Aircraft icing remains a significant threat to aviation safety. Software that predicts the impingement and ice accretion on full aircraft geometries and aircraft components are in demand and NASA Glenn is committed to produce software that meets this need. One of the key parameters affecting an accurate prediction of iced geometry is the effect of ice roughness on the heat transfer coefficient. While many efforts have been made to implement the roughness in the flow solver, this report takes a correlation for roughness height distribution that is based on experimental measurements and demonstrates how to relate those measurements to an augmentation to the heat transfer coefficient provided by the flow solution. The outcome of this effort was the callibration of defaults for user supplied parameters to this correlation through comparison with 95 large glaze conditions from experiment by adjusting user-supplied parameters in the roughness augmentation equation.

To numerically approximate water collection on a surface in a Lagragian framework, many particles are released from upstream and tracked to the impact location. By producing many impacts on each triangular element (or face), the collection efficiency can be approximated. The objective of this paper is to investigate two methods for deciding that enough particles have impacted the face for reasonable accuracy. The convergence process progresses by adding an additional set of particles at each refinement level. One convergence criterion, referred to as mass flow difference, looks at the change in the result from one refinement level to the next. When that change falls below a user settable value, no more particles are introduced in that area. A second convergence criterion, referred to as fraction contained, computes a ratio of mass flow that very likely belongs entirely on the impact face to the mass flow that may be shared with neighboring faces. When that ratio rises above a user settable value, no more particles are introduced in that area. Results demonstrate that as the user settable values for each of the criteria are modified, errors in the prediction can be reduced. The net result being that fewer trajectories are required when compared to simply specifying a certain number of refinement levels.

GlennICE (Glenn Icing Computational Environment) is a computational tool designed to calculate ice growth on complex three-dimensional geometries using the input from a user-supplied computational fluid dynamics (CFD) solution for the geometry of interest. The NASA John H. Glenn Research Center at Lewis Field is developing this tool to aid those evaluating, designing and certifying aircraft, engines, and aircraft components for flight in icing conditions. This domestically available software is being developed to enable the introduction of new icing physics into a computational environment in a manner that is open for evaluation and eventual use by industry, academia, and other government organizations. This paper will document the current capabilities for version 2.1 of this software and provide example cases with comparison to available experimental data.

Computational methods for ice accretion can simulate the impact of water drops and ice crystals on an aircraft surface in a Lagrangian reference frame or in the Eulerian reference frame. In the Eulerian reference frame, particles are considered a continuous fluid while in the Lagrangian frame individual particle trajectories are calculated. Methods that use the Eulerian reference frame are typically easier to develop as established modules used for continuum mechanics can be leveraged. The Eulerian systems can also be faster since the user does not have to simulate millions of particles in order to achieve good results. It is imperative therefore that a Lagrangian method optimize the release points of trajectories such that accurate solutions can be obtained while minimizing as much as possible the number of trajectories computed. This paper will present a methodology for this refinement process and demonstrate its effectiveness on sample three dimensional test cases.

This paper will describe two recent modifications to the Glenn ICE software. First, a capability for modeling ice crystals and mixed phase icing has been modified based on recent experimental data. Modifications have been made to the ice particle bouncing and erosion model. This capability has been added as part of a larger effort to model ice crystal ingestion in aircraft engines. Comparisons have been made to ice crystal ice accretions performed in the NRC Research Altitude Test Facility (RATFac). Second, modifications were made to the run back model based on data and observations from thermal scaling tests performed in the NRC Altitude Icing Tunnel.

The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that were attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was one or more of the following anomalies: degraded engine performance, engine roll back, compressor surge and stall, and flameout of the combustor. The main focus of this research is the development of a computational tool that can estimate whether there is a risk of ice accretion by tracking key parameters through the compression system blade rows at all engine operating points within the flight trajectory. The tool has an engine system thermodynamic cycle code, coupled with a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor blade rows. Assumptions are made to predict the complex physics involved in engine icing. Specifically, the code does not directly estimate ice accretion and does not have models for particle breakup or erosion. Two key parameters have been suggested as conditions that must be met at the same location for ice accretion to occur: the local wet-bulb temperature to be near freezing or below and the local melt ratio must be above 10%. These parameters were deduced from analyzing laboratory icing test data and are the criteria used to predict the possibility of ice accretion within an engine including the specific blade row where it could occur. Once the possibility of accretion is determined from these parameters, the degree of blockage due to ice accretion on the local stator vane can be estimated from an empirical model of ice growth rate and time spent at that operating point in the flight trajectory. The computational tool can be used to assess specific turbine engines to their susceptibility to ice accretion in an ice crystal environment.

