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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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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Accuracy Study of the Space-Time CE/SE Method for Computational Aeroacoustics Problems Involving Shock Waves

The space-time conservation element and solution element(CE/SE) method is used to study the sound-shock interaction problem. The order of accuracy of numerical schemes is investigated. The linear model problem.govemed by the 1-D scalar convection equation, sound-shock interaction problem governed by the 1-D Euler equations, and the 1-D shock-tube problem which involves moving shock waves and contact surfaces are solved to investigate the order of accuracy of numerical schemes. It is concluded that the accuracy of the CE/SE numerical scheme with designed 2nd-order accuracy becomes 1st order when a moving shock wave exists. However, the absolute error in the CE/SE solution downstream of the shock wave is on the same order as that obtained using a fourth-order accurate essentially nonoscillatory (ENO) scheme. No special techniques are used for either high-frequency low-amplitude waves or shock waves.

Wang, Xiao Yen↗
DOE OSTI2020

Autoignition delay times measurements of linear unsaturated jet fuel compounds inside a shock tube

Autoignition delay times measurements and CO time histories were studied for 2-pentene, a hydrocarbon in aviation fuel and an important species in the development of aviation fuel surrogates. Three mechanisms from the literature were compared against the measured data, and a sensitivity analysis for CO was performed for all mechanisms. Shock tube experiments were performed between 1246 K – 1372 K and 8.8 atm – 9.3 atm at an equivalence ratio of 1, a fuel loading of 0.25% was used and was balanced in oxygen and argon. Discrepancies between the available literature mechanisms exist, the measured data herein is essential for validation of these mechanisms and the reduction of validated mechanisms for coupling into CFD.

09 BIOMASS FUELS↗
NASA NTRS1991

Exact and approximate solutions to the oblique shock equations for real-time applications

The derivation of exact solutions for determining the characteristics of an oblique shock wave in a supersonic flow is investigated. Specifically, an explicit expression for the oblique shock angle in terms of the free stream Mach number, the centerbody deflection angle, and the ratio of the specific heats, is derived. A simpler approximate solution is obtained and compared to the exact solution. The primary objectives of obtaining these solutions is to provide a fast algorithm that can run in a real time environment.

Hartley, T. T.↗
NASA NTRS1975

Acceleration of charged particles in oblique MHD shocks

The motion of high energy charged particles in ideal oblique MHD shocks has been studied extensively. The orbits of charged particles can be solved exactly from Lorentz force equation. It is found that a charged particle may cross the shock front many times before it leaves the shock and it is energized during crossings. The most energetic particles are those with initial pitch and phase near the boundary between crossing and reflected particles. The reflected particles cross the shock about twice as many times as the passing particles do. The energy gain increases for larger values of shock strength and speed. If reflection occurs, the energy gain is larger for smaller angles between the field and shock surface. The introduction of scattering results in a few more higher energy particles.

Chen, G.↗
NASA NTRS1999

Ionospheric response to the CME Passage of September 24,1998

On September 24, 1998, a solar coronal mass ejection struck the Earth's magnetosphere. The magnetosphere/ionosphere system exhibited a response in several ways one of which was an increase in ion outflow from the ionosphere, ionospheric mass ejections in response to the pressure pulse from the shock passage at the front of the magnetosphere. However, the timing of the incidence of the pressure pulse and the ionospheric response has not been examined in detail. Images from the Ultraviolet Imager show a brightening in the dayside aurora at the same time the shock is seen at Polar at about 23:45 UT on the 24th. . We examine the temporal and spatial relationship (using simple models ) of these two events to determine the correlation of the particles seen at Polar and the regions of increased energy input seen in the aurora and discuss the physical implications of the results.

Craven, Paul D↗
NASA NTRS1988

ISEE-3 observations of the earth's radio continuum through the bow shock and magnetosheath and in the magnetosphere

On October 1 1983, ISEE-3 crossed the earth's bow shock several times and entered the magnetosphere while continuously recording the nonthermal continuum (NTC) radio emission which is generated inside the magnetosphere. The effects of the solar wind, the bow shock, the magnetosheath, and the magnetopause on the propagation of the NTC are studied. On that day it is found that: (1) the relative values of the NTC low frequency cut-off in the solar wind and in the magnetosheath is due to an unusually high density overshoot in the bow shock, 7 to 11 times the solar wind density; (2) refraction at the interface between the magnetosheath and the solar wind can explain most of the decrease in the source angular size when the observer travels away from the earth; (3) plasma density irregularities in the magnetosheath cause considerable scattering of the NTC, and this effect gives a large apparent size to the NTC source when observed from inside the magnetosheath; and (4) the apparent source is also relatively large inside the magnetosphere, probably due to an approach to ray isotropy caused by oblique reflections from the magnetopause.

