Gravity currents interacting with a bottom triangular obstacle and implications on entrainment

Abstract

Laboratory experiments investigating the interaction of a lock-exchange dense gravity current and a submerged obstacle with a triangular section have been conducted to determine the influence of the relative obstacle height, i.e. the ratio between the heights of the current and the obstacle, on the dynamics of the overflowing dense current. Experimental measurements were aimed to obtain detailed instantaneous density fields through an image analysis technique based on light attenuation. The dense current is deeply affected by the interaction, depending on the relative obstacle height. When the height of the current approaching the obstacle is small, a lower percentage of overflow propagates downstream and a large reduction in the gravity current velocity is observed. The analysis of the density fields highlights that the formation of a macro vortex downstream of the obstacle is the mechanism responsible for the enhanced dilution of the overflow. Nevertheless, the bulk entrainment parameter is slightly affected by the presence of a bottom obstacle. Results deepen our understanding of the entrainment processes related to the interaction with the obstacle and confirm the role of relevant non-dimensional numbers.