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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Dynamic Nucleation of Supercooled Melts and Measurement of the Surface Tension and Viscosity

We investigate the phenomenon of acoustic pressure-induced nucleation by using a novel approach involving the large amplitude resonant radial oscillations and collapse of a single bubble intentionally injected into a supercooled liquid. Using a combination of previously developed and proven techniques, the bubble is suspended in a fluid host by an ultrasonic field which supplies both the levitation capability as well as the forcing of the radial oscillations. We observe the effects of an increase in pressure (due to bubble collapse) in a region no larger than 100 microns within the supercooled melt to rigorously probe the hypothesis of pressure-induced nucleation of the solid phase. The use of single bubbles operating in narrow temporal and spatial scales will allow the direct and unambiguous correlation between the origin and location of the generation of the disturbance and the location and timing of the nucleation event. In a companion research effort, we are developing novel techniques for the non-contact measurements of the surface tension and viscosity of highly viscous supercooled liquids. Currently used non-invasive methods of surface tension measurement for the case of undercooled liquids generally rely of the quantitative determination of the resonance frequencies of drop shape oscillations, of the dynamics of surface capillary waves, or of the velocity of streaming flows. These methods become quickly ineffective when the liquid viscosity rises to a significant value. An alternate and accurate method which would be applicable to liquids of significant viscosity is therefore needed. We plan to develop such a capability by measuring the equilibrium shape of levitated undercooled melt droplets as they undergo solid-body rotation. The experimental measurement of the characteristic point of transition (bifurcation point) between axisymmetric and two-lobed shapes will be used to calculate the surface tension of the liquid. Such an approach has already been validated through the experimental verification of numerical modeling results. The experimental approach involves levitation, melting, and solidification of undercooled droplets using a hybrid ultrasonic-electrostatic technique in both a gaseous as well as a vacuum environment. A shape relaxation method will be investigated in order to derive a reliable method to measure the viscosity of undercooled melts. The analysis of the monotonic relaxation to equilibrium shape of a drastically deformed and super-critically damped free drop has been used to derive interfacial tension of immiscible liquid combinations where one of the component has high viscosity. A standard approach uses the initial elongation of a droplet through shear flows, but an equivalent method could involve the initial deformation of a drop levitated in a gas by ultrasonic radiation pressure, electric stresses, or even solid body rotation. The dynamic behavior of the free drop relaxing back to equilibrium shape will be modeled, and its characteristic time dependence should provide a quantitative means to evaluate the liquid viscosity.

Trinh, E. H.↗
NASA NTRS1988

A survey of oscillating flow in Stirling engine heat exchangers

Similarity parameters for characterizing the effect of flow oscillation on wall shear stress, viscous dissipation, pressure drop and heat transfer rates are proposed. They are based on physical agruments and are derived by normalizing the governing equations. The literature on oscillating duct flows, regenerator and porous media flows is surveyed. The operating characteristics of the heat exchanger of eleven Stirling engines are discribed in terms of the similarity parameters. Previous experimental and analytical results are discussed in terms of these parameters and used to estimate the nature of the oscillating flow under engine operating conditions. The operating points for many of the modern Stirling engines are in or near the laminar to turbulent transition region. In several engines, working fluid does not pass entirely through heat exchangers during a cycle. Questions that need to be addressed by further research are identified.

Simon, Terrence W.↗
NASA NTRSDate not supplied

Serial Propellant Tank Pressure Behavior in Artemis 1 Orion-ESM Propulsion System

An oscillatory pressure behavior was observed throughout the Orion-ESM propulsion system during the Artemis I mission. This behavior was attributed to propellant oscillations within the serial line connecting the two propellant tanks for each commodity. A linearized dynamic model of the serial propellant tank system was derived to explain this behavior. The model showed excellent agreement with the flight data, with the predicted system natural frequencies matching the flight data within 1%.

Liquid propulsion systems↗
NASA NTRSDate not supplied

Towards Simultaneous Multi-Parameter Measurements Using Burst-Mode Frequency-Scanning Planar Laser-Induced Fluorescence

While planar laser-induced fluorescence (PLIF) can provide valuable flow visualization, there are many challenges in extracting quantitative measurements from the fluorescence intensity. To overcome the multi-parameter dependence of the signal intensity, frequency scanning planar laser-induced fluorescence (FS-PLIF) provides the potential for 2D temperature, pressure, and velocity measurements by spectrally resolving the excitation spectrum of one or more fluorescence transitions to extract the Doppler shift, Doppler- and collisional-broadening of absorption lines, and the relative signal intensities of multiple transitions. This work aims to characterize a burst-mode FS-PLIF system consisting of a Spectral Energies, LLC burst-mode laser coupled with a Spectral Energies, LLC optical parametric oscillator using nitric oxide (NO) static pressure cell measurements. The effect of the OPO cavity on intensity fluctuations during frequency-scanning is investigated. A NO PLIF model is implemented to investigate the feasibility of property measurements using single- and two-NO-line scans.

