Wind Velocity Profiles Research Articles

A New Aerodynamic Parametrization for Real Urban Surfaces

This study conducted large-eddy simulations (LES) of fully developed turbulent flow within and above explicitly resolved buildings in Tokyo and Nagoya, Japan. The more than 100 LES results, each covering a 1,000 $$\times $$ 1,000 m $$^{2}$$ area with 2-m resolution, provide a database of the horizontally-averaged turbulent statistics and surface drag corresponding to various urban morphologies. The vertical profiles of horizontally-averaged wind velocity mostly follow a logarithmic law even for districts with high-rise buildings, allowing estimates of aerodynamic parameters such as displacement height and roughness length using the von Karman constant $$=$$ 0.4. As an alternative derivation of the aerodynamic parameters, a regression of roughness length and variable Karman constant was also attempted, using a displacement height physically determined as the central height of drag action. Although both the regression methods worked, the former gives larger (smaller) values of displacement height (roughness length) by 20–25 % than the latter. The LES database clearly illustrates the essential difference in bulk flow properties between real urban surfaces and simplified arrays. The vertical profiles of horizontally-averaged momentum flux were influenced by the maximum building height and the standard deviation of building height, as well as conventional geometric parameters such as the average building height, frontal area index, and plane area index. On the basis of these investigations, a new aerodynamic parametrization of roughness length and displacement height in terms of the five geometric parameters described above was empirically proposed. The new parametrizations work well for both real urban morphologies and simplified model geometries.

Sensitivity of inflow boundary conditions on downstream wind and turbulence profiles through building obstacles using a CFD approach

This study investigates the sensitivity on inflow turbulence profiles for predicting the downstream wind velocity and turbulent kinetic energy profiles within the street arrays of urban environments. Computational fluid dynamics (CFD) techniques, and the realizable k–ε turbulence model are used to model the wind environment and the CFD model is validated by wind tunnel measurement. The results show that turbulence is internally generated by the upwind building obstacles. The shape and magnitude of downwind velocity and turbulence profiles are not greatly affected by different input turbulence profiles deviating from the baseline turbulence profile (within an envelope of ±50%) as the flow advances from the upstream to downstream regions within the building arrays. Various profiles of turbulent kinetic energy magnitude (within an envelope of ±50%) and with the same velocity profile are input as inlet boundary conditions to three different geometric settings, and also to an actual urban setting. Turbulent kinetic energy and wind speed ratios are obtained at different locations within the computational domain, and used as indicators for comparison and investigation. The study finds that even with a significant deviation (50%) in magnitude from the inflow turbulent kinetic energy profile, there is less than 15% difference in the wind speed and turbulent kinetic energy in the downwind region of the urban area.

Three-dimensional Computational Fluid Dynamic experiments over a complex dune topography

Wakes, S., 2013. Three-dimensional Computational Fluid Dynamic experiments over complex dune topography In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.)For modeling coastal dune systems the topography is often complex with complicating factors such as dune vegetation, sediment transport and the sand properties. Strategies such as simplifying the geometry and vegetation and no sediment transportation have been applied and provided insight into mechanisms of flow over the coastal dunes at Mason Bay, Stewart Island, New Zealand. Simulations building on the complexity of this modeling process are undertaken with a targeted mesh. Included was surface roughness signifying areas of vegetation but no Aeolian sediment transportation. Comparing preliminary results against the existing two and three-dimensional simulations and field data shows that although the strategy of splitting the domain in order to achieve three-dimensional results originally is workable simulating the whole domain is ideal. Grid adaption allows targeting of mesh in areas of most interest, mostly close to the dune surface and within the first 10m above the surface but needs to be done with care. There were distinct differences in wind velocity profile when comparing the results. It is also showed that the model choice has significance for turbulence parameters, with possible implications for sediment transportation, particularly at lower heights. In spite of the complex topography, the flow is strongly two-dimensional in some parts of the domain whilst strongly three dimensional in other areas. Therefore each level of simulation has a role in understanding the underlying flow mechanisms involved and what insight to the flow is required. Understanding gained from the previous work was invaluable in the extension to full three-dimensional simulations.

