Gravity currents propagating over periodic arrays of blunt obstacles: Effect of the obstacle size

Gravity currents are considered that propagate over a series of identical ribs with square cross sections. Both large-eddy simulations and a shallow-water approach are applied to assess the influence of rib height and Reynolds number. The simulations elucidate the physical mechanisms governing the time-dependent evolution of the drag force, which are dominated by the formation of a recirculation region immediately downstream of each rib, in conjunction with a supercritical, jet-like flow region above and behind the rib, and an upstream propagating hydraulic jump that forms as a result of the interaction between the gravity current and the neighboring rib immediately downstream. The corresponding shallow-water analysis yields fair agreement, indicating that simplified models can provide useful information for the present class of flows.