Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Wind shear”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Development of a category 2 approach system model

An analytical model is presented which provides, as its primary output, the probability of a successful Category II approach. Typical applications are included using several example systems (manual and automatic) which are subjected to random gusts and deterministic wind shear. The primary purpose of the approach system model is to establish a structure containing the system elements, command inputs, disturbances, and their interactions in an analytical framework so that the relative effects of changes in the various system elements on precision of control and available margins of safety can be estimated. The model is intended to provide insight for the design and integration of suitable autopilot, display, and navigation elements; and to assess the interaction of such elements with the pilot/copilot.

Johnson, W. A.↗
NASA NTRS1972

A case study of persistent, intense, clear air turbulence in an upper level frontal zone.

Widespread and persistent clear air turbulence (CAT) occurred over the Eastern Seaboard of the U.S. between New York and South Carolina on 18 March 1969. The major synoptic features and a qualitative discussion of the factors contributing to the development of the large vertical wind shears associated with the turbulence are presented. The turbulent region in the vicinity of Wallops Island, Va., was probed with a NASA T-33 research aircraft and with sensitive radars. The clear air radar echoes and the most intense turbulence occurred principally within an upper level frontal zone of about 2 km depth which was produced by the confluence of two currents of widely different origin.

Reed, R. J.↗
NASA NTRS1972

Elliptical storm cell modeling of digital radar data

A model for spatial distributions of reflectivity in storm cells was fitted to digital radar data. The data were taken with a modified WSR-57 weather radar with 2.6-km resolution. The data consisted of modified B-scan records on magnetic tape of storm cells tracked at 0 deg elevation for several hours. The MIT L-band radar with 0.8-km resolution produced cross-section data on several cells at 1/2 deg elevation intervals. The model developed uses ellipses for contours of constant effective-reflectivity factor Z with constant orientation and eccentricity within a horizontal cell cross section at a given time and elevation. The centers of the ellipses are assumed to be uniformly spaced on a straight line, with areas linearly related to log Z. All cross sections are similar at different heights (except for cell tops, bottoms, and splitting cells), especially for the highest reflectivities; wind shear causes some translation and rotation between levels. Goodness-of-fit measures and parameters of interest for 204 ellipses are considered.

Altman, F. J.↗
NASA NTRS1973

A manual control theory analysis of vertical situation displays for STOL aircraft

Pilot-vehicle-display systems theory is applied to the analysis of proposed vertical situation displays for manual control in approach-to-landing of a STOL aircraft. The effects of display variables on pilot workload and on total closed-loop system performance was calculated using an optimal-control model for the human operator. The steep approach of an augmentor wing jet STOL aircraft was analyzed. Both random turbulence and mean-wind shears were considered. Linearized perturbation equations were used to describe longitudinal and lateral dynamics of the aircraft. The basic display configuration was one that abstracted the essential status information (including glide-slope and localizer errors) of an EADI display. Proposed flight director displays for both longitudinal and lateral control were also investigated.

Baron, S.↗
NASA NTRS1972

Meteorological measurements from satellite platforms

Quantitative exploitation of meteorological data from geosynchronous satellites is starting to move from the laboratory to operational practice. Investigations of the data applications portion of the total meteorological satellite system include: (1) tropospheric wind shear and the related severe storm circulations; (2) kinematic properties of the tropical atmosphere as derived from cloud motion vectors; (3) application of a geostationary satellite rake system to measurements of rainfall; and (4) pointing error analysis of geosynchronous satellites.

Suomi, V. E.↗
NASA NTRS1972

Nighttime sporadic-E.

At night, internal atmospheric gravity waves are able to induce drift instabilities in the ionospheric plasma. Nighttime constant height type sporadic-E(Esc) may then be explained as an effect due to the combined effect of ionization movement due to the wind shear mechanism and due to the cross-field gradient drifts. This combined concept provides a qualitative explanation of the rocket observed nighttime electron density profiles, of the speeds of the Esc irregularities and of the variations of Esc with latitude and electric field strength.-

Beer, T.↗
NASA NTRS1973

Correlation of microthermal turbulence data with meteorological soundings in the troposphere.

Recent measurements of vertical profiles of microthermal turbulence structure are reported. Data obtained by balloon-borne temperature sensors are presented in terms of the temperature structure coefficient. Free-floating balloon flights allowed this type of measurement to be extended to an altitude of 15 km above sea level. This series of flights was accompanied by vertical profiles of wind speed and temperature that permitted calculation of wind shear and gradient Richardson number profiles. The observed correlations found to exist between microthermal turbulence layers and the standard meteorological data are discussed briefly in light of the theory.

