Abstract
This study focuses on predicting the pollution dispersion in a street canyon using Large-Eddy Simulations (LES). The predictions are compared to wind tunnel experiments done at Karlsruhe Institute of Technology (KIT), Germany. The geometry consists of a long canyon with width-to-height, W/H = 1, placed in a turbulent boundary layer flow perpendicular to the length of the canyon. Pollutant (SF6 in the experiments) is injected in the canyon at street level through a series of flush-mounted equidistant hypodermic 0.4 mm diameter tubes acting as two line sources near the leading and trailing side of the canyon to simulate vehicular exhaust. A multi-species, variable property LES is conducted in a domain 41H × 8H × H/190 by using periodic boundary conditions along the length of the canyon on a grid of 1.6 million cells. The predicted mean concentration of pollutant is compared to experimental measurements at two locations within the canyon. The two are in satisfactory agreement considering that only a small fraction of the canyon length is modeled. A greater deviation in concentration prediction is found closer to the ground level, implying less dispersion of the pollutant. The over-prediction has also been observed in other LES investigations. The rms concentration fluctuations are much larger in comparison to previous LES on the full canyon length. This is attributed to the large-scale coherence of turbulent structures resulting from the absence of any three-dimensional long wavelength instabilities developing in the lateral direction.
