Dynamics and Characteristics of the Self-trapping of Intense Light Beams
Dynamics and characteristics of self-trapping of intense light beams
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Dynamic satellite geodesy
The paper describes operation of the GEOS-3 and Lageos spacecraft launched by NASA as part of the Earth and Ocean Dynamic Program. The investigations conducted by using GEOS-3 include the determination of tracking station coordinates, polar motion, and the use of altimetry in orbit determination. Lageos was designed as a precision target for making geodetic measurements with ground laser systems. Consideration is given to the progress made in the investigation and determination of tidal parameters by means of satellite perturbation methods. Satellite geodetic methods based on the ability to determine precise satellite orbits and orbit determination are outlined. Emphasis is placed on the future studies employing Spaceborne Laser and Global Positioning System concepts.
Smith, D. E.↗
Time-Variable Gravity Signal due to Extratropic Pacific Water Mass Redistribution
Using the satellite-laser-ranging (SLR) data, Cox and Chao [2002] reported the detection of a large post-1998 anomaly (in the form of a positive jump) in the time series of Earth s lowest-degree gravity harmonic 52, or the dynamic oblateness. Among several groups now examining the mass redistribution in the global geophysical fluids in search of the cause(s), we report here a temporally coinciding anomalies found in the extratropic north + south Pacific basins. Clearly seen in the leading EOFPC mode for extratropic Pacific, these anomalies occurred in sea-surface height, sea-surface temperature, and temperature- and salinity-depth profiles. We based our analysis on two different data sources: TOPEX/Poseidon altimetry, and the ECCO ocean general circulation model output assimilating T/P data. The magnitude of these changes, when converted to equivalent J2 change, appears to be a few times too small to explain the observed J2 directly. These findings, and the fact that the anomalies occurred following the strong 1997-98 El Nino, suggest strong geophysical connection of the interannual-to-decadal variation of 52 with the Pacific Decadal Oscillation (PDO) and the ultimate global-change processes that cause PDO. More work is underway, and additional independent data sources are examined, paying close attention to the fact that the J2 anomaly has been reversing back to normal since 2001. These include: (1) cryospheric contributions (melting of glaciers and ice sheets); (2) land hydrological contributions; (3) polar sea influences ( e g , via deep flow); (4) fluid flow in Earth's core; (5) time-variable gravity signals from SLR in higher harmonic degree/order, including J3,J4, (2,1), and (2,2) coefficients, considering their lower signal-to-noise ratios; (6) Earth rotation data in terms of length-of-day and polar motion.
Chao, B. F.↗
Laser-Based Flowfield Imaging in a Lean Premixed Prevaporized Sector Combustor
OH and fuel planar laser-induced fluorescence (PLIF) is used qualitatively in this study to observe the flame structure resultant from different fuel injector dome configurations within the 3-cup sector combustor test rig. The fluorescence images are compared with some computational fluid dynamics (CFD) results. Interferences in obtaining OH fluorescence signals due to the emission of other species are assessed. NO PLIF images are presented and compared to gas analysis results. The comparison shows that PLIF NO can be an excellent method for measuring NO in the flame. Additionally, we present flow visualization of the molecular species C2.
Hicks, Yolanda R.↗
Failure Mechanisms and Life Prediction of Thermal and Environmental Barrier Coatings under Thermal Gradients
Ceramic thermal and environmental barrier coatings (TEBCs) will play an increasingly important role in gas turbine engines because of their ability to further raise engine temperatures. However, the issue of coating durability is of major concern under high-heat-flux conditions. In particular, the accelerated coating delamination crack growth under the engine high heat-flux conditions is not well understood. In this paper, a laser heat flux technique is used to investigate the coating delamination crack propagation under realistic temperature-stress gradients and thermal cyclic conditions. The coating delamination mechanisms are investigated under various thermal loading conditions, and are correlated with coating dynamic fatigue, sintering and interfacial adhesion test results. A coating life prediction framework may be realized by examining the crack initiation and propagation driving forces for coating failure under high-heat-flux test conditions.
Zju, Dongming↗
Hypervelocity Impact Test Fragment Modeling: Modifications to the Fragment Rotation Analysis and Lightcurve Code
Hypervelocity impact tests on test satellites are performed by members of the orbital debris scientific community in order to understand and typify the on-orbit collision breakup process. By analysis of these test satellite fragments, the fragment size and mass distributions are derived and incorporated into various orbital debris models. These same fragments are currently being put to new use using emerging technologies. Digital models of these fragments are created using a laser scanner. A group of computer programs referred to as the Fragment Rotation Analysis and Lightcurve code uses these digital representations in a multitude of ways that describe, measure, and model on-orbit fragments and fragment behavior. The Dynamic Rotation subroutine generates all of the possible reflected intensities from a scanned fragment as if it were observed to rotate dynamically while in orbit about the Earth. This calls an additional subroutine that graphically displays the intensities and the resulting frequency of those intensities as a range of solar phase angles in a Probability Density Function plot. This document reports the additions and modifications to the subset of the Fragment Rotation Analysis and Lightcurve concerned with the Dynamic Rotation and Probability Density Function plotting subroutines.
