Dispersion from courtyards and other enclosed spaces.

The paper describes small scale wind tunnel experiments on the dispersion of contaminants discharged from the bottom of courtyards and other enclosed spaces. The experiments covered a range of courtyards with ratios of depth to width from 5- (consistent with light wells and other very deep cavities) down to 0.1 (consistent with shallow enclosed squares and piazzas that are frequently found in the urban environment). A variety of parameters within these shapes were investigated, including the depth of the walls around the courtyard, the presence of openings in the walls, the effects of wind direction, the presence of surface clutter and stratification of the air in the courtyard. In general courtyards are poorly ventilating spaces and high residual concentrations of any discharged contaminant occur. However, this behaviour may also be used to advantage in using courtyards as a method of modifying the local climate. The effects of the parameters investigated on contaminant concentrations were complex and quite variable, which allows for the possibility of designing courtyards to suit specific needs.