Wind Flow Model Research Articles

Effects of Wind Flow on Self-Heating Characteristics of Coal Stockpiles

The oxidation process occurring in stockpiles of reactive materials, such as coal, induces a natural convection flow field within the pile. Due to porosity of the stockpile, this flow field is affected by the wind flow in the surrounding air. The wind sets up pressure variation around the pile and, therefore, builds up a forced gas advection field within the pile. The present work studies the effects of such a wind-driven flow field on self-heating characteristics of typical coal stockpiles. For this purpose, the calculations of the heat and mass transfer processes within a realistically shaped coal stockpile have been coupled to a wind flow model in which the wind is assumed to blow in a fixed direction relative to the pile. The calculations have been performed using the computational fluid dynamics packaged FLUENT. The calculations indicate that the wind flow significantly alters the dynamics of the flow field inside the pile and thereby affects the self-heating process. In particular, the external 'fixed direction' wind instigates non-symmetrical heating/concentration profiles within the pile.

Source regions of the slow solar wind in coronal streamers

Recent SOHO/UVCS observations of the O5+ ion line emission at 1032Å in coronal streamers indicate that the emission is stronger by an order of magnitude at the edges (legs) of streamers than in the central core of streamers. In contrast, the brightness of the Ly‐α emission peaks in the core of streamers. I have developed the first 2.5D, three‐fluid numerical MHD model of the slow solar wind flow in a coronal streamer. Using the model I find that the enhancement of the oxygen line emission occurs due to the enhanced abundances of O5+ ions in the legs of streamer caused by the Coulomb friction with the outflowing protons. Thus, the enhanced O5+ emission traces the source regions of the slow solar wind in coronal streamers. The identification of these regions helps to understand the origins and the composition of the slow solar wind.

Simulation of above treeline snowdrift formation using a numerical snow-transport model

A physically based, numerical snow-transport model (SnowTran-3D) is used to successfully simulate the above treeline snowdrift evolution around Montgomery Pass in the Northern Colorado Rocky Mountains. The model accounts for key snow-transport components including: saltation, suspension, deposition, erosion, and sublimation. The snow-transport model requires static inputs of vegetation type and topography, and temporally evolving spatial distributions of air temperature, humidity, precipitation, wind speed, and wind direction. A simple wind-flow model, driven by data from a ridge-top meteorological station, is used to simulate the flow field over the topographic drift catchment. The snow-transport model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation, saltation and suspension transport, and sublimation. The model is forced using SNOTEL and meteorological data from the 1997–1998 winter, and the resulting model outputs are compared with observed snowdrift distributions.

Hotchkiss River Mixedwood Timber Harvesting Study

The Hotchkiss River Mixedwood Timber Harvesting Study is a cooperative project involving Canadian Forest Service, Daishowa-Marubeni International Ltd., Manning Diversified Forest Products Ltd., the Forest Engineering Research Institute of Canada and Alberta Land and Forest Service aimed at developing new approaches to natural regeneration and harvesting systems for western Canada's boreal mixedwood forests, at a site near the Hotchkiss River in northwestern Alberta. The study used conventional harvesting equipment to test eleven harvesting and silvicultural systems designed to protect and minimize wind damage to immature white spruce residuals and encourage vigorous hardwood regeneration following harvest of the aspen overstory. Research areas include wind damage, wind firmness and growth response of the immature white spruce, effects of harvesting disturbance and timing on soil properties, conifer and hardwood regeneration after harvest, efficiency of equipment and harvesting costs, modelling of wind flow and long-term growth and yield. Already in its sixth year, the project has a planned 20year series of harvests and surveys. Technology transfer is an important component of this study for delivery and promotion of research results on behalf of the proponents and all related research collaborators. Products include demonstration maps and field guides, self-guided tour trails with interpretive signage and field tours (including active operations) as required. Hotchkiss River has also been designated a Forest Ecosystem Research Network (FERN) site. Key words: silviculture systems, white spruce, Picea glauca, aspen, Populus tremuloides, understory protection, harvesting, Alberta, boreal mixedwoods, technology transfer

The assessment of volcanic gas hazard by means of numerical models: An example from Vulcano Island (Sicily)

