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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Lead-acid battery construction

The power characteristics of a lead-acid battery are improved by incorporating a dispersion of 1 to 10% by weight of a thermodynamically stable conductivity additive, such as conductive tin oxide coated glass fibers (34) of filamentary glass wool (42) in the positive active layer (32) carried on the grid (30) of the positive plate (16). The avoiding of positive plate reversal to prevent reduction of the tin oxide is accomplished by (a) employing an oversized positive plate and pre-charging it; (b) by pre-discharging the negative plate; and/or (c) by placing a circuit breaker (26) in combination with the plates (16, 18) and terminals (22, 24) to remove the load when the voltage of the positive plate falls below a pre-selected level.

Rowlette, John J.↗
NASA NTRS2015

Electronegative Gas Thruster

The project is an international collaboration and academic partnership to mature an innovative electric propulsion thruster concept to Technology Research Level-3 (TRL-3) through direct thrust measurement. The project includes application assessment of the technology ranging from small spacecraft to high power. The Plasma propulsion with Electronegative GASES(PEGASES) basic proof of concept has been matured to TRL-2 by Ane Aanesland of Laboratoire de Physique des Plasma at Ecole Polytechnique. The concept has advantages through eliminating the neutralizer requirement and should yield longer life and lower cost over conventional gridded ion engines. The objective of this research is to validate the proof of concept through the first direct thrust measurements and mature the concept to TRL-3.

Dankanich, John↗
NASA NTRSDate not supplied

Comparison of Inlet Broadband Acoustic Liner Predictions to Quiet Technology Demonstrator 3 Flight Data

Companion acoustic liner attenuation predictions and flight data representative of certification conditions are analyzed to determine the validation quality and gain an understanding of current prediction shortcomings. These comparisons are limited to the inlet broadband component of fan noise. Two prediction methods are assessed: a traditional, semiempirical model, and a computational approach with a parabolic duct propagation code coupled with a Ffowcs Williams-Hawkings solver for free-field propagation. The semiempirical method is widely used for aircraft system noise predictions, but does not explicitly account for several physical parameters important for sound attenuation. The computational approach includes these effects, but requires a significant increase in cycle time. For the three-degree-of-freedom (3DOF) liner tested, both methods have a bias error less than 0.5 dB for cutback and takeoff power settings, and a much larger 3–4 dB bias for approach power setting. The standard deviation of each method varies between 1–2 dB for different conditions. The similar performance of both approaches illustrates that, in this instance, the additional complexity of the computational approach does not provide a clear improvement over the semiempirical method. Planned improvements to the numerical grid and source assumptions may result in reevaluation of this conclusion in later work.

aircraft system noise↗
NASA NTRS2013

Ion Beam Deflection (AKA Push-Me/Pull-You)

The Ion Beam Deflection provides the following potential advantages over other asteroid deflection systems. Like the gravity tractor, it doesn't require despinning of the asteroid. Unlike the gravity tractor, it provides a significantly higher coupling force that is independent of the asteroid size. The concept could be tested as part of the baseline Asteroid Redirect Robotic Mission. The thrust and total impulse are entirely within the design of the SEP vehicle. The total impulse is potentially competitive with kinetic impactors and eliminates the need for a second rendezvous spacecraft.Gridded ion thrusters provide beam divergence angles of a few degrees enabling long stand-off distances from the asteroid. Mitigating control issues. Minimizing back-sputter contamination risks

high-power, low-beam-divergence ion thruster (NEXI↗
NASA NTRS1993

Computational Fluid Dynamics (CFD) applications in rocket propulsion analysis and design