Bufton, J. L.↗
NASA NTRS1973

Resonant oscillations of intermediate frequency in a stratified atmosphere.

A class of solutions to a model of forced oscillations in a rotating stratified atmospheric layer is derived and analyzed. The basic model is found to reduce to a boundary value problem with a second-order linear partial differential equation of the hyperbolic type for this range of forcing frequencies. The forced solutions are shown to exhibit resonances with the normal modes of oscillation of the layer. The characteristics of the resonant modes are analyzed in terms of mean tropospheric values of temperature, temperature lapse, wind speed, horizontal and vertical wind shears, latitude, and the frequency and horizontal wavelength of the forcing mechanism. These solutions are compared with solutions to the model for a different (subinertial) range of forcing frequencies. This comparison leads to an elliptic boundary value problem. The solutions in that case do not exhibit the same type of resonance and generally decay away from the region of forcing.

Thompson, O. E.↗
NASA NTRS1974

Studies of aircraft wake chemistry and dispersion

Use of aerospace technology to study aircraft wakes is reviewed. It is shown how aerospace vehicles can be used to provide data for increased understanding of the atmosphere and of aircraft exhaust trails where knowledge is inadequate to evaluate fully the potential impact of the engine emissions. Models of aircraft near-field exhaust wakes are characterized by jet, vortex, and dispersion regimes. Wake growth in the jet regime is self-determined and rapid, whereas further spreading is inhibited in the vortex regime because of circulating vortex motion. Wake diffusion in the dispersion regime is initially influenced by aircraft induced turbulence but is dominated later by small-scale atmospheric turbulence. Computed fluid mechanical results show the importance of effects such as wake buoyancy, wind shear, turbulence, and traffic corridor exhaust buildup on dispersion of the wake. In the jet regime the exhaust characteristics and thermochemistry serve to illustrate initial chemical changes involving potential pollutant species.

Poppoff, I. G.↗
NASA NTRS1974

Multiple contrail streamers observed by radar

An unusual case of multiple streamers or filaments with the characteristic mare's tail pattern in vertical section has been observed by radar where the generating elements were condensation trails laid by high-altitude aircraft. The contrails were laid perpendicular to the wind, and, as they drifted, a multitude of streamers formed along each trail. The streamers extended from 9 km to the ground. RHI and PPI photographs at X and S band taken over a 2-hr period show the three-dimensional shape of the streamers due to the wind shear. Doppler measurements were also taken. The resulting velocity spectra are very narrow indicating little or no turbulence. Reflectivity factors were measured at various altitudes and show a decrease in reflectivity with distance from the generating line. Fall velocities based on the slopes of the streamer patterns varied from 0.4 to 1.4 m/sec. In general, the characteristics of the precipitation streamers were quite similar to those previously measured in naturally occurring cloud forms such as cirrus uncinus.

Konrad, T. G.↗
NASA NTRS1975

A general algorithm for relating ground trajectory distance, elapsed flight time, and aircraft airspeed and its application to 4-D guidance

A general solution using an elliptic integral approximation which relates flight time, aircraft airspeed, and ground distance on straight-line and circular-arc trajectory segments is developed. The solution procedure is applicable to both constant and accelerating aircraft flight. In addition, wind shear including both magnitude and heading change is incorporated in the solution. The solution equations are used in a four-dimensional (4-D) control algorithm where both flight time and final airspeed are specified. The results show that the algorithm converges rapidly and accurately.

Foudriat, E. C.↗
NASA NTRS1975

Comparison of two head-up displays in simulated standard and noise abatement night visual approaches

Situation and command head-up displays were evaluated for both standard and two segment noise abatement night visual approaches in a fixed base simulation of a DC-8 transport aircraft. The situation display provided glide slope and pitch attitude information. The command display provided glide slope information and flight path commands to capture a 3 deg glide slope. Landing approaches were flown in both zero wind and wind shear conditions. For both standard and noise abatement approaches, the situation display provided greater glidepath accuracy in the initial phase of the landing approaches, whereas the command display was more effective in the final approach phase. Glidepath accuracy was greater for the standard approaches than for the noise abatement approaches in all phases of the landing approach. Most of the pilots preferred the command display and the standard approach. Substantial agreement was found between each pilot's judgment of his performance and his actual performance.

Cronn, F.↗
NASA NTRS1975

Behaviour of nitric oxide trails deposited in the mesosphere and stratosphere

The transient behavior of a nitric oxide trail deposited at approximately 60 km altitude is studied by the solution of the appropriate multidimensional diffusion equation which includes terms representing the effects of wind shear. Similar analysis is then carried out for the situation in the stratosphere. Trail behavior is found to be relatively independent of altitude and background ozone, but strongly dependent on the magnitude of eddy diffusity and the initial nitric oxide concentration. The nitric oxide trail reacts with ambient ozone to form nitrogen dioxide. For a trail 100 m initial radius, an ozone hole will form to a maximum size in 4 to 6 hours and then decay. The overall recovery time of the atmosphere following the creation of the trail is less than 12 hours.

