Dean Miller

Validation of NASA thermal ice protection computer codes. I - Program overview

The Icing Technology Branch at NASA-Lewis has been involved in an effort to validate two thermal ice protection codes developed at the NASA-Lewis Research Center: LEWICE/Thermal (electrothermal de-icing & anti-icing), and ANTICE (hot-gas & electrothermal anti-icing). The Thermal Code Validation effort was designated as a priority during a 1994 “peer review” of the NASA-Lewis Icing program, and was implemented as a cooperative effort with industry. During April 1996, the first of a series of experimental validation tests was conducted in the NASA-Lewis Icing Research Tunnel (IRT). The purpose of the April 96 test was to acquire experimental data to validate the electrothermal predictive capabilities of both LEWICE/Thermal, and ANTICE. A heavily instrumented test article was designed and fabricated to simulate electrothermal de-icing and anti-icing modes of operation. Thermal measurements were then obtained over a range of test conditions, for comparison with analytical predictions. This paper presents an overview of the test, including a detailed description of (1) test article design, (2) test matrix development, (3) test procedures, and (4) validation process. Selected experimental results are presented for de-icing and anti-icing modes of operation. Finally, the status of the validation effort at this point is summarized. NOMENCLATURE AOA Angle-Of-Attack (degrees) Beta Collection Efficiency IRT Icing Research Tunnel LWC Liquid Water Content (g/m) MVD Median Volumetric Diameter (μm) ON/OFF Heater On / Off Time (seconds) Q Heater Flux (Watts/in) POI Point Of Interest RTD Resistance Temperature Device S Wrap Distance (inches) Tevap Evaporative Anti-Icing Temp. (°F) Twet Running Wet Anti-Icing Temp. (°F) Ttot Total Temperature (°F) TTMS Test Thermal Management System V Airspeed (mph)

Preliminary Investigation of Ice Shape Sensitivity to Parameter Variations

A parameter sensitivity study was conducted at the NASA Glenn Research Centers Icing Research Tunnel (IRT) using a 36 in. chord (0.91 m) NACA-0012 airfoil. The objective of this preliminary work was to investigate the feasibility of using ice shape feature changes to define requirements for the simulation and measurement of SLD icing conditions. It was desired to identify the minimum change (threshold) in a parameter value, which yielded an observable change in the ice shape. Liquid Water Content (LWC), drop size distribution (MVD), and tunnel static temperature were varied about a nominal value, and the effects of these parameter changes on the resulting ice shapes were documented. The resulting differences in ice shapes were compared on the basis of qualitative and quantitative criteria (e.g., mass, ice horn thickness, ice horn angle, icing limits, and iced area). This paper will provide a description of the experimental method, present selected experimental results, and conclude with an evaluation of these results, followed by a discussion of recommendations for future research.

Additional Investigations of Ice Shape Sensitivity to Parameter Variations

Abstract A second parameter sensitivity study was conducted at the NASA Glenn Research Center’s Icing Research Tunnel (IRT) using a 36 in. chord (0.91 m) NACA–0012 airfoil. The objective of this work was to further investigate the feasibility of using ice shape feature changes to define requirements for the simulation and measurement of SLD and appendix C icing conditions. A previous study concluded that it was feasible to use changes in ice shape features (e.g., ice horn angle, ice horn thickness, and ice shape mass) to detect relatively small variations in icing spray condition parameters ( LWC , MVD , and temperature). The subject of this current investigation extends the scope of this previous work, by also examining the effect of icing tunnel spray-bar parameter variations (water pressure, air pressure) on ice shape feature changes. The approach was to vary spray-bar water pressure and air pressure, and then evaluate the effects of these parameter changes on the resulting ice shapes. This paper will provide a description of the experimental method, present selected experimental results, and conclude with an evaluation of these results.

