Calibration of the NACA Icing Wind Tunnels

Published: Sun 24 July 2022
Updated: Sat 18 May 2024

tags: icing 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 calibrations (compared to today's standards 2).

NACA-TN-339, 1930 (Langley Refrigerated Wind Tunnel) 3:

Certain preliminary tests were made in the wind tunnel to determine the best form of water spray necessary to produce ice of smooth appearance and which would be similar in structure and form to that observed in flight (Reference 12), in order to make a study of possible preventives. It was found that the character of the formations obtained depended to a great degree on the quantity of water admitted to the tunnel per unit of time. A spray which consisted of large drops was found to use excessive quantities of water which could not be properly regulated without giving very poor dispersion in the jet, and which gave formations of ice on the model of a very different shape from any obtained in flight. A spray, which consisted of very small drops, was found to be quite satisfactory and was used in all the following tests, as it could be easily controlled to give even dispersion across the air stream at any desired rate of water output.

NACA-TN-712, 1939 (Langley 7-foot by 10-foot wind tunnel) 4:

Natural precipitations were simulated by admitting water to the air stream through a spray nozzle. The tunnel test section with the model and the spray are diagrammatically shown in figure 1.

Figure 1 of NACA-TN-712. Illustration showing spray that will give rime ice. If nozzle is raised, large drops will strike model, giving glaze ice.

[There will be a discussion of this figure when we get to "Large Drop Icing" in the Icing Wind Tunnel Test thread]

The range of control over the formation of ice was such that a simulation of all typical ice formations found in flight could be produced.

Calibrations in the IRT

Calibrations methods in the NACA Lewis Icing Research Tunnel (IRT) evolved over time.

Drop size calibration methods:

1946 NACA-TN-1134 pool of castor oil
1947 NACA-TN-1246 rotating multicylinders
1948 NACA-RM-E8A27 rotating multicylinder "by volume maximum"
(new nozzles design circa 1949, per "We Freeze to Please")
1950 NACA-RM-E50I08 rotating multicylinder MVD
1951 NACA-RM-E51B12 "in the range of natural icing conditions"
1951 NACA-TN-2480 (apparently multicylinder) "the mean-effective droplet diameter was varied from about 8 to 12 microns by adjusting the nozzle-air pressure" *
1952 NACA-TN-2615 absorbent cylinders (special purpose in transonic tunnel)
1953 NACA-TN-2962 "The icing conditions were determined from a previous calibration of the tunnel and periodically checked with a pressure-type icing-rate meter"
1955 NACA-RM-E54I03 "the results shown were calculated from unpublished wind-tunnel water-droplet impingement data obtained by means of water droplets carrying dye in solution."

* I note this because it implies that they had enough confidence in the control systems and prior calibrations so that conditions could be set just by the spray control parameters.

LWC calibration methods:

1946 NACA-TN-1134 free-water sampling rake
1947 NACA-TN-1246 rotating multicylinders
1948 NACA-TN-1586 rotating cylinder grid
1952 NACA-TN-2615 absorbent cylinders (special purpose in transonic tunnel)
1953 NACA-TN-2962 "The icing conditions were determined from a previous calibration of the tunnel and periodically checked with a pressure-type icing-rate meter"
1955 NACA-TN-3338 cylinders, ribbon, aspirator
1955 NACA-TN-3564 "Liquid-water content was measured by means of a pressure-type icing-rate meter"
1956 NACA-TN-3839 Joukowski-aspirator
1957 NACA-TN-4155 "Liquid-water content was measured by means of a pressure-type icing-rate meter"
1958 NACA-TN-4268 "The cloud total liquid-water content was obtained by collecting dye from the spray cloud in an aspirating device (a tube that draws in the cloud at free-stream conditions)"

Selected images

Figure 3 of NACA-TN-1134. Free-water sampling rake and water trap.
from NACA-TN-1134

