Combined effects of terrain orography and thermal stratification on pollutant dispersion in a town valley: a T-RANS simulation

Abstract

Combined effects of terrain orography and thermal stratification on the dispersion of pollutants in a mountainous town valley over a diurnal cycle are numerically simulated by a time-dependent Reynolds-averaged Navier-Stokes (T-RANS) approach. The T-RANS model was incorporated into a finite volume NS solver for three-dimensional non-orthogonal domains, using Cartesian vector and tensor components and a collocated variable arrangement. Prior to the full scale simulations, the T-RANS approach was validated in test situations where the effects of thermal stratification and terrain orography are separated, showing good agreement with the available experimental and simulation data. The full scale simulations were performed in a realistic orography over two diurnal cycles for two cases of the initial thermal stratification, both with a prescribed time and space variation of ground temperature and pollutant emission—reflecting the daily activities in the town. The results confirmed that the T-RANS approach can serve as a reliable tool for predicting local air movement and pollutant dispersion at micro and meso scales. This article was chosen from selected Proceedings of the Second International Symposium on Turbulence and Shear Flow Phenomena (KTH-Stockholm, 27-29 June 2001) ed E Lindborg, A Johansson, J Eaton, J Humphrey, N Kasagi, M Leschziner and M Sommerfeld.