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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Application of aerial photography to the study of small scale upper ocean phenomena

The industrial waste dumped 180 n. miles south of Galveston was monitored in July 1977 by water sampling, hydrographic measurements, acoustic tracking on board two vessels, and by aerial photography. The plume of the waste diffused vertically and horizontally. Photodensitometry of aerial photos of the plume showed lateral dispersion of the plume in agreement with two other methods: acoustic tracking of the waste suspensoid and transmissometer sampling. In addition, the method showed small scale features like the lateral and longitudinal variations in the photodensity, indicating the waste concentration. This waste concentration showed periodic changes in its axial distance, with the spectral peak at about 160 m wave length. It shows a sharp increase at the windward edge of the plume as do the acoustic records. This phenomenon is explained in terms of the shearing current near the surface together with vertical diffusion. The periodic change along the axis is explained in terms of the Langmuir circulation and in terms of internal ship waves.

Ichiye, T.↗
NASA NTRS1984

A case study illustrating time scales and operational responses for a wind shear episode during the JAWS project

A microburst event on 14 July 1983 illustrates the short time scales involved in responding to this type of wind shear. The event also illustrates how a controller used information from several sources in helping a number of aircraft avoid a dangerous wind shear situation. The implications of this event are discussed for the design of future wind shear detection systems, and these observations are related to data obtained during the JAWS experiment.

Bedard, A. J., Jr.↗
NASA NTRS1989

Risk-Based Fire Safety Experiment Definition for Manned Spacecraft

Risk methodology is used to define experiments to be conducted in space which will help to construct and test the models required for accident sequence identification. The development of accident scenarios is based on the realization that whether damage occurs depends on the time competition of two processes: the ignition and creation of an adverse environment, and the detection and suppression activities. If the fire grows and causes damage faster than it is detected and suppressed, then an accident occurred. The proposed integrated experiments will provide information on individual models that apply to each of the above processes, as well as previously unidentified interactions and processes, if any. Initially, models that are used in terrestrial fire risk assessments are considered. These include heat and smoke release models, detection and suppression models, as well as damage models. In cases where the absence of gravity substantially invalidates a model, alternate models will be developed. Models that depend on buoyancy effects, such as the multizone compartment fire models, are included in these cases. The experiments will be performed in a variety of geometries simulating habitable areas, racks, and other spaces. These simulations will necessitate theoretical studies of scaling effects. Sensitivity studies will also be carried out including the effects of varying oxygen concentrations, pressures, fuel orientation and geometry, and air flow rates. The experimental apparatus described herein includes three major modules: the combustion, the fluids, and the command and power modules.

Apostolakis, G. E.↗
NASA NTRS1993

Meso-beta scale numerical simulation studies of terrain-induced jet streak mass/momentum perturbations

The first section is on 3-D numerical modeling of terrain-induced circulations and covers the following: (1) additional insights into gravity wave generation mechanisms based on the control simulation; (2) ongoing nested-grid numerical simulations; (3) work to be completed during the remainder of FY-93; and (4) work objectives for FY-94. The second section is on linear theory and theoretical modeling and covers the following: (1) the free response of a uniform barotropic flow to an initially stationary unbalanced (ageostrophic) zonal wind anomaly; and (2) the free response of a uniform barotropic flow to an initially stationary balanced zonal wind anomaly.

Lin, Yuh-Lang↗
NASA NTRS1994

Meso-beta scale numerical simulation studies of terrain-induced jet streak mass/momentum perturbations

An in-depth analysis of observed gravity waves and their relationship to precipitation bands over the Montana mesonetwork during the 1981 CCOPE case study indicates that there were two episodes of coherent internal gravity waves. One of the fundamental unanswered questions from this research, however, concerns the dynamical processes which generated the observed waves, all of which originated from the region encompassing the borders of Montana, Idaho, and Wyoming. While geostrophic adjustment, shearing instability, and terrain where all implicated separately or in concert as possible wave generation mechanisms, the lack of upper-air data within the wave genesis region made it difficult to rigorously define the genesis processes from observations alone. In this report we employ a mesoscale numerical model to help diagnose the intricate early wave generation mechanisms during the first observed wave episode.

