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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A drag measurement technique for free piston shock tunnels

A new technique is described for measuring drag with 100-microsecond rise time on a nonlifting model in a free piston shock tunnel. The technique involves interpretation of the stress waves propagating within the model and its support. A finite element representation and spectral methods are used to obtain a mean square optimal estimate of the time history of the aerodynamic loading. Thus, drag is measured instantaneously and the previous restriction caused by the mechanical time constant of balances is overcome. The effectiveness of the balance is demonstrated by measuring the drag on cones with 5 and 15 deg semi-vertex angles in nominally Mach 5.6 flow with stagnation enthalpies from 2.6 to 33 MJ/kg.

Sanderson, S. R.↗
NASA NTRS2014

Resilient and Corrosion-Proof Rolling Element Bearings Made from Superelastic Ni-Ti Alloys for Aerospace

Mechanical components (bearings, gears, mechanisms) typically utilize hardened construction materials to minimize wear and attain long life. In such components, loaded contact points (e.g., meshing gear teeth, bearing balls-raceway contacts) experience high contact stresses. The combination of high hardness and high elastic modulus often leads to damaging contact stress and denting, particularly during transient overload events such as shock impacts that occur during the launching of space vehicles or the landing of aircraft. In this webinar, Dr. DellaCorte will introduce the results of a research project that employs a superelastic alloy, Ni-Ti for rolling element bearing applications. Bearings and components made from such alloys can alleviate many problems encountered in advanced aerospace applications and may solve many terrestrial applications as well

intermetallics↗
DOE OSTI2023

Three-dimensional full-field velocity measurements in shock compression experiments using stereo digital image correlation

Shock compression plate impact experiments conventionally rely on point-wise velocimetry measurements based on laser-based interferometric techniques. This study presents an experimental methodology to measure the free surface full-field particle velocity in shock compression experiments using high-speed imaging and three-dimensional (3D) digital image correlation (DIC). The experimental setup has a temporal resolution of 100 ns with a spatial resolution varying from 90 to 200 μm/pixel. Experiments were conducted under three different plate impact configurations to measure spatially resolved free surface velocity and validate the experimental technique. First, a normal impact experiment was conducted on polycarbonate to measure the macroscopic full-field normal free surface velocity. Second, an isentropic compression experiment on Y-cut quartz–tungsten carbide assembly is performed to measure the particle velocity for experiments involving ramp compression waves. To explore the capability of the technique in multiaxial loading conditions, a pressure shear plate impact experiment was conducted to measure both the normal and transverse free surface velocities under combined normal and shear loading. The velocities measured in the experiments using digital image correlation are validated against previous data obtained from laser interferometry. Numerical simulations were also performed using established material models to compare and validate the experimental velocity profiles for these different impact configurations. The novel ability of the employed experimental setup to measure full-field free surface velocities with high spatial resolutions in shock compression experiments is demonstrated for the first time in this work.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Design of a shipping fixture for a compact cryomodule hermetic assembly

Two conduction-cooled 915 MHz superconducting radio frequency hermetic assemblies must be safely transported from the Jefferson Lab in Newport News, VA to General Atomics in San Diego, CA for perfor-mance testing in a custom horizontal test cryostat. One hermetic assembly consists of a 2-cell 915 MHz cavity, a coaxial fundamental power coupler, and the warm-to-cold transition beam tubes. The second hermetic assembly consists of a 2-cell 915 MHz cavity only. The assemblies will be transported on a flatbed air-ride trailer over the approximate 4000 km distance. Design requirements included adequate attenuation of 4g vertical axis, 5g beamline axis, and 1.5g lateral axis shock events. The isolation system was designed using helical wire-rope isolators with modal and transient finite element analysis performed in Ansys. Results show shock attenuation of a 10 ms half-sine pulse input to < 1g in the vertical axis, < 1.5g in the beam-line axis, and < 0.5g in the lateral axis for both assem-blies at the specified design loads and all structural stresses are kept below the material yield limits. Addi-tionally, the natural frequencies of both isolation sys-tems adequately attenuate the fundamental modes of the critical structures.

