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At least 379 records · Page 21

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NASA NTRS1985

On the effects of islands' geometry and size on inducing sea breeze circulation

Model scaling of the characteristics of the sea breeze circulation involved with circular and slab elongated-symmetric midlatitude islands was performed. Larger horizontal and vertical velocities were indicated over the small circular islands as compared to those over corresponding elongated islands. The circulation characteristics of both types of islands become similar when the half-width of the island is about the same as the distance of inland penetration of the sea breeze in a nonisland case. Evaluation of the results through a scale analysis is presented.

Mahrer, Y.↗

NASA NTRS1983

Influence of radiative heating and cumulus convection on development of mean monsoon circulation in July

Numerical simulations of July mean monsoon circulation in the tropics are described. The model used in the simulations was based on a series of primitive equations for the combined effects of variations of solar radiation, radiative diurnal warming, and large-scale and deep cumulus condensation, and the kinematic effects of topography. The initial states of the model were derived from the observed mean distributions of pressure and humidity. Analysis of the numerical results showed that the large-scale features of the mean July monsoon circulation in the tropics are created mainly by differential diabatic heating under the influence of the specific topography. The time necessary to establish the large scale features was only about 5 days when the diurnal variation of solar radiation was taken into account. Graphic illustrations of the simulated mean July flow conditions are provided.

Kuo, H. L.↗

NASA NTRS1985

Numerical simulations of a transverse indirect circulation and low-level jet in the exit region of an upper-level jet

A numerical study was performed of a severe weather event (tornado) which occurred on May 10, 1973 in the Ohio region. The situation was modeled with a primitive equation mesoscale dynamic formulation. Account was taken of precipitation, the planetary boundary layer parameters as bulk quantities, the vertical pressure gradient, and lateral boundary conditions based on radiosonde data. Two 12-hr simulations, adiabatic and nondivergent, respectively, were analyzed for relationships between upper and lower level jets. In the adiabatic formulation, a transverse circulation with a low level jet formed at the exit region of the upper level jet. The nondivergent situation led to similar, but weaker, phenomena. Both forms suggest that indirect circulation in the exit zone of an upper level jet is strongly influenced by the initial structure of the jet.

Brill, K. F.↗

NASA NTRS1986

Circulation-Control Variable-Pitch Propeller

Circulation-control variable-pitch propeller has large lift value at moderate blowing coefficients. Based on circulation-control airfoil concept, has no moving parts other than needed for propeller rotation. Substituted for conventional variable-pitch propeller airfoil, lowers manufacturing costs, reduces maintenance, and improves reliability.

Garner, H. D.↗

NASA NTRS1985

Dynamic response characteristics of a circulation control rotor model pneumatic system

Numerical and experimental simulation of unsteady airflow through the control valve and slotted air duct of a circulation control rotor is described. The numerical analysis involves the solution of the quasi-one-dimensional compressible fluid-dynamic equations in the blade air duct together with the coupled isentropic flow equations for flow into the blade through the valve and out of the blade through the Coanda slot. Numerical solutions are compared with basic experimental results obtained for a mockup of a circulation control rotor and its pneumatic valving system. The pneumodynamic phenomena that were observed are discussed with particular emphasis on the characteristic system time lags associated with the response of the flow variables to transient and periodic control valve inputs.

Watkins, C. B.↗

NASA NTRS1985

Middle atmosphere general circulation statistics

With the increased availability of remote sensing data for the middle atmosphere from satellites, more analyses of the middle atmosphere circulation are being published. Some of these are process studies for limited periods, and some are statistical analyses of middle atmosphere general circulation statistics. Results from the latter class of studies will be reviewed. These include analysis of the zonally averaged middle atmosphere structure, temperature, and zonal winds; analysis of planetary wave structures, analysis of heat and momentum fluxes; and analysis of Eliassen-and-Palm flux vectors and flux divergences. Emphasis is on the annual march of these quantities; Northern and Southern Hemisphere asymmetries; and interannual variability in these statistics. Statistics involving the global ozone distribution and transports of ozone are also discussed.

Geller, M. A.↗

NASA NTRS1984

Spaceborne studies of ocean circulation

The history and near-term future of ocean remote sensing to study ocean circulation are examined. Seasat provided the first-ever global data sets of sea surface topography (altimeter) and marine winds (scatterometer) and laid the foundation for the next generation of satellite missions planned for the late 1980s. The future missions are the next generation of altimeter and scatterometer to be flown aboard TOPEX (TOPography EXperiment) and NROSS (Navy Remote Sensing System), respectively. The data from these satellites will be coordinated with measurements made at sea to determine the driving forces of ocean circulation and to study the oceans' role in climate variability. The significance of such studies to such matters as climatic changes, fisheries, commerce, waste disposal, and national defense is noted.

