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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The subtropical mesospheric jet observed by the Nimbus 7 Limb Infrared Monitor of the Stratosphere

Nimbus 7 Limb Infrared Monitor of the Stratosphere observations of wave-mean flow interactions in the winter 1978-1979 middle atmosphere are surveyed, extending up to 0.05 mbar. These observations describe the evolution of the subtropical mesospheric jet and its polar mixed layer. Quasi-steady mean wind patterns are disrupted by three transitions in this winter: one primarily affecting the mesosphere (December 15, 1978), a minor warming affecting both regions (January 26-February 8, 1979), and a major warming largely confined to the stratosphere (February 22, 1979). The zonally averaged flow is barotropically unstable in the wings of the subtropical mesospheric jet. All the major decelerations of the mean flow are correlated with D(F), the body force per unit mass directly attributable to planetary Rossby waves, indicating that these waves make a significant contribution to the momentum budget in the lower half of the mesosphere.

Dunkerton, T. J.↗
NASA NTRS1974

Jet exhaust noise suppressor

Noise suppression for a jet engine exhaust is provided by an annular divergent body attached to an exhaust nozzle. The smallest diameter of the divergent body is larger than the diameter of the exhaust nozzle exit to form an annular step which produces a shock wave in the exhaust as it passes the step. An annular shroud is disposed around the divergent body and causes outside air to pass through voids in the divergent body to mix with the jet exhaust gas. The divergent body includes a plurality of channels with separators between the channels.

Huff, R. G.↗
NASA NTRS2023

Variably Premixed Rotating Detonation Engine for Evaluation of Detonation Cycle Dynamics

A variably premixed rotating detonation engine using gaseous hydrogen and air reactants is introduced to enable investigation of key cycle processes while varying the homogeneity of the reactant inlet conditions. Two chamber configurations are investigated, the first with reactants filling the entire span of a straight annular channel and the second with a slightly larger channel and a backward-facing step. The first configuration permits both premixed and non-premixed fuel injection, enabling mixing quality modulation. The second configuration is operated only at fully premixed conditions. Operating modes and detonation wave speeds are characterized using exhaust-plume imaging, while the chamber heat release field is captured by transverse imaging through a transparent outer body. Tests using the first configuration were characterized by unstable counterpropagating modes with low detonation wave speeds regardless of the state of premixing, while the second configuration rendered single-wave behavior with wave speeds up to 86% of the Chapman–Jouguet velocity. Comparisons with a simple computational fluid dynamics model of the second configuration indicate that reactant preheating significantly influences the detonation wave topology, highlighting the potential utility of the test platform for isolating key physics associated with the effects of reactant premixing, preheating, and chamber geometry on rotating detonation engine operation.

Detonation↗
NASA NTRS2020

Elastic wave analyzer for icy sub-surfaces (EWAIS) in the solar system

The sub-surface structures of water-bearing icy worlds (e.g., Europa, Enceladus, and Titan) and the structures of icy regions on Mars contain critical information about their origin and evolution. These bodies have been identified as high-priority targets in the NRC Planetary Science Decadal Survey, which noted a lack of technology readiness as one impediment to related missions. An Elastic Wave Analyzer for Icy Sub-surfaces (EWAIS) instrument is being developed to acquire data that can provide answers to fundamental science questions related to these bodies. The EWAIS instrument generates and receives elastic waves using an array of piezoelectric transducers capable of operating at temperatures as low as 30K. A developed breadboard acquires reflected signals from discontinuities in the traveled materials’ impedance (the product of wave velocity and density) along the wave path. Analysis of the acquired data can be used to determine the elastic properties, presence of cracks, locations of cavities and other discontinuities, as well as the thicknesses of ice and liquid layers. The EWAIS instrument is being developed with a novel dual-frequency transmitter array that will enable reaching distances of kilometers through ice, as well as resolving smaller acoustic reflectors nearer the EWAIS instrument. The selected dual frequencies correspond to two depth ranges that can be analyzed, with resolutions of tens of centimeters in the region of tens to hundreds of meters and tens of meters on the kilometers scale, respectively. The EWAIS will be applicable for operation from any in-situ platform, including surface assets (e.g., lander and rover) and sub-surface assets (e.g., melting probes).

