Impacts of the side ratio of isolated buildings on airflows and pollutant dispersion under different temperature stratifications: Numerical investigations

Based on the Reynolds-averaged Navier-Stokes (RANS) method, the standard k-ε turbulence model was used to simulate the effects of the side ratio (SR: building depth/building width, SR = 0.5, 1.0, 1.5, and 2.0, respectively) of isolated buildings on the flow field and pollutant of ethylene dispersion under unstable temperature stratification and neutral conditions. The results showed that under unstable temperature stratification, the updraft on the leeward side of the building caused the high temperature gas to flow upward and the temperature gradient to drop. Compared with the neutral condition, the length of the recirculation zone was shorter, and with the decrease in SR, the vortex in the recirculation zone became larger and more stable. Because the pollution source was located on the leeward side of the building, the pollutant gas was concentrated in the area between the pollution source and the leeward side of the building. The near-ground concentration of pollutants under unstable temperature stratification was lower than that under neutral conditions, and with the decrease in SR, the near-ground axis concentration decreased while the width of the pollutant plumes increased.