Articles with tag: "LEWICE"

1. Swept Airfoil Cases in IceVal

   "Use of these relationships allows the direct determination of ice shapes adjusted for any given icing and flight condition as well as for size and sweep of the airfoil" ¹

   
   

   Experimental ice shapes compared to a LEWICE analysis.

   Summary

   There are 41 swept airfoil cases in the IceVal database ².

   The quote at the top from Wilder briefly describes the the empirically based analytical method he described in ¹. However, it is not directly applicable to airfoils other than the ones he considered, which had dozens of icing tunnel ice shapes tests each. For more details on Wilder's method, see Wilder.

   LEWICE ³, and other codes, offer potentially more widely applicable methods of ice shape prediction in swept airfoils.

   LEWICE analysis for these cases tends to produce ice shapes that are consistently too small compared to experiment.

   Empirically derived adjustments to the inputs to LEWICE are discussed that improve the …

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2. Running LEWICE version 3.2.3 for the IceVal cases

   "The resulting analysis showed that LEWICE compared well to the available experimental data." ¹

   
   

   An example of a good comparison between analysis and experiment.

   Introduction

   The IceVal database ², and its predecessors, were originally assembled to validate the LEWICE ³ ice shape prediction code.

   Here, we will repeat that analysis with a more recent version of LEWICE, and look at the effects of using "corrected" angle of attack values in the analysis.

   The LEWICE ice shapes results in the IceVal database were apparently run with LEWICE version 3.2.2 (We will abbreviate that as the Database LEWICE shape). The IceVal users guide is not explicit, other than "the latest version of the LEWICE ice shape prediction code". The 2008 LEWICE validation report was written at about the same time. It does not mention IceVal, but the validation report was for LEWICE version 3.2.2.

   Comparisons with all IceVal …

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3. A Geometric Analysis Method

   "This demonstrates that the automated process cannot (yet) be substituted for good engineering judgment."

   From the LEWICE manual. ¹

   
   

   A case where two methods detected similar upper surface ice horns.

   Introduction

   Reviewing 6000+ ice shape assessments to verify that they agree with engineering judgement is a daunting task. Even with professionalism and due-diligence, debatable results may be missed. So, there is motivation to automate the process as much as possible.

   Here, I describe a step toward that goal. It is a work in progress, not a completed product.

   Using the IceVal database to validate an assessment method

   The IceVal database will be used here to validate a different comparison assessment method. This is one of the uses envisioned when compiling the database ²:

   ... by compiling a comprehensive database consisting of a standardized, reliable data set, and combining that with an easy-to-use graphical user interface (GUI), providing quick and easy access …

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4. Overall comparison assessments between experiment and LEWICE

   "It is possible for any (or all!) ... parameters to be incorrectly output."

   
   

   A case with identified horn locations that are debatable.

   Introduction

   Assessments of LEWICE ice shapes compared to experiment have been published twice.

   The LEWICE THICK utility program was uses to identify ice horn locations and maximum heights. However, engineering judgement was used to adjust some values in the IceVal database. Cases with questionable ice horn identifications can be found in the database.

   The difficulty of consistently identifying ice horns affects the comparison assessment between LEWICE and experiment.

   Published assessments

   The overall comparison of LEWICE ¹ analysis to experimental data to has been published twice.

   The first was in 1999 ², and included 800 experiment cases. The second was in 2008 ³, and had more than 3000 experimental cases. These are the data that are included in the IceVal database ⁴.

   The 1999 Assessment

   The assessment published in 1999 …

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5. Challenges Using the IceVal Database

   "No data is clean, but most is useful."

   attributed to Dean Abbott.

   
   

   Ice shape tracing points that are mis-ordered and mis-aligned with the airfoil.

   Introduction

   The IceVal database is a significant achievement that is still yielding dividends, decades later.

