Articles with tag: "icing tunnel"

1. Radomes and Antennas

   "The current use of improved airplane ice-prevention equipment has extended operations in icing conditions and thus accentuated the need for protecting aircraft antennas against structural failures resulting from ice accretions"

   

   These reviews are for studies of the effect of ice on radomes and antennas.

   • Gowan, W. H., Jr.: Vibration and Investigation of CAA Type V-I09 Very-High-Frequency Aircraft Antenna. NACA-RM-SE9D20. 1949.

     "After 7 minutes of icing, however, one antenna element experienced a vibratory failure"
     > review: NACA-RM-SE9D20

   • Kepple, W. L.: Determination of Aircraft Antenna Loads Produced by Natural Icing Conditions. NACA-RM-E7H26a, 1948.

     "The current use of improved airplane ice-prevention equipment has extended operations in icing conditions and thus accentuated the need for protecting aircraft antennas against structural failures resulting from ice accretions"
     > review: NACA-RM-E7H26a

   • Lewis, James P., and Blade, Robert J.: Experimental Investigation of Radome Icing and Icing Protection. NACA-RM-E52J31, 1953.

     "At present very little is known of the effect of radome …

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2. NACA-RM-E57G09

   "the contour plots indicate that cowl-lip disturbances are the more controlling factor"

   "Total Pressure Distortion and Recovery of Supersonic Nose Inlet with Conical Centerbody in Subsonic Icing Conditions" ¹

   

   Abstract

   Ice was formed on a full-scale unheated supersonic nose inlet in the NACA Lewis icing tunnel to determine its effect on compressor-face total-pressure distortion and recovery. Inlet angle of attack was varied from 0° to 12°, free-stream Mach number from 0.17 to 0.28, and compressor-face Mach number from 0.10 to 0.47. Icing-cloud liquid-water content was varied from 0.65 to 1.8 grams per cubic meter at free-stream static air temperatures of 15° and 0° F.

   The addition of ice to the inlet components increased total-pressure- distortion levels and decreased recovery values compared with clear-air results, the losses increasing with time in ice. The combination of glaze ice, high corrected weight flow, and high angle of …

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3. NACA-TN-4093

   "Rotational speeds up to 1200 rpm had no apparent effect on the heat-transfer characteristics of the spinner"

   "Investigation of Heat Transfer from a Stationary and Rotating Conical Forebody"

   

   Abstract

   The convective heat transfer from the surface of a conical forebody having a hemispherical nose, an included angle of approximately 30°, and a maximum diameter of 18.9 inches was investigated in a wind tunnel for both stationary and rotating operation. The range of test conditions included free-stream velocities up to 400 feet per second, rotational speeds up to 1200 rpm, and. angles of attack of 0° and 6°. Both a uniform surface temperature and a uniform heater input power density were used.

   The Nusselt-Reynold's number relations provided good correlation of the heat-transfer data for the complete operating range at 0° angle of attack with and without spinner rotation, and for 6° angle of attack with rotation. Rotational speeds up to …

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4. NACA-TN-3837

   "Many aircraft components are essentially simple bodies of revolution; examples of these are radomes, body noses, engine accessory housings, and the large spinners of turboprop engines"

   "Investigation of Heat Transfer from a Stationary and Rotating Ellipsoidal Forebody of Fineness Ratio 3" ¹

   

   Abstract

   The convective heat transfer from the surface of an ellipsoidal fore-body of fineness ratio 3 and 20-inch maximum diameter was investigated in clear air for both stationary and rotating operation over a range of conditions including air speeds up to 240 knots, rotational speeds up to 1200 rpm, and angles of attack of 0°, 3°, and 6°. The results are presented in the form of heat-transfer coefficients and the correlation of Nusselt and Reynolds numbers. Both a uniform surface temperature and a uniform input heater density distribution were used.

