Showing papers by "Langley Research Center published in 1999"

Overview of the SABER experiment and preliminary calibration results

Abstract: The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment is one of four experiments that will fly on the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission to be launched in May 2000. The primary science goal of SABER is to achieve major advances in understanding the structure, energetics, chemistry, and dynamics, in the atmospheric region extending from 60 km to 180 km altitude. This will be accomplished using the space flight proven experiment approach of spectral broadband limb emission radiometry. SABER will scan the horizon in 10 selected bands ranging from 1.27 micrometer to 17 micrometer wavelength. The observed vertical horizon emission profiles will be processed on the ground to provide vertical profiles with 2 km altitude resolution, of temperature, O3, H2O, and CO2; volume emission rates due to O2(1(Delta) ), OH((upsilon) equals 3,4,5), OH((upsilon) equals 7,8,9), and NO; key atmospheric cooling rates, solar heating rates, chemical heating rates, airglow losses; geostrophic winds, atomic oxygen and atomic hydrogen. Measurements will be made both night and day over the latitude range from the southern to northern polar regions. The SABER instrument uses an on-axis Cassegrain design with a clam shell reimager. Preliminary test and calibration results show excellent radiometric performance.

Oscillatory Control of Separation at High Reynolds Numbers

Abstract: An experiment conducted in a pressurized, cryogenic wind tunnel demonstrates that unsteady flow control using oscillatory blowing (with essentially zero mass flux) can effectively delay flow separation and reattach separated flow on an airfoil at chord Reynolds numbers as high as 38 × 10 6 . Oscillatory blowing at frequencies that generate one to three vortices over the controlled region at all times are effective over the entire Reynolds number range, in accordance with previous low-Reynolds-number tests. Stall is delayed and poststall characteristics are improved when oscillatory blowing is applied from the leading-edge region of the airfoil, whereas flap effectiveness is increased when control is applied at the flap shoulder. Similar gains in airfoil performance require steady blowing with a momentum coefficient that is two orders of magnitude greater. A detailed experimental and theoretical investigation was undertaken to characterize the oscillatory blowing disturbance, in the absence of external flow, and to estimate the oscillatory blowing momentum coefficient used in the cryogenic wind tunnel experiment. Possible approaches toward closed-loop active separation control are also presented

The 1997 spectroscopic GEISA databank

Abstract: The current version GEISA-97 of the computer-accessible database system GEISA (Gestion et Etude des Informations Spectroscopiques Atmospheriques: Management and Study of Atmospheric Spectroscopic Information) is described. This catalogue contains 1,346,266 entries. These are spectroscopic parameters required to describe adequately the individual spectral lines belonging to 42 molecules (96 isotopic species) and located between 0 and 22,656 cm-1. The featured molecules are of interest in studies of the terrestrial as well as the other planetary atmospheres, especially those of the Giant Planets. GEISA-97 contains also a catalog of absorption cross-sections of molecules such as chlorofluorocarbons which exhibit unresolvable spectra. The modifications and improvements made to the earlier edition (GEISA-92) and the data management software are described. GEISA-97 and the associated management software are accessible from the ARA/LMD (Laboratoire de Meteorologie Dynamique du CNRS, France) web site: http://ara01.polytechnique.fr/registration.

Optimization with variable-fidelity models applied to wing design

Abstract: This work discusses an approach, the Approximation Management Framework (AMF), for solving optimization problems that involve computationally expensive simulations. AMF aims to maximize the use of lower-fidelity, cheaper models in iterative procedures with occasional, but systematic, recourse to higher-fidelity, more expensive models for monitoring the progress of the algorithm. The method is globally convergent to a solution of the original, high-fidelity problem. Three versions of AMF, based on three nonlinear programming algorithms, are demonstrated on a 3D aerodynamic wing optimization problem and a 2D airfoil optimization problem. In both cases Euler analysis solved on meshes of various refinement provides a suite of variable-fidelity models. Preliminary results indicate threefold savings in terms of high-fidelity analyses in case of the 3D problem and twofold savings for the 2D problem.

