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NASA NTRS1999

Parametric Experimental Study of the Formation of Glaze Ice Shapes on Swept Wings

An experiment was conducted to study the effect of velocity and sweep angle on the critical distance in ice accretion formation on swept wings at glaze ice conditions. The critical distance is defined as the distance from the attachment line to the beginning of the zone where roughness elements develop into glaze ice feathers. Icing runs were performed on a NACA 00 1 2 swept wing tip at velocities of 75, 100, 150, and 200 miles per hour. At each velocity and tunnel condition, the sweep angle was changed from 0 deg to 45 deg at 5 deg increments. Casting data, ice shape tracings, and close-up photographic data were obtained. The results showed that at given velocity and tunnel conditions, as the sweep angle is increased from 0 deg to 25 deg the critical distance slowly decreases. As the sweep angle is increased past 25 deg, the critical distance starts decreasing more rapidly. For 75 and 100 mph it reaches a value of 0 millimeters at 35 deg. For 150 and 200 mph it reaches a value of 0 millimeters at 40 deg. On the ice accretion, as the sweep angle is increased from 0 deg to 25 deg, the extent of the attachment line zone slowly decreases. In the glaze ice feathers zone, the angle that the preferred direction of growth of the feathers makes with respect to the attachment line direction increases. But overall, the ice accretions remain similar to the 0 deg sweep angle case. As the sweep angle is increased above 25 deg, the extent of the attachment line zone decreases rapidly and complete scallops form at 35 deg sweep angle for 75 and 100 mph, and at 40 deg for 150 and 200 mph.

Vargas, Mario↗

NASA NTRS2016

Preliminary Results From a Heavily Instrumented Engine Ice Crystal Icing Test in a Ground Based Altitude Test Facility

Preliminary results from the Heavily Instrumented ALF503R-5 Engine test conducted in the NASA Glenn Research Center Propulsion Systems Laboratory will be discussed. The effects of ice crystal icing on a full scale engine is examined and documented. This model engine, serial number LF01, was used during the inaugural icing test in the PSL facility. The reduction of thrust (rollback) events experienced by this engine in flight were replicated in the facility. Limited instrumentation was used to detect icing. Metal temperature on the exit guide vanes and outer shroud and the load measurement were the only indicators of ice formation. The current study features a similar engine, serial number LF11, which is instrumented to characterize the cloud entering the engine, detect characterize ice accretion, and visualize the ice accretion in the region of interest.

enigine icing↗

NASA NTRS2004

Manual of Scaling Methods

This manual reviews the derivation of the similitude relationships believed to be important to ice accretion and examines ice-accretion data to evaluate their importance. Both size scaling and test-condition scaling methods employing the resulting similarity parameters are described, and experimental icing tests performed to evaluate scaling methods are reviewed with results. The material included applies primarily to unprotected, unswept geometries, but some discussion of how to approach other situations is included as well. The studies given here and scaling methods considered are applicable only to Appendix-C icing conditions. Nearly all of the experimental results presented have been obtained in sea-level tunnels. Recommendations are given regarding which scaling methods to use for both size scaling and test-condition scaling, and icing test results are described to support those recommendations. Facility limitations and size-scaling restrictions are discussed. Finally, appendices summarize the air, water and ice properties used in NASA scaling studies, give expressions for each of the similarity parameters used and provide sample calculations for the size-scaling and test-condition scaling methods advocated.

Bond, Thomas H.↗

NASA NTRS1992

A combined analytical-experimental tensile test technique for brittle materials

A semiconventional tensile test technique is developed for impact ices and other brittle materials. Accurate results have been obtained on ultimate strength and modulus of elasticity in a refrigerated ice test. It is noted that the technique can be used to determine the physical properties of impact ices accreted inside icing wind tunnels or other brittle materials.

Chu, M. L.↗

NASA NTRS2014

Ice Shapes on a Tail Rotor

Testing of a thermally-protected helicopter rotor in the Icing Research Tunnel (IRT) was completed. Data included inter-cycle and cold blade ice shapes. Accreted ice shapes were thoroughly documented, including tracing, scanning and photographing. This was the first time this scanning capability was used outside of NASA. This type of data has never been obtained for a rotorcraft before. This data will now be used to validate the latest generation of icing analysis tools.