Patzert, W. C.↗

NASA NTRS1984

The evolution of misoscale circulations in a downburst-producing storm and comparison to numerical results

Data from three NCAR radars are used in both single and dual Doppler analyses to trace the evolution of a June 30, 1982 Colorado convective storm containing downburst-type winds and strong vortices 1-2 km in diameter. The analyses show that a series of small circulations formed along a persistent cyclonic shear boundary; at times as many as three misocyclones were present with vertical vorticity values as large as 0.1/s using a 0.25 km grid interval. The strength of the circulations suggests the possibility of accompanying tornadoes or funnels, although none were observed. Dual-Doppler analyses show that strong, small-scale downdrafts develop in close proximity to the misocyclones. A midlevel mesocyclone formed in the same general region of the storm where the misocylones later developed. The observations are compared with numerical simulations from a three-dimensional cloud model initialized with sounding data from the same day.

Kessinger, C. J.↗

NASA NTRS1986

Mean neutral circulation in the winter polar F region

A description of the mean global-scale circulation in the Northern Hemisphere F region has been synthesized by collating and averaging data from a global network of ground-based Fabry-Perot interferometers and from satellite sensors. An analysis of the results obtained shows that the combination of measurements made from multiple, strategically located ground-based observatories with satellite data provides a powerful technique for specifying the mean dynamic state of the earth's thermosphere. It is also found that a three-dimensional time-dependent numerical model with appropriate inputs for mean ionospheric convection can adequately predict the general characteristics observed in the mean thermospheric circulation.

Killeen, T. L.↗

NASA NTRS1986

Determining the general circulation of the ocean - A nonlinear inverse problem

The usual inversion procedures for determining the oceanic circulation take the density field as given. This does not explicitly account for the mismatch between the data (which are typically a single realization of the density field) and the circulation being estimated (which may be a time mean or some other smoothed quantity), but explicit consideration of the uncertainty of the density data renders the problem nonlinear, and new estimation methods have to be used. As an example, a nonlinear inversion is successfully applied here to the simple analytical model of Stommel and Veronis (1981). It is also shown that their linear procedure, if properly used, yields a much better result than they obtained.

Mercier, H.↗

NASA NTRS1986

A simple biosphere model (SiB) for use within general circulation models

A simple realistic biosphere model for calculating the transfer of energy, mass and momentum between the atmosphere and the vegetated surface of the earth has been developed for use in atmospheric general circulation models. The vegetation in each terrestrial model grid is represented by an upper level, representing the perennial canopy of trees and shrubs, and a lower level, representing the annual cover of grasses and other heraceous species. The vegetation morphology and the physical and physiological properties of the vegetation layers determine such properties as: the reflection, transmission, absorption and emission of direct and diffuse radiation; the infiltration, drainage, and storage of the residual rainfall in the soil; and the control over the stomatal functioning. The model, with prescribed vegetation parameters and soil interactive soil moisture, can be used for prediction of the atmospheric circulation and precipitaion fields for short periods of up to a few weeks.

Sellers, P. J.↗

NASA NTRS1986

Circulating transportation orbits between earth and Mars

This paper describes the basic characteristics of circulating (cyclical) orbit design as applied to round-trip transportation of crew and materials between earth and Mars in support of a sustained manned Mars Surface Base. The two main types of nonstopover circulating trajectories are the socalled VISIT orbits and the Up/Down Escalator orbits. Access to the large transportation facilities placed in these orbits is by way of taxi vehicles using hyperbolic rendezvous techniques during the successive encounters with earth and Mars. Specific examples of real trajectory data are presented in explanation of flight times, encounter frequency, hyperbolic velocities, closest approach distances, and Delta V maneuver requirements in both interplanetary and planetocentric space.

Friedlander, A. L.↗

NASA NTRS1985

Theoretical and experimental design studies for the Atmospheric General Circulation Experiment

The major criterion for the Atmospheric General Circulation Experiment (AGCE) design is that it be possible to realize strong baroclinic instability in the spherical configuration chosen. A configuration was selected in which a hemispherical shell of fluid is subjected to latitudinal temperature gradients on its spherical boundaries and the latitudinal boundaries are insulators. Work in the laboratory with a cylindrical version of this configuration revealed more instabilities than baroclinic instability. Since researchers fully expect these additional instabilities to appear in the spherical configuration also, they decided to continue the laboratory cylindrical annulus studies. Four flow regimes were identified: an axisymmetric Hadley circulation, boundary layer convection, baroclinic waves and deep thermal convection. Regime diagrams were prepared.

