Showing papers on "Wind profile power law published in 1994"
TL;DR: In this article, the mean and standard deviation for the exponent of the power-law wind profile over the ocean under near-neutral atmospheric stability conditions were determined to be 0.11 ± 0.03.
Abstract: On the basis of 30 samples from near-simultaneous overwater measurements by pairs of anemometers located at different heights in the Gulf of Mexico and off the Chesapeake Bay, Virginia, the mean and standard deviation for the exponent of the power-law wind profile over the ocean under near-neutral atmospheric stability conditions were determined to be 0.11 ± 0.03. Because this mean value is obtained from both deep and shallow water environments, it is recommended for use at sea to adjust the wind speed measurements at different heights to the standard height of 10 m above the mean sea surface. An example to apply this P value to estimate the momentum flux or wind stress is provided.
406 citations
TL;DR: In this paper, the authors used NWP models combined with models (either physical or statistical) taking local effects into account, to predict the wind locally better than the models commonly used today (as eg persistence).
Abstract: Using Numerical Weather Prediction (NWP) models it has been shown that they, combined with models (either physical or statistical) taking local effects into account, can be used to predict the wind locally better than the models commonly used today (as eg persistence). By “local” is meant at one distinct spot, as eg the location of a meteorological mast. The physical model of local effects takes the following into account: shelter from near-by obstacles, the effect of roughness changes and the effect of the local orography. The large-scale flow is linked to the surface flow by the geostrophic drag law, and the logarithmic wind profile. The predictions are made up to 36 hours ahead. The model is tested on data from 50 meteorological stations scattered all over Europe.
181 citations
TL;DR: In this article, the authors report detailed velocity measurements which further suggest that no single logarithmic expression, based on fixed values of κ and τ, adequately represents the full wind profile which includes the inner saltation cloud above 0.01 m and the outer grain-free region of the boundary layer.
Abstract: In wind tunnel studies of aeolian transport, the number and position of pitot tubes are decided by the researcher, so that there are important variations in the computation ofU* between studies. Velocity measurements seldom are made very close to mobile surfaces because the tubes become blocked by drifting sand grains. This practice is fortuitous as demonstrated by recent selfregulatory models of saltation which indicate that fluid and grain-borne shear stress vary substantially within the lowest 0.01 m and application of the logarithmic law is therefore unsound. This study reports detailed velocity measurements which further suggest that no single logarithmic expression, based on fixed values of κ and τ, adequately represents the full wind profile which includes the inner saltation cloud above 0.01 m and the outer grain-free region of the boundary layer. A much improved fit over the logarithmic wind profile model is achieved with a square root relation, although there is no known physical basis for this specific form of power model. Relatively shallow boundary-layer development in wind tunnels forces the velocity gradient above the region of momentum extraction to attain exceptionally large values, uncommon in natural settings.
107 citations
TL;DR: In this article, the authors show that the wind stress direction is influenced by the direction of the surface waves, especially for stronger winds, and that the stress vector lies between the mean wind and the mean wave directions.
Abstract: Sonic anemometer data were taken during the Surface Waves Processes Program (SWAPP) in March 1990 in the North Pacific. Measurements of the wind stress vector span several strong wind events. Significant angles between the wind stress vector and the mean wind vector are seen. Simultaneous measurements of the directional wave field were made with a surface scanning Doppler sonar. The data suggest that the wind stress direction is influenced by the direction of the surface waves, especially for stronger winds. Overall, the stress vector lies between the mean wind and the mean wave directions. At the higher wind speeds (over 8.6 m/s), there is a nonzero correlation between the variations in wave directions and stress directions as well. Finally, the stress and wave component directions have similar frequency dependence over the frequency band where wave energy is nonnegligible, suggesting a dynamic link.
