Judith F. Van Zante

NASA/FAA TAILPLANE ICING PROGRAM OVERVIEW.

The effects of tailplane icing were investigated in a four-year NASA/FAA Tailplane Icing, Program (TIP). This research program was developed to improve the understanding, of iced tailplane aeroperformance and aircraft aerodynamics, and to develop design and training aides to help reduce the number of incidents and accidents caused by tailplane icing. To do this, the TIP was constructed with elements that included icing, wind tunnel testing, dry-air aerodynamic wind tunnel testing, flight tests, and analytical code development. This paper provides an overview of the entire program demonstrating the interconnectivity of the program elements and reports on current accomplishments.

In-Flight Aerodynamic Measurements of an Iced Horizontal Tailplane

The effects of tailplane icing on aircraft dynamics and tailplane aerodynamics were investigated using, NASAs modified DHC-6 Twin Otter icing research aircraft. This flight program was a major element of the four-year NASA/FAA research program that also included icing wind tunnel testing, dry-air aerodynamic wind tunnel testing, and analytical code development. Flight tests were conducted to obtain aircraft dynamics and tailplane aerodynamics of the DHC-6 with four tailplane leading-edge configurations. These configurations included a clean (baseline) and three different artificial ice shapes. Quasi-steady and various dynamic flight maneuvers were performed over the full range of angles of attack and wing flap settings with each iced tailplane configuration. This paper presents results from the quasi-steady state flight conditions and describes the range of flow fields at the horizontal tailplane, the aeroperformance effect of various ice shapes on tailplane lift and elevator hinge moment, and suggests three paths that can lead toward ice-contaminated tailplane stall. It was found that wing, flap deflection was the most significant factor in driving the tailplane angle of attack toward alpha(tail stall). However, within a given flap setting, an increase in airspeed also drove the tailplane angle of attack toward alpha(tail stall). Moreover, increasing engine thrust setting also pushed the tailplane to critical performance limits, which resulted in premature tailplane stall.

Advanced Optical Diagnostics for Ice Crystal Cloud Measurements in the NASA Glenn Propulsion Systems Laboratory

A light extinction tomography technique has been developed to monitor ice water clouds upstream of a direct connected engine in the Propulsion Systems Laboratory (PSL) at NASA Glenn Research Center (GRC). The system consists of 60 laser diodes with sheet generating optics and 120 detectors mounted around a 36-inch diameter ring. The sources are pulsed sequentially while the detectors acquire line-of-sight extinction data for each laser pulse. Using computed tomography algorithms, the extinction data are analyzed to produce a plot of the relative water content in the measurement plane. To target the low-spatial-frequency nature of ice water clouds, unique tomography algorithms were developed using filtered backprojection methods and direct inversion methods that use Gaussian basis functions. With the availability of a priori knowledge of the mean droplet size and the total water content at some point in the measurement plane, the tomography system can provide near real-time in-situ quantitative full-field total water content data at a measurement plane approximately 5 feet upstream of the engine inlet. Results from ice crystal clouds in the PSL are presented. In addition to the optical tomography technique, laser sheet imaging has also been applied in the PSL to provide planar ice cloud uniformity and relative water content data during facility calibration before the tomography system was available and also as validation data for the tomography system. A comparison between the laser sheet system and light extinction tomography resulting data are also presented. Very good agreement of imaged intensity and water content is demonstrated for both techniques. Also, comparative studies between the two techniques show excellent agreement in calculation of bulk total water content averaged over the center of the pipe.

An Initial Study of the Fundamentals of Ice Crystal Icing Physics in the NASA Propulsion Systems Laboratory

This paper presents results from an initial study of the fundamental physics of ice-crystal ice accretion using the NASA Propulsion Systems Lab (PSL). Ice accretion due to the ingestion of ice-crystals is being attributed to numerous jet-engine power-loss events. The NASA PSL is an altitude jet-engine test facility which has recently added a capability to inject ice particles into the flow. NASA is evaluating whether this facility, in addition to full-engine and motor-driven-rig tests, can be used for more fundamental ice-accretion studies that simulate the different mixed-phase icing conditions along the core flow passage of a turbo-fan engine compressor. The data from such fundamental accretion tests will be used to help develop and validate models of the accretion process. The present study utilized a NACA0012 airfoil. The mixed-phase conditions were generated by partially freezing the liquid-water droplets ejected from the spray bars. This paper presents data regarding (1) the freeze out characteristics of the cloud, (2) changes in aerothermal conditions due to the presence of the cloud, and (3) the ice accretion characteristics observed on the airfoil model. The primary variable in this test was the PSL plenum humidity which was systematically varied for two duct-exit-plane velocities (85 and 135 m/s) as well as two particle size clouds (15 and 50 μm MVDi). The observed clouds ranged from fully glaciated to fully liquid, where the liquid clouds were at least partially supercooled. The air total temperature decreased at the test section when the cloud was activated due to evaporation. The ice accretions observed ranged from sharp arrow-like accretions, characteristic of ice-crystal erosion, to cases with doublehorn shapes, characteristic of supercooled water accretions.

