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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Lunar Seismology: the Internal Structure of the Moon

The direct P and S wave arrival times are the primary data set that can be measured on the seismograms of natural lunar seismic events. Polarization filtering techniques allow the enhancement of secondary body wave arrivals and record curves to identify the secondary phases and deduce structural information. Finally, shear wave amplitude vs. distance curves yield information on the location and magnitude of seismic velocity gradients in the interior. The results of these analyses show that the moon appears to have a two-layer crust at all four seismic stations: a 20 km upper crust that seems to be constant at all sites and a lower crust that is 40 km thick at stations 12 and 14 (mare), 55 + or - 10 km at station 16 (highland), and tentatively either 40 km or 70 km at station 15. The lower mantle extends from 480 km to at least 1100 km depth which is the maximum depth of penetration of all but a few seismic waves used as data. No definitive evidence for or against a lunar core exists.

Goins, N. R.↗
NASA NTRS2016

Stationary Crossflow Breakdown due to Mixed Mode Spectra of Secondary Instabilities

Numerical simulations are used to study laminar breakdown characteristics associated with stationary crossflow instability in the boundary-layer flow over a subsonic swept-wing configuration. Previous work involving the linear and nonlinear development of individual, fundamental modes of secondary instability waves is extended by considering the role of more complex, yet controlled, spectra of the secondary instability modes. Direct numerical simulations target a mixed mode transition scenario involving the simultaneous presence of Y and Z modes of secondary instability. For the initial amplitudes investigated in this paper, the Y modes are found to play an insignificant role during the onset of transition, in spite of achieving rather large, O(5%), amplitudes of RMS velocity fluctuation prior to transition. Analysis of the numerical simulations shows that this rather surprising finding can be attributed to the fact that the Y modes are concentrated near the top of the crossflow vortex and exert relatively small influence on the Z modes that reside closer to the surface and can lead to transition via nonlinear spreading that does not involve interactions with the Y mode. Finally, secondary instability calculations reveal that subharmonic modes of secondary instability have substantially lower growth rates than those of the fundamental modes, and hence, are less likely to play an important role during the breakdown process involving complex initial spectra.

Li, Fei↗
NASA NTRS1981

The secondary flow near a baroclinic planetary wave critical line

A critical line (CL) is the surface where the phase speed of a wave in a fluid is equal to the speed of the background flow. The considered investigation is concerned with one aspect of the simplest model of a CL in which the CL is assumed to totally absorb energy from steady, stationary, planetary waves. The aspect of interest is the secondary mean circulation near a CL in a baroclinic atmosphere. The motivation for this study is the observation of the nearly vertical CL by O'Neill and Taylor (1979) which appeared during the sudden warming of 1976/77. Even though the treatment of the CL is highly idealized in the investigation, there is evidence which indicates a very large rate of change in the zonally averaged temperature along a CL may occur. The Lagrangian-mean properties of an idealized baroclinic CL are also examined. It is found that the Lagrangian jets may provide an important transport process for exchange of stratospheric and tropospheric air.

Schoeberl, M. R.↗
NASA NTRS1984

The interpretation of SIR-B imagery of surface waves and other oceanographic features using in-situ, meteorological satellite, and infrared satellite data

The overall aim is to interpret Shuttle Imaging Radar-B imagery of selected ocean areas near the United Kingdom using available data from ships and buoys, with particular emphasis on understanding the mechanisms involved in the backscattering of microwaves from the sea surface and their relationship to surface gravity waves. The secondary objective is to use a multispectral approach to study sea-surface expressions such as slicks, internal waves, and eddies. Data acquisition, handling, and analysis approaches and expected results are discussed.

Allan, T.↗
DOE OSTI2022

Nonidealities in Rotating Detonation Engines

A rotating detonation engine (RDE) is a realization of pressure-gain combustion, wherein a traveling detonation wave confined in a chamber provides shock-based compression along with chemical heat release. Due to the high wave speeds, such devices can process high mass flow rates in small volumes, leading to compact and unconventional designs. RDEs involve unsteady and multiscale physics, and their operational characteristics are determined by an equilibrium between large- and small-scale processes. While RDEs can provide a significant theoretical gain in efficiency, achieving this improvement requires an understanding of the multiscale coupling. Specifically, unavoidable nonidealities, such as unsteady mixing, secondary combustion, and multiple competing waves associated with practical designs, need to be understood and managed. The secondary combustion processes arise from fuel/air injection and unsteady and incomplete mixing, and can create spurious losses. In addition, a combination of multiple detonation and secondary waves compete and define the dynamical behavior of mixing, heat release distribution, and the overall mode of operation of the device. This review discusses the current understanding of such nonidealities and describes the tools and techniques used to gain insight into the extreme unsteady environment in such combustors.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS1991

Square patterns and secondary instabilities in driven capillary waves

Amplitude equations (including nonlinear damping terms) are derived which describe the evolution of patterns in large-aspect-ratio driven capillary wave experiments. For drive strength just above threshold, a reduction of the number of marginal modes (from traveling capillary waves to standing waves) leads to simpler amplitude equations, which have a Lyapunov functional. This functional determines the wavenumber and symmetry (square) of the most stable uniform state. The original amplitude equations, however, have a secondary instability to transverse amplitude modulation (TAM), which is not present in the standing-wave equations. The TAM instability announces the restoration of the full set of marginal modes.

