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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Combustion and Emissions Study Using a 7-Point Lean Direct Injector Array Focus on Flame Stability

This paper continues a parametric study in which we consider the effect of air swirler configuration on the flame structure and combustor performance using a circular 7-point Lean Direct Injector Array for gas turbine applications. The injector array consists of a center swirler element surrounded by six swirler elements. Parameters considered in this study include swirler angle (60° or 52°), handedness (co-swirling or counter-swirling) and center swirler offset. The primary focus considers flame stability, comparing four key air swirler configurations: for 1) fuel-lean flames; 2) high cold flow air reference velocity flames. We determined that the baseline swirler configuration had the best lean stability and could sustain the highest reference velocity. For this baseline configuration, we also compare the lean-blowout limits of four aircraft gas turbine reference fuels. With regard to lean blow-out, we determined that C4 could sustain the leanest flame, followed closely by A2. A1 was a poor performer.

fluid mixing↗
NASA NTRS1962

Design Reliability Measurement and Evaluation

Reliability measurement by data collection and evaluation is considered. Parameters are defined and restrictions established. Reliability estimation of sub-systems and parts as a preliminary to system estimation is reviewed, and rules are established. Confidence levels of sub-systems and parts versus combined system are analyzed. Estimation planning is discussed. Tests planned for accept-reject reliability decision are very briefly considered.

RELIABILITY↗
NASA NTRS1982

A middle and upper tropospheric cloud model

The interplay of the various physical processes involved in the formation, maintenance, and decay of middle and upper tropospheric stratiform clouds is discussed. Ice phase fair weather cloud forms are considered. Simulations of cirriform clouds which attempt to incorporate the physical processes in an interactive manner were performed. A two dimensional time dependent Eulerian numerical model, which incorporates all of the important physical processes in a simplified way, is employed to investigate the role of these processes in the evolution of a cloud in an isolated atmospheric layer. Physical parameters considered are the eddy viscosity and the thermal, water vapor, and ice water eddy diffusivities.

Source record↗
NASA NTRS1979

Theoretical study of VTOL tilt-nacelle axisymmetric inlet geometries

A systematic theoretical study of VTOL tilt-nacelle inlet design parameters is reported. The parameters considered are internal-lip contraction ratio, internal-lip major-to-minor axis ratio, diffuser-exit-area to throat-area ratio, maximum diffuser wall angle and shape. Each of the inlets was analyzed at the same given flow condition of free-stream velocity, angle between the free stream and centerline of the inlet, and diffuser-exit Mach number. The effects of these geometric parameters on surface static-pressure distribution, peak surface Mach number, diffusion velocity ratio, and tendency for the inlet flow to separate are presented.

Hawk, J. D.↗
NASA NTRS2009

Control-Relevant Modeling, Analysis, and Design for Scramjet-Powered Hypersonic Vehicles

Within this paper, control-relevant vehicle design concepts are examined using a widely used 3 DOF (plus flexibility) nonlinear model for the longitudinal dynamics of a generic carrot-shaped scramjet powered hypersonic vehicle. Trade studies associated with vehicle/engine parameters are examined. The impact of parameters on control-relevant static properties (e.g. level-flight trimmable region, trim controls, AOA, thrust margin) and dynamic properties (e.g. instability and right half plane zero associated with flight path angle) are examined. Specific parameters considered include: inlet height, diffuser area ratio, lower forebody compression ramp inclination angle, engine location, center of gravity, and mass. Vehicle optimizations is also examined. Both static and dynamic considerations are addressed. The gap-metric optimized vehicle is obtained to illustrate how this control-centric concept can be used to "reduce" scheduling requirements for the final control system. A classic inner-outer loop control architecture and methodology is used to shed light on how specific vehicle/engine design parameter selections impact control system design. In short, the work represents an important first step toward revealing fundamental tradeoffs and systematically treating control-relevant vehicle design.

Rodriguez, Armando A.↗
NASA NTRS1990

A computational parametric study of three-dimensional sidewall compression scramjet inlets at Mach 10

A computational parametric study of three-dimensional sidewall compression scramjet inlets has been performed. The parameters considered for the study include the leading edge sweep angle, varied between 30 and 60 degrees, and the cowl position, located at the throat and at two forward positions. Additionally, the effects of laminar and turbulent boundary layers as well as adiabatic and cold wall boundary conditions are assessed. The parametric study is performed for a Mach number of 10 and a unit freestream Reynolds number of 2 x 10 to the 6th/ft at a geometric contraction ratio of 5. Comparisons among the various configurations are made in terms of the gross parameters of mass capture, throat Mach number, total pressure recovery, and area weighted internal pressure ratios, as well as more detailed flow field phenomena comparisons. The inclusion of one 0-deg sweep computation indicates that the leading edge may be swept by up to 30 deg before significant changes in the gross flow field parameters occur. It is found that a 45-deg sweep configuration provides a good compromise of mass capture, total pressure recovery, and internal compression.