Figure 7 of NACA-TN-1520. Icing-survey equipement for liquid-water concentrations and droplet-size measurements.
from NACA-TN-1520

Figure 1 of NACA-RM-E51E16. Principle of operation of NACA pressure-type icing-rate indicator.
from NACA-RM-E51E16

Figure 6 of NACA-RM-E51E16. Rotating-disk type icing-rate meter.
from NACA-RM-E51E16

Figure 7 of NACA-TN-2615. Absorbent cylinder used in the measurement of liquid-water content in the cloud duct.
from NACA-TN-2615

Figure 3 of NACA-TN-3839. Dimensionless droplet-size distribution of tunnel spray obtained on 36.5 percent Joukowski airfoil (see Appendix B).
from NACA-TN-3839

NACA water spray calibrations

(In approximate chronological order)
Note that while NACA-RM-E50K10 was published in 1951, it contains data from a test conducted in 1945.

Publication LWC calibration MVD calibration
NACA-RM-E50K10a not stated not stated, 35 micrometer "based on volume maximum"
NACA-TN-1134 free-water sampling rake Castor oil pool
NACA-TN-1246 multicylinder multicylinder 55 MVD
NACA-TN-1520 rotating cylinder grid multicylinder 55 MVD
NACA-TN-1691 rotating cylinder grid multicylinder 55 MVD
NACA-TN-1586 NACA-TN-1587 NACA-TN-1588 rotating cylinder grid multicylinder 55 MVD
NACA-RM-E8A27 NACA-RM-E8A28 NACA-RM-E8A29 multicylinder multicylinder 12 to 15 micrometer "by volume maximum"
NACA-RM-E9EO6 multicylinder multicylinder "in the range of natural icing conditions"
NACA-RM-E9E12 not stated not stated
NACA-TN-1789 multicylinder multicylinder 15 to 20 micrometer "by volume maximum"
NACA-RM-E50I08 multicylinder multicylinder 10 to 15 MVD
NACA-RM-E50E03 multicylinder multicylinder 10 MVD
NACA-RM-E50H29 "measured" "measured" 15 MVD
NACA-TN-2480 rotating cylinder (apparently multicylinder) "the mean-effective droplet diameter was varied from about 8 to 12 microns by adjusting the nozzle-air pressure"
NACA-RM-E51E16 not stated not stated
NACA-RM-E51B12 multicylinder multicylinder "in the range of natural icing conditions"
NACA-RM-E51J29 not stated not stated
NACA-RM-E51J30 multicylinder multicylinder 6 to 10 MVD
NACA-RM-E53C27 not stated not stated 8 to 18 MVD
NACA-TN-2962 "The icing conditions were determined from a previous calibration of the tunnel and periodically checked with a pressure-type icing-rate meter" dye-tracer technique 10 to 16 MVD
NACA-RM-E53E07 not stated not stated
NACA-RM-E52J31 not stated not stated
NACA-RM-E53C26 not stated not stated
NACA-RM-E53J30 not stated not stated
NACA-RM-E54I03 pressure-type icing-rate meter "the results shown were calculated from unpublished wind-tunnel water-droplet impingement data obtained by means of water droplets carrying dye in solution."
NACA-TN-3338 cylinders, ribbon, aspirator cylinders
NACA-TN-3564 "Liquid-water content was measured by means of a pressure-type icing-rate meter" "Icing - cloud droplet size was obtained from a previous calibration obtained by using water droplets carrying dye in solution"
NACA-TN-3839 Joukowski-aspirator multicylinder
NACA-RM-E56B23 not stated not stated
NACA-RM-E56E11 not stated not stated
NACA-TN-4155 "Liquid-water content was measured by means of a pressure-type icing-rate meter" "Icing-cloud-droplet size as a function of spray-nozzle pressure settings was determined from a previous calibration of droplet size obtained with water droplets carrying dye in solution"
NACA-RM-E57G09 not stated not stated
NACA-TN-4268 "The cloud total liquid-water content was obtained by collecting dye from the spray cloud in an aspirating device (a tube that draws in the cloud at free-stream conditions)" "The cloud droplet size and size distribution were determined by experimental and theoretical impingement on a 36.5-percent-thick symmetrical Joukowski airfoil"

Natural icing conditions characterizations

Calibration may be thought of as understanding the conditions that a facility can achieve.

