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At least 73 records · Page 4
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NASA NTRS2016

Compressible 2D Flow Field Interaction of Two Contra-Rotating Blades

The blades of coaxial, contra-rotating rotor systems cross each other in close proximity and at high relative speeds. This crossing event is a potential source of noise and severe blade loads. Effects of compressibility can aggravate the interaction and significantly alter the pressure field signature and phase relationships. A 2-D analysis of this phenomenon is performed by simulating two airfoils passing each other at specified speeds and vertical separation distances. Several test cases spanning a relevant range of Reynolds numbers, angles of attack, and relative Mach number are considered. The Mach number is varied to simulate the radial variation of velocity from the root to tip of a rotor blade to capture the pressure signature, lift, and drag of the airfoils. The velocity and pressure distributions on the airfoils, and in the space between the airfoils are computed before, at, and after airfoil crossing. The variations of lift and drag coefficients through the interaction are captured. The upper airfoil experiences an increase in lift followed by a very sharp drop in lift during the interaction. When relative Mach numbers are transonic, the region of interaction is greatly extended, with shock interactions occurring. The results show the complex nature of the aerodynamic and fluid dynamic impulses generated by blade-blade interactions, with implications to aeroelastic loads and aeroacoustic sources.

Barbely, Natasha L.↗
NASA NTRS1994

On the dynamics of a shock-bubble interaction

We present a detailed numerical study of the interaction of a weak shock wave with an isolated cylindrical gas inhomogenity. Such interactions have been studied experimentally in an attempt to elucidate the mechanisms whereby shock waves propagating through random media enhance mixing. Our study concentrates on the early phases of the interaction process which are dominated by repeated refractions of acoustic fronts at the bubble interface. Specifically, we have reproduced two of the experiments performed by Haas and Sturtevant : M(sub s) = 1.22 planar shock wave, moving through air, impinges on a cylindrical bubble which contains either helium or Refrigerant 22. These flows are modelled using the two-dimensional, compressible Euler equations for a two component fluid (air-helium or air-Refrigerant 22). Although simulations of shock wave phenomena are now fairly commonplace, they are mostly restricted to single component flows. Unfortunately, multi-component extensions of successful single component schemes often suffer from spurious oscillations which are generated at material interfaces. Here we avoid such problems by employing a novel, nonconservative shock-capturing scheme. In addition, we have utilized a sophisticated adaptive mesh refinement algorithm which enables extremely high resolution simulations to be performed relatively cheaply. Thus we have been able to reproduce numerically all the intricate mechanisms that were observed experimentally (e.g., transitions from regular to irregular refraction, cusp formation and shock wave focusing, multi-shock and Mach shock structures, jet formation, etc.), and we can now present an updated description for the dynamics of a shock-bubble interaction.

Quirk, James J.↗
NASA NTRS1986

JPL pyro shock test approaches and results

This paper presents the overall approach at JPL in performing spacecraft pyrotechnic shock qualification testing. Initially, the assembly shock requirements are developed early in the program based on previous spacecraft test experience and data. Pyrotechnic device development testing firings and spacecraft Development Test Model (DTM) pyro firings are then conducted to verify the adequacy of the assembly shock requirements and to determine the subsystem test firing and the subsequent system level test firing requirements. The electro-dynamic shaker, through shock synthesis techniques, is utilized to qualify the shock sensitive flight equipment with margins applied. Actual pyrotechnic device firings on spacecraft equipment or science instruments are performed when the influence of the pyros is localized and can be ignored at the system level. Full spacecraft system level shock tests, which include multiple firings of certain critical pyro devices, are conducted to verify the spacecraft design structural integrity and functions as well as to qualify hardware items which have not been previously qualified. These tests also provide a source of data from which assembly level requirements can be evaluated and compared. For example, during the Galileo program, the results demonstrated that good agreement between predicted and measured shock environments and adequate qualification of the flight spacecraft was achieved.

