CFD simulation of airflow over a regular array of cubes. Part I: Three-dimensional simulation of the flow and validation with wind-tunnel measurements

Air flow inside an array of cubes is simulated. Cubes (edge length 0.15 m) are arranged in a regular array, separated by 0.15 m in the streamwise and spanwise directions. Numerical simulations are performed based on Reynolds-averaged Navier–Stokes equations (RANS), solved in a computational fluid dynamics model (CFD), with standard k–ε turbulent closure (two prognostic equations are solved for the turbulent kinetic energy k and its dissipation ε, respectively). Simulations are validated against wind-tunnel data using a technique based on hit-rate calculations, and calculated statistical parameters. The results show that the horizontal velocity is very well modelled, and despite some discrepancies, the model that fulfils the hit-rate test criteria gives useful results that are used to investigate three-dimensional (3-D) flow structures. The 3-D analysis of the flow shows interesting patterns: the centre of the canyon vortex is at 3/4 of the canyon height, and stronger downward than upward motions are present within the canyon. Such behaviour is explained by the presence of a compensation flow through the side of the canyon, which enters the canyon from the upper part and exits from the lower part. This complex 3-D structure affects the tracer dispersion, and is responsible for pollutant transport and diffusion.

[1]  Erich J. Plate,et al.  Wind-tunnel study of concentration fields in street canyons , 1999 .

[2]  A. Chan,et al.  Strategic guidelines for street canyon geometry to achieve sustainable street air quality—part II: multiple canopies and canyons , 2003 .

[3]  J. Santiago,et al.  Modelling the air flow in symmetric and asymmetric street canyons , 2005 .

[4]  Jong-Jin Baik,et al.  A Numerical Study of Flow and Pollutant Dispersion Characteristics in Urban Street Canyons , 1999 .

[5]  W. Hung,et al.  Validation of a two-dimensional pollutant dispersion model in an isolated street canyon , 2002 .

[6]  Fue-Sang Lien,et al.  A comparison of large Eddy simulations with a standard k–ε Reynolds-averaged Navier–Stokes model for the prediction of a fully developed turbulent flow over a matrix of cubes , 2003 .

[7]  B. P. Leonard,et al.  A stable and accurate convective modelling procedure based on quadratic upstream interpolation , 1990 .

[8]  D. Olivari,et al.  Numerical and experimental modelling of pollutant dispersion in a street canyon , 2002 .

[9]  S. Patankar.  Numerical Heat Transfer and Fluid Flow , 2018, Lecture Notes in Mechanical Engineering.

[10]  Fue-Sang Lien,et al.  Numerical Modelling of the Turbulent Flow Developing Within and Over a 3-D Building Array, Part I: A High-Resolution Reynolds-Averaged Navier—Stokes Approach , 2004 .

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

[12]  Alberto Martilli,et al.  CFD simulation of airflow over a regular array of cubes. Part II: analysis of spatial average properties , 2007 .

[13]  P. Louka,et al.  Measurements of Traffic-Induced Turbulence within a Street Canyon during the Nantes'99 Experiment , 2002 .

[14]  B. Launder,et al.  THE NUMERICAL COMPUTATION OF TURBULENT FLOW , 1974 .

[15]  Christer Johansson,et al.  Simulation of NOx and ultrafine particles in a street canyon in Stockholm, Sweden , 2004 .

[16]  Sandrine Anquetin,et al.  Pollutant dispersion and thermal effects in urban street canyons , 1996 .

[17]  B. Launder,et al.  The numerical computation of turbulent flows , 1990 .

[18]  Michael Schatzmann,et al.  Study of line source characteristics for 2-D physical modelling of pollutant dispersion in street canyons , 1996 .

[19]  Weeratunge Malalasekera,et al.  An introduction to computational fluid dynamics - the finite volume method , 2007 .

[20]  D. Olivari,et al.  Analysis of pollutant dispersion in an urban street canyon , 1999 .