Wind Flow Characteristics Research Articles

Fundamental Study for Estimation of Wind Energy Resources (2nd Report, Turbulence Characteristics of Wind Flow over Complex Terrain)

While the use of WTGS expands over the world, complex terrain has become important candidate as the site proposed for a WTGS. In the complex terrain, contribution of local topographic effects to the wind energy resources is quite large and intensity of wind turbulence, which brings about complicated aerodynamics loads on the wind turbine, is much larger than that over the flat terrain. The purpose of the present work is to investigate the turbulence characteristics of the wind flow over complex terrain such as mountainous region. The wind measurements were carried out at Shitara-cho in Aichi during the period from November 19th to December 10th in 2003, using three meteorological masts and ten anemometers. The influence of the slope on the turbulence has been evaluated by examining the power spectrum of the wind fluctuation.

Numerical method study of how buildings affect the flow characteristics of an urban canopy

The study of how buildings affect wind flow is an important part of the research being conducted on urban climate and urban air quality. NJU-UCFM, a standard <TEX>$k-{\varepsilon}$</TEX> turbulence closure model, is presented and is used to simulate how the following affect wind flow characteristics: (1) an isolated building, (2) urban canyons, (3) an irregular shaped building cluster, and (4) a real urban neighborhood. The numerical results are compared with previous researchers' results and with wind tunnel experiment results. It is demonstrated that the geometries and the distribution of urban buildings affect airflow greatly, and some examples of this include a changing of the vortices behind buildings and a "channeling effect". Although the mean air flows are well simulated by the standard <TEX>$k-{\varepsilon}$</TEX> models, it is important to pay attention to certain discrepancies when results from the standard <TEX>$k-{\varepsilon}$</TEX> models are used in design or policy decisions: The standard <TEX>$k-{\varepsilon}$</TEX> model may overestimate the turbulence energy near the frontal side of buildings, may underestimate the range of high turbulence energy in urban areas, and may omit some important information (such as the reverse air flows above the building roofs). In ideal inflow conditions, the effects of the heights of buildings may be underestimated, when compared with field observations.

Some aspects of air pollution in Buenos Aires city

This paper presents three aspects of air pollution in the city of Buenos Aires (Argentina). First, we describe the main features of air pollution climatology in the city: the characteristics of wind flow, atmospheric stability and mixing heights. Then, we present the results of the application of DAUMOD and ISCST3 atmospheric dispersion models to calculate spatial and temporal distributions of carbon monoxide and nitrogen oxides background concentrations. Finally, we present the main features of carbon monoxide concentrations observed in a narrow street canyon located downtown.

Hurricane Bonnie wind flow characteristics as determined from WEMITE

The Wind Engineering Mobile Instrumented Tower Experiment (WEMITE) successfully gathered high-resolution wind speed data from within Hurricane Bonnie as it made landfall near Wilmington, North Carolina, on 27 August 1998, at 04:00 UTC. This data is used to inspect the variations in turbulent characteristics of the wind during the passage of the storm. Specifically, turbulence intensities, integral scales, gust factors and power spectral densities are evaluated. Results indicate there is general agreement with the Krayer/Marshall gust factor curve, additional low-frequency energy in the longitudinal power spectral density compared to various model spectra, and a wide variation in integral scales even within the same roughness regime.

A High-Resolution Numerical Simulation of the Wind Flow in the Ross Island Region, Antarctica

Abstract A detailed description of the characteristics of the three-dimensional wind flow for the Ross Island region of Antarctica is presented. This region of Antarctica has complex topographic features, and the wind flow is dependent on the topography and the local meteorological conditions. High-resolution nonhydrostatic numerical simulations are conducted over a high-resolution domain in the Ross Island region. Two simulations are performed corresponding to the two dominant wind flow patterns in the Ross Island region. The first simulation is a light wind case with a stable lower atmosphere and the second is a high wind speed event. Froude number calculations, along with a study of the equation of motion, are included for a more complete understanding of the dynamics of the wind flow. The results of the simulations show a favorable correlation to past research results and observations, and provide a more complete understanding of the three-dimensional wind flow in the region. In addition to a more tho...

