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Results for “confined extension”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Experiments on opposed lateral jets injected into swirling crossflow

Experiments have been conducted to obtain the time-mean and turbulent quantities of opposed lateral jets in a low speed, nonreacting flowfield. A jet-to-crossflow velocity ratio of R = v sub J/u sub 0 = 4 was used throughout the experiments, with swirl vane angles of d = 0 (swirler removed), 45 and 70 deg used with the crossflow. Flow visualization techniques used were neutrally-buoyant helium-filled soap bubbles and multispark photography in order to obtain the gross flowfield characteristics. Measurements of time-mean and turbulent quantities were obtained utilizing a six-orientation single hot-wire technique. For the nonswirling case, the jets were found not to penetrate past the test-section centerline, in contrast to the single lateral jet with the same jet-to-crossflow velocity ratio. In the swirling cases, the crossflow remains in a narrow region near the wall of the test section. The opposed jets are swept from their vertical courses into spiral trajectories close to the confining walls. Extensive results are presented in r-x plane plots.

Mcmurry, C. B.↗
NASA NTRS1987

Two opposed lateral jets injected into swirling crossflow

Experiments have been conducted to obtain the time-mean and turbulent quantities of opposed lateral jets in a low speed, nonreacting flowfield. A jet-to-crossflow velocity ratio of R = 4 was used throughout the experiments, with swirl vane angles of 0 (swirler removed), 45 and 70 degrees used with the crossflow. Flow visualization techniques used were neutrally-buoyant helium-filled soap bubbles and multispark photography in order to obtain the gross flowfield characteristics. Measurements of time-mean and turbulent quantities were obtained utilizing a six-orientation single hot-wire technique. For the nonswirling case, the jets were found not to penetrate past the test-section centerline, in contrast to the single lateral jet with the same jet-to-crossflow velocity ratio. In the swirling cases, the crossflow remains in a narrow region near the wall of the test section. The opposed jets are swept from their vertical courses into spiral trajectories close to the confining walls. Extensive results are presented in r-x plane plots.

Lilley, D. G.↗
NASA NTRS1984

Confined Turbulent Swirling Recirculating Flow Predictions

Turbulent swirling flow, the STARPIC computer code, turbulence modeling of turbulent flows, the k-xi turbulence model and extensions, turbulence parameters deduction from swirling confined flow measurements, extension of the k-xi to confined swirling recirculating flows, and general predictions for confined turbulent swirling flow are discussed.

Abujelala, M. T.↗
NASA NTRS2022

The Coronal Veil

Coronal loops, seen in solar coronal images, are believed to represent emission from magneticflux tubes withcompact cross sections. We examine the 3D structure of plasma above an active region in a radiativemagnetohydrodynamic simulation to locate volume counterparts for coronal loops. In many cases, a loop cannot belinked to an individual thin strand in the volume. While many thin loops are present in the synthetic images, thebright structures in the volume are fewer and of complex shape. We demonstrate that this complexity can formimpressions of thin bright loops, even in the absence of thin bright plasma strands. We demonstrate the difficulty ofdiscerning from observations whether a particular loop corresponds to a strand in the volume, or a projectionartifact. We demonstrate how apparently isolated loops could deceive observers, even when observations frommultiple viewing angles are available. While we base our analysis on a simulation, the mainfindings areindependent from a particular simulation setup and illustrate the intrinsic complexity involved in interpretingobservations resulting from line-of-sight integration in an optically thin plasma. We propose alternativeinterpretation for strands seen in Extreme Ultraviolet images of the corona. The“coronal veil”hypothesis ismathematically more generic, and naturally explains properties of loops that are difficult to address otherwise—such as their constant cross section and anomalously high density scale height. We challenge the paradigm ofcoronal loops as thin magneticflux tubes, offering new understanding of solar corona, and by extension, of othermagnetically confined bright hot plasmas

A Malanushenko↗
NASA NTRS1984

Limitations and empirical extensions of the k-epsilon model as applied to turbulent confined swirling flows

Shortcomings and recommended corrections to the standard two-equation k-epsilon turbulence model suggested by previous investigators are presented. They are assessed regarding their applicability to turbulent swirling recirculating flow. Recent experimental data on swirling confined flows, obtained with a five-hole pitot probe and a six-orientation hot-wire probe, are used to obtain optimum values of the turbulence parameters C-mu, C2, and sigma-epsilon for swirling flows. General predictions of moderately and strongly swirling flows with these values are more accurate than predictions with the standard or previous simple extensions of the k-epsilon turbulence model.

