Dynamics and mixing of gravity currents over an array of cylindrical obstacles

This study investigates the dynamics and mixing of gravity currents propagating over an array of cylindrical obstacles using laboratory experiments. The effects of obstacle spacing (l/d) and submergence ratio (d/H0) on flow structure, dynamics, entrainment, and energy distribution are examined. High-resolution density measurements reveal that the submergence ratio plays a critical role in controlling current diversion, while obstacle spacing governs the flow pathway. An increase in d/H0 enhances the interactions between the current and the roughness elements, resulting in marked fluctuations in potential energy and mixing intensity that significantly affect the current evolution. Although bottom roughness generally reduces the front velocity and alters entrainment behavior, the effect of obstacle spacing is less important, particularly for low d/H0. Notably, for large d/H0, the current exhibits a shift in mixing dynamics, deviating from the near-linear growth of background potential energy observed in smoother cases. Furthermore, by applying the Thorpe scale to assess turbulent mixing, the study demonstrates that larger obstacle spacing promotes stronger turbulence, leading to greater vertical displacements and enhanced mixing.