Aircraft Icing: Modeling and Simulation

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

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.

In-flight ice accretion may possibly jeopardise the safety of fixed-and rotary-wing aircraft. Icing can possibly occur if supercooled water droplets in clouds impinge on the aircraft surfaces and freeze upon impact. A major issue related to ice accretion is the possibility of ice shedding from the main body and impacting other parts of the aircraft or being ingested by the engines. A multi-physics framework is presented to simulate ice accretion and shedding from wings and engine nacelles due to aerodynamic forces. The aerodynamics is computed using the open-source tool-kit SU2. Cloud droplet trajectories are computed using the arbitrary-precision Lagrangian in-house solver PoliDrop. Then, the in-house ice accretion tool-kit PoliMIce is used to determine the ice layer. A FEM structural analysis is performed on the accreted ice shape by means of the open-source code MoFEM. Internal stresses within the ice geometry due to aerodynamic forces are computed. The possibility of the occurrence of cracks in the ice layer is assessed and its propagation is determined numerically. Two-dimensional ice accretion simulations are performed to check the validity of the present approach and compare fairly well with available results.

Many experimental research efforts in the past two decades have revealed that the complete picture of aircraft ice accretion has many components, resulting in a complex physical structure. Although overwhelmingly complex, the icing phenomenon needs to be understood because of its impact on aircraft performance and safety. This requires a detailed knowledge of ice accretion physics, subsequent flow over the aircraft, and the resulting modified aircraft performance. Experimental and numerical studies to address these issues have their own advantages, disadvantages, and limitations, which further limit the analysis of the icing phenomena. The motivation behind this study is the belief that complex phenomena in nature have an orderly structure on the large scale. Based on this premise, it is thought that icing phenomena also have orderly, albeit nonlinear, behavior that can be modeled by neural networks, which have a proven capability for modeling nonlinear systems. The methodology developed in the present study incorporates the Fourier series expansion of an ice shape following a conformal mapping, which suppresses the effect of airfoil geometry, and then utilizes neural networks to model the Fourier coefficients and the downstream extent of the ice shape. The neural network can be trained to make ice accretion predictions, given a set of data including the flight and atmospheric conditions, along with the Fourier coefficients and the extent of the resulting ice shape. The neural network also provides statistical output of the relative significance of the input parameters in the training. The preliminary results show that the proposed method has reasonable capabilities and has merit for further investment, because it can be coupled with other systems to create advanced computational ice accretion models and ice protection systems. Nomenclature ai, bi = coefficients of the cosine and sine functions of the Fourier series expansion, respectively f = actual perturbation geometry from the parabola surface ˜ f = approximated perturbation geometry LWC = liquid water content of oncoming air in grams per cubic meter M = number of Fourier terms for the truncated Fourier series expansion MVD = median volumetric diameter in micrometers N = number of data points of the actual ice geometry T∞ = static temperature in the oncoming air in kelvin V∞ = free stream velocity in meters per second x‐y = data coordinates of the experimental ice shape x � ‐y � = ice shape coordinates nondimensionalized by the leading-edge radius (LER) of the airfoil ξ ‐η = coordinates of the ice shape in the transformed plane ξ � ‐η � = coordinates of the ice shape after separation

In-flight atmospheric ice accretion poses a significant threat to the stable operation of unmanned aerial vehicles (UAVs), as most lack ice protection systems (IPSs). This study presents a detailed comparative analysis of ice accretion dynamics and its aerodynamic effects on UAV propellers with varying geometric design parameters. The investigations are performed using FENSAP-ICE software under two icing cloud conditions: continuous and intermittent maximum icing envelopes. The outcomes reveal that accreted ice structures and their aerodynamic penalties are highly sensitive to propeller geometry, with airfoil design playing a crucial role in mitigating icing impacts on smaller UAV propellers. Propellers with smaller blade chords were more vulnerable, showing greater leading-edge ice buildup and significant reduction in propulsive efficiency compared to those with larger blade chords. Under the same icing conditions (−5°C, continuous maximum icing envelope) for an icing duration of 120 s, the thrust coefficient of iced propellers reduced from 11.94 to 49.49% across different propeller designs. In contrast, the power coefficient increased from 34.10 to 98.46%, depending on propeller geometric parameters. These findings emphasize the importance of geometric parameters on the ice accretion process and aerodynamic performance, providing valuable insights for the design of UAV propellers operating in icy conditions.