99 citations
TL;DR: In this article, the main flow distortion effects caused by the sonic probe (i.e., deflection and attenuation/amplification of the wind vector) as a function of the azimuth angle of the incoming flow were examined by means of wind tunnel measurements at four different wind speeds and 11 different elevation angles of the flow with respect to the probe.
Abstract: Main flow distortion effects caused by the sonic probe (i.e., deflection and attenuation/amplification of the wind vector) as a function of the azimuth angle of the incoming flow were examined by means of wind tunnel measurements at four different wind speeds and 11 different elevation angles of the flow with respect to the probe. The dependence of the distortion on wind speed and elevation angle turned out to be small compared with the dependence on the azimuth angle. Based on wind tunnel data, a set of calibration coefficients for each azimuth was evaluated. Application of this calibration on wind tunnel data shows an average compensation of the flow distortion of about 61 %. A comparative application of the calibration supplied by the manufacturer leads to an increase of the flow distortion effects, especially at higher wind speeds. Application of the obtained calibration on field data leads to a change of about 20% in momentum flux over forest and grass field. The flux of sensible heat change...
82 citations
TL;DR: In this article, an analysis of wind data for the ten-year period 1979-1988 in Nigeria is presented, and the need for the provision of new data stations in order to enable a complete and reliable assessment of the overall wind power potential of the country is identified.
Abstract: An analysis of wind data for the ten-year period 1979–1988 in Nigeria is presented. Surface and upper winds were considered as well as maximum gusts. The need for the provision of new data stations in order to enable a complete and reliable assessment of the overall wind power potential of the country is identified and specific locations suggested. Socioeconomic and political factors affecting the development of wind energy development in Nigeria are also discussed.
49 citations
TL;DR: In this article, the authors measured streamwise and vertical variations in the mean field for a variety of atmospheric stability conditions over Cooper's Ridge, a 115 m high elongated ridge with low surface roughness.
Abstract: Measurements of mean wind flow and turbulence parameters have been made over Cooper's Ridge, a 115 m high elongated ridge with low surface roughness. This paper describes measurements of the streamwise and vertical variations in the mean field for a variety of atmospheric stability conditions. In near-neutral conditions, the normalised speedup over the ridge compares well with measurements from Askervein (Mickleet al., 1988). The near-neutral results are also compared to an analytical flow model based on that of Huntet al. (1988a). Measured streamwise variations show less deceleration at the foot of the hill and slightly more acceleration at the crest of the hill than does the model. In non-neutral conditions, the speedup over the ridge reduces slightly in unstable conditions and increases by up to a factor of two in stable conditions. The model is modified to allow boundary-layer stability to change the upwind wind profile and the depths of the inner and middle layers. Such a modification is shown to describe the observations of speedup well in unstable and weakly stable conditions but to overestimate the speedup in moderate to strongly stable conditions. This disagreement can be traced to the model's overestimation of the upstream scaling velocity at the height of the middle layer through its use of a stable wind profile form which has greater shear than that of the observed profiles, in possible combination with the three-dimensionality of the ridge which would allow enhanced flow around, rather than over, the feature in more stable conditions.
49 citations
TL;DR: In this article, the effects of atmospheric wind and temperature fluctuations on acoustic signal variability are discussed, with emphasis on the effect of large scale turbulence (motions having size larger than or comparable to the integral length scale).
Abstract: The effects of atmospheric wind and temperature fluctuations on acoustic signal variability is discussed, with emphasis on the effects of large‐scale turbulence (motions having size larger than or comparable to the integral length scale). Such large‐scale turbulence is anisotropic, is generated by both shear and buoyancy instabilities, and has structure that depends strongly on the meteorological conditions as well as the distance from the ground. Previous research in the atmospheric sciences literature regarding length scales and anisotropy is reviewed and incorporated into an acoustic propagation model. The model is based on a multiply scaled, six‐termed, sound‐speed correlation function. A second, simpler model, based on fluctuating curvature of the vertical wind profile, is also proposed. Both models are compared with experimental measurements of amplitude and travel‐time fluctuations obtained during the Rock Springs Tomography Experiment, which involved concurrent monitoring of acoustic fluctuations ...
