Perturbations of the interplanetary magnetic field by the lunar wake.
Interplanetary magnetic field perturbations by lunar wake using plasma flow model
Behannon, K. W.↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Investigation of the stability of the tip vortex generated by hovering propellers and rotors.
The objective of this experimental and theoretical investigation was to determine what factors and mechanisms are involved in vortex interaction and instability and how these phenomena manifest themselves. To answer these questions, the schlieren method of flow visualization was used to observe the wakes generated by two- and four-bladed model propellers and rotors. A concurrent free-wake analysis was conducted for comparative purposes. Schlieren pictures showing wake asymmetry, interaction, and instability are presented. Various factors and mechanisms believed to be responsible for these are discussed along with the effects produced by the number of blades, collective pitch, and tip speed. Free-wake calculations that qualitatively confirm those factors responsible for wake asymmetry and interaction are also presented.
Tangler, J. L.↗
Investigating complex aerodynamic flows with a laser velocimeter
The paper discusses the application of the laser velocimeter in the study of two highly complex aerodynamic flows. In the first experiment, the laser velocimeter has been used with frequency tracking electronics to survey the multiple vortex wake structure behind a model of a large jet transport. The second application is to the study of the induced instantaneous inflow velocities near the blades of a model helicopter rotor; counter type processing was used in these measurements. In each experiment, the data output channels of these processors were handled in an on-line fashion, including both velocity computations and the plotting of fully reduced data.
Orloff, K. L.↗
Investigating complex aerodynamic flows with a laser velocimeter
The application of the laser velocimeter in the study of two highly complex aerodynamic flows is discussed. In the first experiment, the laser velocimeter was used with frequency tracking electronics to survey the multiple vortex wake structure behind a model of a large jet transport. The second application is to the study of the induced instantaneous inflow velocities near the blades of a model helicopter rotor; counter-type processing was used in these measurements. In each experiment, the data output channels of these processors were handled in an on-line fashion, including both velocity computations and the plotting of fully reduced data.
Orloff, K. L.↗
Free Wake Techniques for Rotor Aerodynamic Analysis. Volume 3: Vortex Filament Models
Results obtained using a vortex filament model, as opposed to sheets are discussed, against using various modeling techniques and including the computer codings.
Brower, M.↗
1985 Annual Conference on Nuclear and Space Radiation Effects, 22nd, Monterey, CA, July 22-24, 1985, Proceedings
Basic mechanisms of radiation effects in structures and materials are discussed, taking into account the time dependence of interface state production, process dependent build-up of interface states in irradiated N-channel MOSFETs, bias annealing of radiation and bias induced positive charges in n- and p-type MOS capacitors, hole removal in thin-gate MOSFETs by tunneling, and activation energies of oxide charge recovery in SOS or SOI structures after an ionizing pulse. Other topics investigated are related to radiation effects in devices, radiation effects in integrated circuits, spacecraft charging and space radiation effects, single-event phenomena, hardness assurance and radiation sources, SGEMP/IEMP phenomena, EMP phenomena, and dosimetry and energy-dependent effects. Attention is given to a model of the plasma wake generated by a large object, gate charge collection and induced drain current in GaAs FETs, simulation of charge collection in a multilayer device, and time dependent dose enhancement effects on integrated circuit transient response mechanisms.
Jones, C. W.↗
Numerical methods in laminar and turbulent flow; Proceedings of the 7th International Conference, Stanford Univ., CA, July 15-19, 1991. Vol. 7, pts. 1 & 2
Consideration is given to the impulse response of a laminar boundary layer and receptivity; numerical transition to turbulence in plane Poiseuille flow; large eddy simulation of turbulent wake flow; a viscous model and loss calculation of a multisplitter cascade; vortex initiation during dynamic stall of an airfoil; a numerical analysis of isothermal flow in a combustion chamber; and compressible flow calculations with a two-equation turbulence model and unstructured grids. Attention is also given to a 2D calculation of a buoyant flow around a burning sphere, a fast multigrid method for 3D turbulent incompressible flows, a streaming flow induced by an oscillating cascade of circular cylinders, an algebraic multigrid scheme for solving the Navier-Stokes equations on unstructured meshes; and nonlinear coupled multigrid solutions to thermal problems employing different nodal grid arrangements and convective transport approximations.
Taylor, C.↗
Final Report for The Creation of a Physics-based Ground-effect Model, Phase 2 - Inclusion of the Effects of Wind, Stratification, and Shear into the New Ground Effect Model
The reduction of the separation of the leading and following aircrafts is desirable to enhance the airport capacity provided that there is a physics-based operational model applicable to all regions of the flight domain (out of ground effect, OGE; near ground effect, NGE; and in ground effect, IGE) and that the quality of the quantitative input from the measurements of the prevailing atmospheric conditions and the quality of the total airport operations regarding the safety and the sound interpretation of the prevailing conditions match the quality of the analysis and numerical simulations. In the absence of an analytical solution, the physics of the flow is best expressed by a mathematical model based on numerical simulations, field and laboratory experiments, and heuristic reasoning. This report deals with the creation of a sound physics-based real-time IGE model of the aircraft wake vortices subjected to crosswind, stratification and shear.
