Large-Eddy Simulation for the Mechanism of Pollutant Removal from a Two-Dimensional Street Canyon |
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| Authors: | Takenobu Michioka Ayumu Sato Hiroshi Takimoto Manabu Kanda |
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| Institution: | 1.Environmental Science Research Laboratory,Central Research Institute of Electric Power Industry,Chiba-ken,Japan;2.Department of International Development Engineering,Tokyo Institute of Technology,Tokyo,Japan |
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| Abstract: | Large-eddy simulation (LES) is conducted to investigate the mechanism of pollutant removal from a two-dimensional street canyon
with a building-height to street-width (aspect) ratio of 1. A pollutant is released as a ground-level line source at the centre
of the canyon floor. The mean velocities, turbulent fluctuations, and mean pollutant concentration estimated by LES are in
good agreement with those obtained by wind-tunnel experiments. Pollutant removal from the canyon is mainly determined by turbulent
motions, except in the adjacent area to the windward wall. The turbulent motions are composed of small vortices and small-scale
coherent structures of low-momentum fluid generated close to the plane of the roof. Although both small vortices and small-scale
coherent structures affect pollutant removal, the pollutant is largely emitted from the canyon by ejection of low-momentum
fluid when the small-scale coherent structures appear just above the canyon where the pollutant is retained. Large-scale coherent
structures also develop above the canyon, but they do not always affect pollutant removal. |
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