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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1959

Effect of Surface Roughness on Characteristics of Spherical Shock Waves

Measurements of peak overpressure and Mach stem height were made at four burst heights. Data were obtained with instrumentation capable of directly observing the variation of shock wave movement with time. Good similarity of free air shock peak overpressure with larger scale data was found to exist. The net effect of surface roughness on shock peak overpressures slightly. Surface roughness delayed the Mach stem formation at the greatest charge height and lowered the growth at all burst heights. A similarity parameter was found which approximately correlates the triple point path at different burst heights.

Huber, Paul W.↗
NASA NTRS1972

Auto-ignition of hydrocarbons behind reflected shock waves.

The paper reports on the study of auto-ignition of hydrocarbon-oxygen mixtures behind reflected shock waves. Because of their bearing on the problem of knock in internal combustion engines, n-heptane and iso-octane were chosen as the combustible species. Their stoichiometric mixtures with oxygen had to be diluted with 70% argon to reduce the influence of the boundary layer. Photographic records demonstrated the existence of two different modes of ignition, as has been previously established for the hydrogen-oxygen system. The pressure-temperature limits between these regions of mild and strong ignition were determined. From the same experimental tests, induction time data were obtained over the pressure range of 1-4 atm and the temperature interval of 1200-1700 K.

Vermeer, D. J.↗
NASA NTRS1992

Intersecting Shock-Wave/Turbulent Boundary-Layer Interactions at Mach 8.3

Experimental data for two three-dimensional intersecting shock-wave/turbulent boundary-layer interaction flows at Mach 8.3 are presented. The test bodies, composed of two sharp fins fastened to a flat-plate test bed, were designed to generate flows with varying degrees of pressure gradient, boundary-layer separation, and turning angle. The data include surface pressure and heat transfer distributions as well as mean flow-field surveys both in the undisturbed and interaction regimes. The data are presented in a convenient form to be used to validate existing or future computational models of these hypersonic flows. The data are also on a 3.5-inch diskette included and are available through E-mail.

Kussoy, M. I.↗
NASA NTRS1961

Ground Measurements of the Shock-Wave Noise from Supersonic Bomber Airplanes in the Altitude Range from 30,000 to 50,000 Feet

Shock-wave ground-pressure measurements have been made for supersonic bomber airplanes in the Mach number range from 1.24 to 1.52, for altitudes from about 30,000 to 50,000 feet, and for a gross-weight range from about 83,000 to 120,000 pounds. The measured overpressures were generally higher than would be predicted by the theory which accounts only for volume effects. There is thus a suggestion that lift effects on sonic-boom intensity may be significant for this type of airplane for the altitude range of the present tests.

Maglieri, Domenic J.↗
NASA NTRS1993

Direct numerical simulation of isotropic turbulence interacting with a weak shock wave

Direct numerical simulations are used to investigate the interaction of isotropic quasi-incompressible turbulence with a weak shock wave. A linear analysis of the interaction is conducted for comparison with the simulations. Both the simulations and the analysis show that turbulence is enhanced during the interaction. Turbulent kinetic energy and transverse vorticity components are amplified, and turbulent lengthscales are decreased. It is suggested that the amplification mechanism is primarily linear. Simulations also showed a rapid evolution of turbulent kinetic energy just downstream of the shock, a behavior not reproduced by the linear analysis. Analysis of the budget of the turbulent kinetic energy transport equation shows that this behavior can be attributed to the pressure transport term. Multiple compression peaks were found along the mean streamlines at locations where the local shock thickness had increased significantly.

Lee, Sangsan↗
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 NTRS1981

On the acceleration of ions by interplanetary shock waves. 3: High time resolution observations of CIR proton events

Observations within + or - 3 hours of corotating interaction region (CIR) shock waves of proton intensities, pitch angle distribution and crude differential energy spectra of the range of 0.6 E sub p 3.4 MeV are presented. The principle result is the evidence for the persistent flow of particles away from the shock. The observations are found to be in good agreement with the hypothesis of local interplanetary shock acceleration by the shock drift and compression mechanisms. The same set of observations strongly suggest that transit time damping does not play an important role in the acceleration of protons to 1 MeV in the immediate vicinity of CIR shocks.

