Direct numerical simulation of lock-exchange density currents over the rough wall in slumping phase.

Direct numerical simulation (DNS) is used to simulate lock-exchange flow to understand density currents over rough surfaces. This work is one of the first DNS to simulate density currents over rough walls. The simulations are performed at a Grashof number of 1.6×107. The non-dimensional height of the roughness elements with respect to the half-height of the channel is 0.12. Roughness reduces the speed of the front. Furthermore, the instabilities are significantly enhanced resulting in secondary instabilities that arise much earlier in time. Roughness introduces an additional vorticity generation mechanism which is comparable to the vorticity generated from Kelvin–Helmholtz and lobe–cleft type of instabilities. Flow exhibits significant differences near the leading edge or the nose of the front of the density currents due to roughness. [ABSTRACT FROM AUTHOR]