<div class="section abstract"><div class="htmlview paragraph"> For nearly a century, ice build-up on aircraft surfaces has presented a safety concern for the aviation industry. Pilot observations of visible moisture and temperature has been used a primary means to detect conditions conducive to ice accretion on aircraft critical surfaces. To help relieve flight crew workload and improve aircraft safety, various ice detection systems have been developed. Some ice detection systems have been successfully certified as the primary means of detecting ice, negating the need for the flight crew to actively monitor for icing conditions. To achieve certification as a Primary ice detection system requires detailed substantiation of ice detector performance over the full range of icing conditions and aircraft flight conditions. Some notable events in the aviation industry have highlighted certain areas of the icing envelope that require special attention. </div><div class="htmlview paragraph"> Following the CRJ accident in Fredericton, New Brunswick, Canada, in December 1997, industry interest and scrutiny in the performance of ice detection systems at warmer temperatures has increased. [ <span class="xref"> 1 </span> ] In particular, the concern lies in potential differences between ice accretion on the ice detector sensing surfaces and the critical aircraft surfaces (e.g. wing, nacelle). This has led both the FAA and EASA to update advisory material to ensure that ice detector performance at low freezing fractions is addressed. </div><div class="htmlview paragraph"> To minimize this concern and alleviate the risk, Collins Aerospace (Rosemount Aerospace, Inc.) has developed an enhanced ice detection algorithm for its magnetostrictive ice detector (MID). Traditionally the MID has only been used to detect ice accretion resulting from supercooled liquid water. This new algorithm enables the MID to sense the presence of non-freezing liquid water on its sensing surface and couple that with ambient temperature information to provide a signal when conditions may be conducive for ice accretion on critical aircraft surfaces. </div><div class="htmlview paragraph"> The discussion in this paper describes the development of this new algorithm for the MID and performance verification of the algorithm through icing wind tunnel testing and icing flight tests. </div></div>

Ice accretion and aerodynamic effects on a turbofan engine nacelle under takeoff conditions

Numerical simulation of three-dimensional ice accretion on an aircraft wing

An experimental study on dynamic ice accretion and its effects on the aerodynamic characteristics of stay cables with and without helical fillets

For wind turbines operating in cold weather conditions, ice accretion is an established issue that remains an obstacle in effective turbine operation. While the aerodynamic performance of wind turbine blades with ice accretion has received considerable research attention, few studies have investigated the structural impact of blade ice accretion. This work proposes an adaptable projection-based method to superimpose complex ice configurations onto a baseline structure. The proposed approach provides an efficient methodology to include ice accretion in the high-fidelity isogeometric shell analysis of a realistic wind turbine blade. Linear vibration and nonlinear deflection analyses of the blade are performed for various ice configurations to demonstrate the impact of different ice accretion distributions on structural performance. These analyses indicate decreases in the blade natural frequencies and deflection under icing conditions. Such ice-induced changes clearly reveal the need for structural design consideration for turbines operating under icing conditions.

Chapter 26 - Synergic Effects of Passive and Active Ice Protection Systems

A new method of particle sizing for mixed-phase and ice clouds proposed and tested by numerical simulation in authors' papers is applied here to experimentally measured scattering phase function. The method enables us to identify each component of a bi-component cloud composed of ice crystals and water droplets and to retrieve separately a size distribution for each cloud component. We use mainly available referenced data to test the inversion method with respect to the retrieval of size composition of mixed-phase and ice cloud under both single- and bi-component assumption and try to explain the known fact of the discrepancy between measured scattering phase functions for an ice cloud and those theoretically predicted by the ray tracing treatment, for instance, for convex ice crystals. Applying the inversion method enables us to show that one of effective ways to describe the scattering phase function behavior of mixed-phase and ice clouds is the bi-component assumption. It is rather natural for a mixed-phase cloud because of the existence of water droplets and ice crystals in the cloud simultaneously. On the other hand, one of an important physical reason for the bi-component assumption in an ice cloud lies in the well known fact that, as the cloud is transformed from water phase to ice one a high proportion of the particles can frequently stay as small supercooled water droplets even at very low temperature.