Computational Fluid Dynamics (CFD) has been used in recent applications to affect subcomponent designs in liquid propulsion rocket engines. This paper elucidates three such applications for turbine stage, pump stage, and combustor chamber geometries. Details of these applications include the development of a high turning airfoil for a gas generator (GG) powered, liquid oxygen (LOX) turbopump, single-stage turbine using CFD as an integral part of the design process. CFD application to pump stage design has emphasized analysis of inducers, impellers, and diffuser/volute sections. Improvements in pump stage impeller discharge flow uniformity have been seen through CFD optimization on coarse grid models. In the area of combustor design, recent CFD analysis of a film cooled ablating combustion chamber has been used to quantify the interaction between film cooling rate, chamber wall contraction angle, and geometry and their effects of these quantities on local wall temperature. The results are currently guiding combustion chamber design and coolant flow rate for an upcoming subcomponent test. Critical aspects of successful integration of CFD into the design cycle includes a close-coupling of CFD and design organizations, quick turnaround of parametric analyses once a baseline CFD benchmark has been established, and the use of CFD methodology and approaches that address pertinent design issues. In this latter area, some problem details can be simplified while retaining key physical aspects to maintain analytical integrity.

Mcconnaughey, P. K.↗
NASA NTRS1994

The length-scaling properties of topography

The scaling properties of synthetic topographic surfaces and digital elevation models (DEMs) of topography are examined by analyzing their 'structure functions,' i.e., the qth order powers of the absolute elevation differences: delta h(sub q) (l) = E((absolute value of h(x + l) - h(x))(exp q)). We find that the relation delta h(sub 1 l) approximately equal cl(exp H) describes well the scaling behavior of natural topographic surfaces, as represented by DEMs gridded at 3 arc sec. Average values of the scaling exponent H between approximately 0.5 and 0.7 characterize DEMs from Ethiopia, Saudi Arabia, and Somalia over 3 orders of magnitude range in length scale l (approximately 0.1-150 km). Differences in appparent topographic roughness among the three areas most likely reflect differences in the amplitude factor c. Separate determination of scaling properties in the x and y coordinate directions allows us to assess whether scaling exponents are azimuthally dependent (anisotropic) or whether they are isotropic while the surface itself is anisotropic over a restricted range of length scale. We explore ways to determine whether topographic surfaces are characterized by simple or multiscaling properties.

Weissel, Jeffrey K.↗
NASA NTRS1995

Safety analysis

We are engaged in a research program in safety-critical computing that is based on two case studies. We use these case studies to provide application-specific details of the various research issues, and as targets for evaluation of research ideas. The first case study is the Magnetic Stereotaxis System (MSS), an investigational device for performing human neurosurgery being developed in a joint effort between the Department of Physics at the University of Virginia and the Department of Neurosurgery at the University of Iowa. The system operates by manipulating a small permanent magnet (known as a 'seed') within the brain using an externally applied magnetic field. By varying the magnitude and gradient of the external magnetic field, the seed can be moved along a non-linear path and positioned at a site requiring therapy, e.g., a tumor. The magnetic field required for movement through brain tissue is extremely high, and is generated by a set of six superconducting magnets located in a housing surrounding the patient's head. The system uses two X-ray cameras positioned at right angles to detect in real time the locations of the seed and of X-ray opaque markers affixed to the patient's skull. the X-ray images are used to locate the objects of interest in a canonical frame of reference. the second case study is the University of Virginia Research Nuclear Reactor (UVAR). It is a 2 MW thermal, concrete-walled pool reactor. The system operates using 20 to 25 plate-type fuel assemblies placed on a rectangular grid plate. There are three scramable safety rods, and one non-scramable regulating rod that can be put in automatic mode. It was originally constructed in 1959 as a 1 MW system, and it was upgraded to 2 MW in 1973. Though only a research reactor rather than a power reactor, the issues raised are significant and can be related to the problems faced by full-scale reactor systems.

