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  • 1
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    Atmospheric Turbulence Estimates from a Pulsed Lidar (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-27
    Description: Estimates of the eddy dissipation rate (EDR) were obtained from measurements made by a coherent pulsed lidar and compared with estimates from mesoscale model simulations and measurements from an in situ sonic anemometer at the Denver International Airport and with EDR estimates from the last observation time of the trailing vortex pair. The estimates of EDR from the lidar were obtained using two different methodologies. The two methodologies show consistent estimates of the vertical profiles. Comparison of EDR derived from the Weather Research and Forecast (WRF) mesoscale model with the in situ lidar estimates show good agreement during the daytime convective boundary layer, but the WRF simulations tend to overestimate EDR during the nighttime. The EDR estimates from a sonic anemometer located at 7.3 meters above ground level are approximately one order of magnitude greater than both the WRF and lidar estimates - which are from greater heights - during the daytime convective boundary layer and substantially greater during the nighttime stable boundary layer. The consistency of the EDR estimates from different methods suggests a reasonable ability to predict the temporal evolution of a spatially averaged vertical profile of EDR in an airport terminal area using a mesoscale model during the daytime convective boundary layer. In the stable nighttime boundary layer, there may be added value to EDR estimates provided by in situ lidar measurements.
    Keywords: Air Transportation and Safety
    Type: AIAA Paper 2013-0512 , NF1676L-14858 , 51st AIAA Aerospace Sciences Meeting; 7-`0 Jan. 2013; Grapevine, TX; United States
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  • 2
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    An Aircraft Encounter with Turbulence in the Vicinity of a Thunderstorm (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Large eddy simulations of three convective turbulence events are investigated and compared with observational data. Two events were characterized with severe turbulence and the other with moderate turbulence. Two of the events occurred during NASA s turbulence flight experiments during the spring of 2002, and the third was an event identified by the Flight Operational Quality Assurance (FOQA) Program. Each event was associated with developing or ongoing convection and was characterized by regions of low to moderate radar reflectivity. Model comparisons with observations are favorable. The data sets from these simulations can be used to test turbulence detection sensors.
    Keywords: Air Transportation and Safety
    Type: AIAA Paper 2003-4075 , 21st AIAA Applied Aerodynamics Conference; Jun 23, 2003 - Jun 26, 2003; Orlando, FL; United States
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  • 3
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    A Windshear Hazard Index (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An aircraft exposed to hazardous low-level windshear may suffer a critical loss of airspeed and altitude, thus endangering its ability to remain airborne. In order to characterize this hazard, a nondimensional index was developed based oil aerodynamic principals and understanding of windshear phenomena, 'This paper reviews the development and application of the Bowles F-tactor. which is now used by onboard sensors for the detection of hazardous windshear. It was developed and tested during NASA/I:AA's airborne windshear program and is now required for FAA certification of onboard radar windshear detection systems. Reviewed in this paper are: 1) definition of windshear and description of atmospheric phenomena that may cause hazardous windshear. 2) derivation and discussion of the F-factor. 3) development of the F-factor hazard threshold, 4) its testing during field deployments, and 5) its use in accident reconstructions,
    Keywords: Air Transportation and Safety
    Type: ; 482-487|Aviation, Range and Aerospace Meteorology; Sep 11, 2000 - Sep 15, 2000; Orlando, FL; United States
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  • 4
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    Terminal Area Simulation System User's Guide - Version 10.0 (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The Terminal Area Simulation System (TASS) is a three-dimensional, time-dependent, large eddy simulation model that has been developed for studies of wake vortex and weather hazards to aviation, along with other atmospheric turbulence, and cloud-scale weather phenomenology. This document describes the source code for TASS version 10.0 and provides users with needed documentation to run the model. The source code is programed in Fortran language and is formulated to take advantage of vector and efficient multi-processor scaling for execution on massively-parallel supercomputer clusters. The code contains different initialization modules allowing the study of aircraft wake vortex interaction with the atmosphere and ground, atmospheric turbulence, atmospheric boundary layers, precipitating convective clouds, hail storms, gust fronts, microburst windshear, supercell and mesoscale convective systems, tornadic storms, and ring vortices. The model is able to operate in either two- or three-dimensions with equations numerically formulated on a Cartesian grid. The primary output from the TASS is time-dependent domain fields generated by the prognostic equations and diagnosed variables. This document will enable a user to understand the general logic of TASS, and will show how to configure and initialize the model domain. Also described are the formats of the input and output files, as well as the parameters that control the input and output.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2014-218150 , NF1676L-17801 , L-20345
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  • 5