Lin, Yuh-Lang↗
NASA NTRS1995

Meso-beta scale numerical simulation studies of terrain-induced jet streak mass/momentum perturbations

Mesoscale model simulations provide insight into the complex jet streak adjustments on 11-12 July 1981 that preceded the first of two significant gravity wave events to have been generated over the Rocky Mountains in Montana. Simulations employing a variety of terrain treatments indicate that prior to wave formation, geostrophic adjustment processes modified the structure of the mid-upper tropospheric jet streak by creating secondary jetlets to the southeast of the polar jet streak in proximity to the gravity wave generation region. This simulated restructuring of the mid-upper tropospheric jet streak is the result of a four stage process. During stage 1, the wind adjusts to the mass field as the jet streak exit region propagates into the inflection point between the upstream trough and downstream ridge in the height field. Stage 2 is initiated as the mass field is forced to adjust to the new ageostrophic wind field created during stage 1. Stage 3 is defined by a second geostrophic adjustment process occurring in a similar manner but to the south and east of the adjustment which occurs during stage 1. A low-level mesoscale jetlet is formed during stage 4 in response to the low-level pressure falls that are established during stage 3. The perturbation of this jetlet, caused by orographically-induced adiabatic and diabatic physical processes, is the likely mechanism responsible for the generation of the first and second episode of observed gravity waves. The dynamics responsible for this wave episode are discussed as differential surface sensible heating inducing an orographically-forced mountain-plains solenoid, resulting in the formation of additional mesoscale jetlets and internal gravity waves. Also discussed is how convective latent heating modifies the numerically simulated terrain-induced internal gravity waves, especially their amplitude and phase velocities, which provide better agreement with those wave characteristics observed in nature. Finally, the three-dimensional linear response of a zonally uniform barotropic flow in a vertically unbounded, continuously stratified, Boussinesq atmosphere which is perturbed from geostrophic equilibrium is investigated.

Lin, Yuh-Lang↗
NASA NTRS1995

Studies of planetary scale waves and instabilities in support of the geophysical fluid flow cell experiment on USML-2

High resolution numerical simulations of thermal convection in a rapidly rotating channel with gravity perpendicular to the rotation vector are described. The convecting columns are subject to a beta-effect resulting from cross-channel topographic vortex stretching. The symmetries of the problem allow many invariant wavenumber sets, and this property is associated with the existence of stable multiple-equilibria at modest supercriticality. The transition to chaotic behavior involves the production of intermittent unstable orbits off a two-torus in energy space. At very high Rayleigh number (of order 10(exp 6) to 10(exp 7)) the motion can be turbulent, depending on the size of beta. However, the turbulence is usually characterized by an almost-periodic formation of patches of small scale convection that cause regular pulsations in the accompanying strong zonal jets. The processes maintaining these flows may be related to those responsible for the zonal currents on Jupiter and for cyclic variability on the Sun.

Hart, J. E.↗
NASA NTRSDate not supplied

A Study of Large Scale Power Extraction and Insertion on Turbofan Performance and Stability

This paper describes the effects of turbofan power extraction and insertion (augmentation) on engine performance and stability. The purpose of this paper is to present how power augmentation affects a dual spool gas turbine engine cycle where the engine will also be required to provide thrust. The goals for the paper are to describe effective limits of power augmentation and offer strategies, utilizing spool choice and variable geometries, to maximize augmentation effect. While Analysis is general two potential uses are explored: Power extraction for electrified aircraft propulsion purposes. And, Power insertion for thrust assist. Results of the paper show it is possible to extract over 20% (at 85% max thrust) and gain roughly 12% of maximum thrust through power insertion.

Gas Turbine Engines↗
NASA NTRSDate not supplied

A Study of Large Scale Power Extraction and Insertion on Turbofan Performance and Stability

This describes the effects of turbofan power extraction and insertion (augmentation) on engine performance and stability. The purpose of this paper is to present how power augmentation affects a dual spool gas turbine engine cycle where the engine will also be required to provide thrust. The goals for the paper are to describe effective limits of power augmentation and offer strategies, utilizing spool choice and variable geometries, to maximize augmentation effect. While Analysis is general, two potential uses are explored: Power extraction for electrified aircraft propulsion and power insertion for thrust assist. Results of the paper show it is possible to extract over 20% (at 85% max thrust) and gain roughly 12% of maximum thrust through power insertion.