burst-mode laser↗
NASA NTRS2016

North Pacific Decadal Variability: Insights from a Biennial ENSO Environment

This study examines the mechanisms of the Pacific decadal oscillation (PDO) in the NASA GEOS-5 general circulation model (GCM). Similar to several other state-of-the-art GCMs, the El Niño-Southern Oscillation (ENSO) simulated by the GEOS-5 has a strong biennial periodicity. Since this is a model bias that precludes a strong role of ENSO, it provides a unique environment to assess the other leading mechanisms of North Pacific decadal variability. Despite the biennial ENSO periodicity, the model simulates a realistic PDO pattern in the North Pacific that is resolved as the first empirical orthogonal function (EOF) of winter mean sea surface temperature (SST). The spectrum of the PDO indicates no preferred periodicity. The SST anomalies associated with the PDO, particularly its basin wide structure, are primarily forced by the Aleutian low through Ekman transport. The slow geostrophic transport in association with the meridional adjustment of the subtropical gyre is limited to a narrow region in the Kuroshio-Oyashio extension, north of 40degN. The atmosphere's response to the PDO, while weak, projects onto the North Pacific Oscillation (NPO), a meridional dipole in sea level pressure. Both the lack of preferred periodicity and the weak atmospheric response indicate an air-sea coupled oscillation is an unlikely mechanism in this model. In agreement with recent studies, the NPO is correlated with the North Pacific Gyre Oscillation, which is another leading EOF of North Pacific SST variability. The results emphasize the role of atmospheric variability in the North Pacific SST modes, thereby bringing into question the potential for their predictability.

GCM↗
NASA NTRS2017

Acoustic Effects in Classical Nucleation Theory

The effect of sound wave oscillations on the rate of nucleation in a parent phase can be calculated by expanding the free energy of formation of a nucleus of the second phase in powers of the acoustic pressure. Since the period of sound wave oscillation is much shorter than the time scale for nucleation, the acoustic effect can be calculated as a time average of the free energy of formation of the nucleus. The leading non-zero term in the time average of the free energy is proportional to the square of the acoustic pressure. The Young-Laplace equation for the surface tension of the nucleus can be used to link the time average of the square of the pressure in the parent phase to its time average in the nucleus of the second phase. Due to the surface tension, the pressure in the nuclear phase is higher than the pressure in the parent phase. The effect is to lower the free energy of formation of the nucleus and increase the rate of nucleation.

Baird, J. K.↗
DOE OSTI2024

FY-24 Progress on Computational Modeling of the Water Based NSTF

This report summarizes the computational modeling of the Natural Convection Shutdown Heat Removal Test Facility (NSTF) completed in FY24. This year’s modeling campaign focuses on the continual testing of the RELAP5 model against experimental data. Several fault cases were simulated with the RELAP5 model in FY23 to study the accuracy of the model under complex flow conditions. Similarly, in FY24, a case is simulated where the chimney outlet is throttled with a valve while the flow is undergoing two-phase oscillations. The purpose of this case is to study the effects of increasing pressure drop in the two-phase region on the system behavior. Even though the model is able to capture the experimental data qualitatively, it overpredicts the pressure drops experienced by the flow in the two-phase regime. Nevertheless, the model and the experiment show that oscillations are stabilized with increased pressure drop in the two-phase region.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2020

Fluctuations in Jupiter’s Equatorial Stratospheric Oscillation

The equatorial stratospheres of the Earth, Jupiter, and Saturn all exhibit a remarkable periodic oscillation of their temperatures and winds with height. Earth’s Quasi-Biennial Oscillation (QBO) and Saturn’s Quasi-Periodic Equatorial Oscillation (QPO) have recently been observed to experience disruptions in their vertical structure as a consequence of atmospheric events occurring far from the equator. Here we reveal that Jupiter’s Quasi-Quadrennial Oscillation (QQO) can also be perturbed by strong tropospheric activity at the equatorial and off-equatorial latitudes. Observations of Jupiter’s stratospheric temperatures between 1980 and 2011 show two significantly different periods for the QQO, with a 5.7-year period between 1980 and 1990 and a 3.9-year period between 1996 and 2006. Major disruptions to the predicted QQO pattern in 1992 and 2007 coincided with dramatic planetary-scale disturbances in the equatorial and low-latitude troposphere, suggesting that they are connected to vertically propagating waves generated by meteorological sources in the deeper troposphere (i.e. 500-4000 mbar pressures). Disruptions in Jupiter’s periodic oscillations are thus inherently different than those at Saturn or the Earth. This interconnectivity between the troposphere and stratosphere that is likely common to all planetary atmospheres shows that seemingly regular cycles of variability can switch between different modes when subjected to extreme meteorological events

