Development of the Cox Icing Research Facility

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

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

Populations of “urban” raptors are increasing globally. Trained falcons are now being flown in city golf courses to scare off geese in hopes of reducing accumulated droppings along the fairways. In both the Old World and New, tens of thousands of vultures rummage through urban garbage dumps in search of humans’ leftovers. In Spain, lesser kestrels (Falco naumanni) raise their young in the center of cities and towns, where they are attracted to and feed on swarms of insects flying above night-lit cathedrals and other historic buildings. Peregrine falcons (Falco peregrinus) routinely hunt for birds attracted to the brightly lit Empire State Building in downtown New York City, and red-tailed hawks (Buteo jamaicensis) nest in and around Central Park, feeding on pigeons, rats, and squirrels. Many other species serve as additional examples of a growing number of “urban” birds of prey, whose populations are increasing as human attitudes shift from a “shoot-on-sight” mentality to indifference and tolerance. But before exploring this topic further, first we will offer a bit of linguistics to explore the nuances of the phrase “urban raptor.”

Aircraft icing is an area of research that has drawn attention since the early times of powered flight at high altitudes. Since World War II, aircraft icing research has gained a great deal of momentum, and several branches of research have developed as a result. These branches include the experimental, analytical and computational methods. With the advent of high-speed computers, the computational methods are becoming the leading icing research area due to their low cost requirements. However, a significant hindrance is the lack of a complete understanding of the icing phenomena, which leads to discrepancies between the predictions and the experiments. In recent years, there have been efforts to improve this situation by accounting for several mechanisms within the computational models. These mechanisms include the droplet splash and re-impingement, water film dynamics, and different heat transfer mechanisms. In support of enhancing the understanding of the aircraft icing process, this Ph.D. study focuses on the relative humidity effects and the interaction of the induced vortices with the droplets and the surface water.;Currently the relative humidity effects are neglected in the icing prediction codes with the assumption that it can at best be a second-order effect. This Ph.D. study looks at the conditions in which the relative humidity effects can pose significant impact on the accreted ice shape. It was seen that the flow around the airfoil suction surfaces and the vortices, which have low-pressure cores, shed from the existing ice shape are highly supersaturated. Therefore, the suction surfaces and the aft regions of the main ice shape are exposed to condensation/deposition due to relative humidity effects. The time scales involved in the relative humidity effects were also investigated by using a numerical droplet growth experiment. In the particular case considered in this study, the required time to re-establish equilibrium, i.e. recover saturation conditions, varied from 12 milliseconds for droplets with 1 micron diameter to 5 seconds for droplets with 20 micron diameter. In an actual flight scenario, the direct impingement region mostly overlaps with the stagnation region, where the local flow is subsaturated. (Abstract shortened by UMI.).

Purpose The purpose of this paper is to analyse an actual representation of ice accretions, which are important during the certification process. Design/methodology/approach Ice accretion experiments are conducted in a low-speed subsonic wind tunnel testing facility to evaluate the influence of various ice shapes around the airfoil sections. Ice accumulation changes the shapes of local airfoil sections and thereby affects the aerodynamic performance characteristics of the considered NACA 23012 profile. The ice profiles are impregnated using balsa wood with glace, horn and mixed ice accretion cases for the detailed experimental investigation. Findings Computational fluid dynamics analysis is done to compute the influence of different ice shapes on the aerodynamic coefficients (Cl and Cd) while ice accretion occurs at the leading edge of the airfoil sections. It is observed that the Cl and Cd modified immediately more than 40% as compared to the clean wing configuration. In the same fashion, the skin friction coefficient also abruptly changes for different ice shapes that have the potential to induce flutter at the critical speed of the airplane. The computational solutions are further validated through wind tunnel experiments and recent literature concerning certification for flight in icing conditions. Social implications The ice accretion study on the aerodynamic surfaces can also be extended for wind turbine blades installed at different cold regions around the globe. Further, the propeller icing influences the entire rotorcraft aerodynamics at low temperature conditions and the findings of this study are strongly connected with such problems. Originality/value The aerodynamic characteristics of the baseline airfoil are greatly affected by the ice accretion problem. Although flight through icing condition endures for a short duration, the takeoff path and decision speed are determined based on airplane drag as per federal aviation regulations. Hence, the proposed study is focussed on a cost-effective approach to predict the effect of ice accretion to achieve optimum performance.

