Estimation of Wind Speeds in Urban Areas Using Look-up Tables for Wind-speed Change Rate Simulated by a CFD Model

2020 ◽  
Author(s):  
Jang-Woon Wang ◽  
Jae-Jin Kim ◽  
Ho-Jin Yang
Keyword(s):  
Wind Speed ◽  
Urban Areas ◽  
Urban Morphology ◽  
Average Height ◽  
Target Area ◽  
Cfd Model ◽  
Parameterization Method ◽  
Wind Speeds ◽  
Speed Change ◽  
Morphology Parameters

<p>In this study, we developed a new urban parameterization method of wind speeds. The parameterization method uses building morphology parameters (the volumetric fraction, the plane area fraction, and the average height of buildings) for three different areas. For this, we investigated the relationships between the wind speed change rates by buildings and the urban parameters in three target areas. Each target area includes an automated weather station (AWS) at its center. We conducted the multiple regression analysis to make look-up tables for the relationships between the wind speed change rates and the urban morphology parameters for 32 inflow directions in the target areas. For validation, we simulated the wind speeds at the AWSs using a CFD model coupled to the local data assimilation and prediction system (LDAPS), one of the operational numerical prediction systems of the Korean Meteorological Administration. The results showed that the estimated wind speeds at the AWSs in the three target areas were very similar to those simulated by the LDAPS-CFD coupled model as well as those observed at the AWSs.</p>

Comparison of Various Blade Profiles in a Two-Blade Conventional Savonius Wind Turbine

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Rahim Hassanzadeh ◽  
Milad Mohammadnejad ◽  
Sajad Mostafavi
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Power Output ◽  
Urban Areas ◽  
Cost Effective ◽  
Maximum Power ◽  
Power Coefficient ◽  
Total Power ◽  
Wind Speeds ◽  
Savonius Wind Turbine

Abstract Savonius turbines are one of the old and cost-effective turbines which extract the wind energy by the drag force. Nowadays, they use in urban areas to generate electricity due to their simple structure, ease of maintenance, and acceptable power output under a low wind speed. However, their efficiency is low and the improvement of their performance is necessary to increase the total power output. This paper compares four various blade profiles in a two-blade conventional Savonius wind turbine. The ratios of blade diameter to the blade depth of s/d = 0.3, 0.5, 0.7, and 1 are tested under different free-wind speeds of 3, 5, and 7 m/s and tip speed ratios (TSRs) in the range from 0.2 to 1.2. It is found that the profile of blades in a Savonius rotor plays a considerable role in power characteristics. Also, regardless of blades profile and free-wind speed, the maximum power coefficient develops in TSR = 0.8. In addition, increasing the free-wind speed enhances the rotor performance of all cases under consideration. Finally, it is revealed that the rotor with s/d = 0.5 provides maximum power coefficients in all free-wind speeds and TSR values among the rotors under consideration, whereas the rotor with s/d = 1 is the worth cases.

scholarly journals Evaluating the Influence of Urban Morphology on Urban Wind Environment Based on Computational Fluid Dynamics Simulation

2020 ◽  
Vol 9 (6) ◽  
pp. 399
Author(s):  
Chia-An Ku ◽  
Hung-Kai Tsai
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Urban Areas ◽  
Urban Morphology ◽  
Dynamics Simulation ◽  
Wind Environment ◽  
Study Region ◽  
Wind Speeds ◽  
The Impact ◽  
The Relationship

Due to urbanization around the world, people living in urban areas have been suffering from a series of negative effects caused by changes in urban microclimate, especially when it comes to urban heat islands (UHIs). To mitigate UHIs, management of urban wind environments is increasingly considered as a crucial part of the process. Computational fluid dynamics (CFD) simulation of wind fields has become a prevailing method to explore the relationship between morphological factors and wind environment. However, most studies are focused on building scale and fail to reflect the effects of comprehensive planning. In addition, the combined influence of different morphological factors on wind environment is rarely discussed. Therefore, this study tries to explore the relationship between urban morphology and wind environment in a new-town area. CFD method was applied to simulate the wind field, and 11 scenarios based on criteria according to existing literature, planning regulations and local characteristics were developed. The simulation results from different scenarios show that the impact of the five selected factors on wind speeds was non-linear, and the impact varied significantly among different areas of the study region. Simulation of the differences in regional wind speeds among different planning scenarios can provide strong decision-making support.