Airfoil↗

NASA NTRS2019

Independent Effects of Reynolds Number and Mach Number on the Aerodynamics of an Iced Swept Wing

Aerodynamic assessment of icing effects on swept wings is an important component of a larger effort to improve three-dimensional (3D) icing simulation capabilities. An understanding of ice-shape geometric fidelity and Reynolds and Mach number effects on the iced-wing aerodynamics is needed to guide the development and validation of ice-accretion simulation tools. To this end, wind tunnel testing was carried out for a 13.3-percent-scale semispan wing based upon the Common Research Model airplane configuration. The wind tunnel testing was conducted at the Office National d’Etudes et de Recherches Aérospatiales (ONERA) F1 pressurized wind tunnel with Reynolds numbers of 1.6 x 10(exp 6) to 11.9 x 10(exp 6 ) and Mach numbers of 0.09 to 0.34. Five different configurations were investigated using fully 3D, high-fidelity artificial ice shapes that maintain nearly all of the 3D ice-accretion features documented in prior icing wind tunnel tests. These large, leading-edge ice shapes were nominally based upon airplane holding in icing conditions scenarios. For three of these configurations, lower fidelity simulations were also built and tested. The results presented in this paper show that while Reynolds and Mach number effects are important for quantifying the clean-wing performance, there is very little to no effect for an iced wing with 3D, high-fidelity artificial ice shapes or 3D smooth ice shapes with grit roughness. These conclusions are consistent with the large volume of past research on iced airfoils. However, some differences were also noted for the associated stalling angle of the iced swept wing and for various lower fidelity versions of the leading-edge ice accretion. More research is planned to further investigate the key features of ice-accretion geometry that must be simulated in lower fidelity versions in order to capture the essential aerodynamics.

Aircraft icing↗

NASA NTRS2018

Ice Crystal Icing Physics Study using a NACA 0012 Airfoil at the National Research Council of Canada's Research Altitude Test Facility

This paper presents results from a study of the fundamental physics of ice-crystal ice accretion using a NACA 0012 airfoil at the National Research Council of Canada (NRC) Research Altitude Test Facility in August 2017. These tests were a continuation of work which began in 2010 as part of a joint collaboration between NASA and NRC. The research seeks to generate icing conditions representative of those that occur inside a jet engine when ingesting ice crystals. In this test, an airfoil was exposed to mixed-phase icing conditions and the resulting ice accretions were recorded and analyzed. This paper details the specific objectives, procedures, and measurements which included the aero-thermal and cloud measurements. The objectives were built upon observations and hypothesis generated from several previous test campaigns regarding mixed-phase ice-crystal icing. The specific objectives included (A) ice accretions under different wet-bulb temperatures, (B) investigations of steady-state ice shapes previously reported in the literature, (C) total water content variations in search of a threshold for accretion, and (D) probe characterization related to measuring melt fraction which is important to characterize the mixed-phase condition. The resulting ice accretions and conditions leading to such accretions are intended to help extend NASA’s predictive ice-accretion codes to include conditions occurring in engine ice-crystal icing.

Icing↗

NASA NTRS2019

Scaling Evaluation of Ice-Crystal Icing on a Modern Turbofan Engine in PSL Using the COMDES-MELT Code