Gas Turbine engines↗
NASA NTRS2003

A Preliminary Study of Ice-Accretion Scaling for SLD Conditions

Proposed changes to aircraft icing certification rules are being considered by European, Canadian, and American regulatory agencies to include operation in super-cooled large droplet conditions (SLD). This paper reports results of an experimental study in the NASA Glenn Icing Research Tunnel (IRT) to evaluate how well scaling methods developed for Appendix C conditions might apply to SLD conditions. Until now, scaling studies have been confined to the FAA FAR-25 Appendix C envelope of atmospheric cloud conditions. Tests were made in which it was attempted to scale to a droplet MVD of 50 microns from clouds having droplet MVDs of 175, 120, 100, and 70 microns. Scaling was based on the Ruff method with scale velocities found either by maintaining constant Weber number or by using the average of the velocities obtained by maintaining constant Weber number and constant Reynolds number. Models were unswept NACA 0012 wing sections. The reference model had a chord of 91.4 cm. Scale models had chords of 91.4, 80.0, and 53.3 cm. Tests were conducted with reference airspeeds of 100 and 150 kt (52 and 77 m/s) and with freezing fractions of 1.0, 0.6, and 0.3. It was demonstrated that the scaled 50-micron cloud simulated well the non-dimensional ice shapes accreted in clouds with MVD's of 120 microns or less.

Anderson, David N.↗
NASA NTRS2007

Comparisons of Instantaneous TRMM Ground Validation and Satellite Rain Rate Estimates at Different Spatial Scales

This study provides a comprehensive inter-comparison of instantaneous rain rates observed by the two rain sensors aboard the TRMM satellite with ground data from two regional sites established for long-term ground validation: Kwajalein Atoll and Melbourne, Florida. The satellite rain algorithms utilize remote observations of precipitation collected by the TRMM microwave imager (TMI) and the Precipitation Radar (PR) aboard the TRMM satellite. Three standard Level I1 rain products are generated from operational applications of the TMI, PR and Combined (COM) rain algorithms using rain information collected from the TMI and the PR along the orbital track of the TRMM satellite. In the first part of the study, 0.25 x 0.25 instantaneous rain rates obtained from the TRMM 3668 product were analyzed and compared to instantaneous GV rain rates gridded at a scale of 0.5deg x 0.5. In the second part of the study, TMI, PR, COM and GV rain rates were spatio-temporally matched and averaged at the scale of TMI footprint (- 150 sq km). This study covered a six-year period 1999-2004 and consisted of over 50,000 footprints for each GV site. In the first analysis our results showed that all of the respective rain rate estimates agree well, with some exceptions. The more salient differences were associated with heavy rain events in which one or more of the algorithms failed to properly retrieve these extreme events. Also, it appears that there is a preferred mode of precipitation for TMI rain rates at or near 2 mm/hr over the ocean. This mode was noted over ocean areas of Kwajalein and Melbourne and has been observed in TRMM tropical-global ocean areas as well.

Wolff, David B.↗
NASA NTRS1986

Feedback systems and multiple time-scales

A study is conducted of feedback design for systems with multiple time-scale structure uncovering an intrinsic time-scale structure for a state feedback system with full state output. From this a multiple time-scale asymptotic observer and a system with state feedback via a two time-scale asymptotic observer is considered. Finally more general results for a restricted class of systems are obtained.

Silva-Madriz, R.↗
NASA NTRS2002

A Parametric Study of Fine-scale Turbulence Mixing Noise

The present paper is a study of aerodynamic noise spectra from model functions that describe the source. The study is motivated by the need to improve the spectral shape of the MGBK jet noise prediction methodology at high frequency. The predicted spectral shape usually appears less broadband than measurements and faster decaying at high frequency. Theoretical representation of the source is based on Lilley's equation. Numerical simulations of high-speed subsonic jets as well as some recent turbulence measurements reveal a number of interesting statistical properties of turbulence correlation functions that may have a bearing on radiated noise. These studies indicate that an exponential spatial function may be a more appropriate representation of a two-point correlation compared to its Gaussian counterpart. The effect of source non-compactness on spectral shape is discussed. It is shown that source non-compactness could well be the differentiating factor between the Gaussian and exponential model functions. In particular, the fall-off of the noise spectra at high frequency is studied and it is shown that a non-compact source with an exponential model function results in a broader spectrum and better agreement with data. An alternate source model that represents the source as a covariance of the convective derivative of fine-scale turbulence kinetic energy is also examined.

