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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Table and charts of equilibrium normal-shock and shock-tube properties for pure carbon dioxide with velocities from 1 to 16 km/sec

Equilibrium thermodynamic and flow properties are presented in tabulated and graphical form for moving, standing, and reflected normal shock waves in pure CO2. Properties include pressure, temperature, density, enthalpy, speed of sound, entropy, molecular weight ratio, isentropic exponent, velocity, and species mole fractions. Incident (moving) shock velocities are varied from 1 to 16 km/sec for a range of initial pressure of 5 N/sq m to 500 kN/sq m. The present results are applicable to shock tube flows and to freeflight conditions for a blunt body at high velocities. Working charts illustrating idealized shock tube performance with CO2 test gas and heated helium and hydrogen driver gases are also presented.

Miller, C. G., III↗
NASA NTRS1974

Tables and charts of equilibrium normal shock and shock-tube solutions for helium-hydrogen mixtures with velocities to 70 km/sec

Equilibrium thermodynamic and flow properties are presented in tabulated and graphical form for moving, standing, and reflected normal shock waves into helium-hydrogen mixtures representative of proposed outer planet atmospheres. The volumetric compositions of these mixtures are 0.35He-0.65H2, 0.20He-0.80H2, and 0.05He-0.95H2. Properties include pressure, temperature, density, enthalpy, speed of sound, entropy, molecular-weight ratio, isentropic exponent, velocity, and species mole fractions. Incident (moving) shock velocities are varied from 4 to 70 km/sec for a range of initial pressure of 5 N/sq m to 100 kN/sq m. The present results are applicable to shock-tube flows and to free-flight conditions for a blunt body at high velocities. A working chart illustrating idealized shock-tube performance with a 0.20He-0.80H2 test gas and heated helium driver gas is also presented.

Miller, C. G., III↗
NASA NTRS1990

Numerical simulations of the rebound shock model for solar spicules

Using time-dependent numerical simulations, the proposed rebound shock mechanism for spicules has been examined. At temperatures above a critical value, T(c), the radiation is characteristic of the conditions in the optically thin corona and near optically thin transition region. When T less than T(c), the atmosphere has a radiative cooling time, tau(rad) characteristic of chromosphere. The spicule is initiated with a quasi-impulsive force in the low chromosphere, which drives a train of upward propagating rebound shocks along the rigid magnetic flux tube. These shocks then move the transition region upward. The material below the displaced transition region has temperatures and densities similar to those of spicules when T(c) = 20,000 K or more and tau(rad) = 500 s or more, but not when T(c) = 10,000 K, and probably not when tau(rad) = 100 s. For all the cases where the cross sectional area diverges rapidly with height, the upward velocity of the transition region is less than that of spicules. Moreover, the maximum height is less than that of average spicules. Taller, higher velocity spicules result when the magnetic field cross sectional area is constant. In all cases, the rebound shock mechanism produces substantial motions and temperature and density variations in chromospheric and transition region material. It is suggested that this may be a partial explanation for the continuous dynamic state of the lower solar atmosphere.

Sterling, Alphonse C.↗
NASA NTRS1995

On the upstream boundary of electron foreshocks in the solar wind

The upstream boundary of electron foreshocks is defined as the path of the fastest electrons reflected by collisionless shocks and moving along the magnetic field in the solar wind. Considerable levels of magnetic fluctuations are found in these regions of the solar wind, and their effect is to create both a broadening and a fine structure of the electron foreshock boundary. The magnetic structure is studied by means of a 3-D numerical simulation of a turbulent magnetic field. Enhanced, anomalous diffusion is found, (Delta x(exp 2)) varies as s(sup alpha), where alpha is greater than 1 for typical values of the parameters (here, Delta x(exp 2) is the mean square width of the tangent magnetic surface and s is the field line length). This corresponds to a Levy flight regime for the magnetic field line random walk, and allows very efficient electron propagation perpendicular to the magnetic field. Implications on the observations of planetary foreshocks and of the termination shock foreshock are considered.