Arrate Antunano↗
NASA NTRS1982

Numerical simulations of unsteady transonic flow in diffusers

Forced and naturally occurring, self-sustaining oscillations of transonic flows in two-dimensional diffusers were computed using MacCormack's hybrid method. Depending upon the shock strengths and the area ratios, the flow was fully attached or separated by either the shock or the adverse pressure gradient associated with the enlarging diffuser area. In the case of forced oscillations, a sinusoidal plane pressure wave at frequency 300 Hz was prescribed at the exit. A sufficiently large amount of data were acquired and Fourier analyzed. The distrbutions of time-mean pressures, the power spectral density, and the amplitude with phase angle along the top wall and in the core region were determined. Comparison with experimental results for the forced oscillation generally gave very good agreement; some success was achieved for the case of self-sustaining oscillation despite substantial three-dimensionality in the test. An observation of the sequence of self-sustaining oscillations was given.

Liou, M.-S.↗
NASA NTRS1980

Induction powered biological radiosonde

An induction powered implanted monitor for epidurally measuring intracranial pressure and telemetering the pressure information to a remote readout is disclosed. The monitor utilizes an inductance-capacitance (L-C) oscillator in which the C comprises a variable capacitance transducer, one electrode of which is a small stiff pressure responsive diaphragm. The oscillator is isolated from a transmitting tank circuit by a buffer circuit and all electric components in the implanted unit except an input and an output coil are shielded by a metal housing.

Fryer, T. B.↗
NASA NTRS1987

Water-absorbing capacitor system for measuring relative humidity

A method and apparatus using a known water-absorbent polymer as a capacitor which is operated at a dc voltage for measuring relative humidity is presented. When formed as a layer between porous electrically-conductive electrodes and operated in an RC oscillator circuit, the oscillator frequency varies inversely with the partial pressure of the moisture to be measured. In a preferred embodiment, the capacitor is formed from Nafion and is operated at a low dc voltage with a resistor as an RC circuit in an RC oscillator. At the low voltage, the leakage current is proper for oscillation over a satisfactory range. The frequency of oscillation varies in an essentially linear fashion with relative humidity which is represented by the moisture being absorbed into the Nafion. The oscillation frequency is detected by a frequency detector.

Laue, Eric G.↗
NASA NTRS2000

Spontaneous fluctuations in cerebral blood flow: insights from extended-duration recordings in humans

To determine the dependence of cerebral blood flow (CBF) on arterial pressure over prolonged time periods, we measured beat-to-beat changes in mean CBF velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (Finapres) continuously for 2 h in six healthy subjects (5 men and 1 woman, 18-40 yr old) during supine rest. Fluctuations in velocity and pressure were quantified by the range [(peak - trough)/mean] and coefficients of variation (SD/mean) in the time domain and by spectral analysis in the frequency domain. Mean velocity and pressure over the 2-h recordings were 60 +/- 7 cm/s and 83 +/- 8 mmHg, associated with ranges of 77 +/- 8 and 89 +/- 10% and coefficients of variation of 9.3 +/- 2.2 and 7.9 +/- 2.3%, respectively. Spectral power of the velocity and pressure was predominantly distributed in the frequency range of 0.00014-0.1 Hz and increased inversely with frequency, indicating characteristics of an inverse power law (1/f(alpha)). However, linear regression on a log-log scale revealed that the slope of spectral power of pressure and velocity was steeper in the high-frequency (0.02-0.5 Hz) than in the low-frequency range (0.002-0.02 Hz), suggesting different regulatory mechanisms in these two frequency ranges. Furthermore, the spectral slope of pressure was significantly steeper than that of velocity in the low-frequency range, consistent with the low transfer function gain and low coherence estimated at these frequencies. We conclude that 1) long-term fluctuations in CBF velocity are prominent and similar to those observed in arterial pressure, 2) spectral power of CBF velocity reveals characteristics of 1/f(alpha), and 3) cerebral attenuation of oscillations in CBF velocity in response to changes in pressure may be more effective at low than that at high frequencies, emphasizing the frequency dependence of cerebral autoregulation.