Unmanned Aerial Vehicles (UAVs) are necessary tactical tools for Army field commanders requiring surveillance, targeting aids, and communication links. Icing and freezing precipitation can create serious problems for Army UAVs. Though the Army UAVs were not initially flown in Kosovo between October and April because of icing, and flights were not launched when icing was forecast, 25% of UAV flights encountered icing. The Army's present icing avoidance approach is to not fly when icing is forecast. While this solves, in part, the problem of aircraft icing, it negatively impacts mission success. To explore the impact of icing on UAVs and the potential use of low weight, low-power remote sensing systems to allow UAVs and other aircraft to avoid or minimize icing conditions during flight, we have looked at the environmental conditions conducive to icing potential, sources of field measurements and models for characterizing natural icing conditions, and models that predict ice accretion on airfoils. Techniques have been developed to simulate ice accretion rates, type, and shape on airfoils for flights in natural icing conditions. This paper discusses our approach and simulation techniques and presents some preliminary results.

In-flight ice accretion poses a major safety concern in aviation. It occurs due to the icing from clouds of supercooled water droplets, the accumulation of ice crystals at high altitudes, or snow buildup. Assessing the detrimental effects of ice accretion on aircraft performance and handling qualities is a complex, multidisciplinary task, as it requires modeling the dynamics of the dispersed phase (water droplets, ice crystals, and snowflakes), the particle impact dynamics and its interaction with the aircraft surfaces, the liquid film dynamics, the solidification process, and possibly ice shedding. The ice protection systems must also be modeled. The present review addresses the status of ice accretion models and simulation tools. The intrinsically stochastic nature of ice accretion, combined with substantial operational and modeling uncertainties, makes it challenging to validate these tools against experimental observations and use simulation as a reliable means of compliance for certification in icing conditions, especially for innovative aircraft configurations such as wing-body and advanced urban air mobility vehicles.

When an aircraft flies in cold, moist air, especially at low altitudes, ice can form rapidly on the leading edges of aerofoils and other structures. Ice growth can disturb the local airflow and therefore affect the aerodynamic performance and aircraft handling characteristics, leading to the use of in-flight ice-protection systems on modern commercial aircraft. Research into future wing design, e.g. Natural Laminar Flow and morphing leading-edges serves to indicate that the icing environment will have an even greater effect on these new wing shapes than on the current state of the art. Furthermore, the increasing exploitation of composite materials and the trend towards more-electric aircraft suggest that conventional methods of preventing such ice accretion, e.g. engine bleed air or pneumatic boots, are becoming increasingly difficult to implement or are no longer viable. However, one well-established technique for continued ice protection is via electro-thermal methods. GKN Aerospace - Luton have many decades of experience in delivering reliable electro-thermal ice protection and have demonstrated the capability of reliably protecting composite and other structures whilst maintaining critical aerofoil geometry. One of the major engineering hurdles to be overcome in the design of effective electrothermal ice protection systems is that the thermal performance requirements of the materials of construction are almost directly contrary to those for adequate lightning protection. The necessarily high power densities required for ice protection drive the requirement for very low thermal resistances between heating element and the protected surface. However, the aerodynamic surface to be ice-protected, by its very nature, is frequently in a lightning strike zone [1] and the operation of in-flight ice-protection systems often coincides with the greatest probability of lightning strike [2][3]. The requirements for lightning protection demand very high insulation resistances at very high voltages (several kilovolts), requirements that inherently drive thermal resistances upwards. The current results of GKN Aerospace's on-going efforts to resolve these conflicting requirements are presented here. These efforts include material choices and their drivers, as well as methods of construction.

The design of efficient thermal ice protection systems is a challenging task as these systems operate in complex environments involving several coupled physical phenomena such as phase change, boundary-layer flow, and heat transfer. Moreover, certification rules are becoming more stringent, and there is a strong incentive for the reduction of fuel consumption. In this context, numerical tools provide a powerful asset during the design phase but also to gain insight into the physical mechanisms at play. This article presents modeling and simulation strategies for thermal ice protection systems. First, the model describing the behavior of the thermal protection system is presented. Second, a model and associated numerical method is presented for unsteady ice accretion. Third, the coupling methodology between the ice accretion solver and the heat conduction solver is described. In the fourth part, different methods to simulate the boundary-layer flow are described. Finally, some relevant examples are presented, both in steady and unsteady configurations.