Volcanic activity can inject large quantities of gases and aerosols into the atmosphere both during and between eruptions, creating a health risk for the local population. The paper describes how the volcanic gas concentration in the air can be computed by a flow model simulating the wind field over a digital terrain model of the volcano coupled with a Lagrangian particle model that uses the known (measured) gas emission rates to simulate gas dispersion. The coupling provides hazard maps for a number of meteorological conditions, introduced as boundary and initial conditions to the wind flow model, and permits the estimation of the risk both for actual and increased emission rates. An application for Vulcano Island (Sicily, Italy) is presented. According to the results, the risk at Vulcano is mainly related to: i) SO2 from the fumaroles of La Fossa cone; ii) the diffuse soil emission of CO2 from the cone flanks and from the plane around the cone. Although the conclusion is that there is no major hazard for passive degassing at present flux rates, the situation could change in the future. If gaseous emission rates would increase by one order of magnitude above the peak values of a few years ago, the gas concentrations could reach dangerous thresholds for the people of Vulcano Porto village, 1 km NW to the cone.

Wind and remnant tree sway in forest cutblocks. III. a windflow model to diagnose spatial variation

Root-mean-square tree sway angle ( σ θ ) can be related to the r.m.s. value ( σ u| u| ) of the wind `force' u| u|, specified nearby. Therefore the spatial pattern of wind statistics over the landscape, if known, arguably maps the relative risk of windthrow – suggesting a wind model can provide the basis to interpret spatial patterns of windthrow, and guide strategies with respect to that concern. To test this idea, we adopt a simple flow model able to describe both the mean wind ( U) and kinetic energy of the turbulence ( k), viz. Reynolds' equations closed using eddy-viscosity K∝ λk 1/2, where λ is the turbulence lengthscale. We first compare this model with others' measurements of wind near forest edges, then simulate our own observations, which spanned arrays of cutblocks and intervening forest blocks in the Boreal forest (periodic spacing 1.7 h or 6.1 h, where h is mean tree height). We show that the model predicts well the spatial variation of the mean windspeed and turbulent kinetic energy, these being the wind statistics having greatest impact upon tree sway. Model-implied spatial patterns of r.m.s. wind force ( σ u| u| ) agree closely with those observed, and in conjunction with a tree-motion model, imply tree sway ( σ θ ).

The effect of the tilt of the HCS on the solar wind speed in the outer heliosphere

The flow of solar wind from the Sun is bimodal. High speed, low density plasma comes from high magnetic latitude regions and low speed, high density flow from near the heliospheric current sheet (HCS). We investigate whether this bimodal flow combined with the HCS tilt controls the solar wind velocities in the outer heliosphere near solar minimum when the Sun's magnetic field is roughly dipolar. We present a simple model of radial solar wind flow with regions of fast and slow flow and a HCS tilt provided by the Wilcox Solar Observatory. This is the first time a model has been used to make quantitative predictions of the solar wind speed in the outer heliosphere based on solar observations. A reasonable fit to the main features of the observed velocity profile at Voyager 2 is obtained if the full‐width of the slow speed region is 30°. We conclude that the main physical parameter determining the solar wind speed observed by Voyager 2 near solar minimum in the outer heliosphere is the tilt of the HCS.

Urban wind flows: wind tunnel and numerical simulations—a preliminary comparison

Previous studies have indicated that wind flow models based on the k−ε formulation are able to simulate the broad features of flows as observed in field programs and wind tunnel studies. k−ε models are increasingly being used to investigate the dispersion of pollutants and the transfer of heat within and out of urban canyons. In these situations realistic modelling requires greater fidelity on the part of the wind flow specification in that some confidence needs to be placed on the actual magnitude of the wind speeds and turbulent viscosities used in the dispersive components of the models. To this end a preliminary comparison of wind tunnel and numerical modelling was undertaken. It has demonstrated general agreement between the two types of modelling but has also indicated some differences. These are in the variation of concentration with height at the windward wall and in the concentration gradients away from the canyon boundaries.

MHD model of magnetosheath flow: comparison with AMPTE/IRM observations on 24 October, 1985