Update On SLD Engineering Tools Development

ABSTRACT The airworthiness authorities (FAA, JAA, Transport Canada) will be releasing a draft rule in the 2006 timeframe concerning the operation of aircraft in a Supercooled Large Droplet (SLD) environment aloft. The draft rule will require aircraft manufacturers to demonstrate that their aircraft can operate safely in an SLD environment for a period of time to facilitate a safe exit from the condition. It is anticipated that aircraft manufacturers will require a capability to demonstrate compliance with this rule via experimental means (icing tunnels or tankers) and by analytical means (ice prediction codes). Since existing icing research facilities and analytical codes were not developed to account for SLD conditions, current engineering tools are not adequate to support compliance activities in SLD conditions. Therefore, existing capabilities need to be augmented to include SLD conditions. In response to this need, NASA and its partners conceived a strategy or Roadmap for developing experimental & analytical SLD simulation tools. Following review and refinement by the airworthiness authorities and other international research partners, this technical strategy has been crystallized into a project plan to guide the SLD Engineering Tool Development effort. This paper will provide a brief overview of the latest version of the project plan and technical rationale, and provide a status of selected SLD Engineering Tool Development research tasks which are currently underway.

Numerical Simulation of Ice Shapes from a Bimodal Large Droplet Icing Cloud

†† The NASA ice accretion code LEWICE was used to simulate ice shapes generated from a bimodal large droplet icing cloud. An experimental effort was recently undertaken to simulate an icing cloud containing Super-cooled Large Droplets (SLD) in the Icing Research Tunnel (IRT) at the NASA Glenn Research Center. A spray sequencing method was used to reproduce the bimodal droplet distribution normally found in SLD clouds in nature. The numerical results are compared to ice shape tracings obtained from the experiments. Results indicate that agreement between code results and experiments is as good as or better than variations in the experiments resulting from differing methods for simulation of the natural icing cloud.

Simulation of a Bi-modal Large Droplet Icing Cloud in the NASA Icing Research Tunnel

‡† ‡ ‡ An experimental effort was recently undertaken to simulate an icing cloud containing Super-cooled Large Droplets (SLD) in the Icing Research Tunnel (IRT) at the NASA Glenn Research Center. A spray sequencing method was used to reproduce the bimodal droplet distribution normally found in SLD clouds in nature. The spray sequencing process consisted of setting two different spray bar manifold pressures, each representing separate drop size and Liquid Water Content (LWC) conditions, and then spraying a target airfoil using several different sequence patterns. The spray bar conditions used were selected to produce the same freezing fraction conditions at the stagnation line on the airfoil in order to maintain thermal continuity from one spray exposure to the next. Results of the experiments include ice shape tracings and photographs of the various exposures. Ice shape tracings are then compared to identify differences in ice shape features resulting from the various sequencing patterns.

Validation of NASA Thermal Ice Protection Computer Codes Part 2 - LEWICE/Thermal

The Icing Technology Branch at NASA Lewis has been involved in an effort to validate two thermal ice protection codes developed at the NASA Lewis Research Center: LEWICE/Thermal 1 (electrothermal de-icing and anti-icing), and ANTICE 2 (hot gas and electrothermal anti-icing). The thermal code validation effort was designated a priority during a 1994 “peer review” of the NASA Lewis icing program and was implemented as a cooperative effort with industry. During April 1996, the first of a series of experimental validation tests was conducted in the NASA Lewis Icing Research Tunnel (IRT). The purpose of this test was to acquire experimental data to validate the electrothermal predictive capabilities of both LEWICE/Thermal and ANTICE. A heavily instrumented test article was designed and fabricated to simulate electrothermal de-icing and anti-icing modes of operation. Thermal measurements were then obtained over a range of test conditions for comparison with analytical predictions. This paper will present the comparison between the experimental data and the most recent version of the LEWICE/Thermal computer code, LEWICE 1.6/ Thermal (alpha version). The paper will also provide a description of the model used in this code and the improvements which have been made to this code since its creation in 1991. Several capabilities have been added to this code especially within the last year in order to better model the phenomena observed in the April 1996 test. Nomenclature α angle of attack, degrees k thermal conductivity, W/m/ ° K LWC liquid water content, g/m 3 MVD median volume drop diameter, μ m Q heater wattage, W/in 2 V velocity, mph T temperature, ° F x surface direction, m y direction normal to surface, m t time, seconds Introduction In 1994 the Icing Technology Branch at the NASA Lewis Research Center conducted a “peer review” process to prioritize its programs based on technological needs identified by industry partners. The need for validated thermal ice protection computer codes was identified as a priority during this peer review process. As a result, NASA Lewis established an experimental program to validate two thermal ice protection codes developed by NASA Lewis: LEWICE/Thermal (electrothermal de-icing and antiicing) and ANTICE (hot gas and electrothermal antiicing). Two experimental tests were designed for the initial validation activity. The first test utilized an airfoil