Analytical and numerical study on transient urban street air warming induced by anthropogenic heat emission

Abstract

Anthropogenic heat emission is an important factor for street air warming. In this study, the transient street air warming process caused by anthropogenic heat is investigated by both the analytical model and Large-Eddy Simulation (LES). A new analytical model is developed based on the empirical exchange velocity modelling and heat exchange rate estimation. In the model, the buoyancy effect is included by introducing a buoyancy coefficient. With the new analytical model, both transient time and steady-state street air temperature increment (Θc) can be easily estimated in urban areas. This new model is calibrated and validated by cross-comparing with LES results. A good agreement is found between the results after including the buoyancy coefficient into the analytical model. Modelling results indicate that Θccould be limited because the buoyancy effect increases the exchange velocity between the urban canopy layer and overlying atmosphere. Furthermore, the buoyancy is also important to the transient air exchange process. A transformation of the urban canopy layer flow structure is found in the transient period, suggesting a large scale turbulence structure induced by anthropogenic heat. Lastly, the air temperature increment in the residential areas of Singapore is estimated with GIS (Geography Information System) tool to show the application of the analytical model in practice.