Knight, John C.↗
NASA NTRS2002

Visualizing Spatially Varying Distribution Data

Box plot is a compact representation that encodes the minimum, maximum, mean, median, and quarters information of a distribution. In practice, a single box plot is drawn for each variable of interest. With the advent of more accessible computing power, we are now facing the problem of visual icing data where there is a distribution at each 2D spatial location. Simply extending the box plot technique to distributions over 2D domain is not straightforward. One challenge is reducing the visual clutter if a box plot is drawn over each grid location in the 2D domain. This paper presents and discusses two general approaches, using parametric statistics and shape descriptors, to present 2D distribution data sets. Both approaches provide additional insights compared to the traditional box plot technique

Kao, David↗
NASA NTRS2008

Investigation of Flow Instabilities in the Inlet Ducts of DP-1C VTOL Aircraft

An investigation of flow instabilities in the inlet ducts of a two-engine vertical takeoff and landing aircraft DP-1C is described in this report. Recent tests revealed that the engines stall during run ups while the aircraft is operating on the ground. These pop stalls occurred at relatively low power levels, sometimes as low as 60 percent of the engine full speed. Inability to run the engines up to the full speed level is attributed to in-ground effects associated with hot gas ingestion. Such pop stalls were never experienced when the aircraft was tested on a elevated grid platform, which ensured that the aircraft was operating in out-of-the-ground-effect conditions. Based on available information on problems experienced with other vertical takeoff and landing aircraft designs, it was assumed that the engine stalls were caused by partial ingestion of hot gases streaming forward from the main exit nozzle under the aircraft inlets, which are very close to the ground. It was also suggested that the nose wheel undercarriage, located between the inlets, may generate vortices or an unstable wake causing intense mixing of hot exit gases with incoming inlet flow, which would enhance the hot gas ingestion. After running a short three-day series of tests with fully instrumented engine inlets, it is now believed the most probable reason for engine pop stalls are random ingestions of a vortex generated between the two streams moving in opposite directions: outbound hot gas stream from the main nozzle close to the ground and inbound inlet flow above. Originally, the vortex is in a horizontal plane. However, at a certain velocity ratio of these two streams, the vortex attaches either to the ground or the aircraft surface at one end and the other end is swallowed by one of the aircraft inlets. Once the vortex enters the inlet duct, a puff of hot air can be sucked through the vortex core into the engine, which causes a serious inlet flow field distortion followed by an engine stall. Once the engine stalls, the outflow from the inlet pushes the vortex away and the engine resumes normal operation. This hypothesis needs to be verified experimentally; e.g., by extensive smoke flow visualization ahead of the aircraft inlets.

Lepicovsky, Jan↗
NASA NTRS2017

Comparison of Satellite Rainfall Estimates and Rain Gauge Measurements in Italy, and Impact on Landslide Modeling

Landslides can be triggered by intense or prolonged rainfall. Rain gauge measurements are commonly used to predict landslides even if satellite rainfall estimates are available. Recent research focuses on the comparison of satellite estimates and gauge measurements. The rain gauge data from the Italian network (collected in the system database Verifica Rischio Frana" (VRF)) are compared with the National Aeronautics and Space Administration (NASA) Tropical Rainfall Measuring Mission (TRMM) products. For the purpose, we couple point gauge and satellite rainfall estimates at individual grid cells, evaluating the correlation between gauge and satellite data in different morpho-climatological conditions. We then analyze the statistical distributions of both rainfall data types and the rainfall events derived from them. Results show that satellite data underestimates ground data, with the largest differences in mountainous areas. Power-law models, are more appropriate to correlate gauge and satellite data. The gauge and satellite-based products exhibit different statistical distributions and the rainfall events derived from them differ. In conclusion, satellite rainfall cannot be directly compared with ground data, requiring local investigation to account for specific morpho-climatological settings. Results suggest that satellite data can be used for forecasting landslides, only performing a local scaling between satellite and ground data.

landslide; satellite rainfall; TRMM; rain gauges; ↗
NASA NTRS1975

Experimental evaluation of trailing edge and incidence fluctuation noise theories