Chang, Kurng Y.↗
NASA NTRS1994

Development and application of computational aerothermodynamics flowfield computer codes

Research was performed in the area of computational modeling and application of hypersonic, high-enthalpy, thermo-chemical nonequilibrium flow (Aerothermodynamics) problems. A number of computational fluid dynamic (CFD) codes were developed and applied to simulate high altitude rocket-plume, the Aeroassist Flight Experiment (AFE), hypersonic base flow for planetary probes, the single expansion ramp model (SERN) connected with the National Aerospace Plane, hypersonic drag devices, hypersonic ramp flows, ballistic range models, shock tunnel facility nozzles, transient and steady flows in the shock tunnel facility, arc-jet flows, thermochemical nonequilibrium flows around simple and complex bodies, axisymmetric ionized flows of interest to re-entry, unsteady shock induced combustion phenomena, high enthalpy pulsed facility simulations, and unsteady shock boundary layer interactions in shock tunnels. Computational modeling involved developing appropriate numerical schemes for the flows on interest and developing, applying, and validating appropriate thermochemical processes. As part of improving the accuracy of the numerical predictions, adaptive grid algorithms were explored, and a user-friendly, self-adaptive code (SAGE) was developed. Aerothermodynamic flows of interest included energy transfer due to strong radiation, and a significant level of effort was spent in developing computational codes for calculating radiation and radiation modeling. In addition, computational tools were developed and applied to predict the radiative heat flux and spectra that reach the model surface.

Venkatapathy, Ethiraj↗
NASA NTRS1995

A new technique for ground simulation of hypervelocity debris

A series of hypervelocity damage experiments were preformed on spacecraft materials. These experiments employed a technique which accelerates micro flyer plates simulating space debris traveling at 3 to 8 km/sec. The apparatus used to propel the micro flyer plates was compact and fit well into a space environmental chamber equipped with instrumentation capable of analyzing the vapor ejected from the sample. Mechanical damage to the sample was also characterized using optical and scanning electron microscpopy. Data for this work was obtained from hypervelocity impacts on a polysulfone resin and a graphite polysulfone composite. Polysulfone was selected because it was flown on the Long Duration Exposure Facility (LDEF) which spent several years in low earth orbit (LEO). Chemistry of the vapor produced by the impact was analyzed with a time of flight mass spectrometer, (TOFMS). This represents the first time that ejected vapors from hypervelocity collisions were trapped and analyzed with a mass spectrometer. With this approach we are able to study changes in the vapor chemistry as a function of time after impact, obtain a velocity measurement of the vapor, and estimate a temperature of the surface at time of impact using dynamic gas equations. Samples of the vapor plume may be captured and examined by transmission electron microscopy. Studies were also conducted to determine mechanical damage to a graphite polysulfone composite and a polysulfone resin. Impact craters were examined under optical and scanning electron microscopes. The collision craters in the matrix were typical of those shown in conventional shock experiments. However, the hypervelocity collisions with the graphite polysulfone composite were remarkably different than those with the resin.

Roybal, R.↗
NASA NTRS1992

Stagnation-point heat-transfer rate predictions at aeroassist flight conditions

The results are presented for the stagnation-point heat-transfer rates used in the design process of the Aeroassist Flight Experiment (AFE) vehicle over its entire aeropass trajectory. The prediction methods used in this investigation demonstrate the application of computational fluid dynamics (CFD) techniques to a wide range of flight conditions and their usefulness in a design process. The heating rates were computed by a viscous-shock-layer (VSL) code at the lower altitudes and by a Navier-Stokes (N-S) code for the higher altitude cases. For both methods, finite-rate chemically reacting gas was considered, and a temperature-dependent wall-catalysis model was used. The wall temperature for each case was assumed to be radiative equilibrium temperature, based on total heating. The radiative heating was estimated by using a correlation equation. Wall slip was included in the N-S calculation method, and this method implicitly accounts for shock slip. The N-S/VSL combination of projection methods was established by comparison with the published benchmark flow-field code LAURA results at lower altitudes, and the direct simulation Monte Carlo results at higher altitude cases. To obtain the design heating rate over the entire forward face of the vehicle, a boundary-layer method (BLIMP code) that employs reacting chemistry and surface catalysis was used. The ratio of the VSL or N-S method prediction to that obtained from the boundary-layer method code at the stagnation point is used to define an adjustment factor, which accounts for the errors involved in using the boundary-layer method.

