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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 289 records · Page 16
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NASA NTRS1989

Zonal Winds Between 25 and 120 Km Retrieved from Solar Occultation Spectra

Atmospheric winds at heights between 25 and 120 km have been retrieved with precisions of 5/ms from the Doppler shifts of atmospheric absorption lines measured from a satellite-borne instrument. Lines of the upsilon 3 CO2 and upsilon 2 H2O rotation-vibration bands caused by gases in the instrument allowed the instrumental frequency scale to be absolutely calibrated so that accurate relative speeds could be obtained. By comparing the positions of both sets of instrumental lines the calibration of the frequency scale was determined to be stable to a precision of less than 2 x 10(-5) cm during the course of each occultation. It was found that the instrumental resolution of 0.015 cm after apodization, the signal to noise ratio of about 100 and stable calibration allowed relative speeds to be determined to a precision of 5 ms or better by using small numbers of absorption lines between 1600 and 3200 cm. Absolute absorption line positions were simultaneously recovered to precisions of 5 x 10(-5) cm or better. The wind speed profiles determined from four sunset occultations and one sunrise occultation show remarkable similarities in the magnitudes and directions of the zonal wind velocities as functions of height. These wind profiles appear to be manifestations of atmospheric tides.

Vancleef, Garrett Warren↗
NASA NTRS1988

Simulation of transonic viscous wing and wing-fuselage flows using zonal methods

The thin-layer Navier-Stokes equations are coupled with a zonal scheme (or domain-decomposition method) to develop the Transonic Navier-Stokes (TNS) wing-alone code. TNS has a total of four zones and is extended to a total of 16 zones for the wing-fuselage version of the code. Results are computed on the Cray X-MP-48 and compared with experimental data.

Flores, Jolen↗
NASA NTRS1988

Navier-Stokes simulation of transonic wing flow fields using a zonal grid approach

The transonic Navier-Stokes code was used to simulate flow fields about isolated wings for workshop wind-tunnel and free-air cases using the thin-layer Reynolds-averaged Navier-Stokes equations. An implicit finite-difference scheme based on a diagonal version of the Beam-Warming algorithm was used to integrate the governing equations. A zonal grid approach was used to allow efficient grid refinement near the wing surface. The flow field was sensitive to the turbulent transition model, and flow unsteadiness was observed for a wind-tunnel case but not for the corresponding free-air case. The specification of experimental pressure at the wind-tunnel exit plane is the primary reason for the difference of these two numerical solutions.

Chaderjian, Neal M.↗
NASA NTRS1988

A study of cloud-generated radiative heating and its generation of available potential energy. I - Theoretical background. II - Results for a climatological zonal mean January

The effect of radiative heating and cooling by clouds on the available potential energy (APE) is theoretically discussed. It is shown that the cloud radiative contribution to the generation of APE is determined by the net cloud radiative heating and the efficiency factor, which is a function of the temperature distribution of the atmosphere. Results are presented for low and middle cloud effects for three atmospheric layers. Cloud radiative heating is found to be a single function of cloud optical thickness for all classes designed in terms of cloud top heights and optical thickness. Low clouds at low latitudes destroy APE an midclouds generate APE. A concept is developed to relate the cloud radiative heating to cloud heights and optical depths. Cloud-generated radiative heating is computed for January zonal mean conditions for low and midclouds. For both cases, the strongest influence is found in the low troposphere, with marked differences in signs and magnitudes. At extratropical latitudes, both cloud classes generate net radiative cooling. In the tropics, the effect of low cloud changes from net cooling to the net heating as the optical thickness increases, and midclouds cause net heating. A mechanism is described whereby this dependence produces a strong positive feedback effect on the development of SST anomalies in the tropical oceans.

Stuhlmann, R.↗
NASA NTRS1989

Low-latitude zonal and vertical ion drifts seen by DE 2

Horizontal and vertical ion drift data from the DE 2 spacecraft have been used to determine average zonal and vertical plasma flow (electric field) characteristics in the +/- 26-deg dip latitude region during a time of high solar activity. The 'average data' local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time ((SLT) with a maximum westward velocity of 80 m/s in the early afternoon. There is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m/s. A secondary nighttime maximum exists at 0430 SLT preceeding the reversal to westward flow. This profile is in good agreement with Jicamarca, Peru, radar measurements made under similar solar maximum conditions. Haramonic analysis indicates a net superrotation which is strongest at lower apex altitudes. The diurnal term is dominant, but higher order terms through the quatradiurnal are significant.

