Articles with tag: "icing tunnels"

1. 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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2. 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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3. 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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4. 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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5. 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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6. 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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7. 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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8. 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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9. 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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10. 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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11. 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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12. 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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