Articles with tag: "impingement"

1. Water Drops

   The size of water drops in clouds

   The water that causes most aircraft in-flight icing is small drops in clouds. Average drop sizes are typically 10 to 50 "Micrometers" (μm) in diameter (for comparison, a human hair is about 50 to 100 micrometers in diameter).

   
   Typical drop sizes, approximately proportional. Public domain image by Donald Cook.

   In a particular cloud, not all water drops are the same size. The "Langmuir Drop Size Distributions" describe an idealized approximation of how the drop sizes vary in a cloud about an average or median drop size. It has seven bins, each with a representative drop size and fraction of the total water content in the cloud.

   
   from "Aircraft Icing Handbook", DOT/FAA/CT-88/8-1 apps.dtic.mil

   The impingement of water drops on aircraft surfaces

   Calculating the amount of water that hits or impinges on the surface of an airplane as it flies …

   read more

2. Conclusions of the Impingement on Surfaces thread

   "It is thus desirable to have an economical method for solving the basic water droplet trajectory equations for an arbitrary airfoil." ¹

   

   The Use of Ko for Impingement Correlations

   The use of a modified water droplet inertia parameter Ko permits consolidation into only a few graphs of most of the published water drop trajectory data. ¹

   To paraphrase NACA-TN-3839 ², the studies in this Impingement on Surfaces thread "were a rather ad hoc collection of shapes and sizes". One unifying parameter emerged to correlate the results, the "Ko" modified water drop inertia parameter.

   "Mathematical Investigation of Water Droplet Trajectories" ³

   "Mathematical Investigation of Water Droplet Trajectories" ³ defined a term Ko (see the link for definitions of other terms):

   

   Ko is not given a name, it is only defined in relation to K:

   The quantity Κ that occurs in Eqs. (4) and (5) measures the inertia of the droplet and …

   read more

3. A Tentative Identification of Water Drop Trajectory Investigators

   NACA-TN-2094 and investigators operating the water-drop-trajectory analog

   
   Figure 15 of NACA-TN-2904

   Summary

   While no one is identified in Figure 15 of NACA-TN-2904, I speculate that these investigators are Helen M. Gallagher, and Dorothea E. Vogt. (I do not know which name goes with which individual). While neither Gallager nor Vogt is credited in NACA-TN-2904, it is possible that they contributed to the analysis, as they did in several other water-drop trajectory publications.

   Discussion

   Yes, I have used this figure a lot, as it is one of the best of the hundreds I have viewed from the NACA-era. This image is also notable in that of the hundreds of NACA-era documents that I have read, this is the only one where the people appear to be women.

   I have not been able to find photos of Gallager or Vogt for comparison (and photos of any NACA-era authors are hard to find …

   read more

4. Impingement on Other Surfaces

   "the ideal flow field ahead of a ribbon is not a very satisfactory representation of the actual flow field in front of a rectangular body"

   

   NACA-TN-3658, "Impingement of Water Droplets on a Rectangular Half Body in a Two-Dimensional Incompressible Flow Field" ¹

   Summary

   Water-drop impingement on a rectangular body is calculated.

   Abstract

   Trajectories of water droplets moving in the ideal two-dimensional flow field ahead of a body of rectangular cross section and infinite extent in the downstream direction have, been calculated by means of a differential analyzer. Data on collection efficiency and distribution of water impingement are presented.

   Discussion

   We have already seen most of the titles on the "Impingement on Other Surfaces" topic:

   • Brun, Rinaldo J., and Mergler, Harry W.: 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 …

   read more

5. Impingement on Airfoils

   "Although the airfoils used in these studies were a rather ad hoc collection of shapes and sizes, this report makes these data generally available and correlates the data as much as possible."

   
   From NACA-TN-3839.

   NACA-TN-2931, "A Method for Determining Cloud-Droplet Impingement on Swept Wings"

   and

   NACA-TN-3839, "Experimental Droplet Impingement on Several Two-Dimensional Airfoils with Thickness Ratios of 6 to 16 Percent"

   Summary

   Several airfoils were analyzed and tested for water-drop impingement in the NACA-era.