Steinberg, J.-L.↗
NASA NTRS1977

Numerical solution of the viscous hypersonic flow past blunted cones at angle of attack

Hypersonic viscous flow over spherically blunted cones of large half angle is computed at small angles of attack in the plane of symmetry of the flow field. Time-dependent viscous shock-layer equations in body-oriented coordinates are used to describe the flow field. The shock wave is treated as a discontinuity, across which the Rankine-Hugoniot relations are used to compute the flow conditions behind the shock. A time-marching second-order finite-difference method is used to solve the equations for a perfect gas. The local CFL (Courant-Friedrich-Lewy) time increment is used to advance the solution in time at each grid point. A fourth-order damping is used to damp the oscillations in the flow quantities. The numerical results of the present analysis for quantities such as shock standoff distance, surface-pressure distribution, and heating rates compare well with the existing theoretical and experimental results.

Kumar, A.↗
NASA NTRS1991

Filament disappearances and associated shocks of May 1979

In late May 1979 a shock was seen at each of two locations separated by about 90 deg in heliolongitude and at about the same time. A shock was detected near the earth, and a shock was detected at Helios 1 when it was off the sun's west limb. Some authors have considered that these shocks were part of the same event, which originated with a filament disappearance near 65 deg W. The paper discusses the observations which show that a large complex filament, extending from 20 deg to 70 deg W, disappeared in several places, probably generating more than one shock. The shock detected near earth was probably associated with a filament section which disappeared near the central meridian. If this is the case, then the interplanetary scintillation observations of this time period can be explained without invoking highly anisotropic shock propagation.

Cane, H. V.↗
NASA NTRS1990

A time-accurate adaptive grid method and the numerical simulation of a shock-vortex interaction

A time accurate, general purpose, adaptive grid method is developed that is suitable for multidimensional steady and unsteady numerical simulations. The grid point movement is performed in a manner that generates smooth grids which resolve the severe solution gradients and the sharp transitions in the solution gradients. The temporal coupling of the adaptive grid and the PDE solver is performed with a grid prediction correction method that is simple to implement and ensures the time accuracy of the grid. Time accurate solutions of the 2-D Euler equations for an unsteady shock vortex interaction demonstrate the ability of the adaptive method to accurately adapt the grid to multiple solution features.

