Experimental results are reported to explore the role of release location and release volume on the dispersion of a dense gas cloud around an isolated cubic building. The experiments are analogous to the Thorney Island dense gas dispersion field tests, and the results are qualitatively similar to those of the full-scale tests. Water bath experiments were used in this study with fresh water in a flume representing the atmospheric wind and dyed saltwater representing the dense gas. Results are presented for different relative density flows, quantified using the Richardson number (Ri), for five different release volumes ranging from 10% to 60% of the building volume. Results are also presented for different upstream release distances ranging from 50% to 150% of the building height. Measurements show that there is a complex interaction between release volume, release distance, and Richardson number, and the resulting flow over and around the building. For releases close to the building, the cloud has little distance over which to adjust before being swept around the building and into the building wake. However, for larger release distances, there is adequate distance for the cloud to adjust, with the nature of the adjustment being a function of the Richardson number. For small Ri (low density difference), the cloud spreads out as it moves downstream, mixes with the ambient fluid, and increases in volume such that the volume of the cloud interacting with the building is larger than the initial release. For higher Ri flows (larger density difference), the dense cloud collapses down onto the channel bed, where it spreads out radially as it is advected downstream. The clouds are, therefore, much shallower than the building height when they collide with the building. This competition between the collapse of the cloud and its advection downstream is parameterized using a novel ‘adjusted Richardson number’ Ri*.
Akhter et al. (Fri,) studied this question.