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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Low-frequency oscillations in radiative-convective systems

Although eastward propagation has long been considered one of the essential features of the Madden-Julian waves, recent observations have revealed a stationary or quasi-stationary component in the oscillations, particularly in measures of the diabatic heating rate. Wave-CISK theories of the low-frequency oscillations have struggled to explain the observed period and vertical structure of the waves. On the other hand, theoretical and numerical studies have shown that low-frequency waves strongly resembling the observed oscillations can be excited by specified low-frequency oscillations of the convective heating. A problem with the latter set of theories is that the cause of the oscillatory heating has not been satisfactorily explained. It is proposed here that the observed low-frequency wave motions are the response to forcing by an essentially stationary, self-excited oscillating heat source that is produced by nonlinear interactions among radiation, cumulus convection, and the surface fluxes of sensible heat and moisture. Feedback of the large-scale motions on the latent heating is not required. Results from two very different one-dimensional models are presented to support this hypothesis. The physical processes included in the models are essentially the same, that is, radiation, cumulus convection, and the surface fluxes of sensible heat and moisture; the first model is highly simplified, however, while the second includes relatively sophisticated parameterizations of all the relevant physical processes. Results from both models show low-frequency oscillations of the latent heating, temperature, and moisture. Experiments show that the oscillations are favored by a warm sea surface and weak surface wind speeds, consistent with the observed conditions over the Indian Ocean and the tropical western Pacific Ocean.

Hu, QI↗
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 NTRS1986

The quasi-biennial oscillation of ozone in the tropical middle stratosphere - A one-dimensional model

A one-dimensional model of the quasi-biennial oscillation (QBO) of ozone in the tropical middle stratosphere is derived based on assumed (observed) zonal wind QBO in a coupled dynamic, radiative/photochemical system. It is found that the derived vertical variation of the ozone QBO amplitude has two maxima, one at 32 km and the other at 22 km, and a minimum at 28 km. These are in qualitative agreement with observations. In the height interval 30-35 km, the ozone QBO is closely related to temperature dependent photochemistry, and the ozone and temperature variations are out of phase. Below 28 km, where vertical ozone and thermal transports are important, ozone and temperature oscillations are in phase, but both are approximately 270 deg out of phase with the vertical wind variation.

Ling, Xiu-De↗
NASA NTRS1995

Magellan radio occultation measurements of atmospheric waves on Venus

Radio occultation experiments were conducted at Venus on three consecutive orbits of the Magellan spacecraft in October 1991. Each occultation occurred over the same topography (67 deg N, 127 deg E) and at the same local time (22 hr 5 min), but the data are sensitive to zonal variations because the atmosphere rotates significantly during one orbit. Through comparisons between observations and predictions of standard wave theory, we have demonstrated that small-scale oscillations in retrieved temperature profiles as well as scintillations in received signal intensity are caused by a spectrum of vertically propagating internal gravity waves. There is a strong similarity between the intensity scintillations observed here and previous measurements, which pertain to a wide range of locations and experiment dates. This implies that the same basic phenomenon underlies all the observations and hence that gravity waves are a persistent, global feature of Venus' atmosphere. We obtained a fairly complete characterization of a gravity wave that appears above the middle cloud in temperature measurements on all three orbits. The amplitude and vertical wavelength are about 4 K and 2.5 km respectively, at 65 km. A model for radiative damping implies that the wave intrinsic frequency is approximately 2 x 10(exp 4) rad/sec, the corresponding ratio between horizontal and vertical wavelengths is approximately 100. The wave is nearly stationary relative to the surface or the Sun. Radiative attenuation limits the wave amplitude at altitudes above approximately 65 km, leading to wave drag on the mean zonal winds of about +0.4 m/sec per day (eastward). The sign, magnitude, and location of this forcing suggest a possible role in explaining the decrease with height in the zonal wind speed that is believed to occur above the cloud tops. Temperature oscillations with larger vertical wavelengths (5-10 km) were also observed on all three orbits, but we are able unable to interpret these unambiguously.

Hinson, David P.↗
NASA NTRS1978

Data analysis of the LPSP experiment on OSO-8

The first and statistically most reliable step in the data analysis - the computation of the vertical phase lag between photospheric and chromospheric oscillations - was completed. Unfortunately, the error associated with this calculated phase lag is so great that the result has no physical significance. Since the subsequent data analysis that was originally planned would have much larger associated errors, it was concluded that the data available is insufficient to allow any meaningful results to be derived. Accordingly, the project was terminated. The reasons for the failure of the data are discussed. There are two basic reasons for this failure; (1) the very low signal to noise ratio of the raw data, and (1) the small statistical sample that resulted from the very small number of usable orbits. The final phase of data analysis is described. Finally, some comments and recommendations of a general nature are made concerning this entire contract effort. It is hoped that at least some lessons can be learned from this particular Guest Investigator project, so that future Guest Investigator programs can be pursued more effectively, and with less risk.