48 citations
TL;DR: In this article, an active simulating procedure of the time history of wind velocity in a wind tunnel was described, and the simulated time histories of the wind velocity by this technique fitted well the target ones.
37 citations
TL;DR: In this paper, the authors present three different models for calculating the average output power of a wind turbine, taking into account the dynamic characteristics of the phenomenon of wind power and wind speed.
37 citations
TL;DR: In this paper, experimental investigations have been conducted in a wind tunnel on flow and dispersion of pollutants around an isolated building, where a neutrally stable atmosphere at 1 75 scale was simulated.
TL;DR: In this paper, the authors present results of a fundamental, experimental study on wind loading of porous facade systems, including relative building dimensions, porosity, and gap width, which have been varied systematically in a model scale study.
TL;DR: The wind farm at Norddeich as mentioned in this paper consists of 5 wind turbines of 16 m rotor diameter and 55 kW power rating. The turbines are arranged in a straight line with a spacing of approximately 4 rotor diameters.
TL;DR: In this paper, full-scale wind profile and surface pressure measurements made at Silsoe are compared with a series of 1:100 scale experiments conducted in the University of Western Ontario's Boundary Layer wind-tunnel No. 1.
TL;DR: In this article, a three dimensional, nonlinear hydrodynamic model of the Irish Sea is used to examine the response of the region to forcing along its open boundary and wind stress over the area.
Abstract: A three dimensional, nonlinear hydrodynamic model of the Irish Sea is used to examine the response of the region to forcing along its open boundary and wind stress over the area. Frictional dissipation at the bed is parameterized with a quadratic law of bottom friction, which can take account of enhanced frictional effects due to wind wave/current interaction. A standard finite difference grid is used in the horizontal, with an expansion of functions through the vertical, giving a continuous current profile from sea surface to seabed. The model has a grid resolution of the order of 3 km and hence can resolve some features of the nearshore region. The model is forced with M2 tidal input along its open boundary, and time invariant wind fields, corresponding initially to spatially uniform northerly and westerly wind stresses of 1 N/m2 and subsequently to a west-east gradient wind changing from −1 N/m2 to +1 N/m2 going from west to east, and a north-south gradient wind changing from 1 N/m2 to −1 N/m2 going from north to south. The response to open boundary forcing through both elevations and currents is also examined, and the influence of the effects of enhanced bottom friction due to wind waves is also briefly considered.
TL;DR: A vector wind model has been developed for launch vehicle design as discussed by the authors, which produces wind profiles for evaluation of vehicle control and trajectory variables required for assessment of proposed designs for new NASA launch vehicles.
Abstract: A vector wind model has been developed for launch vehicle design. The model produces wind profiles for evaluation of vehicle control and trajectory variables required for assessment of proposed designs for new NASA launch vehicles. The wind model is based on the concept that the wind components of vectors at two altitudes have a probability distribution function that is quadravariate normal. Given a wind vector at one altitude, the conditional distribution of the wind components at any other altitude is bivariate normal. A process is described for derivation of vector wind profiles based on the statistical model. The process produces wind profiles that are a reasonable substitute for measured wind profile samples. The model wind profiles produce dispersions in aerodynamic load indicators (ALI) that cover the dispersion range of ALI calculated from an extensive sample of Jimsphere wind profiles; this is accomplished at a selected altitude with only 12 model wind profiles compared to 1800 measured Jimsphere profiles. This represents an opportunity for a considerable reduction of computational effort during design phases that require many iterations to establish a launch vehicle design philosophy.
TL;DR: In this article, the results of wind tunnel tests and response analyses were conducted in order to obtain data for the wind resistant design of a large span roof, which is planned to be constructed in Kariya Japan.
