Special Issue "Wake Flows and Air Quality in the Atmosphere"

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Air Quality".

Deadline for manuscript submissions: 1 March 2020.

Special Issue Editors

Dr. Frederic Murzyn
E-Mail Website
Guest Editor
Air Quality and Depollution Group, Department of Mechanical Engineering, ESTACA, 53061 Laval, France
Interests: pollutant dispersion; wind tunnel; air quality; experimental fluid mechanics; turbulence; flow around obstacles; aerodynamics; two-phase flows; flow-structure interaction
Dr. Georges Fokoua
E-Mail Website
Guest Editor
Air Quality and Depollution Group, Department of Mechanical Engineering, ESTACA, 53061 Laval, France
Interests: pollutant dispersion; wind tunnel; air quality; experimental fluid mechanics; turbulence; flow around obstacles; aerodynamics; CFD
Prof. Dr. Ram Balachandar
E-Mail Website
Guest Editor
Department of Civil and Environmental Engineering, University of Windsor, 401 Sunset Ave., N9B 3P4 Windsor, ON, Canada
Interests: Hydraulic engineering; Fluid Mechanics; Turbulence; Scour; Jets and Wakes; Fluid-Structure interaction

Special Issue Information

Dear Colleagues,

We invite researchers to contribute original research articles, as well as review articles, dealing with all aspects of wake flows and air quality related to the atmosphere. Pollutants are released in the atmosphere by transportation systems (cars, trains, buses, planes, etc.) and industries. Once in the surrounding air, their behavior and dynamics are strongly influenced by different parameters, such as (but not limited to) obstacles, buildings, vehicles, canopy, street architecture, etc. Thus, the interaction between wake flows and pollutant dispersion/concentration is a major concern. In the present Special Issue, we are interested in this topic in the context of air quality. Related issues are of primary importance in terms of health and environmental purposes. The expected contributions should include recent experimental (in situ, wind tunnel, etc.) and modeling (CFD, analytical) works, techniques, and developments dedicated to the understanding of related wake flows and their interaction with pollutant dispersion and air quality. Papers dealing with these concerns are particularly expected. Topics of interest include but are not limited to:

  • Pollutant dispersion in the wake of cars, trains, and buses;
  • Wake flow and flow topology applied to transportation systems;
  • Interaction between vehicles;
  • Pollution around buildings related to air quality;
  • Urban flow and street network;
  • Chimney and chemical release;
  • Boundary layer and interaction with canopy;
  • Dispersion modeling;
  • Data from new field campaigns in cities and wind tunnel experiments;
  • Estimation of pollutant infiltration in cabins and/or dispersion;
  • Comparison between CFD models and experiments;
  • Particle emissions.

Dr. Frederic Murzyn
Dr. Georges Fokoua
Prof. Ram Balachandar
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atmosphere is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • wake flows
  • pollutant dispersion/emission/infiltration
  • air quality
  • atmospheric pollution
  • building and canyon streets
  • atmospheric boundary layer
  • CFD
  • pollutant related to transportation systems
  • experimental investigations (wind tunnel, in situ measurements, etc.)

Published Papers (1 paper)

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Research

Open AccessArticle
Car Wake Flows and Ultrafine Particle Dispersion: From Experiments to Modelling
Atmosphere 2020, 11(1), 39; https://doi.org/10.3390/atmos11010039 - 28 Dec 2019
Abstract
Improving air quality in urban environments and transportation systems is crucial. Concerns are related to health and environmental issues associated with huge costs. Car cabin is a microenvironment where pollutants can accumulate with possible risks for occupants. In automotive engineering, it has then [...] Read more.
Improving air quality in urban environments and transportation systems is crucial. Concerns are related to health and environmental issues associated with huge costs. Car cabin is a microenvironment where pollutants can accumulate with possible risks for occupants. In automotive engineering, it has then become mandatory to study the path and dispersion of such pollutants emitted from the tailpipe of a car. In the present paper, the relation between the flow topology and the dispersion of ultrafine particles (UFP) in the wake of a vehicle is discussed. Experiments were undertaken at a reduced scale using simplified car models. Experimental conditions were defined to be representative of a vehicle in an urban environment. Based on experimental data, a simplified analytical model is developed, which aims at describing the concentration fields of UFP in the wake of a single vehicle for different rear slant angles. The strengths and limits of the present model are discussed and ways of improvements are suggested. Additional experiments are presented to assess the influence of the inter-vehicle distance on this recirculation region. Critical inter-vehicle distances were determined based on defined criteria for different rear slant angles of the leading vehicle and compared to safety clearances. Full article
(This article belongs to the Special Issue Wake Flows and Air Quality in the Atmosphere)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Boundary Layer Characterization of Compacted Soils Degraded by Traffic: Application to Dust Emissions
Mickael Le Vern 1,*, Andry Razakamanantsoa 1, Frédéric Murzyn 2 and Frédérique Larrarte 1
1 IFSTTAR, GERS Department, Centre de Nantes, Allée des Ponts et Chaussées, 44344 Bouguenais, France
2 ESTACA West Campus, Department of Mechanical Engineering, Rue Georges Charpak, 53000 Laval, France

