Dense gas simulation flows over rough surfaces

Mixing within a gravity current head, passing over a rough surface, is assessed using a two-dimensional quantitative full-field flow visualization technique. The method combines salt-water modelling, laser-induced dye fluorescence and video image enhancement. The mixing mechanisms that occur internal to the head structure are shown to play a major role in the overall dilution process and to be significantly affected by surface roughness. The effect of surface roughness is consequential for the accurate prediction of heavier-than-air gas dispersions, for instance. Flows with Reynolds numbers of 500, 1000 and 1500 and density differences of 0.5, 1.0 and 1.5% are considered. Results are presented for flows over two surface types - smooth and rough with a relative roughness element height of 0.35 and frontal obstruction of 50% based on roughness element diameter.