Wind Turbine Power Output Assessment in Built Environment

In future planning of the city, it is very important to consider the proper intelligent integration of renewable energy sources into the built environment for developing smart cities. Analysis of the wind velocity profile in the built environment is very important for finding out the energy content in the wind and also to analyze the performance of wind turbines in the built environment. In this study, building topologies of smart city are investigated for finding out the wind velocity profile and the wind turbine power output in the built environment. The wind velocity distribution across buildings is numerically simulated by using commercial CFD (Computational Fluid Dynamics) software CFD-ACE+. Wind turbine power output is estimated by using the power curve of real commercial wind turbine and wind velocity distribution simulated by CFD software. It has been observed that the wind is accelerated in the intervening space between the buildings irrespective of distance between the walls of adjacent buildings under the condition, which are investigated in this study. The wind is accelerated across buildings, and is reduced rapidly after blowing through buildings, and recovered gradually. Since the wind is accelerated in the intervening space between buildings and reduced in the area at the back of buildings, a wind turbine should be installed at the area at the back of the buildings and located on center between the buildings. In this work, it is observed that size dimensions and layout of the building are effective in realizing a smart city for utilizing renewable energy such as wind turbine in the built environment.

Bushfire-enhanced wind load on structures

The association of bushfires with wind has long been recognised, but the mechanism of this interaction has not received due attention. In the current study, a computational fluid dynamics approach was used to reveal the impact of fire-enhanced wind on low-rise building structures. This paper presents the results of a numerical study on bushfire, wind and structure interactions. The fire-enhanced wind was found to significantly distort the wind velocity profile and enhance turbulence properties, and alter the pressure coefficient distributions around a simple building structure represented by a 6 m cube. In particular, the simulated results revealed a significant increase in windward wall pressure coefficient due to the presence of a fire source upstream compared to that without fire. These findings are expected to have a significant impact on the development of improved design practice for the protection of buildings from fire-induced wind storms.

Numerical Simulation and Water Tank Experiment on Atmospheric Wind Field over a Mountain under Neutral Stability Condition

Analysis and forecast atmospheric wind velocity profiles have the important roles in research the dispersion of the pollutants and its effects to surrounding environment. A three-dimensional numerical modeling on atmospheric wind flow over a mountain under neutral condition was processed to attain the velocity contours of atmospheric wind field on complex terrains. Meteorological conditions and geographical conditions including four downwind velocities and two underlying surface roughness characteristics were considered in the present study. Water tank experiment and Particle Image Velocimetry (PIV) technology were used to gain typical wind flow field and validate the simulation results. The numerical results agree well with the experimental results, which prove the numerical methods used in this paper could be the alternative good tool to research and forecast atmospheric wind field.

Numerical Simulation of Flow over Mountainous Valley Terrain

With the increase of the span length of bridge, the wind field characteristics at bridge site play crucial role for the safety of bridge. The present paper discusses the results of a numerical simulation of the wind flow over mountainous area called Aizhai, located in Hunan province, where a super long span bridge with main span of 1176m will be constructed. The results indicate that it is inappropriate to describe the mean wind velocity profiles by power law using the same roughness exponent along the span wise direction in the mountainous valley terrain. The speed-up effect and the significant change in wind direction of the mean flow were observed, which provide the information necessary for determining the design wind speed such as for a long span bridge across the valley.

Infrasound propagation in the atmosphere in a presence of a fine-scale wind velocity structure

The results of modeling infrasound propagation in the atmosphere from 100-t surface explosion in Israel, and volcano eruptions in Ecuador and Kamchatka are presented. The signal as a function of a range from a source is calculated by parabolic equation method for the vertical profile of wind velocity and temperature obtained from the Ground-to-Space atmospheric model. The effects of fine-scale layered structure of wind velocity and temperature fields on infrasound propagation in the atmosphere have been also taken into account. The one-dimensional (vertical and horizontal) wavenumber spectra of the wind and temperature fluctuations associated with the fine-scale structure are close to the observed spectra in the middle and upper atmosphere. The calculated wave forms, amplitudes and durations of the stratospheric and thermospheric arrivals are compared with those observed in the experiments. It is shown that the scattering of infrasonic signals by anisotropic fluctuations leads to a significant increase in the duration of the stratospheric and thermospheric arrivals in comparison with the case when these fluctuations are absent. The acoustic field scattered from anisotropic nonhomogenerities may be responsible for the arrivals of the acoustic pulses observed in the acoustic shadow zones.