A Climatology of Surface Radiation Budget Derived from Satellite Data

Abstract: Climatological averages of surface radiation budget parameters, namely, the shortwave and longwave surface radiative fluxes, have been derived for each month of the year on a global scale. These climatological averages were derived from an 8-yr (96 month) time series of monthly average fluxes. The monthly averages were computed using fast radiation parameterizations and satellite data from the International Satellite Cloud Climatology Project and the Earth Radiation Budget Experiment. Results are presented as time series of hemispheric and global averages and as geographical distributions and time–latitude cross sections of climatological averages. The spatial/temporal variabilities of the results were found to be clearly related to the corresponding variabilities of meteorological and other inputs to the parameterizations. Numerous comparisons of the present results were made with available surface measurements for the purpose of validation. In most cases, the differences were found to be within...

Design of Three-Dimensional Hypersonic Inlets with Rectangular-to-Elliptical Shape Transition

Abstract: A methodology has been devised for the design of three-dimensional hypersonic Inlets, This methodology makes extensive use of inviscid stream-tracing techniques to generate an inlet with smooth shape transition from a rectangular-like capture to an elliptical throat. Highly swept leading edges and a significantly notched cowl enable use of these inlets in fixed geometry configurations. The design procedure includes a three-dimensional viscous correction and uses established correlations to check for boundary-layer separation caused by shock wave interactions. Complete details of the design procedure are presented and the characteristics of a modular inlet with a design point of Mach 6.0 are examined. Comparison with a classical two-dimensional inlet optimized for maximum total pressure recovery indicates that these three-dimensional inlets demonstrate good inviscid performance even when operating well below the design point. An estimate of the on-design viscous performance corresponds with that of an efficient inlet for scramjet applications.

Real-Time Parameter Estimation in the Frequency Domain

Abstract: A method for real-time estimation of parameters in a linear dynamic state space model was developed and studied. The application is aircraft dynamic model parameter estimation from measured data in flight for indirect adaptive or reconfigurable control. Equation error in the frequency domain was used with a recursive Fourier transform for the real-time data analysis. Linear and nonlinear simulation examples and flight test data from the F-18 High Alpha Research Vehicle HARV) were used to demonstrate that the technique produces accurate model parameter estimates with appropriate error bounds. Parameter estimates converged in less than 1 cycle of the dominant dynamic mode natural frequencies, using control surface inputs measured in flight during ordinary piloted maneuvers. The real-time parameter estimation method has low computational requirements, and could be implemented aboard an aircraft in real time.

Time-Frequency Analysis of the Dispersion of Lamb Modes

Abstract: Accurate knowledge of the velocity dispersion of Lamb modes is important for ultrasonic nondestructive evaluation methods used in detecting and locating flaws in thin plates and in determining their elastic stiffness coefficients. Lamb mode dispersion is also important in the acoustic emission technique for accurately triangulating the location of emissions in thin plates. In this research, the ability to characterize Lamb mode dispersion through a time-frequency analysis (the pseudo Wigner-Ville distribution) was demonstrated. A major advantage of time-frequency methods is the ability to analyze acoustic signals containing multiple propagation modes, which overlap and superimpose in the time domain signal. By combining time-frequency analysis with a broadband acoustic excitation source, the dispersion of multiple Lamb modes over a wide frequency range can be determined from as little as a single measurement. In addition, the technique provides a direct measurement of the group velocity dispersion. The technique was first demonstrated in the analysis of a simulated waveform in an aluminum plate in which the Lamb mode dispersion was well known. Portions of the dispersion curves of the A0, A1, S0, and S2 Lamb modes were obtained from this one waveform. The technique was also applied for the analysis of experimental waveforms from a unidirectional graphite/epoxy composite plate. Measurements were made both along, and perpendicular to the fiber direction. In this case, the signals contained only the lowest order symmetric and antisymmetric modes. A least squares fit of the results from several source to detector distances was used. Theoretical dispersion curves were calculated and are shown to be in good agreement with experimental results.