ABSTRACT During the past two decades the occurrence of ice accretionwithin commercial high bypass aircraft turbine engines undercertain operating conditions has been reported. Numerousengine anomalies have taken place at high altitudes that wereattributed to ice crystal ingestion such as degraded engineperformance, engine roll back, compressor surge and stall,and even flameout of the combustor. As ice crystals areingested into the engine and low pressure compressionsystem, the air temperature increases and a portion of the icemelts allowing the ice-water mixture to stick to the metalsurfaces of the engine core. The focus of this paper is onestimating the effects of ice accretion on the low pressurecompressor, and quantifying its effects on the engine systemthroughout a notional flight trajectory. In this paper it wasnecessary to initially assume a temperature range in whichengine icing would occur. This provided a mechanism tolocate potential component icing sites and allow thecomputational tools to add blockages due to ice accretion in aparametric fashion. Ultimately the location and level ofblockage due to icing would be provided by an ice accretioncode. To proceed, an engine system modeling code and amean line compressor flow analysis code were utilized tocalculate the flow conditions in the fan-core and low pressurecompressor and to identify potential locations within thecompressor where ice may accrete. Note that there is abaseline value of aerodynamic blockage due to low velocityair near the compressor inner and outer walls and bladesurfaces (boundary layer blockage). There is also a blockagedue to the blade metal thickness. In this study, the “additionalblockage” refers to blockage due to the accretion of ice on themetal surfaces. Once the potential locations of ice accretionare identified, the levels of additional blockage due toaccretion were parametrically varied to estimate the effectson the low pressure compressor blade row performanceoperating within the engine system environment. This studyincludes detailed analysis of compressor and engineperformance during cruise and descent operating conditionsat several altitudes within the notional flight trajectory. Thepurpose of this effort is to develop the codes to provide apredictive capability to forecast the onset of engine icingevents, such that they could help in the avoidance of theseevents.It has been reported that ice crystal accretion in gas turbineengines is dependent on the amount of mixed phaseconditions (liquid and solid) that exist. In addition, theproblem of ice accretion is highly multi-disciplinary, since itinvolves heat transfer from the air to the compressor metalsurfaces. The first phase of this study focuses on addressingthe thermodynamic cycle through the engine system code andthe mean line flow analysis through the compressor through aflight trajectory. The second phase of this study focuses on

duce computer software that can accurately predict ice growth under any meteorological conditions for any aircraft surface. An extensive comparison of the results in a quantifiable manner against the database of ice shapes that have been generated in the NASA Glenn Icing Research Tunnel (IRT) has been performed, including additional data taken to extend the database in the Super-cooled Large Drop (SLD) regime. The project shows the differences in ice shape between LEWICE 3.2.2, GlennICE, and experimental data. The Icing Branch at NASA Glenn has produced several computer codes over the last 20 years for performing icing simulation. While some of these tools have been collaborative projects, most have been developed primarily by one person, with some assistance by others. The state of computing has also changed dramatically in that time period. As these codes have grown in complexity and have been accepted by users as production icing tools, there has arisen a need for the developers to adhere to standard software practices used to develop commercial software. The project addresses the validation of the software against a recent set of iceshape data in the SLD regime. This validation effort mirrors a similar effort undertaken for previous validations of LEWICE. Those reports quantified the ice accretion prediction capabilities of the LEWICE software. Several ice geometry features were proposed for comparing ice shapes in a quantitative manner. The resulting analysis showed that LEWICE compared well to the available experimental data. The effects of super-cooled large droplets in icing have been researched Comparison of Aircraft Icing Growth Assessment Software The goal is to provide software that can predict ice growth under any condition for any aircraft surface. John H. Glenn Research Center, Cleveland, Ohio ern numerical methods. Among these methods are efficient Kepler’s-equation time-of-flight solutions and self-starting numerical integration with time as the independent variable. Self-starting numerical integration satisfies the requirements for accuracy, reproducibility, and efficiency (and, hence, speed). Self-starting numerical integration also supports fully analytic regulation of integration step sizes, thereby further increasing speed while maintaining accuracy. This work was done by Jonathan K. Weaver of Johnson Space Center and Daniel R. Adamo of United Space Alliance. For further information, contact the JSC Innovation Partnerships Office at (281) 483-3809. MSC-23802-1