   The experimental results agree well with theoretical predictions for uniform surface temperature distribution. Complete agreement was not obtained …

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5. NACA-RM-E50H29

   "Experience has shown that ... the inlet guide vanes of an axial-flow turbojet engine constitute the most critical component to be protected from icing"

   "Investigation of Power Requirements for Ice Prevention and Cyclical De-Icing of Inlet Guide Vanes with Internal Electric Heaters" ¹

   

   Abstract

   An investigation was conducted to determine the electric power requirements necessary for ice protection of inlet guide vanes by continuous heating and by cyclical de-icing. Data are presented to show the effect of ambient-air temperature, liquid-water content, air velocity, heat-on period, and cycle times on the power requirements for these two methods of ice protection.
   The results showed that for a hypothetical engine using 28 inlet guide vanes under similar icing conditions, cyclical de-icing can provide a total power saving as high as 79 percent over that required for continuous heating. Heat-on periods in the order of 10 seconds with a cycle ratio of about 1:7 …

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6. NACA-RM-E50I08

   "Ice formations ... may have the following effects, which when combined may become serious enough to necessitate a shutdown of the engine: reduced engine thrust, increased,fuel consumption, and increased tail-pipe temperature."

   "Icing Characteristics and Anti-Icing Heat Requirements for Hollow and Internally Modified Gas-Heated Inlet Guide Vanes" ¹

   

   Abstract

   A two-dimensional inlet-guide-vane cascade was investigated to determine the effects of ice formations on the pressure losses across the guide vanes and to evaluate the heated gas flow and temperature required to prevent icing at various conditions. A gas flow of approximately 0.4 percent of the inlet-air flow was necessary for anti-icing a hollow guide-vane stage at an inlet-gas temperature of 500° F under the following icing conditions: air velocity, 280 miles per hour; water content, 0.9 gram per cubic meter; and inlet-air static temperature, 0° F. Also presented are the anti-icing gas flows required with modifications of the hollow …

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7. NACA-TN-2126

   "Use of the hot-gas method of anti-icing has been restricted ... because of difficulty in controlling the rate of heat dissipation"

   "Improvements in Heat Transfer for Anti-Icing of Gas-Heated Airfoils with Internal Fins and Partitions" ¹

   

   Abstract

   The effect of modifying the gas passage of hollow metal airfoils by the additIon of internal fins and partitions was experimentally investigated and comparisons were made among a basic unfinned airfoil section and two airfoil designs having metal fins attached at the leading edge of the internal gas passage. An analysis considering the effects of heat conduction in the airfoil metal was made to determine the internal modification effectiveness that may be obtained in gas-heated components, such as turbojet-inlet guide vanes, support struts, hollow propeller blades, arid. thin wings.

   Over a wide range of heated-gas flow and tunnel-air velocity, the increase in surface-heating rates with internal fin was marked (up to 3.5 times …

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8. NACA-TN-1246

   "The icing of the unprotected installation presents a serious operational problem"

   "Wind-Tunnel Investigation of Icing of an Engine Cooling-Fan Installation" ¹

   

   Abstract

   An investigation was made of the icing characteristics and means of ice protection of a typIcal radial-engine cooling-fan installation, The investigation was made at various icing and performance conditions in the icing research tunnel of the NACA Cleveland laboratory.

   The icing of the unprotected cooling-fan installation was found to present a serious operational problem. Reduction in air flow below the minimum value required for engine cooling occurred within 2 minutes and complete stoppage of the cooling-air flow through the fan assembly occurred in as little as 5 minutes under normal icing conditions.

   Steam de-icing was found to be effective for the cowling lip and inlet duct. Alcohol de-icing of the fan blades and stator vanes was found to be unsatisfactory. Electrical heat de-icing of the fan blades was …

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9. Engine Inlet Icing

   "The desirability for all-weather operation of turbojet aircraft has necessitated extensive research on methods of icing protection for the various engine components"

   
   From NACA-RM-E8C18.

   Discussion

   Publications taken largely from The Historical Selected Bibliography of NACA-NASA Icing Publications, "Turbine-Type Engine and Inlet Icing Studies" section are reviewed here.

