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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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NASA NTRS1973

Effects of insulator ablation on the operation of a quasi-steady MPD arc

Multimegawatt operation of quasi-steady MPD arcjets can involve serious ablation of the insulator surfaces within the arc discharge chamber. Various degrees of insulator ablation manifest themselves by significantly perturbing the voltage-current characteristics and the exhaust velocity profiles. Voltage-current characteristics for two different insulator materials, Plexiglas and boron nitride, are interpreted in terms of an empirical Ohm's law. Use of the refractory insulator material eliminates the ablation-dominated nature of the terminal voltage, but the exhaust stream is still disturbed by insulator material. An Alfven critical velocity model can be applied to this influence of insulator ablation on exhaust velocity. Appropriate changes in the propellant injection geometry eliminate this influence and result in arcjet operation which is independent of insulator material. A particular combination of propellant injection geometries reduces the terminal voltage for a given current and mass flow while maintaining insulator-independent operation, thus implying an improvement in the overall efficiency of the device.

Boyle, M. J.↗

NASA NTRS1984

Intraplate extensional tectonics of the eastern Basin-Range Inferencess on structural style from seismic reflection data, regional tectonics, and thermal-mechanical models of brittle-ductile deformation

Using 1500 km of industry-released seismic reflection data, surface geology, velocity models from refraction data, and earthquake data, the large extensional structures in the crust of the eastern Basin-Range and its transition into the Middle Rocky Mountains and Colorado Plateau have been studied. It is suggested that the close spatial correlation between normal faults and thrust fault segmentation along the Wasatch Front reflects major east-trending structural and lithological boundaries inherited from tectonic processes associated with the evolution of the cordilleran miogeocline, which began in the Precambrian.

Smith, R. B.↗

NASA NTRS1994

Orbital velocities induced by surface waves

During the third intensive observational period of the Surface Wave Dynamics Experiment (SWADE), an aircraft-based experiment was conducted on 5 March 1991 by deploying slow-fall airborne expendable current profilers (AXCPs) and airborne expendable bathythermographs (AXBTs) during a scanning radar altimeter (SRA) flight on the NASA NP-3A research aircraft. As the Gulf Stream (GS) moved into the SWADE domain in late February, maximum upper-layer currents of 1.98 m/s were observed in the core of the baroclinic jet where the vertical current shears were O(10(exp -2)/s). The SRA concurrently measured the sea surface topography, which was transformed into two-dimensional directional wave spectra at 5-6-km intervals along the flight tracks. The wave spectra indicated a local wave field with wavelengths of 40-60 m propagating southward between 120 deg and 180 deg, and a northward-moving swell field from 300 deg to 70 deg associated with significant wave heights of 2-4 m. As the AXCP descended through the upper ocean, the profiler sensed orbital velocity amplitudes of 0.2-0.5 m/s due to low-frequency surface waves. These orbital velocities were isolated by fitting the observed current profiles to the three-layer model based on a monochromatic surface wave, including the steady and current shear terms within each layer. The depth-integrated differences between the observed and modeled velocity profiles were typically less than 3 cm/s. For 17 of the 21 AXCP drop sites, the rms orbital velocity amplitudes, estimated by integrating the wave spectra over direction and frequency, were correlated at a level of 0.61 with those derived from the current profiles. The direction of wave propagation inferred from the AXCP-derived orbital velocities was in the same direction observed by the SRA. These mean wave directions were highly correlated (0.87) and differed only by about 5 deg.

Shay, Lynn K.↗

NASA NTRS2003

A Tabletop Tool for Modeling Life Support Systems

This paper describes the development plan for a comprehensive research and diagnostic tool for aspects of advanced life support systems in space-based laboratories. Specifically it aims to build a high fidelity tabletop model that can be used for the purpose of risk mitigation, failure mode analysis, contamination tracking, and testing reliability. We envision a comprehensive approach involving experimental work coupled with numerical simulation to develop this diagnostic tool. It envisions a 10% scale transparent model of a space platform such as the International Space Station that operates with water or a specific matched index of refraction liquid as the working fluid. This allows the scaling of a 10 ft x 10 ft x 10 ft room with air flow to 1 ft x 1 ft x 1 ft tabletop model with water/liquid flow. Dynamic similitude for this length scale dictates model velocities to be 67% of full-scale and thereby the time scale of the model to represent 15% of the full- scale system; meaning identical processes in the model are completed in 15% of the full- scale time. The use of an index matching fluid (fluid that matches the refractive index of cast acrylic, the model material) allows making the entire model (with complex internal geometry) transparent and hence conducive to non-intrusive optical diagnostics. So using such a system one can test environment control parameters such as core flows (axial flows), cross flows (from registers and diffusers), potential problem areas such as flow short circuits, inadequate oxygen content, build up of other gases beyond desirable levels, test mixing processes within the system at local nodes or compartments and assess the overall system performance. The system allows quantitative measurements of contaminants introduced in the system and allows testing and optimizing the tracking process and removal of contaminants. The envisaged system will be modular and hence flexible for quick configuration change and subsequent testing. The data and inferences from the tests will allow for improvements in the development and design of next generation life support systems and configurations.