Numerical Analysis of Mixed-Phase Icing Cloud Simulations in the NASA Propulsion Systems Laboratory

This paper describes the development of a numerical model that couples the thermal interaction between ice particles, water droplets, and the flowing gas of an icing wind tunnel for simulation of NASA Glenn Research Center’s Propulsion Systems Laboratory (PSL). The ultimate goal of the model is to better understand the complex interactions between the test parameters and have greater confidence in the conditions at the test section of the PSL tunnel. The model attempts to explain the observed changes in test conditions by coupling the conservation of mass and energy equations for both the cloud particles and flowing gas mass. The model uses isentropic relations to relate gas temperature, velocity, density and pressure with respect to the PSL geometry. Measurements were taken at the PSL during wind tunnel tests simulating ice-crystal and mixed-phase icing that relate to ice accretions within turbofan engines in May 2015. The model was compared to experimentally measured values, where test conditions varied gas temperature, pressure, velocity and humidity levels, as well as the cloud total water content, particle initial temperature, and particle size distribution. Wet-bulb temperatures were generally within a few degrees of freezing. The model showed good agreement with experimentally measured values, to within approximately 30% of the measured change in gas temperature and humidity at the tunnel test section. The model did reasonably well in predicting melt content (liquid mass to total mass) at the test section, especially for clouds with larger particle sizes. In addition, the model predicted particle size at the tunnel exit with good agreement, however, the comparison was limited to clouds consisting of a small particle size distribution. One of the key findings from this work is that there was a nearly constant but slight increase in total wet-bulb temperature when the spray cloud was activated for every test and simulation. In addition, the total wet-bulb temperature in the tunnel plenum was a large factor in determining cloud phase.

INVESTIGATION OF DYNAMIC FLIGHT MANEUVERS WITH AN ICED TAILPLANE.

Judith Foss Van ZanteDynacs Engineering Co., Inc., Brook Park, OhioThomas P. RatvaskyLewis Research Center, Cleveland, OhioPrepared for the37th Aerospace Sciences Meeting & Exhibitsponsored by the American Institute of Aeronautics and AstronauticsReno, Nevada, January 11-14, 1999National Aeronautics andSpace AdministrationLewis Research Center

NASA Glenn Icing Research Tunnel: 2012 Cloud Calibration Procedure and Results

In 2011, NASA Glenn s Icing Research Tunnel underwent a major modification to it s refrigeration plant and heat exchanger. This paper presents the results of the subsequent full cloud calibration. Details of the calibration procedure and results are presented herein. The steps include developing a nozzle transfer map, establishing a uniform cloud, conducting a drop sizing calibration and finally a liquid water content calibration. The goal of the calibration is to develop a uniform cloud, and to build a transfer map from the inputs of air speed, spray bar atomizing air pressure and water pressure to the output of median volumetric droplet diameter and liquid water content.

An Assessment of the Icing Blade and the SEA Multi-Element Sensor for Liquid Water Content Calibration of the NASA GRC Icing Research Tunnel

The NASA Glenn Icing Research tunnel has been using an Icing Blade technique to measure cloud liquid water content (LWC) since 1980. The IRT conducted tests with SEA Multi-Element sensors from 2009 to 2011 to assess their performance in measuring LWC. These tests revealed that the Multi-Element sensors showed some significant advantages over the Icing Blade, particularly at higher water contents, higher impingement rates, and large drop sizes. Results of these and other tests are presented here.

Air Flow and Liquid Water Concentration Simulations of the 2012 NASA Glenn Icing Research Tunnel

Three-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations using the Menter-SST turbulence model were performed on the new 2012 configuration of the NASA Glenn Icing Research Tunnel (IRT). The IRT was simulated from the exit of the heat exchanger to the test section. A two-dimensional simulation was first performed on a crosssection of the heat exchanger to provide initial conditions for three-dimensional flow predictions through the turning vanes, spray bars, tunnel contraction and test section. The simulations showed a general increase in turbulence intensity within the test section as compared to previous IRT configurations (in 2000 and 2009) which can be attributed to wake effects from both the heat exchanger and spray bars. In addition, the heat exchanger produced variations in the yaw flow angles after the turning vanes which are consistent with experiments while the corner geometry resulted in higher flow turbulence gradients for the inner wall regions. Using these simulated time-averaged flowfields, droplet trajectories were predicted using Lagrangian calculations with an unsteady Discrete Random Walk (DRW) model to mimic turbulent fluctuations. A transfer map was developed by mapping the water droplet locations at the test section by tracking peak concentration contours associated with both nozzle rows and nozzle columns. In addition, the liquid water concentration (LWC) distribution at the test section was predicted using the 2012 calibrated nozzle locations. The simulated transfer map and LWC distribution were both qualitatively similar to experiments but demonstrate that the RANS model may not be capturing unsteadiness associated with the spray bar wakes and the jets. An appendix was provided with data on a hybrid RANS/LES simulation of a section of the IRT which captured the unsteady behavior of the airflow. The hybrid model predicts significantly higher turbulence in the spray bar wake than the RANS model which would explain the disparities between with the droplet trajectory calculations and experiments.

Update on the NASA Glenn Propulsion Systems Lab Icing and Ice Crystal Cloud Characterization (2017) [STUB]

NASA Glenn’s Propulsion Systems Lab, an altitude engine test facility, generates icing clouds with a spray system. While the spray system is used mostly to create ice crystal clouds (Appendix D/P), the 2017 cloud characterization effort added the requirement to produce exactly supercooled liquid clouds in Appendix C and Appendix O. Success was demonstrated to supercool the largest drops at the warmest conditions, but not freeze out the smallest drops at the coldest conditions. This paper documents primarily the total water content characterization methodology and results from an Iso-Kinetic Probe in ice crystals and Multi-Wire sensor in supercooled liquid, along with the cloud uniformity provided by light extinction tomography. Particle size distribution results from High Speed Imaging probes and a Phase Doppler Interferometer are discussed. Also, a new numerical model for tracking the thermodynamics of the air-drop interactions in PSL from the plenum toward the cloud characterization plane are noted. Both of these latter topic are more fully documented in companion papers.