Abstract: Haul and vehicle traffic on unpaved roads or on earthworks runways during construction works are an important source of dust emission. This traffic involved takes place on compacted soils, which become progressively degraded as the number of wheel passes increases. The surface roughness of the soil changes, modyfing the boundary layer properties and the wind skin friction. This friction leads to the lift of the soil particles, which causes the worsening of air quality and reduction of visibility. If this occurs, it may not only have serious consequences on health for people who live around and workers but it can also cause accidents. Limiting particle lift is then mandatory. The present paper reports an experimental characterization of boundary layers developing above different sets of traffic degraded soils at different inflow velocities. The study is based on a double approach combining soil and fluid mechanics. Mixtures of kaolin clay and sand were compacted using a laboratory roller compactor. Soils were degraded using a vehicle simulator. 5 000 and 10 000 cycles of wheel passages were simulated with two different tyre treads. Surface roughness profiles were measured on degraded soils. Then, the velocity profiles above each soil sample were obtained in a wind tunnel using a non-intrusive measurement technique (LASER Doppler Velocimetry). The Reynolds number based on the momentum thickness ranged from 390 to 1800. The defect law was used to estimate the skin friction at various points along the samples. The experimental results are analysed to assess the influence of soil properties and soil traffic degradation on skin friction. A better knowledge of these complex interactions would be helpful for the improvement of methods limiting particle lift (such as watering).

 

Wake Flows and Ultrafine Particle Dispersion: From Experiments to Modelling
Frédéric Murzyn 1,*, Georges Fokoua 2, Romain Rodriguez 1, Chenhao Shen 1, Frédérique Larrarte 3 and Amine Mehel 2
1 ESTACA West Campus, Department of Mechanical Engineering, France
2 ESTACA Paris Saclay Campus, Department of Mechanical Engineering, France
3 IFSTTAR, Department of Geotechnics, Environment, Natural Risks and Earth Sciences, France

Abstract: Improving air quality in urban environments and transportation systems is crucial. Concerns are related to health and environmental issues associated with huge costs. In major cities, pedestrians and commuters are exposed to high levels of pollutants. Car cabin is a microenvironment where these pollutants (NOx, CO2, particles) can accumulate with possible risks for occupants. In automotive engineering, it has then become mandatory to study the path and dispersion of such pollutants emitted from the tailpipe of a car. Indeed, when released in the atmosphere, they can either disperse in the surrounding environment or infiltrate the following car. In the present paper, based on different experimental campaigns in wind tunnel, we aim at discussing the relation between the flow topology (wake) and the dispersion of ultrafine particles (UFP) in the wake of a vehicle. Experiments were undertaken at a reduced scale using simplified car models known as Ahmed bodies. For them, the most important parameter governing the wake is the rear slant angle. Experimental conditions were defined to be representative of a vehicle in an urban environment. Based on the work of Rodriguez (2018), we developed a simplified analytical model, which aims at describing the concentration fields of UFP in the wake of a single vehicle for different rear slant angles. The originality of our experimental approach is based on the use of solid particles representative of those emitted by a real car while gaseous tracers were used in most of the previous works. The strengths and limits of the present model are discussed and ways of improvements are presented. Assuming that the size of the recirculation region plays an important role, we present additional experiments to assess the influence of the inter-vehicle distance on this recirculation region. Data analysis was conducted and critical inter-vehicle distances were determined based on defined criteria for different rear slant angles of the leading vehicle and compared to safety clearances. In further experiments, UFP will be injected from this leading car and links between the wake flow properties and UFP concentration fields will be determined.

Rodriguez, R. (2018). Etude expérimentale de la dispersion de particules ultrafines dans le sillage de modèles simplifiés de véhicules automobiles, PhD Thesis, Ecole Centrale de Nantes, 270 pages.

 

Effects of Rear Slant Angle on the Turbulent Wake Flow Between Two In-line Ahmed Bodies
Ebenezer E. Essel *, Subhadip Das and Ram Balachandar
Department of Civil and Environmental Engineering, University of Windsor, Canada

Abstract: In-car air pollution is a major issue in vehicle transportation because of the serious health risks associated with the intake of pollutants from the emissions of surrounding vehicles into the cabin of the car. Most of these pollutants in the cabin come from the vehicle immediately ahead. In order to reduce the harmful effects of in-car air pollution, it is important to understand the wake characteristics behind the leading vehicle and its influence on the airflow approaching the rear vehicle. Previous studies have indicated that the wake characteristics behind a simplified car model, known as Ahmed body, are strongly dependent on the rear slant angle, θ. However, the effects of the rear slant angle on the flow dynamics and topography of the wake between two in-line Ahmed bodies interacting with each other is not well understood. Accordingly, an experimental investigation was conducted with two in-line Ahmed bodies separated by a car’s length and placed in a fully developed turbulent boundary layer. The gap between the channel floor and the base of the Ahmed body was 15 mm while the height of the body is h = 54 mm. The relative boundary layer thickness of the approach flow was δ/h =2.5. Detailed particle image velocimetry (PIV) measurements were performed with a constant Reynolds number based on the freestream velocity and water depth, Re = 37,000. Four test conditions were examined. First, a reference test case with measurements taken upstream of the Ahmed body without any leading body to characterize the approach turbulent boundary layer. Afterwards, the effects of the presence of the leading Ahmed body are examined using three rear slant angles, a blunt rear (0^°), a high-drag rear angle of 25^° and a low-drag rear angle of 35^°. In the final paper, results of the mean velocities and higher-order statistics such as the Reynolds stresses and quadrant analysis within the wake region between the two bodies will be presented and discussed. It is expected that the present investigations will improve our understanding of the influence of rear slant angles on air-pollutant intake of vehicles following each other closely. Such knowledge will help engineers design more efficient in-car air pollution control systems. The experimental data can also be used for validating turbulence models which in turn can be used to examine the effects of other extensive geometric and initial conditions that influence in-car air pollution.

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