Ramachandran, N.↗

NASA NTRS2005

Space Laboratory on a Table Top: A Next Generative ECLSS design and diagnostic tool

This paper describes the development plan for a comprehensive research and diagnostic tool for aspects of advanced life support systems in space-based laboratories. Specifically it aims to build a high fidelity tabletop model that can be used for the purpose of risk mitigation, failure mode analysis, contamination tracking, and testing reliability. We envision a comprehensive approach involving experimental work coupled with numerical simulation to develop this diagnostic tool. It envisions a 10% scale transparent model of a space platform such as the International Space Station that operates with water or a specific matched index of refraction liquid as the working fluid. This allows the scaling of a 10 ft x 10 ft x 10 ft room with air flow to 1 ft x 1 ft x 1 ft tabletop model with water/liquid flow. Dynamic similitude for this length scale dictates model velocities to be 67% of full-scale and thereby the time scale of the model to represent 15% of the full- scale system; meaning identical processes in the model are completed in 15% of the full- scale-time. The use of an index matching fluid (fluid that matches the refractive index of cast acrylic, the model material) allows making the entire model (with complex internal geometry) transparent and hence conducive to non-intrusive optical diagnostics. So using such a system one can test environment control parameters such as core flows (axial flows), cross flows (from registers and diffusers), potential problem areas such as flow short circuits, inadequate oxygen content, build up of other gases beyond desirable levels, test mixing processes within the system at local nodes or compartments and assess the overall system performance. The system allows quantitative measurements of contaminants introduced in the system and allows testing and optimizing the tracking process and removal of contaminants. The envisaged system will be modular and hence flexible for quick configuration change and subsequent testing. The data and inferences from the tests will allow for improvements in the development and design of next generation life support systems and configurations. Preliminary experimental and modeling work in this area will be presented. This involves testing of a single inlet-exit model with detailed 3-D flow visualization and quantitative diagnostics and computational modeling of the system.

Ramachandran, N.↗

NASA NTRS2002

Multiple-Relaxation-Time Lattice Boltzmann Models in 3D

This article provides a concise exposition of the multiple-relaxation-time lattice Boltzmann equation, with examples of fifteen-velocity and nineteen-velocity models in three dimensions. Simulation of a diagonally lid-driven cavity flow in three dimensions at Re=500 and 2000 is performed. The results clearly demonstrate the superior numerical stability of the multiple-relaxation-time lattice Boltzmann equation over the popular lattice Bhatnagar-Gross-Krook equation.

dHumieres, Dominique↗

NASA NTRS1992

Bow shock models for the velocity structure of ultracompact H II regions

The velocity structure of ultracompact H II regions is modeled assuming that O stars moving supersonically through molecular clouds sweep up bow shocks to produce the observed objects. The expected radio recombination line emission is calculated for the case of an optically thin continuum and the strong effect of changing the viewing angle is shown. The kinematic information removes the degeneracy with ram pressure of a previous model, allowing measurement of stellar velocity vectors and cloud densities. A detailed model for G29.96-0.02 shows good agreement with observations by Wood and Churchwell, supporting the bow shock hypothesis. It is found that the exciting star of G29 is moving at 20 km/s relative to the gas, suggesting that O stars acquire a large velocity dispersion early in their lives.

Van Buren, Dave↗

NASA NTRS1980

Problems of interior structure, the solar dynamo and the role of SCADM in providing interior diagnostics

What is already known about the structure of the Sun, the motion of its convective zone, and the solar cycle is reviewed. Topics discussed include solar variability, solar 'seismology', velocity patterns, magnetic fields, and the dynamo theory. Observations are needed to determine global properties (solar luminosity and radius), oscillations (p and g models), velocities (variation of rotation with time and depth), and magnetic fields.

Weiss, N. O.↗

NASA NTRS1976

Martian atmospheric lee waves

Areas of extensive mountain lee wave phenomenon in the northern midlatitudes during late winter are observed in Mariner 9 television pictures of Mars. The lee wave pattern is due to the discrete spectrum of waves generated by a crater ridge in an airstream. The cloud patterns resulting from the waves generated by the flow across a mountain or crater are dependent on the velocity profile of the airstream and the vertical stability of the atmosphere. A two-layer velocity model of the airstream is used in calculations based on the theory of mountain lee waves. Regardless of the simple model used for the airstream, the calculations appear to be capable of reproducing the observed wave patterns. The many observations of lee waves suggest that the near surface wind speeds as implied by the lower stream velocities do not greatly exceed, and most of the time are less than, 40 m/sec in the northern midlatitudes during late winter except possibly on a very localized scale. Results are in agreement with circulation models, especially the Leovy and Mintz (1969) two-layer numerical model.

