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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Zonal superrotation above Venus' cloud base induced by the semidiurnal tide and the mean meridional circulation

The equilibrium zonal wind structure resulting from the interaction of the semidiurnal tide and the mean meridional circulation driven by the zonally averaged solar heating above the Venus cloud base were calculated. The results show that the tidal mechanism proposed by Fels and Lindzen (1974) can account for a substantial fraction (and possibly all) of the increase of the equatorial wind speed above the cloud base. Above the cloud tops, tidal deceleration may be too small to produce the zonal wind decrease with height inferred from thermal data. Tidal forcing does not explain the superrotation below the clouds, and additional eddy sources are needed to account for the zonal wind structure at mid and high latitudes.

Hou, Arthur Y.↗
NASA NTRS1993

A kinematic analysis of the high-latitude thermospheric neutral circulation pattern

'Synthesized' thermospheric neutral wind fields for solar maximum, December solstice conditions for both quiet and active levels of geometric activity, are provided on the basis of averaged measurements from the Dynamics Explorer 2 (DE 2) satellite combined with theoretical model calculations. High-latitude DE 2 wind data obtained from multiorbit averages are merged with modeled winds from the NCAR thermosphere-ionosphere general circulation model. A 'kinematic analysis' is performed to decompose the merged semiempirical wind fields into their respective divergent and nondivergent components at high latitudes and to calculate the corresponding potential and stream functions. It is concluded that the nondivergent component of the high-latitude thermospheric neutral wind is representative of the convection-driven component of the neutral wind at F region altitudes. The nondivergent wind component comprises a large percentage of the total wind field for both quiet and active geomagnetic conditions.

Thayer, J. P.↗
NASA NTRS1985

Mars atmospheric circulation - Aspects from Viking Landers

Winds measured by the two Viking Landers have been filtered and then compared with predictions from the general circulation model and to Orbiter observations of clouds and surface phenomena that indicate wind direction. This was done to determine the degree to which filtered winds may represent aspects of the general circulation. Excellent agreement was found between wind direction data from Lander 1 and the model predictions and Orbiter observations. For Lander 2, agreement was generally good, but there were periods of disagreement which indicate that the filtering did not remove other extraneous effects. It is concluded that Lander 1 gives a good representation of the general circulation at 22.5 deg N latitude but that Lander 2 is suspect. Most wind data from Lander 1 have yet to be analyzed. It appears that when analyzed these Lander 1 data (covering 3.5 Mars years) can provide information about interannual variations in the general circulation at the Lander latitude.

Ryan, J. A.↗
NASA NTRS2017

Transonic Drag Reduction Through Trailing-Edge Blowing on the FAST-MAC Circulation Control Model

A third wind tunnel test of the FAST-MAC circulation control semi-span model was completed in the National Transonic Facility at the NASA Langley Research Center where the model was configured for transonic testing of the cruise configuration with 0deg flap detection to determine the potential for transonic drag reduction with the circulation control blowing. The model allowed independent control of four circulation control plenums producing a high momentum jet from a blowing slot near the wing trailing edge that was directed over a 15% chord simple-hinged ap. Recent upgrades to transonic semi-span flow control testing at the NTF have demonstrated an improvement to overall data repeatability, particularly for the drag measurement, that allows for increased confidence in the data results. The static thrust generated by the blowing slot was removed from the wind-on data using force and moment balance data from wind-o thrust tares. This paper discusses the impact of the trailing-edge blowing to the transonic aerodynamics of the FAST-MAC model in the cruise configuration, where at flight Reynolds numbers, the thrust-removed corrected data showed that an overall drag reduction and increased aerodynamic efficiency was realized as a consequence of the blowing.

Chan, David T.↗
NASA NTRS2007

Parametric Evaluation of Thin, Transonic Circulation-Control Airfoils

Wind-tunnel tests were conducted in the NASA Langley Transonic Dynamics Tunnel on a 6 percent-thick, elliptical circulation-control airfoil with upper-surface and lower-surface blowing capability. Results for elliptical Coanda trailing-edge geometries, biconvex Coanda trailing-edge geometries, and leading-edge geometries are reported. Results are presented at subsonic and transonic Mach numbers of 0.3 and 0.8, respectively. When considering one fixed trailing-edge geometry, for both the subsonic and transonic conditions it was found that the [3.0:1] ratio elliptical Coanda surface with the most rounded leading-edge [03] performed favorably and was determined to be the best compromise between comparable configurations that took advantage of the Coanda effect. This configuration generated a maximum. (Delta)C(sub 1) = 0.625 at a C(sub mu) = 0.06 at M = 0.3, alpha = 6deg. This same configuration generated a maximum (Delta)C(sub 1) = 0.275 at a C(sub mu) = 0.0085 at M = 0.8, alpha = 3deg.

