Author(s): Talia E. Tokyay
Linked Author(s): Talia Tokyay
Keywords: No Keywords
Abstract: The effect of presence of large scale roughness elements on propagation of compositional gravity currents in lock-exchange configurations is investigated using High-resolution Large Eddy Simulation (LES). The top and bottom boundaries are defined as no-slip walls to maintain the symmetry of the flow with respect to the initial lock position. Two simulations at a Reynolds number of 1,000,000 are performed, one with a flat bottom and one in which the forward and backward currents propagate over a series of identical two-dimensional dunes. The shape of the dunes is identical to the ones used in the study of Mierlo and de Ruiter (1988). The Reynolds number is defined with the buoyancy velocity and the channel depth, H. In the simulations, the volume of the heavier lock fluid is very large such that there are no interactions between the gravity current and the channel extremities. Large volume of release also ensures that the Boussinesq current stays in slumping phase throughout the simulation time. It is found that the presence of dunes with a height of 0.15H and a wavelength of 3H reduces the mean front velocity during the slumping phase by about 19%. The bed shear stress distributions in the later stages of the slumping phase are found to be much more uniform in the flat bed case. On the contrary, in the regions where gravity current plunges downward as a jet-like flow after passing over crest of each dune, amplifications of bed shear stress are observed. These amplifications in bed-shear stress results in changes in capacity of the flow to entrain sediment from the channel bottom.
Year: 2009