Effect of Directional Array Size on the Measurement of Airframe Noise Components

Abstract: A study was conducted to examine the effects of overall size of directional (or phased) arrays on the measurement of aeroacoustic components An airframe model was mounted in the potential core of an open-jet windtunnel, with the directional arrays located outside the flow in an anechoic environment Two array systems were used; one with a solid measurement angle that encompasses 316 degrees of source directivity and a smaller one that encompasses 72 degrees The arrays, and sub-arrays of various sizes, measured noise from a calibrator source and flap edge model setups In these cases, noise was emitted from relatively small, but finite size source regions, with intense levels compared to other sources Although the larger arrays revealed much more source region detail, the measured source levels were substantially reduced due to finer resolution compared to that of the smaller arrays To better understand the measurements quantitatively, an analytical model was used to define the basic relationships between array to source region sizes and measured output level Also, the effect of noise scattering by shear layer turbulence was examined using the present data and those of previous studies Taken together, the two effects were sufficient to explain spectral level differences between arrays of different sizes An important result of this study is that total (integrated) noise source levels are retrievable and the levels are independent of the array size as long as certain experimental and processing criteria are met The criteria for both open and closed tunnels are discussed The success of special purpose diagonal-removal processing in obtaining integrated results is apparently dependent in part on source distribution Also discussed is the fact that extended sources are subject to substantial measurement error, especially for large arrays

An accurate curved boundary treatment in the lattice Boltzmann method

Abstract: The lattice Boltzmann equation (LBE) is an alternative kinetic method capable of solving hydrodynamics for various systems. Major advantages of the method are owing to the fact that the solution for the particle distribution functions is explicit, easy to implement, and natural to parallelize. Because the method often uses uniform regular Cartesian lattices in space, curved boundaries are often approximated by a series of stairs that leads to reduction in computational accuracy. In this work, a second-order accurate treatment of boundary condition in the LBE method is developed for a curved boundary. The proposed treatment of the curved boundaries is an improvement of a scheme due to Filippova and Hänel. The proposed treatment for curved boundaries is tested against several flow problems: 2-D channel flows with constant and oscillating pressure gradients for which analytic solutions are known, flow due to an impulsively started wall, lid-driven square cavity flow, and uniform flow over a column of circular cylinders. The second-order accuracy is observed with solid boundary arbitrarily placed between lattice nodes. The proposed boundary condition has well behaved stability characteristics when the relaxation time is close to 1/2, the zero limit of viscosity. The improvement can make a substantial contribution toward simulating practical fluid flow problems using the lattice Boltzmann method. Key words, kinetic method, lattice Boltzmann equation, Navier-Stokes equation, second order boundary conditions Subject classification. Fluid Mechanics

Airfoil Design on Unstructured Grids for Turbulent Flows

Abstract: An aerodynamic design algorithm for turbulent e ows using unstructured grids is described. The current approachusesadjoint (costate)variablestoobtainderivativesofthecostfunction.Thesolutionoftheadjointequations is obtained by using an implicit formulation in which the turbulence model is fully coupled with the e ow equations when solving for the costate variables. The accuracy of the derivatives is demonstrated by comparison with e nite difference gradients, and a few sample computations are shown. Recommendations on directions of further research into the Navier ‐Stokes design process are made. Nomenclature A = area of control volume a = speed of sound C ¤ = constant used in Sutherland’ s law for viscosity cb1;cb2;cv1; = constants used in Spalart ‐Allmaras cw1;cw2;cw3 turbulence model cd = drag cl = lift c1

Examination of large-scale structures in a turbulent plane mixing layer. Part 1. Proper orthogonal decomposition