On the small-scale turbulence parameters in the atmosphere of venus and their use in the global circulation models

Vertical profiles of the turbulence parameters calculated for the planet-averaged conditions from the experimental data on the turbulent fluctuations of temperature and wind velocity are presented. Improved formulas accounting for the difference between the atmospheric gas on Venus and an ideal one, and the large difference in its thermal capacity at different altitudes, are used. The commonly used formula for the potential temperature describing the atmospheres of the Earth and Mars is inapplicable to the atmosphere of Venus. It has been shown that the opinion on the absence of turbulence in the atmosphere of Venus is based on overestimated values of the dynamic Richardson number obtained from the smoothed profiles of wind velocity, while its actual values are below unity due to the large wind velocity gradients produced by buoyancy waves. To improve the global circulation models of the atmosphere of Venus, it is necessary to use the currently available turbulence parameters calculated from experimental data.

NEW SOLAR WIND DIAGNOSTIC USING BOTH IN SITU AND SPECTROSCOPIC MEASUREMENTS

We develop a new diagnostic technique that utilizes, at the same time, two completely different types of observations—in situ determinations of solar wind charge states and high-resolution spectroscopy of the inner solar corona—in order to study the temperature, density, and velocity of the solar wind as a function of height in the inner corona below the plasma freeze-in point. This technique relies on the ability to calculate the evolution of the ion charge composition as the solar wind escapes the Sun given the wind temperature, density, and velocity profiles as a function of distance. The resulting charge state composition can be used to predict frozen-in charge states as well as spectral line intensities. The predicted spectra and ion charge compositions can be compared with observations carried out when spectrometers and in situ instruments are in quadrature configuration to quantitatively test a set of assumptions regarding density, temperature, and velocity profiles in the low corona. Such a comparison can be used in two ways. If the input profiles are predicted by a theoretical solar wind model, this technique allows the benchmarking of the model. Otherwise, an empirical determination of the velocity, temperature, and density profiles can be achieved below the plasma freeze-in point applying a trial-and-error procedure to initial, user-specified profiles. To demonstrate this methodology, we have applied this technique to a state-of-the-art coronal hole and equatorial streamer model.

Dome C Site Characterization in 2006 with Single-Star SCIDAR

ABSTRACTWe present observations made in 2006 with the single-star SCIDAR (SSS) at Dome C in Antarctica, allowing us to determine optical turbulence and velocity V(h) profiles from ice levels up to about 25 km above sea level (a.s.l.). SSS is a 16 inch telescope placed on an equatorial mount that continuously tracks the Canopus star. About 90,000 individual profiles are analyzed from March to September, where surface-layer contribution to seeing can be separated from the rest of the atmosphere. Medians of high angular resolution parameters relevant to astronomy are statistically studied, such as seeing (1.0′′), isoplanatic angle (6.9′′), and wavefront coherence time (3.4 ms). For a telescope placed above the turbulent surface layer, superb conditions are encountered (medians of seeing better than 0.3′′, isoplanatic angle better than 6.9′′, and coherence time larger than 10 ms). Astronomical conditions are twice as good at the beginning of the night, with ε0 ≈ 0.5′′, θ0 ≈ 11.5′′, and τ0 ≈ 15 ms. SSS wind-velocity profiles are consistent with National Oceanic and Atmospheric Administration analysis up to 17 km (a.s.l.), within a error bar. Coherence étendue (which is a combination of ε0, θ0, and τ0), well adapted to adaptive optics performances, is likely 4 times better at Dome C than at the already-known observatories such as Mauna Kea or ORM.