Bockelie, Michael J.↗
NASA NTRS1994

The Balmer-dominated northeast limb of the Cygnus loop supernova remnant

We present a comprehensive investigation of the Balmar-dominated northeast limb of the Cygnus Loop supernova remnant. Data presented include H alpha (O III), and X-ray images, UV and visible spectrophotometry, and high-resolution spectroscophy. The two relatively bright Balmer-dominated filaments visible on the POSS prints are seen to be part of a very smooth and regular complex of filaments. These filaments mark the current location of the blast wave and are seen to bound the sharply limb-brightened X-ray emission, including the previously reported X-ray, 'halo.' The (O III)/h beta ratio throughout the region is approximately 0.1, except for regions in which the shock is undergoing a transition from nonradiative to incomplete radiative to incomplete radiative conditions. At these locations (O III) emission from the cooling region is quite strong, while collisionally excited Balmer-line emission can be weak because of photoionization of the preshock medium by UV from the nascent cooling region. As a result (O III)/H beta is greater than 100 in some locations. The nonradiative/radiative transition is best studied along the length of the northwestern of the two brightest filaments, where the shock velocity and swept-up column go from approximately 180 km/s and 10(exp 17)/sq cm at one end to approximately 140 km/s and 8 x 10(exp 17)/cm at the other. There are also a number of locations of such incomplete radiative emission where the shock has recently encountered denser regions with characteristic sizes of approximately 10(exp 18) cm. There is a considerable amount of evidence that the shock has decelerated from approximately 400 km/s to less than 200 km/s in the last 1000 yr. We interpret this as the result of the blast wave hitting the wall of a cavity which surround the supernova precursor and succeed in matching a wide range of data with a reflected shock model in which the density ofthe cavity wall is approximately 1.2/cu cm and the density in the interior of the cavity is about 0.09/cu cm. This analysis supports previous suggestions that the Cygnus Loop was a cavity explosion. We opredict that the X-ray shell will continue to brighten for the next 1000 years or so, during which time the shock front will become radiative throughout the northeast region. The similarity of the time scales for post-shock cooling, shock deceleration, and the 1ressure evolution of the region violates assumptions of steady flow, and greatly complicated interpretation of shock specptra in the region. This may be a common and important effect in many supernova remnants. High-resolutoin spectroscopy of the H alpha line profile shows that the broad component is surprisingly narrow (approximately 130 km/s). Consistency between this line width and the shock velocity inferred from spectrophotometry requires either rapid postshock equilibration of T(sub i) and T(sub e), or that the shock front has declerated from 180 km/s to 150 km/s in the last approximately 200 yr. While we cannot unambiguously distinquish between these models, the required deceleration is consistent with extrapolation of the shock decleration rate inferred over the last 1000 years. The width of the narrow component of the h alpha line profile is approximately 3 km/s, which indicates that the preshock medium has been heated to approximately 25,000 K by a shock precursor. The most promising types of precursor are heating either by fast neutrals which overtake the shock or by cosmic rays. In the latter case the observed properties of the precursor constrain the cosmic-ray diffusion coefficient to be between about 10(exp 23) sq cm/s. The characteristics of the precursor seem to be about right to explain the presence of weak (S II) and (N II) emission previously reported by Fesen & Itoh (1985).

Hester, J. Jeff↗
DOE OSTI2020

Heat Loss Correction Factor for Fireball Yield Measurements

Fireball yield calculations are performed using Taylor’s radius equation. However, at early times, the x-ray diffusion process has a significant effect on the size of the fireball, and at late times the shock wave degenerates into an acoustic wave. Thus, earlier research determined that the range of validity for Taylor’s equation was in the scaled time regime of 0.004–0.008 s. So, when performing a yield calculation, the only values that are analyzed are those that lie within that range of validity. While Taylor’s equations offer an approximation of the scaled yield, they also rely on several assumptions. For example, the equations assume that the shock wave is adiabatic, when, in fact, the first light pulse on the nuclear test films, which occurs as the shock wave is forming, suggests that the shock wave is not adiabatic. Furthermore, the amount of heat loss from the shock wave that occurs prior to the scaled time regime of 0.004–0.008 s can change significantly as a function of air density. This may cause the shock wave radius to be smaller relative to the assumed adiabatic shock wave. Therefore, the objective of this project was to determine the correction factor for heat transfer, which should be applied in order to produce a more accurate approximation of the weapon’s yield.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2021

Magnetic Velocity Gauges: Effects of Misalignment

Embedded velocity gauges are standardly used at LANL on gas gun experiments of a shock to-detonation transition. The experiments are intended to be one-dimensional with a planar shock driven by the projectile from a gas gun propagating along the axis of the HE cylinder. As disussed by Gustavsen et al. [1999], the accuracy of the gauges depends on the alignment of the directions of shock propagation, magnetic field and the active gauge element. A source of inaccuracies is from tilt or misalignment angle at impact between the projectile surface and the HE surface; typically a few milliradians. This leads to the shock propagating at a slight angle to the axis of the HE cylinder and can affect the shock rise time of the velocity gauges, the time offset between the tracker gauges for the trajectory of the lead shock, and the gauge positions in the direction of propagation. It is important to note that tilt is characterized by 2 parameters; the magnitude of the angle relative to the HE axis and the direction in the plane transverse to the HE axis. Here we derive the uncertainties from tilt to leading order in the tilt angle.