   Abstract

   The rate and area of cloud droplet impingement on several two-dimensional swept and unswept airfoils were obtained experimentally in the NACA Lewis icing tunnel with a dye-tracer technique. Airfoil thickness ratios of 6 to 16 percent; angles of attack from 0° to 12°, and chord sizes from 13 to 96 inches were included in the study. The data were obtained at 152 knots and are extended to other conditions by dimensionless impingement parameters.
   In general …

   read more

6. Impingement in Elbow Ducts

   "Icing of air-intake ducts and scoops with subsequent reduction in pressure recovery and in air flow may adversely affect the operation of the aircraft."

   From NACA-TN-2999. ¹

   

   NACA-TN-2999, "Impingement of Droplets in 90° Elbows with Potential Flow" ¹

   and

   NACA-TN-3770, "Impingement of Droplets in 60° Elbows with Potential Flow" ²

   Summary

   The impingement of water-drops in idealized elbow ducts is calculated with potential flow.

   Abstract

   NACA-TN-2999

   Trajectories were determined for droplets in air flowing through 90° elbows especially designed for two-dimensional potential motion with low pressure losses. The elbows were established by selecting as walls of each elbow two streamlines of the flow field produced by a complex potential function that establishes a two-dimensional flow around a 90° bend. An unlimited number of elbows with slightly different shapes can be established by selecting different pairs of streamlines as walls. The elbows produced by the complex potential function selected are suitable …

   read more

7. Impingement in Engine Inlets

   "In spite of the simplicity, the configurations are reasonable approximation of those found on aircraft"

   NACA-TR-1317.

   
   From NACA-TR-1317.

   NACA-TR-1317, "Cloud-Droplet Ingestion in Engine Inlets with Inlet Velocity Ratios of 1.0 and 0.7."

   and

   NACA-TN-4268, "Droplet Impingement and Ingestion by Supersonic Nose Inlet in Subsonic Tunnel Conditions."

   Summary

   "Important general concepts" of impingement on engine inlets are illustrated.

   Introduction

   In the first title here, the use of potential flow to determine water-drop trajectories gets pushed to the limit. In a demonstration of the pragmatism that ran through much of the ice protection development at NACA, investigators produced results on configurations that could be analyzed that were close enough to real aircraft geometries.

   In NACA-TN-3770, we enter the supersonic jet age, with a dye-tracer method test of a supersonic inlet (but at a lower Mach number). We will see a test of "the configurations are reasonable approximation".

   Discussion

   Inlet impingement …

   read more

8. Shadow Zones and Concentration Zones

   "... local concentration factors should be considered when choosing the location of devices that protrude into the stream from aircraft fuselages or missiles, or when determining anti-icing heat requirements for the protection of these devices."

   
   From NACA-TN-3410.

   NACA-TN-3153, "Variation of Local Liquid-Water Concentration about an Ellipsoid of Fineness Ratio 5 Moving in a Droplet Field" ¹

   and

   NACA-TN-3410, "Variation of Local Liquid-Water Concentration about an Ellipsoid of Fineness Ratio 10 Moving in a Droplet Field" ²

   Summary

   The concentration of water-drops varies with distance from a surface in flight.

   Abstract

   Trajectories of water droplets about an ellipsoid of revolution with a fineness ratio of 5 (which often approximates the shape of an aircraft fuselage or missile) were computed with the aid of a differential analyzer. Analyses of these trajectories indicate that the local concentration of liquid water at various points about an ellipsoid varies considerably and under some conditions may be …

   read more

9. Bodies of Revolution

   "The presence of radomes and instruments that are sensitive to water films or ice formations in the nose section of all-weather aircraft and missiles necessitates a knowledge of the droplet impingement characteristics of bodies of revolution."

   ¹

   

   Summary

   Water-drop impingement on several bodies of revolution is quantified.

   Discussion

   NACA-TN-4092 ⁴ notes:

   The impingement characteristics of bodies of revolution are of interest because such bodies are representative of many aircraft components subject to icing such as radomes, body noses, engine accessory housings, and the large spinners of turboprop engines.