Accelerator Physics↗
NASA NTRSDate not supplied

OVERFLOW Analysis of Supersonic Retropropulsion Testing on a Blunt Mars Entry Vehicle Concept

Supersonic Retropropulsion (SRP) flow over a Hypersonic Inflatable Aerodynamic Decelerator (HIAD) blunt-body vehicle was simulated using the OVERFLOW Computational Fluid Dynamics (CFD) solver. Two nozzle configurations were tested (1E and 1F) as a subset of the seven total configurations in the Descent Systems Study (DSS) testing campaign. A generalized, Adaptive Mesh Refinement (AMR) shock capturing and plume refinement technique was developed and calibrated for producing automatic and optimized grid systems unique to any given testing condition. Simulations were subjected to successive levels of grid refinement in order to determine solution independence from grid resolution. OVERFLOW Reynolds Averaged Navier-Stokes (RANS) solutions produced realistic SRP flow phenomena, including Mach disk normal shocks contained in high-thrust plumes and bow shock triple-points. Solutions for the 1E nozzle configuration were steady. Conversely, a subset of the 1F test conditions were unsteady and exhibited periodic, non-sinsoidal expansions and contractions of the streamwise-oriented plume, resulting in unsteady aerodynamic loads on the vehicle.

Supersonic Retropropulsion↗
DOE OSTI2020

A description of structured waves in shock compressed particulate composites

Dynamic compression of composite materials is of scientific interest because the mechanical mismatch between internal phases challenges continuum theories. Typical assumptions about steady wave propagation and quasi-instantaneous state changes require reexamination along with the need for time-dependent models. To that end, data and models are presented here for the shock compression of an idealized particulate composite. To serve as a generic representative of this material class, a polymer matrix was filled with tungsten particles, ranging from 1 to 50 vol. %. This creates a simple microstructure containing randomly scattered particles with an extreme impedance mismatch to the binding matrix. These materials were parallel plate impact loaded by Al flyers traveling at 1.8–5.0 km/s. Velocimetry provided records of the equilibrium state and the compression wave structure for each case with trends quantified by an empirical fit. The same quantities were also studied as a function of the wave's propagation distance. A homogenized viscoelastic model then made it possible to progress from cataloging trends to making predictions. Starting from a Mie–Gruneisen equation of state, additional time varying terms were added to capture the transient response. After calibration, accurate predictions of the steady wave structure were possible.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2011

Design, Development and Test Challenges: Separation Mechanisms for the Orion Pad Abort-1 Flight Test

On May 6, 2010, NASA launched the first successful integrated flight test, Pad Abort-1, of the Orion Project from the White Sands Missile Range in Las Cruces, New Mexico. This test demonstrated the ability to perform an emergency pad abort of a full-scale 4.8 m diameter, 8200 kg crew capsule. During development of the critical separation mechanisms for this flight test, various challenges were overcome related to environments definition, installation complications, separation joint retraction speed, thruster ordnance development issues, load path validation and significant design loads increases. The Launch Abort System retention and release (LAS R&R) mechanism consisted of 6 discrete structural connections between the LAS and the crew module (CM) simulator, each of which had a preloaded tension tie, Superbolt torque-nut and frangible nut. During the flight test, the frangible nuts were pyrotechnically split, permitting the CM to separate from the LAS. The LAS separation event was the driving case in the shock environment for many co-located hardware items. During development testing, it was necessary to measure the source shock during the separation event so the predicted shock environment could be validated and used for certification testing of multiple hardware items. The Lockheed Martin test team measured the source separation shock due to the LAS R&R function, which dramatically decreased the predicted environment by 90% at 100 Hz. During development testing a hydraulic tensioner was used to preload the joint; however, the joint relaxation with the tensioner proved unsatisfactory so the design was modified to include a Superbolt torque-nut. The observed preload creep during lab testing was 4% after 30 days, with 2.5% occurring in the first 24 hours. The conversion of strain energy (preload) to kinetic energy (retraction) was measured to be 50-75%. Design features and careful monitoring of multiple strain gauges on each tension tie allowed a pure tensile load to be applied after stacking at the launch pad. Following installation, preload in each joint was monitored for 24 hours. Due to unforeseen complications and the influence of temperature on the portable data acquisition system, the team encountered difficulty in tracking the joint relaxation. In some cases, bond-line failure of the strain gauges occurred.

