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MIL-STD-810D, Method 521.0, "Icing/Freezing Rain," contains guidance for testing equipment exposed to freezing rain. This method was developed around a narrow set of meteorological conditions resulting in the buildup of clear glaze ice. The icing procedures described in Method 521.0 can be applied to a wide range of equipment and will help to predict equipment operations during natural freezing rain. However, the procedures do not give any indication of the operation of equipment during exposure to rime ice. The physical properties of rime and glaze ice differ significantly, as do their effects on equipment. Until MIL-STD-810D is modified to include rime icing, program managers and environmental test engineers will find no guidance or procedures in MIL-STD-810D for half of the icing (rime vs. glaze) that equipment can be exposed to in nature.

A time-dependent numerical model of ice accretion on wires, such as overhead conductors, is presented. Simulations of atmospheric icing are made with the model in order to examine the dependence of the accreted ice amount on atmospheric conditions. The results show that in wet growth (glaze formation) under constant atmospheric conditions, the growth rate increases with time until the process changes to dry growth. In dry growth (rime formation) the growth rate typically increases with time at the beginning of the icing process, but later decreases with time when the ice deposit has grown bigger. The effect of air temperature on the ice load turns out to be rather small for the first 24 hours of icing in typical dry growth conditions, but it is important for long-term icing. The ultimate ice load may either increase or decrease with decreasing air temperature, depending on the other atmospheric conditions and on the duration of icing. These results largely explain the difficulties encountered in estimating the formation of ice loads by simple methods using the routinely measured meteorological parameters.

The literature reporting scientific and engineering investigations on ice has grown rapidly in the past 50 years, and increased by a factor of at least ten in the past 20 years. A review is presented of advances in engineering for ice problems during this period, including ice formation in rivers, lakes, and oceans; ice forces on structures; bearing capacity of ice covers; and atmospheric icing. The difficulties faced by engineers due to the unique physical and mechanical properties of ice and its normal thermal state are emphasized.

Natural and artificial icing tests were conducted on a JUH-1H helicopter. An ice phobic coating was applied to both the main and tail rotor blades. A total of 4.0 productive hours were flown in the artificial environment, and 9.3 hours in natural icing conditions. Artificial tests were conducted utilizing the Helicopter Icing Spray System (HISS) with ambient temperatures ranging from -6 to -23 deg C, and relative humidities of 60 to 90 percent. Natural icing tests were conducted within the ambient temperature range of -2 to -12.5 deg C, with liquid water contents (LWC) ranging from 0.1 to 0.32 gm/ cu m. The artificial icing tests verified proper operation of the test helicopter ice protection system for use as a safety device in subsequent tests. Natural icing tests were conducted to determine the operational potential of G661 ice phobic compound and to gather data to aid in defining icing phenomenon and ice protection equipment design requirements. Due to insufficient quantitative baseline UH-1H rotor blade icing data, it was not possible to determine if the G661 ice phobic compound affected the operational icing capability of the UH-1H helicopter. Nine minor asymmetric ice sheds were encountered, however, no predetermined limit conditions were reached during testing. Excessive equipment and man-hour requirements degrade the practicality of G661 use. The LWC indicators were not adequate to determine ice accretion level and the Integrating Rate Unit (IRU) did not provide a repeatable cue of impending asymmetric ice shed.

Icing measurements were carried out in Spain during the Precipitation Enhancement Project experiment in 1979, with an instrumented DC-7 aircraft. The energy balance at the riming surface of a cylinder allows the prediction of the ice growth regime (wet or dry) for the present measurements with 85% success. The mixed conditions encountered show that the ice phase plays an important role in the ice accretion process. For a range of temperature from −21 to −8°C, the icing rate appears to be reduced ∼50% by the presence of large ice particles in concentrations above 5 L−1. The proposed explanation is that the ice particles erode the ice deposit formed by the supercooled water.

Aircraft exposed to an atmospheric icing environment can accumulate ice, resulting in a sharp increase in drag, a reduction in lift, control surface fouling, and engine damage all of which result in a hazardous flight situation. NASA Lewis Research Center (LeRC) has conducted a program to examine, with the aid of high-speed computer codes, how the trajectories of particles contribute to the ice accumulation on airfoils and engine inlets. For this effort, a computer code was developed to calculate icing particle trajectories and impingement limits for axisymmetric inlets. The original research-oriented NASA code was upgraded and modified to meet the requirements of the design engineer. The improved code is capable of performing trajectory calculations for any atmospheric conditions and droplet sizes. It can handle single droplets or a distribution of various droplet sizes. The four programs that comprise the code are described and the results of a test case using flight conditions for a Fokker F100 icing tunnel test are presented.

The literature on sea spray (superstructure) icing is almost entirely based on observations on moving ships. However, icing on stationary offshore platforms with their fixed vertical columns will differ significantly from ship icing, which is influenced by ship movement and wind and wave directions. An observation program on offshore drilling vessels is proposed, using 1-in.-diam x 8-in.-long cylinders in arrays as a standard measuring technique for spray icing. Atmospheric icing may be a source of ice accretion on derricks in some locations, and the best commercial device currently available for measuring it is the Rosemount detector. Improved devices for both spray and atmospheric ice accretion measurements should be developed. Icephobic coatings have the potential for reducing ice accretion, and testing of candidate materials should be undertaken. Well-documented icing reports by all types of ships or platforms should be made and collected at a central clearinghouse.