The Supercooled Large Droplet (SLD) problem in aircraft icing has gained more and more importance during last years. Several experimental, numerical and regulation eorts have been spent to bridge the knowledge gap. New phenomena have been unveiled and studied to address and explain the peculiar features which characterizes the dynamics of a SLD water cloud. With reference to the impact behaviour of a SLD cloud onto an aircraft surface, the authors present a numerical method to model the basic impact phenomena and eects at aircraft component level. Several semi-empirical models drawn by literature ndings are presented and implemented in a software code to evaluate the water droplet impingement sensitivity in the SLD regime. The computational framework is Eulerian, thus a PDE problem is solved for the water droplet

The LeClerc Icing Research Laboratory was designed and constructed at Cox & Company in downtown New York City (Manhattan). The facility was engineered to meet a number of design criteria in addition to being environmentally non-intrusive to the surroundings. It consists of a closed-loop refrigerated wind tunnel with the capability to simulate a cloud of supercooled water droplets as specified in the FAR's Part 25-C. Two test sections are provided with an airspeed up to 220 mph in the main test section and 120 mph in the secondary one. Provision for testing engine inlet nacelles is provided with a scavenge system that is capable of simulating engine core air flows of up to 15 Ib/sec. The tunnel air temperature can be controlled down to -22 °F at the maximum heat load conditions. XTENSIVE testing, in-flight and ground, is normally required in the design and evaluation of ice protection systems. The cost involved can be somewhat prohibitive. Flight testing requires searching for natural icing conditions orflying behind an icing tanker which is time consuming and very costly. Furthermore, natural icing conditions tend to be short and uncontrollable. The cost and development period involved can be reduced by testing in ground facilities that can reliably produce controlled icing environments. Additionally, experimental data (ice shapes and ice protection system performance) in conjunction with icing simulation computer codes may be utilized in the certification process to shorten the required flight testing matrix, once approved by the FAA. The LeClerc Icing Research Laboratory (LIRL) was constructed in Cox's plant, in a business district of downtown New York City. It is completely enclosed, engineered and constructed to be quiet and nonintrusive to the surroundings. It was designed to meet the company's need for its own product development, to support the certification process of these products, and to provide industry with an

<div class="htmlview paragraph">Ice protection systems were installed on DC-3s, B-29s and other aircraft during World War II. Initially ice detection was not considered a requirement for aircraft safety.</div> <div class="htmlview paragraph">One of the earliest ice detectors installed on a production aircraft (C-130) was pneumatic. Subsequently many other technologies have been applied to detect the presence of meteorological icing. Ice detectors employing visible light, infrared light, alpha radiation, natural resonance frequency, capacitance, speed of sound, heat of fusion, and microwaves have all been developed over the years.</div> <div class="htmlview paragraph">This paper will review the different ice detection technologies and explore some of the similarities, differences, benefits and drawbacks for the purposes of performing their intended function.</div> <div class="htmlview paragraph">One of the drivers for developing new ice detection technology has been aircraft icing accidents and incidents. For example, a number of MD-80 accidents caused by engine flame-outs during take-off have prompted development of surface-based ice detection solutions that could detect ice accretion on wing surfaces prior to take-off. Other accidents such as the Comair CRJ crash in Fredericton, New Brunswick, Canada and the American Eagle ATR-42/72 crash in Roselawn, Indiana have spurred research into different ice detection technologies related to the Ludlam Limit and Supercooled Large Droplets (SLD) respectively. This paper will review various aircraft accidents and incidents that have had an impact on ice detection technology.</div> <div class="htmlview paragraph">While no Federal Aviation Regulations (FARs) exist today which deal specifically with ice detection systems, there has been some industry guidance material published which provides information on the design of ice detection systems. Due to the increased industry awareness of aircraft icing issues, a number of industry committees such as EUROCAE and IPHWG have been established to develop new guidance material and proposed regulation changes related to ice detection systems. The release of the ED-103/104 Minimum Operational Performance Specifications and other guidance material such as the recent updates to AC 20 73 published by the FAA have had an impact on the development and certification of ice detection systems.</div> <div class="htmlview paragraph">This paper will review the regulation changes that impact ice detection system design and certification, including a discussion regarding the ability of ice detection technologies to meet these requirements and to be certified as a Primary system.</div>