Improved prediction of the turbulence-shear contribution to wind noise pressure spectra

In previous research [Raspet et al., J. Acoust. Soc. Am. 123(3), 1260-1269 (2008)], predictions of the low frequency turbulence-turbulence and turbulence-mean shear interaction pressure spectra measured by a large wind screen were developed and compared to the spectra measured using large spherical wind screens in the flow. The predictions and measurements agreed well except at very low frequencies where the turbulence-mean shear contribution dominated the turbulence-turbulence interaction pressure. In this region the predicted turbulence-mean shear interaction pressure did not show consistent agreement with microphone measurements. The predicted levels were often much larger than the measured results. This paper applies methods developed to predict the turbulence-shear interaction pressure measured at the ground [Yu et al., J. Acoust. Soc. Am. 129(2), 622-632 (2011)] to improve the prediction of the turbulence-shear interaction pressure above the ground surface by incorporating a realistic wind velocity profile and realistic turbulence anisotropy. The revised prediction of the turbulence-shear interaction pressure spectra compares favorably with wind-screen microphone measurements in large wind screens at low frequency.

Conditional simulation of non-Gaussian wind velocity profiles: Application to buffeting response of Vincent Thomas suspension bridge

For a proper prediction of wind-induced vibrations of a long suspension bridge, it is necessary to use a representative wind velocity profile at the bridge site. However, as the simultaneous collection of wind velocity data at closely spaced locations of the entire bridge is not a viable option, simulation has become a powerful tool for this purpose. In this study, a new iterative approach of non-Gaussian conditional simulation is proposed to conditionally simulate the wind velocity profiles by utilizing the measured wind velocities at a few locations. The approach utilizes the well-known spectral representation technique in conjunction with nonlinear Gaussian to non-Gaussian mapping technique. Focusing on Vincent Thomas suspension bridge on which three anemometers have been installed recently at three strategic locations, this study compares buffeting responses evaluated using different simulation schemes. It has been found that the bridge response evaluated using the non-Gaussian simulation scheme may be higher when compared with other simulation schemes.

Overview of the Martian atmospheric submillimetre sounder FIRE

We propose a submillimetre-wave atmospheric emission sounding instrument, called Far-InfraRed Experiment (FIRE), for the Japanese Martian exploration programme “Mars Exploration with Lander-Orbiter Synergy” (MELOS). The scientific target of FIRE/MELOS is to understand the dust suspended meteorology of the Mars. FIRE will provide key meteorological parameters, such as atmospheric temperature profiles for outside and inside dust storms, the abundance profile of the atmospheric compositions and their isotopes, and wind velocity profiles. FIRE will also provide the local time dependency of these parameters. The observational sensitivity of FIRE/MELOS is discussed in this paper. FIRE will explore the meteorological system of the Martian atmosphere including the interaction between its surface and atmosphere.

Composite hodographs and inertial oscillations in the nocturnal boundary layer

AbstractIn this work the dynamic behaviour of the wind in the nocturnal boundary layer is studied, with a particular focus on systematic behaviour of the near‐surface wind. Recently, an extension of the well‐known Blackadar model for frictionless inertial oscillations above the nocturnal boundary layer was proposed by Van de Wiel et al., which accounts for frictional effects within the nocturnal boundary layer. It appears that the nocturnal wind velocity profile tends to perform an inertial oscillation around an equilibrium wind profile, rather than around the geostrophic wind vector (as in the Blackadar model).In the present study we propose the concept of ‘composite hodographs’ to evaluate the ideas and assumptions of the aforementioned analytical model. Composite hodographs are constructed based on a large observational dataset from the Cabauw observatory. For comparison and deeper analysis, this method is also applied to single‐column model simulations that represent the same dataset. From this, it is shown that winds in the middle and upper part of the nocturnal boundary layer closely follow the dynamics predicted by the model by Van de Wiel et al. In contrast, the near‐surface wind shows more complex behaviour that can be described by two different stages: (1) a decelerating phase where the wind decreases rapidly in magnitude due to enlarged stress divergence in the transition period near sunset (an aspect not included in the analytical model), and (2) a regular type of inertial oscillation, but with relatively small amplitude as compared to the oscillations in the middle and upper parts of the nocturnal boundary layer. Copyright © 2011 Royal Meteorological Society