Bar-Cohen, Y.↗
NASA NTRS2012

Vibration Propagation of Gear Dynamics in a Gear-Bearing-Housing System Using Mathematical Modeling and Finite Element Analysis

Vibration and noise caused by gear dynamics at the meshing teeth propagate through power transmission components to the surrounding environment. This study is devoted to developing computational tools to investigate the vibro-acoustic propagation of gear dynamics through a gearbox using different bearings. Detailed finite element/contact mechanics and boundary element models of the gear/bearing/housing system are established to compute the system vibration and noise propagation. Both vibration and acoustic models are validated by experiments including the vibration modal testing and sound field measurements. The effectiveness of each bearing type to disrupt vibration propagation is speed-dependent. Housing plays an important role in noise radiation .It, however, has limited effects on gear dynamics. Bearings are critical components in drivetrains. Accurate modeling of rolling element bearings is essential to assess vibration and noise of drivetrain systems. This study also seeks to fully describe the vibro-acoustic propagation of gear dynamics through a power-transmission system using rolling element and fluid film wave bearings. Fluid film wave bearings, which have higher damping than rolling element bearings, could offer an energy dissipation mechanism that reduces the gearbox noise. The effectiveness of each bearing type to disrupt vibration propagation in explored using multi-body computational models. These models include gears, shafts, rolling element and fluid film wave bearings, and the housing. Radiated noise is mapped from the gearbox surface to surrounding environment. The effectiveness of rolling element and fluid film wave bearings in breaking the vibro-acoustic propagation path from the gear to the housing is investigated.

Parker, Robert G.↗
NASA NTRS2007

Apparatus for enhancing tissue repair in mammals

An apparatus is disclosed for enhancing tissue repair in mammals, with the apparatus comprising: a sleeve for encircling a portion of a mammalian body part, said sleeve comprising an electrically conductive coil capable of generating an electromagnetic field when an electrical current is applied thereto, means for supporting the sleeve on the mammalian body part; and means for supplying the electrically conductive coil with a square wave time varying electrical current sufficient to create a time varying electromagnetic force of from approximately 0.05 gauss to 0.05 gauss within the interior of the coil in order that when the sleeve is placed on a mammalian body part and the time varying electromagnetic force of from approximately 0.05 gauss to 0.05 gauss is generated on the mammalian body part for an extended period of time, tissue regeneration within the mammalian body part is increased to a rate in excess of the normal tissue regeneration rate that would occur without application of the time varying electromagnetic force.

Goodwin, Thomas J.↗
NASA NTRS1983

A travelling wave approach to the dynamic analysis of large space structures

This paper investigates the dynamic analysis of certain large space structures via travelling wave mathematics. It is assumed that large space structures may be modelled as networks of interconnected one-dimensional structural members. Bodies with a finite number of internal dynamic degrees of freedom may be scattered throughout the network. The wave propagation behavior of one-dimensional continuous and periodic structural elements is investigated. A scattering matrix description of junctions and discontinuities is proposed. A time domain method of calculating network transient response using the wave propagation characteristics of the elements is briefly described.

Von Flotow, A. H.↗
NASA NTRS1986

Alfven-wave dissipation: A support mechanism for quiescent prominences

High resolution filtergrams or spectrograms of the main body of quiescent prominences often show a very vivid dynamical picture that cannot be reconciled with static models. Even if large differences exist between individual prominences in this respect, at least parts of the prominence are usually found to be in a 'choppy', turbulent state. Evidence for systematic flows are found in local regions in the prominence and also in the transition zone in the surroundings. These two regions are probably decoupled magnetically. Alfven waves are generally believed to be responsible for the heating in the upper chromosphere and corona (Hollweg 1986). Since evidence for the presence of Alfven-waves has also been found in the solar wind field, it is highly probable that such waves are generated in the convection zone of the sun and propagated outwards in the solar atmosphere wherever a proper magnetic field is present to carry the waves. The most basic magnetic formations in the solar atmosphere are simple loops. They occur all over the solar surface and cover a large range of magnetic field strengths. Loops with the strongest magnetic fields are found in active regions. It is to be expected that the Alfven-wave flux which is channelled into the loops from below, could show considerable variation both with heliocentric latitude, with time and locally between neighbouring loops. What happens when a magnetic loop is exposed to the appropriate Alfven-wave flux required to heat the upper solar atmosphere is examined.

Jensen, Eberhart↗
NASA NTRS1993

Modal Ring Method for the Scattering of Electromagnetic Waves

The modal ring method for electromagnetic scattering from perfectly electric conducting (PEC) symmetrical bodies is presented. The scattering body is represented by a line of finite elements (triangular) on its outer surface. The infinite computational region surrounding the body is represented analytically by an eigenfunction expansion. The modal ring method effectively reduces the two dimensional scattering problem to a one-dimensional problem similar to the method of moments. The modal element method is capable of handling very high frequency scattering because it has a highly banded solution matrix.

