On the effect of drag on the propagation of compositional gravity currents
ABSTRACT: Highly resolved 3-D Large Eddy Simulation (LES) are used to study the effects of the additional drag induced by the presence of obstacles on the propagation of lock-exchange Boussinesq Gravity Currents (GCs) in a straight horizontal channel. Two types of configurations are considered. In the first case, a number of identical rectangular cylinders are uniformly distributed over the whole depth and length of the channel. This test case corresponds to a GC propagating in a porous medium of uniform porosity in which the additional drag induced by the cylinders acts over the whole height of the GC. In the second case, an array of identical obstacles in the form of square ribs or 2-D dunes is mounted on the bottom surface of the channel. The additional drag acts only over the lower part of the GC as the obstacle height is smaller than the height of the GC. Both cases are relevant for practical applications, as in most environmental applications GCs propagate over a rough bed (e.g., GCs at the bottom of rivers and oceans), interact with flow retarding devices (e.g., snow avalanches) or advance in a porous medium (e.g., a layer of vegetation). The study analyses the propagation of the GC during the slumping and drag dominated regimes.