprehensive numerical model for ice accretion and Ice Protection System (IPS) simulation over a 2D component, such as an airfoil. The model is based on the Myers model for ice accretion and extended to include the possibility of a heated substratum. Six different icing conditions that can occur during in-flight ice accretion with an Electro-Thermal Ice Protection System (ETIPS) activated are identified. Each condition presents one or more layers with a different water phase. Depending on the heat fluxes, there could be only liquid water, ice, or a combination of both on the substratum. The possible layers are the ice layer on the substratum, the running liquid film over ice or substratum, and the static liquid film between ice and substratum caused by ice melting. The last layer, which is always present, is the substratum. The physical model that describes the evolution of these layers is based on the Stefan problem. For each layer, one heat equation is solved. At the ice-water interface, a Stefan condition governs the phase transition. Lastly, mass conservation is imposed. Numerical simulations are compared to reference results, both experimental measurements and numerical simulations for both ice accretion and ETIPS operating in anti-icing and de-icing mode, showing good agreement. A posterior ice shedding analysis is then performed, taking into account the IPS in both anti-icing and de-icing operation modes. The stresses internal to the ice shapes when subjected to the aerodynamic loads are compared with the mechanical properties of ice such as the tensile and adhesion strength. The results show that the de-icing mode is more efficient in causing shedding due to the decrease in adhesion surface and the presence of the under-ice liquid film that tends to break the ice shape.</div></div>

Foreword. 1. Modern Meteorology and Atmospheric Icing Svein M. Fikke et al. 1.1 Introduction. 1.2 Atmospheric Icing - A Brief Survey of Icing Processes and their Meteorological Aspects. 1.3 Icing Models. 1.4 Introduction of Numerical Weather. Prediction Models. 1.5 Some Preliminary Applications of Fine-Scale Models. 1.6 Condensation Schemes in NWP Models - Relevance for Icing Prediction. 1.7 A Case Study: Using Numerical Weather Prediction Models to Forecast In-cloud Atmospheric Icing. Episodes. 1.8 Concluding Comments. 2. Statistical Analysis of Icing Event Data for Transmission Line Design Purposes Masoud Farzaneh and Konstantin Savadjiev. 2.1 Introduction. 2.2 Measurements and Database. 2.3 Statistical Analysis and Modelling Ice Loads on Overhead Transmission Lines. 2.4 Conclusions. 3. Numerical Modelling of Icing on Power Network Equipment Lasse Makkonen, Edward P. Lozowsk. 3.1 Introduction. 3.2 The Fundamental Equation of Icing. 3.3 Computing the Rate of Icing. 3.4 Numerical Modelling. 3.5 Conclusions. 4. Wet Snow Accretion on Overhead Lines Pierre Admirat. 4.1 Introduction. 4.2 Microphysics of Wet Snow. 4.3 Thermodynamic Analysis of Heat Exchanges. 4.4 Modelling the Cylindrical Growth of Wet Snow Sleeves. 4.5 Simulation of Accretion Mechanisms in Wind Tunnel Conditions. 4.6 Observation of Accretion Mechanisms in Natural Climatic Conditions. 4.7 Applications to Forecasting, Preventing, and Mapping the Wet Snow Overload Hazard. 5. Effect of Ice and Snow on the Dynamics of Transmission Line Conductors Pierre Van Dyke et al. 5.1 Introduction. 5.2 Aeolian Vibrations. 5.3 Wake-induced Oscillation. 5.4 Galloping Conductors. 5.5 Protection Methods. 5.6 Galloping Amplitudes. 5.7 Ice Shedding. 5.8 Bundle Rolling. 5.9 Conclusion. 6. Anti-icing and De-icing Techniques for Overhead Lines Masoud Farzaneh et al. 6.1 Introduction. 6.2 Anti-icing Techniques. 6.3 De-icing Techniques. 6.4 Joule-Effect Methods. 6.5 Methods for Limiting IceAccretion Weight. 6.6 Practical Aspects. 6.7 New Developments in Anti-icing Methods. 6.8 Conclusions. 7. Effects of Ice and Snow on the Electrical Performance of Power Network Insulators Masoud Farzaneh, William A. Chishol. 7.1 Introduction. 7.2 Insulator Functions, Dimensions and Materials. 7.3 Ice and Snow Accretion on Insulators. 7.4 Ice Flashover Processes and Mechanisms. 7.5 Cold-Fog Flashover Process and Mechanisms. 7.6 Snow Flashover Process and Mechanisms. 7.7 Mathematical Modelling of Flashovers on Insulators Covered with Ice or Snow. 7.8 Recommended Test Methods. 7.9 Insulation Coordination for Ice and Snow Conditions. 7.10 Mitigation Options to Improve Network Reliability in Winter Flashover Conditions. 7.11 Conclusions and Recommendations. 8. Design of Transmission Lines for Atmospheric Icing Anand Goel. 8.1 Introduction. 8.2 Types of Atmospheric Icing Accretion. 8.3 Ice Accretion on Overhead Line Conductors and Structures. 8.4 Ice Load Measurements. 8.5 Standards for Ice Loads. 8.6 Transmission Line System. 8.7 Design Methodology. 8.8 Deterministic Design Approach. 8.9 Reliability-based Design (RBD) Approach. 8.10 Return Period. 8.11 Variability of Component Resistance. 8.12 Other Loads. 8.13 Ice/Snow Accretion Mitigation Techniques. 8.14 Lessons from the 1998 Ice Storm. 8.15 Concluding Remarks. Appendix 8.A. Index.

Ice crystal ingestion at high altitude is a menace to the safe operation of jet engines. Because the core airflow in jet engine has higher temperature, ice crystals may partially melt into droplets when they enter the core airflow. A mixed-phase condition is seen consisting of both water droplets and ice crystals, which will cause ice accretion on both the static surfaces and rotating components in a compressor. This ice accretion may give rise to compressor surge or even mechanical damage of jet engine. In order to analyze this in depth, a numerical method of mixed-phase icing was developed. The Reynolds-averaged Navier–Stokes equations were used for the airflow solution. The Lagrangian method was employed for determining the trajectories of ice crystals and droplets. An ice crystal impingement model was created, in which the breakup and rebounding of ice crystals and splashing of film were considered. A thermodynamic model was proposed for ice crystals and droplets on the basis of the first law of thermodynamics. An icing simulation was developed under mixed-phase conditions with different liquid water contents and ice water contents, and the results were compared with experimental data from the literature. The comparison showed a fairly good correlation, which supports the validity and rationality of the method of mixed-phase icing.