TL;DR: In this article, a small-scale physical model was used to simulate strong gap winds in Howe Sound, British Columbia, using a small scale physical model and field observations of the wind layer.
Abstract: Strong gap winds in Howe Sound, British Columbia, are simulated using a small-scale physical model. Model results are presented and compared with observations recorded in Howe Sound during a severe gap wind event in December 1992. Hydraulic theory is utilized to explain along-channel variation in wind. Field observations affirm the findings of the physical modeling with both, indicating the presence and location of controls and hydraulic jumps in the wind layer. Hydraulic behavior is found to change as the synoptic pressure gradient and the flow rate increase. In particular, field results indicate two distinct hydraulic situations: one during relatively weak wind, the other, which is more strongly controlled, during the period of peak wind. An additional comparison is made with output from the computer model hydmod of Jackson and Steyn. Numerical simulations, configured for the conditions present in Howe Sound during the December 1992 event, indicate channel hydraulics (and thus spatial wind spee...
TL;DR: In this article, the aerodynamic performance of propeller type and multi-bladed horizontal axis wind turbines with three different airfoil blade sections (flat-plate, symmetric and circular-arc airfoils) was investigated as functions of wind turbine design parameters (blade angle, rotor solidity, drag-to-lift coefficient ratio and blade section).
TL;DR: In this paper, a small 915-MHz profiler has been operated continuously in downtown Montreal, where the reflectivities of the clear air and the precipitation are comparable, and the best conditions for observing interactions between precipitation and clear air are when light rain falls through a reflective layer associated with a frontal surface or inversion.
Abstract: . Since May 1992 a small, 915-MHz profiler has been operated continuously in downtown Montreal. It is a five-beam system employing a microstrip array antenna, located atop a 14-story office building that houses several academic departments of McGill University. The data are used for research on precipitation physics and the clear-air reflectivity in addition to wind profiling. We are especially interested in situations in which the reflectivities of the clear air and the precipitation are comparable. This permits the study of interactions between the precipitation and the clear air, a new area of research made possible by wind profilers. On clear days in the summer, 30-min consensus winds can often be measured to an altitude of 3 km, but ground clutter in the antenna sidelobes interferes with measurements below 600 m. Rain when present often permits wind profiling down to 100 m and up to 6 km or higher. On cold winter days there are some periods when the reflectivity is too weak at all levels to permit wind estimation. Falling snow, however, provides readily detectable echoes and serves as a good tracer of the wind and so allows profiling over its full altitude extent. The best conditions for observing interactions between precipitation and the clear air are when light rain falls through a reflective layer associated with a frontal surface or inversion. Unexpectedly, flocks of migrating birds sometimes completely dominate the signal at night in the spring and fall seasons.
TL;DR: In this paper, the structure of the wind field in near calm conditions is established by considering a bivariate Gaussian distribution for the components of wind speed, which becomes a circular distribution in low wind speeds.
Abstract: In this paper the structure of the wind field in near calm conditions is established. First, the main parameters that characterize the wind field are defined. By considering a bivariate Gaussian distribution for the components of the wind speed, which becomes a circular distribution in low wind speeds, simple relations among those parameters have been obtained. Some experimental evidence supporting the proposed formulation is given.
TL;DR: In this paper, a sonic anemometer was used to collect data from a flat terrain near Calgary, Alberta, from 1988 to 1989, and the data have been analyzed with respect to wind speed and stability.
Abstract: Turbulence data were collected with the use of a sonic anemometer from October 1988 to September 1989. The study site was situated amid flat terrain near Calgary, Alberta. The data have been analyzed with respect to wind speed and stability. Simple empirical equations have been established that relate median standard deviations of transverse, longitudinal, and vertical wind fluctuations (σv, σu, σw) to wind speed and static stability. One-to-one correlation coefficients between predicted and observed data were typically in excess o.90. Dispersion models utilize the ratios of turbulence parameters to wind speed (i.e., σv/U, σu/U, σw/U). These ratios, referred to as standard deviations of the wind angles, have been derived as functions of wind speed and potential temperature gradients. Values of the standard deviation of the transverse wind angle σθ are shown to be independent of stability. Standard deviations of the longitudinal and vertical wind angles (σφ, σϕ) have the same exponential dependenc...
