Measurements and Computations of Flow in an Urban Street System
We present results from laboratory and computational experiments on the turbulent flow over an array of rectangular blocks modelling a typical, asymmetric urban canopy at various orientations to the approach flow. The work forms part of a larger study on dispersion within such arrays (project DIPLOS) and concentrates on the nature of the mean flow and turbulence fields within the canopy region, recognising that unless the flow field is adequately represented in computational models there is no reason to expect realistic simulations of the nature of the dispersion of pollutants emitted within the canopy. Comparisons between the experimental data and those obtained from both large-eddy simulation (LES) and direct numerical simulation (DNS) are shown and it is concluded that careful use of LES can produce generally excellent agreement with laboratory and DNS results, lending further confidence in the use of LES for such situations. Various crucial issues are discussed and advice offered to both experimentalists and those seeking to compute canopy flows with turbulence resolving models.
KeywordsDirect numerical simulation Large-eddy simulation Urban environment Wind-tunnel modelling
The DIPLOS project is funded by the UK’s Engineering and Physical Sciences Research Council—Grants EP/K04060X/1 (Southampton), EP/K040731/1 (Surrey) and EP/K040707/1 (Reading) and is coordinated by one of us (OC). The EnFlo wind tunnel is an NCAS facility and we gratefully acknowledge ongoing NCAS support. We are also grateful for comments and ongoing discussions with other colleagues at Reading, Surrey, and elsewhere. The authors confirm that all wind-tunnel data are fully available without restriction. Details of the data and how to request access are available from the University of Surrey: http://dx.doi.org/10.15126/surreydata.00809438. The LES and DNS data are, likewise, available from the University of Southampton, http://dx.doi.org/10.5258/SOTON/396364 and the University of Reading, http://dx.doi.org/10.17864/1947.71, respectively. We also wish to thank Dr Bharathi Boppana for some initial scoping LES computations.
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