Lilley, D. G.↗
NASA NTRS2010

Human Habitation in a Lunar Electric Rover During a 14-Day Field Trial

Various military and commercial entities, as well as the National Aeronautics and Space Administration (NASA), have conducted space cabin confinement studies. However, after an extensive literature search, only one study was found using a simulated lunar rover (LUNEX II), under laboratory conditions, with a crew of two for an eighteen day lunar mission. Forty-three years later, NASA human factors engineers conducted a similar study using the Lunar Electric Rover (LER) in a dynamic real-world lunar simulation at the Black Point Lava Flow in Arizona. The objective of the study was to obtain human-in-the-loop performance data on the vehicle s interior volume with respect to human-system interfaces, crew accommodations, and habitation over a 14-day mission. Though part of a larger study including 212 overall operational elements, this paper will discuss only the performance of fifty different daily habitational elements within the confines of the vehicle carried out by two male subjects. Objective timing data and subjective questionnaire data were collected. Results indicate, much like the LUNEX II study, the LER field study suggest that a crew of two was able to maintain a satisfactory performance of tasks throughout the 14-day field trail within a relative small vehicle volume.

Litaker, Harry, Jr.↗
NASA NTRS1985

Confined turbulent swirling recirculating flow predictions

The capability and the accuracy of the STARPIC computer code in predicting confined turbulent swirling recirculating flows is presented. Inlet flow boundary conditions were demonstrated to be extremely important in simulating a flowfield via numerical calculations. The degree of swirl strength and expansion ratio have strong effects on the characteristics of swirling flow. In a nonswirling flow, a large corner recirculation zone exists in the flowfield with an expansion ratio greater than one. However, as the degree of inlet swirl increases, the size of this zone decreases and a central recirculation zone appears near the inlet. Generally, the size of the central zone increased with swirl strength and expansion ratio. Neither the standard k-epsilon turbulence mode nor its previous extensions show effective capability for predicting confined turbulent swirling recirculating flows. However, either reduced optimum values of three parameters in the mode or the empirical C sub mu formulation obtained via careful analysis of available turbulence measurements, can provide more acceptable accuracy in the prediction of these swirling flows.

Abujelala, M. T.↗
NASA NTRS1987

Confined separated-swirling flows in diffusing ducts

The objective is to establish a detailed experimental data base for evaluation of Navier-Stokes codes for confined separated flows in diffusing s-ducts. The computational thrusts include the following: (1) extension and validation of the LeRC parabolized Navier-Stokes solver, PEPSIG, into the separated flow regime using 'flare' type approximations; (2) evaluation and extensions of state-of-the-art turbulence models for confined separated flow with and without swirl; and (3) evaluation and validation of LeRC time marching 3-D Navier-Stokes code, PROTEUS, into confined separate flow regime. Various aspects of the study are presented in viewgraph form.

Anderson, Bernhard H.↗
NASA NTRS1994

Method for confining the magnetic field of the cross-tail current inside the magnetopause

A method is presented for analytically representing the magnetic field due to the cross-tail current and its closure on the magnetopause. It is an extension of a method used by Tsyganenko (1989b) to confine the dipole field inside an ellipsoidal magnetopause using a scalar potential. Given a model of the cross-tail current, the implied net magnetic field is obtained by adding to the cross-tail current field a potential field B = - del gamma, which makes all field lines divide into two disjoint groups, separated by the magnetopause (i.e., the combined field is made to have zero normal component with the magnetopause). The magnetopause is assumed to be an ellipsoid of revolution (a prolate spheroid) as an approximation to observations (Sibeck et al., 1991). This assumption permits the potential gamma to be expressed in spheroidal coordinates, expanded in spheroidal harmonics and its terms evaluated by performing inversion integrals. Finally, the field outside the magnetopause is replaced by zero, resulting in a consistent current closure along the magnetopause. This procedure can also be used to confine the modeled field of any other interior magnetic source, though the model current must always flow in closed circuits. The method is demonstrated on the T87 cross-tail current, examples illustrate the effect of changing the size and shape of the prescribed magnetopause and a comparison is made to an independent numerical scheme based on the Biot-Savart equation.

