Articles with tag: "cylinders"

1. NACA-TR-1215 Thermodynamics

   "... the effect on final results of droplets that do not freeze completely on the cylinders"

   

   "Impingement of Cloud Droplets and Procedure for Measuring Liquid-Water Content and Droplet Sizes in Supercooled Clouds by Rotating Multicylinder Method" [Thermodynamics topics] ¹

   Summary

   Conditions where not all water drops freeze are considered.

   Key points

   1. Conditions where not all water drops freeze on the multicylinder instrument are considered.
   2. Rotating cylinder Ludlam limits are compared to flight test data.

   Abstract

   Evaluation of the rotating multicylinder method for the measurement of droplet-size distribution, volume-median droplet size, and liquid-water content in clouds showed that small uncertainties in the basic data eliminate the distinction between different cloud droplet-size distributions and are a source of large errors in the determination of the droplet size. Calculations of the trajectories of cloud droplets in incompressible and compressible flow fields around a cylinder were performed on a mechanical analog constructed for the study …

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2. Conclusions of the Cylinder Thread

   "The collection of ice by the cylinders is similar to the collection of ice by airplane components." ¹

   

   Summary

   Data from the post-NACA era are used to resolve open questions

   Key points

   1. The Cylinders thread is summarized
   2. Post-NACA era data is used to resolve some open questions.
   3. NACA era data that are still used today are summarized

   Discussion

   Review of the Cylinders thread so far

   In the Cylinders thread, we saw:

   • A pioneering analysis of water drop impingement on a cylinder (NACA-TN-779)
   • The most cited aircraft icing publication, with more detail of water drop impingement on a cylinder, and the rotating multicylinder instrument ("Mathematical Investigation of Water Droplet Trajectories")
   • In flight icing measurements and an icing severity index (NACA-TN-1393)
   • An additional way to estimate drop size on a fixed cylinder (NACA-TN-1424)
   • Nine icing instruments compared (NACA-RM-A9C09)
   • The ability of the multicylinder method to determine drop distribution was questioned several times …

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3. NACA-TN-3338

   "a method has been developed ... to determine the droplet size distribution of the impinging cloud"

   "A Dye-Tracer Technique for Experimentally Obtaining Impingement Characteristics of Arbitrary Bodies and a Method for Determining Droplet Size Distribution" ¹

   Summary

   A pioneering test method is described, and a drop size measurement analysis is proposed.

   Key points

   1. A dye-tracer blotter-paper water drop impingement measurement technique is described.
   2. An analysis of test results to determine the water spray drop size distribution is described.
   3. The analysis method accuracy is unknown due to the lack of an independent measurement of drop sizes.
   4. We see the use of the Icing Research Tunnel for the first time in the Cylinders thread.

   Abstract

   A dye-tracer technique has been developed whereby the quantity of dyed water collected on a blotter-wrapped body exposed to an air stream containing a dyed-water spray cloud can be colorimetrically determined in order to obtain local collection efficiencies …

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4. NACA-TR-1215

   "... the effect on final results of droplets that do not freeze completely on the cylinders"

   

   "Impingement of Cloud Droplets and Procedure for Measuring Liquid-Water Content and Droplet Sizes in Supercooled Clouds by Rotating Multicylinder Method." ¹

   Summary

   Conditions where not all water drops freeze are considered.

   Key points

   1. NACA-TN-2903, NACA-TN-2904, and NACA-RM-E53D23 are "superseded" (collected together).
   2. Conditions where not all water drops freeze on the multicylinder instrument are considered.
   3. The terms "freezing fraction" is introduced into the NACA publications.

   Abstract

   Evaluation of the rotating multicylinder method for the measurement of droplet-size distribution, volume-median droplet size, and liquid-water content in clouds showed that small uncertainties in the basic data eliminate the distinction between different cloud droplet-size distributions and are a source of large errors in the determination of the droplet size. Calculations of the trajectories of cloud droplets in incompressible and compressible flow fields around a cylinder were performed on a …

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5. NACA-RM-E53D23

   "The meteorological data obtained with the multicylinder method are the only data available for the design of ice-protection equipment for aircraft"

   "Procedure for Measuring Liquid-Water Content and Droplet Sizes in Super-cooled Clouds by Rotating Multicylinder Method"¹

   

   Summary

   Detailed procedures for the use of multicylinders are described.

