Wind tunnel simulation of field tracer release in London

The first field campaign of the DAPPLE project was completed in May 2003, the measurement was performed around the intersection of Marylebone Road and Gloucester Place in central London. In this study, the wind tunnel simulation of the field tracer release will be described. A low-resolution model with a scale of 1:200, which covered approximately 300m in radius surrounding the intersection, was constructed. The laboratory experiments were conducted at a free stream velocity of 2.5m/s at three different wind directions. The time duration of the tracer release and the locations of release and sample matched those of the full-scale measurements. At each location 83 releases were performed in the wind tunnel, and the maximum concentration from one field release were compared with the mean, maximum, minimum and the concentration corresponding to the 10% and 90% of the cumulative PDF from the wind tunnel simulations. It is found that the field data is a possible outcome, and is in the lower end of the probable values from the wind tunnel simulation. The likely reasons for the discrepancy between the full-scale and model-scale are discussed. The variation of the wind direction with height at reference position was also investigated.