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At least 793 records · Page 44

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NASA NTRS2008

Initial Results from the Variable Intensity Sonic Boom Propagation Database

An extensive sonic boom propagation database with low- to normal-intensity booms (overpressures of 0.08 lbf/sq ft to 2.20 lbf/sq ft) was collected for propagation code validation, and initial results and flight research techniques are presented. Several arrays of microphones were used, including a 10 m tall tower to measure shock wave directionality and the effect of height above ground on acoustic level. A sailplane was employed to measure sonic booms above and within the atmospheric turbulent boundary layer, and the sailplane was positioned to intercept the shock waves between the supersonic airplane and the ground sensors. Sailplane and ground-level sonic boom recordings were used to generate atmospheric turbulence filter functions showing excellent agreement with ground measurements. The sonic boom prediction software PCBoom4 was employed as a preflight planning tool using preflight weather data. The measured data of shock wave directionality, arrival time, and overpressure gave excellent agreement with the PCBoom4-calculated results using the measured aircraft and atmospheric data as inputs. C-weighted acoustic levels generally decreased with increasing height above the ground. A-weighted and perceived levels usually were at a minimum for a height where the elevated microphone pressure rise time history was the straightest, which is a result of incident and ground-reflected shock waves interacting.

Haering, Edward A., Jr.↗

NASA NTRS2016

Outer Radiation Belt Dropout Dynamics Following the Arrival of Two Interplanetary Coronal Mass Ejections

Magnetopause shadowing and wave-particle interactions are recognized as the two primary mechanisms for losses of electrons from the outer radiation belt. We investigate these mechanisms, sing satellite observations both in interplanetary space and within the magnetosphere and particle drift modeling. Two interplanetary shocks sheaths impinged upon the magnetopause causing a relativistic electron flux dropout. The magnetic cloud (C) and interplanetary structure sunward of the MC had primarily northward magnetic field, perhaps leading to a concomitant lack of substorm activity and a 10 day long quiescent period. The arrival of two shocks caused an unusual electron flux dropout. Test-particle simulations have shown 2 to 5 MeV energy, equatorially mirroring electrons with initial values of L 5.5can be lost to the magnetosheath via magnetopause shadowing alone. For electron losses at lower L-shells, coherent chorus wave-driven pitch angle scattering and ULF wave-driven radial transport have been shownto be viable mechanisms.

Alves, L. R.↗

NASA NTRS1978

Radiative shock dynamics. II - Hydrogen continua

The interaction between radiation and a shock wave propagating through a stellar atmosphere is investigated. Departures from local thermodynamic equilibrium (LTE) are permitted in the first two levels of a 10-level hydrogen atom; levels 3-10 are in LTE. A piston moving at constant velocity into the bottom of the atmosphere drives a shock wave. This shock produces precursor radiation that diffuses through the gas well ahead of the shock and causes a mild luminosity flash in the emergent Balmer and free-free radiation when it reaches the surface. The precursor wave deposits a large amount of radiative energy in the outer layers of the atmosphere, initiating a radiation-induced pressure wave. The process of energy transfer from the radiation field to the compression wave is similar to the Eddington valve mechanism which drives stellar pulsations. Material is accelerated outward by the radiation-induced wave; eventually it free-falls inward, hits the quasistationary atmosphere, and forms an accretion shock. The piston driven shock is weakened by radiative energy losses. When it reaches the surface, the shock is invisible in the continuum radiation.

Klein, R. I.↗

NASA NTRS1994

Calibration of Axisymmetric and Quasi-1D Solvers for High Enthalpy Nozzles

The proposed paper will present a numerical investigation of the flow characteristics and boundary layer development in the nozzles of high enthalpy shock tunnel facilities used for hypersonic propulsion testing. The computed flow will be validated against existing experimental data. Pitot pressure data obtained at the entrance of the test cabin will be used to validate the numerical simulations. It is necessary to accurately model the facility nozzles in order to characterize the test article flow conditions. Initially the axisymmetric nozzle flow will be computed using a Navier Stokes solver for a range of reservoir conditions. The calculated solutions will be compared and calibrated against available experimental data from the DLR HEG piston-driven shock tunnel and the 16-inch shock tunnel at NASA Ames Research Center. The Reynolds number is assumed to be high enough at the throat that the boundary layer flow is assumed turbulent at this point downstream. The real gas affects will be examined. In high Mach number facilities the boundary layer is thick. Attempts will be made to correlate the boundary layer displacement thickness. The displacement thickness correlation will be used to calibrate the quasi-1D codes NENZF and LSENS in order to provide fast and efficient tools of characterizing the facility nozzles. The calibrated quasi-1D codes will be implemented to study the effects of chemistry and the flow condition variations at the test section due to small variations in the driver gas conditions.