Abstract. We compare numerical results obtained from a steady-state MHD model of solar wind flow past the terrestrial magnetosphere with documented observations made by the AMPTE/IRM spacecraft on 24 October, 1985, during an inbound crossing of the magnetosheath. Observations indicate that steady conditions prevailed during this about 4 hour-long crossing. The magnetic shear at spacecraft entry into the magnetosphere was 15°. A steady density decrease and a concomitant magnetic field pile-up were observed during the 40 min interval just preceding the magnetopause crossing. In this plasma depletion layer (1) the plasma beta dropped to values below unity; (2) the flow speed tangential to the magnetopause was enhanced; and (3) the local magnetic field and velocity vectors became increasingly more orthogonal to each other as the magnetopause was approached (Phan et al., 1994). We model parameter variations along a spacecraft orbit approximating that of AMPTE/IRM, which was at slightly southern GSE latitudes and about 1.5 h post-noon Local Time. We model the magnetopause as a tangential discontinuity, as suggested by the observations, and take as input solar wind parameters those measured by AMPTE/IRM just prior to its bow shock crossing. We find that computed field and plasma profiles across the magnetosheath and plasma depletion layer match all observations closely. Theoretical predictions on stagnation line flow near this low-shear magnetopause are confirmed by the experimental findings. Our theory does not give, and the data on this pass do not show, any localized density enhancements in the inner magnetosheath region just outside the plasma depletion layer.Key words. Steady-state magnetosheath · Plasma depletion layer · Stagnation line flow

A mathematical model of wind flow, vehicle wake, and pollutant concentration in urban road microenvironments. Part II: model results

Theoretical formulations of the proposed model for prediction of pollutant dispersion in microenvironments was previously introduced in part I of this paper ( Karim and Matsui, 1998). This paper discusses the new model findings and presents model evaluation results. This paper first explains the current problems that the road environment plays in employing field data for wind and temperature collected along a road north of Nagoya, Japan. A complete simulation is done on wind components in street-canyon and wind distribution, including vehicle wake effect, and is evaluated with experimental results. Next, the paper provides the atmospheric stability and dispersion parameters and then predicts pollutant buildups estimated using several techniques: a numerical model, modified Gaussian dispersion model, and a stochastic model. The stochastic model is specially developed to predict pollutant buildups in microenvironments. Model sensitivity analysis is done, varying the physical parameters; vehicle dimensions to wind speed in microenvironments, vehicle dimensions to dispersion parameter, and wind speed to pollutant concentrations. The modeled results are then compared to experimental data collected in micro-environmental locations in a road of Nagoya City, Japan. Finally, the implications of the research findings are discussed.

A mathematical model of wind flow, vehicle wake, and pollutant concentration in urban road microenvironments. part I: model description

A computer model consisting of wind distribution, emission dispersion, modified Gaussian equation, and stochastic prediction models has been developed to identify street canyon and vehicle wake effects on the transport air pollution from urban road microenvironments. In this work, wind flow and their components in the street canyon are simulated and analyzed considering a two-dimensional street canyon flow pattern. Wind parameters obtained from the analysis are then applied to estimate wind speed and vehicle wake turbulence in microenvironments. Turbulent parameters are integrated in Gaussian equations to estimate pollutant concentrations. A stochastic method has also been considered for predicting maximum concentration in road microenvironments. The model takes traffic data, emission rates, meteorological data, vehicle dimensions, and canyon geometry, and outputs pollutant concentration in microenvironments in an uninterrupted traffic flow section in numerical and graphical form. The model has the predictive capability for CO and NO x.

MHD model of magnetosheath flow: comparison with AMPTE/IRM observations on 24 October, 1985

We compare numerical results obtained from a steady-state MHD model of solar wind flow past the terrestrial magnetosphere with documented observations made by the AMPTE/IRM spacecraft on 24 October, 1985, during an inbound crossing of the magnetosheath. Observations indicate that steady conditions prevailed during this about 4 hour-long crossing. The magnetic shear at spacecraft entry into the magnetosphere was 15°. A steady density decrease and a concomitant magnetic field pile-up were observed during the 40 min interval just preceding the magnetopause crossing. In this plasma depletion layer (1) the plasma beta dropped to values below unity; (2) the flow speed tangential to the magnetopause was enhanced; and (3) the local magnetic field and velocity vectors became increasingly more orthogonal to each other as the magnetopause was approached (Phan et al., 1994). We model parameter variations along a spacecraft orbit approximating that of AMPTE/IRM, which was at slightly southern GSE latitudes and about 1.5 h post-noon Local Time. We model the magnetopause as a tangential discontinuity, as suggested by the observations, and take as input solar wind parameters those measured by AMPTE/IRM just prior to its bow shock crossing. We find that computed field and plasma profiles across the magnetosheath and plasma depletion layer match all observations closely. Theoretical predictions on stagnation line flow near this low-shear magnetopause are confirmed by the experimental findings. Our theory does not give, and the data on this pass do not show, any localized density enhancements in the inner magnetosheath region just outside the plasma depletion layer.Key words. Steady-state magnetosheath · Plasma depletion layer · Stagnation line flow

A comparison of predictions of an MHD model solar wind flow past the magnetopause with AMPTE/IRM observations on 24 October, 1985

