A Laboratory Simulation of Urban Heat-Island-Induced Circulation in a Stratified Environment

Abstract

A three-dimensional, axisymmetric, heat-island simulation is done in the convection tank of the U.S. EPA Fluid Modeling Facility. The laboratory model is capable of simulating the temperature and velocity fields induced by an urban heat island in a calm and stably stratified environment. The flow in the laboratory experiments is essentially Reynolds-number independent. The scaling parameters for velocity and temperature fields associated with the heat-island plume are determined by the heat-island diameter D, surface heat flux H0, and the Brunt-Vaisalla frequency N of ambient stratification. From these, one can define a convective velocity scale wD and a convective temperature scale TD. The normalized mixing height zi/D is shown to be a function of Froude number wD/ND only, while the normalized heat-island intensity is a function of wDN/gβ, where β is the coefficient of thermal expansion. These and other characteristics of simulated heat island induced circulation are compared with nighttime observations over several real cities. There is good agreement, in spite of several limitations of the laboratory simulation.