Milner, S. T.↗
NASA NTRS1980

The secondary circulation associated with a vertically aligned planetary wave critical line

An analytic model of the secondary circulation associated with a vertically aligned, energy absorbing, planetary wave critical line shows that strong zonal mean vertical motions and heating (or cooling) can develop even though no eddy transport of heat occurs. The type of secondary circulation which develops around a vertically aligned critical line may provide a mechanism for stratosphere-troposphere exchange of air. The model predictions are discussed with reference to the 76/77 sudden warming.

Schoeberl, M. R.↗
NASA NTRS1991

A laser velocimeter investigation of the normal shock-wave boundary layer interaction

Nonintrusive 3-D measurements were made of a normal shock wave/turbulent boundary layer interaction. The measurements were made through a quadrant of a square test section of a continuous flow supersonic wind tunnel in which a normal shock wave had been stabilized. Two dimensional measurements were made throughout the interaction region while 3-D measurements were made near the corner in the vicinity of the shock where 3-D flow effects were expected to be significant. Laser Doppler velocimetry, surface static pressure measurements, and flow visualization techniques were used for two freestream nominal Mach number test cases: 1.6 and 1.3. No turbulence information was obtained. The mean velocity measurements were converted to Mach number by recording the wind tunnel total temperature. Some shock oscillation was present during both of the test cases. After startup of the wind tunnel, the shock oscillated with an amplitude of approx. + or - 1 cm, however, after reaching steady condition, the shock oscillation amplitude was greatly reduced, as evidenced by the laser velocimeter results. The Mach 1.3 test case resulted in a nearly uniform flow without secondary shock waves and with no or very isolated corner separation.

Chriss, Randall M.↗
DOE OSTI2024

Shock-induced twinning/detwinning and spall failure in Cu–Ta nanolaminates at atomic scales

Here, this study provides new insights into the role of interfaces on the deformation and failure mechanisms in shock-loaded Cu–Ta–Cu trilayer system. The thickness of the Ta layer, piston velocities, and shock pulse durations were varied to explore the impact of impedance mismatch and loading conditions on spallation behavior and twin formation. It was found that the interfaces play a crucial role in the dynamic response of these multilayered systems since secondary reflection waves generated at the interfaces significantly affected the peak stress and pressure profiles, influencing void nucleation and failure modes. In the trilayer systems, failure predominantly occurred at interfaces and within the Ta layer, with void nucleation sites and twinning behavior being markedly different compared to single-crystal Cu and Ta. Increasing the Ta layer thickness modified the wave interactions, leading to different failure locations. Higher piston velocities were associated with increased spall strength by enhancing wave interactions and void formation, particularly at the interfaces and within the Ta layer, under specific configurations. Additionally, shorter shock pulse durations facilitated earlier initiation of the release fan, reducing twin formation and altering the failure dynamics by accelerating twin annihilation and pressure release.

36 MATERIALS SCIENCE↗
DOE OSTI2026

WaveDP

We developed a robust deep learning model designed to effectively reduce background noise and measure signal arrival times from seismic waveforms. This model processes a 57-second, three-component seismogram to predict the probability of Primary (P) and Secondary (S) waves for each timestamp, while also generating a denoised seismogram. Training was conducted using the benchmark STEAD dataset, which includes globally distributed earthquake signals recorded at local distances ranging from 0 to 350 kilometers.

Chai, Chengping [Oak Ridge National Laboratory (OR↗
NASA NTRS1975

Symbol synchronizer assembly instability study, part 2

Data processing to develop a third-order phase model and to translate all such processed data to the frequency realm for further analysis was described. The frequency study yields a long frequency modulation (FM) drift sinusoid (1600-sec period), an impressed secondary drift wave with a period of about 116 sec, and a set of even harmonics of twice the ramp period-the latter arising from, and used to modify, the phase detector model. The result is applied secondarily to estimate the strong-signal SSA phase detector response "out-of-lock." Finally, the main drift components are verified against all available data, and the result is used to estimate minimum lock conditions and the SSA drift effect under normal operating modes. The instability problem appears marginally resolvable if the acquisition technique is modified.

