Simulating urban flow and dispersion in Beijing by coupling a CFD model with the WRF model

The airflow and dispersion of a pollutant in a complex urban area of Beijing, China, were numerically examined by coupling a Computational Fluid Dynamics (CFD) model with a mesoscale weather model. The models used were Open Source Field Operation and Manipulation (OpenFOAM) software package and Weather Research and Forecasting (WRF) model. OpenFOAM was firstly validated against wind-tunnel experiment data. Then, the WRF model was integrated for 42 h starting from 0800 LST 08 September 2009, and the coupled model was used to compute the flow fields at 1000 LST and 1400 LST 09 September 2009. During the WRF-simulated period, a high pressure system was dominant over the Beijing area. The WRF-simulated local circulations were characterized by mountain valley winds, which matched well with observations. Results from the coupled model simulation demonstrated that the airflows around actual buildings were quite different from the ambient wind on the boundary provided by the WRF model, and the pollutant dispersion pattern was complicated under the influence of buildings. A higher concentration level of the pollutant near the surface was found in both the step-down and step-up notches, but the reason for this higher level in each configurations was different: in the former, it was caused by weaker vertical flow, while in the latter it was caused by a downward-shifted vortex. Overall, the results of this study suggest that the coupled WRF-OpenFOAM model is an important tool that can be used for studying and predicting urban flow and dispersions in densely built-up areas.

[1]  A. Clappier,et al.  An Urban Surface Exchange Parameterisation for Mesoscale Models , 2002 .

[2]  Rex Britter,et al.  Simulations of pollutant dispersion within idealised urban-type geometries with CFD and integral models , 2007 .

[3]  Zavisa Janjic,et al.  The Step-Mountain Coordinate: Physical Package , 1990 .

[4]  Michael Schatzmann,et al.  Wind tunnel measurements of concentration fluctuations in an urban street canyon , 1999 .

[5]  Robert N. Meroney,et al.  Concentration and flow distributions in urban street canyons: wind tunnel and computational data , 2003 .

[6]  Jong-Jin Baik,et al.  A Laboratory Model of Urban Street-Canyon Flows , 2000 .

[7]  Jong-Jin Baik,et al.  Urban Flow and Dispersion Simulation Using a CFD Model Coupled to a Mesoscale Model , 2009 .

[8]  李磊,et al.  An Application of the RAMS/FLUENT System on the Multi-Scale Numerical Simulation of the Urban Surface Layer A Preliminary Study , 2007 .

[9]  Liang Bin,et al.  A Laboratory model for the flow in urban street canyons induced by bottom heating , 2003 .

[10]  H. Kondo,et al.  A Simple Single-Layer Urban Canopy Model For Atmospheric Models: Comparison With Multi-Layer And Slab Models , 2001 .

[11]  S. Murakami,et al.  Wind tunnel experiments on how thermal stratification affects flow in and above urban street canyons , 2000 .

[12]  Fei Chen,et al.  Formation of horizontal convective rolls in urban areas , 2008 .

[13]  Z. Janjic.  The Step-Mountain Eta Coordinate Model: Further Developments of the Convection, Viscous Sublayer, and Turbulence Closure Schemes , 1994 .

[14]  K. J. Allwine,et al.  OVERVIEW OF URBAN 2000 A Multiscale Field Study of Dispersion through an Urban Environment , 2002 .

[15]  B. Grisogono,et al.  Parameterization of vertical diffusion and the atmospheric boundary layer height determination in the EMEP model , 2009 .

[16]  N. Dinar,et al.  A lagrangian dispersion model for calculating concentration distribution within a built-up domain , 1996 .

[17]  J. Dudhia.  Numerical Study of Convection Observed during the Winter Monsoon Experiment Using a Mesoscale Two-Dimensional Model , 1989 .

[18]  Andrzej A. Wyszogrodzki,et al.  Impact of coupling a microscale computational fluid dynamics model with a mesoscale model on urban scale contaminant transport and dispersion , 2010 .

[19]  Helen ApSimon,et al.  A numerical study of atmospheric pollutant dispersion in different two-dimensional street canyon configurations , 2003 .

[20]  Michael Schatzmann,et al.  BUBBLE – an Urban Boundary Layer Meteorology Project , 2005 .

[21]  J. Dudhia,et al.  Coupling an Advanced Land Surface–Hydrology Model with the Penn State–NCAR MM5 Modeling System. Part I: Model Implementation and Sensitivity , 2001 .

[22]  Hu Fei,et al.  An application of the RAMS/FLUENT system on the multi-scale numerical simulation of the urban surface layer—A preliminary study , 2007 .

[23]  Fei Chen,et al.  A Study of the Urban Boundary Layer Using Different Urban Parameterizations and High-Resolution Urban Canopy Parameters with WRF , 2011 .

[24]  M. Leach,et al.  A Validation of FEM3MP with Joint Urban 2003 Data , 2006 .

[25]  Riccardo Buccolieri,et al.  Dispersion study in a street canyon with tree planting by means of wind tunnel and numerical investigations – Evaluation of CFD data with experimental data , 2008 .

[26]  B. Grisogono,et al.  Justifying the WKB approximation in pure katabatic flows , 2002 .

[27]  Fei Chen,et al.  An Observational and Modeling Study of Characteristics of Urban Heat Island and Boundary Layer Structures in Beijing , 2009 .

[28]  J. Noilhan,et al.  The urban boundary-layer field campaign in marseille (ubl/clu-escompte): set-up and first results , 2005 .

[29]  Hiroyuki Kusaka,et al.  Thermal Effects of Urban Canyon Structure on the Nocturnal Heat Island: Numerical Experiment Using a Mesoscale Model Coupled with an Urban Canopy Model , 2004 .