   NACA-TN-3099 ¹ is the first in a series and has a rather complete description of the analysis methods, so the discussion below refers to that, unless noted otherwise.

   Flow field

   Potential flow can be determined in 2D radial coordinates as well as 2D Cartesian coordinates. This was used to assess several geometries.

   The air velocity components for incompressible nonviscous flow about a …

   read more

10. Methods of Water Drop Impingement Quantification

    "One of the first essentials ... is a method for estimating or calculating the area over which water will strike the wing, and the distribution of water impingement over that area"

    From NACA-TN-1397.

    
    From NACA-TN-3839.

    Summary

    Several methods were used to quantify the water-drop impingement on a surface, such as a wing.

    Discussion

    We already saw in the Icing on Cylinders thread calculations made for impingement on a cylinder. The technique was expanded in NACA-TN-1397 to include Joukowski type airfoils. This allowed a transformation of the flow solution around a cylinder to be mapped into airfoil coordinates, and then used to solve for water drop trajectory calculations, similar to those used for cylinders.

    NACA-TN-1397 said one could calculate "the trajectory a single drop without the utilization of a differential analyzer". We saw the differential analyzer in the Icing on Cylinders thread, in particular detail in NACA-TN-2904. However, the example given (Table …

    read more

11. Water Drop Impingement on Surfaces

    "For a complete appraisal of the problem of ice prevention on aircraft, further water-droplet impingement data are needed" ¹

    
    Figure 5 of NACA-TN-1397

    Water Drop Impingement on Surfaces Thread

    Summary

    Water-drop impingement quantification is key to aircraft ice protection design.

    Introduction

    Part of designing for aircraft icing is determining how much ice the airplane can accumulate. For ice protection systems, determining how much water that might freeze hits a surface is a key detail.

    An important effect is that the airflow around a surface such as a wing airfoil deflects water-drops, so that all of the water-drops in the frontal area view will not hit the surface.

    Water-drop impingement quantification methods were developed to assess how many drops can hit where on a surface. Direct test methods involved the use of blotter paper to absorb water drops on a surface. Mathematical analysis of the paths individual water drops were developed …

    read more

12. AEDC1DMP

    "The third part of the study comprised some numerical computations of two-phase, dilute, air and entrained water particle flows, using a new version of the AEDC one-dimensional, multiphase flow code, AEDC1DMP."

    

    The AEDC 1-Dimensional Multi-Phase code (AEDC1DMP) and the iads1dmp

    Abstract

    The AEDC1DMP calculates the water drop speed and evaporation in an icing wind tunnel. The AEDC1DMP is described in "Second Report for Research and Modeling of Water Particles in Adverse Weather Simulation Facilities" ¹. AEDC is the Arnold Engineering Development Complex, formerly the Arnold Engineering Development Center.

    1.0 INTRODUCTION TO THE RESEARCH
    This report describes a continuation of research into the modeling of water particle freezing for application to adverse weather simulation facilities. The research was initiated in FY1996 to investigate the physics of freezing of submillimeter supercooled water particles or droplets in both natural and artificial or simulated adverse weather environments. The first phase of the research …

    read more

13. Let's Build a 1D Water Drop Trajectory Simulation

    

    "The discrepancies are of the magnitude to be expected from ... the step by step integration". ¹

    Let's build a 1D water drop trajectory simulation

    Summary

    Water impingement values on a cylinder are calculated with step-by-step integration.

    Key points

    1. 1D equations of motion were implemented.
    2. Results agree well with the minimum drop size required for impingement.
    3. Water drops may contact the cylinder at very low K values.
    4. The methods appears accurate enough to use for other applications.

    Discussion

    We are going to start with a one dimensional simulation along a single line, the stagnation line of flow around a cylinder, y=0 in the figure above.

    We will implement the equations of motions for a drop around a cylinder from "Mathematical Investigation of Water Droplet Trajectories" ¹.

    Readers unfamiliar with "Mathematical Investigation of Water Droplet Trajectories" may wish to review it before proceeding further herein, especially to be familiar with the …

    read more