Holland, Scott D.↗
NASA NTRS1998

Molecular Static Third-Order Polarizabilities of Carbon-Cage Fullerene and Their Correlation with Three Geometric Properties: Symmetry, Aromaticity, and Size

The static third-order polarizabilities (gamma) of C60, C70, five isomers of C78 and two isomers of C84 were analyzed in terms of three properties, from a geometric point of view: symmetry, aromaticity and size. The polarizability values were based on the finite field approximation using a semiempirical Hamiltonian (AM1) and applied to molecular structures obtained from density functional theory calculations. Symmetry was characterized by the molecular group order. The selection of 6-member rings as aromatic was determined from an analysis of bond lengths. Maximum interatomic distance and surface area were the parameters considered with respect to size. Based on triple linear regression analysis, it was found that the static linear polarizability (alpha) and gamma in these molecules respond differently to geometrical properties: alpha depends almost exclusively on surface area while gamma is affected by a combination of number of aromatic rings, length and group order, in decreasing importance. In the case of alpha, valence electron contributions provide the same information as all-electron estimates. For gamma, the best correlation coefficients are obtained when all-electron estimates are used and when the dependent parameter is ln(gamma) instead of gamma.

Moore, C. E.↗
NASA NTRSDate not supplied

Curvature, Variable Density and Compressibility Effects in Turbulent Shear Layers

The combined effects of variable density, curvature, and convective Mach number on turbulence in time-developing free shear layers are studied using turbulence-resolving simulations. The range of parameters considered include the convective Mach number at 0.2 and 0.8, the density ratio at 1/7, 1 and 7, and the level of streamwise curvature, measured by the shear layer thickness ratio to the radius of curvature at 0.001 and 0.01. Simulations at the limit of zero curvature exhibit mean profiles and turbulent stresses comparable with previously simulated planar (non-curved) shear layers. Growth rate changes depending on compressibility, curvature and density ratio are compared with expected behavior and unexpected trends due to combined effects are investigated. Standard turbulent shear layer statistics are presented, including spreading rates, turbulent stresses, and stress budgets to characterize individual and combined effects of the selected physical parameters.

shear layer↗
NASA NTRS1977

Antenna concepts for interstellar search systems

An evaluation is made of microwave receiving systems designed to search for signals from extraterrestrial intelligence. Specific design concepts are analyzed parametrically to determine whether the optimum antenna system location is on earth, in space, or on the moon. Parameters considered include the hypothesized number of transmitting civilizations, the number of stars that must be searched to give any desired probability of receiving a signal, the antenna collecting area, the search time, the search range, and the cost. This analysis suggests that (1) search systems based on the moon are not cost-competitive, (2) if the search is extended only a few hundred light years from the earth, a Cyclops-type array on earth may be the most cost-effective system, (3) for a search extending to 500 light years or more, a substantial cost and search-time advantage can be achieved with a large spherical reflector in space with multiple feeds, (4) radio frequency interference shields can be provided for space systems, and (5) cost can range from a few hundred million to tens of billions of dollars, depending on the parameter values assumed.