Effect of protective shields on drift and deposition characteristics of field sprayers

1993 ◽  
Vol 73 (4) ◽  
pp. 1261-1273 ◽  
Author(s):  
Thomas M. Wolf ◽  
Raj Grover ◽  
Keith Wallace ◽  
Stan R. Shewchuk ◽  
John Maybank
Keyword(s):  
Wind Speed ◽  
Droplet Size ◽  
Field Trials ◽  
Application Rate ◽  
Target Area ◽  
High Wind ◽  
Ground Speed ◽  
Wind Speeds ◽  
Spray Solution ◽  
Deposition Uniformity

Field trials were conducted to determine the effectiveness of shields in reducing off-target droplet drift from ground-rig sprayers. Sprayer booms ranging in width from 10 to 13.5 m and equipped with commercially available shields were operated along a 150-m swath in a field of approximately 20-cm-tall spring wheat in wind speeds ranging from 10 to 35 km h−1. Airborne drift was measured using aspirated air samplers. The use of an 80 flat fan tip (8001) at a pressure of 275 kPa and a ground speed of 8 km h−1 resulted in 7.5% of the 50 L ha−1 spray solution drifting off the target area. The use of protective cones with 8001 tips without lowering the boom reduced airborne drift by 33% at a 20 km h−1 wind speed, while a 65–85% drift reduction was accomplished with the combination of solid or perforated shielding and lowering the sprayer boom. Increasing the application rate to 100 L ha−1 by using 8002 tips reduced drift of the unshielded sprayer by 65%. Decreasing application rate to 15 L ha−1 by using 800017 tips increased drift by 29% despite the use of a shield. Off-target drift increased with increasing wind speeds for all sprayers, but the increase was less for shielded sprayers and coarser sprays. The decreased droplet size of spray from 110 tips increased drift when the boom height was the same as for 80 tips. High wind speeds, lower carrier volumes and finer sprays, 110 tips, and solid shields tended to decrease on-swath deposit uniformity, whereas a perforated shield or cones did not affect deposit uniformity. Key words: 2,4-D amine, droplet drift, aspirated air samplers, flat fan tips, deposition uniformity, droplet size

scholarly journals Monitoring and Modeling Roof-Level Wind Speed in a Changing City

Atmosphere ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 87
Author(s):  
Kathrin Baumann-Stanzer ◽  
Sirma Stenzel ◽  
Gabriele Rau ◽  
Martin Piringer ◽  
Felix Feichtinger ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Energy ◽  
Wind Turbine ◽  
Urban Areas ◽  
Dispersion Model ◽  
Flow Direction ◽  
Energy Yield ◽  
Wind Speeds ◽  
Small Wind Turbine ◽  
Roof Level

Results of an observational campaign and model study are presented demonstrating how the wind field at roof-level in the urban area of Vienna changed due to the construction of a new building nearby. The investigation was designed with a focus on the wind energy yield of a roof-mounted small wind turbine but the findings are also relevant for air dispersion applications. Wind speed profiles above roof top are simulated with the complex fluid dynamics (CFD) model MISKAM (Mikroskaliges Klima- und Ausbreitungsmodell, microscale climate and dispersion model). The comparison to mast measurements reveals that the model underestimates the wind speeds within the first few meters above the roof, but successfully reproduces wind conditions at 10 m above the roof top (corresponding to about 0.5 times the building height). Scenario simulations with different building configurations at the adjacent property result in an increase or decrease of wind speed above roof top depending on the flow direction at the upper boundary of the urban canopy layer (UCL). The maximum increase or decrease in wind speed caused by the alternations in building structure nearby is found to be in the order of 10%. For the energy yield of a roof-mounted small wind turbine at this site, wind speed changes of this magnitude are negligible due to the generally low prevailing wind speeds of about 3.5 m s−1. Nevertheless, wind speed changes of this order could be significant for wind energy yield in urban areas with higher mean wind speeds. This effect in any case needs to be considered in siting and conducting an urban meteorological monitoring network in order to ensure the homogeneity of observed time-series and may alter the emission and dispersion of pollutants or odor at roof level.