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    Flight Tests of the Turbulence Prediction and Warning System (TPAWS) (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Flight tests of the National Aeronautics and Space Administration's Turbulence Prediction And Warning System (TPAWS) were conducted in the Fall of 2000 and Spring of 2002. TPAWS is a radar-based airborne turbulence detection system. During twelve flights, NASA's B-757 tallied 53 encounters with convectively induced turbulence. Analysis of data collected during 49 encounters in the Spring of 2002 showed that the TPAWS Airborne Turbulence Detection System (ATDS) successfully detected 80% of the events at least 30 seconds prior to the encounter, achieving FAA recommended performance criteria. Details of the flights, the prevailing weather conditions, and each of the turbulence events are presented in this report. Sensor and environmental characterizations are also provided.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2012-217337 , NF1676L-13490 , L-20125
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  • 6
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    Characterizing the Severe Turbulence Environments Associated With Commercial Aviation Accidents (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: A 44 case study analysis of the large-scale atmospheric structure associated with development of accident-producing aircraft turbulence is described. Categorization is a function of the accident location, altitude, time of year, time of day, and the turbulence category, which classifies disturbances. National Centers for Environmental Prediction Reanalyses data sets and satellite imagery are employed to diagnose synoptic scale predictor fields associated with the large-scale environment preceding severe turbulence. These analyses indicate a predominance of severe accident-producing turbulence within the entrance region of a jet stream at the synoptic scale. Typically, a flow curvature region is just upstream within the jet entrance region, convection is within 100 km of the accident, vertical motion is upward, absolute vorticity is low, vertical wind shear is increasing, and horizontal cold advection is substantial. The most consistent predictor is upstream flow curvature and nearby convection is the second most frequent predictor.
    Keywords: Air Transportation and Safety
    Type: NASA/CR-2002-211918/PT1 , NAS 1.26:211918/PT1
    Format: application/pdf
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  • 7
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    Numerical Simulation of the Aircraft Wake Vortex Flowfield (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The near wake vortex flowfield from a NACA0012 half-wing was simulated using a fully unstructured Navier-Stokes flow solver in three dimensions at a chord Reynolds number of 4.6 million and a Mach number of approximately 0.15. Several simulations were performed to examine the effect of boundary conditions, mesh resolution and turbulence scheme on the formation of wingtip vortex and its downstream propagation. The standard Spalart-Allmaras turbulence model was compared with the Dacles-Mariani and Spalart-Shur corrections for rotation and curvature effects. The simulation results were evaluated using the data from experiment performed at NASA Ames' 32in x 48in low speed wind tunnel.
    Keywords: Air Transportation and Safety
    Type: NF1676L-15576 , AIAA Atmospheric and Space Environment Meeting; Jun 24, 2013 - Jun 27, 2013; San Diego, CA; United States
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  • 8
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    Evaluation of Fast-Time Wake Vortex Prediction Models (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Current fast-time wake models are reviewed and three basic types are defined. Predictions from several of the fast-time models are compared. Previous statistical evaluations of the APA-Sarpkaya and D2P fast-time models are discussed. Root Mean Square errors between fast-time model predictions and Lidar wake measurements are examined for a 24 hr period at Denver International Airport. Shortcomings in current methodology for evaluating wake errors are also discussed.
    Keywords: Air Transportation and Safety
    Type: LF99-7143 , 47th AIAA Aerospace Sciences Meeting and Exhibit; Jan 05, 2009 - Jan 08, 2009; Orlando, FL; United States
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  • 9
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    Meteorology and Wake Vortex Influence on American Airlines FL-587 Accident (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The atmospheric environment surrounding the crash of American Airlines Flight 587 is investigated. Examined are evidence for any unusual atmospheric conditions and the potential for encounters with aircraft wake vortices. Computer simulations are carried out with two different vortex prediction models and a Large Eddy Simulation model. Wind models are proposed for studying aircraft and pilot response to the wake vortex encounter.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2004-213018 , L-18371
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  • 10
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    An Estimation of Turbulent Kinetic Energy and Energy Dissipation Rate Based on Atmospheric Boundary Layer Similarity Theory (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Algorithms are developed to extract atmospheric boundary layer profiles for turbulence kinetic energy (TKE) and energy dissipation rate (EDR), with data from a meteorological tower as input. The profiles are based on similarity theory and scalings for the atmospheric boundary layer. The calculated profiles of EDR and TKE are required to match the observed values at 5 and 40 m. The algorithms are coded for operational use and yield plausible profiles over the diurnal variation of the atmospheric boundary layer.
    Keywords: Air Transportation and Safety
    Type: NASA/CR-2000-210298 , NAS 1.26:210298
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