Due to numerous engine power-loss events associated with high-altitude convective weather, ice accretion within an engine due to ice-crystal ingestion is being investigated. The National Aeronautics and Space Administration (NASA) and the National Research Council (NRC) of Canada are starting to examine the physical mechanisms of ice accretion on surfaces exposed to ice-crystal and mixed-phase conditions. In November 2010, two weeks of testing occurred at the NRC Research Altitude Facility utilizing a single wedge-type airfoil designed to facilitate fundamental studies while retaining critical features of a compressor stator blade or guide vane. The airfoil was placed in the NRC cascade wind tunnel for both aerodynamic and icing tests. Aerodynamic testing showed excellent agreement compared with CFD data on the icing pressure surface and allowed calculation of heat transfer coefficients at various airfoil locations. Icing tests were performed at Mach numbers of 0.2 to 0.3, total pressures from 93 to 45 kPa, and total temperatures from 5 to 15 C. Ice and liquid water contents ranged up to 20 and 3 grams per cubic meter, respectively. The ice appeared well adhered to the surface in the lowest pressure tests (45 kPa) and, in a particular case, showed continuous leading-edge ice growth to a thickness greater than 15 millimeters in 3 minutes. Such widespread deposits were not observed in the highest pressure tests, where the accretions were limited to a small area around the leading edge. The suction surface was typically ice-free in the tests at high pressure, but not at low pressure. The icing behavior at high and low pressure appeared to be correlated with the wet-bulb temperature, which was estimated to be above 0 C in tests at 93 kPa and below 0 C in tests at lower pressure, the latter enhanced by more evaporative cooling of water. The authors believe that the large ice accretions observed in the low pressure tests would undoubtedly cause the aerodynamic performance of a compressor component such as a stator blade to degrade significantly, and could damage downstream components if shed.

at Lewis FieldIt has been demonstrated that ice crystals bounced off sub-freezing surface shaped like wing leading edge, how about large stagnation regions like the turn inside a scoop? Can ice crystals accrete in large stagnation regions without liquid water? Where is the probable source of water in this zone? Would an anti-iced stage upstream be responsible for the recreation of liquid water ?

The focus of this study is on utilizing a mean line compressor flow analysis code coupled to an engine system thermodynamic code, to estimate the effects of ice accretion on the low pressure compressor, and quantifying its effects on the engine system throughout a notional flight trajectory. In this paper a temperature range in which engine icing would occur was assumed. This provided a mechanism to locate potential component icing sites and allow the computational tools to add blockages due to ice accretion in a parametric fashion. Ultimately the location and level of due to icing would be provided by an ice accretion code. To proceed, an engine system modeling code and a mean line compressor flow analysis code were utilized to calculate the flow conditions in the fan-core and low pressure compressor and to identify potential locations within the compressor where ice may accrete. In this study, an blockage due to the accretion of ice on the metal surfaces, has been added to the baseline aerodynamic due to boundary layer, as well as the blade metal blockage. Once the potential locations of ice accretion are identified, the levels of additional due to accretion were parametrically varied to estimate the effects on the low pressure compressor blade row performance operating within the engine system environment. This study includes detailed analysis of compressor and engine performance during cruise and descent operating conditions at several altitudes within the notional flight trajectory. The purpose of this effort is to develop the computer codes to provide a predictive capability to forecast the onset of engine icing events, such that they could ultimately help in the avoidance of these events.

A capability for modeling ice crystals and mixed phase icing has been added to GlennICE. Modifications have been made to the particle trajectory algorithm and energy balance to model this behavior. This capability has been added as part of a larger effort to model ice crystal ingestion in aircraft engines. Comparisons have been made to four mixed phase ice accretions performed in the Cox icing tunnel in order to calibrate an ice erosion model. A sample ice ingestion case was performed using the Energy Efficient Engine (E3) model in order to illustrate current capabilities. Engine performance characteristics were supplied using the Numerical Propulsion System Simulation (NPSS) model for this test case.

