Numerical study of the thermal effects of buildings on low-speed airflow taking into account 3D atmospheric radiation in urban canopy

A three-dimensional atmospheric radiative model which evaluates the thermal-radiative transfers in the lower atmosphere was implemented in the atmospheric module of a Computational Fluid Dynamics code. This model can study the thermal effects of buildings on the local atmospheric flow with a coupled dynamic-radiative model. Previously, we have validated this approach and discussed the impact of the convective flux on the surface temperatures by comparing a detailed wind and temperature field with the Mock Urban Setting Test (MUST) experiment dataset. In this paper our objective is to demonstrate the ability of our radiative model to simulate the thermal effect of buildings on the local atmospheric flow under low wind speed condition. Therefore, we present different numerical simulations for low wind speed and higher building density than in MUST, comparing the neutral case with different levels of thermal exchange model and analyzing the differences. The results show first that taking into account the thermal stratification has a significant influence on the wind field. Then we show that the difference between the case for which we impose the temperatures and the case with temperatures calculated with a 3D radiative transfer scheme can also be important near the buildings. In addition, with the 3D radiative model, the temperature and vertical motion show an important sensitivity to changes in the physical parameters of the wall surfaces, such as the surface albedo.

► We simulate the thermal effects of buildings on the local atmosphere.
► The results show the importance of the thermal stratification at low wind speed.
► We analyze the contribution of 3D radiative transfers on the wind structure.
► Heating conditions and surface properties can have an important effect on the flow.