Gouge, Michael F.↗
Self-Aligned Focusing Schlieren and OH Planar Laser-Induced Fluorescence Flow Visualization in a Dual-Mode Scramjet
Ahigh-speed self-aligned focusing schlieren (SAFS) system was used to visualize density gradients in and around the cavity flameholder of the combustor section of the University of Virginia Supersonic Combustion Facility (UVASCF). Images with this system were acquired at a framing rate of 110 kHz with no fuel injection, with fuel injection but no flame, and for fuel injection with combustion corresponding to a global equivalence ratio of 𝜙 = 0.18. Images with an air throttle in operation to modify the shock train location with fuel injection and with flame were also acquired. Simultaneous OH planar laser-induced fluorescence (PLIF) images were also acquired at a framing rate of 20 Hz. Results obtained with both visualization techniques are compared to one another to highlight how SAFS can complement more advanced flow visualization techniques and resolve dynamic behavior that may not otherwise be captured. Both proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) analysis techniques are applied to the SAFS image sequences to identify coherent periodic structures for the runs with fuel injection and combustion.
Brett F Bathel↗
Argus: a new instrument for the measurement of the stratospheric dynamical tracers, N2O and CH4
We describe here a new instrument for the simultaneous, in situ measurement of the stratospheric tracer molecules, nitrous oxide (N2O) and methane (CH4). Argus is unique in its small size making it well suited for limited payload atmospheric research platforms. Argus employs second harmonic spectroscopy using tunable lead-salt diode lasers emitting in the mid-infrared. We first explain the Argus design philosophy followed by detailed descriptions of the instrument's optical, mechanical, and thermal sub-systems. Argus employs an in-flight calibration system providing real time calibrations and tightly constrained uncertainty estimates of the returned data. Data analysis is carried out using non-linear least-squares model fits to the acquired second harmonic spectra. A sampling of Argus data acquired on a recent stratospheric research campaign in the Arctic winter is presented.
Methane/analysis↗
Design, development, and test of a laser velocimeter for high speed turbomachinery
The paper describes the design, development, and test of a laser Doppler velocimeter (LDV) to map the velocity fields in a small, high speed, 8:1 pressure ratio, 0.91 kg/s (2 lbm/s), centrifugal compressor. This instrument is being used as a diagnostic tool for the study of the basic fluid dynamics of the inducer, impeller and the diffuser regions of high pressure ratio, small, centrifugal compressors. The LDV instrumentation has been optimized to permit the measurement of instantaneous velocities up to approximately 500 m/s, measured in absolute coordinates, within a rotating compressor impeller. Velocities of the same magnitude can also be measured in the two-dimensional radial plane of the diffuser. It is shown that LDV can make nondisturbing gas velocity measurements and surmount the difficulties found in applying other types of aerodynamic instrumentation to this measurement problem.
Runstadler, P. W., Jr.↗
Studies of atmospheric refraction effects on laser data
The refraction effect from three perspectives was considered. An analysis of the axioms on which the accepted correction algorithms were based was the first priority. The integrity of the meteorological measurements on which the correction model is based was also considered and a large quantity of laser observations was processed in an effort to detect any serious anomalies in them. The effect of refraction errors on geodetic parameters estimated from laser data using the most recent analysis procedures was the focus of the third element of study. The results concentrate on refraction errors which were found to be critical in the eventual use of the data for measurements of crustal dynamics.
Dunn, P. J.↗
The Sacramento Peak fast microphotometer
The Sacramento Peak Observatory Fast Microphotometer translates an optical system that includes a laser and photodiode detector across the film to scan the Y direction. A stepping motor moves the film gate in the X direction. This arrangement affords high positional accuracy, low noise (0.002 RMS density units), modest speed (5000 points/second), large dynamic range (4.5 density units), high stability (0.005 density units), and low scattered light. The Fast Microphotometer is interfaced to the host computer by a 6502 microprocessor.
Arrambide, M. R.↗
Application of laser velocimetry to unsteady flows in large scale, high speed tunnels
The optical, seeding, and data reduction procedures which have been used in the successful application of laser velocimetry to large-scale, unsteady, transonic wind-tunnel testing are described. Flowfield measurements obtained at several facilities are presented. These results include vortex flow measurements and ensemble-averaged data obtained under conditions of vortex-shedding, dynamic stall airfoil oscillation, oscillating trailing-edge control flaps, and helicopter rotor flow fields.
Owen, F. K.↗
ICIASF '85 - International Congress on Instrumentation in Aerospace Simulation Facilities, 11th, Stanford University, CA, August 26-28, 1985, Record
Developments related to laser Doppler velocimetry are discussed, taking into account a three-component dual beam laser-Doppler-anemometer to be operated in large wind tunnels, a new optical system for three-dimensional laser-Doppler-anemometry using an argon-ion and a dye laser, and a two-component laser Doppler velocimeter by switching fringe orientation. Other topics studied are concerned with facilities, instrumentation, control, hot wire/thin film measurements, optical diagnostic techniques, signal and data processing, facilities and adaptive wall test sections, data acquisition and processing, ballistic instrument systems, dynamic testing and material deformation measurements, optical flow measurements, test techniques, force measurement systems, and holography. Attention is given to nonlinear calibration of integral wind tunnel balances, a microcomputer system for real time digitized image compression, and two phase flow diagnostics in propulsion systems.