A research project is underway at the NASA Glenn Research Center (GRC) to produce computer software that can accurately predict ice growth under any meteorological conditions for any aircraft surface. This report will present results from two different computer programs. The first program, LEWICE version 3.2.2, has been reported on previously. The second program is GlennICE version 0.1. An extensive comparison of the results in a quantifiable manner against the database of ice shapes that have been generated in the GRC Icing Research Tunnel (IRT) has also been performed, including additional data taken to extend the database in the Super-cooled Large Drop (SLD) regime. This paper will show the differences in ice shape between LEWICE 3.2.2, GlennICE, and experimental data. This report will also provide a description of both programs. Comparisons are then made to recent additions to the SLD database and selected previous cases. Quantitative comparisons are shown for horn height, horn angle, icing limit, area, and leading edge thickness. The results show that the predicted results for both programs are within the accuracy limits of the experimental data for the majority of cases.

As with any scientific endeavor, the foundation of icing research at the NASA Glenn Research Center (GRC) is the data acquired during experimental test ing . In the case of the GRC Icing Branch , an important part of th is data consists of ice tracings taken following tests carried out in the GRC Icing Research Tunnel (IRT) , as well as the associated operational and environmental conditions documented during the se tests . Over the years, the large number of experimental runs completed has served to emphasize the need for a consistent strategy for managing th is da ta. To address the situation, the Icing Branch has recently elected to implement the IceVal DatAssistant automated data management system. With the release of this system, all publicly available IRT -generated experimental ice shapes with complete and verif iable conditions have now been compiled into one electronically searchable database . Simulation software results for the equivalent conditions, generated using the latest version of the LEWICE ice shape prediction code , are likewise included and are linked to the corresponding experimental runs. In addition to t his comprehensive database , the IceVal system also includes a graphically -oriented data base access utility , which provide s reliable and easy access to all data contained in the database . In this pape r, the issues surrounding historical icing data management practices are discussed, as well as the anticipated benefits to be achieved as a result of migrating to th e new system. A detailed description of the software system features and database content is also provided; and, finally, known issues and plans for future work are presented.

Fundamental dynamic periods of Quaternary deposits beneath the peninsula of Charleston, South Carolina, are characterized spatially using an updated isopach map of Quaternary thickness, characteristic small-strain shear wave velocity information, a 1:24,000 geologic map, and a simple approximating equation. The updated isopach map is developed from subsurface information from 266 investigation sites. Estimates of fundamental periods for the Quaternary sediments primarily range between 0.3 and 0.7 s. These periods are lower end estimates of actual ground periods, based on a comparison with modeled response-spectra ratios. Estimates of fundamental periods range from 0.1 to 0.4 s for over 95% of the buildings present in 1886. Thus, the overlap between the range of building periods and the range in periods corresponding to high spectral ratios is not great. This finding agrees with the observation of Marciano and Elton that damage was independent (or only slightly dependent) of building height.

Six major geologic units in Charleston, South Carolina, are characterized in terms of shear-wave velocity ( V S ) in this article. The characterization is based on in situ V S measurements at 91 sites. The six units are man-made fills, Holocene and late Pleistocene deposits, the Wando Formation, the Ten Mile Hill beds, the Penholoway Formation and the Daniel Island beds, and Tertiary deposits. Median V S values for these units in the top 25 m are 145, 111, 189, 176, 285, and 399 m/ sec, respectively. For Tertiary deposits in the depth intervals of 25–55 m, 55–75 m, and 75–100 m, median V S values are 435, 533, and 663 m/sec, respectively. A seismic-response parametric study is conducted assuming several soil/rock models and two input rock outcrop motions with peak accelerations of 0.3 g and 0.1 g . It is found that Quaternary sections with V S of 190 m/sec (e.g., the Wando Formation) and thicknesses of about 7 m to 15 m exhibit predominant peaks in the acceleration- response spectra at periods of about 0.25 to 0.4 sec. These predominant peaks match fundamental periods of many existing buildings in the old city district of Charleston. The results suggest that local site conditions contributed to building damage in the 1886 Charleston earthquake.