Sotirelis, T.↗
NASA NTRS1993

Positivity-preserving numerical schemes for multidimensional advection

This report describes the construction of an explicit, single time-step, conservative, finite-volume method for multidimensional advective flow, based on a uniformly third-order polynomial interpolation algorithm (UTOPIA). Particular attention is paid to the problem of flow-to-grid angle-dependent, anisotropic distortion typical of one-dimensional schemes used component-wise. The third-order multidimensional scheme automatically includes certain cross-difference terms that guarantee good isotropy (and stability). However, above first-order, polynomial-based advection schemes do not preserve positivity (the multidimensional analogue of monotonicity). For this reason, a multidimensional generalization of the first author's universal flux-limiter is sought. This is a very challenging problem. A simple flux-limiter can be found; but this introduces strong anisotropic distortion. A more sophisticated technique, limiting part of the flux and then restoring the isotropy-maintaining cross-terms afterwards, gives more satisfactory results. Test cases are confined to two dimensions; three-dimensional extensions are briefly discussed.

Leonard, B. P.↗
NASA NTRS1996

Response of Tropical Clouds to the Interannual Variation of Sea Surface Temperature

Connections between the large-scale interannual variations of clouds, deep convection, atmospheric winds. vertical thermodynamic structure, and SSTs over global tropical oceans are examined over the period July 1983 - December 1990. The SST warming associated with El Nino had a significant impact on the global tropical cloud field, although the warming itself was confined to the equatorial central and eastern Pacific. Extensive variations of the total cloud field occurred in the northeastern Indian, western and central Pacific, and western Atlantic Oceans. The changes of high and middle clouds dominated the total cloud variation in these regions. Total cloud variation was relatively weak in the eastern Pacific and the Atlantic because of the cancellation between the changes of high and low clouds. The variation of low clouds dominated the total cloud change in those areas. The destabilization of the lapse rate between 900 and 750 mb was more important for enhancing convective instability than was the change of local SSTs in the equatorial central Pacific during the 1997 El Nino. This destabilization is associated with anomalous rising motion in that region. As a result. convection and high and middle clouds increased in the equatorial central Pacific, In the subtropical Pacific, both the change of lapse rate between 900 and 750 mb associated A,ith anomalous subsidence and the decrease of boundary-layer buoyancy due to a decrease of temperature and moisture played an important role in enhancing convective stability. Consequently, convection, as well its high and middle clouds, decreased in these areas. The change ot'low clouds in the equatorial and southeastern Atlantic was correlated to both local SSTs and the SST changes in the equatorial eastern Pacific. In this area. the increase of low clouds was consistent with the sharper inversion during the 1987 El Nino, The strengthening of the inversion was not caused by a local SST change. although the local SST change appeared to he correlated to the change of low clouds. The coherence between clouds and SST tendency shows that SST tendency leads cloud variation in the equatorial Pacific. Thus, the change of clouds does not dominate the sign of SST tendency even though the cloud change was maximum during the 1987 El Nino. In some ideas of the Indian, subtropical Pacific, and North Atlantic Oceans, cloud change leads SST tendency. Cloud change might affect SST tendency in these regions.

Fu, Rong↗
NASA NTRS1987

Some aspects of double layer formation in a plasma constrained by a magnetic mirror

The shift from wave-generated anomalous resistivity toward the more large-scale effects of magnetic confinement of current carrying plasmas was inspired by the more extensive data on auroral particle distribution functions that were made available, data that may often seem consistent with a dissipation-free acceleration of auroral electrons over an extended altitude range. Efforts to interpret these data have brought new vigor to the concept that a smooth and static electric field can be self-consistently generated by suitable pitch angle anisotropies among the high altitude particle populations, different for electrons and ions, and that such an electric field is both necessary and sufficient to maintain the plasma in a quasi-neutral steady state. Certain aspects of this concept are reviewed and criticized, both from a general theoretical standpoint and from the standpoint of what is known about the magnetospheric environment. It is argued that this concept has flaws and that the actual physical problem is considerably more complicated, requiring a more complex electric field, possibly including double layer structures.