Baumeister, Kenneth J.↗
NASA NTRS1959

Supersonic and Moment-of-Area Rules Combined for Rapid Zero-Lift Wave-Drag Calculations

The concepts of the supersonic area rule and the moment-of-area rule are combined to develop a new method for calculating zero-lift wave drag which is amenable to the use of ordinary desk calculators. The total zero-lift wave drag of a configuration is calculated by the new method as the sum of the wave drag of each component alone plus the interference between components. In calculating the separate contributions each component or pair of components is analyzed over the smallest allowable length in order to improve the convergence of the series expression for the wave drag. The accuracy of the present method is evaluated by comparing the total zero-lift wave-drag solutions for several simplified configurations obtained by the present method with solutions given by slender-body and linearized theory. The accuracy and computational time required by the present method are also evaluated relative to the supersonic area rule and the moment-of-area rule. The results of the evaluation indicate that total zero-lift wave-drag solutions for simplified configurations can be obtained by the present method which differ from solutions given by slender-body and linearized theory by less than 6 percent. This accuracy for simplified configurations was obtained from only nine terms of the series expression for the wave drag as a result of calculating the total zero-lift wave drag by parts. For the same number of terms these results represent an accuracy greater than that for solutions obtained by either of the two methods upon which the present method is based, except in a few isolated cases. For the excepted cases, solutions by the present method and the supersonic area rule are identical. Solutions by the present method are obtained in one fifth the computing time required by the supersonic area rule. This difference in computing time of course would be substantially reduced if the complete procedures for both methods were programmed on electronic computing machines.

Levy, Lionel L., Jr.↗
NASA NTRS1973

Mach Reflection, Mach Disc, and the Associated Nozzle Free Jet Flows

The numerical method involving both the method of integral relations and the method of characteristics have been applied to investigate the steady flow phenomena associated with the accurrence of Mach reflection and Mach disc from nozzle flows. The solutions of triple-shock intersection are presented. The regime where Mach configuration appears is defines for the inviscid analysis. The method of integral relations developed for the blunt body problem is modified and extended to the attached shock wave and to internal nozzle flow problems.

Chang, I.↗
NASA NTRS1976

Numerical simulation of small perturbation transonic flows

The results of a systematic study of small perturbation transonic flows are presented. Both the flow over thin airfoils and the flow over wedges were investigated. Various numerical schemes were employed in the study. The prime goal of the research was to determine the efficiency of various numerical procedures by accurately evaluating the wave drag, both by computing the pressure integral around the body and by integrating the momentum loss across the shock. Numerical errors involved in the computations that affect the accuracy of drag evaluations were analyzed. The factors that effect numerical stability and the rate of convergence of the iterative schemes were also systematically studied.

Seebass, A. R.↗
NASA NTRS1980

Transonic Flow Field Analysis for Wing-Fuselage Configurations

A computational method for simulating the aerodynamics of wing-fuselage configurations at transonic speeds is developed. The finite difference scheme is characterized by a multiple embedded mesh system coupled with a modified or extended small disturbance flow equation. This approach permits a high degree of computational resolution in addition to coordinate system flexibility for treating complex realistic aircraft shapes. To augment the analysis method and permit applications to a wide range of practical engineering design problems, an arbitrary fuselage geometry modeling system is incorporated as well as methodology for computing wing viscous effects. Configuration drag is broken down into its friction, wave, and lift induced components. Typical computed results for isolated bodies, isolated wings, and wing-body combinations are presented. The results are correlated with experimental data. A computer code which employs this methodology is described.

Boppe, C. W.↗
NASA NTRS1985

Quick-Change Holder for Aeronautical-Research Microphones

Mounting holds microphone flush with aircraft surface and maintains pressure seal. Microphones, which measure dynamic pressure and shock waves as they pass over aircraft fuselage or other experimental body, mounted through fuselage flush with outside surface. Besides being faster and easier to use than older mounts, new mount prevents damage to microphone on removal because no sealant to be cut and scraped away.

Cohn, R.↗
NASA NTRS1985

Spectral methods for the Euler equations. II - Chebyshev methods and shock fitting

The Chebyshev spectral collocation method for the Euler gasdynamic equations is described. It is used with shock fitting to compute several two-dimensional gasdynamic flows. Examples include a shock/acoustic wave interaction, a shock/vortex interaction, and the classical blunt-body problem. With shock fitting, the spectral method has a clear advantage over second-order finite differences in that equivalent accuracy can be obtained with far fewer grid points.

Hussaini, M. Y.↗
NASA NTRS1991

Ultrasonic linear measurement system

An ultrasonic linear measurement system uses the travel time of surface waves along the perimeter of a three-dimensional curvilinear body to determine the perimeter of the curvilinear body. The system can also be used piece-wise to measure distances along plane surfaces. The system can be used to measure perimeters where use of laser light, optical means or steel tape would be extremely difficult, time consuming or impossible. It can also be used to determine discontinuities in surfaces of known perimeter or dimension.

Marshall, Scot H.↗