Abstract: Large-scale structures in a plane turbulent mixing layer are studied through the use of the proper orthogonal decomposition (POD). Extensive experimental measurements are obtained in a turbulent plane mixing layer by means of two cross-wire rakes aligned normal to the direction of the mean shear and perpendicular to the mean flow direction. The measurements are acquired well into the asymptotic region. From the measured velocities the two-point spectral tensor is calculated as a function of separation in the cross-stream direction and spanwise and streamwise wavenumbers. The continuity equation is then used for the calculation of the non-measured components of the tensor. The POD is applied using the cross-spectral tensor as its kernel. This decomposition yields an optimal basis set in the mean square sense. The energy contained in the POD modes converges rapidly with the first mode being dominant (49% of the turbulent kinetic energy). Examination of these modes shows that the first mode contains evidence of both known flow organizations in the mixing layer, i.e. quasi-two-dimensional spanwise structures and streamwise aligned vortices. Using the shot-noise theory the dominant mode of the POD is transformed back into physical space. This structure is also indicative of the known flow organizations.

A Psuedo-Temporal Multi-Grid Relaxation Scheme for Solving the Parabolized Navier-Stokes Equations

Abstract: A multi-grid, flux-difference-split, finite-volume code, VULCAN, is presented for solving the eliptic and parabolized form of the equations governing three-dimensional, turbulent, calorically perfect and non-equilibrium chemically reacting flows. The space marching algorithms developed to improve convergence rate and or reduce computational cost are emphasized. The algorithms presented are extensions to the class of implicit pseudo-time iterative, upwind space-marching schemes. A full approximate storage, full multi-grid scheme is also described which is used to accelerate the convergence of a Gauss-Seidel relaxation method. The multi-grid algorithm is shown to significantly improve convergence on high ratio grids.

Optimization Strategies for Sensor and Actuator Placement

Abstract: This paper provides a survey of actuator and sensor placement problems from a wide range of engineering disciplines and a variety of applications. Combinatorial optimization methods are recommended as a means for identifying sets of actuators and sensors that maximize performance. Several sample applications from NASA Langley Research Center such as active structural acoustic control are covered in detail. Laboratory and flight tests of these applications indicate that actuator and sensor placement methods are effective and important. Lessons learned in solving these optimization problems can guide future research.

A Pseudo-Temporal Multi-Grid Relaxation Scheme for Solving the Parabolized Navier-Stokes Equations

Abstract: A multi-grid, flux-difference-split, finite-volume code, VULCAN, is presented for solving the elliptic and parabolized form of the equations governing three-dimensional, turbulent, calorically perfect and non-equilibrium chemically reacting flows. The space marching algorithms developed to improve convergence rate and or reduce computational cost are emphasized. The algorithms presented are extensions to the class of implicit pseudo-time iterative, upwind space-marching schemes. A full approximate storage, full multi-grid scheme is also described which is used to accelerate the convergence of a Gauss-Seidel relaxation method. The multi-grid algorithm is shown to significantly improve convergence on high aspect ratio grids.

Computational Aeroacoustic Analysis of Slat Trailing-Edge Flow

Abstract: An acoustic analysis based on the Ffowcs Williams and Hawkings equation was performed for a high-lift system. As input, the acoustic analysis used un- steady flow data obtained from a highly resolved, time-dependent, Reynolds-averaged Navier-Stokes calculation. The analysis strongly suggests that vor- tex shedding from the trailing edge of the slat results in a high-amplitude, high-frequency acoustic signal, similar to that which was observed in a correspond- ing experimental study of the high-lift system.

Surface Emissivity Maps for Use in Satellite Retrievals of Longwave Radiation

Abstract: Accurate accounting of surface emissivity is essential for the retrievals of surface temperature from remote sensing measurements, and for the computations of longwave (LW) radiation budget of the Earth''s surface. Past studies of the above topics assumed that emissivity for all surface types, and across the entire LW spectrum is equal to unity. There is strong evidence, however, that emissivity of many surface materials is significantly lower than unity, and varies considerably across the LW spectrum. We have developed global maps of surface emissivity for the broadband LW region, the thermal infrared window region (8-12 micron), and 12 narrow LW spectral bands. The 17 surface types defined by the International Geosphere Biosphere Programme (IGBP) were adopted as such, and an additional (18th) surface type was introduced to represent tundra-like surfaces. Laboratory measurements of spectral reflectances of 10 different surface materials were converted to corresponding emissivities. The 10 surface materials were then associated with 18 surface types. Emissivities for the 18 surface types were first computed for each of the 12 narrow spectral bands. Emissivities for the broadband and the window region were then constituted from the spectral bnad values by weighting them with Planck function energy distribution.