Zimbardo, G.↗
NASA NTRS1985

Numerical simulation of compressible, turbulent, two-phase flow

A computer program for numerically simulating compressible, turbulent, two-phase flows is described and applied. Special attention is given to flows in which dust is ingested into the turbulent boundary layer behind shock waves moving over the earth's surface. it is assumed that the two phases are interpenetrating continua which are coupled by drag forces and heat transfer. The particle phase is assumed to be dilute, and turbulent effects are modeled by zero- and two-equation eddy viscosity models. An important feature of the turbulence modeling is the treatment of surface boundary conditions which control the ingestion of particles into the boundary layer by turbulent friction and diffusion. The numerical method uses second-order implicit upwind differencing of the inviscid terms of the equations and second-order central differencing of the viscous terms. A diagonal form of the implicit algorithm is used to improve efficiency, and the transformation to a curvilinear coordinate system is accomplished by the finite volume techniques. Applications to a series of representative flows include a two-phase nozzle flow, the steady flow of air over a sand bed, and the air flow behind a normal shock wave in uniform motion over a sand bed. Results of the latter two applications are compared with experimental results.

Coakley, t. J.↗
DOE OSTI2026

Optimizing time integration for accurate recovery of shockwave interface location in radiography

We present simulations and experiments of time integrated radiographic imaging of a moving 1D shock wave front and a quantitative method for determining the statistical error in locating the shock front as a function of integration time and noise in the radiograph. We discuss the trade-off between increasing motion blur, which leads to decreased shock front location certainty, and increasing signal-to-noise, which leads to improved image quality with increasing integration time. We find an optimum integration time between a short integration time, where noise limits the error, and a long integration time, where motion blurring limits the error. This methodology can be used to tune experimental configurations to obtain the highest quality radiograph for a given experimental configuration.

Bremsstrahlung↗
NASA NTRS1962

Pressure Distribution Induced on a Flat Plate at a Free-Stream Mach Number of 1.39 by Rockets Exhausting Upstream and Downstream

An experimental investigation was made of the pressures induced on a flat plate at a free-stream Mach number of 1.39 by a supersonic rocket jet exhausting upstream and downstream. Measurements of the pressure distribution on a flat plate were made at zero angle of attack for 11 different locations of the jet exhaust nozzle beneath the wing. Measurements were made at ratios of rocket-exit total pressure to freestream static pressure from 6 to 60 and at a Reynolds number per foot of approximately 10 x 10 6 . The rocket when exhausted upstream produced a strong shock that moved further upstream with increasing rocket-exit total-pressure ratio. Positive incremental normal-force coefficients were obtained at all test positions. Data at 11 test positions are tabulated for rocket-on and rocket-off pressure coefficients as well as for incremental pressure coefficients for the 48 orifices of the flat plate for the range of ratio of rocket-exit total pressure to free-stream static pressure of the investigation. Changing the location of the model with respect to the plate had a negligible effect when the rocket was varied in the chordwise direction, but the pressure coefficients were reduced as the rocket was lowered away from the flat-plate wing.

Supersonic jet↗
NASA NTRS1974

Evaluate ERTS imagery for mapping and detection of changes of snowcover on land and on glaciers

The author has identified the following significant results. The area of snowcover on 10 individual drainage basins in the North Cascades, Washington, has been determined by use of a semi-automatic radiance threshold technique. The result is a unique record of the changing water storage as snow in these important hydrologic units, the runoff of which is utilized for hydroelectric power, dilution of wastes and heat, support of salmon migration, and irrigation. These data allow a new type of hydrologic modelling to proceed which should permit more accurate forecasts of streamflow. A new technique has been developed for measuring snow-covered area or snowline altitude semi-automatically. This variable contour overlay method permits the snowcover to be matched efficiently to the best fit contour of altitude. The motion of the Yentna Glacier during the concluding phase of its surge was successfully measured by a flicker technique using images of two dates. It appears that displacements as small as 100 to 200 m can be measured. Motion of the Tweedsmuir Glacier in Alaska was measured using ERTS-1 images enlarged to 1:50,000. Changes detected included a shock wave moving down the glacier, the margin expanding, the moraine pattern deforming, and the marginal valley deepening.