Another step is knowing what the flight conditions are that one wants to simulate.

The understanding of natural icing conditions was also evolving in the NACA-era. This topic merits a thread of its own, but for now I will very briefly summarize.

In 1947 there was some understanding of MVD and LWC targets. This figure is from a presentation by William Lewis 5.

Figure 3 from William Lewis presentation. Liquid-water content, W, and average drop diameter in icing clouds.

This had advanced by 1949 to something close to our current understanding. As mentioned in the Conclusions of the Cylinder Thread, the current icing regulations environment definition was largely determined by a few NACA publications, NACA-TN-1855 6 being one of them. Readers may recognize the values of "II-M Intermittent Maximum" and "III-M Continuous Maximum" in Table I below as being part of the current regulations.

Table I of NACA-TN-1855. Recommended values of meteorological factors for consideration in the design of aircraft ice-prevention equipment.

It was fortunate that by 1949 the IRT spray system was able to produce sprays similar to at least a portion of these values.

So, by 1951, NACA-RM-E51B12 could declare that the test conditions were "in the range of natural icing conditions".

References

  • von Glahn, Uwe H., and Renner, Clark E.: Development of a Protected Air Scoop for the Reduction of Induction-System Icing. NACA-TN-1134, 1946.
  • Lewis, James P.: Wind-Tunnel Investigation of Icing of an Engine Cooling-Fan Installation. NACA-TN-1246, 1947.
  • Lewis, James P.: De-Icing Effectiveness of External Electric Heaters for Propeller Blades. NACA-TN-1520, 1948.
  • Lewis, James P., and Stevens, Howard C., Jr.: Icing and De-Icing of a Propeller with Internal Blade Heaters. NACA-TN-1691, 1948.
  • Mulholland, Donald R., and Perkins, Porter J.: Investigation of Effectiveness of Air-Heating a Hollow Steel Propeller for Protection against Icing, I - Unpartitioned Blades. NACA-TN-1586, 1948.
  • Mulholland, Donald R., and Perkins, Porter J.: Investigation of Effectiveness of Air-Heating a Hollow Steel Propeller for Protection against Icing, III - 25-Percent Partitioned Blades. NACA-TN-1588, 1948.
  • Perkins, Porter J., and Mulholland, Donald R.: Investigation of Effectiveness of Air-Heating a Hollow Steel Propeller for Protection against Icing, II- 50-Percent Partitioned Blades. NACA-TN-1587, 1948.
  • von Glahn, Uwe H.: Ice Protection of Turbojet Engines by Inertia Separation of Water, I - Alternate-Duct System. NACA-RM-E8A27, 1948.
  • von Glahn, Uwe H.: Ice Protection of Turbojet Engines by Inertia Separation of Water, II - Single-Offset-Duct System. NACA-RM-E8A28, 1948.
  • von Glahn, Uwe H.: Ice Protection of Turbojet Engines by Inertia Separation of Water, III - Annular Submerged Inlets. NACA-RM-E8A29, 1948.
  • Dallas, Thomas, and Ellisman, Carl: Analysis and Preliminary Investigation of Eddy-Current Heating for Icing Protection of Axial-Flow-Compressor Blades. NACA-RM-E9EO6, 1949.
  • Ruggeri, Robert S., and Callaghan, Edmund E.: Experimental Investigation of Hot-Gas Bleedback for Ice Protection of Turbojet Engines, III - Nacelle with Short Straight Air Inlet. NACA-RM-E9E12, 1949.
  • Ruggeri, Robert S., von Glahn, Uwe H., and Rollin, Vern G.: Investigation of Aerodynamic and Icing Characteristics of Recessed Fuel-Vent Configurations. NACA-TN-1789, 1949.
  • Gray, Vernon H., and Bowden, Dean T.: Icing Characteristics and Anti-Icing Heat Requirements for Hollow and Internally Modified Gas-Heated Inlet Guide Vanes. NACA-RM-E50I08, 1950.
  • von Glahn, Uwe H., and Blatz, Robert E.: Investigation of Aerodynamic and Icing Characteristics of Water-Inertia-Separation Inlets for Turbojet Engines. NACA-RM-E50E03, 1950.
  • von Glahn, Uwe H., and Blatz, Robert E.: Investigation of Power Requirements for Ice Prevention and Cyclical De-Icing of Inlet Guide Vanes with Internal Electric Heaters. NACA-RM-E50H29, Dec. 1950.