   Key points

   1. Detailed procedures for the in-flight use of multicylinders are described.
   2. Detailed procedures for analyzing results from of multicylinders are described, with a flight data case.
   3. Differences in analysis method details can drive MVD and LWC differences in the range of 5% to 10%.

   Abstract

   The rotating multicylinder method for in-flight determination of liquid-water content, droplet size, and droplet-size distribution in icing clouds is described. The theory of operation, the apparatus required, the technique of obtaining data in flight, and detailed methods of calculating the results, including necessary charts and tables, are presented.

   Discussion

   Procedures

   A set of rotating cylinders were constructed …

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6. NACA-TN-2903

   "For most practical problems involving measurements of droplet impingement on cylinders, the compressibility effect may be ignored."

   "Impingement of Cloud Droplets on Aerodynamic Bodies as Affected by Compressibility of Air Flow Around the Body"

   Summary

   The effect of the compressibility of air on the water-drop impingement calculations is found to be "negligible".

   Key points

   1. The effect of the compressibility of air on the water-drop impingement calculations is found to be "negligible"

   Abstract

   The trajectories of water droplets in a compressible-air flow field around a cylinder were computed with a mechanical analog. The results of the calculations at approximately the flight critical Mach number were compared with calculations of trajectories in an incompressible flow field. For a cylinder, the effect of compressibility of the air on the droplet trajectories was negligible up to the flight critical Mach number. The results obtained with the cylinder were extended to airfoils. This extension is …

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7. NACA-TN-2904

   "Many data points were carefully calculated in order to determine precisely the rate of droplet impingement on the surface of a right circular cylinder."

   

   "Impingement of Water Droplets on a Cylinder in an Incompressible Flow Field and Evaluation of Rotating Multicylinder Method for Measurement of Droplet-Size Distribution, Volume-Median Droplet Size, and Liquid-Water Content in Clouds" ¹

   Summary

   Detailed water drop impingement analysis (independent of prior analysis) is presented.

   Key points

   1. Detailed water drop impingement analysis (independent of prior analysis) is presented
   2. Error estimates are detailed.
   3. Detailed Beta curves are provided.
   4. A difference from Langmuir and Blodgett for drop size distributions calculations is noted.

   Abstract

   Evaluation of the rotating multicylinder method for the measurement of droplet-size distribution, volume-median droplet size, and liquid-water content in clouds shoved that small uncertainties in the basic data eliminate the distinction between different cloud droplet-size distributions and are a source of large errors in the determination …

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8. A Langmuir B drop size distribution is (almost) a normal distribution

   "Upon comparing this chart with Langmuir's tables, it was found that his selections of the representative radii for the various sub-divisions of the volume were in error." ¹

   Summary

   The Langmuir B drop size distribution is almost a normal distribution.

   Key points

   1. The Langmuir B drop size distribution is almost a normal distribution.
   2. Perhaps it was originally intended that it be exactly a normal distribution.
   3. The proposed alternatives in NACA-TN-2708 appears to have larger errors, rather than correcting errors.
   4. The other Langmuir distributions (C, D, E) do not fit a normal distribution as well.

   Discussion

   Normal drop size distributions

   Normal distributions show up many places in nature, so it is not surprising that drop sizes in clouds can approximate a normal distribution.

   In NACA-TN-2708 ¹, it was "presumed" that water-volume distribution with the drop size is a Gaussian [normal] distribution:

   Drop-Size Distribution. - In the present report it is presumed, following …

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9. NACA-TN-2708

   "...At low airspeeds and with large cylinders, the determination should be relatively good."

   "Comparison of Three Multicylinder Icing Meters and Critique of Multicylinder Method" ¹

   Summary

   Multicylinder instruments had good agreement for liquid water content and median effective drop diameter, but poor agreement for the distribution type.

   Key points

   1. Three multicylinder instruments had good agreement for liquid water content and median effective drop diameter, but poor agreement for the distribution type
   2. The Langmuir drop size distributions were revised (but the revised versions were not widely adopted)

   Abstract

   Three multicylinder cloud meters, fundamentally similar but differing in important details, were compared in use at the Mount Washington Observatory. Determinations of liquid water content were found to agree within the limits of the probable error, but the two instruments designed by the National Advisory Committee for Aeronautics indicated larger drop sizes than did the Observatory's instrument, apparently because of spurious ice catch …

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10. NACA-TN-1904

    "... the rotating-cylinder indications of drop-size distribution are so unreliable that they are of little or no value"

    NACA-TN-1904, "Observations of Icing Conditions Encountered in Flight During 1948" ¹

    Summary

    Meteorological data from flight observations in icing conditions during the first 5 months of 1948 are presented.