Pirraglia, J. A.↗

NASA NTRS1981

Some observations of surface pressures and the near wake of a blunt trailing edge airfoil

Experiments with a truncated and untruncated airfoils of profiles NACA 640A10, were carried out in subsonic wind tunnels in a velocity range of 19m/s to 54m/s corresponding to Reynolds numbers of 200,000 to 468,000 based on the chord. Airfoil spanned the test section to achieve two dimensionality of the model. Velocity measurements, pressure measurements, and vortex shedding in the wake were measured using a hotwire and pressure transducers. The measured chordwise static pressure distribution on the smooth trailing edge airfoil along the midspan plane, agreed with the theoretical results calculated on the basis of the potential flow for that airfoil. Boundary layer profiles measured in the midspan plane, behind the maximum thickness of the airfoil show no separation of the flow. Spanwise distribution of the measured static pressure on the upper surface of the airfoil shows uniformity for both configurations with and without the boundary layer trip. This uniformity of pressure distribution and separation indicates that the flow on the airfoil was uniform and two dimensional in character.

Digumarthi, R. V.↗

NASA NTRSDate not supplied

Estimation With Range Dependent Sensor Model

This paper focuses on the improvement of target tracking accuracy taking into account the sensor’s reading degradation as the relative range increases. The approach is based on the assumption that range measurement error depends on the actual range. Specifically, we model the measurement error as a proportional to the actual range term plus a zero-mean, Gaussian distributed, and uncorrelated process. We present two approaches to tracking a target with constant velocity model. The first approach uses Extended Kalman Filter (EKF) framework to estimate target's states and the unknown proportionality coefficient with linearization on the observation model on the predicted states at each time step. The second one uses a measurement conversion method to estimate the target's scaled by the unknown constant term states, which is shown to be unbiased. This conversion results in linear state and observation models, hence the standard Kalman filter can be applied. The actual target state is computed by application of back scaling with the estimate of unknown scale factor. We evaluate the approaches in desktop simulations.

Target tracking↗

NASA NTRS2004

Low and High Speed STOVL Configurations in Ground Effect

The problem of hot gas ingestion in V/STOL and STOVL aircraft has motivated a set of experimental studies. Two-, three-, and four-jet configurations in cross flow were studied in ground effect. The results presented here were based on a quantitative, concentration measurement technique know as marker nephelometry. The effects of configuration, velocity ratio (freestream over jet velocity), model height, and inlet suction were investigated. The experiments were conducted in three parts. In the first part, comparisons of low speed two-, three-, and four-jet configurations were made. Measurements were made in the planes beneath the models in ground effect. As the number of jets increased, the vortical structures in the flowfield were found to move further upstream due to the increased total momentum. In the second part of the experiments, measurements were made at the inlet entry plane of the low speed two- and three-jet configurations in ground effect. The results indicated that ingestion occurred intermittently, especially in the upper portions of the inlets. The highest levels of concentrations were measured at a model height of two jet diameters. As the model height increased, the concentration levels decreased. Finally, a high speed, two-jet configuration without inlet suction was studied. The flowfield structures were generally found to move further downstream as the jet velocity increased at a constant velocity ratio.

Holdeman, James D.↗

NASA NTRS2010

Navier-Stokes Dynamics by a Discrete Boltzmann Model

This work investigates the possibility of particle-based algorithms for the Navier-Stokes equations and higher order continuum approximations of the Boltzmann equation; such algorithms would generalize the well-known Pullin scheme for the Euler equations. One such method is proposed in the context of a discrete velocity model of the Boltzmann equation. Preliminary results on shock structure are consistent with the expectation that the shock should be much broader than the near discontinuity predicted by the Pullin scheme, yet narrower than the prediction of the Boltzmann equation. We discuss the extension of this essentially deterministic method to a stochastic particle method that, like DSMC, samples the distribution function rather than resolving it completely.