   The IceVal description ¹ discusses some of the challenges of assembling the database:

   While all of this data is available, in theory, for every test run, as a practical matter, this is often not the case. Because the data is managed by the individual researcher, and much of it is stored in hardcopy form, locating a specific data set may require a significant effort. Furthermore, because of differences in experimental technique from one researcher to the next, the extent to which the relevant conditions have been explicitly documented can vary widely. Moreover, since plans made prior to a test may change during the test based on interim results, it is not …

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6. A Tour of the IceVal DatAssistant

   "... all publicly available IRT-generated experimental ice shapes with complete and verifiable conditions have now been compiled into one electronically-searchable database"

   NASA Report E-16236 ¹.

   
   Public Domain image from NASA Report Number: E-16236.

   A quick tour of the IceVal DatAssistant

   The IceVal DatAssistant is available from NASA. It runs on the Windows operating system (only).

   The IceVal DatAssistant can do several functions. The main interest here is the database of experimental run conditions and results.

   The tables of primary interest are IceShapeData, RunSpecs, and SprayConditions.

   
   Public Domain image from NASA Report Number: E-16236.

   In the time span 1988 to 2008 that the database covers, experimental test results were measured by cutting a thin slot into the ice, inserting a pre-made cardboard template, and manually tracing the ice shape. These were later digitized, and included in the database.

   
   Public Domain image from NASA Report Number: E-16236.

   Range of conditions tested

   The primary …

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7. 6000 Ice Shapes - the IceVal DatAssistant

   "As with any scientific endeavor, the foundation of icing research ... is the data acquired during experimental testing."

   NASA Report E-16236 ¹.
   
   

   
   

   4132 ice shapes for the NACA0012 airfoil.

   [Yes, that is how it is spelled.]

   The IceVal DatAssistant ¹, ² from NASA contains 6330 ice shapes from experiments in the NASA Icing Research Tunnel ³ (3665 shape tracings) and from analysis with LEWICE ⁴ (2965 ice shapes).

   Significant uses of the data were the LEWICE validation reports published in 1998 ^{5 6} and 2008 ⁷, which established measures for the comparison of LEWICE analysis results to experimental data.

   These data are tremendous aids to researchers and developers of icing analysis codes and test methods. It has been 27 and 18 years since these were published (respectively), and we should celebrate that the utility of the data has held up well. However, given that an entire generation of workers in the …

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8. Using Appendix C for Ice Shape Analysis

   
   Public domain image by Donald Cook.

   Summary

   Search within the Appendix C Continuous Maximum Icing definition for the thickest ice shape.

   Prerequisites

   You need to have completed Run a 2D simulation.

   Introduction

   "Aircraft Ice Protection" AC 20-73A faa.gov offers guidance on analysis for icing conditions. We will not cover the certification aspects in detail.

   Much of the detail is on ice protection systems.

   This advisory circular (AC) tells type certificate and supplemental type certificate applicants how to comply with the ice protection requirements of Title 14 of the Code of Federal Regulations (14 CFR) parts 23, 25, 27, 29, 33, and 35.

   However, it is also useful for analysing ice shapes on unprotected surfaces.

   It is noted that:

   Determination of critical ice shape configurations is not straightforward and may require engineering judgment.

   SAE AIR5903, "Droplet Impingement and Ice Accretion Computer Codes" sae.org notes:

   A balancing of accurate and …

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9. Introduction to Variations

   
   From AC 20-73A faa.gov.

   Summary

   • Different methods (test, analysis methods) can yield different ice shapes for the same conditions
   • Measurements of ice shape parameters characterize the differences
   • What is "too large" of a difference depends on unique factors for a particular case
   • Engineering judgment is required to navigate the differences

   Discussion

   A method to characterize ice shapes

   "Aircraft Ice Protection" AC 20-73A faa.gov lists ice shape parameters that can be used to compare ice shapes:

   Applicants may use the lists of ice shape and water catch evaluation parameters in tables R-1 and R-2, ranked against their adverse airplane effects, to compare simulated and natural ice shapes. These lists are from SAE ARP5903 (Reference R20).

