The present work investigated the outdoor thermal environment for different urban forms under the summer conditions of Sendai, Japan and Guangzhou, China. Sendai has a moderate humid subtropical climate, whereas Guangzhou has a humid subtropical climate. Numerical simulations were performed with a coupled simulation method of convection, radiation, and conduction. A cubic non-linear k–ε model proposed by Craft et al. was selected as the turbulence model and three-dimensional multireflections of shortwave and longwave radiations were considered in the radiation simulation. Seven urban forms (the ratios of building distance to building height were 0.24, 0.36, 0.48, 0.71, 0.95, 1.19, and 1.43.) were studied. The openness and compactness of the urban forms were compared by developing a new assessment system. The following results were obtained. (1) The distributions of wind velocity around the buildings became polarized as building distance decreased, and the proportion of low wind velocity grew large. These conditions mainly caused poor ventilation and thermal discomfort. (2) The cooling effects of building shade became increasingly significant as building distance decreased because of the low level of exposure to strong sunshine in compact forms. (3) Safe outdoor thermal conditions (standard effective temperature ≤37 °C) can be partially achieved in Sendai by decreasing building distance, whereas the same could not be achieved in Guangzhou. Further countermeasures are essential in Guangzhou.
- outdoor thermal environment
- standard effective temperature (SET*)
- urban form
- urban ventilation