Frazier, E. N.↗
NASA NTRS1982

Vertical axis wind turbine drive train transient dynamics

Start up of a vertical axis wind turbine causes transient torque oscillations in the drive train with peak torques which may be over two and one half times the rated torque of the turbine. A computer code, based on a lumped parameter model of the drive train, was developed and tested for the low cost 17 meter turbine; the results show excellent agreement with field data. The code was used to predict the effect of a slip clutch on transient torque oscillations. It was demonstrated that a slip clutch located between the motor and brake can reduce peak torques by thirty eight percent.

Clauss, D. B.↗
NASA NTRS1988

A new look at equatorial quasi-biennial oscillation models

Simplified quasi-biennial oscillation models are studied, taking bifurcation theory into account. It is found that the model has a trivial steady solution of no mean zonal flow when the two components of the wave forcing are symmetric. The steady solution becomes unstable with respect to an oscillatory eigenmode when the amplitude of the wave forcing exceeds a critical value. Periodic solutions branch off from the steady solution at this point because of Hopf bifurcation. If the two components are not symmetric, the model has a nontrivial steady solution with nonzero mean zonal flow. Hopf bifurcation takes place and periodic solutions which are not symmetric with respect to time appear. A two-level model is developed to analyze the quasi-biennial oscillation mechanism. It is shown that both vertical diffusion and the shielding effect are needed to obtain periodic solutions.

Yoden, Shigeo↗
NASA NTRS1990

Fluid dynamics and low gravity effects of chemical vapor deposition

Based on the comparison between experimental data and numerical results for the growth of GaAs from TMGa, it was shown that 3D simulations are necessary to simulate rectangular CVD reactors even when operated under subcritical (Ra) conditions. The important points found are summarized in the three attached reprints. The experimental studies of mixed convection in horizontal channels have shown three regimes of high Ra (22,220) number flows. At Re = 18.5, the rolls develop very quickly, significantly modulating the axial velocity even before it reaches the beginning of the hot plate. A few centimeters downstream, the velocities become asymmetric about the vertical centerplane and at x = 12 cm, become unsteady. These asymmetries were predicted theoretically, but experimental evidence has not been published prior to this work. At Re = 36, the axial velocity is only slightly modified at x = 0. Although the flow remains steady and symmetric about the vertical centerplane, there is a small spatial oscillation in the velocities over the length of the channel. The period of this oscillation was around 5 cm. At Re = 54, the longitudinal rolls developed smoothly over a length of 30 cm, with no asymmetries, unsteadiness, or spatial oscillations. Comparison of numerical simulations of these flows to experiments has revealed the importance and difficulty of setting proper thermal boundary conditions on the sidewalls. Calculated flows and experimentally measured flows showed very similar profiles, but at different axial locations, with the rolls developing more rapidly in the experiments. This is directly attributable to partially conducting sidewalls of the apparatus being hotter in the entrance section than the adiabatic walls of the simulations. A thorough comparison of the experimental data and numerical results for a variety of sidewall boundary conditions is in preparation.

Nyce, Thomas A.↗
NASA NTRS1991

Transonic shock-induced dynamics of a flexible wing with a thick circular-arc airfoil

Transonic shock boundary layer oscillations occur on rigid models over a small range of Mach numbers on thick circular-arc airfoils. Extensive tests and analyses of this phenomena have been made in the past but essentially all of them were for rigid models. A simple flexible wing model with an 18 pct. circular arc airfoil was constructed and tested in the Langley Transonic Dynamics Tunnel to study the dynamic characteristics that a wing might have under these circumstances. In the region of shock boundary layer oscillations, buffeting of the first bending mode was obtained. This mode was well separated in frequency from the shock boundary layer oscillations. A limit cycle oscillation was also measured in a third bending like mode, involving wind vertical bending and splitter plate motion, which was in the frequency range of the shock boundary layer oscillations. Several model configurations were tested, and a few potential fixes were investigated.

Bennett, Robert M.↗
NASA NTRS1984

Thermospheric gravity waves near the source - Comparison of variations in neutral temperature and vertical velocity at Sondre Stromfjord

Theoretical predictions of thermospheric gravity wave oscillations are compared with observed neutral temperatures and velocities. The data were taken in February 1983 using a Fabry-Perot interferometer located on Greenland, close to impulse heat sources in the auroral oval. The phenomenon was modeled in terms of linearized equations of motion of the atmosphere on a slowly rotating sphere. Legendre polynomials were used as eigenfunctions and the transfer function amplitude surface was characterized by maxima in the wavenumber frequency plane. Good agreement for predicted and observed velocities and temperatures was attained in the 250-300 km altitude. The amplitude of the vertical velocity, however, was not accurately predicted, nor was the temperature variability. The vertical velocity did exhibit maxima and minima in response to corresponding temperature changes.

