Stratified shear flows over a simulated three-dimensional urban heat island
Date
1973-08
Authors
SethuRaman, S., author
Cermak, J. E. (Jack E.), author
Fluid Dynamics and Diffusion Laboratory, College of Engineering, Colorado State University, publisher
Journal Title
Journal ISSN
Volume Title
Abstract
Three-dimensional airflow over a rectangular heat island was studied for various conditions of approach flow in a wind tunnel. Three different thermal stratifications of the approach flow were selected for the study -- neutral, ground based and elevated inversions. For each of these flows studies were conducted with and without roughness over the heat island for the conditions with and without heating of the island. Approach flow temperature profiles were modeled according to atmospheric data available in the literature. For each of the twelve cases mentioned above, measurements of mean wind velocity, longitudinal velocity fluctuations, mean temperature and temperature fluctuations were made. In addition, mean concentration measurements of a radioactive gas released from a two-dimensional, ground-level line source upwind of the heat island were also made. Flow patterns were visualized for different cases with the help of a passive smoke source. Comparisons of data from the wind-tunnel measurements with the field data were made. Three-dimensional measurements of the mean wind velocity, temperature and turbulence have yielded valuable information concerning the flow of air around a typical urban heat island. The mechanisms of the heat island observed in the wind tunnel for different stratified flows were very similar to those observed in the field. The urban heat island plume that passes aloft downwind causes an appreciable reverse flow onto the heat island. The helical vortices at the edge of the heat island cause a reduction in the turbulence level resulting in high concentrations of the mass released from a continuous line source upwind of the heat island. A theoretical model based on linearized equations of motions incorporating a boundary layer type velocity profile has been developed to predict the urban excess temperatures and velocities. Theoretical results compare fairly well with data obtained in the laboratory and in the field.
Description
CER73-74SS-JEC4.
August 1973.
Includes bibliographical references.
Prepared under Office of Naval Research, project no. NR 062-414/6-6-68 (Code 438).
August 1973.
Includes bibliographical references.
Prepared under Office of Naval Research, project no. NR 062-414/6-6-68 (Code 438).
Rights Access
Subject
Atmospheric circulation
Diffusion
Air -- Pollution
Urban climatology