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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Measurements in a Transitional Boundary Layer Under Low-Pressure Turbine Airfoil Conditions

This report presents the results of an experimental study of transition from laminar to turbulent flow in boundary layers or in shear layers over separation zones on a convex-curved surface which simulates the suction surface of a low-pressure turbine airfoil. Flows with various free-stream turbulence intensity (FSTI) values (0.5%, 2.5% and 10%), and various Reynolds numbers (50,000, 100,000 200,000 and 300,000) are investigated. Reynold numbers in the present study are based on suction surface length and passage exit mean velocity. Flow separation followed by transition within the separated flow region is observed for the lower-Re cases at each of the FSTI levels. At the highest Reynolds numbers and at elevated FSn, transition of the attached boundary layer begins before separation, and the separation zone is small. Transition proceeds in the shear layer over the separation bubble. For both the transitional boundary layer and the transitional shear layer, mean velocity, turbulence intensity and intermittency (the fraction of the time the flow is turbulent) distributions are presented. The present data are compared to published distribution models for bypass transition, intermittency distribution through transition, transition start position, and transition length. A model developed for transition of separated flows is shown to adequately predict the location of the beginning of transition, for these cases, and a model developed for transitional boundary layer flows seems to adequately predict the path of intermittency through transition when the transition start and end are known. These results are useful for the design of low-pressure turbine stages which are known to operate under conditions replicated by these tests.

Simon, Terrence W.↗
NASA NTRS2003

Compact Laser-Based Sensors for Monitoring and Control of Gas Turbine Combustors

Research is reported on the development of sensors for gas turbine combustor applications that measure real-time gas temperature using near-infrared water vapor absorption and concentration in the combustor exhaust of trace quantities of pollutant NO and CO using mid-infrared absorption. Gas temperature is extracted from the relative absorption strength of two near-infrared transitions of water vapor. From a survey of the water vapor absorption spectrum, two overtone transitions near 1800 nm were selected that can be rapidly scanned in wavelength by injection current tuning a single DFB diode laser. From the ratio of the absorbances on these selected transitions, a path-integrated gas temperature can be extracted in near-real time. Demonstration measurements with this new temperature sensor showed that combustor instabilities could be identified in the power spectrum of the temperature versus time record. These results suggest that this strategy is extremely promising for gas turbine combustor control applications. Measurements of the concentration of NO and CO in the combustor exhaust are demonstrated with mid-infrared transitions using thermo-electrically cooled, quantum cascade lasers operating near 5.26 and 4.62 microns respectively. Measurements of NO are performed in an insulated exhaust duct of a C2H4-air flame at temperatures of approximately 600 K. CO measurements are performed above a rich H2-air flame seeded with CO2 and cooled with excess N2 to 1150 K. Using a balanced ratiometric detection technique a sensitivity of 0.36 ppm-m was achieved for NO and 0.21 ppm-m for CO. Comparisons between measured and predicted water-vapor and CO2 interference are discussed. The mid-infrared laser quantum cascade laser technology is in its infancy; however, these measurements demonstrate the potential for pollutant monitoring in exhaust gases with mid-IR laser absorption.

Hanson, Ronald K.↗
NASA NTRS2012

Observations of Traveling Crossflow Resonant Triad Interactions on a Swept Wing

Experimental evidence indicates the presence of a triad resonance interaction between traveling crossflow modes in a swept wing flow. Results indicate that this interaction occurs when the stationary and traveling crossflow modes have similar and relatively low amplitudes (approx.1% to 6% of the total freestream velocity). The resonant interaction occurs at instability amplitudes well below those typically known to cause transition, yet transition is observed to occur just downstream of the resonance. In each case, two primary linearly unstable traveling crossflow modes are nonlinearly coupled to a higher frequency linearly stable mode at the sum of their frequencies. The higher-frequency mode is linearly stable and presumed to exist as a consequence of the interaction of the two primary modes. Autoand cross-bicoherence are used to determine the extent of phase-matching between the modes, and wavenumber matching confirms the triad resonant nature of the interaction. The bicoherence results indicate a spectral broadening mechanism and the potential path to early transition. The implications for laminar flow control in swept wing flows are significant. Even if stationary crossflow modes remain subcritical, traveling crossflow interactions can lead to early transition.

Eppink, Jenna L.↗
NASA NTRSDate not supplied

Trajectory Shaping of Lunar Descent Approach Phase for Human Landing Systems

NASA’s Artemis program will have many mission phases but perhaps the most dangerous and dynamic is the powered descent and landing phase. NASA’s HLS Program has developed a candidate lunar approach concept of operations to address the needs of both hazard detection sensors and crew visibility of the landing site. The descent trajectory is shaped such that the approach phase is initiated at a steep trajectory path angle for hazard map generation then transitions to a shallow trajectory path angle to facilitate crew landing site visibility. The results show this tailored approach concept is a viable option to reduce risk during landing with minimal performance impacts.

