681 research outputs found
Feasibility of remote evaporation and precipitation estimates
Remote sensing by means of stereo images obtained from flown cameras and scanners provides the potential to monitor the dynamics of pollutant mixing over large areas. Moreover, stereo technology may permit monitoring of pollutant concentration and mixing with sufficient detail to ascertain the structure of a polluted air mass. Consequently, stereo remote systems can be employed to supply data to set forth adequate regional standards on air quality. A method of remote sensing using stereo images is described. Preliminary results concerning the planar extent of a plume based on comparison with ground measurements by an alternate method, e.g., remote hot-wire anemometer technique, are supporting the feasibility of using stereo remote sensing systems
Effects of turbulence on laminar separation on aerodynamic surfaces such as airfoils and compressor blading
Activities report include (1) completion of measurements of turbulence amplification in flow about a circular cylinder; (2) initiation of the measurements of turbulence characteristics in flow about a single symmetric airfoil; and, (3) further examination of various matching numerical methods. Emphasis is placed on the experimental program conducted to obtain data on the amplification of the oncoming turbulence and its management
Coherent substructure of turbulence near the stagnation zone of a bluff body
The evolution of freestream turbulence in crossflow about a circular cylinder was studied in order to identify the existence of a coherent substructure which is the outcome of the amplification of freesteam turbulence by the stretching mechanism in diverging flow about a bluff body. Visualization of the flow events revealed the selective stretching of cross-vortex tubes and the emergence of an organized turbulent flow pattern near the cylinder stagnation zone. Significant amplification of the total turbulent energy of the streamwise fluctuating velocity was consistently monitored. Realization of selective amplification at scales larger than the neutral scale of the stagnation flow was indicated by the variation of the discrete streamwise turbulent energy. A most amplified scale, characteristic of the energy containing eddies within the coherent substructure and commensurate with the boundary-layer thickness, was detected. Penetration of the amplified turbulence into the cylinder boundary layer led to the retardation of separation and to a concurrent decrease in the drag coefficient at subcritical cylinder-diameter Reynolds numbers
Turbulence effect on crossflow around a circular cylinder at subcritical Reynolds numbers
An investigation of the effect of freestream turbulence on the flow around a smooth circular cylinder at subcritical Reynolds numbers from 5.2 x 10 to the 4th power to 2.09 x 10 to the 5th power was conducted. Measurements show that the interaction of incident turbulence with the initial laminar boundary layer: (1) modifies the characteristics of the mean surface pressure distribution; (2) induces an aft shift in the separation point ranging from 5 to 50 beyond the laminar separation angle of 80 degrees; and, (3) reduces the mean drag coefficient to values between 97 and 46% of its nearly constant laminar counterpart. The extent of these changes depends on the particular Reynolds number background turbulence combination. These results demonstrate that a boundary-layer flow similar to that found in critical, supercritical and/or transcritical flow regimes is induced by turbulence at subcritical Reynolds numbers and, hence, the effect of turbulence is equivalent to an effective increase in the Reynolds number. The change in the nature and properties of the boundary layer in the subcritical regime, consequent upon the penetration of turbulence into it, is in agreement with the model proposed by the vorticity-amplification theory
A visual investigation of turbulence in stagnation flow about a circular cylinder
A visual investigation of turbulence in stagnation flow around a circular cylinder was carried out in order to gain a physical insight into the model advocated by the corticity-amplification theory. Motion pictures were taken from three different viewpoints, and a frame by frame examination of selected movie strips was conducted. Qualitative and quantitative analyses of the flow events focused on tracing the temporal and spatial evolution of a cross-vortex tube outlined by the entrained smoke filaments. The visualization supplied evidence verifying: (1) the selective stretching of cross-vortex tubes which is responsible for the amplification of cross vorticity and, hence, of streamwise turbulence; (2) the streamwise tilting of stretched cross-vortex tubes; (3) the existence of a coherent array of vortices near the stagnation zone; (4) the interaction of the amplified vorticity with the body laminar boundary layer; and, (5) the growth of a turbulent boundary layer
