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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Low-Temperature Rate Coefficients of C2H with CH4 and CD4 from 154 to 359 K

Rate coefficients for the reaction C2H + CH4 yields C2H2 + CH3 and C2H + CD4 yields C2HD + CD3 are measured over the temperature range 154-359 K using transient infrared laser absorption spectroscopy. Ethynyl radicals are produced by pulsed laser photolysis of C2H2 in a variable temperature flow cell, and a tunable color center laser probes the transient removal of C2H (Chi(exp 2) Sigma(+) (0,0,0)) in absorption. The rate coefficients for the reactions of C2H with CH4 and CD4 both show a positive temperature dependence over the range 154-359 K, which can be expressed as k(sub CH4) = (1.2 +/- 0.1) x 10(exp -11) exp((-491 +/- 12)/T) and k(sub CD4) = (8.7 +/- 1.8) x 10(exp -12) exp((-650 +/- 61)/T) cm(exp 3) molecule(exp -1) s(exp -1), respectively. The reaction of C2H + CH4 exhibits a significant kinetic isotope effect at 300 K of k(sub CH4)/k(sub CD4) = 2.5 +/- 0.2. Temperature dependent rate constants for C2H + C2H2 were also remeasured over an increased temperature range from 143 to 359 K and found to show a slight negative temperature dependence, which can be expressed as k(sub C2H2) = 8.6 x 10(exp -16) T(exp 1.8) exp((474 +/- 90)/T) cm(exp 3) molecule(exp -1) s(exp -1).

Opansky, Brian J.↗
NASA NTRS2000

Three-Dimensional Nacelle Aeroacoustics Code With Application to Impedance Education

A three-dimensional nacelle acoustics code that accounts for uniform mean flow and variable surface impedance liners is developed. The code is linked to a commercial version of the NASA-developed General Purpose Solver (for solution of linear systems of equations) in order to obtain the capability to study high frequency waves that may require millions of grid points for resolution. Detailed, single-processor statistics for the performance of the solver in rigid and soft-wall ducts are presented. Over the range of frequencies of current interest in nacelle liner research, noise attenuation levels predicted from the code were in excellent agreement with those predicted from mode theory. The equation solver is memory efficient, requiring only a small fraction of the memory available on modern computers. As an application, the code is combined with an optimization algorithm and used to reduce the impedance spectrum of a ceramic liner. The primary problem with using the code to perform optimization studies at frequencies above I1kHz is the excessive CPU time (a major portion of which is matrix assembly). The research recommends that research be directed toward development of a rapid sparse assembler and exploitation of the multiprocessor capability of the solver to further reduce CPU time.

Watson, Willie R.↗
NASA NTRS1999

Development of a Computational Chemical Vapor Deposition Model: Applications to Indium Nitride and Dicyanovinylaniline

A computational chemical vapor deposition (CVD) model is presented, that couples chemical reaction mechanisms with fluid dynamic simulations for vapor deposition experiments. The chemical properties of the systems under investigation are evaluated using quantum, molecular and statistical mechanics models. The fluid dynamic computations are performed using the CFD-ACE program, which can simulate multispecies transport, heat and mass transfer, gas phase chemistry, chemistry of adsorbed species, pulsed reactant flow and variable gravity conditions. Two experimental setups are being studied, in order to fabricate films of: (a) indium nitride (InN) from the gas or surface phase reaction of trimethylindium and ammonia; and (b) 4-(1,1)dicyanovinyl-dimethylaminoaniline (DCVA) by vapor deposition. Modeling of these setups requires knowledge of three groups of properties: thermodynamic properties (heat capacity), transport properties (diffusion, viscosity, and thermal conductivity), and kinetic properties (rate constants for all possible elementary chemical reactions). These properties are evaluated using computational methods whenever experimental data is not available for the species or for the elementary reactions. The chemical vapor deposition model is applied to InN and DCVA. Several possible InN mechanisms are proposed and analyzed. The CVD model simulations of InN show that the deposition rate of InN is more efficient when pulsing chemistry is used under conditions of high pressure and microgravity. An analysis of the chemical properties of DCVA show that DCVA dimers may form under certain conditions of physical vapor transport. CVD simulations of the DCVA system suggest that deposition of the DCVA dimer may play a small role in the film and crystal growth processes.