Flow characteristics above a forest using light detection and ranging measurement data

New wind velocity measurement method using a light detection and ranging instrument was conducted. Based on the presented experimental data, the airflow characteristics above a forest were investigated: wind velocity distribution, friction (shear) wind velocity, roughness length, stream lines, drag force, and depth of the boundary layer. The results demonstrated that windward the forest, the boundary layer is shifted and sloped above the forest. Thereby, the fluid streamlines cannot abruptly change direction, as a consequence flat wind velocity profiles, wavy inflected wind velocity profiles, eddies, and flow recirculation were developed; hence, flow separation at a forest ratio x/ h of 2, flow contraction at x/ h of 12, and flow expansion at x/ h of 22 appeared. The shear wind velocity was about 1/10 of the mean wind velocity and the roughness length 1/15 of the forest height. Within a boundary layer depth of about 130 m, the drag force of the forest was 1300 times greater than that of the grass. Behind the forest, the air flow expands and eddies were developed at x/ h of about 7. Passing through the agriculture area and the forest, the physical parameters (turbulent kinetic energy, friction wind velocity, drag force, and depth of the boundary layer) are increasing at the point of roughness increase. To decrease such parameters and to avoid energy and friction losses and damage to trees due to divergence, convergence, separation, and recirculation of airflow, the sharp edge of the forest should be rounded in the range x/ h up to 2. A curved cutting of the front area of the forest may allow to decrease the slope of the boundary layer and the streamlines before, above, and behind the forest and hence lead to a quasi-steady and stable flow with less turbulence, momentum, heat, and mass transfer between the canopy and the atmosphere.

Low-Level Jets in the Moscow Region in Summer and Winter Observed with a Sodar Network

We evaluate the statistical properties of low-level jets (LLJs) observed by means of a network of Doppler sodars in the Moscow region, Russia. Continuous long-term measurements of the echo-signal intensity and wind-velocity profiles were carried out in July 2005 and in 2008–2010 synchronously in the centre of Moscow and at a rural site. The summertime nocturnal LLJs have a very clear diurnal cycle and exhibit features predicted by the Blackadar mechanism. In contrast, the long-lasting wintertime jets do not have any clear diurnal variability. The urban environment strongly influences LLJs in both seasons: above the city LLJs are higher, weaker and observed more rarely than at the rural site. In very cold periods (air temperature below −8°C) no LLJs were observed over the city, instead convection emerged in the urban boundary layer. The results are based on observations made in July 2005, January and December 2009, and January 2011.

Charging dynamics of metal hydride hydrogen storage bed for small wind hybrid systems

Small hybrid wind systems are capable of storing and supplying power for residential applications. In this paper, the excess wind energy is converted into hydrogen by electrolysis and is stored in a metal hydride. Metal hydride beds are known for their high volumetric capacity compared to the compressed hydrogen storage, and offers hydrogen storage at a reasonable operating temperature and pressure. A system simulation model is developed in Matlab/Simulink platform for the dynamics of the metal hydride hydrogen storage system, which is charged by the wind energy. The thermal loads of the metal hydride storage system is met by passing water at ambient temperature for cooling the bed while hydrogen is being absorbed. The effect of the transient turbulent wind velocity profile on the storage system is analyzed. The thermal management of the storage system plays an important role in the overall design, and hence it is discussed in detail.

The Analysis of the Impact of the Louver on the Natural Ventilation

The louver affects natural ventilation rate and indoor air distribution. In this paper, the wind velocity profile and pressure distribution in the natural ventilation model building were simulated through CFD. And how different rotation angles of the shutter and different incidence angles of the wind affect natural ventilation rate were studied. Then, the influences of shutters on the discharge coefficients were analyzed, and use principles of the louver equipped in the building were proposed.

Using dispersion modeling for ground level concentration

A short range model calculating ground-level concentration from elevated sources is estimated, which realized a Fickian-type formula. Taking the source and mixing height are functions of the wind velocity and eddy diffusivity profiles. The model estimated with an exact solution of the advection diffusion equation is compared with experimental ground level concentrations using meteorological data collected near the ground.