scholarly journals A numerical analysis of pollutant dispersion in street canyon: influence of the turbulent Schmidt number

2017 ◽  
Vol 26 (4) ◽  
pp. 423-436
Author(s):  
Bouabdellah Abed ◽  
Lakhdar Bouarbi ◽  
Mohamed Bouzit ◽  
Mohamed-Kamel Hamidou
Keyword(s):  
Urban Areas ◽  
Schmidt Number ◽  
Turbulent Transport ◽  
Pollutant Dispersion ◽  
Substantial Effect ◽  
Motor Vehicles ◽  
Street Canyons ◽  
Engine Exhaust ◽  
Climate Conditions ◽  
Turbulent Schmidt Number

Realizing the growing importance and availability of motor vehicles, we observe that the main source of pollution in the street canyons comes from the dispersion of automobile engine exhaust gas. It represents a substantial effect on the micro-climate conditions in urban areas. Seven idealized-2D building configurations are investigated by numerical simulations. The turbulent Schmidt number is introduced in the pollutant transport equation in order the take into account the proportion between the rate of momentum turbulent transport and the mass turbulent transport by diffusion. In the present paper, we attempt to approach the experimental test results by adjusting the values of turbulent Schmidt number to its corresponding application. It was with interest that we established this link for achieving our objectives, since the numerical results agree well with the experimental ones. The CFD code ANSYS CFX, the k, e and the RNGk-e models of turbulence have been adopted for the resolutions. From the simulation results, the turbulent Schmidt number is a range of 0.1 to 1.3 that has some effect on the prediction of pollutant dispersion in the street canyons. In the case of a flat roof canyon configuration (case: runa000), appropriate turbulent Schmidt number of 0.6 is estimated using the k-epsilon model and of 0.5 using the RNG k-e model.

Test of chemistry boundary conditions large-eddy simulations in urban areas

2020 ◽  
Author(s):  
Renate Forkel ◽  
Basit Khan ◽  
Johannes Werhahn ◽  
Sabine Banzhaf ◽  
Edward C. Chan ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Urban Areas ◽  
Turbulent Transport ◽  
Pollutant Dispersion ◽  
Time Dependent ◽  
Street Canyons ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model ◽  
Turbulence Generator

<p>Large-Eddy Simulation (LES) allow to simulate pollutant dispersion at a fine-scale turbulence-resolving scale with explicitly resolved turbulent transport around building structures and in street canyons. The microscale urban climate model with atmospheric chemistry PALM-4U (i.e. PALM for Urban applications; Maronga et al., 2019, Met. Z., https://doi.org/10.1127/metz/2019/0909) has been developed within the collaborative project MOSAIK (Model-based city planning and application in climate change). With such a large-eddy simulation (LES) model, pollutant dispersion around buildings and within street canyons can be simulated, with explicitly resolving the turbulent transport in urban environments.</p><p>Cyclic boundaries are frequently applied in LES in order to obtain lateral boundary conditions for the turbulent quantities. In addition to the default cyclic boundary conditions, PALM-4U allows also time-dependent boundary conditions from regional models to account for variable weather conditions and regional scale pollutant transport. Turbulent fluctuations, which are not included in the boundary conditions from the regional simulation but are needed as additional boundary conditions for the LES model are produced by a turbulence generator (Maronga et al, 2019, GMDD, https://doi.org/10.5194/gmd-2019-103).</p><p>PALM-4U simulations with and without time dependent boundary conditions from regional simulations with WRF-Chem are performed for different setups in order to test the impact of the domain configuration. The simulations indicate that cyclic boundary conditions can lead to unrealistic accumulation of pollutants over urban areas with strong sources, which is not the case when time-dependent boundary conditions are applied. However, even though a turbulence generator is applied, explicit setting of time-dependent boundary conditions requires large model domains, in order to obtain fully developed turbulence within the domain of interest, increasing the computational demand of the simulation.</p>

scholarly journals Numerical simulation of pollutant dispersion near obstacle based on k - ɛ turbulence closure scheme

2002 ◽  
Vol 24 (4) ◽  
pp. 219-235
Author(s):  
Duong Ngoc Hai ◽  
Nguyen The Duc
Keyword(s):  
Fluid Dynamics ◽  
Numerical Simulation ◽  
Schmidt Number ◽  
Recirculation Zone ◽  
Measurement Data ◽  
Pollutant Dispersion ◽  
Numerical Code ◽  
Closure Scheme ◽  
Turbulent Schmidt Number ◽  
Calculation Results