    Key points

    1. The average liquid water content varies over distance traveled in icing.
    2. The value of the multicylinder method for determining drop size distributions is questioned.
    3. Other flight test instruments are described.

    Abstract

    Meteorological data from flight observations in icing conditions during the first 5 months of 1948 are presented. A total of 335 measurements of liquid-water content and mean-effective drop diameter were obtained by the multicylinder method in the course of 40 flights in icing conditions covering most of northern United States. Cumulus clouds were predominant during approximately two-thirds of the flights. A continuous record of liquid-water content covering a major portion of …

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11. NACA-RM-A9C09

    "The [multicylinder] method has assumed the position of a standard against which other instruments are calibrated, and is apt to remain so..."

    

    "A Review of Instruments Developed for the Measurement of the Meteorological Factors Conducive to Aircraft Icing"

    ¹

    Summary

    The multicylinder is the "standard against which other instruments are calibrated"

    Key points

    1. Nine instruments, including the fixed cylinder and rotating multicylinder, are qualitatively assessed.
    2. "The [multicylinder] method has assumed the position of a standard against which other instruments are calibrated, and is apt to remain so..."
    3. The effect of mass measurements errors on multicylinder results were assessed.
    4. "A reliable method for the measurement of drop-size distribution should be developed"

    Abstract

    The status of instrument suitable for the measurement of the meteorological factors conducive to aircraft icing is reviewed. The meteorological factors to be evaluated are listed, and tentative values for the desired and acceptable accuracy of measurement for each …

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12. NACA-TN-1424

    "In spite of the inconsistency it is believed that the data on mean-effective diameters are fairly reliable."

    "A Further Investigation of the Meteorological Conditions Conducive to Aircraft Icing" ¹

    Summary

    The value of the multicylinder data for determining drop size distribution is questioned.

    Key points

    1. Two methods for determining drop size distributions are compared.
    2. The difference in water drop concentration around an aircraft body is proposed as an explanation for results from the two methods.
    3. A temperature effect of icing conditions is noted.
    4. Previously proposed design values from NACA-TN-1393 were verified.

    Abstract

    Meteorological data from flight observations in icing conditions during the winter of 1946-47 are presented. Data on liquid water content, temperature, and mean-effective drop diameter are shown to be consistent with values previously proposed for maximum icing conditions. Data on drop-size distribution as obtained by the rotating-cylinder method, although consistent with measurements previously made, were found to be …

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13. NACA-TN-1393

    "The rotating-cylinder method of measuring liquid water content is generally regarded as being the most accurate and dependable procedure thus far developed"

    

    “A Flight Investigation of the Meteorological Conditions Conducive to the Formation of Ice on Airplanes"

    ¹

    Summary

    A multicylinder and other instruments measure natural icing conditions in flight.

    Key points

    1. The accuracy of multicylinder instruments used to determine liquid water content and median water drop size is assessed.
    2. An icing intensity index as related to the ice growth rate on a 3-inch diameter cylinder is detailed.
    3. Results from agree well with the Python implementation of the cylinder analysis.
    4. "Tentative" values for icing design conditions were determined.
    5. An effect of distance on icing conditions is noted.

    Abstract

    Data from flight measurements of the meteorological factors related to the intensity of icing conditions are presented. The physical factors that establish the distribution of liquid water in clouds of various types …

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14. Implementation of multicylinder calculations in Python

    "This effect would be expected if the droplets were of non-uniform size, since the largest droplets could reach the largest collector while those of average size could not." ¹

    Summary

    The calculations to determine drop median volumetric diameter with a multicylinder instrument are implemented in Python.

    Key points

    1. A manual method of multicylinder calculation is illustrated.
    2. The drop median effect diameter is reproduced well from a multicylinder example in "Mathematical Investigation of Water Droplet Trajectories"

    Discussion

    Manual method of drop size analysis

    By measuring the differential rates of ice collection on cylinders of different sizes the drop median volumetric diameter (MVD) can be determined.

    Some typical multicylinder instruments (from NACA-TN-2708 ¹):

    "Mathematical Investigation of Water Droplet Trajectories" ² provides an example of the multicylinder calculations method in the section "Example of the Application of the D.A. Data to Experimental Data".

