Numerical Simulations of the Thermal Effect on Flow and Dispersion around an Isolated Building

The effect of temperature on flow and pollutant dispersion around an isolated building was investigated by computational fluid dynamics. First, the accuracy of the standard k-epsilon turbulence model in simulating the thermal effect on the flow and dispersion was assessed. The results showed that the reattachment of the numerical simulation behind the building was longer than that in the experiment because it could not reproduce the periodic fluctuations in the wake region and that the momentum transfer in the lateral direction was underestimated. Despite this, the temperature and concentration of the numerical simulation were in good agreement with the experimental results. Then, the standard k-epsilon turbulence model was adopted to investigate the effect of the ground temperature on flow and dispersion. The result indicated that, with the increase in temperature, the reattachment length behind the building significantly decreased and the vertical upward velocity increased, suggesting that rising temperature changed the flow. As the flow changed, the pollutant dispersion also changed. The pollutant plume depth increased while its width decreased with increasing ground temperature. It can be seen from the pollutant flux analysis that both convective transport and turbulent transport play important roles in vertical dispersion. The influence of ground temperature on convective motion was more obvious than that on turbulent motion because of the changed airflow. Significance Statement(i) The accuracy of the standard k-epsilon turbulence model in simulating the thermal effect on the flow and dispersion was assessed. The results showed that the reattachment of the numerical simulation behind the building was longer than that in the experiment because it could not reproduce the periodic fluctuations in the wake region and that the momentum transfer in the lateral direction was underestimated. Despite this, the temperature and concentration of the numerical simulation were in good agreement with the experimental results. (ii) Rising temperature not only increases turbulent motion but also alters airflow and pollutant plume morphology.