Overview of Sensitivity Analysis and Shape Optimization for Complex Aerodynamic Configurations

Abstract: This paper presents a brief overview of some of the more recent advances in steady aerodynamic shape-design sensitivity analysis and optimization, based on advanced computational fluid dynamics. The focus here is on those methods particularly well- suited to the study of geometrically complex configurations and their potentially complex associated flow physics. When nonlinear state equations are considered in the optimization process, difficulties are found in the application of sensitivity analysis. Some techniques for circumventing such difficulties are currently being explored and are included here. Attention is directed to methods that utilize automatic differentiation to obtain aerodynamic sensitivity derivatives for both complex configurations and complex flow physics. Various examples of shape-design sensitivity analysis for unstructured-grid computational fluid dynamics algorithms are demonstrated for different formulations of the sensitivity equations. Finally, the use of advanced, unstructured-grid computational fluid dynamics in multidisciplinary analyses and multidisciplinary sensitivity analyses within future optimization processes is recommended and encouraged.

Radiative forcing by contrails

Abstract: . A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm-2 daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover. Key words. Atmospheric composition and structure (aerosols and particles) · Meteorology and atmospheric dynamics (climatology · radiative processes)

Computational Aeroacoustic Analysis of Slat Trailing-Edge Flow

Abstract: An acoustic analysis based on the Ffowcs Williams and Hawkings equation was performed for a high-lift system. As input, the acoustic analysis used unsteady flow data obtained from a highly resolved, time-dependent, Reynolds-averaged Navier-Stokes caclulation. The analysis strongly suggests that vortex shedding from the trailing edge of the slat results in a high-amplitude, high-frequency acoustic signal, similar to that which was observed in a corresponding experimental study of the high-lift system.

The 1997 fires in Kalimantan and Sumatra, Indonesia : Gaseous and particulate emissions

Abstract: Extensive and widespread vegetation and peat fires swept throughout Kalimantan and Sumatra, Indonesia, from August 1997 through March 1998. The fires resulted from routine burning for land clearing and land-use change. However, the severe drought conditions resulting from El Nino caused small land-clearing fires to become large uncontrolled wildfires. Analysis of SPOT images indicate that a total of 45,600 km² burned between August and December 1997. In this paper, the gaseous and particulate emissions resulting from the 1997 fires are estimated. On a daily basis, the calculated emissions of CO2, CO, CH4, NOx, and particulates from the Kalimantan and Sumatra fires of 1997 significantly exceeded the emissions from the Kuwait oil fires of 1991.

On the origin of tropospheric ozone and NOx over the tropical South Pacific

Abstract: The budgets of ozone and nitrogen oxides (NOx = NO + NO2) ill the tropical South Pacific troposphere are analyzed by photochemical point modeling of aircraft observations at 0-12 km altitude from the Pacific Exploratory Mission-Tropics A campaign flown in September- October 1996. The model reproduces the observed NO2/NO concentration ratio to within 30% and has similar success in simulating observed concentrations of peroxides (H202, CH3OOH), lending confidence in its use to investigate ozone chemistry. It is found that chemical production of ozone balances only half of chemical loss in the tropospheric column over the tropical South Pacific. The net loss is 1.8 x 1011 molecules cm -2 S '1. The missing source of ozone is matched by west- erly transport of continental pollution into the region. Independent analysis of the regional ozone budget with a global three-dimensional model corroborates the results from the point model and reveals the importance of biomass burning emissions in South America and Africa for the ozone budget over the tropical South Pacific. In this model, biomass burning increases average ozone concentrations by 7-8 ppbv throughout the troposphere. The NOx responsible for ozone produc- tion within the South Pacific troposphere below 4 km can be largely explained by decomposition of peroxyacetylnitrate (PAN) transported into the region with biomass burning pollution at higher altitudes.