Tests were conducted to evaluate conflicting theories for trailing edge noise and for incidence fluctuation noise. A flat-plate airfoil with flush-mounted surface pressure transducers was tested in an anechoic wind tunnel at velocities from 31.5 to 177 m/sec and nominal 4 and 6% grid-generated turbulence levels. In one series of runs, the airfoil was faired into the tunnel nozzle and extended beyond the nozzle lip for studies of trailing edge noise without a leading edge and with flow on only one side. Such noise was found to vary with velocity to the fifth power and turbulence level squared as predicted by Ffowcs Williams and Hall (1970) and by Chase (1972). Power spectral density at high frequencies decayed approximately inversely with frequency to the 10/3 power as predicted by Chase. The data were poorly predicted by Hayden's correlation (1969, 1972).

Fink, M. R.↗
NASA NTRS1976

Electric-discharge-pumped nitrogen ion laser

The routine operation is described of an N2(+) laser oscillating on the first negative band system of N2(+) which is produced in a preionized transverse discharge device. The discharge design incorporates features which favor the efficient production of the excitation transfer reaction of He2(+) with N2. A capacitive discharge switched by means of a high-current grounded grid thyratron is used to meet the design requirement of a volumetric discharge in high-pressure gas mixtures where the electric discharge need not have an ultrafast rise time (greater than 10 nsec) but should be capable of transferring large quantities of stored electric energy to the gas. A peak power of 180 kW in an 8-nsec laser pulse was obtained with a 0.1% mixture of N2 in helium at a total pressure of 3 atm. The most intense laser oscillations were observed on the (0,1) vibrational transition at 427.8 microns.

Laudenslager, J. B.↗
NASA NTRS1993

Direct simulation of isothermal-wall supersonic channel flow

The motivation for this work is the fact that in turbulent flows where compressibility effects are important, they are often poorly understood. A few examples of such flows are those associated with astrophysical phenomena and those found in combustion chambers, supersonic diffusers and nozzles, and over high-speed airfoils. For this project, we are primarily interested in compressibility effects near solid surfaces. Our main objective is an improved understanding of the fundamentals of compressible wall-bounded turbulence, which can in turn be used to cast light upon modeling concepts such as the Morkovin hypothesis and the Van Driest transformation. To this end, we have performed a direct numerical simulation (DNS) study of supersonic turbulent flow in a plane channel with constant-temperature walls. All of the relevant spatial and temporal scales are resolved so that no sub grid scale or turbulence model is necessary. The channel geometry was chosen so that finite Mach number effects can be isolated by comparing the present results to well established incompressible channel data. Here the fluid is assumed to be an ideal gas with constant specific heats, constant Prandtl number, and power-law temperature-dependent viscosity. Isothermal-wall boundary conditions are imposed so that a statistically stationary state may be obtained. The flow is driven by a uniform (in space) body force (rather than a mean pressure gradient) to preserve stream wise homogeneity, with the body force defined so that the total mass flux is constant.

Coleman, Gary N.↗
NASA NTRS2003

Development of a Thin Film Solar Cell Interconnect for the Powersphere Concept

Progressive development of microsatellite technologies has resulted in increased demand for lightweight electrical power subsystems including solar arrays. The use of thin film photovoltaics has been recognized as a key solution to meet the power needs. The lightweight cells can generate sufficient power and still meet critical mass requirements. Commercially available solar cells produced on lightweight substrates are being studied as an option to fulfill the power needs. The commercially available solar cells are relatively inexpensive and have a high payoff potential. Commercially available thin film solar cells are primarily being produced for terrestrial applications. The need to convert the solar cell from a terrestrial to a space compatible application is the primary challenge. Solar cell contacts, grids and interconnects need to be designed to be atomic oxygen resistant and withstand rapid thermal cycling environments. A mechanically robust solar cell interconnect is also required in order to withstand handling during fabrication and survive during launch. The need to produce the solar cell interconnects has been identified as a primary goal of the Powersphere program and is the topic of this paper. Details of the trade study leading to the final design involving the solar cell wrap around contact, flex blanket, welding process, and frame will be presented at the conference.