NASA Discipline Cardiopulmonary↗
NASA NTRS1990

Unsteady potential flow past a propeller blade section

An analytical study was conducted to predict the effect of an oscillating stream on the time dependent sectional pressure and lift coefficients of a model propeller blade. The assumption is that as the blade sections encounter a wake, the actual angles of attack vary in a sinusoidal manner through the wake, thus each blade is exposed to an unsteady stream oscillating about a mean value at a certain reduced frequency. On the other hand, an isolated propeller at some angle of attack can experience periodic changes in the value of the flow angle causing unsteady loads on the blades. Such a flow condition requires the inclusion of new expressions in the formulation of the unsteady potential flow around the blade sections. These expressions account for time variation of angle of attack and total shed vortices in the wake of each airfoil section. It was found that the final expressions for the unsteady pressure distribution on each blade section are periodic and that the unsteady circulation and lift coefficients exhibit a hysteresis loop.

Takallu, M. A.↗
NASA NTRS2001

Experimental Investigation of Transition to Turbulence as Affected By Passing Wakes

This paper presents experimental results from a study of the effects of periodically passing wakes upon laminar-to-turbulent transition and separation in a low-pressure turbine passage. The test section geometry is designed to simulate unsteady wakes in turbine engines for studying their effects on boundary layers and separated flow regions over the suction surface by using a single suction surface and a single pressure surface to simulate a single turbine blade passage. Single-wire, thermal anemometry techniques are used to measure time-resolved and phase averaged, wall-normal profiles of velocity, turbulence intensity and intermittency at multiple streamwise locations over the turbine airfoil suction surface. These data are compared to steady-state wake-free data collected in the same geometry to identify the effects of wakes upon laminar-to-turbulent transition. Results are presented for flows with a Reynolds number based on suction surface length and stage exit velocity of 50,000 and an approach flow turbulence intensity of 2.5%. While both existing design and experimental data are primarily concerned with higher Reynolds number flows (Re greater than 100,000), recent advances in gas turbine engines, and the accompanying increase in laminar and transitional flow effects, have made low-Re research increasingly important. From the presented data, the effects of passing wakes on transition and separation in the boundary layer, due to both increased turbulence levels and varying streamwise pressure gradients are presented. The results show how the wakes affect transition. The wakes affect the flow by virtue of their difference in turbulence levels and scales from those of the free-stream and by virtue of their ensemble- averaged velocity deficits, relative to the free-stream velocity, and the concomitant changes in angle of attack and temporal pressure gradients. The relationships between the velocity oscillations in the freestream and the unsteady velocity profile shapes in the near-wall flow are described. In this discussion is support for the theory that bypass transition is a response of the near-wall viscous layer to pressure fluctuations imposed upon it from the free-stream flow. Recent transition models are based on that premise. The data also show a significant lag between when the wake is present over the surface and when transition begins.cous layer to pressure fluctuations imposed upon it from the free-stream flow. Recent transition models are based on that premise. The data also show a significant lag between when the wake is present over the surface and when transition begins.cous layer to pressure fluctuations imposed upon it from the free-stream flow. Recent transition models are based on that premise. The data also show a significant lag between when the wake is present over the surface and when transition begins.

Kaszeta, Richard W.↗
NASA NTRS1973

A method for calculating unsteady turbulent boundary layers in two- and three-dimensional flows.

The governing equations for an unsteady turbulent boundary layer on a swept infinite cylinder, composed of a continuity equation, a pair of momentum equations and a pair of rate equations for the shear stress, based on the turbulent kinetic-energy equation, are solved numerically. These rate equations for the shear-stress express a balance between the convection, production, dissipation and diffusion of the turbulent shear stress components. Due to the physical model of turbulence employed, this system of equations is hyperbolic. An explicit, second-order accurate, conditionally stable difference scheme for this system, together with appropriate boundary and initial conditions, is formulated and developed into a computer program. Calculations for oscillating free stream flows with no pressure gradient show significant unsteady effects on the turbulent boundary layer.

Singleton, R. E.↗
NASA NTRS1976

Early meteorological results from the Viking 2 lander

Early results from the meteorological instruments on the Viking 2 lander are presented. As on lander 1, the daily patterns of temperature, wind, and pressure have been highly repetitive during the early summer period. The average daily maximum temperature was 241 K and the diurnal minimum was 191 K. The wind has a vector mean of 0.7 meter per second from the southeast with a diurnal amplitude of 3 meters per second. Pressure exhibits both diurnal and semidiurnal oscillations, although of substantially smaller amplitude than those of lander 1. Departures from the repetitive diurnal patterns begin to appear on sol 37.

Hess, S. L.↗