    The method has been revised as a result of …

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15. A Detailed Comparison of Water Drop Impingement Calculations

    "The discrepancies are of the magnitude to be expected from ... the step by step integration"

    Summary

    Water drop impingement calculations on a cylinder from "Mathematical Investigation of Water Droplet Trajectories" ¹ and NACA-TN-779 ² are compared.

    Key Points

    1. There are differences in conditions in Table IV(a) of "Mathematical Investigation of Water Droplet Trajectories" compared to NACA-TN-779.
    2. When the conditions are revised to match, the comparison with NACA-TN-779 data improves.

    Discussion

    NACA-TN-779

    In NACA-TN-779, the water drop impingement on a cylinder 12 inch in diameter, with an airspeed of 200 mph, was analyzed. The altitude was not noted. Water drop diameters from 0.002 inch (about 8 micrometer) to 0.1 inch (about 4000 micrometer) were considered, as shown below.

    

    The “swept area of cleared drops” represents what fraction of the water drops in the forward projected area of the cylinder impinge on the cylinder. In more modern terms, this …

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16. Implementation of cylinder impingement correlations in Python

    "The equations were found to fit the experimental data over a wider range of values..." ¹

    Summary

    The correlations for water drop impingement on a cylinder from "Mathematical Investigation of Water Droplet Trajectories" ¹ are implemented in the Python programming language.

    Key points

    1. The cylinder impingement correlations were implemented and reproduced values from "Mathematical Investigation of Water Droplet Trajectories"
    2. A subtlety about calculations with drop size distributions is noted.

    Discussion

    Implementation of cylinder impingement correlations

    Alas, I do not have access to a differential analyzer as was used in ¹, so I will have to use a modern, digital computer. Also, we will not be integrating the water drop equations of motion; we will be using the data in ¹ to determine water drop impingement on a cylinder.

    The Anaconda distribution of Python version 3.7 was used ², as this includes the third party modules matplotlib, numpy, and scipy …

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17. "Mathematical Investigation of Water Droplet Trajectories"

    "IT IS DESIRED to calculate the trajectories of small water droplets (fog) in air moving at high velocities across a cylinder."

    

    Summary

    Langmuir drop size distributions are defined, and water drop impingement on a collection of cylinders for use as an icing instrument is described.

    Key points

    1. The Langmuir drop size distributions are defined
    2. The water drop impingement terms E, Beta, K, and Ko are defined
    3. The use of cylinders of different sizes and detailed calculations to determine water drop sizes

    Abstract

    Calculations are given of the trajectories of small water droplets moving in air at high velocities across a cylinder. The calculations were made by means of a differential analyzer (D.A.). A few calculations are also given for the case of a sphere and a ribbon.

    Each D. A. trajectory represents the motion of a single particle. The theoretical curves for the efficiency of deposition of very large …

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18. NACA-TN-779

    "In order to provide qualitative information ..., numerical calculations of the drop paths in air flowing ... around a circular cylinder were made"

    

    “Aerodynamic Heating and Deflection of Drops by an Obstacle in an Airstream in Relation to Aircraft Icing"

    Summary

    Water drop impingement on a cylinder is calculated.

    Key points

    1. The effect of aerodynamic heating is predictable
    2. The impingement of water drops on a cylinder is calculated

    Abstract

    Two topics of interest to persons attempting to apply the heat method of preventing ice formation on aircraft are considered. Surfaces moving through air at high speed are shown, both theoretically and experimentally, to be subject to important aerodynamic heating effects that will materially reduce the heat required to prevent ice.

    Numerical calculations of the paths of water drops in an air stream around a circular cylinder are given. From these calculations, information is obtained on the percentage of the swept area cleared …

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19. Icing on Cylinders

    "The collection of ice by the cylinders is similar to the collection of ice by airplane components." ¹

    

    
    Calculating water drop trajectories with a differential analyzer analog
    (from NACA-TN-2904)

    Summary

    The cylinder has a wide range of current uses in aviation

    Abstract

    The cylinder has a wide range of current uses in aviation:
    - Meteorological instruments for flight and icing wind tunnel tests
    - Aircraft in-flight ice detectors and indicators
    - Structural elements (such as landing gear and cables)
    - An approximation of an airfoil leading edge (used in thermal design and icing wind tunnel test conditions determination ²)

    Icing conditions measurements with instruments based on cylinders were key to developing the current aircraft flight in icing certification regulations.

    One hundred and thirty-two NACA publications related to aircraft icing were identified in "The Historical Selected Bibliography of NACA-NASA Icing Publications", and categorized into 17 topics.

    Publications related to icing on a …

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