   Reviews

   NACA-TN-1246 "Wind-Tunnel Investigation of Icing of an Engine Cooling-Fan Installation"

   • "The icing of the unprotected installation presents a serious operational problem"

   NACA-RM-E8C18 "Preliminary Results of Natural Icing of an Axial-Flow Turbojet Engine"

   • "Ice formations penetrated to the second-stage rotor blades"

   NACA-RM-E8FO1a "Natural Icing of an Axial-Flow Turbojet Engine in Flight for a Single Icing Condition"

   • "The engine was satisfactorily accelerated to take-off power after approximately 45 minutes in the icing condition"

   NACA-TN-2126 "Improvements in Heat Transfer for Anti-Icing of Gas-Heated Airfoils with Internal Fins and Partitions"

   • "Use of the hot-gas method of anti-icing has been restricted ... because of difficulty in controlling the …

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10. Tools

    Aircraft designs for flight in icing are improved and proven effective by several tools, including analysis, icing wind tunnel test, and flight test in icing conditions.

    Design handbooks

    Design handbooks have charts and tables that can be used to perform analyses for aircraft icing and ice protection.

    
    from "Aircraft Icing Handbook", DOT/FAA/CT-88/8 apps.dtic.mil

    Analysis

    There are computerized icing analysis tools available from NASA, and from commercial vendors. There is also "bespoke" software created for special purposes.

    
    from "Glenn Research Center Software" www1.grc.nasa.gov

    Laboratory tests

    A wind tunnel is a large tube with a fan to produce air flow at a calibrated airspeed. Wind tunnels are used to study many effects on aircraft, including icing. Artificially produced ice shapes (often 3D printed) may be adhered to airplane models, and the effects studied.

    To simulate in-flight icing conditions, "Icing Wind Tunnels" often use refrigeration …

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11. Large Drop Icing Conditions in Icing Wind Tunnels

    "effects are scaled appropriately between Appendix C and SLD conditions using the existing scaling methods"

    

    Summary

    Icing wind tunnel uses and challenges for large drop icing are discussed.

    Key points

    1. Since 2014, supercooled large drop (SLD) icing has been part of (US) 14 CFR Part 25 icing regulations (Appendix O).
    2. Physics make current icing wind tunnels challenged to reproduce the freezing rain portion of Appendix O.
    3. For the "main" leading edge region ice shape, the standard test similarity calculations apply.
    4. Icing extent limits appear to have unexplained variability in test.
    5. Ice protection test similarity has not been addressed in detail for SLD conditions.

    A Very Brief Description of Supercooled Large Drop (SLD) Icing Conditions

    I will keep this brief and focused on icing wind tunnels.

    For a more complete description of SLD icing, see Hu ¹. While Appendix O ² is only 10 page long, AC 25-28 ³ describing acceptable …

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12. AIAA-2017-3927

    "With a thermal IPS, energy reduction can be achieved by operating in a ‘running wet’ mode under more extreme icing conditions."

    

    "Evaluation of Alternative Altitude Scaling Methods for Thermal Ice Protection System in NASA Icing Research Tunnel" ¹

    Summary

    A procedure for scaling conditions for ice protection tests is detailed.

    Key Points

    1. Scaling methods for ice protection testing at sea level conditions were evaluated.
    2. The "WePi3" scaling method was recommended.
    3. The method requires in-test adjustments of heating to match reference surface temperatures.
    4. Test conditions for unheated areas will be different from those for heated areas.

    Abstract

    A test was conducted at NASA Icing Research Tunnel to evaluate altitude scaling methods for thermal ice protection system. Two new scaling methods based on Weber number were compared against a method based on Reynolds number. The results generally agreed with the previous set of tests conducted in NRCC Altitude Icing Wind Tunnel where …

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13. The Effects of Humidity in Icing Wind Tunnel Tests

    "a condition of supersaturation, which promotes the growth of frost deposits"

    Summary

    Supersaturated humidity can affect icing wind tunnel results.

    Key Points

    1. Some observations of supersaturated humidity conditions were made in the NACA-era.
    2. Supersaturation was associated with frost on test article afterbodies.
    3. Recirculating icing wind tunnel conditions are calculated to tend to be supersaturated.
    4. Some potential effects of supersaturation are calculated.

