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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Why ionizing radiation enhances surface wettability

Radiation-Induced Surface Activation is an inherent phenomenon where surfaces that are exposed to gamma irradiation are observed to undergo an increase in wettability. This increase in wettability as a result of the ionizing radiation exposure has so far been demonstrated to have a pronounced impact on Leidenfrost temperature and two-phase fluid dynamics. Test results from previous experiments have shown that incorporation of this effect on heat transfer equipment design may increase the thermal-hydraulic margin leading to higher thermal efficiency. However, the mechanism behind the increased wettability is not clearly understood. In the present work, three different materials (Zircaloy-4, 316 stainless steel, and copper) were exposed at two different dose rates with use of two different gamma irradiation facilities. A detailed surface characterization on the post-irradiated samples is carried out to understand the changes in surface chemistry, wettability and surface morphology. It is observed from the experiments that the increase in wettability upon irradiation depended on the total dose and not on the dose rate. Moreover, localized oxidation and porosity induced by radiolysis was seen to be the predominant mechanism behind increased wettability which leads to improved Leidenfrost temperature.

Seshadria, Arunkumar↗
NASA NTRS1977

On the fragmentation of cosmic gas clouds. II - Opacity-limited star formation

Opacity-limited fragmentation of gravitationally collapsing gas clouds is reexamined with inclusion of realistic dust-grain opacities and cooling rates. A minimum fragment size of approximately 0.01 solar mass is found in spherical collapse, but may be the same or larger for spheroidal collapse. A simple analytic expression is given for the characteristic protostellar mass above which further fragmentation can occur during the early opaque phases of dynamical protostellar collapse. The effects of rotation, fragment collisions, and magnetic fields are also discussed.

Silk, J.↗
NASA NTRS1977

The multiple nesting of mesoscale, submesoscale, and nonhydrostatic microscale numerical models for a case of mesocyclogenesis and severe storm development

A fundamental approach involving the integration of two different numerical models over several different spatial mesh lengths is considered. Model I is a hydrostatic, incompressible, and adiabatic primitive (Newtonian) equation set with no boundary layer forcing, i.e., surface heat or moisture flux or external frictional stresses. Typically this model is initialized from conventional radiosonde data and run for a 12-15 hour forecast period over a 40 km horizontal mesh. If phase I of the tornado developmental processes develops, the data is 'frozen' in space and time, interpolated to a 20 km mesh, and integrated for a shorter time period (3 hours) with a shorter time step. Model II is a nonhydrostatic compressible 18-level complement of model I. If model II indicates the development of the intensification of phase V dynamical processes, the data is frozen and interpolated to finer mesh lengths until the tornadic circulation system is approximated

Kaplan, M. L.↗
NASA NTRS1980

Protostellar formation in rotating interstellar clouds. II - Axially symmetric collapse

A two spatial dimension gravitational hydrodynamics code has been used to calculate the initial isothermal dynamic collapse phase of axially symmetric, rotating interstellar clouds. The Eulerian code has been constructed so as to conserve angular momentum both locally (approximately) and globally (exactly). An axially symmetric, rotating cloud collapses to form a rotating, near-equilibrium ring. The rings so formed are compared with those found previously by Black and Bodenheimer, and Bodenheimer and Tscharnuter, and found to agree in structure fairly well. Numerical tests with the code, as well as an analytic calculation of the collapse of a pressureless, rotating, axially symmetric cloud in a fixed gravitational potential, support the assertion that the observed ring formation is physically realistic.

Boss, A. P.↗
NASA NTRS1980

Fluid dynamics of the unsteady two phase processes leading to DDT in granular solid propellants

Deflagration to Detonation (DDT) was predicted to occur in porous beds of high-energy solid propellants by solving the unsteady fluid mechanical convective heat transfer from hot gas products, obtained from the rapid burning at high pressures, provides the impetus to develop a narrow combustion zone and a resulting strong shock. A parametric study clearly indicates that DDT occurs only when a combination of the solids loading fraction, the burning rate constants, the propellant chemical energy, and the particle size provide for critical energy and gas release to support a detonation wave. Predictions for the run-up length to detonation as a function of these parameters are presented.