Effective aerodynamic roughness estimated from airborne laser altimeter measurements of surface features

Aerodynamic roughness length (z 0) and displacement height (d 0) are important surface parameters for estimating surface fluxes in numerical models. These parameters are generally determined from wind flow characteristics using logarithmic wind profiles measured at a meteorological tower or by balloon release. It would be an advantage to use measurements of land surface characteristics instead of wind flow characteristics to estimate the z 0 and d 0 for large areas. Important land surface characteristics are the size and distribution of roughness elements (obstacles). This research evaluates the use of high resolution laser altimeter data to obtain these land surface characteristics. Data were collected at the US Department of Agriculture, Agricultural Research Service (USDA‐ARS), Jornada Experimental Range in southern New Mexico, USA over a coppice dune dominated area. These dunes are covered by honey mesquite (Prosopis glandulosa Torr.) with flat and mostly bare interdunal areas. For this analysis, three 450 m laser transects with a 2 cm measurement interval were used. The distribution and size of dunes were calculated from these laser transects and used to compute z 0. Analysis gave an average z 0 = 4.3 cm and d 0 = 70 cm for the three laser transects, which compares to z 0 = 7 ± 4 cm and d 0 = 98 ± 48 cm calculated from wind profile data measured at a 10 m tower near the laser transects. These results show that the estimation of z 0 and d 0 for a complex terrain is possible using simple land surface features computed from high resolution laser altimeter data.

Wind flow characteristics and Reynolds stress structure around the two-dimensional embankment of trapezoidal shape with different slope gradients

In this study, wind tunnel measurements for a turbulent boundary layer flow over two-dimensional embankments of trapezoidal shape with different slope gradients were carried out to investigate the wind flow characteristics and the Reynolds stress structure. The quadrant analysis technique was employed to analyze stress component contribution to the Reynolds stress. Measurement on the Reynolds stress structure reveals that both the sweep and ejection events are the major contributors to the Reynolds stress for flow around the embankment with different slope gradients. The contributions to the Reynolds stress made by sweep event are slightly larger than that of ejection event at locations close to the top surface of embankment ( Z/ H=1.2) with mild slope (slope gradient 4:1). But at higher distance from the top surface of the embankment ( Z/ H=2), the ejection event contributes more to the Reynolds stress than the sweep event for all cases (slope gradients, 1:1, 2:1, 4:1).

Wind flow characteristics and their loading effects on flat roofs of low-rise buildings

Wind flow and pressure on the roof of the Texas Tech Experimental Building are studied alongrnwith the incident wind in an effort to understand the wind-structure interaction and the mechanisms of roofrnpressure generation. Two distinct flow phenomena, cornering vortices and separation bubble, are investigated. Itrnis found for the cornering vortices that the incident wind angle that favors formation of strong vortices isrnbounded in a range of approximately 50 degrees symmetrical about the roof-corner bisector. Peak pressures onrnthe roof corner are produced by wind gusts approaching at wind angles conducive to strong vortex formation. Arnsimple analytical model is established to predict fluctuating pressure coefficients on the leading roof corner fromrnthe knowledge of the mean pressure coefficients and the incident wind. For the separation bubble situation, thernmean structure of the separation bubble is established. The role of incident wind turbulence in pressure-generationrnmechanisms for the two flow phenomena is better understood.

Preliminary background ozone concentrations in the mountain and coastal areas of Bulgaria

Urban and non-urban rural ozone (O 3) concentrations are high in Bulgaria and often exceed the European AOT40 ecosystem as well as the AOT60 human health standards. This paper presents preliminary estimates to establish background, non-urban O 3 concentrations for the southern region of Bulgaria. Ozone concentrations from three distinctly different sites are presented: a mountain site influenced by mountain–valley wind flow; a coastal site influenced by sea-breeze wind flow; and a 1700-m mountain peak site without ‘local’ wind flow characteristics. The latter offers the best estimate of 46–50 ppb for a background O 3 level. The highest non-urban hourly value, 118 ppb, was measured at the mountain-valley site.

Flow simulation by wind tunnel with computer-controlled multiple fans

This paper presents the simulation of turbulent flow by controlling multiple fans in a two-dimensional wind tunnel. The main purposes of this study are to generate a large turbulence scale and simulate a turbulent flow fitted to specified power spectrum and co-coherence in a low frequency range, both of which are not easily accomplished only by the means of roughness blocks, spires and grids. It was relatively easy to obtain a large turbulence scale by controlling multiple fans numerically. According to the proposed procedure, turbulent characteristics of wind flow were successfully simulated to satisfy a specified condition for the target power spectrum and co-coherence.