Dinsel, Alison↗
NASA NTRS1995

GHRS observations of mass-loaded flows in Abell 78

Spectroscopic observations of the central star of the planetary nebula Abell 78 were obtained with the Goddard High Resolution Spectrograph (GHRS) onboard the Hubble Space Telescope (HST) in the vicinity of the C IV lambda 1548.2, 1550.8 doublet. We find a series of narrow absorption features superposed on the broad, P Cygni stellar wind profile. These features are seen in both components of the doublet at heliocentric radial velocities of -18, -71, -131, and -192 km/s. At higher velocities, individual components are no longer distinct but, rather, merge into a continuous absorption extending to approximately -385 km/s. This is among the highest velocities ever detected for gas in a planetary nebula. The -18 km/s feature originates in an outer envelope of normal composition, while the -71 km/s feature is produced in the wind-swept shell encircling an irregular wind-blown bubble in the planetary nebula center. The hydrogen-poor ejecta of Abell 78, consisting of dense knots with wind-blown tails, are located in the bubble's interior, in the vicinity of the stellar wind termination shock. The high-velocity C IV lambda 154 absorption features can be explained as due to parcels of ejecta being accelerated to high velocities as they are swept up by the stellar wind during its interaction with dense condensations of H-poor ejecta. As the ablated material is accelerated, it will partially mix with the stellar wind, creating a mass-loaded flow. The abundance anomalies seen at the rim of the bubble attest to the transport of H-poor knot material by such a flow.

Harrington, J. Patrick↗
NASA NTRS1998

Dynamic Load Balancing for Adaptive Unstructured Grids

Dynamic mesh adaptation on unstructured grids is a powerful tool for computing unsteady three-dimensional problems that require grid modifications to efficiently resolve solution features. By locally refining and coarsening the mesh to capture phenomena of interest, such procedures make standard computational methods more cost effective. Highly refined meshes are required to accurately capture shock waves, contact discontinuities, vortices, and shear layers in fluid flow problems. Adaptive meshes have also proved to be useful in several other areas of computational science and engineering like computer vision and graphics, semiconductor device modeling, and structural mechanics. Local mesh adaptation provides the opportunity to obtain solutions that are comparable to those obtained on globally-refined grids but at a much lower cost. Additional information is contained in the original extended abstract.

Biswas, Rupak↗
DOE OSTI2020

Three-dimensional microstructure-explicit and void-explicit mesoscale simulations of detonation of HMX at millimeter sample size scale

Fully three-dimensional (3D) microstructure-explicit and void-explicit mesoscale simulations of the shock-to-detonation (SDT) process of pressed granular HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) are performed. The overall size scale of the models is up to 3 × 3 × 15 mm3, with ∼30 000 grains and 206 265 voids. The models account for the heterogeneous material microstructure, constituent distribution, constituent morphology, and voids. Loading conditions considered involve piston velocities in the range of 600–1200 m/s or pressures in the range of 4–8 GPa. The focus is on analyzing the SDT process and the effects of microstructure and voids on the run-to-detonation distance (RDD). Companion two-dimensional (2D) simulations are also carried out to assess the differences between 2D and 3D. Statistically equivalent microstructure sample sets (SEMSSs) are generated and used for both 2D and 3D, allowing the prediction of the statistical and probabilistic Pop plots (PPs). The predictions are in general agreement with trends in available experimental data in the literature. It is found that both the microstructure (heterogeneous grain size, morphology, and size distribution) and voids significantly affect the RDD and the PPs. These effects are systematically delineated and quantified via the use of SEMSSs with different combinations of attributes. A recently developed probabilistic formulation for the PPs is used to characterize the results, allowing uncertainties in the relations between the shock pressure and RDD arising from material heterogeneities to be quantified. The probabilistic formulation is further used to quantify the confidence levels in the ranked order of influences of different combinations of microstructure and voids on the PPs.

Miller, Christopher (ORCID:0000000206844381)↗
DOE OSTI2022

Crystal plasticity including a phase-field deformation twinning model for the high-rate deformation of cyclotetramethylene tetranitramine

A new finite strain thermomechanical model for the high-rate deformation of the β-polymorph of cyclotetramethylene tetranitramine (β-HMX) has been developed and applied to simulations of plate impact experiments. The crystal plasticity model is based on a model developed previously for RDX (Luscher et al. 2017), which is extended to incorporate deformation twinning. Twinning during normal plate impacts is simulated with a phase-field twin model. First, material parameters governing the kinetics of dislocation slip are calibrated on the subset of simulations which had negative Schmid factors for the twin system. Second, a parametric study of the twin material parameters was performed to find suitable values. Overall, the results of the simulations with the phase-field twinning model are reported for impacts on several crystal orientations. We find that the twin growth decreases with increasing distance from the impact surface because of dissipation of the shock front via dislocation-mediated plasticity, and that the simulated interface velocity with and without phase-field twinning do not show appreciable differences. These modeling results suggest that the significance of twinning in β-HMX cannot be determined with traditional loading configurations and diagnostics.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mechanisms of Mitigating Chloride-Induced Stress Corrosion Cracking of Austenitic Steels by Laser Shock Peening

This study investigates the effect of laser shock peening (LSP) on the chloride-induced stress corrosion cracking (SCC) of 304 austenitic steels. LSP can induce a high compressive residual stress to a depth of 700 µm and plastic deformation structures of dislocations, deformation twins, and stacking faults. Constant-load SCC tests in MgCl2 solution suggested that LSP can retard the crack initiation and slow the crack growth. LSP-treated subsurface layers experience ductile fracture while the central regions exhibit intergranular SCC. The LSP-induced deformation structures may impede dislocation slips, while the LSP-induced compressive residual stress can lessen the stress intensity factor of crack tips and decrease the local stress for film rupture.

