A Laboratory Study of the Urban Heat Island in a Calm and Stably Stratified Environment. Part II: Velocity Field

摘要

A fully turbulent, low-aspect-ratio buoyant plume with no initial momentum under calm and stably stratified conditions is produced in a convection tank. The plume is generated by a circular beat island at the bottom of the tank. Two analytical models,a bulk convection model and a hydrostatic model, are developed to fonmulate similarity relations for the low-aspect-ratio plume. The convective velocity scale W_D, suggested by the analytical models, is used as the similarity parameter for both the meanvelocity and standard deviations of velocity fluctuations. The normalized standard deviations of horizontal and vertical velocities agree with each other for two heating rates, as well as with field observations in the center of Sapporo, Japan. The suggested scaling and empirical relations based on our experimental results may be applied to the velocity fields of other low-aspect-ratio plumes in calm and stably stratified environments. Further investigations are recommended to confirm the results of the current study.