Global Aeroheating Wind-Tunnel Measurements Using Improved Two-Color Phosphor Thermography Method

Abstract: Detailed aeroheating information is critical to the successful design of a thermal protection system (TPS) for an aerospace vehicle. NASA Langley Research Center’ s (LaRC) phosphor thermography method is described. Development of theory is provided for a new weighted two-color relative-intensity e uorescence theory for quantitatively determining surface temperatures on hypersonic wind-tunnel models and an improved application of the one-dimensional conduction theory for use in determining global heating mappings. The phosphor methodology at LaRC is presented including descriptions of phosphor model fabrication, test facilities, and phosphor video acquisition systems. A discussion of the calibration procedures, data reduction, and data analysis is given. Estimates of the total uncertainties (with a 95% cone dence level ) associated with the phosphor technique are shown to be approximately 7 ‐10% in LaRC’ s 31-Inch Mach 10 Tunnel and 8 ‐10% in the 20-Inch Mach 6 Tunnel. A comparison with thin-e lm measurements using 5.08-cm-radius hemispheres shows the phosphor data to be within 7% of thin-e lm measurements and to agree even better with predictions via a LATCH computational e uid dynamics (CFD) solution. Good agreement between phosphor data and LAURA CFD computations on the forebody of a vertical takeoff/vertical lander cone guration at four angles of attack is also shown. In addition, a comparison is givenbetween Mach 6phosphordata andlaminarandturbulentsolutionsgeneratedusing theLAURA,GASP, and LATCH CFD codes on the X-34 cone guration. The phosphor process outlined is believed to provide the aerothermodynamic community with a valuable capability for rapidly obtaining (three to four weeks ) detailed heating information needed in TPS design. Nomenclature A = area of camera array element, m 2 a = effective aperture factor of camera optics, sr b = vehicle wing span from wing tip to wing tip, m C = heat transfer coefe cient constant, h.iw=Tw/ c = specie c heat of model substrate, J/ (kg-K) D = driver constant, iaw.Tw=iw/iTinit F = e ux of light, W/m 2 h = heat transfer coefe cient, kg/ (m 2 -s) I = radiant intensity, W/ (m 2 -sr)

Testing and Analysis of Composite Skin/Stringer Debonding Under Multi-Axial Loading

Abstract: Damage mechanisms in composite bonded skin/stringer constructions under uniaxial and biaxial (in-plane/out-of-plane) loading conditions were examined. Specimens consisted of a tapered composite flange bonded onto a composite skin. Tests were performed under monotonic loading conditions in tension, three-point bending, and combined tension/bending. For combined tension/bending testing, a unique servohydraulic load frame was used that was capable of applying both in-plane tension and out-of-plane bending loads simultaneously. Specimen edges were examined on the microscope to document the damage occurrence and to identify typical damage patterns. The observations showed that, for all three load cases, failure initiated in the flange, near the flange tip, causing the flange to almost fully debond from the skin. A two-dimensional plane-strain finite element model was developed to analyze the different test cases using a geometrically nonlinear solution. For all three loading conditions, principal stresses exceeded the transverse strength of the material in the flange area. Additionally, delaminations of various lengths were simulated in two locations where delaminations were observed. The analyses showed that unstable delamination propagation is likely to occur in one location at the loads corresponding to matrix ply crack initiation for all three load cases.

Global distribution of contrail radiative forcing

Abstract: The global distribution of radiative forcing by persistent linear contrails has been estimated for 1992 and 2050 using global contrail cover computed for aircraft fuel consumption scenarios for the two periods, a detailed prescription of the radiative properties of the Earth's surface and the cloudy atmosphere, and flux computations with an established radiative transfer model. The computed global mean radiative forcing by line-shaped contrails is ∼0.02 Wm−2 in 1992 and ∼0.1 Wm−2 in 2050. At northern mid-latitudes, the zonal mean forcing is five times larger than the global mean. Diffuse contrails and indirect effects of aircraft emissions on natural cirrus are not included in this study. Thus, the results are considered a minimum estimate of contrail effects.