    A brief primer on humidity

    A measurement of water vapor in the air is humidity. Relative humidity is the most common measure. In everyday life 30% to 60% relative humidity is generally considered to be comfortable. Lower humidities feel dry, and higher humidities feel wet or "humid".

    The most water vapor that can usually exist at a given static temperature is termed "saturated", and that condition has 100% relative humidity. Given sufficient time and condensation surfaces, any surplus vapor above this value will condense as liquid water.

    Natural icing …

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14. Manual of Scaling Methods

    "... it was not surprising that scale ice shapes were again a good match for the reference"

    NASA/CR-2004-212875 ¹

    

    Summary

    Similarity calculations for ice shapes are detailed.

    Key Points

    1. Several scaling methods with differing parameters are compared in tests.
    2. "The Ruff method, supplemented with the constant-We_L approach to calculate scale velocity, is recommended"
    3. Examples are included of how to deal with limitations (temperature, lwc, etc.)

    Abstract

    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 …

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15. Bilanin Pi Terms and the Weber Number

    "An unfortunate fact is that if proposed additional scaling parameters prove to be what is required to conduct improved subscale tests, icing wind tunnel subscale tests are likely to be even more restrictive."

    "Proposed Modifications to Ice Accretion/Icing Scaling Theory" ¹

    Summary

    Water surface tension is identified as a factor in ice shapes and test similarity.

    Key points

    1. 18 dimensionless Pi-terms were identified.
    2. "the π method has failed to provide a scaling methodology which can be used to test subscale aerodynamic components"
    3. "however, does not preclude seeking approximate scaling methodologies"
    4. Several later studies investigate the role of water surface tension and the Weber number.

    Abstract

    The difficulty of conducting full-scale icing tests has long been appreciated. Testing in an icing wind tunnel has been undertaken for decades. While aircraft size and speed have increased, tunnel facilities have not, thus making subscale geometric tests a necessity. Scaling laws governing these …

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16. AEDC-TR-87-23

    "drag coefficient (Cd) was used as an index of similitude by quantitatively indicating how much the shape or ice surface changed"

    

    "An Empirical Look at Tolerances in Setting Icing Test Conditions with Particular Application to Icing Similitude" ¹

    Summary

    An investigation into which icing conditions parameters affect icing similtiude as measured by aerodynamic drag effects.

    Abstract

    Often, engine icing tests cannot be conducted at conditions that are considered the critical test points because of aircraft engine test facility operational constraints or the inability to find the desired conditions in natural icing flight tests. The use of ice scaling laws may circumvent this testing limitation. Earlier studies (Refs. 1 and 2) of the application of ice scaling (similitude) to aircraft engine testing indicated that experimental data were needed to determine to what extent icing test conditions [temperature (T), velocity (V), liquid water content (LWC), median volume diameter (MVD), pressure (P)], could …

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17. AEDC-TR-85-30

    "It would be beneficial to the icing community if the feasibility of using scale models in these tests could be proven."

    

    "Analysis and Verification of the Icing Scaling Equations" ¹

    Summary

    An expanded set of icing similarity terms are derived and tested.

    Key Points

    1. Water drop impingement similarity is simplified using Ko.
    2. Icing heat transfer similarity terms derived from Messinger are added.
    3. Tests in an icing wind tunnel validate the selected set of similarity terms.

    Abstract

    1.1 BACKGROUND

    The formation of ice on aircraft surfaces occurs during flight through supercooled droplets. Ice accretions on these surfaces usually degrade both aircraft performance and operational safety. For this reason, it has become important in the design and certification phases of system development to evaluate system performance degradation because of icing.

    The most acceptable method of evaluating the performance characteristics of aircraft and aircraft components for system certification would be to conduct …

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18. Scaling in NACA Icing Wind Tunnel Tests

    "If the values of the K and φ parameters for the model and full-scale nacelle are maintained the same, the icing characteristics of the model will be similar to the icing characteristics of the full-scale"

    Summary

    Early examples of icing test scaling are noted.

    Key Points

    1. Three publication that mention scaling are reviewed.
    2. Some challenges with scaling are noted.
    3. A airfoil design of a full scale leading edge truncated with an aft flap addresses some challenges.