Materials Science↗
NASA NTRS1977

A shock isolator for diode laser operation on a closed-cycle refrigerator

A device developed to isolate the diode laser from impact shocks delivered during the expansion phase of the Solvay cycle of a helium refrigerator is briefly described. The device uses intermediate cold stations in the stand-off, which permit the stand-off to be short and rigid while minimizing the thermal load at the diode mount.

Jennings, D. F.↗
NASA NTRS1985

Solar cycle dependence of the location of the Venus bow shock

Initial measurements of the Venus bow shock obtained by Pioneer Venus in 1979 near solar maximum indicated that the bow shock was on average 2.44 RV from the center of the planet in the terminator plane. This is 0.35 RV further from Venus than observed by Venera 9/10 in 1976. In the past this discrepancy has been attributed to some effect of the solar cycle. Recent measurements by Pioneer Venus support this interpretation. In 1980 the distance to the bow shock reached a maximum of 2.45 RV and since then has been almost steadily declining toward the distance measured by Venera near solar minimum. The variation in bow shock position is well correlated with the sunspot number and the F 10.7 cm flux over this period. This behavior is attributed to the variation in the neutral atmosphere of Venus with the solar cycle and its subsequent effect on the mass-loading of the solar wind.

Alexander, C. J.↗
NASA NTRS1993

Correlation of airloads on a two-bladed helicopter rotor

Airloads measured on a two-bladed helicopter rotor in flight during the Ames' Tip Aerodynamic and Acoustic Test are compared with calculations from a comprehensive helicopter analysis (CAMRAD/JA), and the pressures compared with calculations from a full-potential rotor code (FPR). The flight-test results cover an advance ratio range of 0.19 to 0.38. The lowest-speed case is characterized by the presence of significant blade-vortex interactions. Good correlation of peak-to-peak vortex-induced loads and the corresponding pressures is obtained. Results of the correlation for this two-bladed rotor are substantially similar to those for three- and four-bladed rotors, including the tip-vortex core size for best correlation, calculation of the peak-to-peak loads on the retreating side, and calculation of vortex iduced loads on inboard radial stations. The higher-speed cases are characterized by the presence of transonic flow on the outboard sections of the blade. Comparison of calculated and measured airloads on the advancing side is not considered appropriate because the presence of shocks makes chordwise integration of the measured data difficult. However, good correlation of the corresponding pressures is obtained.

Fernandez, Francisco J.↗
NASA NTRS2010

Counterflowing Jet Subsystem Design

A counterflowing jet design (a spacecraft and trans-atmospheric subsystem) employs centrally located, supersonic cold gas jets on the face of the vehicle, ejecting into the oncoming free stream. Depending on the supersonic free-stream conditions and the ejected mass flow rate of the counterflowing jets, the bow shock of the vehicle is moved upstream, further away from the vehicle. This results in an increasing shock standoff distance of the bow shock with a progressively weaker shock. At a critical jet mass flow rate, the bow shock becomes so weak that it is transformed into a series of compression waves spread out in a much wider region, thus significantly modifying the flow that wets the outer surfaces, with an attendant reduction in wave and skin friction drag and aerothermal loads.

Farr, Rebecca↗
DOE OSTI2020

Gas density structure of supersonic flows impinged on by thin blades for laser-plasma accelerator targets

Density transition injection is an effective technique for controllably loading electrons into a trapped phase for laser plasma accelerators. One common technique to achieve the required fluid structure is to impinge a thin blade on the plume of a supersonic nozzle. Density transitions induced in this way are often assumed to be bow shocks and therefore sharp, but simulations and fluorescence measurements presented in this work show that in many cases of interest, the density transition accessible to a laser propagating transverse to the shock is an intercepting shock, and therefore, shock thickness and density vary with pressure, laser height, and blade position. The fluid dynamics of a supersonic nozzle impinged on by a thin, flat object are explored through simulations and relevant features are verified via planar laser-induced fluorescence measurements. Overall, the implications of the results for tuning electron beam injectors in laser plasma accelerators are discussed.

42 ENGINEERING↗