This paper presents preliminary ice-crystal icing (ICI) altitude scaling evaluation results of a Honeywell Uncertified Research Engine (HURE) that was tested in the NASA Glenn Research Center Propulsion Systems Laboratory (PSL) during January of 2018. This engine geometry features a hidden core design to keep the core less exposed. The engine was fitted with internal video cameras to observe various ice buildup processes at multiple selected locations within the engine core flow path covering the fan stator, the splitter-lip/shroud/strut, and the high pressure compressor (HPC) variable inlet guide vane (IGV) regions. The potential ice accretion risk was pre-determined to occur by using NASA’s in-house 1D Engine Icing Risk assessment code, COMDES-MELT. The code was successful in predicting the risk of ice accretion in adiabatic regions like the fan-stator of the HURE at specific engine operating points. However at several operating points during the test, liquid water was observed running along the shroud toward the variable IGV of the HPC regions with an air temperature well below freezing, thus no particle melting could have occurred due to heating from the air alone. It was reasoned that other sources of heat were present in that region. To account for these heat sources the inlet total temperature was adjusted to give a wet bulb temperature of 24 F below the standard minimum wet bulb temperature of 492 R to allow ice to accrete in the splitter-lip/shroud/strut region, which was determined from a reference case where hard ice was observed in that region. With that adjustment the COMDES-MELT code was successful in providing operating points where there was a risk of ice accretion during the test campaign. In addition to calculating possible conditions at different selected lower altitudes, simulations were run to determine potential inlet conditions that could lead to ice-crystal accretion along the prescribed stations where the cameras were available. From there, scaled test conditions were determined by best matching the following three icing related parameters of the reference condition: (1) the local air total wet bulb temperature, (2) the local ice crystal cloud melt ratio and (3) the engine fan face ice/water to air mass flux ratio of the ice crystal cloud. Instantaneous images taken from the time-lapsed movies of ice buildup were used along with the relevant thermodynamic data of air, water vapor and local icing condition to help evaluate how closely the proposed altitude scaling method could be used in ground based test facility to duplicate selected reference ICI features observed at specific location inside this engine at different scale altitudes. Discussions on observed limitation for engine icing scaling application from this test campaign and needed improvement are provided. A scaling test procedure to help identify potential ICI risk conditions and possible ice accretion locations of a new turbofan engine is evaluated in PSL.

Engine Testing in PSL↗

NASA NTRS2018

Independent Effects of Reynolds and Mach Numbers on the Aerodynamics of an Iced Swept Wing

Aerodynamic assessment of icing effects on swept wings is an important component of a larger effort to improve three-dimensional icing simulation capabilities. An understanding of ice-shape geometric fidelity and Reynolds and Mach number effects on the iced-wing aerodynamics is needed to guide the development and validation of ice-accretion simulation tools. To this end, wind-tunnel testing was carried out for a 13.3%-scale semispan wing based upon the Common Research Model airplane configuration. The wind-tunnel testing was conducted at the ONERA F1 pressurized wind tunnel with Reynolds numbers of 1.6×10(exp 6) to 11.9×10(exp 6) and Mach numbers of 0.09 to 0.34. Five different configurations were investigated using fully 3D, high-fidelity artificial ice shapes that maintain nearly all of the 3D ice accretion features documented in prior icing-wind tunnel tests. These large, leadingedge ice shapes were nominally based upon airplane holding in icing conditions scenarios. For three of these configurations, lower-fidelity simulations were also built and tested. The results presented in this paper show that while Reynolds and Mach number effects are important for quantifying the clean-wing performance, there is very little to no effect for an iced-wing with 3D, high-fidelity artificial ice shapes or 3D smooth ice shapes with grit roughness. These conclusions are consistent with the large volume of past research on icedairfoils. However, some differences were also noted for the associated stalling angle of the iced swept wing and for various lower-fidelity versions of the leading-edge ice accretion. More research is planned to further investigate the key features of ice accretion geometry that must be simulated in lower-fidelity versions in order to capture the essential aerodynamics.

Broeren, Andy P.↗

NASA NTRS2017

Development of Experimental Icing Simulation Capability for Full-Scale Swept Wings: Hybrid Design Process, Years 1 and 2

This report presents the key results from the first two years of a program to develop experimental icing simulation capabilities for full-scale swept wings. This investigation was undertaken as a part of a larger collaborative research effort on ice accretion and aerodynamics for large-scale swept wings. Ice accretion and the resulting aerodynamic effect on large-scale swept wings presents a significant airplane design and certification challenge to air frame manufacturers, certification authorities, and research organizations alike. While the effect of ice accretion on straight wings has been studied in detail for many years, the available data on swept-wing icing are much more limited, especially for larger scales.