Eberstein, I. J.↗
NASA NTRS1975

A feasibility study for the detection of upper atmospheric winds using a ground based laser Doppler velocimeter

A possible measurement program designed to obtain the information requisite to determining the feasibility of airborne and/or satellite-borne LDV (Laser Doppler Velocimeter) systems is discussed. Measurements made from the ground are favored over an airborne measurement as far as for the purpose of determining feasibility is concerned. The expected signal strengths for scattering at various altitude and elevation angles are examined; it appears that both molecular absorption and ambient turbulence degrade the signal at low elevation angles and effectively constrain the ground based measurement of elevation angles exceeding a critical value. The nature of the wind shear and turbulence to be expected are treated from a linear hydrodynamic model - a mountain lee wave model. The spatial and temporal correlation distances establish requirements on the range resolution, the maximum detectable range and the allowable integration time.

Thomson, J. A. L.↗
NASA NTRS1975

Distribution and moments of radial error

An investigation of the moments and probability distribution of the resultant of two normally distributed random variables is presented. This is the so-called generalized Rayleigh distribution which has many applications in the study of wind shear, random noise, and radar. The most general formula was derived, and two special cases were considered for which tables of the moments and probability distribution functions are included as an appendix. One of the special cases was generalized to n-dimensions.

White, R. G.↗
NASA NTRS1975

The study of mesoscale phenomena, winter monsoon clouds and snow area

The author has identified the following significant results. The clouds under a moderate winter monsoon situation taken with S190A camera reveal existence of clouds with band structure of various wavelengths. The wavelength ranges from 0.4 to 3.5 kms. There was a good relationship between the longitudinal cloud band and vertical wind shear. There was a distinct difference in size of clouds between the Japan Sea side or upwind side and the Pacific Ocean side or downwind side of the Japanese mainland. Large solid cumulus clusters have the size of 20 x 35 sq km over the Japan Sea off the coast of Hokuriku District. It was found that S190A aerial color pictures showing shadows of fair weather cumuli over the sea could be successfully used in estimating cloud height while S190A station 1 picture was more useful over the land since it could more clearly distinguish shadow from vegetation. The height of fair weather cumuli estimated from shadows agree with the lifted condensation level. It was also found that these pictures were effectively used in delineating snow cover area. S192 data, especially IR channel, were found to be effective in finding topography of nimbostratus.

Tsuchiya, K.↗
NASA NTRS1976

Tornadoes and other atmospheric vortices

The growth of random vortices in an atmosphere with buoyant instability and vertical wind shear is studied along with the velocities in a single gravity-driven vortex; a frictionless adiabatic model which is supported by laboratory experiments is first considered. The effects of axial drag, heat transfer, and precipitation-induced downdrafts are then calculated. Heat transfer and axial drag tend to have stabilizing effects; they reduce the downdrafts of updrafts due to buoyancy. It is found that downdrafts or tornadic magnitude might occur in negatively-buoyant columns. The radial-inflow velocity required to maintain a given maximum tangential velocity in a tornado is determined by using a turbulent vortex model. Conditions under which radial-inflow velocities become sufficiently large to produce tangential velocities of tornadic magnitude are determined. The radial velocities in the outer regions, as well as the tangential velocities in the inner regions may be large enough to cause damage. The surface boundary layer, which is a region where large radial inflows can occur, is studied, and the thickness of the radial-inflow friction layer is estimated. A tornado model which involves a rotating parent cloud, as well as buoyancy and precipitation effects, is discussed.

Deissler, R. G.↗
NASA NTRS1976

Scanning laser Doppler velocimeter system simulation for sensing aircraft wake vortices

A model that simulates the interaction of a laser-Doppler velocimeter with an aircraft wake flowfield is described. A hydrodynamic model is developed which represents the trailing vortex sheet and wind shear as discrete free vortices distributed over a two-dimensional grid. A sensor model is formulated for scanning both in range and in angle to produce a fan beam configuration without frequency translation. Output of this model is a frequency spectrum vs both range and angle. Once the spectrum is evaluated, simulations of the data analysis procedure are carried out. Patterns of various features of the signature are presented in range-elevation angle plots. The problem of locating the vortex centers is discussed as a pattern recognition problem and as a point target problem.

Thomson, J. A. L.↗