Krier, H.↗
NASA NTRS1985

Liquid rocket combustor computer code development

The Advanced Rocket Injector/Combustor Code (ARICC) that has been developed to model the complete chemical/fluid/thermal processes occurring inside rocket combustion chambers are highlighted. The code, derived from the CONCHAS-SPRAY code originally developed at Los Alamos National Laboratory incorporates powerful features such as the ability to model complex injector combustion chamber geometries, Lagrangian tracking of droplets, full chemical equilibrium and kinetic reactions for multiple species, a fractional volume of fluid (VOF) description of liquid jet injection in addition to the gaseous phase fluid dynamics, and turbulent mass, energy, and momentum transport. Atomization and droplet dynamic models from earlier generation codes are transplated into the present code. Currently, ARICC is specialized for liquid oxygen/hydrogen propellants, although other fuel/oxidizer pairs can be easily substituted.

Liang, P. Y.↗
NASA NTRS1985

Diffusion and localization of a particle in a periodic potential coupled to a dissipative environment

The phase diagram of a Hamiltonian which describes a particle moving in a periodic potential and coupled to an external heat bath has been analyzed in detail. By renormalization-group methods, it is proved that this system exhibits an unusual transition between diffusive behavior and a self-trapped phase. The dynamics along the transition line is shown to be integrable and the order parameter, the mobility, is computed exactly.

Guinea, F.↗
NASA NTRS1986

Protostellar formation in rotating interstellar clouds. V - Nonisothermal collapse and fragmentation

Numerical calculations are presented for rigorous models spanning a four-dimensional parameter space of initial conditions of the three-dimensional collapse of rotating protostellar clouds, encompassing radiative transfer in the Eddington approximation and detailed thermodynamical relations. It is found that protostellar formation may involve a few stages of hierarchical fragmentation terminated by increased thermal pressure in the nonisothermal regime, that high thermal energy clouds remain nearly axisymmetric during the first dynamic collapse phase, and that very slowly rotating clouds can fragment. The presolar nebula was probably formed from a cloud with very little initial rotation.

Boss, Alan R.↗
NASA NTRS1987

The microbursts of 22 June 1982 in JAWS

The development of several large thunderstorms that occurred on June 22, 1982 within the Joint Airport Weather Studies (JAWS) network near Denver, Colorado is examined together with that of six microbursts and one microburst line produced by the storms. From the analysis of single and multiple Doppler radar and surface network data, it is concluded that the microbursts on June 22 were predominantly driven by microphysical and related thermodynamic effects due to precipitation loading and water-phase change; dynamic effects did not appear to be of primary importance. Surface network observations permitted identification of some of the microbursts, but early detection was not possible.

Hjelmfelt, M. R.↗
NASA NTRS1987

Protostellar formation in rotating interstellar clouds. VI - Nonuniform initial conditions

The collapse and fragmentation of rotating protostellar clouds is explored, starting from nonuniform density and nonuniform rotation initial conditions. Whether binary fragmentation occurs during the first dynamic collapse phase depends strongly on the initial density profile. Exponential clouds are only somewhat more resistant to fragmentation than uniform-density clouds, but power-law clouds do not undergo fragmentation for likely values of a relevant parameter. Because binary fragments start from profiles intermediate between uniform density and exponential clouds, minimum protostellar mass for population I stars should be increased to approximately 0.02 solar mass. The axisymmetric Terey et al. (1984) model should be stable with respect to nonaxisymmetric perturbations. Considering the observed binary frequency, collapse from power-law initial conditions appears to be less common than collapse from more uniform initial conditions.

Boss, Alan P.↗
NASA NTRS1989

A simple nonlinear model for the return to isotropy in turbulence

A quadratic nonlinear generalization of the linear Rotta model for the slow pressure-strain correlation of turbulence is developed. The model is shown to satisfy realizability and to give rise to no stable non-trivial equilibrium solutions for the anisotropy tensor in the case of vanishing mean velocity gradients. The absence of stable non-trivial equilibrium solutions is a necessary condition to ensure that the model predicts a return to isotropy for all relaxational turbulent flows. Both the phase space dynamics and the temporal behavior of the model are examined and compared against experimental data for the return to isotropy problem. It is demonstrated that the quadratic model successfully captures the experimental trends which clearly exhibit nonlinear behavior. Direct comparisons are also made with the predictions of the Rotta model and the Lumley model.