Papadopoulos, P. E.↗

NASA NTRS1994

Ion injection and acceleration at quasi-perpendicular shocks

We present and discuss results of a new model for ion injections and acceleration at quasi-perpendicular collisionless shocks. We use the one-dimensional hybrid simulation (kinetic ions/fluid electrons) and impose an assumption on the ion motion so that diffusion across the magnetic field (normal to the shock front) is possible. These motions are otherwise suppressed by both one- and two-dimensional simulations. We find that, even in strictly perpendicular shocks, when scattering normal to the field is included, a fraction of the incident ions are accelerated to suprathermal energies. When reasonable scattering times are considered, only pickup ions are injected, whereas thermal solar wind ions are not. The acceleration of these ions is very rapid. We have found that a few of the initially low-energy pickup ions can reach many tens to a few hundred times the plasma ramming energy in less than 100 gyroperiods. Furthermore, highly field aligned energetic ions are found to exist upstream of the slightly oblique shock. The most direct applications of this study is toward the interpretation of observations of both solar wind and interstellar pickup ion distributions in the vicinity of interplanetary shocks which are most often quasi-perpendicular. This work also directly addresses a fundamental issue with regard to our current understanding of the anomalous component of cosmic rays.

Giacalone, J.↗

DOE OSTI2024

The Impact of the 8–10 March 2012 Geomagnetic Storm on Inner Zone Protons as Measured by Van Allen Probes

The Relativistic Electron Proton Telescope (REPT) instrument on the Van Allen Probes observed a double-peaked inner zone proton population throughout the 7 year lifetime of the mission. M. Hudson et al. (2023) showed that a strong SEP event accompanied by a CME-shock in early March 2012 provided the Solar Energetic Proton (SEP) source for the higher L trapped proton population, which then diffused radially inward to be observed by REPT at L = 2. The study followed trajectories of SEP protons launched isotropically from a sphere at 7 Re for 2.5 hr in fields calculated by the LFM-RCM global MHD model, which includes electric fields needed to model the transport and trapping of the protons by the shock, and then a radial diffusion simulation was run for 2 years using the result from the test-particle simulation as the initial condition. The simulation result was compared with REPT measurement in November 2013 and showed reasonable agreement. However, the simulation overestimated the Phase Space Density by a factor of four due to lack of field line curvature scattering during the storm in the model. In this study, a test-particle simulation is performed for 2 days following the injection and trapping of protons in March 2012 using TS05 fields to simulate the field line curvature scattering of the trapped SEP due to the buildup of the ring current during the geomagnetic storm. The resulting sample distribution was then weighted using the flux at the end of the two-hour MHD-test particle simulation. A radial diffusion simulation is then run using the initial profile that included the loss effect, with improved comparison with REPT measurements after 2 years.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1972

Phenomena after meteoroid penetration of a bumper plate

The results are presented of a study to obtain a computer program for the penetration of a thin plate of aluminum by a sphere of rock. The study was divided into two projects. One project covers the initial impact, the crushing of the sphere of rock, the break up of the aluminum sheet, and the conversion of the sufficiently shock-compressed regions of rock and aluminum into a plasma. The other project considers the ejection of a cone of plasma with entrained particles from the impact zone, its expansion as it traverses a region of free space, and its impact on a stack of paper sheets. The ablation of fragments in penetrating the stack of paper sheets is also considered.

Todd, F. C.↗

NASA NTRS1981

Fluid mechanics mechanisms in the stall process of airfoils for helicopters

Phenomena that control the flow during the stall portion of a dynamic stall cycle are analyzed, and their effect on blade motion is outlined. Four mechanisms by which dynamic stall may be initiated are identified: (1) bursting of the separation bubble, (2) flow reversal in the turbulent boundary layer on the airfoil upper surface, (3) shock wave-boundary layer interaction behind the airfoil crest, and (4) acoustic wave propagation below the airfoil. The fluid mechanics that contribute to the identified flow phenomena are summarized, and the usefulness of a model that incorporates the required fluid mechanics mechanisms is discussed.

Young, W. H., Jr.↗

NASA NTRS1984

Coronal Transients and Their Interplanetary Effects

The role of coronal mass ejections in the context of solar-terrestrial physics is examined. Some of the necessary background material on flares and geomagnetic storms, on interplanetary shock waves, and on coronal mass ejections is described. One of the modern tools available for approaching these questions - theoretical models for the initiation and propagation of transient phenomenon in the solar corona is described. All of this material was extensively reviewed in the recent literature, and the coverage of it is both selective and somewhat abbreviated. The second of the tools - a new generation of coronagraph observation of mass ejections and complementary set of solar and interplanetary observations suitable for correlative studies, is described. Important problems to be solved in answering these questions and some suggested strategies for approaching these problems will be discussed.