Meier, M. F.↗
NASA NTRS1975

Analysis of the 31 Oct 1972 interplanetary shock wave and associated unusual phenomena

We analyze in detail the disturbed time period Oct. 31-Nov. 1, 1972 using magnetic field, plasma, and energetic particle data as well as magnetic field data. In particular, we discuss an interplanetary forward shock wave accompanied by a traditional shock-spike event in the energetic particles, a large tangential discontinuity correlated with a geomagnetic storm main phase, and a reverse interplanetary shock. This forward and reverse shock pair was caused by a 2N solar flare which occurred some 47 hours earlier. We also discuss an unusual rarefaction in the solar wind following (and probably related to) the shock pair, wherein the Alfven Mach number abruptly decreased from about 4.5 to about 1.5, allowing the earth's bow shock to move outward at least 20 earth radii beyond its nominal position.

Ipavich, F. M.↗
NASA NTRS1976

Components in interstellar molecular hydrogen

Results are reported for precise spectrophotometric measurements of the profiles of selected Lyman absorption lines produced by hydrogen molecules in various rotational levels along the line of sight to 13 stars which have shown some evidence for an increase in line width with increasing rotational quantum number (J). The line profiles were measured by multiple scans with the Copernicus satellite telescope. Based on analysis of the radial velocities, derivations of the column densities, and line-profile fitting, the following conclusions are made: (1) the increase in interstellar H2 line width with increasing J results from the presence of the most shortward component, which is relatively weak at low J but becomes more important at higher J; (2) the relative column densities found for the different J levels in each component may be fitted by a theoretical model in which rotational excitation is due to absorption of UV photons followed by radiative quadrupole spontaneous transitions or collisionally induced downward transitions between different J levels; (3) the atomic hydrogen density is between 300 and 1000 per cu cm in the most shortward component for each of three stars; (4) the approaching gas which produces each shortward component must be in the form of thin sheets; and (5) the sheets are the compressed gas behind a shock front moving through the interstellar medium.

Spitzer, L., Jr.↗
NASA NTRS1979

Automated temperature-cycling apparatus

Apparatus is used to test materials reaction to thermal shock by moving specimens between two chambers at high and low temperature extremes for specified number of cycles. Electrically motored system is completely automatic saving time and costs.

Lockard, M. L.↗
NASA NTRS1979

Orion's Cloak - A rapidly expanding shell of gas centered on the Orion OB1 association

The structure of the interstellar gas surrounding the Orion OB1 association and the neighboring lambda Orionis association is detailed. UV absorption lime spectra of various ionization stages of C, N, Si and S in the directions of 12 stars were obtained by means of the spectrometer on board the Copernicus satellite. The presence of a shell of material surrounding the two associations and expanding at 100 to 120 km/sec, designated Orion's Cloak, was revealed, together with sporadically occurring higher column density matter at lower velocities. Results are interpreted to indicate the presence of a rapidly moving radiative shock outside the H II region of the association stars and inside this feature, a lower velocity, higher column density cloud which appears to be directly ionized by association stars. It is suggested that the gas features are caused by the effects of a recent supernova and of multiple supernovae, stellar winds and rocket-accelerated clouds in addition to stellar ionization.

Cowie, L. L.↗
NASA NTRS1980

Pulsational mode-typing in line profile variables. I - Four Beta Cephei stars

The detailed variations of line profiles in the Beta Cephei-type variable stars Gamma Pegasi, Beta Cephei, Delta Ceti and Sigma Scorpii are modeled throughout their pulsation cycles in order to classify the dominant pulsation mode as radial or nonradial. High-dispersion Reticon observations of the variables were obtained for the Si III line at 4567 A, and line profiles broadened by radial or nonradial pulsations, rotation and radial-tangential macroturbulence were calculated based on a model atmosphere. It is found that only a radial pulsation mode can reproduce the radial velocity amplitude, changes in line asymmetry and uniform line width observed in all four stars. Results are in agreement with the color-to-light arguments of Stamford and Watson (1978), and suggest that radial pulsation plays the dominant role in the observed variations in most Beta Cephei stars. Evidence for shocks or moving shells is also found in visual line data for Sigma Scorpii and an ultraviolet line of Beta Cephei, together with evidence of smooth, secular period changes in Beta Cephei and Delta Ceti.