Trajectory Optimization↗
NASA NTRS1972

Revisions to V/STOL handling qualities criteria of AGARD report 408

A brief review of selected handling qualities criteria for V/STOL aircraft shows that although a clearer understanding of the requirements for controversial areas such as roll control power, vertical flight path control, and transition is in hand, considerably more research is needed to refine these criteria for operational IFR activity. Because many items interact to influence the pilots' overall impression of the aircraft's behaviour, additional work of a systematic nature must be done to clarify this aspect. A better definition of a gust model which includes discrete gust effects is needed to firm up criteria for both hover and STOL operation.

Anderson, S. B.↗
NASA NTRS1971

A progress report on the development of an augmentor wing jet STOL research aircraft.

The development of the aircraft has progressed to the point where the design of the modifications to the de Havilland C-8A Buffalo is complete and the engines are being tested. The predicted performance shows that the aircraft will be able to take off and land in less than 1500 ft. Simulation studies indicate that the handling qualities of the aircraft, with stability augmentation, will be acceptable for STOL research missions. Special techniques were required, however, for flight path control and transition from cruise to landing configuration .

Quigley, H. C.↗
NASA NTRS1935

Flight Tests of a Balanced Split Flap with Particular Reference to Rapid Operation

The flight path of a small parasol monoplane equipped with a special type of balanced split flap was determined for a series of glides during which the time taken to deflect or retract the flap was varied from 1 to 15 seconds in order to study the effect of the time taken to complete a flap movement on the motion of an airplane between the start of a flap movement and the attainment of steady flight with the new flap setting. For flap movements accompanied by a change of lift characteristics, and consequently of velocity, there is an appreciable delay in obtaining a desired change in glide angle even though the flap is operated instantaneously. Immediate control of the glide path is obtained only when the speed is maintained during the flap movement. When the speed is changed, the deviation from the desired path during the transition increases in proportion to the rapidity with which the flap is moved so that, with a high-lift flap, abrupt retraction at speeds less than the minimum speed with the flap retracted may be dangerous if practiced close to the ground.

Soule, H A↗
NASA NTRS2007

Water Vapor Profiling From CoSSIR Radiometric Measurements

Previous millimeter-wave radiometry for water vapor profiling, by either airborne or satellite sensors, has been limited to frequencies less than or equal to 183 GHz. The retrievals are generally limited to an altitude range of 0-10 km. The additional measurements at the frequencies of 380.2 plus or minus 0.8, 380.2 plus or minus 1.8, 380.2 plus or minus 3.3, and 380.2 plus or minus 6.2 GHz provided by the new airborne Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) can extend this profiling capability up to an altitude of about 15 km. Furthermore, the retrievals can be performed over both land and water surfaces in the tropics without much difficulty. These properties are demonstrated by recent CoSSIR measurements on board the NASA WB-57 aircraft during CR-AVE in January 2006. Retrievals of water vapor mixing ratio were performed at eight altitude levels of 1, 3, 5, 7, 9, 11, 13, and 15 km from CoSSIR data sets acquired at observational angles of 0 and 53.4 degrees, and the results were compared with other available measurements from the same aircraft and near-concurrent satellites. A comparison of the variations of mixing ratios retrieved from CoSSIR and those derived from the Meteorological Measurement System (MMS) in the aircraft vicinity, along the path of the transit flight on January 14, 2006, appears to show some connection, although the measurements were referring to different altitudes. A very good agreement was found between the collocated values of total precipitable water derived from the CoSSIR-retrieved water vapor profiles and those estimated from TMI (TRMM Microwave Imager)

Wang, J. R.↗
DOE OSTI2023

Statistical Approaches for Pebble Bed Reactor Operations and Safeguards

The design of pebble bed reactors (PBRs) and their method of operation align more closely with statistical approaches used in manufacturing and process control than traditional safeguards statistical approaches. The reason is PBRs will employ a nondestructive assay (NDA) measurement (burnup measurement system [BUMS]) that is part of the fuel handling system supporting discharge decisions in addition to the reactor code which monitor performance. The integration of these two approaches provides the opportunity to monitor reactor performance statistically for both operations and safeguards in ways not achievable using other reactor designs. For light water reactors (LWRs), knowledge about reactor code performance in predicting irradiated special nuclear material (SNM) content historically was only achieved from special measurement campaigns or from fuel reprocessing. Conversely, through statistical comparison of the BUMS with the reactor code-predicted values, PBRs can achieve this in real time. The resulting SNM distribution is an indicator of reactor performance because factors such as transit time and path of the pebble fuel through the reactor determine the plutonium production and uranium depletion. By analyzing the predicted and measured values, opportunities exist to adjust operating parameters, fuel design, and other characteristics to optimize performance and fuel utilization. From a safeguards perspective, this approach also provides the information necessary to validate declared values and evaluate whether the reactor is being operated as expected. This paper outlines statistical approaches for PBRs that can be used to support both operations and safeguards.