Lennartsson, W.↗
NASA NTRS1995

RY Scuti: Infrared and radio observations of the mass-loss wind of a massive binary star system

We report infrared (IR) imaging, IR photometry, IR spectroscopy, optical/IR photopolarimetry, and Very Large Array (VLA) radio observations of the peculiar binary star RY Scuti. These observations provide an unprecedented view of the detailed spatial structure of the equatorial mass-loss wind of a massive, luminous, 'overcontact' binary system. The binary star (0.43 AU separation) is surrounded by a flattened equatorial disk with an outer radius of approximately = 3 x 10(exp 16) cm (2000 AU) that emits strongly in the IR and radio. The inside of the disk is ionized and emits free-free radiation from hydrogen and 12.8 micrometers forbidden-line emission from (Ne II); the outside of the disk emits thermal radiation from silicate dust. Radio continuum emission is also produced in a compact H II region surrounding the binary. The dust may have a polycyclic aromatic hydrocarbon (PAH) component. We use a rudimentary geometric model in which the thermal IR and radio emission from the disk are assumed to arise in a pair of concentric toroidal rings to estimate the physical properties of the disk. The mean radius of the ionized gas toroid is approximately = 1.3 x 10(exp 16) cm (870 AU), and the mean radius of the dust toroid is approximately = 2.2 x 10(exp 16) cm (1470 AU). RY Scuti has a small intrinsic polarization, with the electric vector perpendicular to the equatorial disk, that is probably caused by electron scattering from hot gas close to the central binary. We conclude that neon in the nebula is overabundant with respect to hydrogen and helium by a factor of between 1.6 and 10. Our IR/radio image data suggest that the circumstellar disk is part of an extensive radiation driven mass-loss outflow that is strongly confined to the equatorial plane of the binary system. The sharp spatial separation of the outer dust torous from the inner ionized gas torus confirms earlier suggestions that dust formation in the circumstellar ejecta of very hot stars must occur in regions that are shielded from the hard radiation field.

Gehrz, R. D.↗
NASA NTRS1996

Active Sonic Boom Control

A theory and simulation code are developed to study nonsteady sources as means to control sonic booms of supersonic aircraft. A key result is that the source of sonic boom pressure is not confined to the length of the aircraft but occupies an extensive segment of flight path. An aircraft in nonsteady flight functions as a synthetic aperture antenna, generating complex acoustic waves with no simple relation to instantaneous volume or lift distributions. The theory applies linear acoustics to slender nonsteady sources but requires no far field approximation. The solution for pressure contains a term not seen in Whitham's theory for sonic booms of distant supersonic aircraft. The term describes a pressure field that decays algebraically behind the Mach cone and, in the case of steady flight, integrates to a ground load equal to the weight of the aircraft. The algebraic term is separate from those that describe the sonic boom. Two nonsteady source phenomena are evaluated: periodic velocity changes (surge), and periodic longitudinal lift redistribution (slosh). Surge can attenuate a sonic boom and convert it into prolonged weak reverberation, but accelerations needed to produce the phenomenon seem too large for practical use. Slosh may be practical and can alter sonic booms but does not, on the average, result in boom attenuation. The conclusion is that active sonic boom abatement is possible in theory but maybe not practical

Crow, Steven C.↗
NASA NTRS2010

Psychosocial Characteristics of Optimum Performance in Isolated and Confined Environments (ICE)

The Behavioral Health and Performance (BHP) Element addresses human health risks in the NASA Human Research Program (HRP), including the Risk of Adverse Behavioral Conditions and the Risk of Psychiatric Disorders. BHP supports and conducts research to help characteristics and mitigate the Behavioral Medicine risk for exploration missions, and in some instances, current Flight Medical Operations. The Behavioral Health and Performance (BHP) Element identified research gaps within the Behavioral Medicine Risk, including Gap BMed6: What psychosocial characteristics predict success in an isolated, confined environment (ICE)? To address this gap, we conducted an extensive and exhaustive literature review to identify the following: 1) psychosocial characteristics that predict success in ICE environments; 2) characteristics that are most malleable; and 3) specific countermeasures that could enhance malleable characteristics.