Khavaran, Abbas↗
NASA NTRS1984

Study of large-scale mixing in developing wakes behind streamlined bodies

Heat-tagging and conditional sampling techniques were used to study the large scale mixing process in the developing wake behind a streamlined body. The results were used to understand the manner in which the large eddy length scale evolves from a value appropriate to a boundary layer to that appropriate to the asymptotic far-wake.

Ramaprian, B. R.↗
NASA NTRS1996

Full-Scale Wind-Tunnel Studies of F/A-18 Tail Buffet

Tail buffet studies were conducted on a full-scale, production F/A-18 fighter aircraft in the 80 by 120 ft Wind Tunnel at NASA Ames Research Center. The F/A-18 was tested over an angle-of-attack range of 18-50 deg, and at wind speeds of up to 168 ft/s, corresponding to a Reynolds number of 12.3x10(exp 6) based on mean aerodynamic chord and a Mach number of 0.15. The port, vertical tail fin was instrumented and the aircraft was equipped with a removable leading-edge extension (LEX) fence. Time-averaged, power-spectral analysis results are presented for the tail fin bending moment derived from the integrated pressure field, for the zero side-slip condition, both with and without the LEX fence. The LEX fence significantly reduces the magnitude of the rms pressures and bending moments. Scaling issues are addressed by comparing full-scale results for pressures at the 60%-span and 45%-chord location with small-scale, F/A-18 tail-buffet data. The comparison shows that the tail buffet frequency scales very well with length and velocity. Root-mean-square pressures and power spectra do not scale as well. The LEX fence is shown to reduce tail buffet loads at all model scales.

Meyn, Larry A.↗
NASA NTRS1997

Observational and Model Studies of Large-Scale Mixing Processes in the Stratosphere

The following is the final technical report for grant NAGW-3442, 'Observational and Model Studies of Large-Scale Mixing Processes in the Stratosphere'. Research efforts in the first year concentrated on transport and mixing processes in the polar vortices. Three papers on mixing in the Antarctic were published. The first was a numerical modeling study of wavebreaking and mixing and their relationship to the period of observed stratospheric waves (Bowman). The second paper presented evidence from TOMS for wavebreaking in the Antarctic (Bowman and Mangus 1993). The third paper used Lagrangian trajectory calculations from analyzed winds to show that there is very little transport into the Antarctic polar vortex prior to the vortex breakdown (Bowman). Mixing is significantly greater at lower levels. This research helped to confirm theoretical arguments for vortex isolation and data from the Antarctic field experiments that were interpreted as indicating isolation. A Ph.D. student, Steve Dahlberg, used the trajectory approach to investigate mixing and transport in the Arctic. While the Arctic vortex is much more disturbed than the Antarctic, there still appears to be relatively little transport across the vortex boundary at 450 K prior to the vortex breakdown. The primary reason for the absence of an ozone hole in the Arctic is the earlier warming and breakdown of the vortex compared to the Antarctic, not replenishment of ozone by greater transport. Two papers describing these results have appeared (Dahlberg and Bowman; Dahlberg and Bowman). Steve Dahlberg completed his Ph.D. thesis (Dahlberg and Bowman) and is now teaching in the Physics Department at Concordia College. We also prepared an analysis of the QBO in SBUV ozone data (Hollandsworth et al.). A numerical study in collaboration with Dr. Ping Chen investigated mixing by barotropic instability, which is the probable origin of the 4-day wave in the upper stratosphere (Bowman and Chen). The important result from this paper is that even in the presence of growing, unstable waves, the mixing barriers around

Bowman, Kenneth P.↗
NASA NTRS1992

Numerical study of the small scale structures in Boussinesq convection

Two-dimensional Boussinesq convection is studied numerically using two different methods: a filtered pseudospectral method and a high order accurate Essentially Nonoscillatory (ENO) scheme. The issue whether finite time singularity occurs for initially smooth flows is investigated. The numerical results suggest that the collapse of the bubble cap is unlikely to occur in resolved calculations. The strain rate corresponding to the intensification of the density gradient across the front saturates at the bubble cap. We also found that the cascade of energy to small scales is dominated by the formulation of thin and sharp fronts across which density jumps.

Weinan, E.↗