TL;DR: In this paper, the authors used aircraft radar instruments for sea surface wave measurements, and obtained fetch-limited directional wind wave spectra under steady off-shore wind conditions, showing that the dominant waves propagate at an angle to the wind.
Abstract: Using aircraft radar instruments designed for sea surface wave measurements, we have obtained fetch-limited directional wind wave spectra under steady off-shore wind conditions. The results from these observations in different areas at different times show that, up to a fetch of 150 km, the dominant waves propagate at an angle to the wind. The angle is near to that suggested by the Phillips resonance wind wave generation condition, but with one important difference: The waves are not always symmetric to the left and right of the wind. Most of the cases show the eventual dominance of one side lobe. The asymmetry of the wave direction relative to the wind suggests that the surface wind stress vector may not always be parallel to the mean wind direction.
TL;DR: In this article, a relatively simple scheme is described for increasing the power output of small wind-driven alternators at low wind speeds, along with practical details of the implementation of the scheme along with test results and economic justification.
TL;DR: In this article, the similarity requirements for wind tunnel model studies of buoyant and heavy gases diffusion near buildings are discussed and approximate modeling methods, which relax the requirement of gas density scaling in order to operate at higher wind tunnel speeds, are also examined.
Abstract: The similarity requirements for wind tunnel model studies of buoyant and heavy gases diffusion near buildings are presented and discussed. Exact similarity of buoyant and heavy gases behavior requires explicit scaling of the released gas density and equality of the model and full scale Froude numbers. The latter requirement leads to very low wind speeds for wind tunnel tests when small scale models are used. This condition makes the physical modeling of flow and diffusion fields complicated and thus reliable wind tunnel operation becomes very difficult. Approximate modelling methods, which relax the requirement of gas density scaling in order to operate at higher wind tunnel speeds, are also examined.
TL;DR: In this article, a portable wind tunnel is used to assess the erodibility of prepared surfaces of residue waste, including wind profiles, collections of saltation and suspension material as well as particle sizing by elutriation.
Abstract: A portable wind tunnel is used to assess the erodibility of prepared surfaces of residue waste. The data are extensive and include wind profiles, collections of saltation and suspension material as well as particle sizing by elutriation. Still, the data show no definitive information on the effects of treatment. The experiments, however, can be characterized by the structure of the measured wind profile; a special plot of the friction velocity and dynamic roughness suggests that only one of the six plots is "all erodible". Surfaces may have a fixed roughness, eroding roughness or exhibit an anomalous "constant friction velocity". There are difficulties in the use of the gradient of the log profile and the intercept as measures of the shear stress and the scale.
TL;DR: In this article, the second moment reliability (SMR) approach is combined with wind pressure data from wind tunnel experiments and with the simplified Cook-Mayne approach to calculate local peak wind pressures on buildings with a consistent safety level.
TL;DR: In this paper, the flutter problem associated with the blades of a class of vertical-axis wind turbines called Darrieus is studied in detail, and a three-dimensional linear perturbation pattern is superimposed to determine the dynamic aeroelastic stability of the blade in the presence of free wind speed by means of the Floquet-Lyapunov theory for periodic systems.
Abstract: The flutter problem associated with the blades of a class of vertical-axis wind turbines called Darrieus is studied in detail. The spinning blade is supposed to be initially curved in a particular shape characterized by a state of pure tension at the blade cross section. From this equilibrium position a three-dimensional linear perturbation pattern is superimposed to determine the dynamic aeroelastic stability of the blade in the presence of free wind speed by means of the Floquet-Lyapunov theory for periodic systems.