Schlecht, Robin↗
NASA NTRS1973

The Oregon State University wind studies

The economic feasibility of commercial use of wind generated power in selected areas of Oregon is assessed. A number of machines for generating power have been examined. These include the Savonius rotor, translators, conventional wind turbines, the circulation controlled rotor and the vertical axis winged turbine. Of these machines, the conventional wind turbine and the vertical axis winged turbine show the greatest promise on the basis of the power developed per unit of rotor blade area. Attention has been focused on the structural and fatigue analysis of rotors since the economics of rotary winged, wind generated power depends upon low cost, long lifetime rotors. Analysis of energy storage systems and tower design has also been undertaken. An economic means of energy storage has not been found to date. Tower design studies have produced cost estimates that are in general agreement with the cost of the updated Putnam 110-foot tower.

Wilson, R. E.↗
NASA NTRS1999

Wind Forcing of the Pacific Ocean Using Scatterometer Wind Data

The long-term objective of this research was an understanding of the wind-forced ocean circulation, particularly for the Pacific Ocean. To determine the ocean's response to the winds, we first needed to generate accurate maps of wind stress. For the ocean's response to wind stress we examined the sea surface height (SSH) both from altimeters and from numerical models for the Pacific Ocean.

Kelly, Kathryn 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 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 NTRS2010

Lasers and the Dynamic Mesosphere/Thermosphere of Venus

A review of ground based mid-infrared uniquely high spectral. resolution measurements of Venus dynamics, temperature, and chemistry will be presented. The described studies will focus on the use of CO2 absorption features and the discovery- and use of CO2 thermospheric non-thermal emission: lines as probes of Venus' atmosphere, from the cloud tops to approx.120 km in the thermosphere. The first investigations using infrared heterodyne spectroscopy with resolving power lambda/Delta(lambda) approx. 10(exp 6) to measure true emission line profiles and to determine their non-thermal nature and lasing component will be described. The use of the thermospheric non-thermal CO2 emission to directly measure sub-solar to anti-solar winds and zonal circulation near 110 km altitudes on Venus to approx.2 m/s accuracy will also be described. The measured emission lures are also used to obtain global maps of mesospheric/thermospheric kinetic and rotational temperatures as well as to obtain evidence of the natural lasing phenomena. Carbon dioxide absorption features globally probe lower altitudes in the atmosphere and can be used to determine nightside temperatures. Isotopic 13 CO2 absorption lines are used to probe deeper in the atmosphere to measure the sub-solar to anti-solar return flow at altitudes just above the cloud tops. These results provided a model for global circulation in the 65 - 120 km altitude region first proposed by Goldstein (1989, PhD.Thesis, U. Pennsylvania, Philadelphia, USA). Results of similar wind and temperature measurements made in recent years will be compared to earlier results to investigate changes in the circulation and temperatures since approx.1990. The high resolution infrared heterodyne technique was also used to investigate chemical processes above the cloud tops, specifically evidence and constraints on oxygen-based chemistry. Described measurements were made by infrared heterodyne spectroscopy using the Goddard Space Flight Center Infrared Heterodyne Spectrometer (IRHS) the GSFC Heterodyne Instrument for Planetary wind And Composition (HIPWAC) and the University of Cologne Tuneable Heterodyne Infrared Spectrometer (THIS).

Kostiuk, Theodor↗
NASA NTRS1997

Friction Velocity Estimation Using Dual-Frequency Altimeter Data

Global estimation of wind speeds near the sea-surface can be obtained using normalized radar cross sections sigma(o) from satellite-borne single-frequency altimeters. Indeed recent validation studies of Geosat altimeter-derived wind speeds show that several often cited semiempirical algorithms yield linear trends between wind-speeds from altimeter data and wind speeds from (a) ships of opportunity (Etcheto 1992), (b) buoys (Carter 1992), and (c) atmospheric models (Guillaume 1992). Although the linear trends are striking, there is considerable scatter since the range of standard deviations is from 1.5 to 3 m/s. In fact, the scatter of some particular measurements about the regressions is striking because they depart from the 'standard' by as much as +/- 5 m/s, which is large - even for full gale winds of 20 m/s. These anomalies can cause serious problems for gas exchange, heat, and aerosol estimates. They can also induce considerable errors in wind-driven oceanic circulation models and sea-surface wave models. This paper explores the possibility of improving the accuracy of wind speed estimation using dual-frequency altimeters.