Coley, W. R.↗
NASA NTRS1989

The sensitivity of stationary waves to variations in the basic state zonal flow

A linear, primitive equation stationary wave model having high vertical and meridional resolution is used to examine the sensitivity of orographically forced (primarily by Himalayas) stationary waves at middle and high latitudes to variations in the basic state zonal wind distribution. We find relatively little sensitivity to the winds in high latitudes, but remarkable sensitivity to small variations in the subtropical jet. Fluctuations well within the range of observed variability in the jet can lead to large variations in the stationary waves of the high latitude stratosphere, and to large changes even in tropospheric stationary waves. Implications for both sudden warmings and large-scale weather are discussed.

Nigam, Sumant↗
NASA NTRS1989

Two-dimensional computations of multi-stage compressor flows using a zonal approach

A clear understanding of the fluid dynamics associated with rotor/stator configurations can be very helpful when optimizing the performance of turbomachinery. In this study, a two-dimensional, implicit, thin-layer, Navier-Stokes zonal approach has been used to investigate the flow within a 2 1/2-stage compressor. Relative motion between the rotor and stator airfoils is made possible with the use of systems of patched and overlaid grids that move with respect to each other. The treatment of multistage turbomachines with arbitrary numbers of airfoils per row is made possible by the use of a flexible database system. Results in the form of instantaneous pressure and entropy contours and time-averaged pressures are presented for the 2 1/2-stage compressor. Time-averaged pressures and pressure amplitudes for a single-stage turbine configuration are also presented. The numerical results compare well with experimental data.

Gundy-Burlet, Karen L.↗
NASA NTRS1989

A zonal approach to V/STOL vehicle aerodynamics

A zonal method based on an iterative coupling between an inviscid panel method and two viscous finite difference methods is applied to solve for the region of jets issued from generic V/STOL models in order to assess the influence of the jet upon V/STOL configurations. The low-order panel method, VSAERO, is used to solve for the entire flow region, which includes the V/STOL model and jet boundary. ARC3D, a well known compressible, thin layer Navier-Stokes (NS) code developed at NASA-Ames, and APPL, a parabolized NS code, are used to solve for the jet region subject to the boundary condition provided by the VSAERO calculation. Overlapping boundaries are used for the purpose of coupling. Results are presented with the available experimental data for the jet and V/STOL configurations.

Yoo, Sungyul↗
NASA NTRS1989

A parameterization of eddy transfer coefficients for two-level seasonal statistical dynamical zonally averaged models

This paper examines a parameterization of a quasi-geostrophic eddy transport that takes into account the time variation of eddy transfer coefficients according to Green's (1970) theory. It was found that, in the original eddy transfer relationship of Green, connecting the integral of the northward eddy entropy flux through midlatitudes with the second power of the difference in 500-mb entropy across the region of baroclinic activity, a value of 4 for the exponent is obtained when the temperature gradients at 500 mb are used. When the gradients at 1000 mb are used, an exponent of 1.5 is obtained. The differences in the powers in the eddy transfer relation were explored in a two-level zonally averaged model. It was found that an appropriate choice of power may be of special importance if the model is devised to simulate the seasonal climate cycle or to test astronomical changes inducing different seasonalities.

Neeman, Binyamin U.↗
NASA NTRS1990

A zonal flow analysis method for two-dimensional airfoils

A closed-loop, overlapped, velocity-coupling procedure has been utilized to combine a two-dimensional potential flow panel code and a Navier-Stokes code. The fully coupled, two-zone code has been used to compute the flow past a NACA 0012 airfoil. For this case, the zonal method has shown that the grid domain size can be reduced to 0.14 chord lengths with less than 1 percent loss in accuracy. Further, the required computation time is reduced by a factor of approximately four.

Summa, J. Michael↗
NASA NTRS1990

Nongeostrophic theory of zonally averaged circulation. II - Eliassen-Palm flux divergence and isentropic mixing coefficient

A diagnostic study of Eliassen-Palm flux divergence and isentropic mixing coefficient (Kyy) in the stratosphere is performed for different seasons and for both hemispheres, based on the nongeostrophic theory of zonally averaged circulation of Tung (1986). An easily implementable procedure is described which yields a Kyy field that is consistent with advective transport. It is shown that the resultant time- and space-varying structure of Kyy leads to improved simulation of stratospheric species whose distributions are affected by dynamical transport. In particular, it is shown that the simulation of nitric acid is more satisfactory than previous model calculations.

Yang, H.↗
NASA NTRS1990

Estimates of the zonal slope and seasonal transport of the Atlantic North Equatorial Countercurrent

Data from six inverted echo sounder moorings and the Geosat satellite altimeter are used to examine the seasonal variability of sea surface elevation. Monthly sea level maps are constructed using a contemporaneous subsurface temperature survey to provide a reference sea level field. The maps are then used to describe the origin and structure of the western tropical Atlantic North Equatorial Countercurrent (NECC) during a two-year period beginning in November 1987. The data reveal a zonal current which is confined between 3 deg N and 9 deg N with a typical width of 300 km. The NECC flows strongly eastward during November and December 1986 and May 1987 through January 1988. The reappearance of the current is then delayed until August, but the current flows strongly from August until the end of the record in October 1988. Volume transport is estimated for the two-year period from surface elevation by approximating the vertical structure of the ocean as a two-layer fluid. It is found that the NECC has a maximum transport of 40 x 10 to the 6th cu m/s at 38 deg W.