Gupta, Roop N.↗
NASA NTRS1976

Ultrahigh-accuracy body-pointing system for the Large Space Telescope

The Large Space Telescope (LST) is a 3-m diffraction-limited telescope. Pointing stability requirements necessary to assure diffraction-limited images are plus or minus 0.005 arc-sec, over possible experiment observation times of several hours. In order to determine whether these stringent pointing requirements could be met, a complex simulation model was defined which consisted of detailed dynamic representations of control moment gyros (CMGs) and reaction wheels (RWs), including their noise characteristics, dynamic sensor representations with sensor noise, shock mounts for the CMG actuators, a detailed representation of an image motion compensation (IMC) system, and a detailed flexible body structural model with all significant vehicle and solar panel bending modes. On the basis of both stability and performance studies utilizing this model, it was determined that a body-pointing system will meet LST requirements in the presence of CMG vibrational disturbances and sensor noise. The recommended system consists of three orthogonally mounted RWs for primary short-term control, and a cluster of CMG actuators for continuous RW desaturation and vehicle maneuvering.

Rybak, S. C.↗
NASA NTRS1983

Nonlinear interactions in superfluid dynamics: Nonstationary heat transfer due to second sound shock waves

Second sound techniques were used to study superfluid helium. Second sound shock waves produced relative velocities in the bulk fluid. Maximum counterflow velocities produced in this way are found to follow the Langer-Fischer prediction for the fundamental critical velocity in its functional dependence on temperature and pressure. Comparison of successive shock and rotating experiments provides strong evidence that breakdown results in vorticity production in the flow behind the shock. Schlieren pictures have verified the planar nature of second sound shocks even after multiple reflections. The nonlinear theory of second sound was repeatedly verified in its prediction of double shocks and other nonlinear phenomena.

Liepmann, H. W.↗
NASA NTRS1977

Shock compression and adiabatic release of a titaniferous mare basalt

A report is presented regarding the dynamic properties of a rock indigenous to the mare basins of the moon. The reported data were obtained in a study of sample 70215, a very titanium-rich basalt (58% pyroxene, 18% ilmenite, 15% plagioclase, 6% olivine, and 3% quartz by weight). This rock is probably representative of a class of the earliest mare-filling extrusive rocks which are exposed on the present lunar surface. Two series of experiments were performed. One set of experiments involved the measuring of Hugoniot and release adiabats to 15.7 GPa with a propellant gun apparatus. In the second set of experiments, a light-gas gun was employed to yield Hugoniot data at about 120 GPa and release states at about 90 GPa. Lunar basalt 70215 appears to be among the densest rocks in the present lunar sample collection, having a crystal density of 3.38 g/cu cm and a porosity of about 1.3%. The results of the experiments have important implications for both the degree of shock metamorphism expected for impact processes and the extent of ejecta transport on mare surfaces with high-titanium basalt composition.

Ahrens, T. J.↗
NASA NTRS1973

Valence-bond study of the /H2, D2/ exchange reaction mechanism.

The exchange reaction of H2 with D2 to form 2 HD is important in that it is fundamentally the simplest four-body exchange reaction and should therefore represent a model system on which various theories of reactions dynamics might be tested. A number of theoretical and experimental investigations carried out on this system are reviewed. It is concluded that a Y yields T yields Y mechanism for the (H2, D2) exchange is not a low energy pathway that would make theory compatible with the shock-tube experiments of Bauer and Ossa (1966) and of Burcat and Lifshits (1967).

Freihaut, B.↗
NASA NTRS1992

Recent results on Mars and Venus; Proceedings of Symposium 3 and the Topical Meetings of the Interdisciplinary Scientific Commission C (Meeting C1) and D (Meeting D1) of the COSPAR 28th Plenary Meeting, The Hague, Netherlands, June 25-July 6, 1990

In this volume, latest results on Mars and Phobos studies are discussed along with recent results on Venus and on Martian plasma environment. Papers are presented on the characteristics of aerosol phenomena in Martian atmosphere from KRFM-experiment data, Phobos map and Phobos globe, submicron-sized dust grains in the Martian environment, remote sensing of Venus atmospheric dynamics, the latitude structure of upper clouds of Venus, and Venus thermospheric response to short-term solar variations. Attention is also given to a comparison between the bow shocks and magnetotails of Venus and Mars, comparative studies of the solar wind interaction with weakly magnetized planets, the magnetic field environment of Mars as studied by Phobos-2, waves and cold plasmas near Mars, and multiple-ion effects at Martian plasma boundaries.