   Table R-1. Ranking of Ice Shape Evaluation Parameters

   Rank	Parameter	Units	Conservatism criteria
   1	Upper (suction surface) horn height		Equal or greater horn peak thickness (height)
   2	Upper Horn Angle	degree	Criticality of location …

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10. Computer Freezing Rate Analysis Tools Examples

    
    from Users Manual for the NASA Lewis Ice Accretion Prediction Code (LEWICE) (1990 version) ntrs.nasa.gov

    Prerequisites

    You need to complete the Aircraft Icing Handbook Water Catch Examples.

    You need to select a computerized tool to work with. See Analysis Toolset for obtaining LEWICE, and some other options.

    If you have chosen to use LEWICE, but you have not run it before, see the LEWICE Quick Start.

    Introduction

    We will compare energy balance terms and freezing rates calculated with the Standard Computational Model and LEWICE (or the tool that you have selected).

    The values found by differing methods are generally similar, but rarely identical.

    Aircraft Icing Handbook Example 2-4

    The mass of ice accretion on the NACA 0012 section will be calculated. Using the same flight conditions as Example 2-1. and the droplet size distribution and value from Example 2-3:

    Airfoil                         c = 3.1 foot chord NACA 0012  
    Flight …

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11. Computer Impingement Analysis Tools Examples

    
    from Users Manual for the NASA Lewis Ice Accretion Prediction Code (LEWICE) (1990 version) ntrs.nasa.gov

    Prerequisites

    You need to complete the Aircraft Icing Handbook Water Catch Examples.

    You need to select a computerized tool to work with. See Analysis Toolset for obtaining LEWICE, and some other options.

    Aircraft Icing Handbook Example 2-2

    Example 2-2
    This example illustrates the estimation of the impingement parameters E, β, h, Su and SL using graphical data (reference 2-12). The graphical data is all presented with Ko as the independent variable. Much data is available in this form.

    The conditions of Example 2-1 for a NACA 0012 airfoil are assumed: thus Ko = 0.05. It also is assumed for simplicity that the angle of attack, α, is 0 degrees. From figure 2-11, E, the total impingement efficiency, is estimated to be 0.23 for these conditions. So about 23 percent of the water …

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12. LEWICE Quick Start

    
    from User's Manual for LEWICE Version 3.2 ntrs.nasa.gov

    Summary

    The "least that you need to know" to start using LEWICE, the NASA-provided icing simulation tool.

    Prerequisites

    See Analysis Toolset for how to obtain LEWICE.

    Introduction

    Decades ago there was training available for using LEWICE. I do not know of recent training. You are largely on your own, with the manual and supporting material.

    This certainly does not contain complete information, but it will help you get started in the basics of running LEWICE.

    Discussion

    The LEWICE manual provides these instructions:

    3.1.
    LEWICE Quick Start Guide
    This section is intended for users unfamiliar with LEWICE and/or DOS Shell commands. The commands below (indented bold lines) should be typed at the C:\ prompt in a DOS Shell window on a Windows machine. Alternatively, the user can use the Windows interface for any of the commands shown. Windows …

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13. Analysis Toolset

    
    Figure 15 of NACA-TN-2904 ntrs.nasa.gov.

    Summary

    You will have to choose a toolset to perform the example analyses.

    Example calculations are provided in the Python programming language, and using the NASA-provided LEWICE code.

    Introduction

    You are highly encouraged to perform the analysis described in the examples (and not just read the examples). Some examples can be accomplished with hand calculations, while other require computational capabilities.

    You need to select your toolset.

    Consider your current and future uses

    A toolset is an investment of your time and resources. By performing the calculation of the examples used here, you will build your personal and software capabilities and skills.

    Your toolset at a particular time may not be entirely your choice. Your company, institution, or customer may have policies on which kinds of software are required, encouraged, discouraged, or prohibited. Some codes have by-country use restrictions. You may have signed an …

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