Bunce, R. C.↗
NASA NTRS1981

Structure of the lunar crust at highland site Apollo Station 16

The seismic crustal structure of the moon is known in the region of Oceanus Procellarum from the analysis of artificial impact data. To extend this knowledge we have used data from natural lunar seismic events to search for secondary seismic wave arrivals in the form of peg-leg multiples caused by reflections at crustal interfaces and converted arrivals caused by refractions at crustal interfaces. A polarization filter has been applied to the data to enhance the rectilinear particle motion expected for the onset of these body wave arrivals in the scattered coda of lunar seismograms. The results of this work tentatively indicate that the highland site at station 16 has a 75 km thick crust with an intermediate 20 km interface, compared to the 60 km crust and 20 km interface in Oceanus Procellarum, a mare region. Since the 20 km upper crust appears to exist at both highland and mare sites, it probably does not represent a mare basalt layer but rather a more general feature of the crust. Crustal thickness may partially control elevation by isostasy.

Goins, N. R.↗
DOE OSTI2021

Ground-state phase diagram of the t-t ′ -J model

Significance Theoretical efforts to understand the superconducting cuprates have focused on a few simplified but challenging models: notably the Hubbard and the t - t ′ - J models. Using density matrix renormalization group (DMRG) simulations on width-8 cylinders, we study the ground-state phase diagram of the t - t ′- J model. The next nearest-neighbor hopping t ′ allows one to distinguish between hole ( t ′ < 0 ) and electron doping ( t ′ > 0 ). We find for the magnetic, charge, and single-particle properties that this model roughly captures the differences between the electron- and hole-doped cuprates. However, the superconducting properties differ. For hole doping ( t ′ < 0 ), there is an absence of superconductivity, while for electron doping ( t ′ > 0), we find d -wave superconductivity coexisting with antiferromagnetism and a secondary triplet p -wave pairing component.

Jiang, Shengtao↗
NASA NTRS1977

The generation of sound by vorticity waves in swirling duct flows

Swirling flow in an axisymmetric duct can support vorticity waves propagating parallel to the axis of the duct. When the cross-sectional area of the duct changes a portion of the wave energy is scattered into secondary vorticity and sound waves. Thus the swirling flow in the jet pipe of an aeroengine provides a mechanism whereby disturbances produced by unsteady combustion or turbine blading can be propagated along the pipe and subsequently scattered into aerodynamic sound. In this paper a linearized model of this process is examined for low Mach number swirling flow in a duct of infinite extent. It is shown that the amplitude of the scattered acoustic pressure waves is proportional to the product of the characteristic swirl velocity and the perturbation velocity of the vorticity wave. The sound produced in this way may therefore be of more significance than that generated by vorticity fluctuations in the absence of swirl, for which the acoustic pressure is proportional to the square of the perturbation velocity. The results of the analysis are discussed in relation to the problem of excess jet noise.

Howe, M. S.↗
NASA NTRS1980

Report of secondary flows, boundary layers, turbulence and wave team, report 1

General criteria for a flight test option are that: (1) there be a good opportunity for comparison with other measurement techniques; (2) the flow to be measured is of considerable scientific or practical interest; and (3) the airborne laser Doppler system is well suited to measure the required quantities. The requirement for comparison, i.e., ground truth, is particularly important because this is the first year of operation for the system. It is necessary to demonstrate that the system does actually measure the winds and compare the results with other methods to provide a check on the system error analysis. The uniqueness of the laser Doppler system precludes any direct comparison, but point measurements from tower mounted wind sensors and two dimensional fields obtained from radars with substantially different sampling volumes are quite useful.

Scoggins, J. R.↗
NASA NTRS1980

Report of secondary flows, boundary layers, turbulence and wave team

Correspondence concerning the comparison of horizontal wind fields, two dimensional spectra, heat flux, mesoscale divergence and deformation in the prestorm environment, and thunderstorm gust front winds is presented. Other subjects include the use of radar to determine heating rate and evaporation near the Earth's surface for an unstable boundary layer and statistical considerations in the estimation of wind fields from single Doppler radar and application to prestorm boundary layer observations.

Doviak, R.↗
NASA NTRS1993

On the secondary instability of the most dangerous Goertler vortex

Recent studies have demonstrated the most unstable Goertler vortex mode is found in flows, both two and three-dimensional, with regions of (moderately) large body curvature and these modes reside within a thin layer situated at the base of the conventional boundary layer. Further work concerning the nonlinear development of the most dangerous mode demonstrates that the flow results in a self induced flow reversal. However, prior to the point at which flow reversal is encountered, the total streamwise velocity profile is found to be highly inflectional in nature. Previous work then suggests that the nonlinear vortex state will become unstable to secondary, inviscid, Rayleigh wave instabilities prior to the point of flow reversal. Our concern is with the secondary instability of the nonlinear vortex states, which result from the streamwise evolution of the most unstable Goertler vortex mode, with the aim of determining whether such modes can induce a transition to a fully turbulent state before separation is encountered.

Otto, S. R.↗