scholarly journals Quantifying the impacts of urban morphology on modifying microclimate conditions in extreme weather conditions

2021 ◽  
Vol 2042 (1) ◽  
pp. 012058
Author(s):  
K. Javanroodi ◽  
V.M. Nik ◽  
JL. Scartezzini
Keyword(s):  
Wind Speed ◽  
Air Temperature ◽  
Urban Areas ◽  
Fluid Dynamic ◽  
Heat Removal ◽  
Weather Conditions ◽  
Extreme Weather ◽  
Urban Morphology ◽  
Urban Neighbourhoods ◽  
Microclimate Conditions

Abstract It is well-known that the morphology of urban areas modifies the variations of climate variables at microscale; known as microclimate conditions. The complexity of urban morphology can lead to undesired wind conditions or excessive air temperature; particularly in extreme weather conditions. This study attempts to quantify the impacts of urban morphology on the evolution of wind speed and air temperature at the urban canopy layer using Computational Fluid Dynamic (CFD) simulations. In this regard, three urban neighbourhoods are generated based on a novel urban morphology parameterization method and assessed in two extreme low and high wind conditions. Results showed that wind speed (up to 75%) and air temperature (up to 28%) at the microscale can get amplified or dampened in extreme conditions. A negative correlation was observed between wind speed and air temperature variations indicating a great potential to reduce outdoor air temperature through heat removal in urban canyons. The findings of the study are categorized based on the morphological parameters to present a series of design-based strategies for the newly-built urban neighbourhoods.

scholarly journals Synergistic Influence of Local Climate Zones and Wind Speeds on the Urban Heat Island and Heat Waves in the Megacity of Beijing, China

2021 ◽  
Vol 9 ◽  
Author(s):  
Lian Zong ◽  
Shuhong Liu ◽  
Yuanjian Yang ◽  
Guoyu Ren ◽  
Miao Yu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Urban Heat Island ◽  
Rural Areas ◽  
Urban Areas ◽  
Thermal Environment ◽  
Heat Island ◽  
Wind Speeds ◽  
High Rise ◽  
Urban Heat

Large-scale modifications to urban underlying surfaces owing to rapid urbanization have led to stronger urban heat island (UHI) effects and more frequent urban heat wave (HW) events. Based on observations of automatic weather stations in Beijing during the summers of 2014–2020, we studied the interaction between HW events and the UHI effect. Results showed that the UHI intensity (UHII) was significantly aggravated (by 0.55°C) during HW periods compared to non-heat wave (NHW) periods. Considering the strong impact of unfavorable weather conditions and altered land use on the urban thermal environment, we evaluated the modulation of HW events and the UHI effect by wind speed and local climatic zones (LCZs). Wind speeds in urban areas were weakened due to the obstruction of dense high-rise buildings, which favored the occurrence of HW events. In detail, 35 HW events occurred over the LCZ1 of a dense high-rise building area under low wind speed conditions, which was much higher than that in other LCZ types and under high wind speed conditions (< 30 HW events). The latent heat flux in rural areas has increased more due to the presence of sufficient water availability and more vegetation, while the increase in heat flux in urban areas is mainly in the form of sensible heat flux, resulting in stronger UHI effect during HW periods. Compared to NHW periods, lower boundary layer and wind speed in the HW events weakened the convective mixing of air, further expanding the temperature gap between urban and rural areas. Note that LCZP type with its high-density vegetation and water bodies in the urban park area generally exhibited, was found to have a mitigating effect on the UHI, whilst at the same time increasing the frequency and duration of HW events during HW periods. Synergies between HWs and the UHI amplify both the spatial and temporal coverage of high-temperature events, which in turn exposes urban residents to additional heat stress and seriously threatens their health. The findings have important implications for HWs and UHII forecasts, as well as for scientific guidance on decision-making to improve the thermal environment and to adjust the energy structure.