Effects of a high rise building on wind flow and beach characteristics at Atlantic City, NJ, USA

This study assesses the effects of a high rise building on the beach and dune at an intensively developed shoreline through field investigation of geomorphological and sedimentological characteristics and wind tunnel investigation of wind speed and direction. Results indicate that wind speed is increased close to the building, where wind is often deflected to a more onshore direction. Obliquely offshore northwesterly winds are the most dramatically altered and cause onshore flows (with pronounced upward flows) in the landward portion of the beach near the building. Onshore deflections in wind direction cause besanding of the boardwalk and create highly localized scour and deposition zones. A dune on the backbeach breaks up zones of sediment transport and scour and diminishes the likelihood that scour areas will cause increased hazard to landward buildings as a result of flooding. Generic large-scale studies are required to develop criteria for communities to use to specify optimum dimensions, locations and shapes of landforms that are modified or created by high rise structures.

An experimental study of the near-wake structure of a wind turbine operating over complex terrain

Wind parks are often cited in complex terrain whose features determine the wind flow over the area. Results from a field experiment, comprising in-situ and remote sensing techniques (high-resolution acoustic sounders), concerning the upwind area and the near-wake region behind a single medium-sized wind turbine are presented. The experimental site is the Samos Island Wind Park installed on top of a 390 m-high saddle. Because of the topography, wind speed acceleration and channeling effects are expected; thus, the commonly used logarithmic profile is not valid, and the choice of a representative surface roughness length z o is difficult. Interesting features of the profiles of the standard deviation of the ambient wind speed are also presented. The obtained results reveal a nonlinear interaction of the near wake with the turbine-tower shadowing, while cross-wind wake profiles indicate a potential core structure. The effect of ambient turbulence is apparent, especially at lower wind speeds, even at a distance of one rotor diameter (1 D) behind the turbine. The wake centerline at distances greater than 1 D is often observed at heights greater than the hub-height and attributed to the wind flow characteristics over the Wind Park. Finally, evidence of rotational motion inside the wake is identified.

Wind flows and forces in a model spruce forest

Wind tunnel tests have been conducted on a 1:75 scale model of a Sitka spruce forest in a correctly scaled turbulent boundary-layer flow. 12000 tree models were manufactured with mass, flexibility and aerodynamic drag characteristics chosen to give dynamical similarity with typical 15 m trees in a 30ms−1 gale. To measure the dynamic response of a sample tree, set within this model forest, a miniature, fast response strain-gauge balance was designed and built. Linked to a computer for on-line data sampling, this balance provided measurements of the fluctuating along-wind and acrosswind components of the overturning moment at ground level, leading to values of mean and extreme moments and the frequency spectrum of the sway motion. Associated measurements of local wind flow characteristics were made with hot-wire anemometers and a laser anemometer. The response of the tree has the characteristics of classical lightly damped vibration and there is evidence that resonant sway motion increases the extreme overturning moments significantly above the values produced by wind gust forces alone.

A computer program for determining wind pressures on 2-D structures

A computer program in Fortran for the numerical determination of wind loads on rigid civil-engineering structures is described. The program combines the direct boundary element method with the discrete vortex method in order to simulate the potential and viscous-flow characteristics of wind flow around structures under two-dimensional conditions. The flow chart and the subroutines of the program are given and explained in detail. The program employs linear boundary elements, and the simulation proceeds in a stepwise fashion in time. It is easy to use and can easily run on a personal computer. Numerical examples are presented to illustrate its use and demonstrate its simplicity, speed, and satisfactory accuracy. Thus this program becomes a valuable tool for the design engineer who does not have any further need to resort to expensive experiments or complicated numerical methods for the computation of wind loads on structures.

Wind Flow within Open‐Top Growth Chambers and the Gas Exchange Implications

AbstractField studies of atmospheric pollutant effects on plants commonly use an open‐top plant growth chamber (OTC). Altered wind flow characteristics within an OTC may create aerodynamic and boundary layer transport resistances (ra and rb) which differ from field values, complicating the extension of OTC results to field conditions. An OTC was placed in an enclosed area and the wind velocity was measured at five heights at nine locations using a triple hot‐film sensor. Measurements were made in an empty OTC and at two different surface roughnesses. The flow was turbulent, highly variable with location, and had well‐defined vertical and horizontal circulation patterns. Average wind speed in empty OTC ranged from 0.28 to 1.33 m s−1. Increased roughness decreased the mean flow speed but had little effect on the turbulence level or the circulation pattern. The flow within the OTC was used to estimate the ra and rb for O3 uptake in a hypothetical soybean [Glycine max (L.) Merr.] plant canopy, a representative low stomatal resistance species. Results showed that the variable flow in the OTC results in widely varying rb values within the OTC itself, depending on actual physical location within the chamber. In addition, the OTC ra and rb would differ from field values under typical meteorological conditions. For plants with low stomatal resistance this could create significant differences in gaseous uptake for individual plants within the OTC as well as for the average plant in the OTC vs. that in the field.