Ball, Cory↗
NASA NTRS1977

Airborne navigation system performance during RNAV/MLS transition

Aircraft position error sensitivity to sensor errors and flight path geometry is analyzed during RNAV/MLS transition using a digital computer simulation. The avionics sensitivity data provides information necessary to establish requirements for additional guidance law design and to establish airspace requirements for maneuvering to null out any residual RNAV errors upon MLS transition. The data base is also beneficial as planning information for subsequent flight testing. The parameters varied during the generation of the data base include flight profile, error source content and magnitude, ground facility location, runway/flight path orientation and navigation mode. The avionics, autopilots and aircraft dynamics correspond to the existing NASA Terminal Configured Vehicle. Significant transients were observed during MLS transition, primarily in the vertical channel. These transients have a significant impact on airspace requirements and operational procedures in the RNAV/MLS environment.

Heine, W.↗
DOE OSTI2020

Electronic energy gap closure and metal-insulator transition in dense liquid hydrogen

Here, using quantum Monte Carlo (QMC) calculations, we investigate the insulator-metal transition observed in liquid hydrogen at high pressure. Below the critical temperature of the transition from the molecular to the atomic liquid, the fundamental electronic gap closure occurs abruptly, with a small discontinuity reflecting the weak first-order transition in the thermodynamic equation of state. Above the critical temperature, molecular dissociation sets in while the gap is still open. When the gap closes, the decay of the off-diagonal reduced density matrix shows that the liquid enters a gapless, but localized, phase: there is a crossover between the insulating and the metallic liquids. Compared to different density functional theory (DFT) functionals, our QMC calculations provide larger values for the fundamental gap and the electronic density of states close to the band edges, indicating that optical properties from DFT potentially benefit from error cancellations.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The roles of yield strength mismatch, interface strength, and plastic strain gradients in fatigue crack growth across interfaces

An irreversible cohesive zone model was used to understand how plastic strain gradients and yield strength mismatches affect fatigue crack growth across bi-material and multilayer interfaces for a range of interface strengths. Parametric studies identified regimes of penetration through the interface, deflection into the interface, and a transition where cracks extend on both paths. Plastic strain gradients strongly influence the transition regime, and a yield strength mismatch is necessary to cause deflection. For crack growth across an interlayer, interactions between the interfaces occur when the crack-tip plastic zone spans the interlayer. Plastic strain gradients promote penetration through the interlayer.

42 ENGINEERING↗
NASA NTRS1997

Equally parsimonious pathways through an RNA sequence space are not equally likely

An experimental system for determining the potential ability of sequences resembling 5S ribosomal RNA (rRNA) to perform as functional 5S rRNAs in vivo in the Escherichia coli cellular environment was devised previously. Presumably, the only 5S rRNA sequences that would have been fixed by ancestral populations are ones that were functionally valid, and hence the actual historical paths taken through RNA sequence space during 5S rRNA evolution would have most likely utilized valid sequences. Herein, we examine the potential validity of all sequence intermediates along alternative equally parsimonious trajectories through RNA sequence space which connect two pairs of sequences that had previously been shown to behave as valid 5S rRNAs in E. coli. The first trajectory requires a total of four changes. The 14 sequence intermediates provide 24 apparently equally parsimonious paths by which the transition could occur. The second trajectory involves three changes, six intermediate sequences, and six potentially equally parsimonious paths. In total, only eight of the 20 sequence intermediates were found to be clearly invalid. As a consequence of the position of these invalid intermediates in the sequence space, seven of the 30 possible paths consisted of exclusively valid sequences. In several cases, the apparent validity/invalidity of the intermediate sequences could not be anticipated on the basis of current knowledge of the 5S rRNA structure. This suggests that the interdependencies in RNA sequence space may be more complex than currently appreciated. If ancestral sequences predicted by parsimony are to be regarded as actual historical sequences, then the present results would suggest that they should also satisfy a validity requirement and that, in at least limited cases, this conjecture can be tested experimentally.

