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>

Large-Eddy Simulation of Reactive Pollutant Dispersion Over Street Canyons of Different Aspect Ratios

2014 ◽  
Author(s):  
T. Z. Du ◽  
Chun-Ho Liu ◽  
Y. B. Zhao
Keyword(s):  
Aspect Ratio ◽  
Large Eddy Simulation ◽  
Chemical Reactions ◽  
Pollutant Dispersion ◽  
Pollutant Removal ◽  
Street Canyons ◽  
Eddy Simulation ◽  
Aspect Ratios ◽  
Large Eddy ◽  
Reactive Pollutant

In urban areas, pollutants are emitted from vehicles then disperse from the ground level to the downstream urban canopy layer (UCL) under the effect of the prevailing wind. For a hypothetical urban area in the form of idealized street canyons, the building-height-to-street-width (aspect) ratio (AR) changes the ground roughness which in turn leads to different turbulent airflow features. Turbulence is considered an important factor for the removal of reactive pollutants by means of dispersion/dilution and chemical reactions. Three values of aspect ratio, covering most flow scenarios of urban street canyons, are employed in this study. The pollutant dispersion and reaction are calculated using large-eddy simulation (LES) with chemical reactions. Turbulence timescale and reaction timescale at every single point of the UCL domain are calculated to examine the pollutant removal. The characteristic mechanism of reactive pollutant dispersion over street canyons will be reported in the conference.

Large-eddy Simulation of Plume Dispersion over Hypothetical Urban Areas

2020 ◽  
Author(s):  
Zhangquan Wu ◽  
Chun-Ho Liu
Keyword(s):  
Nitric Oxide ◽  
Air Quality ◽  
Large Eddy Simulation ◽  
Urban Areas ◽  
Turbulent Dispersion ◽  
Anthropogenic Sources ◽  
Plume Dispersion ◽  
Street Canyons ◽  
Eddy Simulation ◽  
Large Eddy

<p>More than 80% of people living in urban areas that exposed to air quality levels that exceed WHO guideline limits both indoors and outdoors. Road transport has been found to be one of major anthropogenic sources of aerosol particles and many gaseous pollutants in urban areas. Dispersion of pollutants emitted from vehicles over urban areas largely affects pedestrian-level air quality. A good understanding of pollutant transport, mixing process and removal mechanism is crucial to effectuate air quality management. In this study, turbulent dispersion of reactive pollutants in the atmospheric boundary layer (ABL) over hypothetical urban area in the form of an array of idealised street canyons is investigated using large-eddy simulation (LES). The irreversible ozone O3 titration oxidizes nitric oxide NO to nitrogen dioxide NO2, representing the typical anthropogenic air pollution chemistry. Nitric oxide (NO) is emitted from the ground level of the first street canyon into the urban ABL doped with ozone (O3). From the LES results, negative vertical NO flux is found at the roof level of the street canyons.  By looking into the different plume behavior and vertical flux between the inert pollutant and chemically reactive pollutant, a fundamental understanding of exchange processes of anthropogenic chemicals between an urban surface and the atmosphere is developed. </p>

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.

scholarly journals Qualitative and Quantitative Investigation of Multiple Large Eddy Simulation Aspects for Pollutant Dispersion in Street Canyons Using OpenFOAM

Atmosphere ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 17 ◽  
Author(s):  
Arsenios E. Chatzimichailidis ◽  
Christos D. Argyropoulos ◽  
Marc J. Assael ◽  
Konstantinos E. Kakosimos
Keyword(s):  
Open Source ◽  
Best Practice ◽  
Pollutant Dispersion ◽  
Navier Stokes ◽  
Street Canyons ◽  
Urban Streets ◽  
Eddy Simulation ◽  
Best Practice Guidelines ◽  
Scale Models ◽  
Large Eddy

Air pollution is probably the single largest environment risk to health and urban streets are the localized, relevant hotspots. Numerous studies reviewed the state-of-the-art models, proposed best-practice guidelines and explored, using various software, how different approaches (e.g., Reynolds-averaged Navier–Stokes (RANS), large eddy simulations (LES)) inter-compare. Open source tools are continuously attracting interest but lack of similar, extensive and comprehensive investigations. At the same time, their configuration varies significantly among the related studies leading to non-reproducible results. Therefore, the typical quasi-2D street canyon geometry was selected to employ the well-known open-source software OpenFOAM and to investigate and validate the main parameters affecting LES transient simulation of a pollutant dispersion. In brief, domain height slightly affected street level concentration but source height had a major impact. All sub-grid scale models predicted the velocity profiles adequately, but the k-equation SGS model best-resolved pollutant dispersion. Finally, an easily reproducible LES configuration is proposed that provided a satisfactory compromise between computational demands and accuracy.

Numerical modelling of odour dispersion around a cubical obstacle using large eddy simulation

2012 ◽  
Vol 66 (7) ◽  
pp. 1549-1557 ◽  
Author(s):  
Harerton Oliveira Dourado ◽  
Jane Meri Santos ◽  
Neyval C. Reis ◽  
Ilias Mavroidis
Keyword(s):  
Large Eddy Simulation ◽  
Pollutant Dispersion ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wind Tunnel Data ◽  
The Mean ◽  
Odour Dispersion ◽  
Intermittency Factor ◽  
Les Model ◽  
Concentration Patterns

In the present work two different large eddy simulation (LES) approaches, namely the Dynamic Smagorinsky model and the Wale model, are used to simulate the air flow and pollutant dispersion around a cubical obstacle. Results are compared with wind tunnel data (WT) and with results from the Smagorinsky LES model. Overall agreement was good between the different LES approaches and the WT results, both for the mean and fluctuating flow and concentration patterns. LES models can provide good estimates of concentration fluctuation intensity and enable the calculation of the intermittency factor. The model results indicate that LES is a viable tool for odour impact assessment.

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