Rubinstein, Robet↗

NASA NTRS1997

Ice velocity at the ice front of the Filchner-Ronne Ice Shelf, Antarctica, as observed with ERS interferometry

ERS images of the two ends of the ice front of the Filchner-Ronne ice shelf (Antarctica) were utilized interferometrically to study the deformation rate of the ice shelf in response to viscous creep. On the western bank of Berkner Island (BI), near Hemmen Ice Rise (HIR), a time series of ERS data acquired in February 1992, in both ascending and descending mode, and with a three-day time interval, were utilized to map the ice velocity in two dimensions. Finite-element ice-shelf flow simulations are compared with the ERS interferograms to interpret the ice motion in terms of the physical constraints on ice-shelf flow. The efforts to fit artificial interferograms generated with model velocity output suggest that the flow regime is strongly influenced by three processes. First, a void-creation process responsible for rifts at coastal margins tends to uncouple the ice shelf from the ice rise and neighboring coast of BI. Secondly, sea ice within the void space appears to act as a binding agent between discrete ice-shelf fragments, allowing rigid-body rotations of these fragments. Third, strain rates appear to be enhanced in a narrow zone adjacent to HIR, implying significant strain softening along the boundary. It is believed that synthetic aperture radar (SAR) interferogram/model intercomparison represents a powerful impetus towards the development of better, more physically realistic ice-shelf flow models.

Rignot, Eric↗

NASA NTRS2012

Trapezoidal Wing Experimental Repeatability and Velocity Profiles in the 14- by 22-Foot Subsonic Tunnel

The AIAA Applied Aerodynamics Technical Committee sponsored a High Lift Prediction Workshop held in June 2010. For this first workshop, data from the Trapezoidal Wing experiments were used for comparison to CFD. This paper presents long-term and short-term force and moment repeatability analyses for the Trapezoidal Wing model tested in the NASA Langley 14- by 22-Foot Subsonic Tunnel. This configuration was chosen for its simplified high-lift geometry, publicly available set of test data, and previous CFD experience with this configuration. The Trapezoidal Wing is a three-element semi-span swept wing attached to a body pod. These analyses focus on configuration 1 tested in 1998 (Test 478), 2002 (Test 506), and 2003 (Test 513). This paper also presents model velocity profiles obtained on the main element and on the flap during the 1998 test. These velocity profiles are primarily at an angle of attack of 28 degrees and semi-span station of 83% and show confluent boundary layers and wakes.

Hannon, Judith A.↗

NASA NTRS1971

A math model for high velocity sensoring with a focal plane shuttered camera.

A new mathematical model is presented which describes the image produced by a focal plane shutter-equipped camera. The model is based upon the well-known collinearity condition equations and incorporates both the translational and rotational motion of the camera during the exposure interval. The first differentials of the model with respect to exposure interval, delta t, yield the general matrix expressions for image velocities which may be simplified to known cases. The exposure interval, delta t, may be replaced under certain circumstances with a function incorporating blind velocity and image position if desired. The model is tested using simulated Lunar Orbiter data and found to be computationally stable as well as providing excellent results, provided that some external information is available on the velocity parameters.

Morgan, P.↗

NASA NTRS1982

Correction of lunar seismograms for instrumental and near-surface effects and constraints on the velocity structure of the lunar interior

Long-period lunar seismograms were studied with the aim of identifying consistent sets of direct shear and secondary wave arrivals, thus constraining the velocities in the lunar mantle and the depths of the velocity discontinuities. Two velocity models were used to locate the natural impacts and the shallow moonquakes and to obtain the travel time residuals. Seismic sections were made of the radial, transverse, and vertical components of ground motion for impacts, shallow, and deep moonquakes in order to search for consistent sets of secondary wave arrivals. No conclusive set of secondary arrivals could be recognized on the seismic sections and thus the velocities and depths of the velocity discontinuities cannot be severely constrained by secondary arrivals. It is likely that the crust is thinner than 50 km and that a first-order discontinuity separates the upper and lower crust at a depth of between 20 and 30 km.

Horvath, P.↗

NASA NTRS1987

Earthquake source mechanisms and transform fault tectonics in the Gulf of California

The source parameters of 19 large earthquakes in the Gulf of California were determined from inversions of long-period P and SH waveforms. The goal was to understand the recent slip history of this dominantly transform boundary between the Pacific and North American plates as well as the effect on earthquake characteristics of the transition from young oceanic to continental lithosphere. For the better recorded transform events, the fault strike is resolved to + or - 4 deg at 90 percent confidence. The slip vectors thus provide important constraints on the direction of relative plate motion. Most centroid depths are poorly resolved because of tradeoffs between depth and source time function. On the basis of waveform modeling, historical seismicity, and other factors, it is appropriate to divide the Gulf into three distinct zones. The difference in seismic character among the three zones is likely the result of differing levels of maturity of the processes of rifting, generation of oceanic crust, and formation of stable oceanic transform faults. The mechanism of an earthquake on the Tres Marias Escarpment is characterized by thrust faulting and likely indicates the direction of relative motion between the Rivera and North American plates. This mechanism requires revision in plate velocity models which predict strike slip motion at this location.

Goff, John A.↗