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Environmental Fluid Mechanics

, Volume 15, Issue 4, pp 823–849 | Cite as

Effect of upstream flow regime on street canyon flow mean turbulence statistics

  • Karin Blackman
  • Laurent Perret
  • Eric Savory
Original Article

Abstract

The effect on the flow over a street canyon (lateral length/height, L/h \(=\) 30) of using either 3D (cube) or 2D (rectangular block) upstream roughness arrays, of the same height as the canyon, has been studied for two streamwise canyon width to height aspect ratios (AR \(=\) W/h) of 1 and 3, in a wind tunnel using Particle Image Velocimetry. The mean streamwise velocity, shear stress, turbulent intensities and length scales, together with shear layer boundaries and mass fluxes across the canyon opening are presented for different combinations of skimming and wake-interference regimes using different upstream roughness and canyon configurations. These results show significant trends with canyon aspect ratio and roughness array plan area packing density \((\uplambda _{\mathrm{p}})\) with respect to 2D and 3D configurations. The mean streamwise velocity for configurations of equal \(\uplambda _{\mathrm{p}}\) is higher in 3D than 2D configurations, while the spatially averaged shear stress is shown to be lower in 3D than 2D configurations. The relative contribution to the total turbulent kinetic energy (TKE) demonstrates that staggered and aligned arrays or 2D and 3D arrays do not produce similar profiles of TKE. Finally, the integral length scale is larger in 2D cases than 3D cases of equal \(\uplambda _{\mathrm{p}}\). Urban air quality is a significant concern for human health. By investigating the influence of upstream roughness on canyon flow one can determine which cases or flow regimes in both the upstream roughness and canyon will result in decreased ventilation and negatively effect the air quality of urban areas. From the present work decreased ventilation occurs in the skimming flow regime and is lowest in the case of upstream 2D bar roughness with \(\uplambda _{\mathrm{p}} = 50~\%\) and canyon AR \(=\) 1.

Keywords

Boundary layer Street canyon Particle Image Velocimetry Wind tunnel 

Notes

Acknowledgments

The authors should like to thank Mr Thibaut Piquet for his technical support during the experimental program and the Ontario Graduate Scholarship Program for providing funding.

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Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.University of Western OntarioLondonCanada
  2. 2.Ecole Centrale de NantesLUNAM UniversitéNantes Cedex 3France

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