Effects of Trees on Wind Flow Variability and Turbulence

This paper describes the results of a field experiment at the Goodnoe Hills, Wash. site to examine the effects of trees on wind flow variability and turbulence. Although vegetation at the site consisted primarily of grass, scattered areas of trees that penetrated the site provided an excellent opportunity to evaluate the effects of surface roughness changes on the wind flow characteristics. Wind data collected at nine towers across the site revealed that surface roughness changes in the upwind fetch caused pronounced variations in the wind flow over site. At two towers that were frequently 200 m to 300 m downwind of a grove of 10-m to 18-m trees, 20–30 percent reductions in wind speed and a factor of two to three increase in turbulence were measured at a height of 32 m. A substantial increase in the magnitude of the wind gusts, as well as a considerable decrease in the mean wind speed, was observed when a tower was downwind of the trees. Implications for a wind turbine located downwind of the trees, with a hub height near 30 m, would be reduced power output, more variable power output, more start/stop cycles, and increased stress caused by the tree-induced turbulence. The effects of the trees on the wind flow characteristics were considerably reduced at heights of 60 m and at distances greater than 500 m.

Solar wind flow characteristics in sector boundaries between 0.3 and 1.0 a.u.

Interplanetary Magnetic Field (IMF) sector boundaries have been selected for studying the dynamical characteristics of the solar wind plasma (such as N ≈ V and T ≈ V) and to compare these characteristics with those in the rest of the solar wind. These boundaries were selected from the general solar wind only if they had been detected by both Helios 1 and 2, which have perihelion and aphelion at 0.3 and 1.0 a.u. respectively. The period used is February 1975–April 1978, and falls mainly into the minimum of solar activity (Solar cycle 21). A correlation of the plasma parameters, such as proton temperature ( T p ), velocity ( V) and density ( N), after normalization of T and N to 1 a.u. for radial variation, has shown that the dependence of T p on V is generally similar to that suggested by other authors, indicating no differentiation for the mechanism of energy transport at sector boundaries and inside sectors and no dominance of cooler plasma. The calculated coefficient of dependence of log N on log V is − 2.1, indicating an invariance of the momentum flux density ( NV 2) in the solar wind along the magnetic boundaries.

The Giotto three-dimensional positive ion analyser

The three-dimensional velocity distribution of positive ions in the neighbourhood of Comet Halley was measured by an instrument which included two complementary sensors. The fast ion sensor measured the energy/charge distribution from 10 eV/q to 20 keV/q once per revolution of the spacecraft. It obtained the characteristics of the solar wind flow near the comet. The implanted ion sensor measured the energy/charge distribution from 90 eV/q to 90 keV/q with discrimination into five mass groups in a period of 32 spacecraft revolutions. These observations provided the angular distribution of the cometary ions formed by the ionisation of gas molecules sublimed from the cometary nucleus. The relation between the raw count rates and the plasma parameters for the fast ion sensor is derived on the basis of a complete energy angle scan of the sensor in a calibration source. The accuracy of the analysis was tested by two techniques using data collected during the mission.

Turbulence characteristics of wind flow at ground level in built-up area

This paper describes the statistical characteristics of wind at ground level. Observations of wind flow at ground level were conducted over a period of 2 years around a high-rise apartment building in a built-up area in Tokyo. The mean and gust wind velocities at ground level are approximated on the basis of the Weibull distribution. The probability distributions of velocity-ratio, gust factor and turbulence intensity are obtained. The relationship between the exceedance probability and the number of storms per annum is derived. The characteristics of the long-term power spectrum of wind velocity are clarified.

Wind structure near a city centre

This paper describes some characteristics of wind flow over a city area. Extensive measurements were made of the wind structure at a particular site in order to provide a reference for a wind-tunnel simulation of flow over the area. Since full-scale measurements of wind flow over a very rough surface are rare, some results of wider interest are presented here.