Herrero, F. A.↗
NASA NTRS2010

Spatio-Temporal Pattern of Saturn's Equatorial Oscillation

Recent ground-based and Cassini CIRS thermal-infrared data have characterized the spatial and temporal characteristics of an equatorial oscillation in the middle atmosphere of Saturn above the 100-mbar level. The CIRS data [I] indicated a pattern of warm and cold anomalies near the equator, stacked vertically in alternating fashion. The ground-based observations s2, although not having the altitude range or vertical resolution of the CIRS observations, covered several years and indicated an oscillation cycle of approx.15 years, roughly half of Saturn's year. In Earth's middle atmosphere, both the quasi-biennial (approx.26 months) and semi-annual equatorial oscillations have been extensively observed and studied (see e.g., [3]), These exhibit a pattern of alternating warmer and cooler zonal-mean temperatures with altitude, relative to those at subtropical latitudes. Consistent with the thermal wind equation, this is also associated with an alternating pattern of westerly and easterly zonal winds. Moreover, the pattern of winds and temperatures descends with time. Momentum deposition by damped vertically propagating waves is thought to play a key role m forcing both types of oscillation, and it can plausibly account for the descent. Here we report the direct observation of this descent in Saturn's equatorial atmosphere from Cassini radio occultation soundings in 2005 and 2009. The retrieved temperatures are consistent with a descent of 0.7 x the pressure scale height. The descent rate is related to the magnitude of the wave forcing, radiative damping, and induced meridional circulations. We discuss possible implications.

Flasar, F. M.↗
NASA NTRS1991

Transonic shock-induced dynamics of a flexible wing with a thick circular-arc airfoil

A simple flexible wing model with an 18-percent circular arc airfoil was constructed and tested in the Langley Transonic Dynamics Tunnel to investigate the dynamic characteristics that a wing might have under these conditions. In the region of shock-boundary layer oscillations, buffeting of the first bending mode was obtained. This mode was well separated in frequency from the shock boundary layer oscillations. A limit cycle oscillation was also measured in a 'third bending-like' mode, involving wing vertical bending and splitter plate motion, which was in the frequency range of the shock-boundary layer oscillations. Several model configurations were tested, and a few potential fixes were investigated.

Bennett, Robert M.↗
NASA NTRS2011

Wave Forcing of Saturn's Equatorial Oscillation

Ground-based measurements and Cassini data from CIRS thermal-infrared spectra and radio-occultation soundings have characterized the spatial structure and temporal behavior of a 15-year equatorial oscillation in Saturn's stratosphere. The equatorial region displays a vertical pattern of alternating warm and cold anomalies and, concomitantly, easterly and westerly winds relative to the cloud-top winds, with a peak-to-peak amplitude of 200 m/s. Comparison of the Cassini data over a four-year period has established that the pattern of mean zonal winds and temperatures descends at a rate of roughly I scale height over 4 years. This behavior is reminiscent of the equatorial oscillations in Earth's middle atmosphere. Here the zonal-mean spatial structure and descending pattern are driven by the absorption of vertically propagating waves. The maximum excursions in the pattern of easterly and westerly winds is determined by the limits of the zonal phase velocities of the waves. Here we report on the characterization of the waves seen in the temperature profiles retrieved from the Cassini radio-occultation soundings. The equatorial profiles exhibit a complex pattern of wavelike structure with dimensions one pressure scale height and smaller. We combine a spectral decomposition with a WKBJ analysis, where the vertical wavelength is assumed to vary slowly with the ambient static stability and doppler-shifted phase velocity of the wave. Use of the temperature and zonal wind maps from CIRS makes this approach viable. On Earth, the wave forcing associated with the equatorial oscillations generates secondary meridional circulations that affect the mean flow and planetary wave ducting well away from the equator. This may relate to the triggering of the recently reported mid-latitude storms on Saturn.