  • Gelder, Thomas F., and Lewis, James P.: Comparison of Heat Transfer from Airfoil in Natural and Simulated Icing Conditions. NACA-TN-2480, 1951.
  • Gowan, W. H., Jr., and Mulholland, D. R.: Effectiveness of Thermal-Pneumatic Airfoil-Ice-Protection System. NACA-RM-E50K10a, 1951.
  • Perkins, Porter J., McCullough, Stuart, and Lewis, Ralph D.: A Simplified Instrument for Recording and Indicating Frequency and Intensity of Icing Conditions Encountered in Flight. NACA-RM-E51E16, 1951.
  • von Glahn, Uwe H., Callaghan, Edmund E., and Gray, Vernon H.: NACA Investigations of Icing-Protection Systems for Turbojet-Engine Installations. NACA-RM-E51B12, 1951.
  • Gray, Vernon H., Bowden, Dean T., and von Glahn, Uwe H.: Preliminary Results of Cyclical De-icing of a Gas-Heated Airfoil. NACA-RM-E51J29, 1952
  • Lewis, James P., and Bowden, Dean T.: Preliminary Investigation of Cyclic De-Icing of an Airfoil Using an External Electric Heater. NACA-RM-E51J30, 1952.
  • Neel, Carr B., Jr., and Steinmetz, Charles P.: The Calculated and Measured Performance Characteristics of a Heated-Wire Liquid-Water-Content Meter for Measuring Icing Severity. NACA-TN-2615, 1952.
  • Gray, Vernon H., and Bowden, Dean T.: Comparison of Several Methods of Cyclic De-Icing of a Gas-Heated Airfoil. NACA-RM-E53C27, 1953.
  • Gray, Vernon H., and von Glahn, Uwe H.: Effect of Ice and Frost Formations on Drag of NACA 651_212 Airfoil for Various Modes of Thermal Ice Protection. NACA-TN-2962, 1953.
  • Lewis, James P.: Investigation of Aerodynamic and Icing Characteristics of Flush Alternate-Inlet Induction-Systems Air Scoop. NACA-RM-E53E07, 1953.
  • Lewis, James P., and Blade, Robert J.: Experimental Investigation of Radome Icing and Icing Protection. NACA-RM-E52J31, 1953.
  • Ruggeri, Robert S.: De-Icing and Runback Characteristics of Three Cyclic Electric, External Deicing Boots Employing Chordwise Shedding. NACA-RM-E53C26, 1953.
  • von Glahn, Uwe H., and Gray, Vernon H.: Effect of Ice Formations on Section Drag of Swept NACA 63A-009 Airfoil with Partial-Span Leading-Edge Slat for Various Modes of Thermal Ice Protection. NACA-RM-E53J30, 1954.
  • Bowden, Dean T.: Investigation of Porous Gas-Heated Leading-Edge Section for Icing Protection of a Delta Wing. NACA-RM-E54I03, 1955.
  • von Glahn, Uwe H., Gelder, Thomas F., and Smyers, William H., Jr.: A Dye-Tracer Technique for Experimentally Obtaining Impingement Characteristics of Arbitrary Bodies and a Method for Determining Droplet Size Distribution. NACA-TN-3338, 1955.
  • Coles, Willard D.: Icing Limit and Wet-Surface Temperature Variation for Two Airfoil Shapes under Simulated High-Speed Flight Conditions. NACA-TN-3396, 1955.
  • Bowden, Dean T.: Effect of Pneumatic De-Icers and Ice Formations on Aerodynamic Characteristics of an Airfoil. NACA-TN-3564, 1956.
  • Gelder, Thomas F., Smyers, William H., Jr., and von Glahn, Uwe H.: Experimental Droplet Impingement on Several Two-Dimensional Airfoils with Thickness Ratios of 6 to 16 Percent. NACA-TN-3839, 1956.
  • Gray, Vernon H., and von Glahn, Uwe H.: Heat Requirements for Ice Protection of a Cyclically Gas-Heated, 36 Swept Airfoil with Partial-Span Leading-Edge Slat. NACA-RM-E56B23, 1956.
  • von Glahn, Uwe H.: Use of Truncated Flapped Airfoils for Impingement and Icing Tests of Full-Scale Leading-Edge Sections. NACA-RM-E56E11, 1956.
  • Gray, Vernon H., and von Glahn, Uwe H.: Aerodynamic Effects Caused by Icing of an Unswept NACA 65A004 Airfoil. NACA-TN-4155, 1957.
  • Gelder, Thomas F.: Total Pressure Distortion and Recovery of Supersonic Nose Inlet with Conical Centerbody in Subsonic Icing Conditions. NACA-RM-E57G09, 1957.
  • Gelder, Thomas F.: Droplet Impingement and Ingestion by Supersonic Nose Inlet in Subsonic Tunnel Conditions. NACA-TN-4268, 1958.

