Thermal Internal Boundary Layer Height by Numerical Simulation of the Fumigation

Abstract

Fumigation is an important subject in air pollution. In a neutral atmosphere, temperature decreases with the height. However, when there is a transient condition of climate like sunrise in the morning which leads to increase the land surface temperature, temperature profile of stable condition will change. In these conditions, convection of air near the ground surface increases the turbulence and dispersion coefficient. In coastal area, there will be a temperature difference between the sea and land. This condition make the pollutants to fumigate when enters to the layer above the ground named as Thermal Internal Boundary Layer (TIBL). The height of TIBL which defines the extent of fumigation is important. Researchers suggested several formulas for estimating the TIBL height based on practical works. In this paper, computational fluid dynamic (CFD) provides discrete phase model (DPM) of dispersion using Reynolds stress transport model of turbulence (RSM) applied for estimating the TIBL height. Study domain is two dimensional, 2500 m in wind direction (sea to land) by 800 m height. Velocity profiles of the neutral atmosphere are forced to the model in neutral steady state atmospheric conditions. Resulted profiles in downwind of the inlet are compared with the forced profiles to evaluate the accuracy of the model. To simulate the fumigation, land temperature fixed to a higher temperature than the sea by 5°c. Resulted velocity profile and
gradient of Reynolds stress parameters u ' u ' and u ' v ' in different elevations is used to estimate the TIBL height. The location of sharp change in the Reynolds stress specified as the
TIBL height at each elevation. A formula covering the coordination of these locations fitted to define the TIBL height and its growing from coastline towards wind direction. Experimental
formula which is used can be substituted by the determined formula this study.