NASA Discipline Exobiology↗
DOE OSTI2023

Assessment of potential impact of magnetic fields from a subsea high-voltage DC power cable on migrating green sturgeon, Acipenser medirostris

Abstract Empirical evidence suggests that marine animals perceive and orient to local distortions in the earth’s natural magnetic field. Magnetic fields (MFs) generated by electrified underwater cables may produce similar local distortions in the earth’s main field. Concern exists that these distortions may impact migration movements of MF-sensitive animals. The Trans Bay Cable (TBC) is a ± 200-kV, 400-megawatt, 85-km high-voltage direct current transmission line buried through San Francisco Bay (37° 56′ 8.81″ N, 122° 27′ 0.19″ W). Detections of adult green sturgeon implanted with acoustic transmitters were used from six cross-bay receiver arrays from 2006 to 2015 to investigate how inbound and outbound migration movements through lower portions of their route to/from upstream breeding grounds are related to the TBC’s energization status (off/on) and other local environmental variables. Here, we assess how these variables impacted transit success, misdirection from the migration route, transit times, and migration path locations within stretches between the Bay’s mouth and the start of the Sacramento River. Overall, there was varied evidence for any effect on migration behavior associated with cable status (off/on). A higher percentage of inbound fish successfully transited after the cable was energized, but this effect was nonsignificant in models including temperature. Outbound fish took longer to transit after cable energization. Inbound and outbound migration path locations were not significantly influenced by cable energization, but results suggest a potential subtle relationship between energization and both inbound and outbound paths. Overall, additional migration-based studies are needed to investigate the impact of anthropogenic cables on marine species.

Wyman, Megan T. (ORCID:0000000256844603)↗
DOE OSTI2024

From anti-Arrhenius to Arrhenius behavior in a dislocation-obstacle bypass: Atomistic simulations and theoretical investigation

Dislocations are the primary carriers of plasticity in metallic materials. Understanding the basic mechanisms for dislocation movement is paramount to predicting the material mechanical response. Relying on atomistic simulations, we observe a transition from non-Arrhenius to Arrhenius behavior in the rate of an edge dislocation overcoming the long-range elastic interaction with a prismatic loop in tungsten. Close to the critical resolved shear stress, the process shows a non-Arrhenius behavior at low temperatures. However, as the temperature increases, the activation entropy starts to dominate, leading to a traditional Arrhenius-like behavior. Here, we have computed the activation entropy analytically along the minimum energy path following Schoeck’s method, which captures the cross-over between anti-Arrhenius and Arrhenius domains. Also, the Projected Average Force Integrator (PAFI), another simulation method to compute free energies along an initial transition path, exhibits considerable concurrence with Schoeck’s formalism. We conclude that entropic effects need to be considered to understand processes involving dislocations bypassing elastic barriers close to the critical resolved shear stress. More work needs to be performed to fully understand the discrepancies between Schoeck’s and PAFI compared to molecular dynamics.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Energy management during the space shuttle transition.

An approach to calculating optimal, gliding flight paths of the type associated with the space shuttle's transition from entry to cruising flight is presented. Kinetic energy and total energy (per unit weight) replace velocity and time in the dynamic equations, reducing the dimension and complexity of the problem. The capability for treating integral and terminal penalties (as well as Mach number effects) is retained in the numerical optimization; hence, stability and control boundaries can be observed as trajectories to the desired final energy, flight path angle, and range are determined. Numerical results show that the 'jump' to the 'front-side of the L/D curve' need not be made until the end of the transition and that the dynamic model provides a conservative range estimate. Alternatives for real-time trajectory control are discussed.

Stengel, R. F.↗
NASA NTRS1972

Energy management during the space shuttle transition

An approach to calculating optimal, gliding flight paths of the type associated with the space shuttle's transition from entry to cruising flight is presented. Kinetic energy and total energy (per unit weight) replace velocity and time in the dynamic equations, reducing the dimension and complexity of the problem. The capability for treating integral and terminal penalties (as well as Mach number effects) is retained in the numerical optimization; hence, stability and control boundaries can be observed as trajectories to the desired final energy, flight path angle, and range are determined. Numerical results show that the jump to the front-side of the L/D curve need not be made until the end of the transition and that the dynamic model provides a conservative range estimate. Alternatives for real time trajectory control are discussed.

Stengel, R. F.↗
NASA NTRS1987

Intracavity absorption with a continuous wave dye laser - Quantification for a narrowband absorber

An experimental investigation of the dependence of intracavity absorption on factors including transition strength, concentration, absorber path length, and pump power is presented for a CW dye laser with a narrow-band absorber (NO2). A Beer-Lambert type relationship is found over a small but useful range of these parameters. Quantitative measurement of intracavity absorption from the dye laser spectral profiles showed enhancements up to 12,000 (for pump powers near lasing threshold) when compared to extracavity measurements. The definition of an intracavity absorption coefficient allowed the determination of accurate transition strength ratios, demonstrating the reliability of the method.

Brobst, William D.↗