To simulate the wind field, pollutant transport and dispersion near an obstacle a numerical code based on the k - Ɛ turbulence model has been built. Beside the standerd k - Ɛ, two other modifications proposed by Detering & Etling and Duynkerke are also considered. The calculation results are verified based on the measurement data of von Karman Institute for Fluid Dynamics (Belgium). Modifications of the turbulent Schmidt number were carried out in order to match the measured results. The code was used to investigate the influence of the recirculation zone behind a building of cubical shape on the transport and disersion of pollutant. For a stack behind and near the obstacle, some conclusions about the effect of the stack height and stack location were derived.

scholarly journals Numerical Simulation of Turbulent Flow and Pollutant Dispersion in Urban Street Canyons

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 683 ◽  
Author(s):  
Van Thinh Nguyen ◽  
Thanh Chuyen Nguyen ◽  
John Nguyen
Keyword(s):  
Numerical Model ◽  
Turbulent Flow ◽  
Flow Pattern ◽  
Pollutant Dispersion ◽  
Experimental Measurements ◽  
Street Canyons ◽  
Urban Street ◽  
Urban Street Canyons ◽  
Aspect Ratios ◽  
Turbulent Schmidt Number

In this study, we have developed a numerical model based on an open source Computational Fluid Dynamics (CFD) package OpenFOAM, in order to investigate the flow pattern and pollutant dispersion in urban street canyons with different geometry configurations. In the new model, the pollutant transport driven by airflow is modeled by the scalar transport equation coupling with the momentum equations for airflow, which are deduced from the Reynolds Averaged Navier-Stokes (RANS) equations. The turbulent flow calculation has been calibrated by various two-equation turbulence closure models to select a practical and efficient turbulence model to reasonably capture the flow pattern. Particularly, an appropriate value of the turbulent Schmidt number has been selected for the pollutant dispersion in urban street canyons, based upon previous studies and careful calibrations against experimental measurements. Eventually, the numerical model has been validated against different well-known laboratory experiments in regard to various aspect ratios (a relationship between the building height and the width of the street canyon), and different building roof shapes (flat, shed, gable and round). The comparisons between the numerical simulations and experimental measurements show a good agreement on the flow pattern and pollutant distribution. This indicates the ability of the new numerical model, which can be applied to investigate the wind flow and pollutant dispersion in urban street canyons.

scholarly journals EMMISION OF POLLUTANTS ORIGINATING FROM MOBILE SOURCES ON THE EXAMPLE OF THE CITY OF KRAGUJEVAC

2019 ◽  
pp. 115
Author(s):  
Zoran Marjanović ◽  
Miomir Raos ◽  
Milena Jovanovic ◽  
Jovana Randjelović
Keyword(s):  
Air Pollution ◽  
Urban Areas ◽  
Motor Vehicles ◽  
Traffic Density ◽  
Human Environment ◽  
Local Climate ◽  
Climate Conditions ◽  
Exhaust Gases ◽  
Mobile Sources ◽  
The City

Traffic jam makes cities less pleasant for living and it also decreases traffic efficiency whereas travel time, fuel consumption and drivers’ stress are increased. A special problem is its influence on people’s health caused by emission of exhaust gases. Emission of pollutants originating from mobile sources is primarily conditioned by a level of technologies applied to the vehicle, vehicle’s technical state, traffic intensity, traffic density, local climate conditions, etc. Air pollution due to use of motor vehicles is becoming one of the major problems in urban areas across the world. With the increase of the number of motor vehicles and traffic intensification, the influence of exhaust gases on human environment also has increased. Considering the average age of the vehicles participating in traffic in the city of Kragujevac and the traffic capacity of traffic arteries, most frequently not designed for such a large number of vehicles concentrated at the core of the city, it is to be expected that the air pollution coming from mobile sources will become a problem that requires detailed analysis. For that purpose, a detailed statistical analysis of the vehicle fleet of the city of Kragujevac is conducted. An estimation of the influence of the vehicles on the air pollution in the city of Kragujevac, has been given in the paper.

scholarly journals High-Resolution Modelling of Thermal Exposure during a Hot Spell: A Case Study Using PALM-4U in Prague, Czech Republic

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 175
Author(s):  
Jan Geletič ◽  
Michal Lehnert ◽  
Pavel Krč ◽  
Jaroslav Resler ◽  
Eric Scott Krayenhoff
Keyword(s):  
Czech Republic ◽  
Urban Areas ◽  
Heat Exposure ◽  
Thermal Exposure ◽  
Urban Environments ◽  
Cooling Effect ◽  
Spatiotemporal Variability ◽  
Climate Index ◽  
Street Canyons ◽  
General Terms