Cardelino, Carlos↗
NASA NTRS2002

Software for Refining or Coarsening Computational Grids

A computer program performs calculations for refinement or coarsening of computational grids of the type called 'structured' (signifying that they are geometrically regular and/or are specified by relatively simple algebraic expressions). This program is designed to facilitate analysis of the numerical effects of changing structured grids utilized in computational fluid dynamics (CFD) software. Unlike prior grid-refinement and -coarsening programs, this program is not limited to doubling or halving: the user can specify any refinement or coarsening ratio, which can have a noninteger value. In addition to this ratio, the program accepts, as input, a grid file and the associated restart file, which is basically a file containing the most recent iteration of flow-field variables computed on the grid. The program then refines or coarsens the grid as specified, while maintaining the geometry and the stretching characteristics of the original grid. The program can interpolate from the input restart file to create a restart file for the refined or coarsened grid. The program provides a graphical user interface that facilitates the entry of input data for the grid-generation and restart-interpolation routines.

Daines, Russell↗
NASA NTRS2002

Software for Refining or Coarsening Computational Grids

A computer program performs calculations for refinement or coarsening of computational grids of the type called "structured" (signifying that they are geometrically regular and/or are specified by relatively simple algebraic expressions). This program is designed to facilitate analysis of the numerical effects of changing structured grids utilized in computational fluid dynamics (CFD) software. Unlike prior grid-refinement and -coarsening programs, this program is not limited to doubling or halving: the user can specify any refinement or coarsening ratio, which can have a noninteger value. In addition to this ratio, the program accepts, as input, a grid file and the associated restart file, which is basically a file containing the most recent iteration of flow-field variables computed on the grid. The program then refines or coarsens the grid as specified, while maintaining the geometry and the stretching characteristics of the original grid. The program can interpolate from the input restart file to create a restart file for the refined or coarsened grid. The program provides a graphical user interface that facilitates the entry of input data for the grid-generation and restart-interpolation routines.

Daines, Russell↗
NASA NTRS1999

DARTFire Sees Microgravity Fires in a New Light--Large Data Base of Images Obtained

The recently completed DARTFire sounding rocket microgravity combustion experiment launched a new era in the imaging of flames in microgravity. DARTFire stands for "Diffusive and Radiative Transport in Fires," which perfectly describes the two primary variables--diffusive flow and radiation effects--that were studied in the four launches of this program (June 1996 to September 1997). During each launch, two experiments, which were conducted simultaneously during the 6 min of microgravity, obtained results as the rocket briefly exited the Earth s atmosphere.

Olson, Sandra L.↗
NASA NTRS2007

Piloted Ignition to Flaming in Smoldering Fire-Retarded Polyurethane Foam

Experimental results are presented on the piloted transition from smoldering to flaming in the fire-retarded polyurethane foam Pyrell . The samples are small rectangular blocks with a square cross section, vertically placed in the wall of a vertical wind tunnel. Three of the vertical sample sides are insulated and the fourth side is exposed to an upward oxidizer flow of variable oxygen concentration and to a variable radiant heat flux. The gases emitted from the smoldering reaction pass upwards through a pilot, which consists of a coiled resistance heating wire. In order to compensate for the solid-phase and gas-phase effects of the fire retardants on the piloted transition from smoldering to flaming in Pyrell, it was necessary to assist the process by increasing the power supplied to the smolder igniter and the pilot (compared to that used for non-fire retarded foam). The experiments indicate that the piloted transition from smoldering to flaming occurs when the gaseous mixture at the pilot passes the lean flammability limit. It was found that increasing the oxygen concentration or the external heat flux increases the likelihood of a piloted transition from smoldering to flaming, and generally decreases the time delay to transition. The piloted transition to flaming is observed in oxygen concentrations of 23% and above in both low-density and high-density Pyrell. Comparisons with previous experiments show that the piloted transition from smoldering to flaming is possible under a wider range of external conditions (i.e. lower oxygen concentration) than the spontaneous transition from smoldering to flaming. The results show that the fire retardants in Pyrell are very effective in preventing the piloted transition to flaming in normal air, but Pyrell is susceptible to smoldering and the piloted transition to flaming in oxygen-enriched environments. Therefore, precautions should be taken in the design of applications of Pyrell in oxygen-enriched environments to reduce to the risk of a piloted transition to flaming.