    Discussion

    NACA-RM-E8A27 "Ice Protection of Turbojet Engines by Inertia Separation of Water, I - Alternate-Duct System" ¹

    This is the earliest example that I have found of using dimensionless water drop impingement terms for test similarity calculations.

    The results of a preliminary investigation of internal water- inertia separation inlets designed to prevent automatically the entrance of large quantities of water into a turbojet engine in icing conditions are presented. A simplified analytical approach to the …

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19. Calibration of the NACA Icing Wind Tunnels

    "Considerable time [was devoted] to means for controlling the amount of water sprayed into the air stream, the size of water particles, and the temperatures of the air and water" ¹

    Summary

    Calibration methods evolved during the NACA-era

    Key Points

    1. Early tests had informal calibrations, partly due to a limited understanding of the natural icing environment.
    2. Rotating multicylinders were the most used means of calibration.
    3. Water spray nozzles were improved circa 1949.
    4. The understanding of the natural icing environment had also advanced by 1949.

    Discussion

    As implied from the quote above from the year 1929, the calibration of an icing wind tunnel is often not just measuring what the facility produces, but also altering and improving the facility to achieve target values for water drop size and liquid water content, and producing a water drop spray that is uniform "enough".

    Early calibrations

    Two early icing wind tunnel tests had informal …

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20. Uses of NACA-Era Icing Wind Tunnels

    "Icing wind tunnels can simulate natural icing with water-spray and refrigeration systems ... to permit safe, convenient and relatively inexpensive testing." ¹

    
    How much of a P-39 can one fit into an icing wind tunnel?

    Summary

    A wide variety of test articles were used in the NACA-era Icing Research Tunnel (IRT)

    Key Points

    1. 37 publications were found describing the use of the IRT.
    2. A wide variety of test articles were used in the NACA-era Icing Research Tunnel

    Discussion

    Readers are encouraged to see "We Freeze to Please": A History of NASA's Icing Research Tunnel and the Quest for Flight Safety, which includes information from NACA-era internal memos and interviews that I have not seen published elsewhere.

    There were five icing wind tunnels used by NACA. The majority of the tests were performed in the Icing Research Tunnel (IRT) as NACA Lewis. The four other tunnels are briefly described in the "Other …

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21. NACA-TN-339

    "A spray, which consisted of very small drops, was found to be quite satisfactory"

    "Refrigerated Wind Tunnel Tests on Surface Coatings for Preventing Ice Formation"

    Summary

    An early icing wind tunnel and test are described

    Key Points

    1. An early icing wind tunnel with most of the components of current tunnels is described.
    2. A test of several coatings to prevent ice is detailed.
    3. Many of the points noted about icing tunnel test reflect current test experience.

    Abstract

    This investigation was conducted in the Refrigerated Wind Tunnel at Langley Memorial Aeronautical Laboratory, Langley Field, Virginia, to determine the effectiveness of various surface coatings as a means for preventing ice formations on aircraft in flight. The substances used as coatings for these tests are divided into two groups: compounds soluble in water, and those which are insoluble in water. It was found that certain soluble compounds were apparently effective in preventing the formation …

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22. NACA-TN-3396

    "into the transonic and supersonic regimes, the frictional heating becomes of considerable importance to icing."

    "Icing Limit and Wet-Surface Temperature Variation for Two Airfoil Shapes under Simulated High-Speed Flight Conditions"

    ¹

    

    Summary

    Predictions of the icing limit temperature were "sufficiently accurate" in tests at Mach 1.35.

    Key points

    1. Surface temperatures in icing conditions are challenging to measure.
    2. Apparently small differences in pressure coefficient and recovery factor values are important at high Mach values.
    3. Partial surface wettedness makes comparisons between analysis and test challenging.
    4. Thermal conduction in the substrate affects runback ice.
    5. Predictions of the icing limit temperature were "sufficiently accurate" in tests at Mach 1.35.

    Abstract

    Frictional heating resulting from flight at high speeds effectively reduces the value of ambient-air temperatures at which ice forms on aircraft surfaces. An experimental study was made of the wet-surface temperature and the stream conditions that result in ice-free surfaces for bodies …

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