Fowlis, W. W.↗

NASA NTRS1987

Na/beta-alumina/NaAlCl4, Cl2/C circulating cell

A study was made of a high specific energy battery based on a sodium negative electrode and a chlorine positive electrode with molten AlCl3-NaCl electrolyte and a solid beta alumina separator. The basic performance of a Na beta-alumina NaAlCl4, Cl2/C circulating cell at 200 C was demonstrated. This cell can be started at 150 C. The use of melting sodium chloroaluminate electrolyte overcomes some of the material problems associated with the high working temperatures of present molten salt systems, such as Na/S and LiAl/FeS, and retains the advantages of high energy density and relatively efficient electrode processes. Preliminary investigations were conducted on a sodium-chlorine static cell, material compability, electrode design, wetting, and theoretical calculations to assure a better chance of success before assembling a Na/Cl2 circulating cell. Mathematical models provide a theoretical explanation for the performance of the NaCl2 battery. The results of mathematical models match the experimental results very well. According to the result of the mathematical modeling, an output at 180 mA/sq cm and 3.2 V can be obtained with optimized cell design.

Cherng, Jing-Yih↗

NASA NTRS1986

Comparative energetics of the observed and simulated global circulation during the special observing periods of FGGE

Energetics of the observed and simulated global circulation are evaluated in the zonal spectral domain for the special observing periods of FGGE. The study utilizes GLA analyses of FGGE observational data and parallel simulation experiments. There are noticeable differences in energy transformations between the observation and simulation during SOP-1. These include the baroclinic conversion C(n) by the zonal mean motion and short-wave disturbances, and the nonlinear wave-wave interaction L(n) at the long and short waves. The energy transformations of the short-wave disturbances are much more intense in the simulated circulation than in the observation. However, good agreement is noted in the conversion and dissipation of kinetic energy in the large- and cyclone-wave range n = 1-10. Spectral distributions of global energy transformations at the long- and cyclone-wave range indicate that the SOP-2 simulation agrees more closely with the observed fields than the SOP-1 simulation. Other pertinent points of energetics diagnosis are also included in the discussion.

Kung, E. C.↗

NASA NTRS1987

Improved algorithms for circulation-control airfoils in transonic flow

A zonal model for aerodynamic analysis of two-dimensional transonic circulation control airfoils has been developed. The present approach combines a transonic full potential method for the global flow field and an integral boundary layer method for regions of the airfoil excluding the wall jet with a parabolized Navier-Stokes code for resolving the wall jet region beyond the slot. Existing methods suffer from two deficiencies: the insensitivity of the calculation to small changes in the Coanda surface geometry; and the inability to predict the shock structure of the underexpanded supersonic wall jets. The present wall jet procedure involves a pressure-split approach in the streamwise sense to enable noniterative solution of the coupled continuity and normal momentum equations for increased surface sensitivity and allows for expansion of applications to sonic slot exit conditions. Encouraging results are obtained in comparison with experimental data for two circulation airfoils with subsonic wall jets.

Dvorak, Frank A.↗

NASA NTRS1987

Boundary-layer and wake measurements on a swept, circulation-control wing

Wind-tunnel measurements of boundary-layer and wake velocity profiles and surface static-pressure distributions are presented for a swept, circulation-control wing. The model is an aspect-ratio-four semispan wing mounted on the tunnel side wall at a sweep angle of 45 deg. A full-span, tangential, rearward-blowing, circulation-control slot is located ahead of the trailing edge on the upper surface. Flow surveys were obtained at mid-semispan at freestream Mach numbers of 0.425 and 0.70. Boundary-layer profiles measured on the forward portions of the wing are approximately streamwise and two-dimensional. The flow in the vicinity of the jet exit and in the near wake is highly three-dimensional. The jet flow near the slot on the Coanda surface is directed normal to the slot. Near-wake surveys show large outboard flows at the center of the wake. At Mach 0.425 and a 5-deg angle of attack, a range of jet blowing rates was found for which an abrupt transition from incipient separation to attached flow occurs in the boundary layer upstream of the slot. The variation in the lower-surface separation location with blowing rate was determined from boundary-layer measurements at Mach 0.425.

Spaid, Frank W.↗

NASA NTRS1986

Venus mesosphere and thermosphere. II - Global circulation, temperature, and density variations

The Dickinson and Ridley (1977) symmetric, two-dimensional hydrodynamical model framework is presently used as the basis of a reexamination of the circulation and structure of the Venus thermosphere recently revealed by Pioneer Venus observations. The observed day-to-night variation of composition and temperatures can largely be derived by a wave-drag parameterization yielding a weaker circulation system than that predicted prior to Pioneer Venus. It is also suggested that eddy diffusion is a minor contributor to the maintenance of observed day and nightside densities, and that eddy coefficients are smaller than than those of one-dimensional composition models previously employed.

Bougher, S. W.↗