Carton, James A.↗
NASA NTRS1990

Barotropic stability of westward-moving waves in realistic stratospheric zonal flows

A linearized barotropic model on a sphere is used to study the stability of a basic state composed of a westward-moving wave and a zonal mean jet. It is found that the inclusion of a very weak jet in the basic state dramatically alters the stability of the flow. The alteration of stability characteristics for realistic summer and winter jets is discussed.

Manney, Gloria L.↗
NASA NTRS1990

Angle-of-attack validation of a new zonal CFD method for airfoil simulations

The angle-of-attack validation of a new concept suggested by Summa (1990) for coupling potential and viscous flow methods has been investigated for two-dimensional airfoil simulations. The fully coupled potential/Navier-Stokes code, ZAP2D (Zonal Aerodynamics Program 2D), has been used to compute the flow field around an NACA 0012 airfoil for a range of angles of attack up to stall at a Mach number of 0.3 and a Reynolds number of 3 million. ZAP2D calculation for various domain sizes from 25 to 0.12 chord lengths are compared with the ARC2D large domain solution as well as with experimental data.

Yoo, Sungyul↗
NASA NTRS1990

Zonally averaged thermal balance and stability models for nitrogen polar caps on Triton

Voyager four-color imaging data of Triton are analyzed to calculate the bolometric hemispheric albedo as a function of latitude and longitude. Zonal averages of these data have been incorporated into a thermal balance model involving insolation, reradiation, and latent heat of sublimation of N2 ice for the surface. The current average bolometric albedo of Triton's polar caps is 0.8, implying an effective temperature of 34.2 K and a surface pressure of N2 of 1.6 microbar for unit emissivity. This pressure is an order of magnitude lower than the surface pressure of 18 microbar inferred from Voyager data (Broadfoot et al., 1989; Conrath et al., 1989), a discrepancy that can be reconciled if the emissivity of the N2 on Triton's surface is 0.66. The model predicts that Triton's surface north of 15 deg N latitude is experiencing deposition of N2 frosts, as are the bright portions of the south polar cap near the equator. This result explains why the south cap covers nearly the entire southern hemisphere of Triton.

Stansberry, John A.↗
NASA NTRS1991

Semiautomatic Design Of Zonal Computational Grids

EZGrid is knowledge-based computer program semiautomatically generating zonal computational grids for use in numerical simulations of two-dimensional flows. Zoning necessary because of limitations imposed by size of available computer memory and by topological complexity of typical flow field. Complexity and amount of required memory reduced by dividing flow field into zones, within each of which computational grid refined only to extent necessary to resolve local high gradients. Developed to speed and systematize zoning.

Vogel, Alison Andrews↗
NASA NTRS1991

Zonal analysis of two high-speed inlets

Using a zonal technique, thin layer Navier-Stokes solutions for two high speed inlet geometries are presented and compared with experimental data. The first configuration consists of a 3-D inlet preceded by a sharp flat plate. Results with two different grids demonstrate the importance of adequate grid refinement in high speed internal flow computations. The fine grid solution has reasonably good agreement with experimental heat transfer and pressure values inside the inlet. The other configuration consists of a 3-D inlet mounted on a research hypersonic forebody. Numerical results for this configuration have good agreement with experimental pressure data along the forebody, but not inside the inlet. A more refined grid calculation is currently being done to better predict the flowfield in the inlet.

Dilley, A. D.↗
NASA NTRS1990

Measurement of a zonal wind profile on Titan by Doppler tracking of the Cassini entry probe

A program, called the Cassini mission, intended to study the Saturn system by utilizing a Saturn orbiter and a probe descending to the surface of Titan, is discussed. Winds are expected to cause perturbations to the probe local horizontal velocity, resulting in an anomalous drift in the probe location and a shift in the frequency of the probe telemetry, due to the Doppler effect. By using an iterative algorithm, in which the time variation of the probe telemetry frequency is monitored throughout the descent, and the probe trajectory is updated to reflect the effect of wind on the probe location, a highly accurate relative wind profile can be recovered. By adding a single wind velocity, measured by independent means, an absolute wind profile can be obtained. However, the accuracy of the zonal winds recovery is limited by errors in trajectory, and frequency.

Atkinson, D. H.↗