Sarpkaya, Turgut↗
Direct Solar Wind Proton Access into Permanently Shadowed Lunar Polar Craters
Recent analyses of Lunar Prospector neutron spectrometer (LPNS) data have suggested that high abundances of hydrogen exist within cold traps at the lunar poles, and it has often been assumed that hydrogen-bearing volatiles sequestered in permanent shadow are topographically shielded from sputtering by solar wind protons. However, recent simulation results are presented showing that solar wind protons clearly access the floor of an idealized, shadowed lunar crater through a combination of thermal and ambipolar processes, in effect creating a plasma "miniwake". These simulations are the first to model the mini-wake environment in two spatial dimensions with a self-consistent lunar surface-plasma interaction. Progress is reported on constraining the nonzero particle fluxes and energies incident on kilometer-scale shadowed topography, such as a small crater embedded within a larger one. The importance of direct solar wind proton bombardment is discussed within the context of understanding the stability and inventory of hydrogen-bearing volatiles in shadow at the lunar poles. The support of the National Lunar Science institute, the DREAM institute, LPROPS, and the NASA Postdoctoral Program at NASA Goddard Space Flight Center administered by ORAU are gratefully acknowledged.
Zimmerman, M. I.↗
Wakes from arrays of buildings
Experiments were carried out in a small wind tunnel in which atmospheric flow around buildings was simulated. Arrays of one, two, three, and four model buildings were tested, and wake profiles of velocity and turbulence were measured. The data indicate the effect of the buildings on the wind environment encountered by aircraft during landing or takeoff operations. It was possible to use the results to locate the boundaries of the air regions affected by the obstacles and to recommend preferred arrangements of buildings to maximize light safety.
Logan, E., Jr.↗
Wakes from arrays of buildings
Experiments were carried out in a small wind tunnel in which atmospheric flow around buildings was simulated. Arrays of one, two, three, and four model buildings were tested, and wake profiles of velocity and turbulence were measured. The data indicate the effect of the buildings on the wind environment encountered by aircraft during landing or takeoff operations. It was possible to use the results to locate the boundaries of the air regions affected by the obstacles and to recommend preferred arrangement of buildings to maximize light safety. Previously announced in STAR as N83-14430
Logan, E., Jr.↗
Blade-Wake Interaction Noise for Small Hovering Rotors, Part I: Characterization Study
This work illustrates the use of artificial neural network modeling to study and characterize broadband blade-wake interaction noise from hovering small unmanned aerial systems rotors subject to varying airfoil geometries, rotor geometries, and operating conditions. Design of experiments was used to create input feature spaces, and a high-fidelity strategy was implemented at the discrete data points defined by the input feature spaces to design airfoils and rotor blades, predict the unsteady rotor aerodynamics and aeroacoustics, and isolate the blade-wake interaction noise from the acoustic broadband noise. A metric for the blade-wake interaction noise was developed, and the ANOPP2 Artificial Neural Network Tool was used to identify an optimal prediction model for the nonlinear relationship between the input features and the metric for blade-wake interaction noise. This optimal artificial neural network was then validated over training/test data and exhibited prediction accuracy over 91% for data previously unseen by the model. A sensitivity analysis was conducted, which showed that input features that directly modify the thrust coefficient had a dominant effect over blade-wake interaction noise. The optimal prediction model along with aerodynamic simulations were used to further study the effect of varying input features on blade-wake interaction noise, and three types of blade-wake interaction noise were identified
Christopher S. Thurman↗
Hover performance analysis of advanced rotor blades
This is an effort aimed at validating recent hover prediction methods. The experimental basis for this validation work is an extensive set of loads, wake and performance data, which were obtained from a pressure instrumented model UH-60 rotor tested at the Sikorsky hover test facility and at Duits-Nederlandse Windtunnel (DNW). This model was equipped with replaceable tips - including a tapered and a BERP-type tip - which permitted studies of the effects of rotor geometry. The central prediction method studied is a free-wake, vortex embedded, full-potential CFD method - called HELIX-I. It is found that the HELIX-I code produces very good comparisons with the data including wake, surface pressure and performance. Comparisons with the measured radial load distributions have permitted an improved understanding of the wake resolution modelling requirements of CFD methods. Since HELIX-I is a combined Eulerian/Lagrangian method, limited comparisons are also made with a Lagrangian boundary element code (called EHPIC) and an Eulerian Navier-Stokes code (called TURNS). In most cases all methods produce good comparisons with the data. It is found that the HELIX-I code provides a good compromise between the speed of boundary integral methods and the comprehensive nature of Navier-Stokes methods.