Putzeys, O.↗
NASA NTRS2003

Software for Refining or Coarsening Computational Grids

A computer program performs calculations for refinement or coarsening of computational grids of the type called structured (signifying that they are geometrically regular and/or are specified by relatively simple algebraic expressions). This program is designed to facilitate analysis of the numerical effects of changing structured grids utilized in computational fluid dynamics (CFD) software. Unlike prior grid-refinement and -coarsening programs, this program is not limited to doubling or halving: the user can specify any refinement or coarsening ratio, which can have a noninteger value. In addition to this ratio, the program accepts, as input, a grid file and the associated restart file, which is basically a file containing the most recent iteration of flow-field variables computed on the grid. The program then refines or coarsens the grid as specified, while maintaining the geometry and the stretching characteristics of the original grid. The program can interpolate from the input restart file to create a restart file for the refined or coarsened grid. The program provides a graphical user interface that facilitates the entry of input data for the grid-generation and restart-interpolation routines.

Daines, Russell↗
NASA NTRS2012

A Framework for Simulating Turbine-Based Combined-Cycle Inlet Mode-Transition

A simulation framework based on the Memory-Mapped-Files technique was created to operate multiple numerical processes in locked time-steps and send I/O data synchronously across to one-another to simulate system-dynamics. This simulation scheme is currently used to study the complex interactions between inlet flow-dynamics, variable-geometry actuation mechanisms, and flow-controls in the transition from the supersonic to hypersonic conditions and vice-versa. A study of Mode-Transition Control for a high-speed inlet wind-tunnel model with this MMF-based framework is presented to illustrate this scheme and demonstrate its usefulness in simulating supersonic and hypersonic inlet dynamics and controls or other types of complex systems.

Le, Dzu K.↗
NASA NTRS2019

Far Field Plume Distribution and Divergence for NEXT: DART Mission

In support of the Double Asteroid Redirection Test (DART) mission, laboratory measurements were made on the NEXT ion engine, which will be used for the spacecraft's in-space propulsion [1]. This study revisits a small range of mission-specific 2.7A throttle levels to understand the effect of in-flight flow rate variability, investigate intermediate throttle conditions, and improve measurement methodology. This paper specifically examines the far-field plume divergence and backflow ion flux distribution of the NEXT, while a companion paper examines the charge state distributions.

Throttle Levels↗
NASA NTRS2019

Uncertainty Analysis of Experimental Discharge Coefficients in Additively Manufactured Liquid Injector Elements

Screening of two additively manufactured liquid injector designs was conducted in the UAH high pressure spray facility. Four variants of each geometry with slightly different dimensions were obtained from eleven separate commercial additive manufacturing services. The devices were manufactured from Inconel 625 using the selective laser melting (SLM) powder bed process. The devices were cold flowed with water over a range of relevant pressure drops (75 psi to 1500 psi) to produce water flow rates from 0.037 to 1.75 lbm/s into ambient back pressure. Discharge coefficients determined from the testing along with the associated uncertainties provide insight into characteristic flow performance variabilities that can be expected from the SLM process for similar geometries.

Venters, James P.↗
NASA NTRSDate not supplied

Twenty-Five Years of Background-Oriented Schlieren: Advances and Novel Applications

Since its introduction in the year 2000, background-oriented schlieren (BOS) has become acornerstone technique for visualizing variable-density flows. In this review, we provide a rigorousexamination of the optical principles underpinning BOS and related refractive-index-basedtechniques, complemented by an appendix linking schlieren imaging to Maxwell’s equations.The core sections delve into the practical aspects of BOS, with detailed discussions on imageprocessing algorithms and critical considerations for experimental setups. We then explorerecent advancements and innovations, including extensions of BOS with tomography, dataassimilation, and event-based imaging. Finally, we present notable applications of BOS inchallenging and unconventional environments, showcasing the method’s versatility and offerinspiration for future research directions.