scholarly journals Automated wind turbine wake characterization in complex terrain

2019 ◽  
Vol 12 (6) ◽  
pp. 3463-3484 ◽  
Author(s):  
Rebecca J. Barthelmie ◽  
Sara C. Pryor
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Atmospheric Stability ◽  
Average Height ◽  
Data Set ◽  
Wind Speeds ◽  
Stable Conditions ◽  
Low Wind Speeds ◽  
Turbine Wake ◽  
Wind Turbine Wake

Abstract. An automated wind turbine wake characterization algorithm has been developed and applied to a data set of over 19 000 scans measured by a ground-based scanning Doppler lidar at Perdigão, Portugal, over the period January to June 2017. Potential wake cases are identified by wind speed, direction and availability of a retrieved free-stream wind speed. The algorithm correctly identifies the wake centre position in 62 % of possible wake cases, with 46 % having a clear and well-defined wake centre surrounded by a coherent area of lower wind speeds while 16 % have split centres or multiple lobes where the lower wind speed volumes are no longer in coherent areas but present as two or more distinct areas or lobes. Only 5 % of cases are not detected; the remaining 33 % could not be categorized either by the algorithm or subjectively, mainly due to the complexity of the background flow. Average wake centre heights categorized by inflow wind speeds are shown to be initially lofted (to two rotor diameters, D, downstream) except when the inflow wind speeds exceed 12 ms−1. Even under low wind speeds, by 3.5 D downstream of the wind turbine, the mean wake centre position is below the initial wind turbine hub height and descends broadly following the terrain slope. However, this behaviour is strongly linked to the hour of the day and atmospheric stability. Overnight and in stable conditions, the average height of the wake centre is 10 m higher than in unstable conditions at 2 D downstream from the wind turbine and 17 m higher at 4.5 D downstream.

scholarly journals Micro-scale modelling of the urban wind speed for air pollution applications

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Thor-Bjørn Ottosen ◽  
Matthias Ketzel ◽  
Henrik Skov ◽  
Ole Hertel ◽  
Jørgen Brandt ◽  
...  
Keyword(s):  
Air Pollution ◽  
Wind Speed ◽  
Urban Areas ◽  
Global Radiation ◽  
Atmospheric Stability ◽  
Sea Breeze ◽  
Building Design ◽  
Obukhov Length ◽  
Wind Speeds ◽  
Scale Modelling

Abstract Modelling wind speeds in urban areas have many applications e.g. in relation to assessment of wind energy, modelling air pollution, and building design and engineering. Models for extrapolating the urban wind speed exist, but little attention has been paid to the influence of the upwind terrain and the foundations for the extrapolation schemes. To analyse the influence of the upwind terrain and the foundations for the extrapolation of the urban wind speed, measurements from six urban and non-urban stations were explored, and a model for the urban wind speed with and without upwind influence was developed and validated. The agreement between the wind directions at the stations is found to be good, and the influence of atmospheric stability, horizontal temperature gradients, land-sea breeze, temperature, global radiation and Monin-Obukhov Length is found to be small, although future work should explore if this is valid for other urban areas. Moreover, the model is found to perform reasonably well, but the upwind influence is overestimated. Areas of model improvement are thus identified. The upwind terrain thus influences the modelling of the urban wind speed to a large extent, and the fundamental assumptions for the extrapolation scheme are fulfilled for this specific case.

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