Source record↗

NASA NTRS1988

Investigation of viscous/inviscid interaction in transonic flow over airfoils with suction

The viscous/inviscid interaction over transonic airfoils with and without suction is studied. The streamline angle at the edge of the boundary layer is used to couple the viscous and inviscid flows. The potential flow equations are solved for the inviscid flow field. In the shock region, the Euler equations are solved using the method of integral relations. For this, the potential flow solution is used as the initial and boundary conditions. An integral method is used to solve the laminar boundary-layer equations. Since both methods are integral methods, a continuous interaction is allowed between the outer inviscid flow region and the inner viscous flow region. To avoid the Goldstein singularity near the separation point the laminar boundary-layer equations are derived in an inverse form to obtain solution for the flows with small separations. The displacement thickness distribution is specified instead of the usual pressure distribution to solve the boundry-layer equations. The Euler equations are solved for the inviscid flow using the finite volume technique and the coupling is achieved by a surface transpiration model. A method is developed to apply a minimum amount of suction that is required to have an attached flow on the airfoil. The turbulent boundary layer equations are derived using the bi-logarithmic wall law for mass transfer. The results are found to be in good agreement with available experimental data and with the results of other computational methods.

Vemuru, C. S.↗

NASA NTRS1988

The gasdynamics of compact relativistic jets

The gasdynamics of compact relativistic jets is explored by analyzing a specific idealized flow problem using the method of characteristics. The basic flow pattern of the gas and pressure waves within a jet experiencing a drop in external pressure is calculated, with analytic expressions given for many of the important parameters. Scaling laws which relate the intrinsic properties of the jet to the pressure of the surrounding medium are obtained and discussed. The physical properties of the jet depend critically on the value and abruptness of the decrease in external pressure, as well as on the initial Lorentz factor of the flow. A variety of the flow patterns can result, including jets of oscillating cross section, jets with standing shocks, and broad, nearly hollow beams which can break up into multiple jets. These results are discussed in relation to the observed characteristics of superluminal radio sources in general and the superluminal quasar 4C 39.25 in particular.

Daly, Ruth A.↗

NASA NTRS1990

Instability of a supersonic shock-free elliptic jet

A comparison of the measured and the computed spatial stability properties of an aspect ratio 2, supersonic, shock free, elliptic jet is presented. The shock free nature of the elliptic jet furnishes a perfect test of the validity of modeling the large scale coherent structures in the initial mixing region of noncircular supersonic jets with the linear hydrodynamic stability theory. Aerodynamic and acoustic data are measured to compute the mean velocity profiles and to provide a description of the spatial composition of pressure waves in the elliptic jet. The measured mean velocity profiles are employed to provide a qualitative model for the cross sectional geometry and the smooth velocity profiles utilized in the stability analysis. It is shown that the measured frequency associated with peak amplitude noise radiation agrees with that frequency predicted to dominate the large scale structure near the end of the potential core.

Baty, Roy S.↗

NASA NTRS1992

Unsteady, one-dimensional gas dynamics computations using a TVD type sequential solver

The efficacy of high resolution convection schemes to resolve sharp gradient in unsteady, 1D flows is examined using the TVD concept based on a sequential solution algorithm. Two unsteady flow problems are considered which include the problem involving the interaction of the various waves in a shock tube with closed reflecting ends and the problem involving the unsteady gas dynamics in a tube with closed ends subject to an initial pressure perturbation. It is concluded that high accuracy convection schemes in a sequential solution framework are capable of resolving discontinuities in unsteady flows involving complex gas dynamics. However, a sufficient amount of dissipation is required to suppress oscillations near discontinuities in the sequential approach, which leads to smearing of the solution profiles.

Thakur, Siddharth↗

NASA NTRS1994

A study of low emissions gas turbine combustions

Analytical studies have been conducted to determine the best methods of reducing NO(x) emissions from proposed civilian supersonic transports. Modifications to the gas turbine engine combustors and the use of additives were both explored. It was found that combustors which operated very fuel rich or lean appear to be able to meet future emissions standards. Ammonia additives were also effective in removing NO(x), but residual ammonia remained a problem. Studies of a novel combustor which reduces emissions and improves performance were initiated. In a related topic, a study was begun on the feasibility of using supersonic aircraft to obtain atmospheric samples. The effects of shock heating and compression on sample integrity were modeled. Certain chemical species, including NO2, HNO3, and ClONO2 were found to undergo changes to their composition after they passed through shock waves at Mach 2. The use of detonation waves to enhance mixing and combustion in supersonic airflows was also investigated. This research is important to the use of airbreathing propulsion to obtain orbital speeds and access to space. Both steady and pulsed detonation waves were shown to improve engine performance.