Sarkar, Sutanu↗
NASA NTRS1989

Mass flow in interacting binaries observed in the ultraviolet

Recent satellite observations of close binary systems show that practically all binaries exhibit evidence of mass flow and that, where the observations are sufficiently detailed, a fraction of the matter flowing out of the mass-losing component is accreted by the companion and the remainder is lost from the binary system. The mass flow is not conservative. During the phase of dynamic mass flow, the companion star becomes immersed in optically-thick plasma and the physical properties of that star elude close scrutiny.

Kondo, Yoji↗
NASA NTRS1986

Independent Orbiter Assessment (IOA): Analysis of the body flap subsystem

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items (PCIs). To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The independent analysis results for the Orbiter Body Flap (BF) subsystem hardware are documented. The BF is a large aerosurface located at the trailing edge of the lower aft fuselage of the Orbiter. The proper function of the BF is essential during the dynamic flight phases of ascent and entry. During the ascent phase of flight, the BF trails in a fixed position. For entry, the BF provides elevon load relief, trim control, and acts as a heat shield for the main engines. Specifically, the BF hardware comprises the following components: Power Drive Unit (PDU), rotary actuators, and torque tubes. The IOA analysis process utilized available BF hardware drawings and schematics for defining hardware assemblies, components, and hardware items. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode. Of the 35 failure modes analyzed, 19 were determined to be PCIs.

Wilson, R. E.↗
NASA NTRS1986

Independent Orbiter Assessment (IOA): Analysis of the elevon subsystem

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. This report documents the independent analysis results for the Orbiter Elevon system hardware. The elevon actuators are located at the trailing edge of the wing surface. The proper function of the elevons is essential during the dynamic flight phases of ascent and entry. In the ascent phase of flight, the elevons are used for relieving high wing loads. For entry, the elevons are used to pitch and roll the vehicle. Specifically, the elevon system hardware comprises the following components: flow cutoff valve; switching valve; electro-hydraulic (EH) servoactuator; secondary delta pressure transducer; bypass valve; power valve; power valve check valve; primary actuator; primary delta pressure transducer; and primary actuator position transducer. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode. Of the 25 failure modes analyzed, 18 were determined to be PCIs.

Wilson, R. E.↗
NASA NTRS1990

A simple nonlinear model for the return to isotropy in turbulence

A quadratic nonlinear generalization of the linear Rotta model for the slow pressure-strain correlation of turbulence is developed. The model is shown to satisfy realizability and to give rise to no stable nontrivial equilibrium solutions for the anisotropy tensor in the case of vanishing mean velocity gradients. The absence of stable nontrivial equilibrium solutions is a necessary condition to ensure that the model predicts a return to isotropy for all relaxational turbulent flows. Both the phase space dynamics and the temporal behavior of the model are examined and compared against experimental data for the return to isotropy problem. It is demonstrated that the quadratic model successfully captures the experimental trends which clearly exhibit nonlinear behavior. Direct comparisons are also made with the predictions of the Rotta model and the Lumley model.

Sarkar, Sutanu↗
NASA NTRS1990

Long-term compression effects on elastomeric O-ring behavior

This paper discusses the results of testing performed on elastomeric seal materials that had been under compression for extended periods of time. Elastomeric seals used in the Space Shuttle redesigned solid rocket motors can experience compression times of up to six months. These seals must be capable of sealing internal motor pressure upon ignition. The tests described herein were performed in order to verify that the seals, which had experienced long-term compression could seal throughout motor operation. Testing was divided into two phases: (1) dynamic high pressure testing, and (2) resiliency testing. Dynamic testing was performed using specialized test fixtures that allowed simulation of the field joint movements during initial motor operation along with high pressure gas. Resiliency testing was performed using specialized test fixtures that also simulated field joint movements and also had the ability to measure the sealing force of the O-ring. Results from all testing indicated that the current elastomeric seals used in the redesigned solid rocket motors will seal during motor operations in the currently defined launch environments.

Clinton, R. G.↗
NASA NTRS1991

Status of heavy rain tests

The heavy rain effects program is presented in the form of the view-graphs. The following topics are covered: rain effects on airfoil performance; two-phase flow dynamics; wind tunnel test results; issues; large-scale results; and summary.

Bezos, Gaudy↗