We compare numerical results of a steady-state MHD model for solar wind flow past the terrestrial magnetosphere with documented observations made by the AMPTE/IRM spacecraft on 24 October, 1985, during an inbound crossing of the magnetosheath. Observations indicate that steady conditions prevail during this ∼ 4 hour-long crossing. The magnetic shear at entry into the magnetosphere was 15 deg. A steady density decrease and a concomitant magnetic field pile-up were observed during the ∼ 40 min interval just preceding the magnetopause crossing. In this so-called plasma depletion layer (i) the plasma beta fell generally below unity; (ii) the flow speed tangential to the magnetopause was enhanced; and (iii) the local magnetic field and velocity vectors became increasingly more orthogonal to each other as the magnetopause was approached (Phan et al., 1994). We model parameter variations along a orbit similar to the AMPTE/IRM trajectory, which was at slightly southerly latitudes and ∼ 1.5 hours post-noon local time (GSE). In our model we consider the magnetopause to be a tangential discontinuity, as suggested by the observations, and take as input solar wind parameters those measured by AMPTE/IRM just prior to its bow shock crossing. We find that theoretical predictions match all observations closely.

High resolution urban morphology data for urban wind flow modeling

The application of urban forestry methods and technologies to a number of practical problems can be further enhanced by the use and incorporation of localized, high resolution wind and temperature fields into their analysis methods. The numerical simulation of these micrometeorological fields will represent the interactions and influences of urban structures, vegetation elements, and variable terrain as an integral part of the dynamics of an urban domain. Detailed information of the natural and man-made components that make up the urban area is needed to more realistically model meteorological fields in urban domains. Simulating high resolution wind and temperatures over and through an urban domain utilizing detailed morphology data can also define and quantify local areas where urban forestry applications can contribute to better solutions. Applications such as the benefits of planting trees for shade purposes can be considered, planned, and evaluated for their impact on conserving energy and cooling costs as well as the possible reconfiguration or removal of trees and other barriers for improved airflow ventilation and similar processes. To generate these fields, a wind model must be provided, as a minimum, the location, type, height, structural silhouette, and surface roughness of these components, in order to account for the presence and effects of these land morphology features upon the ambient airflow. The morphology of Sacramento, CA has been characterized and quantified in considerable detail primarily for wind flow modeling, simulation, and analyses, but can also be used for improved meteorological analyses, urban forestry, urban planning, and other urban related activities. Morphology methods previously developed by Ellefsen are applied to the Sacramento scenario with a high resolution grid of 100 m × 100 m. The Urban Morphology Scheme defines Urban Terrain Zones (UTZ) according to how buildings and other urban elements are structured and placed with respect to each other. The urban elements within the 100 m × 100 m cells (one hectare) are further described and digitized as building height, building footprint (in percent), reflectivity of its roof, pitched roof or flat, building's long axis orientation, footprint of impervious surface and its reflectivity, footprint of canopy elements, footprint of woodlots, footprint of grass area, and footprint of water surface. A variety of maps, satellite images, low level aerial photographs, and street level photographs are the raw data used to quantify these urban properties. The final digitized morphology database resides in a spreadsheet ready for use on ordinary personal computers.

Influence of Building Areal Density and Roof Shape on the Wind Characteristics Above a Town

Flow characteristics in the lower part of theatmospheric boundary layer developing immediatelyabove building roofs have been studied by physicalmodelling under neutral stratification conditions. Thevertical profiles of velocity, turbulence intensityand Reynolds stress were measured in detail above amodel urban fetch consisting of parallel streetcanyons. Two different street densities and roofshapes were tested. It is found that the influence ofthe buildings on the oncoming wind remains confined towithin three overall building heights above ground.Furthermore, the effect on the wind at roof levelfrom the areal building density is relatively weak, butstrong from the roof shape. Thus, altering roof shapecan have a much more beneficial impact on urban airquality than increasing the spacing betweenbuildings. Moreover, these findings yield a novelmethodology for reliable prediction of urban airquality, by combining numerical mesoscale wind flowmodels with physical street canyon pollutiondispersion models.