Simburger, Edward J.↗
NASA NTRS2006

Electrodynamic Tether as a Thruster for LEO Mission Applications

Electrodynamic tether propulsion has a number of attractive features and has been widely discussed for different low earth orbit applications. Despite the commonality of application, the choice of the proper design for any particular mission is a unique problem. The flight trajectory, duration, available power and voltage, and drag force should be taken into consideration with other mission requirements. Characteristics of tether performance such as system acceleration and electrical efficiency should be calculated and assessed based on the system's capability to collect electrical current. We discuss the choice of parameters for circular, tape, and grid-sphere tether anodes and their applicability to International Space Station (ISS) reboost and Momentum Exchange Electrodynamic Reboost (MXER) applications.

Khazanov, G. V↗
NASA NTRS2005

Ferroelectric Devices Emit Charged Particles and Radiation

Devices called solid-state ferroelectric- based sources (SSFBSs) are under development as sources of electrons, ions, ultraviolet light, and x-rays for diverse applications in characterization and processing of materials. Whereas heretofore it has been necessary to use a different device to generate each of the aforementioned species of charged particles or radiation, a single SSFBS can be configured and operated to selectively generate any of the species as needed using a single source. Relative to comparable prior sources based, variously, on field emission, thermionic emission, and gaseous discharge plasmas, SSFBSs demand less power, and are compact and lightweight. An SSFBS exploits the unique physical characteristics of a ferroelectric material in the presence of a high-frequency pulsed electric field. The basic building block of an SSFBS is a ferroelectric cathode -- a ferroelectric wafer with a solid electrode covering its rear face and a grid electrode on its front face (see figure). The application of a voltage pulse -- typically having amplitude of several kilovolts and duration of several nanoseconds -- causes dense surface plasma to form near the grid wires on the front surface.

Bar-Cohen, Yoseph↗
NASA NTRS1991

Developing and utilizing an Euler computational method for predicting the airframe/propulsion effects for an aft-mounted turboprop transport. Volume 2: User guide

This manual explains how to use an Euler based computational method for predicting the airframe/propulsion integration effects for an aft-mounted turboprop transport. The propeller power effects are simulated by the actuator disk concept. This method consists of global flow field analysis and the embedded flow solution for predicting the detailed flow characteristics in the local vicinity of an aft-mounted propfan engine. The computational procedure includes the use of several computer programs performing four main functions: grid generation, Euler solution, grid embedding, and streamline tracing. This user's guide provides information for these programs, including input data preparations with sample input decks, output descriptions, and sample Unix scripts for program execution in the UNICOS environment.

Chen, H. C.↗
NASA NTRS1996

Analysis of Flowfields over Four-Engine DC-X Rockets

The objective of this study is to validate a computational methodology for the aerodynamic performance of an advanced conical launch vehicle configuration. The computational methodology is based on a three-dimensional, viscous flow, pressure-based computational fluid dynamics formulation. Both wind-tunnel and ascent flight-test data are used for validation. Emphasis is placed on multiple-engine power-on effects. Computational characterization of the base drag in the critical subsonic regime is the focus of the validation effort; until recently, almost no multiple-engine data existed for a conical launch vehicle configuration. Parametric studies using high-order difference schemes are performed for the cold-flow tests, whereas grid studies are conducted for the flight tests. The computed vehicle axial force coefficients, forebody, aftbody, and base surface pressures compare favorably with those of tests. The results demonstrate that with adequate grid density and proper distribution, a high-order difference scheme, finite rate afterburning kinetics to model the plume chemistry, and a suitable turbulence model to describe separated flows, plume/air mixing, and boundary layers, computational fluid dynamics is a tool that can be used to predict the low-speed aerodynamic performance for rocket design and operations.

Wang, Ten-See↗