Thursday, 12 June 2008: 9:15 AM
Aula Magna Vänster (Aula Magna)
We study density currents over complex terrain using large-eddy simulations (LES). Density currents in the atmosphere can occur as both natural and man-made phenomena. Naturally occurring density currents result from air density differences of a few percent. Man-made density currents are often associated with accidental releases of dense gases. Since the exact origin and all the parameters controlling the evolution of naturally-occurring density currents in the atmosphere are often unknown or difficult to observe, we focus on man-made density currents. Over last couple of decades, a number of field studies of dense gas releases were carried out. We use data from one such field study to evaluate performance of two subgrid models in simulating density current flows over complex terrain. We carry out LES using both the Smagorinsky subgrid model (Lilly, 1967) and nonlinear subgrid model (Kosoviæ, 1997), and compare results of simulations with observations from the Burro Series field study in which liquefied natural gas was released. In addition to evaluating the simulations of the general characteristics of the dense gas current, such as its speed and spread, we also focus on measured turbulent quantities: turbulent kinetic energy, turbulent stresses and fluxes.
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