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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture

Shock structure during ionization of a hydrogen-helium mixture was studied using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement was achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2 - 0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for H beta and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process.

Leibowitz, L. P.↗
NASA NTRS1973

Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture.

Shock structure during ionization of a hydrogen-helium mixture has been followed using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement has been achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2-0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for H beta and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process.

Leibowitz, L. P.↗
NASA NTRS1984

Collisionless Shock Waves in the Solar Terrestrial Environment

Natural shocks, magnetohydrodynamics, shock extensions, global asymmetries, shock profiles, quasiperpendicular supercritical process; ion dynamics and field structure, numerical simulations, ion reflection machinery, electrons, instabilities, phenomenology, and ion acceleration were described.

Source record↗
NASA NTRS1992

Oblique shock wave with sweep

An attached planar, oblique shock with sweep is investigated for the inviscid flow of a perfect gas. The ratio of specific heats, freestream Mach number, and wedge angle in the plane of the freestream velocity are prescribed, with the sweep angle as a free parameter. Explicit relations are provided for jump and detachment conditions. A number of trends, some nonintuitive, are discussed, e.g., the downstream Mach number may increase with sweep.

Emanuel, G.↗
NASA NTRS1998

Determination of Sun Angles for Observations of Shock Waves on a Transport Aircraft

Wing compression shock shadowgraphs were observed on two flights during banked turns of an L-1011 aircraft at a Mach number of 0.85 and an altitude of 35,000 ft (10,700 m). Photos and video recording of the shadowgraphs were taken during the flights to document the shadowgraphs. Bright sunlight on the aircraft was required. The time of day, aircraft position, speed and attitudes were recorded to determine the sun azimuth and elevation relative to the wing quarter chord-line when the shadowgraphs were visible. Sun elevation and azimuth angles were documented for which the wing compression shock shadowgraphs were visible. The shadowgraph was observed for high to low elevation angles relative to the wing, but for best results high sun angles relative to the wing are desired. The procedures and equations to determine the sun azimuth and elevation angle with respect to the quarter chord-line is included in the Appendix.

Fisher, David F.↗
NASA NTRS1986

The flowfield structure of the 3-D shock wave - Boundary layer interaction generated by a 20 deg sharp fin at Mach 3

The three-dimensional oblique shock wave-turbulent boundary layer interaction generated by a sharp fin attached to a flat plate is investigated experimentally and theoretically for Mach 3 and Reynolds number 9 x 10 to the 5th using two different models. Both models employ the three-dimensional compressible Navier-Stokes equations in mass-averaged variables; one model utilizes the algebraic turbulent eddy viscosity model of Baldwin and Lomax (1978), while the other model employs the two-equation turbulence model of Jones and Launder (1972) coupled with the wall function model of Viegas and Rubesin (1985). The computed surface pressure, surface streamlines, pitot pressure, and yaw angle profiles are found to be in good agreement with experimental data. The three-dimensional velocity fields computed by both models are in close agreement, although the eddy viscosity profiles differ significantly within the three-dimensional interaction. This result indicates that the overall structure of this three-dimensional sharp fin interaction is insensitive to the turbulence model.

Knight, D. D.↗
NASA NTRS1978

Shock wave ignition of magnesium powders

The paper is concerned with magnesium powder ignition caused by the interaction of powder with incident shock wave-induced flows. Experimentally observed ignition delays are correlated with predicted times for particle melting and the onset of thermal erosion, and a good agreement is found between experiment and theory. Ignition delays were measured as functions of particle screening, cloud concentration, incident shock strength, initial pressure, and oxygen concentration (diluted with nitrogen). An expression for the Nusselt number in the Reynolds number range 0-10,000 and the Mach number range 0-6 is proposed. The expression, when applied to predict particle behavior, provides results in agreement with experimental data for M/Re less than 0.5.

Fox, T. W.↗
NASA NTRS1982

Numerical computations of turbulence amplification in shock wave interactions

Numerical computations are presented which illustrate and test various effects pertinent to the amplification and generation of turbulence in shock wave-turbulent boundary layer interactions. Several fundamental physical mechanisms are identified. Idealizations of these processes are examined by nonlinear numerical calculations. The results enable some limits to be placed on the range of validity of existing linear theories. Additional results are given which are of a fundamentally nonlinear nature.