Computer managed learning system: annual report no. 1
April 1, 1970.CER69-70RWH-WL-WZS36.AN CMLS - 1 - 70
Wind study of Kaiser Center office building
CER69-70GH-JEC-WZS-13.September 1969.For Metronics Associates, Inc.Includes bibliographical references.Mean and fluctuating wind loading on a 1:192 scale model of Kaiser Center Office Building 403 ft high was studied in a uniform flow. Pressure measurements were carried out for four different wind directions (N, NE, E, and S). The wind loading was influenced strongly by a tall building immediately to the southeast when the wind was from the south, Generally, the mean pressure was higher at the center portion of an upwind face than near its edges. On the leewind surface relatively uniform negative pressure (suction) was obtained. Its absolute value was about one-third of that along an upwind face. On the other hand, the fluctuating pressure was highest near the building base, in the flow separation region and in the wake of the adjacent building in a southly wind. A model of the upstream topography to the northeast was constructed using a 1:600 scale. This model terrain was 24 ft long (2.7 miles of the prototype terrain) with the Kaiser building site near its trailing edge. Mean velocity and turbulence intensity profiles were measured along the terrain
Survey of micrometeorological parameters within a forest canopy at Fort Polk, Louisiana, A
CER80-81WZS-FWL-WEM44.Includes bibliographical references (page 44).February 1982.A field investigation of micrometeorological parameters inside and above a forest canopy at Fort Polk, Louisiana, was conducted in conjunction with the Atmospheric Sciences Laboratory Dusty Infrared Test IIIA. The three orthogonal components of the wind, ory- and wet-bulb temperatures and total solar radiation were measured inside this forest canopy by means of an instrumented meteorological tower. In addition, turbulence inside the forest canopy was monitored by means of hot-wire anemometers. Tethersonde balloon sounding above the forest canopy was further performed. The meteorological data was reduced by means of three different statistical methods. Single sample period values, one-minute sample averages and sequential sample values were computed. The latter two methods led to the construction of time series which can readily be used to perform advanced statistical analyses. Totals of 27 h 29 min of meteorological tower data and 2 h 50 min of balloon data were reduced. The results are presented in tabular form in 1422 tables and partially displayed in 1795 figures under separate cover in view of their large volume. Selected samples of the results are, however, presented herein. The results supply a data base for analyses of airflow in a forest canopy. Suggestions for future work of significance for mission-oriented cases and for modeling of airflow in a forest canopy are outlined.Contract DAAG29-76-D-0100 conducted for the U.S. Army Atmospheric Sciences Laboratory, White Sands Missile Range
ECFA Detector R&D Panel, Review Report
Two special calorimeters are foreseen for the instrumentation of the very
forward region of an ILC or CLIC detector; a luminometer (LumiCal) designed to
measure the rate of low angle Bhabha scattering events with a precision better
than 10 at the ILC and 10 at CLIC, and a low polar-angle
calorimeter (BeamCal). The latter will be hit by a large amount of
beamstrahlung remnants. The intensity and the spatial shape of these
depositions will provide a fast luminosity estimate, as well as determination
of beam parameters. The sensors of this calorimeter must be radiation-hard.
Both devices will improve the e.m. hermeticity of the detector in the search
for new particles. Finely segmented and very compact electromagnetic
calorimeters will match these requirements. Due to the high occupancy, fast
front-end electronics will be needed. Monte Carlo studies were performed to
investigate the impact of beam-beam interactions and physics background
processes on the luminosity measurement, and of beamstrahlung on the
performance of BeamCal, as well as to optimise the design of both calorimeters.
Dedicated sensors, front-end and ADC ASICs have been designed for the ILC and
prototypes are available. Prototypes of sensor planes fully assembled with
readout electronics have been studied in electron beams.Comment: 61 pages, 51 figure
Equivalences between localisations of categories provided by replacements
We give a characterisation of functors whose induced functor on the level of
localisations is an equivalence and where the isomorphism inverse is induced by
some kind of replacements such as projective resolutions or cofibrant
replacements
- …