Ventilation of idealised urban area, LES and wind tunnel experiment

¹ Charles University in Prague, Faculty of Mathematics and Physics, The Department of Meteorology and Environment Protection, Czech Republic
² Institute of Thermomechanics Academy of Sciences of the Czech Republic, v.v.i, Dolejšskova 1402/5, Prague 182 00, Czech Republic

^a Corresponding author: kukacka@it.cas.cz

Published online: 25 March 2014

Abstract

In order to estimate the ventilation of vehicle pollution within street canyons, a wind tunnel experiment and a large eddy simulation (LES) was performed. A model of an idealised urban area with apartment houses arranged to courtyards was designed according to common Central European cities. In the wind tunnel, we assembled a set-up for simultaneous measurement of vertical velocity and tracer gas concentration. Due to the vehicle traffic emissions modelling, a new line source of tracer gas was designed and built into the model. As a computational model, the LES model solving the incompressible Navier-Stokes equations was used. In this paper, we focused on the street canyon with the line source situated perpendicular to an approach flow. Vertical and longitudinal velocity components of the flow with the pollutant concentration were obtained from two horizontal grids placed in different heights above the street canyon. Vertical advective and turbulent pollution fluxes were computed from the measured data as ventilation characteristics. Wind tunnel and LES data were qualitatively compared. A domination of advective pollution transport within the street canyon was determined. However, the turbulent transport with an opposite direction to the advective played a significant role within and above the street canyon.