42 ENGINEERING↗
NASA NTRSDate not supplied

Shock-Layer Radiation Insights Available Through Flowfield Property Binning

This paper introduces a method for assessing similarity between available shock-layer radiation measurements and the radiative heating to a vehicle of interest. This method will be referred to as the flowfield property binning (FPB) approach. The challenge in developing this approach is that radiometer measurements from a surface normal line of sight, observed radiation measurements of the entire shock-layer from a distance, or measured shock-tube nonequilibrium profiles are notably different geometrically than the radiative flux to a vehicle surface. Therefore, the relative contributions of various regions of the shock-layer to the measurement, and how these relative contributions compare with the radiative heating to a vehicle of interest, are unclear. By tracking the radiation contribution from each flowfield location, and then grouping this contribution based on two local flowfield properties, these geometric differences are removed. This provide a two dimensional group, or bin, distribution that represents the radiation environment in the same format for various types of radiation simulations, such as observed radiation or radiative flux to a vehicle surface. In the limits of optically-thin radiation transport and thermochemical equilibrium flow, the choice of pressure and temperature as the binning flowfield properties is shown to provide a bin distribution that uniquely defines the radiation simulation. This concept is found to be sufficient for establishing similarity between two cases even when the optically-thin radiation transport and thermochemical equilibrium assumptions are not satisfied. A simple metric of comparison between bin distributions from different cases is provided by the histogram intersection algorithm. This algorithm results in a histogram intersection factor (H) between 0 and 1, which represents the fraction of the radiation that is similar between the two cases. Therefore, if H evaluated between bin distributions for two completely different radiation problems is near 1, then they represent essentially the same radiation problem. This means that they depend on the same weighting of various radiation modeling parameters evaluated at the same pressure and temperature. If one of these cases agrees well with a radiation measurement, then the matching bin distributions provide justification for applying this experimental validation to the other case. Even for H values as low as 0.2, the measurement case could be considered relevant if there are no other useful measurements. This approach allows observed radiation measurements to directly inform radiative heating simulations, which allows NASA’s past and future investments in observed radiation measurements to directly inform the radiative heating uncertainty or margins for future vehicle design. This FPB approach is also used to determine shock-tube conditions for informing backshell radiative heating simulations, where the normal shock velocity and Lagrangian time from the shock is used for the binning variables instead of pressure and temperature.

Shock Layer Radiation↗
NASA NTRS1973

Time-resolved spectroscopic measurements behind incident and reflected shock waves in air and xenon

Time-resolved spectra have been obtained behind incident and reflected shock waves in air and xenon at initial pressures of 0.1 and 1.0 torr using a rotating drum spectrograph and the OSU (The Ohio State University) arc-driven shock tube. These spectra were used to determine the qualitative nature of the flow as well as for making estimates of the available test time. The (n+1,n) and (n,n) band spectra of N2(+) (1st negative) were observed in the test gas behind incident shock waves in air at p1=1.0 torr and Us=9-10 km/sec. Behind reflected shock waves in air, the continuum of spectra appeared to cover almost the entire wavelength of 2,500-7,000 A for the shock-heated test gas. For xenon, the spectra for the incident shock wave cases for p1=0.1 torr show an interesting structure in which two intensely bright regions are witnessed in the time direction. The spectra obtained behind reflected shock waves in xenon were also dominated by continuum radiation but included strong absorption spectra due to FeI and FeII from the moment the reflected shock passed and on.

Yoshinaga, T.↗
NASA NTRS1981

Bi-directional streaming of solar wind electrons greater than 80 eV - ISEE evidence for a closed-field structure within the driver gas of an interplanetary shock

In near time coincidence with the arrival of helium enriched plasma driving the shock wave disturbance of November 12-13, 1978, strong bi-directional streaming of solar wind electrons greater than about 80 eV was observed with Los Alamos instrumentation on ISEE 3. The streaming persisted for many hours simultaneously parallel and anti-parallel to the interplanetary magnetic field which was directed roughly perpendicular to the sun-satellite line. This example of bidirectional streaming cannot be explained by field line connection to the earth's bow shock or the outward propagating interplanetary shock which passed ISEE 3 approximately 16 hours earlier. The event is explained if the local interplanetary field was a part of a magnetic bottle rooted at the sun or a disconnected loop propagating outward.

Bame, S. J.↗
NASA NTRS1985

Radiation pressure-driven shocks in winds from hot stars

The dynamical theory of radiation-pressure-driven shocks in winds from early-type stars is outlined. After the principal parameters needed for a description of these shocks are isolated (speeds relative to incoming material and their column densities), the shocks' principal properties as functions of these parameters are estimated. The special case of time-steady shocks is examined, and calculations are given for density, ionization state, temperature, and flow velocity as functions of position; also calculated are X-ray emissivity, UV line emissivity, and total radiation force as functions of shock velocity and postshock column density.

Krolik, J. H.↗