Background-Oriented Schlieren↗
NASA NTRSDate not supplied

Considerations for High-Speed Background-Oriented Schlieren Visualization Capability for Ground Test Facilities

Since its introduction in the year 2000, background-oriented schlieren (BOS) has become a cornerstone technique for visualizing variable-density flows. In this review, we provide a rigorous examination of the optical principles underpinning BOS and related refractive-index-based techniques, complemented by an appendix linking schlieren imaging to Maxwell’s equations. The core sections delve into the practical aspects of BOS, with detailed discussions on image processing algorithms and critical considerations for experimental setups. We then explore recent advancements and innovations, including extensions of BOS with tomography, data assimilation, and event-based imaging. Finally, we present notable applications of BOS in challenging and unconventional environments, showcasing the method’s versatility and offer inspiration for future research directions.

Brett Bathel↗
NASA NTRSDate not supplied

Thermal-Fluid Analysis of a Liquid-Cooled Battery Module for Electrified Aircraft

The development of safe, energy-dense batteries is critical to advancing hybrid electric and fully electrified aircraft propulsion. Achieving this capability requires a thermal management system that can maintain battery performance and safety under demanding operational conditions. The objective of this project is to support the maturation of next-generation lithium-ion batteries for electrified aircraft by conducting performance testing on integrated battery modules, specifically a 2-cell series configuration module housed within an aluminum enclosure. Designed to operate at a nominal 7.2 V with discharge rates up to 2.5C, the module will eventually be used to power an electric motor and DC-DC converter, generating substantial thermal loads that must be effectively managed to increase the usable energy and power density of electrified aircraft. To address these thermal challenges, this study presents the development and thermal-fluid analysis of a liquid-cooled thermal management system. While the full aircraft architecture utilizes an eight-string configuration, the present work evaluates a representative single-string water coolant loop to characterize baseline performance. The active cooling loop circulates water through a reservoir, pump, the battery module, and a variable area flow meter. Key performance metrics including component-level temperatures, mass flow rates, and pressure drops are quantified across the loop. Across discharge rates ranging from 0.5C to 2.5C, the active thermal loop consistently and effectively removed heat from the module, validating the design approach and confirming readiness for further development. The validated thermal performance indicates a path toward scalable battery modules that could enable energy and power dense systems for hybrid electric aircraft.

Electrified Aircraft↗
NASA NTRS1977

Variable cycle gas turbine engines

A technique, method, and apparatus were designed for varying the bypass ratio and modulating the flow of a gas turbine engine in order to achieve improved mixed mission performance. Embodiments include gas flow control system for management of core and bypass stream pressure comprising diverter valve means downstream of the core engine to selectively mix or separate the core and bypass exhaust streams. The flow control system may also include variable geometry means for maintaining the engine inlet airflow at a matched design level at all flight velocities. Earth preferred embodiment thus may be converted from a high specific thrust mixed flow cycle at supersonic velocities to a lower specific thrust separated flow turbofan system at subsonic velocities with a high degree of flow variability in each mode of operation.

Johnson, J. E.↗
NASA NTRS1974

Propagation of plane waves in a variable area duct carrying a compressible subsonic flow

A complete numerical solution is obtained for plane wave propagation in a variable-area duct which carries a mean compressible flow. The equation solved is a matrix formulation of the equations first derived by Tsien in 1952. Sample calculations are presented for four particular flow configurations: (1) a duct-nozzle-duct combination with the acoustic wave traveling with the flow, (2) a duct-nozzle-duct combination with the acoustic wave traveling against the flow, (3) an inlet-nozzle-duct configuration with the acoustic wave traveling against the flow, and (4) a duct-nozzle-exit configuration with the acoustic wave traveling with the flow. For each of these cases, the variation of energy flux with frequency is shown for particular geometry and flow condition.

Davis, S. S.↗
NASA NTRS1976

Mathematical formulation for the propagation of sound through a turbulent jet

The sound propagation through a nonuniform turbulent jet flow field is studied by means of a system of linearized equations governing the acoustic variables. These equations depend on the fluctuating flow-field variables which can be prescribed by experimental results. It is shown that the correlations of the acoustic variables depend throughout the flow field on the space-time correlation of the turbulent velocities and on the mean flow variables and their gradients.

Gunzburger, M.↗