Tung, C.↗
Rotor blade-vortex interaction impulsive noise source identification and correlation with rotor wake predictions
An acoustic source localization scheme applicable to noncompact moving sources is developed and applied to the blade-vortex interaction (BVI) noise data of a 40-percent scale BO-105 model rotor. A generalized rotor wake code is employed to predict possible VBI locations on the rotor disk and is found quite useful in interpreting the acoustic localization results. The highly varying directivity patterns of different BVI impulses generated at the same test condition are explained by both the localization results and predicted tip vortex trajectories. The effects of rotor tip-path-plane angle and advance ratio on the BVI source positions is studied. Decreasing tip-path-plane angle (at constant advance ratio) moves the general interaction region upwind on the rotor disk, significantly changing the interaction geometry. Increasing advance ratio (at constant tip-path-plane angle) shifts the general source region downwind on the rotor disk with the increased convection of the vortices until about 60 deg azimuth, where the BVI sources appear to become acoustically less effective. The region of strongest BVI sources lies between 60 and 70 deg azimuth and 80 and 90 percent radius for the moderate range of advance ratios studied.
Splettstoesser, W. R.↗
Theoretical and experimental study of the drag of multielement airfoils
The viscous/potential flow past single-element and multielement airfoils is studied theoretically and experimentally. A computerized analysis, based on iteratively coupled potential-flow and boundary-layer analysis, is used to predict the flow field of the airfoil. The method yields detailed characteristics of conventional laminar and turbulent boundary layers, turbulent wakes, and confluent boundary layers. The viscous flows are analyzed with a method that uses finite-difference solutions of the boundary-layer equations. Reynolds stress in the boundary layers and wakes is simulated with eddy viscosity models for the various flow zones. The viscous calculations are carried into the wake of the airfoil where the drag is found from the defect in the wake momentum.
Olson, L. E.↗
FLEET and PLIF Velocimetry Within A Mach 10 Hypersonic Air Flow
Femtosecond laser electronic excitation tagging (FLEET) and planar laser-induced fluorescence (PLIF) velocity measurements utilizing molecular tagging velocity (MTV) methods from three recent test campaigns conducted at the 31-in Mach 10 Air Tunnel at the NASA Langley Research Center are highlighted within. The FLEET measurements reported here include the first direct measurement of freestream velocity at this hypersonic wind tunnel facility. Measurement challenges were exasperated by the low gas density of the Mach 10 air freestream (~0.4% of standard temperature and pressure conditions) and even lower gas densities within the hypersonic wake of a 70-degree sphere-cone model. In addition, the hypersonic freestream and very low speed velocities in the wake also tested the measurement dynamic range. To complement the FLEET measurements in the wake of the sphere-cone model, PLIF velocimetry using seeded nitric oxide was also performed. While NO-PLIF velocimetry has been performed at this facility several times by previous researchers, the use of a 1D diffractive optical element for NO-PLIF velocimetry is reported here for the first time. The 1D DOE enabled the generation of up to 75 laser lines simultaneously and improved the spatial extent of the measurement three times compared to previous work. This enabled a wide velocity measurement plane of approximately 130 mm x 130 mm. The velocimetry methods demonstrated here are expected to improve wind tunnel characterization, provide critical data to validate CFD codes, and improve the design of flight vehicles for planetary entry.
FLEET↗
FLEET and PLIF Velocimetry Within A Mach 10 Hypersonic Air Flow
Femtosecond laser electronic excitation tagging (FLEET) and planar laser-induced fluorescence (PLIF) velocity measurements utilizing molecular tagging velocity (MTV) methods from three recent test campaigns conducted at the 31-in Mach 10 Air Tunnel at the NASA Langley Research Center are highlighted within. The FLEET measurements reported here include the first direct measurement of freestream velocity at this hypersonic wind tunnel facility. Measurement challenges were exasperated by the low gas density of the Mach 10 air freestream (~0.4% of standard temperature and pressure conditions) and even lower gas densities within the hypersonic wake of a 70-degree sphere-cone model. In addition, the hypersonic freestream and very low speed velocities in the wake also tested the measurement dynamic range. To complement the FLEET measurements in the wake of the sphere-cone model, PLIF velocimetry using seeded nitric oxide was also performed. While NO-PLIF velocimetry has been performed at this facility several times by previous researchers, the use of a 1D diffractive optical element for NO-PLIF velocimetry is reported here for the first time. The 1D DOE enabled the generation of up to 75 laser lines simultaneously and improved the spatial extent of the measurement three times compared to previous work. This enabled a wide velocity measurement plane of approximately 130 mm x 130 mm. The velocimetry methods demonstrated here are expected to improve wind tunnel characterization, provide critical data to validate CFD codes, and improve the design of flight vehicles for planetary entry.
FLEET↗
Prediction of fatigue-crack growth under variableamplitude and spectrum loading using a closure model
An existing analytical crack closure model was used to study crack growth under various load histories. The model was based on a concept like the Dugdale model, but modified to leave plastically deformed material in the wake of the advancing crack tip. The model was used to correlate crack growth rates under constant amplitude loading, and to predict crack growth under variable amplitude and aircraft spectrum loading on 2219-T851 aluminum alloy sheet material. The predicted crack growth lives agreed well with experimental data. For 80 crack growth tests subjected to various load histories, the ratio of predicted-to-experimental lives (N(P)/n(T)) ranged from 0.5 to 1.8. The mean value of N(P)/N(T) was 0.97 and the standard deviation was 0.27.
Newman, J. C., Jr.↗