Source record↗
Airborne lidar research
The planetary boundary layer (PBL) is the lowest layer of the atmosphere in contact with the Earth's surface. It plays an important role in atmospheric circulation and dynamics by influencing surface fluxes of moisture, heat, and momentum. The PBL is characterized by its turbulence structure. Organized convection within the PBL may generate gravity waves within the free troposphere. These waves can propagate vertically, modifying global circulation. Remote sensing of the PBL using a downward-looking lidar is providing new insight into dynamic processes of this important layer and its connection with wave generation. An airborne lidar is an ideal tool to study the PBL. The lidar is installed on the NASA Electra aircraft. It consists of a frequency doubled Nd:YAG laser aligned with a 40 cm diameter telescope. As the laser beam propagates downward from the aircraft toward the surface, it is scattered by the aerosols and molecules in the atmosphere. Generally, there is a sharp gradient of aerosol scattering associated with the PBL top, with high aerosol scattering from within the PBL, and generally very low scattering from the free atmosphere above. It is this gradient in aerosol scattering that is used to visualize the structure of the PBL. A small portion of the scattered radiation is collected by the telescope, filtered, detected by a photomultiplier, and digitized at 100 nsec rate. The horizontal resolution is typically around 13 m, using a 10 Hz laser and a nominal aircraft moves, the resolution of features in the atmosphere below the aircraft is about 15 x 13 m. Results from several studies are presented and discussed.
Melfi, S. Harvey↗
Comparisons Between NO PLIF Imaging and CFD Simulations of Mixing Flowfields for High-Speed Fuel Injectors
The current work compares experimentally and computationally obtained nitric oxide (NO) planar laser-induced fluorescence (PLIF) images of the mixing flowfields for three types of high-speed fuel injectors: a strut, a ramp, and a rectangular flush-wall. These injection devices, which exhibited promising mixing performance at lower flight Mach numbers, are currently being studied as a part of the Enhanced Injection and Mixing Project (EIMP) at the NASA Langley Research Center. The EIMP aims to investigate scramjet fuel injection and mixing physics, and improve the understanding of underlying physical processes relevant to flight Mach numbers greater than eight. In the experiments, conducted in the NASA Langley Arc-Heated Scramjet Test Facility (AHSTF), the injectors are placed downstream of a Mach 6 facility nozzle, which simulates the high Mach number air flow at the entrance of a scramjet combustor. Helium is used as an inert substitute for hydrogen fuel. The PLIF is obtained by using a tunable laser to excite the NO, which is present in the AHSTF air as a direct result of arc-heating. Consequently, the absence of signal is an indication of pure helium (fuel). The PLIF images computed from the computational fluid dynamics (CFD) simulations are obtained by combining a fluorescence model for NO with the Reynolds-Averaged Simulation results carried out using the VULCAN-CFD solver to obtain a computational equivalent of the experimentally measured PLIF signal. The measured NO PLIF signal is mainly a function of NO concentration allowing for semi-quantitative comparisons between the CFD and the experiments. The PLIF signal intensity is also sensitive to pressure and temperature variations in the flow, allowing additional flow features to be identified and compared with the CFD. Good agreement between the PLIF and the CFD results provides increased confidence in the CFD simulations for investigations of injector performance.
Drozda, Tomasz, G.↗
The LISA Science Ground Segment
The mHz band of the gravitational wave (GW) spectrum contains an unprecedented abundance of galactic, extra-galactic, and cosmological sources. The Laser Interferometer Space Antenna (LISA) will survey the mHz GW band and provide unique observational constraints on the formation and evolution of compact binaries in the Milky Way, the origin and growth of massive black holes throughout cosmic history, the dynamics of dense stellar environments in galactic nuclei, the fundamental nature of gravity and black holes, and more. The richness of the LISA data comes at the price of a more complicated analysis framework than is required for currently operating GW observatories.
Tyson B. Littenberg↗
The ST7-DRS Mission: Status and Plans
ST-7 is developing enabling drag-free control technology with low noise micro-thrusters and drag-free control algorithms. The flight computer & dynamic control software are complete, and colloid micro-newton thrusters are beginning ground-based performance testing.
LISA Pathfrinder↗
Reaction dynamics of H + O2 at 1.6 eV collision energy
The hot hydrogen atom reaction, H + O2 yields OH + O, has been studied at a center of mass collision energy of 1.6 eV. H atoms were generated by 266 nm photolysis of HI in a mixture of HI and O2 at 293 K. The OH product was probed by laser induced fluorescence and the nascent OH vibrational, rotational, and fine structure distributions were determined. The OH(v=0/OH(v=1) vibrational branching ratio was measured to be 1.72 + or - 0.09. The data suggest that the H + O2 reaction at this collision energy proceeds via two competing mechanisms: reaction involving a long-lived complex and direct reaction.
Bronikowski, Michael J.↗