Lateral channeling within rectangular arrays of cubical obstacles

Abstract Water channel experiments were conducted with the goal of obtaining better understanding of flows through urban-like arrays of buildings. Particle Image Velocimetry (PIV) was used for comprehensive flow measurements within a modeled simple urban setup. Building arrays were modeled using acrylic blocks whose refractive index is the same as that of salty water. Such a setup allowed for undisturbed laser sheet illumination through the obstacles enabling detailed flow measurements between the obstacles/buildings. Building array size, measurement plane and flow conditions were varied. A novel flow feature, lateral channeling, observed and quantitatively measured, within regular 3×3 and 5×5 arrays of cubes is reported here. A sideways mean outflow from the building array is observed behind the first row of buildings followed by the mean inflow in the lee of all succeeding rows of buildings. When the central building in a 3×3 array is replaced by a building of double height, due to the strong downdraft caused by this tall building, the lateral outflow becomes significantly more intense. When the central building in a 5×5 array is replaced by a building of double height, the building downdraft blocks the lateral inflow to the array. This is the first time that such detailed measurements are available for a mock urban array of finite size—a real three-dimensional case. The newly identified mean flow pattern may be accountable for the initial plume spread within an array of obstacles.

[1]  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 .

[2]  Walter F. Dabberdt,et al.  Kinematics and dispersion characteristics of flows in asymmetric street canyons , 1988 .

[3]  Mathias W. Rotach,et al.  A wind tunnel study of organised and turbulent air motions in urban street canyons , 2001 .

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

[5]  Robert J. Yamartino,et al.  Development and evaluation of simple models for the flow, turbulence and pollutant concentration fields within an urban street canyon , 1986 .

[6]  Stephen E. Belcher,et al.  Flow over a hill covered with a plant canopy , 2004 .

[7]  R. Adrian,et al.  Effect of resolution on the speed and accuracy of particle image velocimetry interrogation , 1992 .

[8]  Jack E. Cermak,et al.  A Wind Tunnel Study of Gaseous Pollutants in City Street Canyons , 1977 .

[9]  R. Macdonald,et al.  Modelling The Mean Velocity Profile In The Urban Canopy Layer , 2000 .

[10]  Walter F. Dabberdt,et al.  Street canyon dispersion: Sensitivity to block shape and entrainment , 1991 .

[11]  M. Schatzmann,et al.  Dispersion in Urban Environments; Comparison of Field Measurements with Wind Tunnel Results , 2000 .

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

[13]  Michael J. Brown,et al.  COMPARISON OF CENTERLINE VELOCITY MEASUREMENTS OBTAINED AROUND 2D AND 3D BUILDING ARRAYS IN A WIND TUNNEL , 2001 .

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

[15]  Ronald J. Adrian,et al.  Dynamic ranges of velocity and spatial resolution of particle image velocimetry , 1997 .

[16]  E. Esmail,et al.  Refractive index of salt water: effect of temperature , 1993 .

[17]  Eugene Yee,et al.  Comparison of Wind-tunnel and Water-channel Simulations of Plume Dispersion through a Large Array of Obstacles with a Scaled Field Experiment , 2006 .

[18]  T. G. Thomas,et al.  Mean Flow and Turbulence Statistics Over Groups of Urban-like Cubical Obstacles , 2006 .

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

[20]  E. Plate,et al.  Semi-empirical models as a combination of wind tunnel and numerical dispersion modelling , 1996 .

[21]  P. R. Slawson,et al.  Physical Modelling of Urban Roughness using Arrays of Regular Roughness Elements , 2002 .

[22]  S. Grossman-Clarke,et al.  Urban Fluid Mechanics: Air Circulation and Contaminant Dispersion in Cities , 2001 .

[23]  T. Hiyama,et al.  A Momentum Exchange Model for the Surface Layer over Bare-Soil and Canopy-Covered Surfaces , 2004 .

[24]  J. Monteith,et al.  Boundary Layer Climates. , 1979 .

[25]  R. Adrian Review of particle image velocimetry research presented at the symposium on optical methods in flow and particle diagnostics, 6th international congress on applications of lasers and electro-optics, 8–12 November 1987, San Diego, California, USA , 1988 .

[26]  Ian P. Castro,et al.  Near Wall Flow over Urban-like Roughness , 2002 .

[27]  A. Venkatram,et al.  Relating plume spread to meteorology in urban areas , 2005 .

[28]  Fue-Sang Lien,et al.  Numerical modelling of the turbulent flow developing within and over a 3-d building array, part ii: a mathematical foundation for a distributed drag force approach , 2005 .

[29]  H. Cheng,et al.  Near-Wall Flow Development After A Step Change In Surface Roughness , 2002 .

[30]  R. Adrian Particle-Imaging Techniques for Experimental Fluid Mechanics , 1991 .

[31]  Julia E. Flaherty,et al.  Urban Dispersion Program MSG05 Field Study: Summary of Tracer and Meteorological Measurements , 2006 .

[32]  Ingegärd Eliasson,et al.  Wind fields and turbulence statistics in an urban street canyon , 2004 .

[33]  Dispersion within a model urban area , 2005 .

[34]  Mathias W. Rotach,et al.  Mean Flow and Turbulence Characteristics in an Urban Roughness Sublayer , 2004 .

[35]  R. Berkowicz,et al.  The influence of street architecture on flow and dispersion in street canyons , 2004 .

[36]  W. Theurer TYPICAL BUILDING ARRANGEMENTS FOR URBAN AIR POLLUTION MODELLING , 1999 .

[37]  K Jerry Allwine Urban Dispersion Processes Investigated During the Joint Urban 2003 Study in Oklahoma City , 2004 .

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