Pesses, M. E.↗
NASA NTRS1973

Flight test measurements and analysis of sonic boom phenomena near the shock wave extremity

The sonic boom flight test program conducted at Jackass Flats, Nevada, during the summer and fall of 1970 consisted of 121 sonic-boom-generating flights over the 1500 ft instrumented BREN tower. This test program was designed to provide information on several aspects of sonic boom, including caustics produced by longitudinal accelerations, caustics produced by steady flight near the threshold Mach number, sonic boom characteristics near lateral cutoff, and the vertical extent of shock waves attached to near-sonic airplanes. The measured test data, except for the near-sonic flight data, were analyzed in detail to determine sonic boom characteristics for these flight conditions and to determine the accuracy and the range of validity of linear sonic boom theory. The caustic phenomena observed during the threshold Mach number flights and during the transonic acceleration flights are documented and analyzed in detail. The theory of geometric acoustics is shown to be capable of predicting shock wave-ground intersections, and current methods for calculating sonic boom pressure signature away from caustics are shown to be reasonably accurate.

Haglund, G. T.↗
NASA NTRS1998

Shock Wave Dynamics in Weakly Ionized Gases

We have begun a comprehensive series of analyses and experiments to study the basic problem of shock wave dynamics in ionized media. Our objective is to isolate the mechanisms that are responsible for the decrease in the shock amplitude and also to determine the relevant plasma parameters that will be required for a drag reduction scheme in an actual high altitude hypersonic flight. Specifically, we have initiated a program of analyses and measurements with the objective of (i) fully characterizing the propagation dynamics in plasmas formed in gases of aerodynamic interest, (ii) isolating the mechanisms responsible for the decreased shock strength and increased shock velocity, (iii) extrapolating the laboratory observations to the technology of supersonic flight.

Johnson, Joseph A., III↗
NASA NTRS1991

The effects of shock wave precursors ahead of hypersonic entry vehicles

A model has been developed to predict the magnitude and characteristics of the shock wave precursor ahead of a hypervelocity vehicle. This model includes both chemical and thermal nonequilibrium, utilizes detailed mass production rates for the photodissociation and photoionization reactions, and accounts for the effects of radiative absorption and emission on the individual internal energy modes of both atomic and diatomic species. Comparison of the present results with shock tube data indicates that the model is reasonably accurate. A series of test cases representing earth aerocapture return from Mars indicate that there is significant production of atoms, ions and electrons ahead of the shock front due to radiative absorption and that the precursor is characterized by an enhanced electron/electronic temperature and molecular ionization. However, the precursor has a negligible effect on the shock layer flow field.

Stanley, Scott A.↗
NASA NTRS1983

Ignition of SiH4-H2-O2-N2 behind reflected shock waves

The ignition of mixtures of silane, hydrogen, and oxygen diluted with nitrogen was studied in a chemical kinetic shock tube. Ignition delay time measurements were made behind reflected shock waves at pressures of 1.25 atm and 1.35 atm and temperatures ranging from approximately 800 K to 1050 K for two mixtures with silane-oxygen equivalence ratios of 1.0 and 0.5, respectively. Enhancement of the ignition by use of silane was observed experimentally by the failure of a similar mixture containing only hydrogen, oxygen, and nitrogen to ignite during the maximum test time available for these test conditions.

Mclain, A. G.↗
NASA NTRS1998

The Space-Time Conservation Element and Solution Element Method-A New High-Resolution and Genuinely Multidimensional Paradigm for Solving Conservation Laws: Numerical Simulation of Shock Waves and Contact Discontinuities - 2

Without resorting to special treatment for each individual test case, the 1D and 2D CE/SE shock-capturing schemes described previously (in Part I) are used to simulate flows involving phenomena such as shock waves, contact discontinuities, expansion waves and their interactions. Five 1D and six 2D problems are considered to examine the capability and robustness of these schemes. Despite their simple logical structures and low computational cost (for the 2D CE/SE shock-capturing scheme, the CPU time is about 2 micro-secs per mesh point per marching step on a Cray C90 machine), the numerical results, when compared with experimental data, exact solutions or numerical solutions by other methods, indicate that these schemes can accurately resolve shock and contact discontinuities consistently.

Wang, Xiao-Yen↗
NASA NTRS1975

An experimental documentation of a hypersonic shock-wave turbulent boundary layer interaction flow: With and without separation

An experiment, thoroughly documenting the flow field resulting from the interaction of a shock wave with a nonadiabatic hypersonic turbulent boundary layer, is described. Detailed mean flow and surface data are presented for two shock strengths resulting in attached and separated flows, respectively. The surface measurements include continuous pressure, shear and heat-flux distributions upstream, in, and downstream of the interaction regions. At closely spaced intervals along the surface, boundary-layer profiles of static and pitot pressure and total temperature were obtained from which velocity, density and static temperature profiles were derived. The data are presented in both graphical and tabular form. These data are of sufficient detail to validate advanced computer codes and their associated turbulence models.

Kussoy, M. I.↗