Aircraft icing↗

NASA NTRS2017

Ice Roughness and Thickness Evolution on a Swept NACA 0012 Airfoil

Several recent studies have been performed in the Icing Research Tunnel (IRT) at NASA Glenn Research Center focusing on the evolution, spatial variations, and proper scaling of ice roughness on airfoils without sweep exposed to icing conditions employed in classical roughness studies. For this study, experiments were performed in the IRT to investigate the ice roughness and thickness evolution on a 91.44-cm (36-in.) chord NACA 0012 airfoil, swept at 30-deg with 0deg angle of attack, and exposed to both Appendix C and Appendix O (SLD) icing conditions. The ice accretion event times used in the study were less than the time required to form substantially three-dimensional structures, such as scallops, on the airfoil surface. Following each ice accretion event, the iced airfoils were scanned using a ROMER Absolute Arm laser-scanning system. The resulting point clouds were then analyzed using the self-organizing map approach of McClain and Kreeger to determine the spatial roughness variations along the surfaces of the iced airfoils. The resulting measurements demonstrate linearly increasing roughness and thickness parameters with ice accretion time. Further, when compared to dimensionless or scaled results from unswept airfoil investigations, the results of this investigation indicate that the mechanisms for early stage roughness and thickness formation on swept wings are similar to those for unswept wings.

glaze icing↗

NASA NTRS1984

Experimental study of performance degradation of a model helicopter main rotor with simulated ice shapes

An experimental study utilizing a remote controlled model helicopter has been conducted to measure the performance degradation due to simulated ice accretion on the leading edge of the main rotor for hover and forward flight. The 53.375 inch diameter main rotor incorporates a NACA 0012 airfoil with a generic ice shape corresponding to a specified natural ice condition. Thrust coefficients and torque coefficients about the main rotor were measured as a function of velocity, main rotor RPM, angle-of-incidence of the fuselage, collective pitch angle, and extent of spanwise ice accretion. An experimental airfoil data bank has been determined using a two-dimensional twenty-one inch NACA 0012 airfoil with scaled ice accretion shapes identical to that used on the model helicopter main rotor. The corresponding experimental data are discussed with emphasis on Reynolds number effects and ice accretion scale model testing.

Korkan, K. D.↗

NASA NTRS1947

A Method for Calculating the Heat Required for Windshield Thermal Ice Prevention Based on Extensive Flight Tests in Natural Icing Conditions

An equation is presented for calculating the heat flow required from the surface of an internally heated windshield in order to prevent the formation of ice accretions during flight in specified icing conditions. To ascertain the validity of the equation, comparison is made between calculated values of the heat required and measured values obtained for test windshields in actual flights in icing conditions. The test windshields were internally heated and provided data applicable to two common types of windshield configurations; namely the V-type and the type installed flush with the fuselage contours. These windshields were installed on a twin-engine cargo airplane and the icing flights were conducted over a large area of the United States during the winters of 1945-46 and 1946-47. In addition to the internally heated windshield investigation, some test data were obtained for a windshield ice-prevention system in which heated air was discharged into the windshield boundary layer. The general conclusions resulting from this investigation are as follows: 1) The amount of heat required for the prevention of ice accretions on both flush- and V-type windshields during flight in specified icing conditions can be calculated with a degree of accuracy suitable for design purposes. 2) A heat flow of 2000 to 2500 Btu per hour per square foot is required for complete and continuous protection of a V-type windshield in fight at speeds up to 300 miles per hour in a moderate cumulus icing condition. For the same degree of protection and the same speed range, a value of 1000 Btu per hour per square foot suffices in a moderate stratus icing condition. 3) A heat supply of 1000 Btu per hour per square foot is adequate for a flush windshield located well aft of the fuselage stagnation region, at speeds up to 300 miles per hour, for flight in both stratus and moderate cumulus icing conditions. 4) The external air discharge system of windshield thermal ice prevention is thermally inefficient and requires a heat supply approximately 20 times that required for an internal system having the same performance.