Flight tests were made in natural icing conditions with two 8-ft-chord heated airfoils of different sections. Measurements of meteorological variables conducive to ice formation were made simultaneously with the procurement of airfoil thermal data. The extent of knowledge on the meteorology of icing, the impingement of water drops on airfoil surfaces, and the processes of heat transfer and evaporation from a wetted airfoil surface have been increased to a point where the design of heated wings on a fundamental, wet-air basis now can be undertaken with reasonable certainty.

Surfaces exposed to atmospheric cold temperature and humid environments are prone to ice accretion. Airplanes, electrical power transmission cables, and wind turbines are typical examples for which icing has to be considered. The measurement of the resulting ice shapes is a challenging process. While macroscopic characteristics of the ice geometry can be observed using photography and optical scanning techniques, microscopic measurements are difficult to conduct because grooved surface partially occludes the geometry of chasms. To overcome this optical inaccessibility, we propose a method to carry out detailed high-resolution measurements of the accretion surface with microcomputed tomography. This approach provides a unique visualization of the empty spaces in the feather region. The information obtained by this technique can improve the understanding of ice accretion physics and its computational modeling.

The paper presents results of the numerical simulation of a hot-air anti-icing system model. A 20 Navier-Stokes CFD code is used to simulate jet impingement on (a) a flat plate and (b) th e inner surface a slat of a multi-element airfoil, a modified RAE 2822 airfoil. The j?at plate case is used to validate numerical predictions by comparison with known empirical conelations. Since these correlations are being used in most of the anti-icing simulation codes, the slat case is used to determine their applicability to concave surfaces. The results indicate that the empirical correlations are not n&able enough for use in anti-icing simulations. The CFD code is then coupled to an ice accretion and antiicing simulation code, CANICE. The overall computational prvcedum is presented with the help of an example. The merits of using the CFD tool in conjunction with the CANICE code are discussed. NOMENCLATURE c, = specific heat of air = airfoil chord length ii slot-tc+wall distance/height h = heat-transfer coefficient k = thermal conductivity L W C = liquid water content M = freestream Mach number MVD = median volumetric droplet diameter ti ?z mass flow rate NZ6 = Nusselt number, hs/kf Pr = Prandtl number, pk/Cp ke = heat flux = freestream Reynolds number, V,c/v Res = jet Reynolds number, isS/~ S = hydraulic diameter of slot, 2x width St = Stanton number, h/pre,VrerCP FL = surface arc length measured from origin = temperature Tf = film temperature, (Tw + Tin)/2 V = airspeed, velocity Q = angle of attack relative to chord line P = fluid viscosity v = kinematic viscosity, p/p P = fluid density i.2 = mean velocity at the inlet slot * Postdoctoral Fellow. Member AIAA. t Ph. D. Student Member AIAA. 4 Bombardier Aeronautical Chair Professor. Associate Fellow AIAA. Copyright @ 2000 by Farooq Saeed, FranGois Morency, and Ion Paraschivoiu. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. Subscripts: anti = anti-icing f = fluid, film in = inlet out = outlet ref = reference s = static t = total w = wall X = local 00 = freestream value INTRODUCTION Atmospheric icing presents a major hazard to aircraft operat ing under natural icing condit ions and is a cause of major concerns for the certification authorities as well as the aircraft manufacturers. The steady rise in the global aviation traffic means an increased likelihood of encounter ing natural icing conditions. This suggest an increased frequency of icing related accidents unless a considerable amount of effort is focused on the various safety issues concerning in-flight aircraft icing. To enhance flight safety under natural icing conditions, FAA has recently initiated a multi-year icing plan’>’ to address the various issues related to in-flight aircraft icing. One of the several key tasks outl ined in the plan is to ensure the validity and reliability of icing simulation/modeling methods currently being used/developed. In an effort to support the objectives of the FAA Icing Plan, and facilitate Bombardier Aerospace in the certification process, the main focus of research under the Bombardier Aeronautical Chair at l?cole Polytechnique, MontrCal, has been the development of a reliable ice accretion and anti-icing simulation code CANICE.3-5 The development of CANICE has

THERMAL protection from the effects of ice built up can be achieved by means of anti‐icing or de icing. Most aircraft structures are de‐iced since this consumes considerably less power, but in some cases it is essential that the surface be anti‐iced, (e.g. engine intakes, where ice ingestion to the engine is unacceptable and any formation of ice must therefore be prevented).

Icing on stationary structures is an increasingly serious problem as off-shore drilling operations in the sub-polar regions becomes more popular. Since this problem is less complicated than icing on a ship, an attempt was made to calculate accretion rate using existing data. The rate of ice accumulation R can be calculated from R = C f C c F where F is the mass flux of the water drops and C f and Cc are the proportions of spray frozen on the surface and coefficient of capture of drops, respectively. Cc can be close to unity for larger drops such as sea spray. Although many other factors may contribute, C f seems to be a strong function of the air temperature. Mass flux can be written as Vr3 dr where n(r) is the number of drops of radius r in unit volume, V is the wind velocity, ρ is the density of water; n(r) is a function of wind velocity and height of observation. For a stationary structure, the mass flux is primarily dependent upon the wind speed. The ice accretion rate R, calculated using published data on the size distribution of sea spray and using a capture efficiency Cc of I agrees surprisingly well with the diagrams given by previous authors for icing on ships.