Implementation of newly developed algorithms in the simulation of atmospheric turbulent transports

The paper presents a three-dimensional transient numerical model for atmospheric wind flow and industry and/or traffic pollutant dispersion over terrains having a complex topography. The model is based on a finite-volume integration of the equations governing mass, momentum, heat and pollutant transport within the earth's atmospheric boundary layer, using a collocated grid arrangement. The instability provoked by such a formulation was avoided by using a special pressure-velocity coupling. Local refinement of the grid was achieved via a domain decomposition method. The technique of ‘porosity’ used to approximate curved three-dimensional boundaries is incorporated in the procedure, thus avoiding the less accurate and more common approximation by a broken surface with segments parallel to the coordinate lines. The method was validated by simulating the flow over the Attica peninsula for which measurements of wind speed and pollutant emissions are available.

A Method for Estimating the Hydrologic Input from Fog in Mountainous Terrain

A methodology for obtaining estimates of the spatial distribution of fog water volume collected by a tree canopy in complex terrain is described. The method includes assumptions about the shape and spacing of the trees, their fog water collection efficiency, the fog frequency, and the vertical rate of change of the liquid water content (LWC) within ground-based clouds. The method was applied to a 655-km2 area surrounding Roundtop Mountain, Quebec, Canada, during a carefully selected sample period from the summer of 1993. Field measurements of fog water volume were used to estimate the cloud-base height and the rate of change of the LWC with height. Topographic data were used both as a forcing function in the wind flow model and as a means of defining the three-dimensional geometry for deposition calculations. The goal is the development of a simple model that can be used over large geographic areas. Results of the application are presented over various domains ranging from 2 to 164 Km2 in size. Spatial variations in the wind velocity field just above the canopy were found to be related to the main terrain features (summits, ridges, and valleys). The fog water deposition rate was specified as a linear function both of terrain height above cloud base and of wind speed. Near the summit of Roundtop Mountain, variations in terrain height were more pronounced than those of treetop wind speeds. Spatial patterns of fog water deposition, therefore, strongly reflected the pattern of topographic contours, with some modifications being apparent due to spatial variations in wind speed. Calculated deposition values ranged up to 0.69 mm h−1 and were found to be typical of measured values in the literature.

Study of wind flow and pollutant dispersion by newly developed precision-improving methods

The paper presents a three-dimensional transient numerical model for atmospheric wind flow and industry and/or traffic pollutant dispersion over terrains having a complex topography. The model is based on a finite-volume integration of the equations governing mass, momentum, heat and pollutant transport within the earth's atmospheric boundary layer, using a collocated grid arrangement. The instability provoked by such a formulation was avoided by using a special pressure-velocity coupling. Local refinement of the grid was achieved via a domain decomposition method. The technique of “porosity” used to approximate curved three-dimensional boundaries is incorporated in the procedure thus avoiding the less accurate and more common approximation by a broken surface with segments parallel to the coordinate lines. The method was validated by simulating the flow over the Attica peninsula for which measurements of wind speed and pollutant emissions are available.

Surface winds during an intense outbreak of arctic air in Southwestern British Columbia

Abstract An outbreak of arctic air which occurred from 30 January to 2 February 1989, plunging southwestern British Columbia (as well as most of western North America) into extreme cold, is examined and put in context by reference to similar events reported in the literature. Emphasis is placed on the resulting wind fields in Howe Sound and the Lower Fraser Valley. The wind speed in these topographically confined channels during arctic outbreaks is found to be related to the down‐channel pressure gradient. Three simple steady‐state models of wind speed are suggested whose results are compared to observed winds. It is found that the Friction model, representing a balance between friction, acceleration and horizontal pressure gradient, compares best with observations in the Lower Fraser Valley. Hydmod, a hydraulic model of wind flow performs reasonably well, with previous work indicating it produces more realistic along channel flow variability in Howe Sound.

An empirical model of the solar wind flow around Mars

An empirical model that describes the proton velocity around Mars has been developed. The analytical axially symmetric model is based on Automatic Space Plasma Experiment with a Rotating Analyzer three‐dimensional (3‐D) proton velocity observations on the Phobos 2 spacecraft near Mars in early 1989. The model includes a bow shock, a magnetopause, and an impenetrable obstacle a few hundred kilometers above the surface of Mars. The flow model can be used to model both an open and a closed magnetosphere. The model velocity values are found to describe rather well the 3‐D proton velocity observations in the Martian magnetosheath and magnetosphere both on the dayside and on the nightside. Characteristics of the velocity field are studied on the basis of an ideal MHD model, assuming that the magnetic field is frozen into the proton flow and that there are no proton sources or sinks. Under these assumptions the velocity field can be used to calculate the proton density and the magnetic field. When the proton density and the magnetic field are compared with the observations, quite good qualitative agreement between the model and the data is found. Our model shows that a relative simple flow model can predict several observed plasma and field features near Mars.