Palinkas, Lawrence A.↗
NASA NTRS1994

Galactic cosmic ray modulation and interplanetary medium perturbations due to a long-living active region during October 1989

During October 1989, three very energetic flares were ejected by the same active region at longitudes 9 deg E, 32 deg W, and 57 deg W, respectively. The shape of the galactic cosmic ray variations suggests the presence of large magnetic cloud structures (Nagashima et al., 1990) following the shock-associated perturbations. In spite of long data gaps the interplanetary observations at Interplanetary Monitoring Platform (IMP) 8 (near the Earth) and International Cometary Explorer (ICE)(approximately 1 AU, approximately 65 deg W) confirm this possibility for the event related to the 9 deg E flare; the principal axes analysis shows that the interplanetary magnetic field variations at both spacecraft locations are mainly confined on a meridian plane. This result suggests that the western longitudinal extension of this cloud is indeed very large (greater than or equal to 5 deg). The nonnegligible depression in the cosmic ray intensity observed inside the possible cloud related to the 57 deg W flare indicates that also the eastern extension could be very wide. The analysis of neutron monitor data shows clearly the cosmic ray trapping effect of magnetic clouds; this mechanism seems to be responsible for the enhanced diurnal effect often observed during the recovery phase of Forbush decreases. We give an interpretation for the anisotropic cosmic ray peak occurring in the third event, and, related to that, we suggest that the Forbush decrease modulated region at the Earth's orbit could be somewhat wider than the magnetic cloud, as already anticipated by Nagashima et al. (1990). By this analysis, based mainly on cosmic ray data, we show that it is possible to do reasonable inferences on the large-scale structure of flare-related interplanetary perturbations when interplanetary medium data are not completely present.

Bavassano, B.↗
NASA NTRS1999

Comparison of Ground-Based 3-Dimensional Lightning Mapping Observations with Satellite-Based LIS Observations in Oklahoma: Comparison of LMS and LIS Lightning Mapping

3-dimensional lightning mapping observations obtained during the MEaPRS program in central Oklahoma during June, 1998 have been compared with observations of the discharges from space, obtained by NASA's Lightning Imaging Sensor (LIS) on the TRMM satellite. Excellent spatial and temporal correlations were observed between the two sets of observations. Most of the detected optical events were associated with intracloud discharges that developed into the upper part of the storm. Cloud-to-ground discharges that were confined to mid- and lower-altitudes tended not to be detected by LIS. Extensive illumination tended to occur in impulsive bursts toward the end or part way through intracloud flashes and appeared to be produced by energetic K-changes that typically occur at these times.

Thomas, Ronald J.↗
NASA NTRS2002

The Spatial Coherence of Interannual Temperature Variations in the Antarctic Peninsula

Over 50 years of observations from climate stations on the west coast of the Antarctic Peninsula show that this is a region of extreme interannual variability in near-surface temperatures. The region has also experienced more rapid warming than any other part of the Southern Hemisphere. In this paper we use a new dataset of satellite-derived surface temperatures to define the extent of the region of extreme variability more clearly than was possible using the sparse station data. The region in which satellite surface temperatures correlate strongly with west Peninsula station temperatures is found to be quite small and is largely confined to the seas just west of the Peninsula, with a northward and eastward extension into the Scotia Sea and a southward extension onto the western slopes of Palmer Land. Correlation of Peninsula surface temperatures with surface temperatures over the rest of continental Antarctica is poor confirming that the west Peninsula is in a different climate regime. The analysis has been used to identify sites where ice core proxy records might be representative of variations on the west coast of the Peninsula. Of the five existing core sites examined, only one is likely to provide a representative record for the west coast.

King, John C.↗