Basler, R. P.↗
NASA NTRS2000

Stardust Navigation Covariance Analysis

The Stardust spacecraft was launched on February 7, 1999 aboard a Boeing Delta-II rocket. Mission participants include the National Aeronautics and Space Administration (NASA), the Jet Propulsion Laboratory (JPL), Lockheed Martin Astronautics (LMA) and the University of Washington. The primary objective of the mission is to collect in-situ samples of the coma of comet Wild-2 and return those samples to the Earth for analysis. Mission design and operational navigation for Stardust is performed by the Jet Propulsion Laboratory (JPL). This paper will describe the extensive JPL effort in support of the Stardust pre-launch analysis of the orbit determination component of the mission covariance study. A description of the mission and it's trajectory will be provided first, followed by a discussion of the covariance procedure and models. Predicted accuracy's will be examined as they relate to navigation delivery requirements for specific critical events during the mission. Stardust was launched into a heliocentric trajectory in early 1999. It will perform an Earth Gravity Assist (EGA) on January 15, 2001 to acquire an orbit for the eventual rendezvous with comet Wild-2. The spacecraft will fly through the coma (atmosphere) on the dayside of Wild-2 on January 2, 2004. At that time samples will be obtained using an aerogel collector. After the comet encounter Stardust will return to Earth when the Sample Return Capsule (SRC) will separate and land at the Utah Test Site (UTTR) on January 15, 2006. The spacecraft will however be deflected off into a heliocentric orbit. The mission is divided into three phases for the covariance analysis. They are 1) Launch to EGA, 2) EGA to Wild-2 encounter and 3) Wild-2 encounter to Earth reentry. Orbit determination assumptions for each phase are provided. These include estimated and consider parameters and their associated a-priori uncertainties. Major perturbations to the trajectory include 19 deterministic and statistical maneuvers planned for the mission. The spacecraft is three axis stabilized and has unbalanced thrusters for attitude control. Accelerations due to the attitude control system are treated stochastically. The tracking scenario for the study is patterned after the actual schedule employed during the different phases of the mission. Conventional X-band two-way Doppler and SRA range data was simulated and the standard accuracy for these data types was assumed throughout most of the mission. However, a deweighting scheme was used for the Doppler data during times of low Sun-Earth-Probe angles, especially in the case of the DSM. Optical data is assumed to be available starting at 50 days prior to the comet encounter. The optical data will be used to improve the ephemeris of Wild-2, which is considered crucial to properly target the comet flyby. Results of the covariance analysis are presented for all mission phases. Navigation capability will be discussed in terms of the uncertainty in the encounter B-Plane (B.R and B.T) and linearized time of flight. Delivery errors based on the final maneuver prior to the comet encounter will be presented. The most stringent navigation requirement is for the Earth reentry. The uncertainty in the flight path angle must be less than 0.02 degree (orbit determination and maneuver performance) to assure successful recovery of the SRC. Results presented show that this requirement can be met.

Menon, Premkumar R.↗
NASA NTRS1972

User oriented multispectral data processing at the University of Michigan

The feasibility of solving practical multispectral data reduction problems by available processing techniques and the identification of areas for more technical development requirements are considered. Parameter mapping and ratio mapping techniques prove their usefulness in a corn blight watch experiment. A hybrid computer processing system is advocated for complete realization of aircraft and spacecraft sensor potentials.

Thomson, F. J.↗
NASA NTRS1972

Perturbation guidance for minimum time flight paths of spacecraft.

The problem of transferring a rocket vehicle from a given circular orbit to a larger coplanar circular orbit in minimum time, using a constant low-thrust rocket engine, is considered. Parameters are chosen to correspond to a transfer from the earth's orbit in heliocentric space to the orbit of Mars. A path satisfying the first order necessary conditions of variational calculus is shown to be locally minimizing by application of a set of second order conditions. A physical explanation is offered to justify the retrothrust period occurring during the flight. A neighboring optimum feedback control law, based on estimated time-to-go, is applied to this problem. State variable and terminal constraint feedback gains are calculated while one of the second order conditions, involving the backward integration of a matrix Riccati equation, is being tested.

Wood, L. J.↗
NASA NTRS1974

Curve fits of predicted inviscid stagnation-point radiative heating rates, cooling factors, and shock standoff distances for hyperbolic earth entry

Curve-fit formulas are presented for the stagnation-point radiative heating rate, cooling factor, and shock standoff distance for inviscid flow over blunt bodies at conditions corresponding to high-speed earth entry. The data which were curve fitted were calculated by using a technique which utilizes a one-strip integral method and a detailed nongray radiation model to generate a radiatively coupled flow-field solution for air in chemical and local thermodynamic equilibrium. The range of free-stream parameters considered were altitudes from about 55 to 70 km and velocities from about 11 to 16 km.sec. Spherical bodies with nose radii from 30 to 450 cm and elliptical bodies with major-to-minor axis ratios of 2, 4, and 6 were treated. Powerlaw formulas are proposed and a least-squares logarithmic fit is used to evaluate the constants. It is shown that the data can be described in this manner with an average deviation of about 3 percent (or less) and a maximum deviation of about 10 percent (or less). The curve-fit formulas provide an effective and economic means for making preliminary design studies for situations involving high-speed earth entry.

Suttles, J. T.↗
NASA NTRS1974

Two-dimensional Gaussian processes applied to the determination of contact between lubricated rolling surfaces

The effectiveness of a lubricant film preventing metallic contact between two rolling surfaces (such as in ball bearings) as a function of surface roughness parameters was investigated. The parameters considered are the spectral moments of the two-dimensional surface obtained by superposition of the two rolling surfaces. The peak height distribution, estimation of one-dimensional profile spectral moments, and the estimation of two-dimensional surface moments from several profile measurements were considered. Also given is an asymptotic relation between the mean film thickness and contact occurrences.

Sidik, S. M.↗