Adelman, Henry G.↗

NASA NTRS2000

Active Control by Conservation of Energy Concept

Three unrelated experiments are discussed; each was extremely sensitive to initial conditions. The initial conditions are the beginnings of the origins of the information that nonlinearity displays. Initial conditions make the phenomenon unstable and unpredictable. With the knowledge of the initial conditions, active control requires far less power than that present in the system response. The first experiment is on the control of shocks from an axisymmetric supersonic jet; the second, control of a nonlinear panel response forced by turbulent boundary layer and sound; the third, control of subharmonic and harmonics of a panel forced by sound. In all three experiments, control is achieved by redistribution of periodic energy response such that the energy is nearly preserved from a previous uncontrolled state. This type of active control improves the performance of the system being controlled.

Maestrello, Lucio↗

NASA NTRS2007

Screening of Potential Landing Gear Noise Control Devices at Virginia Tech For QTD II Flight Test

In support of the QTD II (Quiet Technology Demonstrator) program, aeroacoustic measurements of a 26%-scale, Boeing 777 main landing gear model were conducted in the Virginia Tech Stability Tunnel. The objective of these measurements was to perform risk mitigation studies on noise control devices for a flight test performed at Glasgow, Montana in 2005. The noise control devices were designed to target the primary main gear noise sources as observed in several previous tests. To accomplish this task, devices to reduce noise were built using stereo lithography for landing gear components such as the brakes, the forward cable harness, the shock strut, the door/strut gap and the lower truck. The most promising device was down selected from test results. In subsequent stages, the initial design of the selected lower truck fairing was improved to account for all the implementation constraints encountered in the full-scale airplane. The redesigned truck fairing was then retested to assess the impact of the modifications on the noise reduction potential. From extensive acoustic measurements obtained using a 63-element microphone phased array, acoustic source maps and integrated spectra were generated in order to estimate the noise reduction achievable with each device.

Ravetta, Patricio A.↗

NASA NTRS1960

Heat Diffusion in Gases, Including Effects of Chemical Reaction

The diffusion of heat through gases is treated where the coefficients of thermal conductivity and diffusivity are functions of temperature. The diffusivity is taken proportional to the integral of thermal conductivity, where the gas is ideal, and is considered constant over the temperature interval in which a chemical reaction occurs. The heat diffusion equation is then solved numerically for a semi-infinite gas medium with constant initial and boundary conditions. These solutions are in a dimensionless form applicable to gases in general, and they are used, along with measured shock velocity and heat flux through a shock reflecting surface, to evaluate the integral of thermal conductivity for air up to 5000 degrees Kelvin. This integral has the properties of a heat flux potential and replaces temperature as the dependent variable for problems of heat diffusion in media with variable coefficients. Examples are given in which the heat flux at the stagnation region of blunt hypersonic bodies is expressed in terms of this potential.

Hansen, C. Frederick↗

NASA NTRSDate not supplied

Voyager 1 and 2 Preliminary Observations Within Interplanetary Space of Upstream Suprathermal < 6 KeV Electrons Evidently Connected to Jupiter’s Bow Shock

We present for the first time the Voyager 1 and 2 plasma instrument observations within the interplanetary space of upstream suprathermal E < 6 keV electrons during times when close < 100 RJ from Jupiter’s bow shock. These measurements are a biproduct of our recovery of the Voyager Jupiter flyby measurements of the plasma electrons made by the Plasma Science Experiment (PLS) (Bridge et al., 1977). The initial ion and electron plasma observations were first reported by Bridge et al. (1979a, b). The periods were chosen to follow those reported by Zwickl et al. (1981) using energetic particle data with E ≥ 30 keV from the Low Energy Charged Particle (LECP) instrument (Krimigis et al., 1977). For this study we also use Voyager magnetic field data (Ness et al., 1979a, b) which is critical for this study. Basically, whenever the interplanetary magnetic field is nearly radially aligned relative to the spacecraft sun line, connection to the Jovian bow shock is believed to occur and one would expect those times when the keV suprathermal electron would be observed, but we also see them when the field is not radial but close to Jupiter’s bow shock. Whenever the magnetic field is radial the plasma instrument’s D cup or side sensor, which makes the electron observations (10 eV ≤ E ≤ 6 keV), is viewing ∼ 90 degree pitch angle electrons but evidently its wide field-of-view (FOV) allows one to see the keV electrons assumed to be field aligned. So, we will be looking into FOV alignment issues relative to the local magnetic field vector and any evidence for pitch angle scattering by plasma waves (see Scarf et al., 1981) that might broaden their width in pitch angle and allow their detection.

E C Sittler, Jr↗