Zang, T. A.↗
NASA NTRS1989

Implications of pressure diffusion for shock waves

The report deals with the possible implications of pressure diffusion for shocks in one dimensional traveling waves in an ideal gas. From this new hypothesis all aspects of such shocks can be calculated except shock thickness. Unlike conventional shock theory, the concept of entropy is not needed or used. Our analysis shows that temperature rises near a shock, which is of course an experimental fact; however, it also predicts that very close to a shock, density increases faster than pressure. In other words, a shock itself is cold.

Ram, Ram Bachan↗
NASA NTRS1975

Control of shock-wave boundary-layer interactions by bleed in supersonic mixed compression inlets

An experimental investigation has been conducted to determine the effect of bleed region geometry and bleed rate on shock wave-boundary layer interactions in an axisymmetric, mixed-compression inlet at a Mach number of 2.5. The full realizable reduction in transformed form factor is obtained by bleeding off about half the incident boundary layer mass flow. Bleeding upstream or downstream of the shock-induced pressure rise is preferable to bleeding across the shock-induced pressure rise. Slanted holes are more effective than normal holes. Two different bleed hole sizes were tested without detectable difference in performance.

Fukuda, M. K.↗
NASA NTRS2014

Quantified Energy Dissipation Rates in the Terrestrial Bow Shock: Waves and Dissipation - 2

We present the first quantified measure of the energy dissipation rates, due to wave-particle interactions, in the transition region of the Earth's collision-less bow shock using data from the Time History of Events and Macro-Scale Interactions during Sub-Storms spacecraft. Our results show that wave-particle interactions can regulate the global structure and dominate the energy dissipation of collision-less shocks. In every bow shock crossing examined, we observed both low-frequency (less than 10 hertz) and high-frequency (approximately or greater than10 hertz) electromagnetic waves throughout the entire transition region and into the magnetosheath. The low-frequency waves were consistent with magnetosonic-whistler waves. The high-frequency waves were combinations of ion-acoustic waves, electron cyclotron drift instability driven waves, electrostatic solitary waves, and whistler mode waves. The high-frequency waves had the following: (1) peak amplitudes exceeding delta B approximately equal to 10 nanoteslas and delta E approximately equal to 300 millivolts per meter, though more typical values were delta B approximately equal to 0.1-1.0 nanoteslas and delta E approximately equal to 10-50 millivolts per meter (2) Poynting fluxes in excess of 2000 microWm(sup −2) (micro-waves per square meter) (typical values were approximately 1-10 microWm(sup −2) (micro-waves per square meter); (3) resistivities greater than 9000 omega meters; and (4) associated energy dissipation rates greater than 10 microWm(sup −3) (micro-waves per cubic meter). The dissipation rates due to wave-particle interactions exceeded rates necessary to explain the increase in entropy across the shock ramps for approximately 90 percent of the wave burst durations. For approximately 22 percent of these times, the wave-particle interactions needed to only be less than or equal to 0.1 percent efficient to balance the nonlinear wave steepening that produced the shock waves. These results show that wave-particle interactions have the capacity to regulate the global structure and dominate the energy dissipation of collision-less shocks.

Terrestrial bow 2↗
NASA NTRS1992

Steady state risetimes of shock waves in the atmosphere

A square wave shape is used in the Pestorius algorithm to calculate the risetime of a step shock in the atmosphere. These results agree closely with steady shock calculations. The healing distance of perturbed shocks due to finite wave effects is then investigated for quasi-steady shocks. Perturbed 100 Pa shocks require on the order of 1.0 km travel distance to return to within 10 percent of their steady shock risetime. For 30 Pa shocks, the minimum recovery distance increases to 3.0 km. It is unlikely that finite wave effects can remove the longer risetimes and irregular features introduced into the sonic boom by turbulent scattering in the planetary boundary layer.

Raspet, Richard↗