A Simple Daily Cycle Temperature Boundary Condition for Ground Surfaces in CFD Predictions of Urban Wind Flows

Abstract

AbstractThe atmospheric boundary exhibits an obvious diurnal cycle. The daily cycle of climate variation has a significant effect on urban airflow, and an understanding of it is very important for city-scale environmental control. A new and simple daily cycle temperature boundary condition for simulations of urban airflows with computational fluid dynamics (CFD) is described herein. An analytical surface temperature formula was obtained after simplifying longwave radiation and sensible heat flux terms. The formula provides a reasonably good prediction of ground surface temperatures on sunny days without adding much complexity. The accuracy of the prediction of daily surface temperature variations in homogeneous soils was evaluated with a benchmark experiment and with weather station data. The new boundary condition was implemented in the commercial CFD software Fluent for a city-scale model. The implementation demonstrates the importance of including diurnal temperature profiles and atmospheric boundary conditions in CFD simulations of urban plumes in which an ideal urban heat island circulation occurs.