Campos, A. J.↗
NASA NTRS1980

Calculations of transonic flow about an airfoil in a wind tunnel

A combined experimental and numerical study was performed to include wind-tunnel wall interference effects in calculations for airfoil flows at transonic speeds. Pressure-survey-tube and laser-Doppler velocimeter measurements were made in the flow field about an airfoil in the 2- by 2-Foot Transonic Wind Tunnel at Ames Research Center. The results were then used as boundary data in a Navier-Stokes code modified by incorporating a pressure condition on the upper and lower computational boundaries. Comparison of calculated results and experimental data obtained from the surface of the airfoil indicates that the pressure-boundary condition is particularly effective in moving the shock to a position near that observed experimentally when the flow remains attached. For flows with large separation, shock position and viscous-layer properties are not well predicted, principally because of the inadequacies of the algebraic turbulence models employed with the method.

King, L. S.↗
NASA NTRS1981

Spectral and compositional variations of low energy ions during an energetic storm particle event

Attention is given to variations in the intensity, energy spectra, and composition of low-energy protons, helium, and heavy ions (C, O, and Fe) in the energy range 0.3-20 MeV per nucleon during an energetic storm particle event on September 28-29, 1978. The intensities of low enery (less than or equal to 0.6 MeV per nucleon) particles are found to increase exponentially with time before the arrival of the moving interplanetary shock front. The increase is largest for the particles of lowest energy. The spectral steepening, expressed in terms of differences in the spectral index, increases for particles of increasing mass per charge ratio from a difference of approximately 1 for protons to approximately 3 for iron. As a consequence, the He/O and C/O ratios at equal energy per nucleon are constant, whereas the He/p, Fe/He, and Fe/O ratios decrease by as much as one order of magnitude before passage of the shock. The observations are analyzed in terms of a first-order Fermi acceleration model with a rigidity dependent interplanetary mean free path.

Klecker, B.↗
NASA NTRS1982

Amplitudes of solar modulation of low energy cosmic rays

There have been differences of opinion regarding the origin and behavior of the solar modulation of galactic cosmic rays. It has been shown that the return to solar maximum intensity levels beginning in early 1978 was dominated by Forbush decreases. These Forbush decreases were caused by radially moving interplanetary shocks resulting from large solar flares. The present investigation is concerned with solar modulation effects which were observed during the previous solar minimum. The effects were associated with high-speed streams in the solar wind. These streams caused the formation of corotating interaction regions with both forward and reverse shocks. The modulation effects seen near earth are intimately connected with these shocks.

Von Rosenvinge, T. T.↗
NASA NTRS1991

A hierarchy for modeling high speed propulsion systems

General research efforts on reduced order propulsion models for control systems design are overviewed. Methods for modeling high speed propulsion systems are discussed including internal flow propulsion systems that do not contain rotating machinery, such as inlets, ramjets, and scramjets. The discussion is separated into four areas: (1) computational fluid dynamics models for the entire nonlinear system or high order nonlinear models; (2) high order linearized models derived from fundamental physics; (3) low order linear models obtained from the other high order models; and (4) low order nonlinear models (order here refers to the number of dynamic states). Included in the discussion are any special considerations based on the relevant control system designs. The methods discussed are for the quasi-one-dimensional Euler equations of gasdynamic flow. The essential nonlinear features represented are large amplitude nonlinear waves, including moving normal shocks, hammershocks, simple subsonic combustion via heat addition, temperature dependent gases, detonations, and thermal choking. The report also contains a comprehensive list of papers and theses generated by this grant.

Hartley, Tom T.↗