ICE FORMATION↗

NASA NTRS2022

Experimental and Computational Icing Simulation for Large Swept Wings

The purpose of this final report is to summarize the key results, findings and contributions of a large, multi-organization, multi-year effort focused on swept wing icing and aerodynamics. This research effort was jointly sponsored by NASA, FAA and ONERA and was supported by Boeing and the Universities of Illinois, Virginia, and Washington. The overall goal of this research was to improve the experimental and computational simulation capability for icing on large swept wings typical of commercial transports. This research included both ice accretion and aerodynamic studies using the NASA Common Research Model (CRM) as the reference geometry. For this work, a 65% scaled version—CRM65—was used as the full-scale baseline airplane geometry. This program marks the first non-proprietary research to generate and document full-scale swept wing ice accretions in an icing tunnel and then conduct semispan wing aerodynamic testing on scaled ice accretions at high Reynolds number (i.e., up to 11.9×106). During this work, several new experimental and computational techniques were developed or documented and new knowledge about swept wing icing aerodynamics was identified. All are documented in this report.

Aircraft icing↗

NASA NTRS1938

Distribution of Temperatures over an Airplane Wing with Reference to the Phenomena of Ice Formation

The results obtained from the present study of temperature distribution over an airplane wing afford means for making the following statements as regards the conditions of ice accretion and the use of a thermic anti-icer or de-icer: 1) Ice can form on a wing only when the temperature is below or hovering around zero. 2) The thermic effects produced on contact of the air with the moving wing rather oppose ice accretion. 3) The thermic procedure in the fight against ice accretion on the wing consists in electrical heating of the leading edge. 4) It seems that the formation of ice on the wing ought to be accompanied by a temperature rise which brings the accretion to 0 degrees. 5) If the thermic effects of friction favor the operation of the thermic anti-icer, the functioning of the de-icer is facilitated by the release of heat which accompanies the deposit of ice.

Brun, Edmond↗

NASA NTRS1986

Airfoil aerodynamics in icing conditions

Methods of analyzing and experimentally measuring the effect of ice accretion on airfoil sections are presented. Empirical and analytical methods for predicting airfoil performance degradation due to ice are discussed. Ice simulation techniques for aerodynamic testing are presented and compared to data with actual ice accretions. The results show that simulation techniques to imitate the effect of ice on airfoil performance work well in most cases. Comparisons between predicted and measured airfoil performance with ice accretions are presented. For rime ice cases, the predictions compared well with experiments; but for glaze ice, a need for improved methods are seen.

Bragg, M. B.↗

NASA NTRS2003

Experimental Study of Supercooled Large Droplet Impingement Effects

Typically, ice accretion results from small supercooled droplets (droplets cooled below freezing), usually 5 to 50 microns in diameter, which can freeze upon impact with an aircraft surface. Recently, ice accretions resulting from supercooled large droplet (SLD) conditions have become a safety concern. Current ice accretion codes have been extensively tested for Title 14 Code of Federal Regulations Part 25, Appendix C icing conditions but have not been validated for SLD icing conditions. This report presents experimental methods for investigating large droplet impingement dynamics and for obtaining small and large water droplet impingement data.

ICE ACCRETION CODE↗

NASA NTRS2016

Generation of Fullspan Leading-Edge 3D Ice Shapes for Swept-Wing Aerodynamic Testing

The deleterious effect of ice accretion on aircraft is often assessed through dry-air flight and wind tunnel testing with artificial ice shapes. This paper describes a method to create fullspan swept-wing artificial ice shapes from partial span ice segments acquired in the NASA Glenn Icing Reserch Tunnel for aerodynamic wind-tunnel testing. Full-scale ice accretion segments were laser scanned from the Inboard, Midspan, and Outboard wing station models of the 65% scale Common Research Model (CRM65) aircraft configuration. These were interpolated and extrapolated using a weighted averaging method to generate fullspan ice shapes from the root to the tip of the CRM65 wing. The results showed that this interpolation method was able to preserve many of the highly three dimensional features typically found on swept-wing ice accretions. The interpolated fullspan ice shapes were then scaled to fit the leading edge of a 8.9% scale version of the CRM65 wing for aerodynamic wind-tunnel testing. Reduced fidelity versions of the fullspan ice shapes were also created where most of the local three-dimensional features were removed. The fullspan artificial ice shapes and the reduced fidelity versions were manufactured using stereolithography.

Icing↗