Bliven, Larry F.↗
NASA NTRSDate not supplied

Martian B Storm Evolution: Modeling Dust Activity over the Receding South Polar CO 2 Ice Cap at Southern Hemisphere Summer Solstice

Observations of annually recurring, elevated (25 km) atmospheric warming and associated dust concentrations over the south polar cap near Southern Hemisphere (SH) summer solstice are the defining features of the regional dust storm known as the B storm [1]. Our observational analysis of MCS and TES temperature and dust retrievals include all Mars Years (MY) lacking a global dust storm (GDS) between MY 26 and MY 33 (Figure 1). The data indicate the B storm is initiated around perihelion (L s =252°) in the southern midlatitudes and reaches maximum height and intensity over the south pole near SH summer solstice at L s ~267°. At peak intensity, mid-level atmospheric temperatures are elevated by as much as 30 K and mid-level atmospheric dust mixing ratios are more than triple pre-B storm levels (1.5-2 ppm to 7-8 ppm). Cap edge lifting may contribute significantly to initial dust mobilization in the B storm since surface wind stress along the receding cap edge is likely strengthened by the combined effects of the sea breeze circulation and katabatic winds at this time of year [2, 3, 4]. We are investigating dust lifting and lofting near the south pole of Mars during SH summer using the NASA Ames Mars Global Climate Model (MGCM). The NASA Ames MGCM is a finite-volume numerical model with a cubed sphere grid ideal for modeling processes at high latitudes. Initial simulations at low resolution (4x4 degrees) capture some elevated dust and associated warming at the south pole around L s =265°, but the model fails to capture the intensity of the B storm. We will examine and present the model-predicted surface stress and vertical velocities near the receding seasonal CO 2 cap edge and at the south pole during solstice. Finally, we will present higher resolution simulations to better capture small-scale dynamics and features at the pole.

Courtney M. L. Batterson↗
NASA NTRS2000

Hurricane Bonnie Landfalling Observed from ER-2 Doppler Radar on 26 August 1998 During CAMEX-3

The NASA ER-2 and DC-8 aircraft collected remote sensing and in situ data sets from Hurricane Bonnie (23, 24, and 26 August 1998) during the Convection And Moisture Experimental-3 (CAMEX-3). Bonnie was an exceptional case where NASA and NOAA had five aircraft sampling both upper levels and lower altitudes. The ER-2 was instrumented with the ER-2 Doppler XBand radar (EDOP) and several radiometers ranging from visible to lower frequency microwaves. EDOP is a fixed dual-beam radar (nadir and forward-looking beams) which allows computation of both vertical and alongtrack horizontal winds. The hurricane secondary circulation is typically difficult to measure at upper levels due to aircraft altitude limitations and sensitivity of the lower altitude airborne radars. EDOP is in principle, well suited to measure these components of the wind. When ER-2 flies across the approximate center of the hurricane circulation, the along-track winds derived from EDOP, are approximately equal to the hurricane radial flow comprising the secondary circulation. Assuming that the hydrometeor fallspeeds can be approximated, the radial and vertical wind components of the secondary circulation can be measured. Since the hydrometeor motions can be estimated with more confidence in the higher altitude ice regions (i.e., graupel and mixed phase are complicated at lower altitudes), the derived radial and vertical winds have higher accuracy at upper levels. On the other hand, the reflectivities are extremely low at higher altitudes, resulting in fewer Doppler velocity estimates.

Heymsfield, G. M.↗
NASA NTRS1981

Determination of wind from NIMBUS 6 satellite sounding data

Objective methods of computing upper level and surface wind fields from NIMBUS 6 satellite sounding data are developed. These methods are evaluated by comparing satellite derived and rawinsonde wind fields on gridded constant pressure charts in four geographical regions. Satellite-derived and hourly observed surface wind fields are compared. Results indicate that the best satellite-derived wind on constant pressure charts is a geostrophic wind derived from highly smoothed fields of geopotential height. Satellite-derived winds computed in this manner and rawinsonde winds show similar circulation patterns except in areas of small height gradients. Magnitudes of the standard deviation of the differences between satellite derived and rawinsonde wind speeds range from approximately 3 to 12 m/sec on constant pressure charts and peak at the jet stream level. Fields of satellite-derived surface wind computed with the logarithmic wind law agree well with fields of observed surface wind in most regions. Magnitudes of the standard deviation of the differences in surface wind speed range from approximately 2 to 4 m/sec, and satellite derived surface winds are able to depict flow across a cold front and around a low pressure center.

Carle, W. E.↗
NASA NTRS1981

The aerodynamics of circulation control

Two dimensional subsonic wind tunnel tests were conducted on a 20% thickness: chord ratio circulation controlled elliptic aerofoil section equipped with forward and reverse blowing slots. Overall performance measurements were made over a range of trailing edge blowing momentum coefficients from 0 to 0.04; some included the effect of leading edge blowing. A detailed investigation of the trailing edge wall jet, using split film probes, hot wire probes and total head tubes, provided measurements of mean velocity components, Reynolds normal and shear stresses, and radial static pressure. The closure of the two dimensional angular momentum and continuity equations was examined using the measured data, with and without correction, and the difficulty of obtaining a satisfactory solution illustrated. Suggestions regarding the nature of the flow field which should aid the understanding of Coanda effect and the theoretical solution of highly curved wall jet flows are presented.

Wood, N. J.↗