Icing is an important disaster-causing factor which threatens the flight safety of civil aircraft and a major safety issue of concern for the airworthiness. The design of icing protection system based on ice-tolerant concept can minimize the impact of icing on aerodynamic characteristics and fully utilize the potential of flight performance, which is the frontier direction of current icing protection research for civil aircraft. This paper aims at the requirements of civil aircraft flight safety design and airworthiness certification. The design method of civil aircraft icing protection system based on the concept of ice-tolerant capacity is analyzed from two aspects. One is the capacity of ice-tolerant for aircraft frame, the other one is the design of ice-tolerant with active control. The optimum design strategy of wing in aerodynamic performance considering icing loss is refined and the design idea of ice-tolerant protection control system based on flight control law reconstruction is formed. The change from passive flight safety of icing to active safety design of icing can effectively improve the survivability and safety of civil aircraft under icing weather conditions.

A study into the effects of altitude on an aircraft thermal ice protection system (IPS) performance has been conducted by the National Research Council Canada (NRC) in collaboration with the NASA Glenn Research Center. The study included tests of an airfoil model, with a heated-air IPS, installed in the NRC’s Altitude Icing Wind Tunnel (AIWT) at altitude and ground level conditions. Two scaling strategies were employed based on Reynolds number and Weber number, the latter combined with matching the ratio of water loading and evaporative rates. The Reynolds number–scaled conditions resulted in greater mass of accreted ice that formed further back from the leading edge, whereas the Weber number approach provided a close match to reference altitude conditions in terms of ice mass, location, and shape.

Icing calculations were performed for a NACA 0012 swept wing tip using LEWICE3D Version 3.48 coupled with the ANSYS CFX flow solver. The calculated ice shapes were compared to experimental data generated in the NASA Glenn Icing Research Tunnel (IRT). The IRT tests were designed to test the performance of the LEWICE3D ice void density model which was developed to improve the prediction of swept wing ice shapes. Icing tests were performed for a range of temperatures at two different droplet inertia parameters and two different sweep angles. The predicted mass agreed well with the experiment with an average difference of 12%. The LEWICE3D ice void density model under-predicted void density by an average of 30% for the large inertia parameter cases and by 63% for the small inertia parameter cases. This under-prediction in void density resulted in an over-prediction of ice area by an average of 115%. The LEWICE3D ice void density model produced a larger average area difference with experiment than the standard LEWICE density model, which doesn't account for the voids in the swept wing ice shape, (115% and 75% respectively) but it produced ice shapes which were deemed more appropriate because they were conservative (larger than experiment). Major contributors to the overly conservative ice shape predictions were deficiencies in the leading edge heat transfer and the sensitivity of the void ice density model to the particle inertia parameter. The scallop features present on the ice shapes were thought to generate interstitial flow and horse shoe vortices which enhance the leading edge heat transfer. A set of changes to improve the leading edge heat transfer and the void density model were tested. The changes improved the ice shape predictions considerably. More work needs to be done to evaluate the performance of these modifications for a wider range of geometries and icing conditions.

A research project is underway at NASA Lewis to produce a computer code which can accurately predict ice growth under any meteorological conditions for any aircraft surface. The most recent release of this code is LEWICE 1.6. This code is modular in design and can use flow codes other than the default potential flow code. Methods for assessing the capabilities of ice accretion prediction codes are examined by comparing geometric and aerodynamic characteristics of computationally generated and experimentally measured ice shapes. The data used in this paper comes from tests performed in the NASA Lewis Icing Research Tunnel (IRT). This paper will present comparisons with that data for both ice shape and performance results. A group of geometric characteristics for quantitatively describing ice shape profiles are introduced and used to assess the differences between profiles. An aerodynamic analysis of computational and experimental ice shapes is performed using a structured-grid, Navier-Stokes, flow code as an alternate method for assessing ice shape similarity. Results indicate that large differences in ice shape are reflected in the resulting aerodynamics but are not necessarily apparent in integrated force parameters such as lift or drag.

Prenatal exposure to polybrominated diphenyl ethers and child attention problems at 3–7 years

In one of the most extensive applications to date of the NASA Lewis ice accretion code LEWI3DGR, certification of the Gulfstream GV ultra-long range business jet was obtained under FAR 25.1419. Analyses were performed to model water droplet impingement on lifting and nonlifting surfaces including those both protected and unprotected from accretion. Heat transfer rates for treating leading edges were determined from dry air flight testing. Ice shapes were calculated and fabricated for artificial ice shape testing. Flight tests were conducted with artificial shapes to verify aircraft performance with heavy ice accretion. The recently required zero-g horizontal stall pushover maneuver was flown. Flight into known icing natural ice tests were conducted to reaffirm aircraft performance and validate the ice protection system design. All testing was completed successfully, and certification was obtained. A list of lessons learned to streamline future icing certification was compiled.