Flasar, F. M.↗
NASA NTRS2002

An Experimental Investigation of Incompressible Richtmyer-Meshkov Instability

Richtmyer-Meshkov (RM) instability occurs when two different density fluids are impulsively accelerated in the direction normal to their nearly planar interface. The instability causes small perturbations on the interface to grow and eventually become a turbulent flow. It is closely related to Rayleigh-Taylor instability, which is the instability of a planar interface undergoing constant acceleration, such as caused by the suspension of a heavy fluid over a lighter one in the earth's gravitational field. Like the well-known Kelvin-Helmholtz instability, RM instability is a fundamental hydrodynamic instability which exhibits many of the nonlinear complexities that transform simple initial conditions into a complex turbulent flow. Furthermore, the simplicity of RM instability (in that it requires very few defining parameters), and the fact that it can be generated in a closed container, makes it an excellent test bed to study nonlinear stability theory as well as turbulent transport in a heterogeneous system. However, the fact that RM instability involves fluids of unequal densities which experience negligible gravitational force, except during the impulsive acceleration, requires RM instability experiments to be carried out under conditions of microgravity. This experimental study investigates the instability of an interface between incompressible, miscible liquids with an initial sinusoidal perturbation. The impulsive acceleration is generated by bouncing a rectangular tank containing two different density liquids off a retractable vertical spring. The initial perturbation is produced prior to release by oscillating the tank in the horizontal direction to produce a standing wave. The instability evolves in microgravity as the tank travels up and then down the vertical rails of a drop tower until hitting a shock absorber at the bottom. Planar Laser Induced Fluorescence (PLIF) is employed to visualize the flow. PLIF images are captured by a video camera that travels with the tank. Figure 1 is as sequence of images showing the development of the instability from the initial sinusoidal disturbance far into the nonlinear regime which is characterized by the appearance of mushroom structures resulting from the coalescence of baroclinic vorticity produced by the impulsive acceleration. At later times in this sequence the vortex cores are observed to become unstable showing the beginnings of the transition to turbulence in this flow. The amplitude of the growing disturbance after the impulsive acceleration is measured and found to agree well with theoretical predictions. The effects of Reynolds number (based on circulation) on the development of the vortices and the transition to turbulence are also determined.

Jacobs, J. W.↗
NASA NTRS1973

The International Planetary Patrol Program - An assessment of the first three years.

Day-to-day and hour-to-hour changes in the large-scale atmospheric and surface features of the planets can now be studied more effectively than previously possible. Since 1969 a network of observatories has obtained almost uninterrupted photographic coverage during all apparitions of Jupiter and Mars, plus some of Venus. Patrol films and catalogs are available to the scientific community. Recent or current analyses include the distribution and motion of clouds on Mars, the development and decay of Martian dust storms, the seasonal, diurnal, and random fluctuations in contrast between adjacent light and dark regions on Mars, the detection of vertical shear in the Jovian atmosphere, the longitudinal oscillation of the Red Spot, the dependence of rotation period on xenographic latitude and on time, the eruption and spread of south equatorial belt disturbances, and the retrograde circulation of the Venus cloud deck.

Baum, W. A.↗
NASA NTRS1981

Stratospheric variability in summer

Rocketsonde observations and infrasound results are used to investigate the variability of the summer stratopause region during one month in summer. Fluctuations of 2-3 days and about 16-day periods are evident, and they appear to be propagating vertically. In this month the 2-3 day oscillations have an amplitude envelope equal in period to the longer period oscillations, implying a connection between the two phenomena. Observations of the diurnal tide and shorter period variability during the month are also presented.

Rind, D.↗
NASA NTRS1992

Linear vestibuloocular reflex during motion along axes between nasooccipital and interaural

Linear vestibuloocular reflexes (LVORs), which stabilize retinal images by producing eye movements to compensate for linear head motion, are of two types: (1) responses to head tilt, which work primarily at low frequencies; and (2) responses to head translation, which act at higher frequencies. This work tested the hypothesis that reflexive eye movements would follow the same kinematics relative to the motion axis regardless of head orientation relative to linear motion. The experiments consisted of recording horizontal and vertical eye movements in squirrel monkeys during linear oscillations at 5 Hz along the head's nasooccipital (NO) axis and along axes lying within +/- 30 deg of the NO axis. It was found that LVORs followed the same kinematics regardless of the eye position in the head or the head orientation relative to motion.

Tomko, David L.↗
NASA NTRS1960

Experimental Investigation of the Natural Frequencies of Liquids in Toroidal Tanks

Several toroidal configurations applicable to missile and space-vehicle liquid storage systems were oscillated to study the natural frequencies of the antisymmetric modes of contained liquids over a range of liquid depths and tank sizes. Natural frequencies for tank oscillations parallel to the free surface of both vertical and horizontal tank orientations. Natural frequencies were obtained. The data are presented in terms of dimensionless parameters which are obtained by relating experimentally determined natural liquid frequencies to analytical expressions developed through consideration of the physics of the problem and from existing solutions for liquids in tanks having similar boundaries at the liquid surface. The experimental results obtained for the toroids indicate that these parameters are applicable to the prediction of the natural frequencies of fluids in toroids of general geometry and size.

McCarty, John Locke↗