The modelling of thermal exposure in outdoor urban environments is a highly topical challenge in modern climate research. This paper presents the results derived from a new micrometeorological model that employs an integrated biometeorology module to model Universal Thermal Climate Index (UTCI). This is PALM-4U, which includes an integrated human body-shape parameterization, deployed herein for a pilot domain in Prague, Czech Republic. The results highlight the key role of radiation in the spatiotemporal variability of thermal exposure in moderate-climate urban areas during summer days in terms of the way in which this directly affects thermal comfort through radiant temperature and indirectly through the complexity of turbulence in street canyons. The model simulations suggest that the highest thermal exposure may be expected within street canyons near the irradiated north sides of east–west streets and near streets oriented north–south. Heat exposure in streets increases in proximity to buildings with reflective paints. The lowest heat exposure during the day may be anticipated in tree-shaded courtyards. The cooling effect of trees may range from 4 °C to 9 °C in UTCI, and the cooling effect of grass in comparison with artificial paved surfaces in open public places may be from 2 °C to 5 °C UTCI. In general terms, this study illustrates that the PALM modelling system provides a new perspective on the spatiotemporal differentiation of thermal exposure at the pedestrian level; it may therefore contribute to more climate-sensitive urban planning.

scholarly journals The Awareness of and Input into Cultural Heritage Preservation by Urban Planners and Other Municipal Actors in Light of Climate Change

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 726
Author(s):  
Paul Carroll ◽  
Eeva Aarrevaara
Keyword(s):  
Climate Change ◽  
Cultural Heritage ◽  
Urban Areas ◽  
Climate Change Impacts ◽  
Town Planning ◽  
Urban Setting ◽  
Heritage Preservation ◽  
Climate Conditions ◽  
The Future ◽  
Cultural Heritage Preservation

Future climate conditions need to be considered in planning for urban areas. As well as considering how new structures would best endure in the future, it is important to take into account factors that contribute to the degradation of cultural heritage buildings in the urban setting. Climate change can cause an increase in structural degradation. In this paper, a review of both what these factors are and how they are addressed by urban planners is presented. A series of inquiries into the topic was carried out on town planning personnel and those involved in cultural heritage preservation in several towns and cities in Finland and in a small number of other European countries. The target group members were asked about observed climate change impacts on cultural heritage, about present steps being taken to protect urban cultural heritage, and also their views were obtained on how climate change impacts will be emphasised in the future in this regard. The results of the inquiry demonstrate that climate change is still considered only in a limited way in urban planning, and more interaction between different bodies, both planning and heritage authorities, as well as current research on climate change impacts, is needed in the field.

scholarly journals Review on pollutant dispersion in urban areas-part A: Effects of mechanical factors and urban morphology

2021 ◽  
Vol 190 ◽  
pp. 107534
Author(s):  
Zhengtong Li ◽  
Tingzhen Ming ◽  
Shurong Liu ◽  
Chong Peng ◽  
Renaud de Richter ◽  
...  
Keyword(s):  
Urban Areas ◽  
Pollutant Dispersion ◽  
Urban Morphology ◽  
Mechanical Factors

scholarly journals A Modified Bare Soil Index to Identify Bare Land Features during Agricultural Fallow-Period in Southeast Asia Using Landsat 8

Land ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 231
Author(s):  
Can Trong Nguyen ◽  
Amnat Chidthaisong ◽  
Phan Kieu Diem ◽  
Lian-Zhi Huo
Keyword(s):  
Remote Sensing ◽  
Land Cover ◽  
Urban Areas ◽  
Near Infrared ◽  
Urban Landscape ◽  
Bare Soil ◽  
Critical Element ◽  
Landsat 8 ◽  
Climate Conditions ◽  
Fallow Period

Bare soil is a critical element in the urban landscape and plays an essential role in urban environments. Yet, the separation of bare soil and other land cover types using remote sensing techniques remains a significant challenge. There are several remote sensing-based spectral indices for barren detection, but their effectiveness varies depending on land cover patterns and climate conditions. Within this research, we introduced a modified bare soil index (MBI) using shortwave infrared (SWIR) and near-infrared (NIR) wavelengths derived from Landsat 8 (OLI—Operational Land Imager). The proposed bare soil index was tested in two different bare soil patterns in Thailand and Vietnam, where there are large areas of bare soil during the agricultural fallow period, obstructing the separation between bare soil and urban areas. Bare soil extracted from the MBI achieved higher overall accuracy of about 98% and a kappa coefficient over 0.96, compared to bare soil index (BSI), normalized different bare soil index (NDBaI), and dry bare soil index (DBSI). The results also revealed that MBI considerably contributes to the accuracy of land cover classification. We suggest using the MBI for bare soil detection in tropical climatic regions.

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