Related

Today, SAE ARP5905, Calibration and Acceptance of Icing Wind Tunnels (Aerospace Recommended Practice) 2 "provides recommended practices for the calibration and acceptance of icing wind tunnels to be used in testing of aircraft components and systems and for the development of simulated ice shapes".

You can see a recent calibration of the NASA Glenn Icing Research Tunnel at ntrs 7.

Notes

I thank Emily Timko (lead author of 7) for reviewing a draft of this post. I edited the post after it was reviewed, and any errors are mine.

  1. NACA Annual Report for 1929 discussing the Langley Refrigerated Wind Tunnel, via NASA-SP-2002-4226, "We Freeze to Please": A History of NASA's Icing Research Tunnel and the Quest for Flight Safety ↩

  2. Aerospace, S. A. E. "SAE ARP 5905 Calibration and acceptance of icing wind tunnels." ARP5905 ↩↩

  3. Knight, Montgomery, and Clay, William C.: Refrigerated Wind Tunnel Tests on Surface Coatings for Preventing Ice Formation. NACA-TN-339, 1930. ↩

  4. Rodert, Lewis A.: A Preliminary Study of the Prevention of Ice on Aircraft by use of Engine Exhaust Heat. NACA-TN-712, 1939. ↩

  5. NACA Conference on Aircraft Ice Prevention A Compilation of Papers Presented by NACA Staff Members. 6505/NACA-1947/8, 1947.
    This is available at DTIC.
    This is also a candidate for "The Greatest Thing That You Have (Probably) Never Read" ↩

  6. Jones, Alun R., and Lewis, William: Recommended Values of Meteorological Factors to be Considered in the Design of Aircraft Ice-Prevention Equipment. NACA-TN-1855, 1949. ↩

  7. Timko, Emily N., et al. NASA Glenn Icing Research Tunnel: 2019 Cloud Calibration Procedure and Results. No. E-19889. 2021. ntrs. ↩↩

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