Shorthill, R. W.↗
NASA NTRS1992

Comparison between computational and experimental data for a hypersonic laser propelled vehicle

A 3-D axisymmetric hypersonic engine inlet was investigated using PARC2D, an ideal gas Computational Fluid Dynamics code. The code was used to predict the results of tests conducted in the Rensselaer Polytechnic Institute Hypersonic Shock Tunnel which measured surface and pitot pressures, and shock positions (through Schlieren photography) at freestream Mach numbers of 10, 13, and 15. A strong viscous/shock interaction was observed in both the experiment and the CFD results, due to the model's parabolic compression ramp. Good agreement was found between the experimental results and the CFD solution both for surface pressures and shock positions. Agreement between pitot pressures was less reliable.

Messitt, D. G.↗
NASA NTRS1975

The University of Iowa Helios solar wind plasma wave experiment /E 5a/

This document describes the University of Iowa solar wind plasma wave experiment for the Helios missions (Experiment 5a). The objective of this experiment is the investigation of naturally occurring plasma instabilities and electromagnetic waves in the solar wind. To carry out this investigation, the experiment consists primarily of a 16-channel spectrum analyzer connected to the electric field antennas. The spectrum analyzer covers the frequency range from 20 Hz to 200 kHz and has an amplitude dynamic range which extends from .3 microvolts/m to 30 mV/m per channel. This spectrum analyzer, the antenna potential measurements, the shock alarm system and the supporting electronics are discussed in detail.

Gurnett, D. A.↗
NASA NTRS1986

Molecular dissociation and shock-induced cooling in fluid nitrogen at high densities and temperatures

Radiative temperatures and electrical conductivities were measured for fluid nitrogen compressed dynamically to pressures of 18-90 GPa, temperatures of 4000-14,000 K, and densities of 2-3 g/cu cm. The data show a continuous phase transition above 30 GPa shock pressure and confirm that (delta-P/delta-T)v is less than 0, as indicated previously by Hugoniot equation-of-state experiments. The first observation of shock-induced cooling is also reported. The data are interpreted in terms of molecular dissociation, and the concentration of dissociated molecules is calculated as a function of density and temperature.

Radousky, H. B.↗
NASA NTRS1982

Data reduction and analysis of ISEE magnetometer experiment

The ISEE-1 and -2 magnetometer data was reduced. The up and downstream turbulence associated with interplanetary shocks were studied, including methods of determining shock normals, and the similarities and differences in laminar and quasi-laminar shock structure. The associated up and downstream turbulence was emphasized. The distributions of flux transfer events, field aligned currents in the near tail, and substorm dynamics in the magnetotail were also investigated.

Russell, C. T.↗
NASA NTRS1975

The magnetosheath electron population at lunar distance - General features

A study was made of the electron population in the earth's magnetosheath at lunar distance. The data used were collected by the Apollo 14 charged particle lunar environment experiment (CPLEE) during four inbound (dusk) and three outbound (dawn) passages of the moon through the magnetosheath. The magnetotail has a diameter of 52 earth radii, while the bow-shock cross section is about 91 earth radii. The average boundary locations computed from the complete data set are consistent with the prediction of fluid dynamics. The electron characteristics for the two least-disturbed passages are presented in detail. An examination of the energy spectra shows that a high-energy (200-2000 eV) tail is superimposed on the expected low-energy (40-200 eV) magnetosheath distribution. It is argued that the high-energy magnetosheath electron population originates at the bow shock, rather than from the plasma sheet.

Reiff, P. H.↗
NASA NTRS1972

Dynamics of the inverse pinch.

Experiments are performed on the plasma produced in a large inverse pinch using argon with no applied magnetic fields or preheating. A direct observation is made of the precursor ionization which initially raises the electron temperature and electrical conductivity. Calculations show that most of the mass is entrained in the current sheet, but that less than complete sweeping occurs at the lower velocities. The shock which is embedded in the current sheet closely resembles an ordinary gasdynamic shock. Consideration of the shock jump condition derived from the induction equation is shown to determine the frequent inability of the shock to separate from the current sheet.

Weisbach, M. F.↗
NASA NTRS1974

Preliminary Pioneer 10 encounter results from the Ames Research Center plasma analyzer experiment

Preliminary results from the Ames Research Center plasma analyzer experiment for the Pioneer 10 Jupiter encounter indicate that Jupiter has a detached bow shock and magnetopause similar to the case at Earth but much larger in spatial extent. In contrast to Earth, Jupiter's outer magnetosphere appears to be highly inflated by thermal plasma and therefore highly responsive in size to changes in solar wind dynamic pressure.

Wolfe, J. H.↗