Non-isothermal flow between heated building models

Abstract

The Urban Heat Island Effect describes the phenomenon that urban areas are typically warmer than the nearby rural areas, as the presence of the city causes an increase in air temperature. Increased temperatures in urban environments lead to increased discomfort, health problems, and higher cooling demands. It is therefore essential to be able to predict the location where higher temperatures tend to occur and to propose mitigation strategies for such local hot-spots. In this study, we present flowfield and temperature measurements from the ETHZ/Empa Atmospheric Boundary Layer wind tunnel. Time-averaged Particle Image Velocimetry is used to examine the non-isothermal flow in two geometric configurations of a three-dimensional street canyon surrounded by a realistic city geometry. We investigate the effect of buoyancy by measuring at forced to mixed convection flow regimes with Richardson (Ri) numbers ranging from 0 to 1.09. The work differs from previous studies, in that a finite-length street canyon with heated surfaces is considered. This set-up results in an increasing flow rate that escapes the street canyon volume as the flow becomes increasingly buoyancy-driven. Turbulent kinetic energy (TKE) levels increase with increasing Ri as flow exiting the street canyon mixes with the freestream flow. (© 2020 Elsevier Ltd)